Trimethylstannyl Group as Pivot in Cleavage of 2-Bromoethyl Esters

Abstract

The recent reports^1,2 on carboxyl protection with 2-trimethyl-silyl residue prompted me to disclose here some pertinent results. For some time I have addressed to developing methods for selective scission of 2-haloethyl esters with the intention of rendering them useful for protection of carboxylic acids. Among the various contemplated feasibilities was a route wherein replacement of the halogen by organometal groups, especially those of group IV_A elements, is followed by fragmentation. This thought was engendered from the knowledge that electrofugal R₃Si/R₃Sn units tend to stabilize positive charge at a β atom, and direct the fragmentation of such species as illustrated by hydride abstractor-promoted elimination⁷ and regiospecific desilylative substitution of vinyl-silanes.^8,9 Of course the presence of a hard base (e.g. F⁻) for attack at the metal is essential to the success of these reactions.