Chemoselective reactions of carbonyl and acetal groups

Abstract

The phosphoniosilylation of an aldehyde with triphenyl phosphine and trimethylsilyl trifluoromethanesulfonate occurs to yield the $\alpha$-silyloxy phosphonium salt, whereas that of a ketone does not take place. On the basis of this result, chemoselective reactions of the keto group in the presence of the aldehyde group have been achieved via preferential in situ conversion of aldehyde into 1-silyloxyphosphonium salt. They include nucleophilic addition of grignard reagents, reduction with lithium aluminum hydride, wittig reaction, and hydrocyanation. Chemoselective reactions of acyclic acetals in the presence of cyclic acetals have been studied. In the presence of trimethylsilyl trifluoromethanesulfonate, selective allylation, reduction, and aldol type reactions of acyclic acetals in the presence of cyclic acetals of ketones and aldehydes have been achieved.