Extremely Regioselective Intramolecular Silylformylation of Alkynes

摘要

The intermolecular silylformylation of alkynes catalyzed by Rh or Co—Rh complexes, which gives the corresponding β-formylvinylsilanes in high yields, has been studied extensively in recent years. Silylcarbocyclizations (SiCACs) of alk-enynes, diynes, aldehydes, and alkynals have also been investigated. In the silylformylation of 1-alkynes, the reaction gives 1-silyl-2-formyl-1-alkenes with complete regioselectivity. This markedly high regioselectivity is useful, but it is more useful if the regioselectivity of the reaction can be controlled so that 3-silyl-2-alken-1-als become accessible. The reaction of simple internal alkynes, however, is virtually nonselective, giving a mixture of regioisomers. Accordingly, we investigated the intramolecular version of the silylformylation of 1-alkynes and internal alkynes by introducing a dimethylsiloxy, i.e., HMe_2SiO, moiety as the directing group. We will describe here our successful preliminary results on the intramolecular silylformylation of ω-(dimethylsiloxy)-i-alkynes catalyzed by Rh and Rh-Co complexes, which proceeds with complete regioselectivity, giving 3-exo-(formylmethylene)oxasilacycloal-kanes with or without an alkyl substituent at the exo-methylene carbon, which are equivalent to ω-siloxy-(i+1)-silyl-i-alken-i-als, in excellent yields.