Diastereoselective Synthesis of Tetrahydrospiro[carbazole-1,3′-indolines] via an InBr<sub>3</sub>-Catalyzed Domino Diels–Alder Reaction
Daqian Wang, Jing Sun, Ruzhang Liu, Yang Wang, Chao‐Guo Yan
Abstract
A simple InBr3-catalyzed domino reaction of indoles, phenylacetylenes, and various 3-methyleneoxindolines in toluene is described. This reaction not only provided a convenient synthetic protocol for polysubstituted tetrahydrospiro[carbazole-1,3′-indolines] in good yields but also gave completely different diastereoisomers of the tetrahydrospiro[carbazole-1,3′-indolines] to that of the previously reported TfOH-catalyzed one-pot reaction of indoles, acetophenones, and 3-methyleneoxindolines. Additionally, the InBr3-catalyzed reaction of the initially prepared 1,1′-bis(indolyl)phenylethanes with 3-phenacylideneoxindolines also gave the corresponding tetrahydrospiro[carbazole-1,3′-indolines] in good yields and with excellent diastereoselectivity. The reaction mechanism involved the sequential in situ generation of reactive dienophilic 3-alkenylindole, the Diels–Alder reaction, and the Lewis acid controlled diastereoisomerization process.