Isolable Analogues of the Breslow Intermediate Derived from Chiral Triazolylidene Carbenes

Since Breslow’s initial report on the thiamine
mode of action,
the study of catalytic acyl carbanion processes has been an area of
immense interest. With the advent of azolylidene catalysis, a plethora
of reactivtiy has been harnessed, but the crucial nucleophilic intermediate
proposed by Breslow had never been isolated or fully characterized.
Herein, we report the isolation and full characterization of nitrogen
analogues of the Breslow intermediate. Both stable and catalytically
relevant, these species provide a model system for the study of acyl
carbanion and homoenolate processes catalyzed by triazolylidene carbenes.