Transition Metal‐Catalyzed Homogeneous Asymmetric Hydrogenation

Abstract

INTRODUCTIONAmong all the catalytic asymmetric methodologies to chiral compounds, homogenous transition metal -catalyzed asymmetric hydrogenation plays a particularly important role [1] . Its highly effi cient, environmental friendly, and cost -effective natures have undoubtly made it one of the most studied methodologies during the past 40 years. As a result, the vast number of catalytic systems developed has also had a signifi cant impact on other areas of asymmetric catalysis [2] . More signifi cantly, the achievements from academia research on asymmetric hydrogenation were frequently acknowledged with industrial applications, which, in turn, provide an important driving force for its basic research [3] .Hundreds of catalytic systems have been developed since the seminal discoveries from Knowles and Sabacky [4] , Kagan and Dang [5] , and Horner et al. [6] . In many cases, series of chiral catalysts were developed based on the similar scaffolds and were prepared for the same reactions. Although these analogous ligands are more likely prepared for the purpose of patent protection other than academic curiosity, they indeed provide us an excellent opportunity to compare, evaluate, and study every aspect of the catalysts in asymmetric hydrogenation. In the meantime, a large number of prochiral unsaturated compounds have been successfully hydrogenated with excellent enantioselectivities. Practical applications with very low catalyst loadings and complex substrate structures have continued to emerge since the publication of the last edition of this book.

Synthesis of E- and Z-trisubstituted alkenes by catalytic cross-metathesis

“…Linear E - and Z -trisubstituted alkenes occur widely in nature and are used regularly in preparative chemistry 1,2 (for example, in catalytic enantioselective hydrogenations 3 , allylic substitutions 4 , or conjugate additions 5 ). Several approaches have been developed for generating acyclic trisubstituted alkenes, but these have key shortcomings.…”

Enantioselective β-Protonation by a Cooperative Catalysis Strategy

“…1 The orchestration of independent catalysts to promote unique transformations is a powerful strategy for reaction discovery. 2 Within the field of N -heterocyclic carbene (NHC) catalysis, 3 cooperative catalysis has been demonstrated as a viable strategy for improving yield, selectivity, and expanding substrate scope.…”

“…7 The proton is effectively the simplest functional group in chemistry, and its manipulation is the basis of many modern catalytic processes. 1a,8 The development of catalytic asymmetric α-protonations of enolates through malonates, silyl enol ethers, ketenes, and α,β-unsaturated carbonyls has led to novel strategies for the synthesis of compounds of interest possessing tertiary carbon stereocenters (Figure 1). 1a,2b,9 By contrast, to the best of our knowledge a highly enantioselective β-protonation has not been achieved.…”

“…1a,8 The development of catalytic asymmetric α-protonations of enolates through malonates, silyl enol ethers, ketenes, and α,β-unsaturated carbonyls has led to novel strategies for the synthesis of compounds of interest possessing tertiary carbon stereocenters (Figure 1). 1a,2b,9 By contrast, to the best of our knowledge a highly enantioselective β-protonation has not been achieved. In addition to general considerations of enantioselective α-protonation—racemization under protonation conditions and selectively generating pure E - or Z -enolates—β-protonation encounters the additional challenges of generating the necessary homoenolate under catalytic conditions and imparting enantioinduction through interactions with remote functional groups of the chiral catalyst.…”

Asymmetric Hydrogenation

“…Fortunately, many exhaustive reviews have been published, together with excellent accounts of asymmetric hydrogenation. The author hopes that this chapter, together with the review articles [15][16][17][18], will provide good references for the process.…”