Chiral Brønsted Acid as a True Catalyst: Asymmetric Mukaiyama Aldol and Hosomi–Sakurai Allylation Reactions

Highly diastereo- and enantioselective
Mukaiyama aldol reaction
catalyzed by a new chiral Brønsted acid, N-(perfluorooctanesulfonyl)­thiophosphoramide,
is described. The perfluorooctyl substituent on the sulfonyl group
of the catalyst plays an essential role in the stereoselection. The
catalyst also allows the asymmetric Hosomi–Sakurai allylation,
which has been considerably challenging due to the low reactivity
of allylsilanes. 29Si and 31P NMR monitoring
reveals the characteristic feature of the thiophosphoramide catalyst,
acting as a strong Brønsted acid even in the presence of excess
silyl nucleophiles, which cannot be found in other related phosphoric
acid analogues.