Tetrahedron Letters (v.52, #36)

Copper-catalyzed direct preparation of diaryl sulfides from aryl iodides using potassium thiocyanate as a sulfur transfer reagent by Christopher B. Kelly; Christopher (Xiang) Lee; Nicholas E. Leadbeater (4587-4589).
A method for direct preparation of diaryl sulfides from aryl iodides using potassium thiocyanate as a sulfur-transfer agent is reported. A catalyst system comprising of a simple copper salt, tetrabutylammonium bromide as a phase-transfer agent and water as the solvent is used. Microwave heating at 200 °C for 60 min allows for the conversion of a range of aryl iodides to the corresponding diaryl sulfides.
Keywords: Copper; Diaryl sulfides; Aryl halides; Potassium thiocyanate; Water;

This study investigates the ability of the mixed-metal reagent [Li(TMP)Zn(tBu)2] 1 to promote direct Zn–H exchange reactions (zincations) of a wide range of N-heterocyclic molecules. The generated metallated intermediates from these reactions are intercepted with I2 and some of them are also employed as precursors in Pd-catalysed Negishi cross-coupling applications. A comparison with recent precedents in metallation chemistry reveals that for some of these heterocycles, 1 allows improved conversions, under milder conditions and in certain cases, even gives unique regioselectivities.
Keywords: Metallation; Zincation; N-Heterocycles; Lithium; Mixed-metal reagents;

Polypropionates from Bulla occidentalis: chemical markers and trophic relationships in cephalaspidean molluscs by Adele Cutignano; Gonçalo Calado; Helena Gaspar; Guido Cimino; Angelo Fontana (4595-4597).
A chemical investigation on the cephalaspidean Bulla occidentalis from the Gulf of Mexico led to known niuhinones A (1) and B (2) along with a new acyclic polypropionate, named niuhinone C (3). A complete NMR assignment of niuhinone A has been achieved by spectroscopic experiments, thus revising the Δ14 configuration. The occurrence of structurally related polypropionates in Bullidae species from different geographical areas is in agreement with a de novo origin in this family of molluscs and adds a further piece of evidence on prey–predator relationships among cephalaspideans.
Keywords: Polypropionates; Niuhinones; Cephalaspidea; Bullidae; Prey–predator relationship; De novo biosynthesis;

Asymmetric synthesis of (E)-dehydroapratoxin A by Jing-Yi Ma; Wei Huang; Bang-Guo Wei (4598-4601).
An asymmetric approach to key intermediate 17 starting from lactone 7 is described, in which Evan’s alkylation and CBS-catalyzed reduction are used for construction of the chiral centers, respectively. Thus, the synthesis of (E)-dehydroapratoxin A 6 could be accomplished in a general fashion, therein FDPP has been proven as an efficient condensation reagent for the coupling of amine 25 and carboxylic acid 24.An asymmetric approach to key intermediate 17 starting from lactone 7 is described, in which Evan’s alkylation and CBS-catalyzed reduction are used for construction of the chiral centers, respectively. Thus, the synthesis of (E)-dehydroapratoxin A 6 could be accomplished in a general fashion, therein FDPP has been proven as an efficient condensation reagent for the coupling of amine 25 and carboxylic acid 24.
Keywords: Depsipeptide; Marine cyanobacteria; Apratoxin; Total synthesis; Macrolactamization;

A facile synthesis of spiro macrocarbocycles via the cycloalumination reaction of cyclic alkynes and alkadiynes by Vladimir A. D’yakonov; Regina A. Tuktarova; Leonard M. Khalilov; Usein M. Dzhemilev (4602-4605).
Zirconium-catalyzed cycloalumination of cycloalkadiynes assisted by Et3Al, subsequent treatment of the in situ generated tricyclic dialuminum compounds with BrCH2OMe and finally cyclopropanation of the obtained dispiro cyclopropyl dimethylene macrocarbocycles with Et3Al–CH2I2 represents an efficient one-pot synthetic approach to prepare di- and tetraspiro cyclopropane-containing macrocarbocycles in very high yields.
Keywords: Homogeneous catalysis; Organoaluminum compounds; Spiranes; Cycloalumination; Dzhemilev reaction; Cyclic diynes; Bis-cyclopropanes; Zirconocene dichloride;

Highly chemo-, regio-, and stereoselective syntheses of novel organoselenium compounds from selenium dichloride or dibromide and unsaturated ethers are described. The reactions of selenium dichloride with allyl and propargyl phenyl ethers afford either annulated products or bis-adducts depending on the conditions. The first examples of annulation of 3-chloromethyl- and 3-chloromethylene-2,3-dihydro-1,4-oxaselenine to the benzene ring are reported.
Keywords: Allyl phenyl ether; Propargyl phenyl ether; Selenium dichloride; Selenium dibromide; Unsaturated ethers; 2,3-Dihydro-1,4-oxaselenine; Vinylic selenides;

Highly enantioselective fluorescent recognition of amino acid derivatives by unsymmetrical salan sensors by Xia Yang; Kang Shen; Xuechao Liu; Chengjian Zhu; Yixiang Cheng (4611-4614).
Novel unsymmetrical salan fluorescent sensors 2a and 2b have been designed and synthesized. The chiral recognition of N-Boc-protected amino acids by 2a and 2b has been investigated. Sensor 2a possesses higher sensitivity and enantioselectivity than sensor 2b does. Job analysis and nonlinear regression results show that 2a can form a 1:1 stoichiometric complex with a N-Boc-protected amino acid. The obtained response selectivities and the association constants indicate that 2a is a highly enantioselective and sensitive fluorescent sensor toward N-Boc-protected amino acids.
Keywords: Chiral recognition; Fluorescent sensor; Unsymmetrical salan; Amino acids; PET;

Diels–Alder reaction of 4-halogenated masked o-benzoquinones with electron-rich dienophiles by Seshi Reddy Surasani; Rama Krishna Peddinti (4615-4618).
Inverse-electron-demand Diels–Alder reaction of masked o-benzoquinones (MOBs) ensuing from the corresponding 4-halo-2-methoxyphenols with styrene, dihydrofuran and ethyl vinyl ether, butyl vinyl ether, phenyl vinyl sulfide and vinyl acetate to afford the highly functionalized halogen substituted bicylclo[2.2.2]octenones are described.
Keywords: Hypervalent iodine reagent; Arene oxidation; Orthoquinone monoketals; 4-Halo masked o-benzoquinones; Cycloaddition reaction;

A short and straightforward synthesis of the racemic tobacco alkaloids anatabine and anabasine in five and six steps, respectively, from 3-pyridinecarboxaldehyde utilizing Barbier-type Zn-mediated allylation and ring-closing olefin metathesis, as the key steps, is reported. Additionally, a complete NMR spectroscopic analysis of the final products is carried out and full assignment of the NMR spectra of anatabine and anabasine with accurate coupling constants is accomplished and reported here for the first time.
Keywords: Barbier-type allylation; Zinc; Ring-closing metathesis; Ruthenium; Tobacco alkaloid;

A Brønsted acidic ionic liquid-[Hmim]HSO4 promoted unexpected reaction of Baylis–Hillman alcohols and diarylmethanols with p-toluenesulfonylmethyl isocyanide (TosMIC) affording the corresponding sulfone derivatives instead of N-tosylmethyl amides is reported. After isolation of the product, the ionic liquid [Hmim]HSO4 was easily recycled for further use.
Keywords: Ionic liquids; Sulfonylation; Baylis–Hillman alcohols; p-Toluenesulfonylmethyl isocyanide (TosMIC); Allylic sulfones;

Target cum flexibility: synthesis of C(3)-spiroannulated nucleosides by Mangesh P. Dushing; C.V. Ramana (4627-4630).
We report a simple strategy for the synthesis of a collection of C(3′)-spirodihydroisobenzo-furannulated nucleosides featuring a [2+2+2]-cyclotrimerization as the key reaction. The cyclotrimerization reactions are facile with the unprotected nucleosides having a diyne unit. When both alkynes of the diyne are terminal, the regioselectivity is poor. However, when one of the terminal alkynes is additionally substituted, the cyclotrimerizations are highly diastereoselective. Since the key bicycloannulation is the final step, this strategy provides flexibility in terms of the alkynes and is thus amenable for the synthesis of a focussed small molecule library.
Keywords: Modified nucleosides; [2+2+2]-Cyclotrimerization; Dihydroisobenzofuran; Tanaka catalyst; Willkinson catalyst;

Herein, we report the highly selective binding of Zn2+ ion by the salicylaldimine based Schiff base chromogenic receptor 1 [(N,N′-bis(salicylidine)-o-phenylenediamine]. Receptor 1 senses Zn2+ ion in aqueous medium by colorimetric and fluorescent response in the presence of other metal ions like Pb2+, Hg2+, Sn2+, Cd2+. Receptor 1 on binding with Zn2+ ion exhibits fluorescence enhancement which is due to the inhibition of (ESIPT) mechanism.Herein, we report the highly selective binding of Zn2+ ion by the salicylaldimine based Schiff base chromogenic receptor 1 [(N,N′-bis (salicylidine)-o-phenylenediamine]. Receptor 1 senses Zn2+ ion in aqueous medium by colorimetric and fluorescent response in the presence of other metal ions like Pb2+, Hg2+, Sn2+, Cd2+. Receptor 1 on binding with Zn2+ ion exhibits fluorescence enhancement which is due to the inhibition of the (ESIPT) mechanism.
Keywords: Schiff base; Zn2+ ion sensors; UV–vis spectroscopy; ESIPT; Fluorescence enhancement;

An efficient and green protocol for the synthesis of dihydropyrano[2,3-c]chromene derivatives by one-pot, three component coupling reaction of aromatic aldehyde, malononitrile, and 3-hydroxycoumarin has been developed using nano-structured ZnO as the catalyst. The formation of self-assembled organic nanofiber arising from low-molecular-weight molecules has also been performed. The optical properties of the nano-structured organic molecules were studied.
Keywords: Dihydropyrano[2,3-c]chromene; Green protocol; Organic nanofibers; Self aggregation;

A simple and efficient procedure for the preparation of silica-bonded propylpiperazine-N-sulfamic acid (SBPPSA) by the reaction of 3-piperazine-N-propylsilica (3-PNPS) and chlorosulfonic acid in chloroform is described. Silica-bonded propylpiperazine-N-sulfamic acid is employed as a recyclable catalyst for the synthesis of highly substituted imidazoles from the reaction of benzil, aromatic aldehydes, ammonium acetate and amines under solvent-free conditions. The heterogeneous catalyst was recycled for five runs upon the reaction of benzil, 4-methylbenzaldehyde, benzylamine, and ammonium acetate without losing its catalytic activity.
Keywords: Silica-bonded propylpiperazine-N-sulfamic acid; 1,2,4,5-Tetrasubstituted imidazoles; Aldehydes; Solvent-free; Catalyst; One-pot synthesis;

Synthesis and binding behaviors of monomethyl cucurbit[6]uril by Mostafa M. Ahmed; Kazutaka Koga; Makoto Fukudome; Hideaki Sasaki; De-Qi Yuan (4646-4649).
By reacting 3a-methylglycoluril and glycoluril with paraformaldehyde, monomethyl cucurbit[6]uril was synthesized in 14% yield. The new host molecule forms stable inclusion complexes with diamine and hexylaminocarbazole derivatives.By reacting 3a-methylglycoluril and glycoluril with paraformaldehyde, monomethyl cucurbit[6]uril was synthesized in 14% yield. The new host molecule forms stable inclusion complexes with diamine and hexylaminocarbazole derivatives.
Keywords: Cucurbituril; Functionalization; Synthesis; Molecular recognition;

Reaction of isoselenocyanates with aminoacetonitriles afforded 4-amino-2-selenoxo-1,3-imidazole-2-selenones, whereas reaction with aminopropionitriles led to selenoureas. We confirmed that it is easy to distinguish between selenoamides and selenoureas by comparison of their chemical shift differences in the 77Se NMR spectra.
Keywords: Isoselenocyanate; Aminoacetonitrile; Imidazole; Selenium;

C–H Nitrooxylation at benzylic positions has been achieved by employing the N-hydroxyphthalimide (NHPI) catalyst/cerium(IV) ammonium nitrate (CAN) reagent system. The nitrooxy groups were demonstrated to function as tentative hydroxy protecting groups, as well as excellent leaving groups for N- and C-substitution reactions. Hence, the present method offers a unique way to synthesize diverse O-, N-, or C-functionalized benzylic compounds from simple alkyl aromatics.
Keywords: Catalysis; Nitrooxylation; Benzylic position; N-Hydroxyphthalimide; Cerium(IV) ammonium nitrate;

PhI(OCOCF3)2 (PIFA) in the presence of trifluoroacetic acid (TFA) in CH2Cl2 efficiently promotes the oxidative cycloisomerization of 2-propargyl 1,3-dicarbonyl compounds to give 4,5-disubstituted furfuryl alcohols. PIFA in hexafluoroisopropanol (HFIP) or PIFA-BF3·OEt2 in CH2Cl2 bring about the direct formation of furfurals from 2-propargyl 1,3-dicarbonyl compounds. In a few cases, PhI=O is suitable for the direct formation of furfurals.
Keywords: Oxidative cycloisomerization; Hypervalent iodine oxidant; Furfuryl alcohol; Furfural; Alkynyl ketone;

Various electron-deficient olefins reacted readily with 1,3-dioxolane or 2-methyl-1,3-dioxlane in the presence of TBAP to afford the corresponding 1,3-dioxolanylated or 2-methyl-1,3-dioxolanylated products in a complete regioselective manner in good to excellent yields.
Keywords: Electron-deficient olefins; Formylation; Acetylation; 1,4-Diketone; Peroxydisulfate;

Synthesis of indolequinones via a Sonogashira coupling/cyclization cascade reaction by Mitsuaki Yamashita; Kazunori Ueda; Koichi Sakaguchi; Akira Iida (4665-4670).
A mild strategy for constructing indolequinone motifs is described on the basis of the Sonogashira reaction and a copper-catalyzed intramolecular cyclization cascade reaction. The first step involves the palladium- and copper-catalyzed reaction between halogenated naphthoquinone and terminal acetylene to generate a coupling product, which then reacts in a copper-catalyzed intramolecular cyclization with the nitrogen functional group adjacent to the carbon–carbon triple bond.
Keywords: Indolequinones; Sonogashira coupling; Cascade reaction; Copper; Palladium;

Organic hydrogen phosphites and hydrogen phosphates catalyzed Friedel–Crafts amidoalkylation of indoles with aryl aldimines by Bei-Lei Wang; Jin-Xin Zhang; Nai-Kai Li; Guo-Gui Liu; Qi Shen; Xing-Wang Wang (4671-4674).
A highly efficient and selective Friedel–Crafts amidoalkylation reaction of indoles with N-Ts aryl aldimines has been developed utilizing dimethyl hydrogen phosphite or diphenyl hydrogen phosphate as the organocatalysts, providing a facile and cost-effective process for synthesis of 3-indolyl methanamine derivatives in good to excellent yields. This transformation displays a broad substrate scope and wide functional-group tolerability, regardless of the electronic and steric properties of N-Ts aryl aldimines. Given that the developed catalytic Friedel–Crafts amidoalkylation reaction exhibits several salient features such as metal-free catalysis, high efficiency, low cost and mild reaction condition, this process might have practical applications in the synthesis of 3-indolyl methanamine derivatives.
Keywords: Hydrogen phosphites; Hydrogen phosphates; Indoles; Friedel–Crafts; Amidoalkylation;

An effective and facile method for highly diastereoselective synthesis of quaternary α-trifluoromethyl α-amino acids was developed in good yields with high diastereoselectivity (dr >20:1) via MgCl2-accelerated addition of benzylzinc reagents (Knochel type organozinc reagents) to (R)-phenylglycinol methyl ether based imines of trifluoropyruvate.
Keywords: Benzylzinc reagents; Diastereoselective synthesis; Ketoimine esters; Quaternary α-trifluromethyl α-amino acids; Trifluoropyruvate;

Direct C-4 arylation of crotonaldehyde with arenediazonium tetrafluoroborates by Florencio Zaragoza; Verena Heinze (4678-4680).
Arenediazonium tetrafluoroborates react with crotonaldehyde (2-butenal) in methanol in the presence of catalytic amounts of Pd(OAc)2 to yield mainly 4,4-dimethoxy-1-butenylarenes. In most of the examples studied, small amounts of an isomeric byproduct were formed, presumably 3,3-dimethoxy-1-methylenepropylarenes. Because crotonaldehyde and arenediazonium salts are cheap and readily available, this reaction is a convenient access to protected 4-arylbutenals.
Keywords: Crotonaldehyde; Arenediazonium tetrafluoroborates; Palladium catalysis; Acetals;

A convenient and efficient method for the construction of indole skeleton was developed via Pd-catalyzed C–H activation of N-aryl amides and subsequent coupling with alkynes. Both stoichiometric and catalytic versions have been successfully achieved.
Keywords: Palladium; C–H activation; Indole; N-aryl amide; Alkyne;

Use of co-grinding as a solvent-free solid state method to synthesize dibenzophenazines by Leslie Carlier; Michel Baron; Alain Chamayou; Guy Couarraze (4686-4689).
Many synthetic methods exist for dibenzoquinoxalines but only a few for dibenzophenazines and their aza derivatives and even less are ‘green’. Some dibenzophenazines and dibenzopyridoquinoxaline have been efficiently obtained with good to excellent yield by a very simple method which does not require use of solvent or catalyst. Solid phase synthesis using co-grinding presents thus many advantages in developing greener synthetic organic pathways.
Keywords: Solid-phase synthesis; Green chemistry; Dibenzophenazines; Pyrido-quinoxaline; Organic mechanochemistry;

Heterogeneous continuous flow synthetic system using cyclohexane-based multiphase electrolyte solutions by Yohei Okada; Tomohiko Yoshioka; Mikio Koike; Kazuhiro Chiba (4690-4693).
The discovery that supporting electrolytes can be effectively confined in typical organic solvents in a c-Hex-based multiphase electrolyte solution has led to the development of a novel heterogeneous continuous flow synthetic system. PTFE fiber functions as a separation filter that can efficiently isolate the c-Hex phase from multiphase electrolyte solutions. This system has demonstrated both electrochemical solvating and carbon–carbon bond forming reactions. Hydrophobic substrates can be introduced into the reactor as c-Hex solutions, which are then electrochemically transformed into the target hydrophobic products that pass through the PTFE fiber as c-Hex solutions.
Keywords: Heterogeneous; Flow synthetic system; Cyclohexane; Multiphase electrolyte solution; PTFE fiber;

Melicodenines A and B, novel Diels–Alder type adducts isolated from Melicope denhamii by Ken-ichi Nakashima; Masayoshi Oyama; Tetsuro Ito; Joko Ridho Witono; Dedy Darnaedi; Toshiyuki Tanaka; Jin Murata; Munekazu Iinuma (4694-4696).
Two novel Diels–Alder type adducts, melicodenines A (1) and B (2), were isolated from the leaves of Melicope denhamii (Seem.) T. G. Hartley and their structures were established by spectroscopic analyses, including extensive 2D NMR experiments. Compound 1 is a bisquinolinone alkaloid comprised of two N-methylflindersines (3), while compound 2 is the first naturally occurring quinolinone–acetophenone conjugate composed of 3 and an evodionol methyl ether (4).
Keywords: Melicope denhamii; Rutaceae; Quinolinone; Diels–Alder cycloaddition;

Basic alumina supported tandem synthesis of bridged polycyclic quinolino/isoquinolinooxazocines under microwave irradiation by Shyamal Mondal; Rupankar Paira; Arindam Maity; Subhendu Naskar; Krishnendu B. Sahu; Abhijit Hazra; Pritam Saha; Sukdeb Banerjee; Nirup B. Mondal (4697-4700).
Basic alumina supported, solvent-free synthesis of novel oxazocines, medium size heterocycles, has been achieved in excellent yields by tandem C-alkylation followed by intramolecular O-alkylation of hydroxyquinoline/isoquinoline(s) with quinolinium salts under microwave irradiation. The method provides a facile and efficient route for the construction of polynuclear bridge-head oxazocines.
Keywords: Basic alumina; Tandem reaction; Bridged heterocycle; Quinolino/isoquinolinooxazocines; Microwave irradiation;

Efficient microwave-assisted synthesis of oximes from acetohydroxamic acid and carbonyl compounds using BF3·OEt2 as the catalyst by Madabhushi Sridhar; Chinthala Narsaiah; Jillella Raveendra; Godala Kondal Reddy; Mallu Kishore Kumar Reddy; Beeram China Ramanaiah (4701-4704).
An efficient synthesis of oximes by reaction of carbonyls with acetohydroxamic acid using BF3·OEt2 as a catalyst is described.
Keywords: Carbonyls; Oximes; Acetohydroxamic acid; Acid catalysis;