Secondary alcohols act as better nucleophiles than primary alcohols in the lipase-catalyzed regioselective deacylation of dihydroxybenzenes acylated at both phenolic hydroxyls

Candida antarctica lipase B (CAL-B) was found to be highly regioselective as well as active in the deacylation of resorcinols and hydroquinones acylated at both phenolic hydroxyls. Contrary to expectation, secondary alcohols acted as better nucleophiles than primary alcohols in these enzymatic deacylations.     

Ca(OH)2-mediated efficient synthesis of 2-amino-5-hydroxy-4H-chromene derivatives with various substituents

A variety of novel 2-amino-5-hydroxy-4H-chromene derivatives with various substituents on the 4H-chromene ring were efficiently synthesized by one-pot reactions of substituted resorcinols and various 2-benzylidenemalononitriles in the presence of calcium hydroxide in methanol at room temperature. This simple method provided 2-amino-5-hydroxy-4H-chromenes with high yields under mild reaction conditions.     

Benzylation of tetraalkylcalix[4]resorcinols

New amphiphilic benzylated calix[4]resorcinols were synthesized by the reaction of tetra-alkylcalix[4]resorcinols with 3,5-di(tert-butyl)-4-hydroxybenzyl acetate. The reaction pathway and the type of the products formed are determined by the structure of the alkyl substituent at the lower rim of tetraalkylcalix[4]resorcinols and the nature of acid used as a catalyst of the process. Self-organization of some synthesized compounds in nonpolar media was studied.     

Palladium-catalyzed direct ortho-acylation through an oxidative coupling of 2-arylbenzothiazoles with benzylic alcohols

An efficient protocol was developed for Pd-catalyzed direct C–H bond acylation by cross-dehydrogenative-coupling of arylbenzothiazoles and benzylic alcohols using tert-butyl hydroperoxide (TBHP) as the oxidant. The acylation reactions exhibit good reactivities and excellent regioselectivity.     

A new method for pyrrole peri-annulation: synthesis of 1H-1,5,7-triazacyclopenta[c,d]phenalenes from 1H-perimidines

New methods for the synthesis of 1H-1,5,7-triazacyclopenta[c,d]phenalenes have been developed based on a sequence involving Schmidt reaction of keto-perimidines and acylation of the intermediate amides with 1,3,5-triazines or carboxylic acids. The same synthetic sequence starting from the corresponding alkylperimidine includes acylation with acetic acid as the first step.     

Reactivities of mixed organozinc and mixed organocopper reagents, 2. Selective n-alkyl transfer in tri-n-butylphosphine-catalyzed acylation of n-alkyl phenylzincs; an atom economic synthesis of n-alkyl aryl ketones

Tri-n-butylphosphine-catalyzed acylation of mixed n-alkyl phenylzincs with aromatic acyl halides in THF is efficient in selective transfer of n-alkyl groups to produce n-alkyl aryl ketones in good yields. This route provides an atom economic organocatalyzed alternative to transition metal-catalyzed acylation of di-n-alkylzincs.     

Synthesis of N,N-Ac,Boc laurylthio sialoside and its application to O-sialylation

The combination of the 5-N-tert-butoxycarbonyl (Boc) group of laurylthio sialoside and cyclopentyl methyl ether (CPME) as a solvent enhanced the reactivity and α-selectivity of the sialyl donor during sialylation. Selective deprotection of the N-Boc group of sialoside, including an acid-sensitive isopropylidene function, was successfully achieved by Yb(OTf)₃-SiO₂. Transformation of N,N-Ac,Boc into an N-acetylglycolyl group of sialoglycoside was easily performed via selective N-deacylation of the mixed Ac-N-Boc carbamate, subsequent Boc group removal, and acylation.     

Synthesis and some properties of tetrakis-3,5-di-<Emphasis Type="Italic">tert</Emphasis>-butyl-4-hydroxybenzylated calix[4]resorcinols

A method for the synthesis of new calix[4]resorcinols tetra-3,5-di-tert-butyl-4-hydroxybenzyl derivatives is developed. Their interaction with methyldichlorophosphonate, dimethyldichlorosilane in the presence of a base leads to formation of organophosphorus-organosilicon cavitands. Acetylation of hydroxybenzylated calix[4]resorcinols with acetic anhydride leads to products of either incomplete or full acetylation depending on experimental conditions.     

Synthesis of rccc- and rctt-diastereoisomers of novel triazole-containing calix[4]resorcinols

Novel calix[4]resorcinols containing four triazole fragments on the aromatic substituents of the calixarene framework were synthesized via a one-step condensation of resorcinol and its derivatives with 4-(1-benzyl-1H-[1,2,3]triazol-4-ylmethoxy)benzaldehyde. The macrocyclic products are rctt- and/or rccc-isomers, which were isolated and characterized by NMR and single crystal X-ray diffraction studies. The same products were also prepared via the click-reaction of benzyl azide with previously synthesized calix[4]resorcinols containing four alkyne terminal groups on the aromatic substituents. In this case, only rctt-diastereomers of the corresponding calixarenes were isolated, which is governed by conformational features of the starting macrocycles.     

Synthesis of C1-alkyl- and acylglycals from glycals using a B-alkyl Suzuki-Miyaura cross coupling approach

A B-alkyl Suzuki-Miyaura cross coupling approach provides a flexible, efficient means to convert glycals to C1-alkylglycals and C1-acylglycals that are versatile synthetic intermediates. This approach uses readily available glycal starting materials and overcomes major limitations associated with direct alkylation or acylation of glycals. Further, a commonly observed side reaction involving reduction of the halide coupling partner is suppressed by preincubation of the borane coupling partner with aqueous base, providing new mechanistic insights into the side reaction.     

A peptide-based catalyst approach to regioselective functionalization of carbohydrates

Two small peptide libraries (150 members and 36 members) have been subjected to screening experiments to evaluate their potential for regioselective (i.e. site-selective) acylation of carbohydrate monomers. Two substrates, one diol derived from N-acetyl glucosamine and one tetraol derived from glucose, have served as the test cases. In each case, the inherent regioselection of catalyzed acylation was defined as that derived from the reaction where N-methylimidazole (NMI) is used as the catalyst. With both substrates, peptides were found to perturb the inherent selectivities from those observed with NMI. From the libraries, the catalysts that provide the largest deviation from NMI were subjected to optimization studies. The work sets the groundwork for studies of expanded peptide libraries and development of structure-selectivity relationships to obtain catalysts that can selectively derivatize the unique sites in stereochemically complex polyols.     

4-Chloro-3-(trifluoroacetyl)coumarin as a novel building block for the synthesis of 7-(trifluoromethyl)-6H-chromeno[4,3-b]quinolin-6-ones

4-Chloro-3-(trifluoroacetyl)coumarin was synthesized for the first time via direct TMSCl-mediated acylation of 4-hydroxycoumarin with TFAA followed by the treatment with POCl₃. The reaction of 4-chloro-3-(trifluoroacetyl)coumarin with commercially available anilines is a two-step method, which affords a set of 7-(trifluoromethyl)-6H-chromeno[4,3-b]quinolin-6-ones in good to excellent yields.     

Substrate scope in the direct imine acylation of ortho-substituted benzoic acid derivatives: the total synthesis (±)-cavidine

The direct imine acylation (DIA) and subsequent cyclisation of a range of imines with ortho-substituted benzoic acid derivatives is described. Variation in the coupling reagents, imine and benzoic acid were all examined. The DIA procedure was also applied in the total synthesis of (±)-cavidine.     

An effective procedure for the preparation of 3-substituted-4- or 6-azaindoles from ortho-methyl nitro pyridines

3-Substituted-4- and 6-azaindoles were prepared from ortho-methyl-nitropyridines in a practically convenient, one-pot process based on the Leimgruber-Batcho reaction. The procedure comprises a sequence of (a) condensation of an ortho-methyl-nitropyridine with N,N-dimethylformamide dimethyl acetal; (b) alkylation or acylation of the enamine intermediate; (c) reduction of the nitro group to an aniline with in situ cyclization and elimination of dimethylamine to generate the 3-substituted azaindole heterocycle.     

Synthesis of novel benzopyrano[3,2-c]coumarins via tandem base promoted nucleophilic substitution and intramolecular electrophilic aromatic cyclization

Efficient and facile synthesis of 7H-benzopyrano[3,2-c]coumarins has been achieved by mild base promoted reaction of 4-chloro-3-formylcoumarin with diversely functionalized resorcinols. All the products were obtained as pure precipitates from the reaction mixture and the structure of the product was confirmed by X-ray analysis.     

Bi(OTf)3-catalyzed acylation of p-quinones: a facile synthesis of acylated hydroquinones

p-Quinones undergo smooth acylation with acetic anhydride in the presence of 2 mol % of bismuth triflate under mild conditions to afford the corresponding 1,4-diacylated-2-acetoxylated hydroquinones in excellent yields with high selectivity.     

Biocatalytic enantioselective preparation of phenothiazine-based cyanohydrin acetates: kinetic and dynamic kinetic resolution

Dynamic kinetic resolution is used for the preparation of a series of novel (+)-10-alkyl-phenothiazin-3-ylcyanomethyl acetates. The method exploits a basic resin both for the racemization and formation of phenothiazine-based cyanohydrins and for the decomposition of acetone cyanohydrin in one pot together with Candida antarctica lipase A-catalyzed enantioselective acylation with vinyl acetate in acetonitrile. The Candida antarctica lipase A-catalyzed methanolysis of racemic 10-alkyl-phenothiazin-3-ylcyanomethyl acetates in acetonitrile with E?100 leads to the corresponding (−)-acetates.     

N-Acyltrifluoromethanesulfonamides as new chemoselective acylating agents for aliphatic and aromatic amines

This work describes advances in the study of the internal condensation of ammonium salts of N-acylsulfonamides. N-Acyltrifluoromethanesulfonamides show considerable advantages over the non fluorinated analogues by virtue of their higher reactivity and acidity. The reaction chemoselectivity has been investigated using a wide range of amines. The sensitivity of the reaction to steric and electronic effects confirms the potential application of these reagents in chemoselective acylation of polyamines.     

A straightforward route to obtain C1-labeled clenbuterol

Singly-labeled ¹³C₁-clenbuterol has been synthesized employing a straightforward pathway starting from easily available acetanilide. The critical step was the Friedel-Crafts acylation of this compound with marked acetyl chloride, being the first example of the use of this methodology applied to the synthesis of a clenbuterol derivative. Subsequent chemical reactions afforded the desired product with good yields.     

Single step preparation and conformational analysis of novel thiophosphorylated ligands based on calix[4]resorcinol matrix

We have synthesized novel calix[4]resorcinols with four 2-thioxo-1,3,2-dioxaphospholane groups introduced in aromatic substituents in the methylidene bridges of macromolecules by the condensation of new thiophosphorylated benzaldehyde with resorcinol and its derivatives in acidic media with high yields. The formation of only one rctt isomer with corresponding chair conformation is observed, which was determined by 2D NMR-experiments.