Mixed Sovents Containing Methanol as Useful Reaction Media for Unique Chemoselective Reductions with Lithium Borohydride

Article abstract of DOI:10.1021/jo00371a017

The reducing ability of lithium borohydride is greatly enhanced in mixed solvents containing methanol.Esters, lactones, and epoxides are reduced chemoselectively more rapidly with LiBH4-MeOH (1 equiv added at the beginning)-ether than with LiBH4-ether in the presence of the other reducible groups such as carboxylic acid, chloro, nitro, and carbamoyl.On the other hand, nitro, nitrile, carboxyl, and primary and tertiary amide groups are reduced with LiBH4-MeOH(4 equiv dropwise addition)-diglyme(or tetrahydrofuran).However, secondary amides derived from aliphatic amines and metal carboxylate are not reduced.Thus, unique chemoselective reductions of primary amide in the presence of secondary amide or metal carboxylate are achieved.