Transition metal compounds and complexes as catalysts in synthesis of acetals and orthoesters: Theoretical, mechanistic and practical aspects

A comprehensive review of the reports concerning the synthesis of symmetrical and, particularly, mixed acetals and orthoesters with transition metal compounds and complexes as catalysts is presented. The following methods for the synthesis of symmetric and mixed acetals are discussed: acetalization of aldehydes or ketones with alcohols or diols; transacetalization; synthesis from vinyl and allyl ethers; synthesis via intra- or intermolecular addition of OH group to a triple bond; oxidation of primary alcohols; tetrahydropyranylation of alcohols or phenols; synthesis from epoxides and aldehydes or ketones; formation of 1,3-dioxanes by Prins cyclization of olefins with paraformaldehyde; oxidative cyclization-carbonylation of ynones; acetalization of ene-diol under Wacker-type catalysis. Reviewed is also the synthesis of mixed orthoesters via addition of alcohols and phenols to acrolein acetals. Presented are methods of the isolation of pure products, recycling of the catalysts (if applicable) and the advantages of the metal complexes compared to classical catalysts, Bronsted acids in particular. The relationship between the structure and reactivity was analyzed and the mechanisms of the reactions of acetal formation catalyzed by transition metal compounds and complexes were discussed. (C) 2012 Elsevier B.V. All rights reserved.