Umpolung of protons from H2O: a metal-free chemoselective reduction of carbonyl compounds via B2pin2/H2O systems.

H2O is routinely described as a proton donor, however, in the presence of diboron compounds, the umpolung reaction of H2O under metal-free conditions was successfully developed, which could afford hydride species, leading to a highly efficient and chemoselective reduction of C[double bond, length as m-dash]O bonds. This strategy exhibits excellent chemoselectivities toward carbonyl groups in the presence of ester, olefin, halogen, thioether, sulfonyl, cyano as well as heteroaromatic groups.