Highly Enantioselective Iridium-Catalyzed Cascade Double Allylation Strategy: Synthesis of Pyrrolidinoindolines with an All-Carbon Quaternary Stereocenter.

Highly enantioselective cascade double allylations of 1-alkyl-3-alkylindolin-2-imine hydrochlorides with (E)-but-2-ene-1,4-diyl dimethyl dicarbonate leading to tetrahydropyrrolo[2,3-b]indoles with an all-carbon quaternary stereocenter have been developed. This transformation was catalyzed by an iridium catalyst together with our developed chiral cyclic phosphoramidite ligand. The method shows some advantages including an operationally simple protocol, fast reaction, and excellent diastereoselectivity and enantioselectivity. Furthermore, reduction of the obtained products with diisobutyl aluminum hydride provided the pyrrolidinoindolines with three chiral centers in high yields with excellent diastereoselectivity and enantioselectivity.