Rhodium(I)‐Catalyzed Enantioselective Hydrogenation of Substituted Acrylic Acids with Sterically Similar β,β‐Diaryls

Abstract

Dedicated to Professor Guo-Qiang Lin on the occasion of his 70th birthday Optically active b,b-diarylpropionic acids are a class of important building blocks for the asymmetric synthesis of chiral diarylmethine compounds, [1] which are structural moieties that are found in many pharmaceuticals and bioactive compounds, including the therapeutically important molecules tolterodine, [1a-b] sertraline, [1c] indatraline, [1d] and natural products, such as cherylline. [1e] Thus far, methods for the asymmetric synthesis of chiral b,b-diarylpropionic acids often involve a multistep sequence and/or stoichiometric transformation using chiral auxiliaries, [2] only a few examples of catalytic asymmetric methods, including Rh I -or Cu II -catalyzed reduction of b,b-diaryl unsaturated acrylates [3,4] or nitriles [5] using either polymethylhydrosiloxanes or diethoxymethylsilane as the reductants, and Rh I -catalyzed 1,4-addition of organoboron reagents to arylidene Meldrums acids, [6] have been reported to provide the corresponding b,b-diaryl propanoates or propanenitriles with good to high enantioselectivities. In terms of atom economy and environmental concerns, asymmetric hydrogenation of b,b-diarylacrylates with molecular H 2 is more advantageous. In this respect, Ir I -or Rh I -catalyzed asymmetric hydrogenation of trisubstituted olefins for the formation of diarylmethine stereogenic centers seems feasible. [7] However, reactions involving 3,3-diarylacrylates (especially free acids) proved to be challenging, as only moderate enantioselectivities were obtained, in most cases under high pressure

Additive Effects on Asymmetric Catalysis

“…Introduction of 1 mol % of PPh 3 additive increased the conversion from 15% to >99% and ee from 38% to 95%. 521 It was proposed that the additive functioned as a coligand in the process. This catalytic system was also effective for asymmetric hydrogenation of α-CF 3 -or β-CF 3 -substituted acrylic acids.…”

Vapor-Phase Deoxygenation of Lactic Acid to Biopropionic Acid over Dispersant-Enhanced Molybdenum Oxide Catalyst

“…1−4 For the latter, it is used in esterification of alcohol to synthesize its corresponding ester and also used in solvent for various reactions. At present, its production mainly relies on the oxidization of propanal obtained from ethylene hydroformylation, 5−10 hydrocarboxylation of ethylene, 11,12 carbonylation of ethanol, 13 hydrogenation of acrylic acid, 14,15 and hydration of acrylonitrile, 16−18 and these processes for propionic acid production are almost all based on petroleum feedstock, thus attributed to nonrenewable resources. The search for new processes for production of propionic acid based on sustainable feedstock is extremely urgent.…”

Cobalt-catalyzed highly enantioselective hydrogenation of α,β-unsaturated carboxylic acids

“…Transition-metal-catalyzed enantioselective hydrogenation of α, β-unsaturated acids is one of the most atom-economic and efficient approaches to access chiral carboxylic acids 19 . Various noble metal-based catalysts, such as Ru catalysts with chiral diphosphine ligands [20][21][22][23][24] , Rh catalysts with chiral phosphorus or nitrogencontaining ligands [25][26][27][28][29][30][31] , and Ir catalysts with chiral P,O- 32 and P, N-ligands [33][34][35][36][37][38][39][40] have been developed for the hydrogenation of different unsaturated carboxylic acids in high enantioselectivities ( Fig. 2a).…”