Pedro J. González-Liste

Highly Enantioselective Hydrogenation of 1-Alkylvinyl Benzoates: A Simple, Nonenzymatic Access to Chiral 2-Alkanols

Going chiral! Highly enantioselective catalytic hydrogenations of enol esters 1 by using a Rh catalyst bearing a P-OP ligand are described (see scheme; NBD=norbornadiene). The catalytic system has a broad scope and allows the preparation of a wide range of chiral esters 2 bearing diverse alkyls or a benzyl group with high enantioselectivities. These esters can easily be converted in highly enantioenriched 2-alkanols.

Chlorophosphines as auxiliary ligands in ruthenium-catalyzed nitrile hydration reactions: application to the preparation of β-ketoamides

The catalytic hydration of nitriles into amides, in water under neutral conditions, has been studied using a series of arene–ruthenium(II) complexes containing commercially available chlorophosphines as auxiliary ligands, i.e. compounds [RuCl2(η6-p-cymene)(PR2Cl)] (R = aryl, heteroaryl or alkyl group). In the reaction medium, the coordinated chlorophosphines readily undergo hydrolysis to generate the corresponding phosphinous acids PR2OH, which are well-known “cooperative” ligands for this catalytic transformation. Among the complexes employed, best results were obtained with [RuCl2(η6-p-cymene){P(4-C6H4F)2Cl}]. Performing the catalytic reactions at 40 °C with 2 mol% of this complex, a large variety of organonitriles could be selectively converted into the corresponding primary amides in high yields and relatively short times. The application of [RuCl2(η6-p-cymene){P(4-C6H4F)2Cl}] in the preparation of synthetically useful β-ketoamides is also presented.

Gold-Catalyzed Regio- and Stereoselective Addition of Carboxylic Acids to Iodoalkynes: Access to (Z)-β-Iodoenol Esters and 1,4-Disubstituted (Z)-Enynyl Esters

In the presence of catalytic amounts of the Au(I) cation [Au(PPh3)]+, a large variety of (Z)-β-iodoenol esters (39 examples) could be synthesized under mild reaction conditions through the regio- and stereospecific intermolecular addition of carboxylic acids to iodoalkynes. Sonogashira coupling of representative (Z)-β-iodoenol esters with terminal alkynes, alkynols, and 1,3-enynes allowed also the access to different 1,4-disubstituted (Z)-enynyl esters in excellent yields.

Broad Scope Synthesis of Ester Precursors of Nonfunctionalized Chiral Alcohols Based on the Asymmetric Hydrogenation of α,β-Dialkyl-, α,β-Diaryl-, and α-Alkyl-β-aryl-vinyl Esters

The catalytic asymmetric hydrogenation of trisubstituted enol esters using Rh catalysts bearing chiral phosphine-phosphite ligands (P-OP) has been studied. Substrates covered comprise α,β-dialkyl, α-alkyl-β-aryl, and α,β-diarylvinyl esters, the corresponding hydrogenation products being suitable precursors to prepare synthetically relevant chiral nonfunctionalized alcohols. A comparison of reactivity indicates that it decreases in the order: α,β-dialkyl > α-alkyl-β-aryl > α,β-diaryl. Based on the highly modular structure of P-OP ligands employed, catalyst screening identified highly enantioselective catalysts for α,β-dialkyl (95-99% ee) and nearly all of α-alkyl-β-aryl substrates (92-98% ee), with the exception of α-cyclohexyl-β-phenylvinyl acetate which exhibited a low enantioselectivity (47% ee). Finally, α,β-diarylvinyl substrates showed somewhat lower enantioselectivities (79-92% ee). In addition, some of the catalysts provided a high enantioselectivity in the hydrogenation of E/Z mixtures (ca. Z/E = 75:25) of α,β-dialkylvinyl substrates, while a dramatic decrease on enantioselectivity was observed in the case of α-methyl-β-anisylvinyl acetate (Z/E = 58:42). Complementary deuteration reactions are in accord with a highly enantioselective hydrogenation for both olefin isomers in the case of α,β-dialkylvinyl esters. In contrast, deuteration shows a complex behavior for α-methyl-β-anisylvinyl acetate derived from the participation of the E isomer in the reaction.