本工作使用In(NTf₂)₃作为金属Lewis酸催化剂, 实现了吲哚-环丙烷分子内的亲核开环反应, 克服了脂肪族取代的环丙烷活性低、不易实现开环反应的难题. 利用该方法可以简单高效地构建吡咯并[1,2-a]-吲哚骨架结构的化合物. 该反应条件温和, 底物普适性广, 最终以15个反应实例, 高达96%收率得到一系列吡咯并[1,2-a]-吲哚化合物.

Donor-acceptor cyclopropanes as efficient three-carbon synthetic building blocks were widely employed in the synthesis of many natural products and complex drug molecules. However, the ring-opening of aliphatic substituted cyclopropanes, owing to their poor reactivity, usually suffers from the harsh reaction conditions such as strong Lewis acid, large amount of catalyst, high reaction temperature and so on. In this paper, In(NTf₂)₃ was found as a powerful Lewis acid to catalyze the intramolecular nucleophilic ring-opening reaction of donor-acceptor cyclopropane with indole. This reaction could be used to construct the pyrrolo[1,2-a]-indole framework structure in a facile way. This method could be conducted in mild reaction conditions with a broad substrate scope (15 examples), leading to the target products in up to 96% yield. The general procedure is as following: To a dry Schlenk tube in a glove box, was placed In(NTf₂)₃ (0.1 equiv.), 4 Å molecular sieve (50 mg) and a stir bar. The tube was capped and brought out of the glovebox. After connected to argon via a typical Schlenk line system, a solution of 1 (1.0 equiv.) in PhCl (1 mL) was added dropwise until the reaction was completed (monitored by thin-layer chromatography). Et₃N was added to quench the reaction and the reaction mixture was filtered through a thin layer of silica gel and eluted with EtOAc (100 mL). After removal of the volatiles under reduced pressure, the residue was purified by flash chromatography over silica gel to afford the product. When indole substrate contains electron-withdrawing substituents, the reaction temperature needs to be increased to 100 ℃ to obtain the target product.