3,10-Dihydro-2H-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.

3,10- Dihydro -2 H -1,3-oxazep​​ino [7,6- b ]吲哚是通过方便的一锅三组分1,4-偶极环加成反应合成的，涉及3-烷基（芳基）咪唑并[ 1,5- α ]吡啶，乙炔二羧酸二甲酯（DMAD）和N-烷基靛红。新合成的杂环的结构由光谱数据证明，并通过单晶X射线衍射进一步证实。推进了可能的反应机理，其中由咪唑并[1,5- a ]吡啶和DMAD原位生成的中间1,4-偶极子最初加到了N的酮基上-烷基靛红形成相应的1，3-恶嗪-螺-氧吲哚环加合物。后者随后通过级联的键断裂和键形成过程经历了前所未有的骨架重排，最终导致环扩大，从而提供了三环氧杂庚并[7,6- b ]吲哚环系统作为最终产物。