L-selectride

L-selectride is a organoboron compound with the chemical formula Li[(CH3CH2CH(CH3))3BH]. A colorless salt, it is usually dispensed as a solution in THF. As a particularly basic and bulky borohydride, it is used for stereoselective reduction of ketones..

Use in synthesis
Like other borohydrides, reductions are effected in two steps: delivery of the hydride equivalent to give the lithium alkoxide followed by hydrolytic workup:
 * R2CO + Li[(CH3CH2CH(CH3))3BH]  ->  R2CHOLi  +  (CH3CH2CH(CH3))3B
 * R2CHOLi + H2O ->  R2CH2OH  +  LiOH

The selectivity of this reagent is illustrated by its reduction of all three methylcyclohexanones to the less stable methylcyclohexanols in >98% yield.

Under certain conditions, L-selectride can selectively reduce enones by conjugate addition of hydride, owing to the greater steric hindrance the bulky hydride reagent experiences at the carbonyl carbon relative to the (also-electrophilic) β-position. L-Selectride can also stereoselectively reduce carbonyl groups in a 1,2-fashion, again due to the steric nature of the hydride reagent.

It reduces ketones to alcohols. Aprepitant is another synthesis example where L-selectride was used.

Related compounds
N-selectride and K-selectride are related compounds, but instead of lithium as cation they have sodium and potassium cations respectively. These reagents can sometimes be used as alternatives to, for instance, sodium amalgam reductions in inorganic chemistry.