Organocatalytic enantioselective reaction of tertiary -(7-indolyl)methanols with tryptamines

With the aid of chiral phosphoric acid, enantioselective 1,6-addition of tryptamines to in situ formed alkynyl 7-methylene-7H-indoles from tertiary alpha-(7-indolyl)methanols has been established for the first time, furnishing a broad range of axially chiral tetrasubstituted allenes featuring indole and hexahydropyrrolo[2,3-b]indole units in good to high yields and with asymmetric induction. DFT calculations have been carried out to shed light on the reaction mechanism and to understand the origin of stereoselectivity. Importantly, this protocol not only enriches the chemistry of alpha-(7-indolyl)methanols but also provides an efficient means for the preparation of structurally diverse axially chiral tetrasubstituted allenes.