Fused polycyclic compounds with benzo[c]isoxazolo[5',4':3,4]pyrrolo[1,2-a]azepine, dibenzo[c,e]isoxazolo[5',4':3,4]pyrrolo[1,2-a]azepine, and benzo[f]isoxazolo[5',4':3,4]pyrrolo[1,2-d]oxazepine cores are readily available via cyclization of the N-acyliminium cation generated from the corresponding 6-hydoxy-5-R-6,6a-dihydro-3aH-pyrrolo[3,4-d]isoxazol-4(5H)-ones in the presence of BF3·Et2O or Sn(NTf2)4.