Catalysis of chlorosilane on the ring-expansion of cyclic acetals bearing a carbene precursor. Lewis acid–base effect on the oxonium ylide intermediate

Abstract

Rhodium catalyzed (1–0.1 mol%) decomposition of 2-(3-diazo-2-oxopropyl)-2-methyldioxolane 1a or 2-(3-diazo-1-methyl-2-oxopropyl)-2-methyldioxolane 1b in the presence of a catalytic amount of TMSCl (10 mol%), yielded 4,7-dioxocane 3a (91%) or 3b (49%), whereas similar reaction in the absence of TMSCl caused 1,2-rearrangement to give bicyclobutanones 2a or 2b, respectively; Lewis acid-base catalysis by TMSCl of the ring-expansion of a bicyclooxonium ylide intermediate is revealed.