Rhenium-catalyzed synthetic method of 1,2-dihydroisoquinolines and isoquinolines by the intramolecular cyclization of 2-alkynylaldimines or 2-alkynylbenzylamines

A rhenium-catalyzed synthetic method of 1,2-dihydroisoquinolines and isoquinolines has been developed. When the 2-alkynylarylaldimines were reacted with various pronucleophiles, such as nitromethane, dimethyl malonate, and phenylacetylene, in the presence of a rhenium catalyst, cyclization and subsequent nucleophilic addition proceeded to give the corresponding 1,2-dihydroisoquinolines in moderate to good yields. When hydrosilane, allylstannane, and ketene silyl acetal instead of pronucleophile were used, hydride, allyl, and –C(CH3)2COOCH3 groups were introduced on the 1-position of 1,2-dihydroisoquinolines. 1,2-Dihydroisoquinolines were also synthesized by the rhenium-catalyzed cyclization of the 2-alkynylbenzylamines. The synthesis of the isoquinolines was attained by the use of N-t-butyl-2-alkynylaldimines, which were prepared by the reaction of 2-alkynylbenzaldehyde and t-butylamine.