The search for tolerant Lewis acid catalysts.: Part 1: Chiral silicon Lewis acids derived from (−)-myrtenal

We have shown that association of a bulky silicon group with the bis(trifluoromethanesulfonyl)imide leaving group unexpectedly enhances the electrophilic character of the R3SiNTf2 silylating agent. The presence of a chiral substituent derived from (−)-myrtenal on the silicon atom led to a Lewis acid, which efficiently catalyzes the Diels–Alder reaction of α,β-unsaturated esters. Although not yet preparatively useful, the enantiomeric excesses (up to 54%) were the highest ever reported for a chiral silicon Lewis acid.