Zinc triflate catalyzed acylation of alcohols, phenols, and thiophenols

Microwave Mediated Acylation of Alcohols, Phenols and Thiophenols in Neat Acetic Anhydride

A microwave-based method for the acylation of alcohols, phenols, and thiols has been developed without the need of a catalyst or base additives. The reaction is far more rapid than previously reported acylation methods, tolerates a wide variety of functional groups, and provides easy isolation of products in excellent yields without the need for chromatography. Most products can be isolated directly via evaporation under reduced pressure or by pouring the reaction mixture into water and filtering.

A Stoichiometric Solvent-Free Protocol for Acetylation Reactions

Considering the remarkable relevance of acetylated derivatives of phenols, alcohols, and aryl and alkyl thiols in different areas of biology, as well as in synthetic organic chemistry, a sustainable solvent-free approach to perform acetylation reactions is proposed here. Acetylation reactions are classically performed using excess of acetic anhydride (Ac2O) in solvent-free conditions or by eventually working with stoichiometric amounts of Ac2O in organic solvents; both methods require the addition of basic or acid catalysts to promote the esterification. Therefore, they usually lead to the generation of high amounts of wastes, which sensibly raise the E-factor of the process. With the aim to develop a more sustainable system, a solvent-free, stoichiometric acetylation protocol is, thus, proposed. The naturally occurring phenol, thymol, can be converted to the corresponding-biologically active-ester with good yields, in the presence of 1% of VOSO4. Interestingly, the process can be efficiently adopted to synthesize other thymyl esters, as well as to perform acetylation of alcohols and aryl and alkyl thiols. Remarkably, a further improvement has been achieved replacing Ac2O with its greener alternative, isopropenyl acetate (IPA).

Efficient O-Acylation of Alcohols and Phenol Using Cp2TiCl as a Reaction Promoter

A method has been developed for the conversion of primary, secondary, and tertiary alcohols, and phenol, into the corresponding esters at room temperature. The method uses a titanium(III) species generated from a substoichiometric amount of titanocene dichloride together with manganese(0) as a reductant, as well as methylene diiodide. It involves a transesterification from an ethyl ester, or a reaction with an acyl chloride. A radical mechanism is proposed for these transformations.