N-Heterocyclic Carbene Catalyzed [2+2] Cycloaddition of Aryl Isothiocyanates and Nitroolefins: An Efficient Synthesis of β-Thiolactams

The first example of a convenient N-heterocyclic carbene (NHC) catalyzed synthesis of beta-thiolactams via [2+2] cycloaddition of aryl isothiocyanates and nitroolefins is reported. The protocol affords beta-thiolactams in excellent yields with high diastereoselectivity in favor of the cis isomer. Operational simplicity, excellent yields of products, efficient synthesis, and no by-product formation are the salient features of this synthetic protocol. Two possible catalytic pathways, initiated by the addition of NHC to aryl isothiocyanates or nitroolefins, are discussed.