Tetrahedron Letters (v.47, #12)

The organomagnesium complex n Bu2 i PrMgLi, readily prepared from n BuLi and i PrMgCl (2:1), is quite efficient for the bromine–magnesium exchange of 5-bromo-2-picoline under noncryogenic conditions (at −10 °C). The resulting picolylmagnesium complex reacts with various electrophiles to afford functionalized picolines.

Regioselective, nucleophilic carbon–carbon bond formation at the C4-position of indoles initiated by the aromatic Pummerer-type reaction by Shuji Akai; Norihito Kawashita; Yasufumi Wada; Hideharu Satoh; Anahita Hessamian Alinejad; Keisuke Kakiguchi; Ikumi Kuriwaki; Yasuyuki Kita (1881-1884).
The treatment of the 5-(phenylsulfinyl)indoles with trifluoroacetic anhydride in the presence of carbon nucleophiles achieved the title reactions with complete regioselectivity.The treatment of the 5-(phenylsulfinyl)indoles with trifluoroacetic anhydride in the presence of carbon nucleophiles achieved the title reactions with complete regioselectivity.
Keywords: Aromatic Pummerer-type reaction; Indole; Carbon–carbon bond formation; Nucleophilic reaction;

Microwave promoted rapid nitration of phenolic compounds with calcium nitrate by Ajay K. Bose; Subhendu N. Ganguly; Maghar S. Manhas; Sheetal Rao; Jeffrey Speck; Uri Pekelny; Esteban Pombo-Villars (1885-1888).
Nitration of phenolic compounds by a green chemistry strategy was conducted with calcium nitrate/acetic acid under microwave irradiation.Highly accelerated and safe nitration of phenolic compounds has been found to be feasible with a mixture of calcium nitrate and acetic acid as an efficient nitration agent under brief microwave irradiation. This method is compatible with the green chemistry approach because calcium salts—the inorganic byproducts—can be useful agrochemicals rather than waste chemicals. Commercially available 15N-labeled calcium nitrate is convenient for the preparation of 15N-labeled compounds for metabolic studies and mass spectrometry. This safe nitration method can be included in laboratory experiments for high school and college students.
Keywords: Microwave-assisted nitration; Green chemistry approach; Mononitro phenol; Calcium nitrate for nitration; 15N-labeled compounds;

Iodine catalyzed conjugate addition of mercaptans to α,β-unsaturated carboxylic acids under solvent-free condition by Shijay Gao; Tingkai Tzeng; M.N.V. Sastry; Cheng-Ming Chu; Ju-Tsung Liu; Chunchi Lin; Ching-Fa Yao (1889-1893).
We have described herein molecular iodine catalyzed Michael addition of thiol to α,β-unsaturated carboxylic acids. This environmentally benign catalytic system (iodine) used under mild and solvent-free conditions to achieve the corresponding adducts in excellent yield.
Keywords: Conjugate addition; Thiols; α,β-Unsaturated carboxylic acid; Iodine; Solvent free;

New water-soluble calix[4]arene-based bipyridyl podands incorporating carboxylate groups by Maxime Mourer; Jean-Bernard Regnouf-de-Vains (1895-1899).
New calixarene-based bis-bipyridyl podands incorporating two sodium (4-oxo)-butanoate or four sodium carboxymethyl groups at the upper rim were synthesised and fully characterised. The (4-oxo)-butanoate derivative bearing unsubstituted bipyridyl arms was not soluble in water at neutral pH, while its 4,4′-dicarboxylate analogue was perfectly soluble, as were the carboxymethyl derivatives. The association of water solubility to the chelating behaviour of the bipyridyl subunits resulted in the ability to complex the unstable copper(I) cation in water, even in the presence of bovine serum albumin.

Highly electron-donating bis(trialkylphosphine) TangPhos and its corresponding ruthenium complexes provided high enantioselectivities for the hydrogenation of β-keto esters. Up to 99.8% and 99.5% ee have been achieved in hydrogenation of β-alkyl and β-aryl substituted β-keto esters, respectively. Asymmetric hydrogenation of ethyl 4-chloro acetoacetate in 98.2% ee is also reported.

Highly selective fluorescent sensing of Pb2+ by a new calix[4]arene derivative by Jun-Min Liu; Jian-Hua Bu; Qi-Yu Zheng; Chuan-Feng Chen; Zhi-Tang Huang (1905-1908).
A new chemosensor was synthesized by the alkylation of p-tert-butyl-calix[4]arene with three N,N-diethylacetamide groups and one methyl 3-ethoxy-naphthalene-2-carboxylate, which exhibited highly selective fluorescent response to Pb2+ over alkali, alkali earth metal ions and some transition metal ions in CH3CN–H2O.
Keywords: Calix[4]arene; Fluorescent chemosensor; Recognition; Lead (II);

The application of organic bases in microwave-promoted Suzuki coupling reactions in water by Florine Chanthavong; Nicholas E. Leadbeater (1909-1912).
Traditionally, mineral bases are used in Suzuki coupling protocols. The use of DBU or DABCO as alternative bases for the reaction is reported and the application discussed.Traditionally, mineral bases are used in Suzuki coupling protocols. The use of DBU or DABCO as alternative bases for the reaction is reported and the application discussed.

The synthesis and the characterization of new multichromophoric boron-dipyrromethene dyes are described. Their absorption, photoluminescence as well as their two-photon absorption properties have been investigated. This work shows that assembling several dyes in conjugated multichromophoric structures is a promising strategy for improving the two-photon absorption properties of such fluorophores in the NIR region while retaining their excellent photoluminescence properties.
Keywords: Two-photon-excited fluorescence (TPEF); Multichromophores; Photoluminescence; BODIPY®;

Clarithromycin–adenine and related conjugates by Jorge Esteban; Anna M. Costa; M. Carmen Cruzado; Montserrat Faja; Pilar García; Jaume Vilarrasa (1919-1922).
Keywords: Macrolide antibiotics; Erythromycin–thymidine chimeras; Clarithromycin–adenine chimeras; Oxime-linked conjugates; Oxazolidinone-linked conjugates;

We describe a simple and versatile method for the catalytic epoxidation of a broad range of olefins (e.g., ketones, esters, and alkyl halides) with aqueous H2O2 using manganese salophen catalysts. Low catalyst loading, short reaction times, and a simple reaction setup (e.g., no pH buffer is required) are salient features of the system, which unites the benefits of H2O2 as an oxidant with the versatility and modularity of salen-based catalysts.

Development of calixarene-based host molecules for peptides in aqueous media by Miwa Kubo; Emi Nashimoto; Tatsuro Tokiyo; Yasushi Morisaki; Mitsuaki Kodama; Hideaki Hioki (1927-1931).
Screening of dye-labeled tripeptides with peptidocalixarene library was run in pH 6.86 phosphate buffer containing 5% Triton X-100.We synthesized a peptidocalix[4]arene library consisting of 1000 members that was suitable for peptide recognition in aqueous media. Some peptidocalix[4]arenes in the library were host molecules for guest peptides. Electrostatic interaction between the host and guest molecules was the most important factor for binding in aqueous media.
Keywords: Calixarene; Combinatorial library; Recognition in aqueous media;

d-Phg-l-Pro Dipeptide-derived prolinol ligands for highly enantioselective Reformatsky reactions by Eun-kyoung Shin; Hyun Jung Kim; Yongtai Kim; Yangmee Kim; Yong Sun Park (1933-1935).

Keywords: Intramolecular C–H⋯O interaction; o-Carboranes; Supramolecular chemistry;

The described polyfunctional arylmagnesium reagents, resulting from the highly regioselective addition of magnesium phenylselenide to functionalized arynes, can be trapped by a range of electrophiles, yielding polyfunctional selenoethers in 45–85% yields. Furthermore, these Grignard reagents can be used in Negishi cross-coupling reactions with iodoarenes after transmetalation to the corresponding arylzinc compounds, furnishing functionalized biaryl products in 55–73% yields.
Keywords: Aryne; Organomagnesium reagent; Selenoether;

A new entry for the synthesis of N-acyl-N′-substituted guanidines by Tetsuro Shinada; Taiki Umezawa; Tsuyoshi Ando; Hayato Kozuma; Yasufumi Ohfune (1945-1947).
An efficient synthesis of N-acyl-N′-substituted guanidines by condensation reaction of thiourea and (Me3Si)2NH in the presence of EDCI is described. Various guanidines were synthesized in a simple manner.
Keywords: Thiourea; Guanidine; Condensation reaction; EDCI; HMDS;

Convenient multi-gram scale synthesis of polybrominated imidazoles building blocks by Mebarek Bahnous; Chabane Mouats; Yves Fort; Philippe C. Gros (1949-1951).
The multi-gram scale polybromination of variously substituted imidazoles has been realized using a stoichiometric amount of the Br2–DMF complex. Good yields have been obtained compared to other methods using large amounts of acetic acid–sodium acetate buffer.

Synthesis of new viologen macrocycles with intramolecular charge transfer by Elena Pía; Rosa Toba; Marcos Chas; Carlos Peinador; José Ma Quintela (1953-1956).
The syntheses of three new macrocycles composed of an acceptor (viologen) and a donor (dioxoaryl) are reported. These compounds exhibit intramolecular charge transfer and their X-ray analyses revealed that the aromatic systems are situated in parallel planes with a mean interplanar distance of 3.32 Å.
Keywords: Intramolecular charge transfer; Cyclophanes; Bipyridinium; Viologens;

Exiguolide, a new macrolide from the marine sponge Geodia exigua by Shinji Ohta; Mylene M. Uy; Mihoko Yanai; Emi Ohta; Toshifumi Hirata; Susumu Ikegami (1957-1960).
The structure of exiguolide was determined on the basis of spectroscopic data.A new 20-membered macrolide designated exiguolide has been isolated from the marine sponge Geodia exigua, and its structure determined by interpretation of spectroscopic data. Exiguolide specifically inhibited fertilization of sea urchin (Hemicentrotus pulcherrimus) gametes but not embryogenesis of the fertilized egg.
Keywords: Marine sponge; Geodia exigua; Macrolide;

Complementary stereoselective conjugate addition reactions on indolo[2,3-a]quinolizine templates by Steven M. Allin; Jagjit S. Khera; Christopher I. Thomas; Jason Witherington; Kevin Doyle; Mark R.J. Elsegood; Mark Edgar (1961-1964).
We report a new and highly stereoselective approach for the construction of a range of functionalized indolo[2,3-a]quinolizine targets from a readily available, nonracemic chiral template. The methods developed allow us to predetermine relative product stereochemistries by judicious choice of substrate sub-structure.

Photolytic decarboxylation of α-arylcarboxylic acids mediated by HgF2 under a dioxygen atmosphere by Saeid Farhadi; Parisa Zaringhadam; Reza Zarei Sahamieh (1965-1968).
Mercuric fluoride (HgF2), as a light-sensitive inorganic compound, in the presence of dioxygen is able to convert various α-aryl- and α,α-diarylcarboxylic acids into the corresponding aldehydes and ketones selectively under photoirradiation via trapping of the benzylic radical by O2.
Keywords: α-Arylcarboxylic acids; Photolytic; Decarboxylation; Mercuric fluoride; Carbonyl compounds;

A route to cyclic peptides and glycopeptides by native chemical ligation using in situ derived thioesters by Jiehao Chen; J. David Warren; Bin Wu; Gong Chen; Qian Wan; Samuel J. Danishefsky (1969-1972).
The synthesis of cyclic peptides and glycopeptides by native chemical ligation using in situ derived thioesters is described.

Reductive Mannich-type reaction using the composite reagents of phosphine and Lewis acid by Satoshi Kikuchi; Takayuki Kobayashi; Yukihiko Hashimoto (1973-1975).
Reductive Mannich-type reaction of S-2,4,6-triisopropylphenyl 2-bromopropanethioate with several imines was smoothly mediated by the combination of Ph3P and TiCl4 in good yields with high anti-selectivity.We found that the combination of Ph3P and TiCl4 was the excellent promoter for reductive Mannich-type reaction of S-2,4,6-triisopropylphenyl 2-bromopropanethioate with several imines and that the corresponding products were obtained in good yields with high anti-selectivity.

Reaction of α-ketoesters with diazo(trimethylsilyl)methyl magnesium bromide followed by in situ treatment with pivalic acid gave α-substituted β-trimethylsilyl-α,β-epoxyesters in an efficient and cis-selective manner.
Keywords: Epoxyesters; Glycidates; α-Ketoesters; One-pot synthesis; Trimethylsilyldiazomethane;

Treatment of 1-chloro-2-methylalkenyl p-tolyl sulfoxides with N-lithio 2-piperidone in THF at room temperature resulted in the formation of 1-chloro-2-(hydroxymethyl)alkenyl p-tolyl sulfides in good yields. This reaction is the first example of the Mislow–Braverman–Evans rearrangement retaining the sulfur atom on the original carbon.
Keywords: Sulfoxide; Vinyl sulfoxide; Sulfoxide–sulfenate rearrangement; Mislow–Braverman–Evans rearrangement; Allylic alcohol;

Solid phase synthesis of 3-(5-arylpyridin-2-yl)-4-hydroxycoumarins by Yannan Liu; Aaron D. Mills; Mark J. Kurth (1985-1988).
A solid phase strategy has been developed for the synthesis of 3-(5-arylpyridin-2-yl)-4-hydroxycoumarins. The key transformation is an intramolecular ipso substitution reaction which forms the coumarin heterocycle and culminates with cleavage of product from the polymer support. The pyridine moiety at C3 can be further modified with Suzuki coupling. A sample library with two diversity elements has been synthesized to demonstrate this ipso substation-based cyclo-elimination strategy.

A one-pot domino reaction in constructing isoorotate bases and their nucleosides by Martín Avalos; Reyes Babiano; Pedro Cintas; Michael B. Hursthouse; José L. Jiménez; Encarnación Lerma; Mark E. Light; Juan C. Palacios (1989-1992).
A domino reaction involving enaminoesters and chlorosulfonyl isocyanate leads to isoorotates. The strategy has been applied to the preparation of N-nucleosides.A novel strategy, involving the coupling of enaminoesters with chlorosulfonyl isocyanate and accelerated by microwave irradiation, enables the straightforward preparation of the biologically important isoorotate bases. Extensions to nucleoside derivatives are also described.
Keywords: Enamines; Isocyanates; Isoorotates; Microwaves; Nucleosides;

Several salen–ruthenium(II) complexes, which are derived from commercial ligands or simple ethylenediamine, can be successfully applied as catalysts for the olefination of a broad variety of aldehydes with high yields and E-selectivities.Several salen–ruthenium(II) complexes, which are derived from commercial ligands or simply ethylenediamine, can be successfully applied as catalysts for the olefination of a broad variety of aldehydes. Depending on the electron richness of the applied aldehydes, good to very good olefin yields and high E:Z selectivities are reached at 60 or 80 °C reaction temperature with ethyl diazo acetate being the reaction partner. The reaction rate depends on the electron donor capabilities of the aldehydes. Electron poor aldehydes undergo faster reactions than electron rich aldehydes, but both electron rich and bulky aldehydes can be transformed to corresponding olefins in very good yields and high E-selectivity.
Keywords: Aldehyde olefination; Homogeneous catalysis; Ruthenium; Salen;

Reason: Subsequent to the publication of the article in Tetrahedron Letters 47 (2006) 1997–2001, it has come to the knowledge of the authors and editor that similar research work had already been published by Professor Marjan Jereb et al. in Green Chemistry 7 (2005) 100–104.The editor and authors have, therefore, requested the article be retracted from Tetrahedron Letters and apologize for the oversight.

Convenient microwave-assisted synthesis of 1-chloroethyl phosphates by Hanna Kumpulainen; Raimo Saari; Marko Lehtonen; Jarkko Rautio; Tomi Järvinen; Jouko Vepsäläinen (2003-2004).
An efficient microwave-assisted synthesis of 1-chloroethyl phosphates was developed. Protected vinyl chlorophosphates undergo a fast conversion to the chloroethylidene phosphates in the presence of HCl with excellent yields up to 900 times faster than at the standard NTP conditions.
Keywords: Microwave-assisted synthesis; 1-Chloroethyl phosphates;

Organosulfur oxidation by hydrogen peroxide using a dinuclear Mn-1,4,7-trimethyl-1,4,7-triazacyclononane complex by John R. Lindsay Smith; Jane Murray; Paul H. Walton; Terry R. Lowdon (2005-2008).
A mechanistic study of organosulfide oxidation by H2O2, using a dinuclear manganese complex as the catalyst, has revealed an unusual switch in the philicity of the oxidant for the first and the second oxygen transfer steps; this switch has been exploited to tune selectivity for each of the products.
Keywords: Oxidation; Sulfide; Sulfoxide; Catalysis; Manganese 1,4,7-trimethyl-1,4,7-triazacyclononane complexes; Hydrogen peroxide;

Hydrogen peroxide (H2O2) in the presence of zirconium tetrachloride is a very efficient reagent for the oxidation of sulfides to sulfoxides and sulfones in methanol at room temperature. It is noteworthy that under such conditions, the sulfide function is highly reactive, and various other functional groups such as alkenes and a ketone are tolerated.

An efficient protocol for the benzylation or allylation of amides using the corresponding benzyl or allyl chlorides as electrophiles under basic conditions with commercially available 5 mol % of [Cu(OH)TMEDA]2Cl2 as catalyst was developed. Under these conditions, unprotected amino acids were benzylated without any racemization.
Keywords: Amidation; Benzylation; Allylation; Copper salts; [Cu(OH)TMEDA]2Cl2;

Chiral bidentate phosphabenzene-based ligands: synthesis, coordination chemistry, and application in Rh-catalyzed asymmetric hydrogenations by Christian Müller; Leire Guarrotxena López; Huub Kooijman; Anthony L. Spek; Dieter Vogt (2017-2020).
Novel hydroxy-functionalized phosphabenzenes were synthesized, which provide the possibility to prepare chiral phosphabenzene–phosphites. These systems act as bidentate ligands toward rhodium centers and the corresponding metal complexes were applied in the rhodium-catalyzed asymmetric hydrogenation of prochiral substrates.Novel hydroxy-functionalized phosphabenzenes were synthesized, which provide the possibility to prepare chiral phosphabenzene–phosphites. These systems act as bidentate ligands toward rhodium centers and the corresponding metal complexes were applied in the rhodium-catalyzed asymmetric hydrogenation of prochiral substrates.
Keywords: Phosphabenzenes; Phosphites; Homogeneous catalysis; Asymmetric hydrogenation; Rhodium;

The stereoselective synthesis of 2,3-unsaturated α-d-glucosides by the SN2′ addition of diverse aglycones onto 4,6-di-O-benzyl-3-O-propargyl glucal was achieved using a catalytic quantity of AuCl3. The Au catalyzed reaction was explored using various aliphatic, aromatic, alicyclic and monosaccharide aglycones. The current protocol tolerates diverse functional groups and is highly stereoselective, fast, catalytic and mild.

Stereoselective synthesis of a novel spiroacetal-dihydropyrone related to auripyrone by Michael V. Perkins; Saba Jahangiri; Max R. Taylor (2025-2028).
A model spiroacetal-dihydropyrone related to that found in auripyrones A and B has been synthesised by a spiroacetalisation dehydration cascade. The route includes an unusual mutual kinetic diastereoselecting aldol reaction combining the key fragments.

A new strategy for the synthesis of optically pure trans-hydrindane systems is reported from an easily available starting material.
Keywords: Stereoselective synthesis; trans-Hydrindane; Terpenes; Claisen rearrangement; Vicinal stereocenters; Fused rings system;

Two air-stable P, N-chelated palladium(II) complexes have been evaluated as highly efficient and simple catalysts for Suzuki cross-coupling reaction between aryl bromides and arylboronic acids. They exhibit high activity and selectivity at room temperature.

The vicinal tricarbonyl system participates in a novel reaction with the zwitterion derived from isocyanide and dimethyl acetylenedicarboxylate to form fully substituted furan derivatives.

A new and versatile Ugi/SNAr synthesis of fused 4,5-dihydrotetrazolo[1,5-a]quinoxalines by Cédric Kalinski; Michael Umkehrer; Sebastien Gonnard; Nadine Jäger; Günther Ross; Wolfgang Hiller (2041-2044).
A combinatorial synthetic route yielding fused tetrazolo[1,5-a]quinoxalines is described. The use of 2-fluorophenylisocyanide in the Ugi-tetrazole reaction (tetrazole-U-4CR) followed by a nucleophilic aromatic substitution (SNAr) affords the tricylic tetrazolo[1,5-a]quinoxaline moiety in good yields and with high diversity.
Keywords: Ugi-reaction; Multi-component reaction; Tetrazole; Fused tetrazoloquinoxaline; Nucleophilic aromatic substitution;

Corrigendum to “Enantioselective synthesis of 1(R)-hydroxypolygodial” by Carmela Della Monica; Giorgio Della Sala; Deborah D’Urso; Irene Izzo; Aldo Spinella (2045).