Alkylation of α-Formyl Esters via Their Thallium(I) Salts

Article abstract of DOI:10.1021/jo01301a005

Treatment of the thallium(I) salt of β-diketones and β-keto esters with alkyl halides had been shown to be a useful method for the regioselective C-alkylation of these compounds.This approach,however,has apparently not been examined for α-formyl esters.In an effort to determine the applicability of this method to aldehyde substrates,the reaction with α-formyl esters which covers a range of properties for α-substituents has been examined.In addition,the effects of various solvents and Et3N catalysis on the course of the reaction were evaluated.The overall yields and ratios of C/O alkylation were determined by using 1H NMR integration.In no case did exclusive C-alkylation result and,furthermore,the results obtained indicate that previous explanations for the observed regioselectivity may not have been accurate and the preference for C-alkylation may be related to the covalent nature of the thallium salt in solution as opposed to reaction on the crystal surface.It is concluded that this method represents a useful synthetic procedure only for cases where the α-formyl ester has a relatively low enolization tendency and the steric demand of the electrophile is small.