The approximate rate and stoichiometry of the reaction of excess pure potassium triisopropoxyborohydride, KIPBH, with 56 selected compounds containing representative functional groups under standardized conditions (tetrahydrofuran, 0 °C) was examined in order to define the characteristics of the reagent for selective reductions. Primary, secondary, and tertiary alcohols evolve hydrogen partially, even after a long period of time. Phenol also generates partial hydrogen, and the reactions of those amines and thiols studied with the reagent are very slow. Aldehydes and ketones are reduced rapidly and quantitatively to give the corresponding alcohols. Unlike sodium and potassium borohydrides, KIPBH is very stereoselective. 2-Methylcyclohexanone can be reduced to the correspondingly less stable isomer, ds-2-methylcyclohexanol, in a high ratio (91% cis isomer). Cinnamaldehyde is rapidly reduced to cinnamyl alcohol, and further reduction is very slow under these conditions. Anthraquinone is cleanly reduced to 9,10-dihydro-9,10-anthracenediol. Carboxylic acids liberate hydrogen only
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