Divergent hetero-[8+n] higher order cycloadditions of tropothione and enals catalyzed by N-heterocyclic carbenes†

Abstract

Divergent asymmetric NHC-catalyzed [8+n] higher-order cycloadditions using tropothione as an electron-poor 8π component were developed. The base-dependent selectivity of the synthetic approach allowed obtaining heterocyclic products bearing either γ- or δ-thiolactone rings with high enantioselectivity. The impact of base on NHC intermediate isomerization was explained by DFT studies. The diastereodivergency of the methodology was confirmed with both diastereomers being easy to isolate with very good results.