Zhanhui Yang

Iridium-catalyzed highly efficient chemoselective reduction of aldehydes in water using formic acid as the hydrogen source

A water-soluble highly efficient iridium catalyst is developed for the chemoselective reduction of aldehydes to alcohols in water. The reduction uses formic acid as the traceless reducing agent and water as a solvent. It can be carried out in air without the need for inert atmosphere protection. The products can be purified by simple extraction without any column chromatography. The catalyst loading can be as low as 0.005 mol% and the turn-over frequency (TOF) is as high as 73 800 mol mol−1 h−1. A wide variety of functional groups, such as electron-rich or deficient (hetero)arenes and alkenes, alkyloxy groups, halogens, phenols, ketones, esters, carboxylic acids, cyano, and nitro groups, are all well tolerated, indicating excellent chemoselectivity.

Iridium-catalyzed efficient reduction of ketones in water with formic acid as a hydride donor at low catalyst loading

A highly efficient and chemoselective transfer hydrogenation of ketones in water has been successfully achieved with our newly developed catalyst. Simple ketones, as well as α- or β-functionalized ketones, are readily reduced. Formic acid is used as a traceless hydride source. At very low catalyst loading (S/C = 10 000 in most cases; S/C = 50 000 or 100 000 in some cases), the iridium catalyst is impressively efficient at reducing ketones in good to excellent yields. The TOF value can be as high as up to 26 000 mol mol−1 h−1. A variety of functional groups are well tolerated, for example, heteroaryl, aryloxy, alkyloxy, halogen, cyano, nitro, ester, especially acidic methylene, phenol and carboxylic acid groups.

Na2S2O8-mediated efficient synthesis of isothiocyanates from primary amines in water

We have developed two green, practical, and efficient procedures, including a one-pot one, to synthesize isothiocyanates from amines and carbon disulfide via desulfurization with sodium persulfate. Water is used as the solvent. Basic conditions are necessary for good chemoselectivity for isothiocyanates. Structurally diverse linear and branched alkyl amines and aryl amines are readily converted to isothiocyanates by the two procedures in satisfactory yields. Halogens, benzylic C–H bonds, methylthio, nitro, ester, alkenyl, electron-rich or -deficient (hetero)aryls, acetylenyl, and even phenolic and alcoholic hydroxyls are well tolerated. The one-pot procedure in water can also be used to realize the preparation of chiral isothiocyanates from chiral amines, and the modification of bioactive structures with free amino groups. In large-scale preparation, simple and practical purification procedures independent of column chromatography are developed.