Diazaphosphinyl Radical-catalyzed Deoxygenation of α-Carboxy Ketones: A New Protocol for Chemo-selective C-O Bond Scission via Mechanism Regulation

C-O bond cleavage is often a key process in defunctionalization of organic compounds as well as in degradation of natural polymers. However, it seldom occurs regioselectively for multi-C-O bonds under metal-free mild conditions. Here we report a facile chemo-selective cleavage of the α-C-O bonds in α-carboxy ketones by commercially available pinacolborane under the catalysis of diazaphosphinane based on a mechanism-switch strategy. This new reaction features a high efficiency, low cost and good group-tolerance, and is also amenable to catalytic deprotection of desyl-protected carboxylic acids and amino acids. Mechanistic studies indicated an electron-transfer-initiated radical process, underlining two crucial steps: 1) initiator azodiisobutyronitrile switches originally hydridic reduction to kinetically more accessible electron reduction; and 2) catalytic phosphorus species upconverts weakly reducing pinacolborane into high-energy diazaphosphinane.