The protection of terminal ethynyl groups in Grignard syntheses

Abstract

The trimethylsilyl group can be used to protect a terminal ethynyl group in Grignard syntheses. For example, a Grignard reagent can be made in tetrahydrofuran from the easily prepared compound (p-bromophenylethynyl)-trimethylsilane, and carbonation gives the acid (p-carboxyphenylethynyl)trimethylsilane, which on treatment with dilute alkali gives p-ethynylbenzoic acid in 55% overall yield. The corresponding meta-acid can be made analogously.

This method of protection has been used in the preparation of the compounds m- and p-HCC·C₆H₄·MR₃, where MR₃= SiMe₃, SiEt₃, or SnMe₃.