Synthesis of Cyclic 2-Aminodienes and Aminobenzofulvenes by Rhodium-Catalyzed Hydroaminative Cyclization of Diynes.

Regioselective hydroaminative cyclizations of 1,5- and 1,6-diynes via double functionalization of an alkyne carbon were achieved using a phosphine-quinolinolato (PNO) rhodium catalyst. While the reaction of 1,6-diynes with secondary amines provided cyclic 2-aminodienes, phenylene-tethered 1,5-diynes were transformed into benzofulvene derivatives. The reaction is considered to proceed via in situ construction of an aminocarbene ligand, [2 + 2] addition with an internal alkyne moiety, and isomerization to an aminodiene structure.