The Reactivity of t-Butyldimethylsilyl Ethers Towards Some Stabilised Carbanions

Abstract

The t-butyldimethylsilyl (TBDMS) protection^1–3 of alcoholic and phenolic hydroxy groups has attained much importance of late. Certain shortcomings, however, of this protective method have recently come to light. These include acyl migration⁴ during the fluoride anion mediated desilylation of acylated/silylated glycerols, and cleavage of TBDMS groups under catalytic hydrogenation conditions intended for benzyl ether cleavage⁴. Further, aryl anions of trimethylsilyl protected phenols have been shown⁵ to rearrange into o-trimethylsilyl-phenolates; similar reaction of a TBDMS protected phenol has been observed⁶ in this laboratory. The more labile trimethylsilyloxy group has also been reported⁷ to act as a leaving group, if present at an allylic or benzylic site, towards a variety of nucleophiles (H⁻, alkyl Grignards, malonate anion). However, benzyl TBDMS ether is stable towards ethylmagnesiumbromide under reflux⁶.