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

Organic Chemistry Frontiers Pub Date: 2023-03-29 DOI: 10.1039/D3QO00308F

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 C[double bond, length as m-dash]C and C[double bond, length as m-dash]O bonds in α,β-unsaturated ketones and the C[double bond, length as m-dash]N 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 C[double bond, length as m-dash]C and C[double bond, length as m-dash]O 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.

Graphical abstract: Utilization of methanol for condensation interrupted chemoselective transfer hydrogenation of C [[double bond, length as m-dash]] C, C [[double bond, length as m-dash]] O, and C [[double bond, length as m-dash]] N bonds under low catalyst loading
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