Both industry and academia place special emphasis on carbonyl reductions due to the versatility of this transformation
for the generation of a wide range of products.Hydrogen gas is the ideal reducing agent in terms of cost and atom efficiency,and has very broad applicability for the reduction of carbonyls. Hydrogenation chemistry is well established (first catalytic example reported in 1874 for olefin reduction and reliable, and typically affords reduction products in high yield and purity with minimal workup.Its drawbacks include the flammability of H2 gas, the frequent need for specialized equipment, and the lack of reactivity toward certain carbonyl groups (e.g.,
carboxylic acids, esters, amides). The discovery of LiAlH4 in 1947 (prepared by treating AlCl3 with LiH)6 and NaBH4 in
1953 (prepared by treating B(OMe)3 with NaH)7 set the foundation for the development of new and more chemoselective reagents that have considerably expanded the scope
of reducing agents