Reduction of chiral acyclic ketones with hydride-transfer agents. Semiempirical analysis of the observed stereoselectivity

Abstract

(±)-2,2,6,6-Tetramethyl-5-phenylheptan-3-one (1), (±)-4,4-dimethyl-1,3-diphenylpentan-1-one (2), (±)-2-methyl-1,3-diphenylpropan-1-one (3), and (±)-2,3,3-trimethyl-1-phenylbutan-1-one (4) have been reduced with lithium tetrahydridoaluminate (LAH), sodium tetrahydridoaluminate (NAH), lithium tri-t-butoxyhydridoaluminate (LTBHA), lithium tetrahydridoborate (LBH), lithium tri-s-butylhydridoborate (LS = lithium selectride) and potassium tri-s-butylhydridoborate (KS = potassium selectride) using different solvents and reaction conditions. For ketones (1) and (2) some correlations with the observed stereoselectivity have been found. The applicability of a semiempirical scale for the effective size of reagent to the stereochemical analysis of the observed asymmetric induction has been tested.