Aromatic boron wheels with more than one carbon atom in the center: C ₂B₈, C₃B₉³⁺, and C ₅B₁₁⁺

A convergent synthesis of α-methylene amides exploits a hybrid radical/ionic concept in which radical carbonylation of alkynes is followed by ionic trapping of the resulting carbonyl-containing radical species with amines (see scheme). The reaction of substituted terminal alkynes with pressurized CO, Bu₃SnH, and 2,2′-azobis-isobutyronitrile in the presence of a large excess of amines gave good yields of the corresponding α-methylene amides.