Lewis base catalysis of three n-π* mediated reactions with N-heterocyclic carbenes (NHCs), isothioureas, bicyclic tertiary amines, and electron-rich pyridyls

摘要

Lewis base catalysis by lone pair donation into anti-bonding π orbitals (n-π*) is a growing field with a range of Lewis bases capable of this type of catalysis. In this review, catalysis of the Morita-Baylis-Hillman reaction, the Steglich rearrangement, and the annulation of α,β- unsaturated acyl Lewis adducts are discussed, using N-heterocyclic carbene (NHC), isothiourea, bicyclic tertiary amine and electron-rich pyridyl catalysts. In many cases, each of these popular Lewis base catalysts is viable for the given reaction, with the degree of utility defined by the catalyst's nucleophilicity and Lewis basicity. 1 Introduction to Lewis Base Catalysis 2 Enolates from 1,4-Addition: Morita-Baylis-Hillman Reaction 3 O→C Carboxyl Transfer: Steglich Rearrangement 4 Annulations of α,β-Unsaturated Acyl Lewis Base Adducts 5 Summary and Outlook