N‐tert‐Butyl Triazolylidenes: Catalysts for the Enantioselective (3+2) Annulation of α,β‐Unsaturated Acyl Azoliums

But(yl) not futile: A range of N-tert-butyl-substituted triazolylidene N-heterocyclic carbenes have been prepared. Of these, the morpholinone-derived catalyst (1) proved best suited to the enantioselective synthesis of cyclopentanes from donor–acceptor cyclopropanes and α,β-unsaturated acyl fluorides. The performance of this catalyst has been correlated to the electronic nature of the catalyst by 13C NMR analysis. M.S.=molecular sieves, TMS=trimethylsilyl.