We report an efficient method for the synthesis of C(1)-carboxamide derivatives by adding isocyanides to 3,4-dihydroisoquinoline N-oxides and 3,4-dihydro-β-carboline 2-oxide in the presence of TMSOAc. 3,4-Dihydroisoquinoline-1-carboxylamide derivatives and 9-dihydro-3H-pyrido[3,4-b]indole-1-carboxamide derivatives were obtained in reasonable yields. The method could be used to synthesize alangiobussine, an alkaloid, in 61% yield.