Regiodivergent Access to Five- and Six-Membered Benzo-Fused Lactams: Ru-Catalyzed Olefin Hydrocarbamoylation

Abstract

We report herein a new strategy of the Ru-catalyzed intramolecular olefin hydrocarbamoylation for the regiodivergent synthesis of five- and six-membered benzo-fused lactams starting from N-(2-alkenylphenyl)formamides. Using a combined catalyst of Ru3(CO)12/Bu4NI in DMSO/toluene cosolvent (catalytic system A), a 5-exo-type cyclization proceeds favorably to form indolin-2-ones as a major product in good to excellent yield. When the reaction was conducted in the absence of halide additives in DMA/PhCl (catalytic system B), 3,4-dihydroquinolin-2-ones were obtained in major in moderate to high yield via a 6-endo cyclization process. An excellent level of regioselectivity was observed with a variety of substrates to deliver 5-exo- or 6-endo-cyclized lactams. It was found that while the selective cyclization was controlled primarily by the choice of catalytic systems employed, it was also greatly influenced by the structural nature of substrates. A halide-bridged trinuclear complex [Ru3(CO)10(μ2-I)](-) is postulated to be an active species in the catalytic system A. Two reaction pathways are proposed, in which the Ru-catalyzed oxidative addition of formyl C-H or N-H bond initiates the subsequent cyclization processes.