Enantioselective Friedel-Crafts Alkylations by Strained Chiral Silacycle

Key words

Friedel-Crafts alkylation - silacycles - Lewis acids

Significance

A chiral silicon Lewis acid has been utilized for the enantioselective Friedel-Crafts alkylation. The strained silacyle is effective at promoting the reaction for electron-rich aromatic systems under mild conditions.

Comment

This is a nice use of a chiral silicon Lewis acid for the important synthesis of hetero­arylglycines. This paper provides another example of the proposed ‘strain-release Lewis acidity’ of silicon to promote reactions. The method uses a strain-induced effect of the five-member silacycle to give a significant increase in the acidity of the silicon center. This is proposed as the origin of the observed high reactivity and selectivity for the reaction. The method is not a truly catalytic reaction; however, the chiral amino alcohol is completely recoverable and reusable.