Narasaka reaction: Desilylative acylation of 1-alkenylsilanes with acid anhydrides

Recent advances in the desilylative acylation of 1-alkenylsilanes with acid anhydrides under transition metal catalysis are summarized. This catalytic desilylative acylation of 1-alkenylsilanes provides an efficient route to α,β-unsaturated ketones by using rhodium or iridium as the catalyst. Moreover, various one pot sequence reactions have been developed, which can synthesize α,β-unsaturated ketones from simple starting materials in an economic way. Additionally, this approach is applied to the asymmetric synthesis of atropisomers possessing silanol groups with excellent enantioselectivity.     

Microwave‐Assisted NiCl2 Promoted Acylation of Alcohols

Abstract

A microwave oven acylation of alcohols by carboxylic acid anhydrides has been developed. NiCl₂ has been proven an efficient catalyst for the acylation of primary, secondary, and tertiary alcohols and phenols under microwave conditions.     

A salt made of 4-N,N-dimethylaminopyridine (DMAP) and saccharin as an efficient recyclable acylation catalyst: a new bridge between heterogeneous and homogeneous catalysis

Here, we report insights into the new recyclable catalyst 1, (DMAP·saccharin). The DMAP·saccharin-catalysed acylation of alcohols has been successfully carried out more than 8 times. Only 1 mol% of catalyst 1 efficiently promotes acylation with almost equimolar amounts of acid anhydrides, under both base-free and solvent-free conditions.     

Highly efficient heterogeneous acylations of aromatic compounds with acid anhydrides and carboxylic acids by montmorillonite-enwrapped titanium as a solid acid catalyst

Montmorillonite-enwrapped titanium hydroxide species (Ti⁴⁺-mont) acted as a highly efficient heterogeneous acid catalyst for the acylation of aromatic compounds with acid anhydrides or carboxylic acids. The catalytic activity of the Ti⁴⁺-mont was higher than those of other acid catalysts such as zeolites, SO ₄ ²⁻ /ZrO₂ and p-toluenesulfonic acid. For example, the reaction of anisole with dodecanoic acid in the presence of the Ti⁴⁺-mont catalyst gave 1-(4-methoxyphenyl)-1-dodecanone in 97% yield. Furthermore, the Ti⁴⁺-mont catalyst was easily separated from the reaction mixture and was recyclable.     

Highly efficient heterogeneous acylations of aromatic compounds with acid anhydrides and carboxylic acids by montmorillonite-enwrapped titanium as a solid acid catalyst

Montmorillonite-enwrapped titanium hydroxide species (Ti⁴⁺-mont) acted as a highly efficient heterogeneous acid catalyst for the acylation of aromatic compounds with acid anhydrides or carboxylic acids. The catalytic activity of the Ti⁴⁺-mont was higher than those of other acid catalysts such as zeolites, SO ₄ ^2? /ZrO₂ and p-toluenesulfonic acid. For example, the reaction of anisole with dodecanoic acid in the presence of the Ti⁴⁺-mont catalyst gave 1-(4-methoxyphenyl)-1-dodecanone in 97% yield. Furthermore, the Ti⁴⁺-mont catalyst was easily separated from the reaction mixture and was recyclable.     

Electrostatic catalysis by ionic aggregates: scope and limitations of Mg(ClO4)2 as acylation catalyst

Alkali and alkaline earth metal perchlorates exhibit electrostatic catalysis in the activation of anhydrides for the acylation reaction. Perchlorates with higher values of the charge-size function of the metal ion exhibit better catalytic activity following the order Mg(ClO₄)₂>Ba(ClO₄)₂>LiClO₄. Acylation of structurally diverse phenols, thiols, alcohols, and amines have been carried out with stoichiometric amounts of anhydride at room temperature under solvent free conditions in the presence of catalytic amount of Mg(ClO₄)₂. Sterically hindered and electron deficient phenols are efficiently acylated. Acylation with sterically hindered anhydrides such as iso-butyric, pivalic, and benzoic anhydrides are carried out with phenols and alcohols in excellent yields. Acid-sensitive alcohols are acylated in excellent yields without any competitive side reactions.     

Scandium Trifluoromethanesulfonate as an Extremely Active Lewis Acid Catalyst in Acylation of Alcohols with Acid Anhydrides and Mixed Anhydrides

Scandium trifluoromethanesulfonate (triflate), which is commercially available, is a practical and useful Lewis acid catalyst for acylation of alcohols with acid anhydrides or the esterification of alcohols by carboxylic acids in the presence of p-nitrobenzoic anhydrides. The remarkably high catalytic activity of scandium triflate can be used for assisting the acylation by acid anhydrides of not only primary alcohols but also sterically-hindered secondary or tertiary alcohols. The method presented is especially effective for selective macrolactonization of omega-hydroxy carboxylic acids.     

Synthesis of indolo[4,3-bc]phenanthridine-6,11(2H,12H)-diones using the schiff base–homophthalic anhydride cyclization reaction

A novel indolophenanthridine ring system has been synthesized via the Schiff base–homophthalic anhydride cyclization followed by thionyl chloride–mediated dehydrogenation and intramolecular Friedel–Crafts acylation. This adds to the array of heterocyclic systems that are available through the cycloaddition reaction of imines with cyclic dicarboxylic acid anhydrides. The cytotoxicities of the indolophenanthridines were investigated in human cancer cell cultures, and the results documented significant antitumor activity in a variety of human cancer cell lines. This provides a new heterocyclic scaffold for anticancer drug design.     

Magnesium bistrifluoromethanesulfonimide as a new and efficient acylation catalyst

Magnesium bistrifluoromethanesulfonimide catalyzed the acetylation of phenols, alcohols, and thiols under solvent-free conditions at room temperature and in short times. Electron-deficient and sterically hindered phenols provided excellent yields. The catalyst was found to be general for acylation with other anhydrides, such as propionic, isobutyric, pivalic, chloroacetic, and benzoic anhydrides. The rate of acylation was influenced by the electronic and steric factors associated with the anhydride. The reaction with less electrophilic anhydrides (e.g., chloroacetic and benzoic anhydrides) required higher temperature (approximately 80 degrees C). Chemoselective acetylation, pivalation, and benzoylation took place with acid-sensitive alcohols without any competitive dehydration/rearrangement.     

Highly efficient and selective biocatalytic acylation studies on triazolylsugars

Different acid anhydrides (of C₂ to C₇ aliphatic fatty acids and benzoic acid) have been used to study the selective acylation of primary/secondary hydroxyl groups in 2-phenyl-4-(d-threo-1′,2′,3′-trihydroxypropyl)-2H-1,2,3-triazole, 2-phenyl-4-(d-erythro-1′,2′,3′-trihydroxypropyl)-2H-1,2,3-triazole, 2-phenyl-4-(d-arabino-1′,2′,3′,4′-tetrahydroxybutyl)-2H-1,2,3-triazole and 2-phenyl-4-(d-lyxo-1′,2′,3′,4′-tetrahydroxybutyl)-2H-1,2,3-triazole in the presence of Candida antarctica lipase B in diisopropyl ether. Among the different acid anhydrides, butanoic anhydride was found to be the most efficient acylating agent (for butanoylation); for acetylation, vinyl acetate gave the best results. The reactions with both these acylating agents were highly selective and efficient yielding exclusively the monoacylated products in 95-99% yields in 1-5 h.     

Selective esterifications of alcohols and phenols through carbodiimide couplings

Esterification of carboxylic acids capable of forming ketene intermediates upon treatment with carbodiimides permits the selective acylation of alcohols in the presence of phenols lacking strong electron-withdrawing groups. The selectivity of acylations involving highly acidic phenols could be reversed through the addition of catalytic amount of acid. Esterification of other carboxylic acids was found to proceed through the formation of symmetric anhydrides and provide the opposite chemoselectivity. In both cases the relative acylation rates of substituted phenols are consistent with a reaction mechanism involving an attack of phenolate anions on electrophilic intermediates such as ketenes and symmetric anhydrides, with the carbodiimides serving both as an activating reagent and as a basic catalyst.     

Palladium‐Catalyzed Catellani ortho‐Acylation Reaction: An Efficient and Regiospecific Synthesis of Diaryl Ketones

A palladium‐catalyzed, norbornene‐mediated Catellani ortho‐acylation reaction was developed by the use of either acyl chlorides or acid anhydrides as acylation reagents. The addition of more than a stoichiometric amount of H₂O is crucial for this transformation when acid chlorides are used, and kinetic studies indicate that the active acylation reagent is possibly an acid anhydride.     

A Convenient and efficient method for the preparation of 6-Acyl-2(3H)-benzoxazolones

Benzoxazolinone derivatives have been found to exhibit various pharmacological properties and 6-acyl-2(3H)-benzoxazolones are considered as key starting materials for the preparation of these compounds. Reported here are the optimal conditions for a regioselective acylation at the 6-position of the benzoxazolinone ring. A general method leading to the expected products in excellent yields consists in using a mixture of aluminum chloride-dimethylformamide as catalyst and acid anhydrides or chlorides as acylating agents.     

Zinc oxide (ZnO) as a new, highly efficient, and reusable catalyst for acylation of alcohols, phenols and amines under solvent free conditions

Zinc oxide (ZnO) is a highly efficient catalyst for the acylation of a variety of alcohols, phenols and amines with acid chlorides or acid anhydrides under solvent free conditions. Primary, secondary, tertiary, allylic and benzylic alcohols, diols and phenols with electron donating or withdrawing substituents can be easily acylated in good to excellent yield.     

Acylation of Alcohols and Amines with Vinyl Acetates Catalyzed by Cp(2)Sm(thf)(2)

Cp(2)Sm(thf)(2) was found to be an efficient catalyst for the acylation of alcohols and amines with esters under mild conditions. In the present acylation, vinyl and isopropenyl acetates served as good acylating agents. Thus, a variety of alcohols and amines underwent acylation with vinyl and isopropenyl acetates in the presence of Cp(2)Sm(thf)(2) to give the corresponding esters and amides in good to excellent yields. This catalytic acylation of alcohols and amines offers an additional useful method by the use of various esters, instead of acid anhydrides and acid chlorides, as acylating agents under very mild conditions.     

Practical acid-catalyzed acylation of sulfonamides with carboxylic acid anhydrides

A highly efficient reaction between sterically and electronically diverse sulfonamides and carboxylic acid anhydrides to furnish monoacylated N-acylsulfonamides is described. This represents the first systematic disclosure of the scope of sulfuric acid-catalyzed acylation of sulfonamides.     

Study of the Acylation Reaction of 2(3H)-Benzothiazolones in the Mixture of ZnCl 2 -DMF

The use of polyphosphoric acid and the complex AlCl 3 -DMF in 6-acylation of 2(3H)-benzothiazolones previously have been reported. Instead of the frequently used AlCl 3 as a catalyst in the Friedl-Crafts reactions, we conducted the acylation of 2(3H)-benzothiazones using zinc chloride as a catalyst in DMF as solvent and acid chlorides or anhydrides as acylating agents.     

A new and efficient method for the facile synthesis of N-acyl sulfonamides under Lewis acid catalysis

The N-acylation of sulfonamides with carboxylic acid anhydrides in the presence of Lewis acids is described. Several Lewis acids such as BF₃·Et₂O, ZnCl₂, MoCl₅, TiCl₄, B(C₆F₅)₃, Sc(OTf)₃ and I₂ were found to catalyze the reaction efficiently to furnish the N-acylated products in good yields under solvent-free conditions. The reactions of various sulfonamides were studied with different carboxylic acid anhydrides including the less reactive benzoic and pivalic anhydrides, in the presence of 3 mol % ZnCl₂ as the catalyst. Carboxylic acids were also successfully used as acylating agents via the mixed anhydride method.     

Susceptibility of Methyl 3-Amino-1H-pyrazole-5-carboxylate to Acylation

In the search for a new method of synthesis of hybrid peptides with aminopyrazole carboxylic acid, we tried to force selective acylation at the aromatic amino group instead of at the ring nitrogen atom with fairly gentle acylating agents. The acylating agents used were acid anhydrides: acetic anhydride, tert-butyl pyrocarbonate, and 2-(2-methoxyethoxy)ethoxyacetic acid/dicyclohexylcarbodiimide. We succceded in acylation at this amino group with almost none at the ring nitrogen atom. Sometimes, however, acylation in small quantities at the ring nitrogen atom was observed as a by-product. To remove this by-product, imidazole was used. Thus, we were able to obtain the hybrid peptides in question with no protection and subsequent removal required. We synthesized a few these free peptides with no protection of the pyrazole ring. This is a simpler method than that being used currently.     

Synthesis of fluorine-containing betulin esters

28-O-Fluoroacylbetulins were synthesized via acylation of betulin by fluorocarboxylic (perfluorobutyric, perfluorooctanoic, 3-fluorobenzoic, perfluorobenzoic) acid chlorides in CHCl₃ in the presence of Py. 3,28-Di-O-fluoroacylbetulins were prepared by treatment of betulin with fluorocarboxylic (trifluoroacetic, pentafluoropropionic) acid anhydrides in Py in the presence of 4-dimethylaminopyridine. 3,28-Di-O- (3-fluorobenzoyl)betulin was obtained from acylation of betulin by 3-fluorobenzoic acid in CH₂Cl₂ in the presence of N,N′-dicyclohexylcarbodiimide and 4-dimethylaminopyridine whereas acylation by perfluorobutyric acid under the same conditions gave 28-O-perfluorobutanoylbetulin.