Organocatalytic Reduction in Stereoselective Synthesis

Abstract

The synthesis of chiral, enantiopure molecules plays an important role in modern chemistry, as stereocenters are omnipresent in natural products and pharmaceuticals. Therefore, is it important to have versatile and reliable methods to introduce stereocenters during the synthesis. An upcoming, powerful way to construct stereocenters is asymmetric organocatalytic reduction. A given prochiral double bond is selectively reduced to give one of the two enantiomers or diastereomers in excess. As substrates, the functional groups containing CN, CO, or CC double bonds come into consideration. These can appear both in linear molecules (e.g., ketones) and in heteroaromatics like pyridine. Catalysis takes place by activation of either the substrate or the reducing agent, thereby also transferring the chiral information. Hydrazine, silanes, and Hantzsch esters are herein the most frequently used reducing agents.

Catalytic Reduction of Oximes to Hydroxylamines: Current Methods, Challenges and Opportunities

“…While several metal‐free systems exist that promote ketone and imine reductions,[ 61 , 62 ] the choice for oximes is rather limited. In a seminal work, in 2014 the group of Oestreich used B(C 6 F 5 ) 3 as catalyst to hydrogenate ketoxime ethers 31 (R 2 ≠H) to racemic hydroxylamine derivatives 32 a – g without scission of the N−O bond (Scheme 8 ).…”