脂肪族酯基选择性还原模型的建立

以不同烷基取代的酯作为模型, 对其进行NaBH4还原研究. 不同取代基酯的起始反应温度和半衰期显示出了明显的差别和一定的选择性; 用B3LYP/6-31++G(d,p)//HF/6-31G(d,p)方法计算得到的过渡态能量与实验得到的活化能变化趋势一致; 实验中观察到了奇偶碳效应; 对NaBH4还原酯基的溶剂影响进行了初步研究.

Chemoselective Reduction Model of Aliphatic Esters with Sodium Borohydride

Sodium borohydride has been widely used in different organic reductions due to its moderate chemical activity.The reductions of ester with sodium borohydride could produce various alcohols as intermediates for further reactions.The esters with different alkyl substituents are used as the models in sodium borohydride reductions,and on-set temperatures,half-life periods and transition state(TS) energies were obtained experimentally.Some of the TS energetics were computed using B3LYP/6-31 G(d,p)//HF/6-31G(d,p) method.The differences of on-set temperatures among these esters were substantial and some observed selectivities were obtained when the aliphatic substituents changed from Me,Et,n-Pr to n-Bu.Odd-even carbon effect,which was first mentioned in our previous report in enantioselective additions of diethylzinc to benzaldehyde,was observed again in the reductions.Traditionally,organic theory uses the size of the substitutents to explain the reaction TS energy order.However,the traditional theory can not be used to explain the observed odd-even carbon effect.The reason for this effect happened in different reactions is still unknown.Furthermore,the effect of solvent in the reductions was investigated primarily.