Cyclizations of Aryl Enynes Containing Propargyl Alcohol and Diallylamine Groups to Yield Indolecarbaldehydes Induced by Ruthenium Complexes

The reactions of RuCl(PPh3)(2)Cp ([Ru] Cl, Cp = cyclopentadienyl) with aryl enynes 1a-1c containing propargyl alcohol and diallylamine groups on the aryl ring give the carbene complexes 2a-2c, each of which contains an indole group. With an additional methylene group, the aryl enyne 1d reacts with [Ru] Cl to afford the dihydroisoquinoline complex 3d. For 1a-1d, the C-N bond-forming process occurs when the triple bond is p-coordinated to the metal center. The reaction of [Ru] Cl with the aryl enyne 1e containing an isoxazole group affords the carbene complex 2e by a C-C bond formation between the isoxazole group and C-beta of the triple bond, accompanied by the opening of the isoxazole ring. The reactions of 2a-2c and 2e with O-2/NEt3 are assisted by visible light to afford the corresponding aldehydes 4a-4c and 5e. From DFT calculations, visible light results in the partial population of the lowest unoccupied molecular orbital (LUMO), which has Ru=C antibonding character; therefore, the bond is weakened, and the oxygenation/demetallation reactions are slightly promoted.