Mild Complementary Cycloisomerization Reactions to N-Fused Heterocycles

Significance

Reported are two mild and complementary cycloisomerization (A) and cascade 1,2-migration-cycloisomerization (B) processes, resulting in the formation of fused 1,3- and 1,2-substituted N-heterocycles. After a thorough screening of metal catalysts, the former was found to be efficiently catalyzed by AgBF₄ and the latter by AuBr₃. The yields range from modest to excellent and the substrate scope was well studied. Starting materials are easily synthesized from the corresponding heterocyclic aldehydes and propargylic Grignard reagents. Of two mechanistic pathways considered, support for one of these was obtained by deuterium-labeling and kinetic-isotope-effect studies.