Enantioselective Alkene Hydrogenation: Introduction and Historic Overview

Abstract

23Enantioselective Alkene Hydrogenation: Introduction and Historic Overview Development of CAMP and DIPAMPDuring the late 1960s, Horner et al. [13] and Knowles and Sabacky [14] independently found that a chiral monodentate tertiary phosphine, in the presence of a rhodium complex, could provide enantioselective induction for a hydrogenation, although the amount of induction was small [15][16][17][18][19][20]. The chiral phosphine ligand replaced the triphenylphosphine in a Wilkinson-type catalyst [10,21,22]. At about this time, it was also found that [Rh(COD) 2 ] + or [Rh(NBD) 2 ] + could be used as catalyst precursors, without the need to perform ligand exchange reactions [23].Knowles found that the monophosphine CAMP (1a) could provide an ee-value of up to 88% for the reduction of dehydroamino acids. CAMP was an extension of PAMP (1b) that provides ee-values of 50-60% in analogous reactions [24]. At this time, Kagan showed that DIOP (2) (vide infra), where the stereogenic centers are not at phosphorus, could also provide enantioselective induction in an hydrogenation. DIOP also showed that a bisphosphine need not have the chirality at phosphorus, and that good stereoselectivity might result from a C 2 -symmetric ligand. Knowles then developed the C 2 -symmetric ligand DIPAMP (3) [22,25]. The use of Rh-DIPAMP for the synthesis of l-Dopa is well known and is still practiced today [12,22,27]. A number of variations of the DIPAMP structure were investigated for the synthesis of this important pharmaceutical, but the parent remains the best ligand in this class [22].

Iron Disilyl Complex as an Effective Catalyst for Hydrogenation of Unfunctionalized Multisubstituted Alkenes

“…Hydrogenation of Mono-Substituted Alkenes Catalyzed by 1 a a All reactions were carried out using 1 mmol of the alkene in the presence of 5 mol % of iron catalyst 1 in toluene (1 mL). b The yield of the product was determined by 1 H NMR spectroscopy in the presence of an internal standard (1,4-bis(trimethylsilyl)benzene). catalyst 1 being susceptible to the coordination of the lone pairs on coordinating functional groups, such as the lone of oxygen in ethers and of nitrogen in pyridine and nitro groups, as well as those of halogens, which causes catalyst poisoning.…”

“…Hydrogenation of Various Alkenes Catalyzed by 1 a a All reactions were carried out using 1 mmol of the alkene in the presence of 5 mol % of iron catalyst 1 in toluene (1 mL). b The yield of the product was determined by 1 H NMR spectroscopy in the presence of an internal standard (1,4-bis(trimethylsilyl)benzene). a longer reaction time was required than in the reaction catalyzed by 1, the corresponding hydrogenated product, ethylbenzene, was obtained as the exclusive product with complete conversion of styrene (Scheme 1).…”

“…The catalytic hydrogenation of alkenes is one of the most frequently used reactions in academic and industrial chemistry. − In conventional homogeneous catalytic hydrogenations, complexes composed of precious metals such as Rh, Ir, and Ru are often used as catalysts. However, due to the increasing interest in the development of cheap and environmentally benign catalytic reactions, the application of base metals has recently received considerable attention. , Particular effort has been devoted to the development of the iron-catalyzed hydrogenation of alkenes, because iron is the least expensive and least toxic transition metal (Figure ).…”

Rhodium-Catalyzed and Zinc(II)-Triflate-Promoted Asymmetric Hydrogenation of Tetrasubstituted α,β-Unsaturated Ketones

“…Homogeneous asymmetric hydrogenation of olefins is a powerful tool for the synthesis of enantiopure chiral materials . Numerous examples of this general methodology exist in the synthesis of molecules of pharmaceutical importance .…”