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

Abstract

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 forma-[a] We have recently reported the mild oxygenation of ruthenium carbene complexes with O 2 /NEt 3 to obtain high yields of aldehydes. [14] As an extension of our previous study, we further develop ruthenium-catalyzed cyclization reactions of propargyl alcohol with nitrogen-containing enynes to afford carbene complexes. Herein, we report the synthesis of these carbene complexes, each with a conjugated ring structure, and when these complexes are treated with O 2 /NEt 3 they afford aldehydes in high yields by oxidation of the carbene ligand.

Ruthenium‐Induced Cyclization of Heteroatom‐Functionalized Alkynes: Progress, Challenges and Perspectives

“…In 2014, they reported the isolation of Ru-indolyl-carbene complexes 4a from the reactions betweena niline-substituted propargyl alcohols S4 a and [CpRu(PPh 3 ) 2 Cl] (Scheme 20). [31] Ru-alkenyl complex 4b was obtained from similar reaction conditions using propargyl alcohol S4 b.F ormation of these complexes were all proposed to come from "non-vinylidene-involving" pathways: 4a came from 5-exo-dig cyclizations of the Ru-alkyne p-intermediates whereas 4b from 6-exo-dig cyclization.…”