Unsymmetrical relay C–H alkenylation and [2 + 2] cycloaddition of N-arylsydnones with allenyl acetates leading to quinoline-fused cyclobutanes

Abstract

In spite of the prevalence of fused cyclobutane skeletons in natural products and pharmaceuticals, synthetic strategies for their assembly from simple starting materials still remain scarce. Herein, we present a direct, effective and atom-economical access toward quinoline-fused cyclobutane derivatives based on Rh(III)-catalyzed cascade reactions of N-arylsydnones with allenyl acetates. This unique reactivity relies on an unprecedented unsymmetrical relay C(sp²)–H bond alkenylation, followed by simultaneous [2 + 2] cycloaddition of the in situ formed bis-dienylation intermediate under the same reaction conditions. This developed protocol is compatible with a number of labile functional groups and competent for substrates derived from natural products. In addition, the potential of this method is further demonstrated by gram-scale application scenarios and versatile transformations of the products into value-added compounds.