Rationalization of an Unusual Solvent‐Induced Inversion of Enantiomeric Excess in Organocatalytic Selenylation of Aldehydes

An unusual solvent‐induced inversion of the sense of enantioselectivity observed in the α‐selenylation of aldehydes catalyzed by a diphenylprolinol silyl ether catalyst is correlated to the presence of intermediates formed subsequent to the highly selective CSe bond‐forming step in the catalytic cycle. This work provides support for a mechanistic concept for enamine catalysis and includes a general role for “downstream intermediates” in selectivity outcomes in organocatalysis.