One-pot synthesis of novel 3,10-dihydro-2H-1,3-oxazepino[7,6-b]indoles via 1,4-dipolar cycloaddition reaction.

3,10-Dihydro-2 H -1,3-oxazepino[7,6- b ]indoles are synthesized via a convenient one-pot three-component 1,4-dipolar cycloaddition reaction, involving 3-alkyl(aryl)imidazo[1,5- a ]pyridines, dimethyl acetylenedicarboxylate (DMAD) and N -alkylisatins. Structures of the newly synthesized heterocycles are evidenced from spectral data and further confirmed by single crystal X-ray diffraction. A plausible reaction mechanism is advanced, whereby the intermediate 1,4-dipole, generated in situ from imidazo[1,5- a ]pyridine and DMAD, initially adds to the keto group of N -alkylisatins to form the corresponding 1,3-oxazin-spiro-oxindole cycloadduct. The latter undergoes subsequent unprecedented skeletal rearrangement through a cascade of bond breaking and bond making processes, eventually leading to ring enlargement, furnishing the tricyclic oxazepino[7,6- b ]indole ring system as the end product. [ABSTRACT FROM AUTHOR]