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

The reactions of RuCl(PPh 3 ) 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 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 O 2 /NEt 3 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.