Asymmetric Hydrogenation ofCOandCNBonds in Stereoselective Synthesis

Abstract

Asymmetric hydrogenation is the simplest way of creating new chiral centers, and the technology is continuing to be an industrial flagship for chiral synthesis. In particular, stereoselective hydrogenation of ketones and imines are of a great importance as it is providing an efficient access to the optically active alcohols and amines. This chapter is focused on a practical approach to homogeneous hydrogenations of CO and CN bonds to provide a variety of valuable, biologically active compounds and natural products under mild reaction conditions with high enantio‐ and diastereoselectivity and excellent atom economy. Asymmetric hydrogenation is a highly application‐oriented method, and therefore, examples of industrial applications of the relevant technologies are appropriately illustrated throughout the text.

Ring Size-Dependent Solution Behavior of Macrocycles: Dipole–Dipole Attraction Counteracted by Excluded Volume Repulsion

“…This enhancement is particularly large for the Fp-based macromolecules due to the presence of highly polar Fp–acyl groups in the repeating units (Scheme a,b). The ring structure restricts the chain conformation and thus the rotation of the polar groups in the repeating units, which minimizes the cancellation of the dipole moments caused by the antiparallel alignment of the polar Fe–acyl groups. − An all-atom simulated configuration of P­( P FpR) 30 macrocycles is illustrated in Figure S2, from which the angles between CO (in Fe–acyl groups) and the plane of the macrocycle are calculated and plotted in Figure b. As shown in the figure, only 8.7% of the angles are larger than 90°, which suggests that most of the polar CO groups point to one side of the ring plane and thus effectively enhance the overall polarity of the macrocycles.…”

Catalytic Enantioselective Decarboxylative Aldol Reactions of Malonic Acid Half Thio(oxy)ester and β‐Ketoacids

“…Enantio-enriched α-nonsubstituted β-hydroxy esters are important intermediates for the synthesis of many natural products and pharmaceutical compounds. [29] Liu, Jiang and co-workers achieved the decarboxylative aldol reaction of less reactive malonic acid half-oxyesters (MAHOs) 48 with various carbonyl compounds 4 and 49 using the chiral Ni-oxazoline complex as a catalyst (Scheme 25). [30] Initially, the authors studied the decarboxylative aldol reaction between MAHOs 48 and aldehydes 4 using a Ni(II)-oxazoline (L 1 ) complex in combination with potassium 2-nitrobenzoate for the efficient synthesis of enantioenriched α-nonsubstituted β-hydroxy esters 50.…”

1,2-Amino Alcohols via Cr/Photoredox Dual-Catalyzed Addition of α-Amino Carbanion Equivalents to Carbonyls

“…In line with this, these reactions are highly chemoselective for aldehydes and tolerate other electrophilic functional groups such as ketones, esters, or nitriles. It is therefore no surprise that the addition of in situ -formed Cr organyls to carbonyls emerged as a valuable tool in total syntheses, which is now known as the Nozaki–Hiyama–Kishi (NHK) reaction . Although various Cr organyls can be formed using classical NHK conditions, i.e., the Ni-catalyzed reductive metalation of organic halides with Cr II species, alkyl-Cr reagents have remained an exception.…”