[Report] Asymmetric Lewis acid organocatalysis of the Diels–Alder reaction by a silylated C–H acid
Silylium ion equivalents have shown promise as Lewis acid catalysts for a range of important C–C bond-forming reactions. Here we describe chiral C–H acids that upon in situ silylation, generate silylium-carbanion pairs, which are extremely active Lewis acid catalysts for enantioselective Diels–Alder reactions of cinnamates with cyclopentadiene. Enantiomeric ratios of up to 97:3 and diastereomeric ratios of more than 20:1 are observed across a diverse set of substitution patterns with 1 mole percent (mol %) of C–H acid catalyst and 10 mol % of a silylating reagent. The results show promise for broad applications of such C–H acid–derived silylium ion equivalents in asymmetric Lewis acid catalysis. Authors: Tim Gatzenmeier, Manuel van Gemmeren, Youwei Xie, Denis Höfler, Markus Leutzsch, Benjamin List