Switching Diastereoselectivity in Proline-Catalyzed Aldol Reactions

摘要

The choice of the anion of an achiral TBDderivednguanidinium salt, used as cocatalyst for proline, allowsnreacting cycloketones with aromatic aldehydes and preparingneither anti- or syn-aldol adducts with very high enantioselectivity.nAs a proof of principle, we show how the judiciousnchoice of an additive allows individual access to all possiblenproducts, thus controlling the stereochemical outcome of the asymmetric aldol reaction. The origin of the syn diastereoselectivitynunfolds from an unusual equilibrium process coupled to the enamine-based catalytic cycle standard for proline.