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

o-Hydroxyarylphosphanes: Strategies for Syntheses of Configurationally Stable, Electronically and Sterically Tunable Ambiphiles with Multiple Applications

o-Hydroxyarylphosphanes are fascinating compounds by their multiple-reactivity features, attributed to the ambident hard and soft Lewis- and also Brønstedt acid-base properties, wide tuning opportunities via backbone substituents with ±mesomeric and inductive, at P and in o-position to P and O also steric effects, and in addition, the configurational stability at three-valent phosphorus. Air sensitivity may be overcome by reversible protection with BH3 , but the easy oxidation to P(V)-compounds may also be used. Since the first reports on the title compounds ca. 50 years ago the multiple reactivity has led to versatile applications. This includes various P-E-O and P=C-O heterocycles, a multitude of O-substituted derivatives including acyl derivatives for traceless Staudinger couplings of biomolecules with labels or functional substituents, phosphane-phosphite ligands, which like the o-phosphanylphenols itself form a range of transition metal complexes and catalysts. Also main group metal complexes and (bi)arylphosphonium-organocatalysts are derived. Within this review the various strategies for the access of the starting materials are illuminated, including few hints to selected applications.

Enantioselective access to chiral aliphatic amines and alcohols via Ni-catalyzed hydroalkylations

Chiral aliphatic amine and alcohol derivatives are ubiquitous in pharmaceuticals, pesticides, natural products and fine chemicals, yet difficult to access due to the challenge to differentiate between the spatially and electronically similar alkyl groups. Herein, we report a nickel-catalyzed enantioselective hydroalkylation of acyl enamines and enol esters with alkyl halides to afford enantioenriched α-branched aliphatic acyl amines and esters in good yields with excellent levels of enantioselectivity. The operationally simple protocol provides a straightforward access to chiral secondary alkyl-substituted amine and secondary alkyl-substituted alcohol derivatives from simple starting materials with great functional group tolerance.

Chiral aliphatic amine and alcohol derivatives are difficult to access due to the challenge to differentiate between spatially and electronically similar alkyl groups. Here the authors show a nickel-catalyzed enantioselective hydroalkylation of acyl enamines and enol esters with alkyl halides to afford enantioenriched α-branched aliphatic acyl amines and esters in good yields with excellent enantioselectivity.

Catalytic Addition of Indole-2-Carboxylic Acid to 1-Hexyne

The synthesis of two novel enol esters, namely hex-1-en-2-yl indole-2-carboxylate and hex-1-en-2-yl 1-(hex-1-en-2-yl)-indole-2-carboxylate, is presented. Both compounds were generated by addition of indole-2-carboxylic acid to 1-hexyne employing [RuCl2(η6-p-cymene)(PPh3)] and [AuCl(PPh3)]/AgPF6, respectively, as catalysts.

Kinetic Analysis as an Optimization Tool for Catalytic Esterification with a Moisture-Tolerant Zirconium Complex

This work describes the use of kinetics as a tool for rational optimization of an esterification process with down to equimolar ratios of reagents using a recyclable commercially available zirconocene complex in catalytic amounts. In contrast to previously reported group IV metal-catalyzed esterification protocols, the work presented herein circumvents the use of water scavengers and perfluorooctane sulfonate (PFOS) ligands. Insights into the operating mechanism are presented.

Gold(I) Complexes with Ferrocenylphosphino Sulfonate Ligands: Synthesis and Application in the Catalytic Addition of Carboxylic Acids to Internal Alkynes in Water

The synthesis and characterization of novel gold(I) complexes containing hydrophilic ferrocenylphosphino sulfonate ligands, i.e., compounds [AuCl{(η5-C5H3PR2(SO3iPr))Fe(η5-C5H5)}] (R = Ph (2a), p-Tol (2b), Cy (2c)), are presented, including a single-crystal X-ray diffraction study on 2a. Complexes 2a–c were checked as catalysts for the intermolecular addition of carboxylic acids to nonactivated internal alkynes using water as a green reaction medium. The best results in terms of activity were obtained with 2a in combination with AgOAc, which was able to promote the selective anti addition of a variety of aromatic, aliphatic, and α,β-unsaturated carboxylic acids to both symmetrical and unsymmetrical internal alkynes at 60 °C, employing metal loadings of only 2 mol %.

Gold(i)-catalyzed addition of carboxylic acids to internal alkynes in aqueous medium

A broad scope catalytic system for the intermolecular addition of carboxylic acids to internal alkynes, in water under mild conditions, has been developed.

Features and Application in Asymmetric Catalysis of Chiral Phosphine-Phosphite Ligands

Chiral phosphine-phosphites are a class of ligands for asymmetric catalysis characterized by two coordinating functionalities with different electronic properties. These ligands also possess a highly modular structure and, due to versatile synthetic processes, they can be tuned precisely in the catalyst optimization process. Research regarding the application of these ligands in several enantioselective catalytic processes has provided outstanding results in a good number of them. These processes include not only Rh catalyzed reactions, such as olefin hydrogenation and hydroformylation, but also other reactions, such as hydrogenation of olefins and imines by Ru complexes, of imines and N-heterocycles by Ir derivatives, allyl alkylation or conjugate addition by Cu catalysts, or hydrocyanation of olefins by Ni ones. Overall, the use of these ligands has led to the preparation of a wide variety of chiral building blocks with high enantiomeric excess. Therefore, phosphine-phosphites have become in an important class of ligands in asymmetric catalysis.