Manganese-Catalyzed Reformation of Vicinal Glycols to α-Hydroxy Carboxylic Acids with the Liberation of Hydrogen Gas

Conversion of readily available feedstocks to valuable platform chemicals via an eco-friendly catalytic pathway has always been one of the key focuses of synthetic chemists. In this context, herein, we report selective transformation of readily available feedstock, vicinal glycols, to value-added α-hydroxycarboxylic acid molecules that are prevalent in bioactive molecules and biodegradable polymers. A bench stable Earth-abundant metal complex, {[HN(C2H4PPh2)2]Mn(CO)2Br}, Mn-I catalyzed the reformation reaction at low temperature in high selectivity with a turnover number reaching 2400, surpassing previously used homogeneous catalysts for such a reaction. Hydrogen gas is evolved as a byproduct without needing an acceptor. The developed protocol is applicable for both aromatic and aliphatic vicinal glycols, delivering the α-substituted hydroxycarboxylic acids in high yields and selectivities. Detailed mechanistic studies elucidated the involvements of different manganese(I)-species during this acceptorless dehydrogenation catalysis.