Cyclizations of aryl enynes containing propargyl alcohol and diallylamine groups to yield indolecarbaldehydes induced by ruthenium complexes

The reactions of RuCl(PPh₃)₂Cp ([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 π-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-β of the triple bond, accompanied by the opening of the isoxazole ring. The reactions of 2a-2c and 2e with O₂/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.