Unexpected Selectivity in Sodium Borohydride Reductions of α‐Substituted Esters: Experimental and Theoretical Studies

The propensity of sodium borohydride to reduce the carbonyl group in eleven alpha-substituted and two aromatic esters has been investigated by experiments and at the B3LYP/631++G(d,p)//HF/6-3lG(d,p) level of theory. The chemoselectivities in nine of these reductions have been examined by experiments. Experimental results agree well with the calculated order of activation energies for hydride transfer to the ester carbonyl group. Methyl a-bromoacetate reduces faster than methyl a-fluoroacetate. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006).