Diisopropylaminoborane
Diisopropylaminoborane has been studied for the mild palladium-catalyzed borylation of aryl bromides to generate arylboronic acids. The procedure tolerated functional groups such as esters, fluorides, methoxy groups and amines. However, nitriles behaved differently, which led to the discovery of new reactions of aminoboranes.
Diisoproylaminoborane is able to reduce esters and carbonyl compounds to the corresponding alcohols and nitriles to amines in the presence of catalytic amounts of LiBH4 or LiBPh4. As both catalysts accelerate the reduction, it seems clear that lithium ion coordination is responsible for the catalysis. Compared with other methods for the reduction of nitriles that often employ toxic transition metal catalysts or harsh reaction conditions, diisopropylaminoborane offers a convenient alternative.
The group of Bakthan Singaram developed two methods for the convenient preparation of solutions of diisopropylaminoborane: one of them generates the pure reagent, whereas the other method also generates traces of LiBH4 too. The solution of reagent prepared by the second method can be used directly for the reduction of nitriles. Both solutions can be stored in an ampule under nitrogen without decomposition for at least 1 year:
For a review of early developments please refer to a publication of Singaram (J. Org. Chem. 2008, 73, 1898. DOI)
Recent Literature
Diisopropylaminoborane [BH2N(iPr)2] in the
presence of a catalytic amount of lithium borohydride (LiBH4) reduces
a large variety of aliphatic and aromatic nitriles in excellent yields.BH2N(iPr)2
can also reduce nitriles in the presence of unconjugated alkenes and alkynes.
Unfortunately, selective reduction of a nitrile in the presence of an aldehyde
is not possible.
D. Haddenham, L. Pasumansky, J. DeSoto, S. Eagon, B. Singaram, J. Org. Chem., 2009,
74, 1964-1970.
