Utilization of methanol for condensation interrupted chemoselective transfer hydrogenation of CC, CO, and CN bonds under low catalyst loading

Abstract

Selective transfer hydrogenation (TH) of unsaturated molecules using methanol is challenging as the in situ generated formaldehyde is prone to react with the active methylene (C-methylation) or amine (N-methylation) core of the desired product. In this work, an effective protocol is demonstrated for the selective transfer hydrogenation of CC and CO bonds in α,β-unsaturated ketones and the CN bond in imines using methanol. Under a considerably lower catalyst loading (0.1–0.5 mol%), an electron-rich bifunctional Ir-catalyst showed prominent catalytic activity towards a wide variety of substrates. Remarkably, α,β-unsaturated ketones were directly transformed into alcohols via double TH of CC and CO bonds. The TH of electron-withdrawing substrates was more favourable than that of electron-donating ones as reflected by a Hammett study. Numerous kinetic studies and DFT calculations were carried out to understand this catalytic process.