Tetrahedron Letters (v.53, #9)

Substituted azabicyclo[2.2.1]heptanes via nitrenium ion rearrangement by David W. Piotrowski; Marianne Rolph; Liuqing Wei (1009-1012).
N-chlorination of aryl substituted azabicycloheptanes and subsequent rearrangement provided the endo arylated azabicyclo[2.2.1]heptanes.
Keywords: Nitrenium ion; Rearrangement; Bicyclic amine; Dehalogenation;

Starting with resin-bound bifunctional 2-(2-aminoethylthio)acetic, an efficient synthesis of a variety of N-cycloakyl thiomopholinones is described utilizing the Ugi four-center three-component reaction (U-4C-3CR).
Keywords: Solid phase synthesis; UGI reaction; MCR; Thiomorpholinones; Heterocycles; Combinatorial chemistry;

Anodic oxidation of cyclooctatetraene (COT) was carried out in acetonitrile containing excess allyltrimethylsilane. Under these conditions COT is oxidized preferentially to afford the COT cation radical, which then undergoes nucleophilic attack by the silane followed by further anodic oxidation. The process results in a substance in which the original eight carbons of COT are highly differentiated by the addition of three allyl groups and the formation of two new rings.
Keywords: Cyclooctatetraene; Anodic oxidation; β-silyl cation; Carbocationic cyclization; Homotropylium ion;

An atom-economical, multicomponent condensation of naphthols, aldehydes, and cyclic 1,3-dicarbonyl compounds catalyzed by HY zeolites under solvent-free conditions is reported. This ecofriendly protocol offers several advantages such as a green and cost-effective procedure with excellent yield, shorter reaction time, simpler work-up, recovery, and reusability of metal-free solid acid heterogeneous catalyst and tolerance of a wide range of functional groups. The biological studies such as in vitro anti-microbial activities of the prepared new compounds and cell imaging studies on K562 leukemia cell lines by selected benzoxanthenones are evaluated.
Keywords: HY zeolite; Heterogeneous catalysts; Benzoxanthenones; Multicomponent reaction; Solvent-free conditions;

Application of [BoPhoz Rh] catalysts in the asymmetric hydrogenation of a pyridyl benzothiophene alkene by Timothy Gross; Shine Chou; Alan Dyke; Beatriz Dominguez; Michelle Groarke; Jonathan Medlock; Michael Ouellette; Jayachandra P. Reddy; Andreas Seger; Scott Zook; Antonio Zanotti-Gerosa (1025-1028).
The asymmetric hydrogenation of a pyridyl benzothiophene alkene has been successfully accomplished using [BoPhoz Rh] catalysts. By tailoring the steric properties of the BoPhoz ligand, the ee of the product could be increased from just 12% to 90%. This research further expands the substrate scope of the conventional class of functionalized alkenes amenable to catalytic asymmetric hydrogenation.
Keywords: Homogeneous asymmetric hydrogenation; Rhodium catalysts; BoPhoz ligands; Enantioselective hydrogenation of alkenes;

A route to selective functionalization of polyhydroxypyrrolidines by Carlos A.D. Sousa; Fabio Rizzo-Aguiar; M. Luísa C. Vale; Xerardo García-Mera; Olga Caamaño; José E. Rodríguez-Borges (1029-1032).
A route to selective functionalization of polyhydroxypyrrolidines is described. The method is based on orthogonal protection/deprotection along the process of synthesis of the referred pyrrolidines, which consist in hydroxylation of the double bond of 2-azabicyclo[2.2.1]hept-5-enes followed by its oxidative cleavage and in situ reduction of the intermediate dialdehyde. The synthesis of a novel N-hydroxypyrrolidine is also described.
Keywords: Polyhydroxypyrrolidines; Orthogonal protection; Selective functionalization; Azasugar;

A new two step strategy for the preparation of 1,4-benzodiazepin-2-ones has been developed starting from the 2-halogenobenzophenone under Buchwald conditions (Pd(OAc)2, XantPhos, Cs2CO3, dioxane 100 °C). This strategy has been extended to two 2-halogeno-3-benzoyl-azines (pyridines, pyridazines).
Keywords: Buchwald; Pd crosscoupling; 1,4-Benzodiazepin-2-one; Pyridine; Pyridazine;

A modified approach for the synthesis of 3-substituted 2-aryl/heteroaryl imidazo[4,5-b]pyridines utilising palladium catalysed cross-coupling reactions under microwave enhanced conditions has been achieved. utilisation of (A-taphos)2PdCl2-catalysed cross-coupling reactions enables rapid derivatization of this (imidazo[4,5-b]pyridines) pharmaceutically relevant core. This catalytic system is compatible with a broad spectrum of arylboronic acids—electron rich, electron poor, and heteroarylboronic acids.
Keywords: Microwave; Imidazo[4,5-b]pyridine; Suzuki coupling; Boronic acids;

Hydroxy-rhodium(I) catalyzed regioselective Michael addition of cyclic enones by Gullapalli Kumaraswamy; Dasa Rambabu (1042-1044).
An efficient protocol has been accomplished for the synthesis of cyclic α-enone adducts with 2 mol % of Rh(I) catalyst. The key feature of this protocol is Rh-OH pre-catalyst performing the carbon–carbon bond formation α- to enone. Further, this method is extended to base-sensitive highly substituted enones and respective dimerized enone adducts are obtained in moderate to good yields.Hydroxy-rhodium catalyzed dimerization of various cyclic enones to the corresponding α-enone adducts is developed. The key feature of this method is that the base-sensitive, highly substituted enones also undergo dimerization and the resultant products are obtained in moderate to good yields.
Keywords: Transition metal; Hydroxy-rhodium; Dimerization; Cyclohexenone; Cycloheptenone;

Insights into sulfinate formation from tosyl hydrazides by Ulf Ragnarsson; Leif Grehn (1045-1047).
Tosyl hydrazides exhibit variable base sensitivity. We compared 1,2-ditosyl- and a few monotosylated derivatives in this respect and determined their relative stabilities. The half-lives were found to vary by more than five orders of magnitude.Benzylation of 1,2-ditosylhydrazine in DMF under various basic conditions results in a benzyl sulfone via intermediary sulfinate formation, providing new insights and allowing practical conclusions to be drawn. The half-lives of 1,2-ditosylhydrazine and several monotosylated hydrazides with 1,1,3,3-tetramethylguanidine in DMSO have been determined by 1H NMR spectroscopy and are found to vary from a few minutes to several months. In the course of this work a benzylated, partly detosylated compound has been identified and a 1,1,3,3-tetramethyl guanidine-containing side-product characterized. A contradictory report is also commented on.
Keywords: Half-life determination; Hydrazide cleavage; Nitrogen formation; Sulfinate; Sulfone;

A general and highly efficient Al(OTf)3-catalyzed methodology has been developed for the direct nucleophilic substitution of the hydroxy group in propargylic alcohols with a variety of carbon- and heteroatom-centered nucleophiles such as alcohols, aromatic compounds, amides, and thiols, leading to the construction of C–C, C–O, C–N and C–S bonds.
Keywords: Aluminum triflate; Propargylic alcohols; Nucleophiles; Regioselectivity;

Synthesis and cross-coupling reactions of imidomethyltrifluoroborates with aryl chlorides by Rammohan Devulapally; Nicolas Fleury-Brégeot; Gary A. Molander; Dave G. Seapy (1051-1055).
Potassium imidomethyltrifluoroborate salts were efficiently synthesized. Potassium phthalimidomethyltrifluoroborate was successfully used in Suzuki–Miyaura-like cross-coupling reactions with a variety of aryl chlorides.
Keywords: Potassium imidomethyltrifluoroborates; Suzuki–Miyaura cross-coupling reaction; N-Benzylphthalimides;

Synthesis of thiophenes and pyranone fused thiophenes by base induced inter and intramolecular C–S and C–C bond formation: a non-catalytic approach by Pushyamitra Mishra; Hardesh K. Maurya; Brijesh Kumar; Vishnu K. Tandon; Vishnu Ji Ram (1056-1059).
An efficient and concise one pot synthesis of highly functionalized thiophenes and pyranone fused thiophenes has been delineated through base induced ring transformation of suitably functionalized 2H-pyran-2-ones by ethyl thioglycolate by inter and intramolecular C–S and C–C bond formation.
Keywords: Thiophene; Thieno[3,2-c]pyran-4-one; Ethyl thioglycolate; Ring transformation reaction; Thienylacetonitrile;

An efficient method for the preparation of mono α-aryl derivatives of diethyl malonate and ethyl cyanoacetate using ethyl-1-imidazole carbamate (EImC) by Manoranjan Behera; R. Venkat Ragavan; M. Sambaiah; Balaiah Erugu; J. Rama Krishna Reddy; K. Mukkanti; Satyanarayana Yennam (1060-1062).
An efficient method for the synthesis of mono α-aryl derivatives of diethyl malonate and ethyl cyanoacetate using ethyl-1-imidazole carbamate (EImC) has been described. Using this method many sterically hindered and highly substituted mono α-aryl derivatives of diethyl malonate and ethyl cyanoacetate were synthesized in high yield.
Keywords: Ethyl-1-imidazole carbamate; LiHMDS; Mono-α-aryl derivatives of diethyl malonate and ethyl cyanoacetate;

Heronamycin A: a new benzothiazine ansamycin from an Australian marine-derived Streptomyces sp. by Ritesh Raju; Andrew M. Piggott; Zeinab Khalil; Paul V. Bernhardt; Robert J. Capon (1063-1065).
Chemical analysis of a marine-derived Streptomyces sp. (CMB-M0392) isolated from sediment collected off Heron Island, Queensland, Australia, yielded a new benzothiazine ansamycin, heronamycin A. The absolute stereostructure of heronamycin A was determined by detailed spectroscopic analysis and X-ray crystallography. Heronamycin A exhibited modest antimicrobial activity against Bacillus subtilis strains ATCC 6051 and 6633 (IC50  = 18 and 14 μM, respectively).
Keywords: Benzothiazine ansamycin; Marine-derived Streptomyces; Herbimycin A; Natural products chemistry;

Efficient solid-phase synthesis of cyclic RGD peptides under controlled microwave heating by Keiichi Yamada; Izuru Nagashima; Masakazu Hachisu; Ichiro Matsuo; Hiroki Shimizu (1066-1070).
Cyclic RGD peptides are potent antagonists for the αvβ3 integrin receptor. In this Letter, microwave-assisted solid-phase synthesis of cyclic RGD peptides is described. In a coupling reaction between Fmoc-Arg(Pbf)-OH and high-loading H-Gly-Trt(2-Cl) resin, multiple coupling reactions were required for completion under the conventional HBTU activation. We found that the use of COMU, a new coupling reagent, under microwave heating to 50 °C accelerated the reaction even inside the resin. This method was applicable to the synthesis of linear pentapeptides, H-Asp(OtBu)-Xxx-Yyy-Arg(Pbf)-Gly-OH (Xxx =  d-Phe(p-Br) or d-Tyr, Yyy = Lys(Boc) or MeVal). Cyclization of these peptides followed by deprotection gave the desired cyclic RGD peptides with high purity.
Keywords: Microwave-assisted synthesis; Solid-phase peptide synthesis; Cyclic RGD peptides; COMU;

Biocatalytic production of tetrahydroisoquinolines by Bettina M. Ruff; S. Bräse; Sarah E. O’Connor (1071-1074).
The promiscuity of the enzyme norcoclaurine synthase is described. This biocatalyst yielded a diverse array of substituted tetrahydroisoquinolines by cyclizing dopamine with various acetaldehydes in a Pictet–Spengler reaction. This enzymatic reaction may provide a biocatalytic route to a range of tetrahydroisoquinoline alkaloids.
Keywords: Biocatalysis; Pictet–Spengler reaction; Norcoclaurine synthase; Tetrahydroisoquinoline alkaloids;

Polystyrene-supported TBD (PS-TBD) catalyzes cyanosilylation of both aldehydes and ketones using TMSCN to give the corresponding products in high yields. Imines were also converted into the desired α-cyanoanimes under the same conditions. PS-TBD was easily recovered and reused without significant loss of catalytic activity.
Keywords: Cyanosilylation; Organocatalyst; Basecatalyst; Polymercatalyst; Guanidine;

Dermcidin (DCD) is a human peptide composed of 110 amino acids. When secreted into sweat, DCD undergoes postsecretory proteolytic processing to give the short antimicrobial peptides SSL-23 and SSL-25. As an initial phase of studies directed toward understanding the structural basis of the biological functions of these peptides, we chemically synthesized naturally occurring SSL-23 and SSL-25, as well as the artificial sequences SSL-21 and SSL-27, and analyzed their molecular interaction with bacterial and mammalian model surfaces. While dynamic-coating HPLC and CD spectroscopy revealed that the four SSL peptides selectively bound to a bacterial model membrane containing 1,2-dimyristoyl phosphatidylglycerol (DMPG) and underwent large structural changes, 31P NMR studies of the liposomes suggested that the attractive interaction between the peptides and DMPG did not lead to ion-pore formation or disruption of the model membrane. Our results strongly indicate that the SSL peptides express their selectivity to microorganisms by recognizing the head groups of their cell surface lipid.
Keywords: Antimicrobial peptides; Membranes; 31P NMR; CD spectroscopy; Dynamic-coating HPLC;

New use of bis(benzotriazolyl)-1,2-(dialkylamino)ethanes for the synthesis of 2-H-3-dialkylamino imidazo[1,2-a]pyrazine derivatives by Joaquín Pastor; Sonsoles Rodríguez-Arístegui; Ana Isabel Hernández; Carmen Varela; Antonio Salgado; Sonia Martínez (1082-1084).
First direct synthesis of 2-H-3-N-dialkyl-imidazo[1,2-a]pyrazines is described. This approach makes use of accessible substituted pyrazines and the assistance of benzotriazole. In such a manner we accomplished the introduction of cyclic amines at C-3 of the scaffold in a convenient formal cyclisation procedure. Detailed examples and utility of this approach are presented herein.
Keywords: 2-H-3-N-Dialkyl-imidazo[1,2-a]pyrazines synthesis; One pot cyclisation; Benzotriazole;

Synthesis of chiral 1,2,3-triols via organocatalyzed α-hydroxylation of protected β-hydroxyaldehydes by Olivier Colin; Philippe Hermange; Christine Thomassigny; Christine Greck (1085-1088).
Protected 1,2,3-triols were prepared by organocatalytic α-hydroxylation of β-hydroxyaldehydes followed by in situ reduction. All diastereoisomers were obtained with correct yields and good to excellent de. The absolute configurations of the new asymmetric centers were confirmed by derivatization into the corresponding epoxide.
Keywords: Hydroxylation; Organocatalysis; Enantioselectivity; Hydroxyaldehydes; 1,2,3-Triols;

Pd/Nb2O5: efficient supported palladium heterogeneous catalyst in the production of key intermediates for the synthesis of ‘sartans’ via the Suzuki reaction by Gizelda O.D. Estrada; Ana Luiza P. Blanco; Joaquim F.M. da Silva; Christian G. Alonso; Nádia R.C. Fernandes-Machado; Lucio Cardozo-Filho; Rodrigo O.M.A. de Souza; Leandro S.M. e Miranda (1089-1093).
Pd/Nb2O5 was prepared, characterized and tested in Suzuki–Miyaura cross-coupling reactions under ligand-free conditions. High yields and selectivities were observed within short reaction times and very low palladium loadings.
Keywords: Heterogeneous palladium catalyst; Solid-supported palladium; Suzuki–Miyaura cross-coupling; Ligand-free; Microwave irradiation;

Facile synthesis of 1-bromo-7-alkoxyl perylene diimide dyes: toward unsymmetrical functionalizations at the 1,7-positions by Xin Zhang; Shufeng Pang; Zhigang Zhang; Xunlei Ding; Shanlin Zhang; Shenggui He; Chuanlang Zhan (1094-1097).
In this Letter, we report a facile approach to synthesize unsymmetrical 1-bromo-7-alkoxyl perylene diimides by the nucleophilic substitution of one of the two 1,7-dibromo units with an alkyl alcohol using K2CO3 as the base. A further replacement of another bromo, for example, by using 4-hydroxylpyridine resulted in unsymmetrical functionalizations at the 1,7-positions. The optical properties of the unsymmetrical PDI derivative were reported and compared with those of the symmetrical derivative.In this Letter, we report a facile approach to synthesize unsymmetrical 1-bromo-7-alkoxyl perylene diimides by the nucleophilic substitution of one of the two 1,7-dibromo units with an alkyl alcohol using K2CO3 as the base. A further replacement of another bromo, for example, by using 4-hydroxylpyridine resulted in unsymmetrical functionalizations at the 1,7-positions. The optical properties of the unsymmetrical PDI derivative were reported and compared with those of the symmetrical derivative.
Keywords: Perylene diimide; Nucleophilic substitution; Unsymmetrical functionalization; Nucleophile;

Toggle-switchable fluorescence of bisindolylmaleimide derivatives by reversible esterification/hydrolysis by Xiaochuan Li; Yunfeng Xu; Bingcai Wang; Young-A. Son (1098-1101).
Isomers based on the bisindolylmaleimide architecture were reported in this Letter. Introducing hydroxyl to this architecture lead to quenching the fluorescence of bisindolylmaleimide. The fluorescence was recovered with its hydroxyl group esterified. Ester group can be easily transformed to hydroxyl group by hydrolysis reaction. Thus, a toggle-switchable fluorescence, ‘off–on’ cycle can be established on the basis of reversible esterification/hydrolysis reaction.
Keywords: Bisindolylmaleimide; Fluorescence; Esterification/hydrolysis; Toggle-switchable; ‘Off–on’;

Synthesis and antitumour activity of inositol phosphonate analogues by Fanbo Song; Jing Zhang; Quanbin Cui; Ting Wang; Wenbin Chen; Luyuan Li; Zhen Xi (1102-1104).
Inositol phosphates regulate important biological functions in intracellular signal transduction events. Phosphonates, because of the stability towards the action of phosphatases, were extensively used to replace phosphates. We herein reported the synthesis of inositol phosphonate analogues using myo-inositol as the starting material, and found that two of phosphonate analogues exhibited relative good cytotoxic activity against non-small cell lung cancer (NSCLC) cell line A549.
Keywords: Inositol phosphate; Inositol phosphonate; Anticancer agents; NSCLC;

Synthesis of novel pyranoquinones using an acyl radical cyclization strategy by Christopher D. Donner; Myriam I. Casana (1105-1107).
The thiol-catalysed cyclization of acyl radicals generated directly from benzaldehyde precursors has been investigated. Hindered β-benzyloxyacrylates cyclize efficiently providing a tin-free radical cyclization approach to the serine/threonine kinase AKT inhibitor frenolicin B, whilst γ-aryloxy crotonates give good yields of benzopyran-4-ones. This method is applied to the synthesis of a novel tetracyclic analogue of the pyranonaphthoquinone antibiotics.
Keywords: Acyl radical cyclization; Polarity reversal catalysis; Pyranonaphthoquinone; Frenolicin B;

An unusual oxidative rearrangement of [7]-helicene by Matthew J. Fuchter; Marko Weimar; Xuezheng Yang; Dilraj K. Judge; Andrew J.P. White (1108-1111).
En route to helicene metal ‘sandwich’ complexes we have discovered an unusual oxidative rearrangement of [7]-helicene. The process involves a substantial skeletal rearrangement with the loss of helicity. We describe the identification of this curious product and its subsequent characterisation data.
Keywords: Helicene; Rearrangement; Diels–Alder; Fragmentation;

Insertion of allenyl carbenoids (3-tosyloxy-1-lithioalk-1-ynes) into organozirconium complexes gave allenyl-zirconocenes via a 1,2-zirconate rearrangement. Trapping of the allenyl-zirconium species with aldehydes and ketones gave, after hydrolysis, a series of homopropargyl alcohols. Enantioenriched products were prepared by insertion of the lithium carbenoid derived from (S)-but-3-yn-2-yl 4-toluenesulfonate into alkyl- and alkenyl-chlorozirconocenes.
Keywords: Homopropargyl alcohol; Metallate rearrangement; Organozirconium chemistry; Asymmetric synthesis; Carbenoids;

New preparation method for Vilsmeier reagent and related imidoyl chlorides by Yoshikazu Kimura; Daisuke Matsuura; Takeshi Hanawa; Yukimoto Kobayashi (1116-1118).
An environmentally benign and inexpensive preparation method is described of some imidoyl chlorides, including the Vilsmeier reagent (VR), by using phthaloyl dichloride. Synthetic applications were demonstrated using the isolated VR or VR prepared in situ for the transformation of acids to acid chlorides, alcohols to chlorides, and the formylation of dimethylaminobenzene.
Keywords: Vilsmeier reagent; Phthaloyl dichloride; 2-Chloro-1,3-dimethylimidazolium chloride; N,N,N′,N′-Tetramethylchloroformamidinium chloride; Chlorination;

Asymmetric synthesis of (−)-(S,S)-homaline by Stephen G. Davies; James A. Lee; Paul M. Roberts; Jeffrey P. Stonehouse; James E. Thomson (1119-1121).
The asymmetric synthesis of (−)-(S,S)-homaline was achieved in 8 steps 18% overall yield, from commercially available starting materials, using the diastereoselective conjugate addition of lithium (R)-N-(3-chloropropyl)-N-(α-methyl-p-methoxybenzyl)amide to methyl cinnamate as the key step.The asymmetric synthesis of (−)-(S,S)-homaline was achieved in 8 steps from commercially available starting materials using the diastereoselective conjugate addition of the novel lithium amide reagent lithium (R)-N-(3-chloropropyl)-N-(α-methyl-p-methoxybenzyl)amide to methyl cinnamate to install the correct stereochemistry. Subsequent functional group manipulation of the resultant β-amino ester and Sb(OEt)3-mediated macrolactamisation was followed by homodimerisation to give (−)-(S,S)-homaline in 18% overall yield, representing the first asymmetric, and by far the most efficient synthesis of this natural product reported to date.
Keywords: (−)-(S,S)-Homaline; Homalium alkaloids; Lithium amide; Conjugate addition; Asymmetric synthesis;

Efficient synthesis of 5,6-dihydro-8H-[1,2,4]thiadiazino[6,5,4-de]phenanthridine 4,4-dioxide and 5,6-dihydro-8H-[1,2,4]-thiadiazino[6,5,4-ij]thieno[2,3-c]quinoline 4,4-dioxide by Umberto M. Battisti; Marina M. Carrozzo; Giuseppe Cannazza; Daniela Braghiroli; Carlo Parenti; Livio Brasili; Cinzia Citti; Luigino Troisi (1122-1125).
A new efficient and versatile synthesis to obtain different substituted 5,6-dihydro-8H-[1,2,4]thiadiazino[6,5,4-de]phenanthridine 4,4-dioxide and 5,6-dihydro-8H-[1,2,4]-thiadiazino[6,5,4-ij]thieno[2,3-c]quinolone 4,4-dioxide was developed. The four cyclic systems are achieved by a three-step synthesis proceeding under mild conditions in high yields.
Keywords: Phenanthridines; Thieno[2,3-c]quinolines; Benzothiadiazines; AMPA receptor;

A novel bioglycerol-based recyclable carbon catalyst for an efficient one-pot synthesis of highly substituted imidazoles by K. Ramesh; S. Narayana Murthy; K. Karnakar; Y.V.D. Nageswar; Kukuma Vijayalakhshmi; Bethala L.A. Prabhavathi Devi; R.B.N. Prasad (1126-1129).
The new bioglycerol-based carbon catalyst acts as an efficient, readily available, and reusable catalyst for the synthesis of 2,4,5-trisubstituted imidazoles/1,2,4,5-tetrasubstituted imidazoles, when aromatic aldehyde, ammonium acetate/amine, and 1,2-diketone are reacted in acetonitrile.
Keywords: Aldehyde; 1,2-Diketones; Amine; Ammonium acetate; Multi-component reaction; Acetonitrile; Catalyst;

Sc(OTf)3-catalyzed, solvent-free domino synthesis of functionalized pyrazoles under controlled microwave irradiation by Kumkum Kumari; Dushyant Singh Raghuvanshi; Viatcheslav Jouikov; Krishna Nand Singh (1130-1133).
An efficient, rapid, and green synthesis of functionalized pyrazoles has been accomplished under solvent-free conditions by the reaction of phenyl hydrazine, aldehydes and ethyl acetoacetate. This approach exploits the synthetic potential of microwave irradiation and scandium triflate combination and offers many advantages such as excellent product yields, shorter reaction time, easy isolation of products, and environmentally benign reaction conditions.
Keywords: Green synthesis; Multicomponent reaction; Microwave; Sc(OTf)3; Functionalized pyrazoles;

AlCl3 induced C-arylation/cyclization in a single pot: a new route to benzofuran fused N-heterocycles of pharmacological interest by K. Shiva Kumar; Raju Adepu; Ravikumar Kapavarapu; D. Rambabu; G. Rama Krishna; C. Malla Reddy; K. Krishna Priya; Kishore V.L. Parsa; Manojit Pal (1134-1138).
A new and one-pot synthesis of benzofuran fused N-heterocycles has been accomplished via AlCl3-mediated C–C followed by C–O bond formation between 2,3-dichloropyrazine or its derivatives and phenols. The methodology provided novel compounds as potential inhibitors of PDE4B. The single crystal X-ray data of a synthesized benzofuran derivative are presented. Scope of the methodology, in vitro pharmacological data of some of the synthesized compounds, along with docking study of an active compound are described.
Keywords: Benzofuran; 2,3-Dichloropyrazine; AlCl3; X-ray; PDE4;

Photophysical properties and dye-sensitized solar cell studies on thiadiazole–triazole–chalcone dendrimers by Perumal Rajakumar; Ayyavu Thirunarayanan; Sebastian Raja; Shanmugam Ganesan; Pichai Maruthamuthu (1139-1143).
Synthesis of charge-separable and hole-transporting dendrimers with chalcone at the periphery, thiadiazole as core and triazole as branching unit has been achieved through ‘click’ reaction. The dendrimers are used as a charge separator in dye-sensitized solar cells (DSSCs) and exhibit higher open-circuit voltage than the bare film through the suppression of back electron transfer. As the dendrimer generations increases the dimension of the dendrimer also increases, resulting in a stronger association with I 3 - redox couple and higher open-circuit.
Keywords: Dendrimers; Chalcone; 1,3,4-Thiadiazole; Alkyne; Azide; Click; Photoisomerization; DSSC;

Facile catalyst-free pseudo five-component domino reactions in the expedient synthesis of 5-aroyl-1,3-diarylhexahydropyrimidines by Sivasubramanian Muthusaravanan; Subbu Perumal; Abdulrahman I. Almansour (1144-1148).
The pseudo five-component domino reactions of (E)-3-(dimethylamino)-1-arylprop-2-en-1-one, formaldehyde and aniline afford 5-aroyl-1,3-diarylhexahydropyrimidines in good yields under catalyst-free conditions. This transformation involving 4 C–N and 1 C–C bond formations in a one pot operation presumably proceeds via Michael addition–elimination–Mannich type reaction-condensative annulation–reduction sequence.
Keywords: Domino reaction; (E)-3-(Dimethylamino)-1-arylprop-2-en-1-one; Formaldehyde; Aniline; 5-Aroyl-1,3-diarylhexahydropyrimidines;

Treatment of 2-(2-oxo-2-arylethylthio)-N-(4H-1,2,4-triazol-3-yl)acetamides with paraformaldehyde in the presence of a base has led to a tandem chemoselective hydroxymethylation followed by cyclization yielding a set of novel 6-aroyl-4-(4H-triazol-3-yl)thiomorpholin-3-ones. The thiomorpholine ring has been found to have a boat like conformation in these compounds as evidenced by NOESY NMR spectrum.
Keywords: Chemoselective hydroxymethylation; Paraformaldehyde; 6-Aroyl-4-(4H-triazol-3-yl)thiomorpholin-3-one; Boat conformation; Tandem cyclization;

Synthesis of stagonolide C from Mulzer epoxide by Jian-Zhong Wu; Zhixia Wang; Chunhua Qiao (1153-1155).
Total synthesis of stagonolide C using chiral pool strategy is described. The two key intermediates were prepared from l-glutamic acid and d-glucono-1,5-lactone, followed by Julia–Lythgoe olefination and Yamaguchi esterification to afford the target compound in an efficient way.
Keywords: Stagonolide C; Mulzer epoxide; Julia–Lythgoe olefination; Yamaguchi esterification; Total synthesis;

Benzylic modifications of meso-alkyl-substituted porphyrins via oxidation with DDQ by Xiaobin Peng; Chao Gao; Yuying Huang; Junbiao Peng; Naoki Aratani; Atsuhiro Osuka (1156-1159).
The reactions at the benzylic positions of meso-alkyl-substituted porphyrins have been achieved via the reaction with DDQ in the presence of alcohol or water for the first time, and ethenyl porphyrins from methoxylated porphyrins and an acetoxy porphyrin from the hydroxyl porphyrin were prepared.
Keywords: Alkyl porphyrin; Benzylic modification; DDQ;

A convenient and efficient K2CO3-promoted tandem reaction of chalcone, malononitrile, and methanol for the synthesis of highly functionalized pyridines has been developed. This multi-component reaction employing the weak nucleophilic agent methanol proceeded smoothly under combined microwave and ultrasound irradiation (CMUI). The reaction mechanism was proposed to consist of a Michael addition, a methoxylation of CN bond, a cyclization to a 1,4-dihydropyridine and an intermolecular hydrogen shift between 1,4-dihydropyridine and initial chalcone.
Keywords: Pyridines; Heterogeneous; Microwave; Ultrasound;

Selective oxidation of organic sulfides by mononuclear and dinuclear peroxotungsten(VI) complexes by Siva Prasad Das; Jeena Jyoti Boruah; Hiran Chetry; Nashreen S. Islam (1163-1168).
Clean conversion of a variety of sulfides and dibenzothiophene (DBT) to the corresponding sulfoxide or sulfone could be achieved in excellent yield at room temperature, using mononuclear as well as dinuclear diperoxo complexes of tungsten as oxidants, by a versatile variation of reaction conditions. The compounds are recoverable, exhibit chemoselectivity and the reactions proceed under mild condition.Clean conversion of a variety of sulfides and dibenzothiophene (DBT) to the corresponding sulfoxide or sulfone could be achieved in high yields at room temperature using mononuclear as well as dinuclear diperoxo complexes of tungsten as oxidants, by a variation of reaction conditions. The compounds could also effectively catalyze oxidation of sulfides by H2O2 to selectively yield sulfone with reasonably good turnover frequency (TOF).
Keywords: Peroxotungsten(VI) complexes; Dinuclear peroxotungstate; Chemoselective sulfoxidation; Dibenzothiophene oxidation;

Highly selective and sensitive fluorescent chemosensor for Hg2+ in aqueous solution by Hsiu-Han Wu; Yao-Lin Sun; Chin-Feng Wan; Shih-Tse Yang; Shau-Jiun Chen; Ching-Han Hu; An-Tai Wu (1169-1172).
A new indole-based fluorescent chemosensor 1 was prepared and its metal ion sensing properties were investigated. It exhibits high sensitivity and selectivity toward Hg2+ among a series of metal ions in H2O–EtOH (7:1, v/v). The association constant of the 1:1 complex formation for 1-Hg2+ was calculated to be 9.57 × 103  M−1, and the detection limit for Hg2+ was found to be 2.25 × 10−5  M. Computational results revealed that 1 and Hg2+ ion formed with a central tetrahedron-coordinated Hg2+.
Keywords: Indole; Sensor; Mercury;

The reaction of thiophene derivatives with Grignard reagent (EtMgCl) and a catalytic amount of amine (Cy2NH) induced the metalation at the α-position. Following addition of several aryl halides in the presence of a nickel or palladium catalyst afforded C–H arylated products in good to excellent yields. The method was successfully applied to facile synthesis of differently-substituted 2,5-diarylthiophenes.
Keywords: Thiophene; C–H arylation; Magnesium amide; PEPPSI; 2,5-Diarylthiophene;

Construction of dihydropyrimidine skeleton using 1,2,4-trisubstituted-1,3-diaza-1,3-butadienes by Hidetsura Cho; Yoshio Nishimura; Yoshizumi Yasui; Masahiko Yamaguchi (1177-1179).
Construction of a dihydropyrimidine ring was developed that involved the cyclization of 1,3-diaza-1,3-butadienes having an N-protecting group (N-Cbz, N-Boc, N-alkyl, or N-benzyl) with α,β-unsaturated carbonyl compounds such as ethyl acrylate and p-chlorophenyl vinyl ketone. Consequently, 4-dimethylamino-2-phenyl-1,4,5,6-tetrahydropyrimidines were synthesized in good yields. Subsequently, the β-elimination of the dimethylamino group was carried out with MeI or SiO2 to afford various N-protecting-2,5-disubstituted-1,6-dihydropyrimidines in good yields. Remarkably, the use of 4-chlorophenyl vinyl ketone directly provided the dihydropyrimidine without the tetrahydropyrimidine intermediate in excellent yield.
Keywords: Dihydropyrimidine; Cycloaddition; Heterocycles; Dienes; Cyclization;

Iridium-catalyzed direct borylation of phenacenes by Shunpei Hitosugi; Yuta Nakamura; Taisuke Matsuno; Waka Nakanishi; Hiroyuki Isobe (1180-1182).
Iridium-catalyzed borylation of phenacenes with bis(pinacolato)diboron proceeds either in an edge-selective manner for diborylation or an edge/side-selective manner for tetraborylation. Multiply borylated [n]phenacenes (n  = 3–5) were synthesized in reasonable yields.
Keywords: Phenacenes; Borylation; Iridium; Regio-selectivity;

Dysoxylentin A (1), the first 21-nortriterpenoid bearing a 2-(propan-2-ylidenyl)furan-3(2H)-one functional group was isolated from the stem of Dysoxylum lenticellatum. Its structure was elucidated by extensive spectroscopic analysis. A plausible biosynthetic pathway was postulated. Dysoxylentin A exhibited selective cytotoxicity against HL-60 tumor cell line.
Keywords: Dysoxylum lenticellatum; Dysoxylentin A; 21-Nortriterpenoid; Cytotoxicity;

Total synthesis of stagonolide B by Tapas Das; Tridib Mahapatra; Samik Nanda (1186-1189).
Asymmetric total synthesis of nonenolide stagonolide-B has been presented in this Letter. The main highlight of our synthetic strategy is the application of hydroxynitrile lyase (ParsHNL) mediated asymmetric synthesis of cyanohydrin, Sharpless asymmetric dihydroxylation, cross metathesis (CM) reaction, stereoselective Keck allylation reaction and Yamaguchi macrolactonization at a late stage enables us to achieve the synthesis of the target molecule in an efficient way.
Keywords: Small ring macrolide; Enzymatic hydrocynation; Asymmetric allylation; Cross metathesis; Macrolactonization;