Iridium-catalyzed Efficient Reduction Of Ketones And Site-selective Deoxygenation Of Alcohols In Water

Transition Metal-catalyzed transfer hydrogenation(TH),as an idea method for chemicals reduction,has the merit of greenness and efficiency,which makes it increasingly important in both academia and industry.In the studies on efficient reduction of ketones and site-selective deoxygenation of Alcohols in water,catalyzed by our newly developed water-soluble iridium catalysts,following results were achieved:(1)A highly efficient and chemoselective transfer hydrogenation of ketones in water has been successfully achieved.Simple ketones,as well as a-or P-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.(2)An highly efficient,and site-selective deoxygenation of primary,secondary,and tertiary alcohols has been realized,under the assistance of a 4-(N-substituted amino)aryl directing group.Only the hydroxyl adjacent to the directing group can be deoxygenated.The deoxygenation is performed in water,with formic acid as both the promoter and hydride donor.Excellent yields and functionality tolerance,as well as high efficiency(S/C up to 1 000 000,TOF up to 445 000 h-1),are obtained.The kinetic isotope effect studies show that hydride formation is the rate-determining step,and the deoxygenation follows an SN1-type pathway.The deoxygenation protocol has been demonstrated useful in the structural modification of naturally occurring ketones and steroids.