A new facile approach to highly selective hydroboration of alkenes with sodium malonyloxyborohydride

Abstract

The preparation and properties of sodium malonyloxyborohydride (SMB) are described. As a white solid, SMB is very sensitive to moisture in air. It is also highly sensitive to the structure of alkenes. Thus SMB, prepared in situ from the reaction of malonic acid with equimolar NaBH₄ in dry THF, hydroborates alkenes showing that terminal aliphatic alkenes undergo facile hydroboration with 98% of the boron moiety placed on the terminal position and 2% at the 2 position. On the other hand, trisubstituted alkenes and cyclohexene show poor reactivity in the hydroboration as compared with terminal alkenes. These characteristics indicate that SMB is a highly regioselective monofunctional hydroborating reagent for terminal alkenes.