Methods of enhancement of reactivity and selectivity of sodium borohydride for applications in organic synthesis

NaBH4 does not reduce carboxylic acids, esters, amides and nitriles under ambient conditions. However, the reactivity of NaBH4 can be enhanced by the addition of certain additives. For example, addition of iodine to NaBH4 in THF provides H3B–THF that is useful for hydroborations and reductions of various functional groups. The aldehydes and ketones are reduced in a fast manner by the NaBH4 reagent. Even so, the selectivities realised in such reductions can be enhanced using NaBH4 along with another additive. In this article, various methods used for the enhancement of reactivity and selectivity of NaBH4 in organic synthesis are described.