Gold-Catalyzed Synthesis of Benzazepines

Significance

Reported here is the cyclization of ortho-acetylenic aniline N-allenyl amides under gold(III) catalysis to give products which vary as a function of substrates and conditions. Thus, cyclization of N-allenyl sulfonamides 1 affords trans-substituted benzazepines 2 using AuCl₃ as catalyst and alcohols as nucleophilic traps at low temperature. Under those conditions, the formation of allene addition product 3 was also observed. This may be rationalized by coordination of the metal to the allene, instead of coordination to the alkyne, promoting nucleophilic addition to afford 3. This may, in turn, undergo deallenylation to give 4 (also an observed product), which leads ultimately to benzazepines 2. The intermediacy of 3 under AuCl₃ catalysis in the presence of methanol was demonstrated in a separate experiment.