Synthesis of enantiopure (R)-(−)-massoialactone through ruthenium-SYNPHOS® asymmetric hydrogenation

Efficient Synthesis of Differentiated syn-1,2-Diol Derivatives by Asymmetric Transfer Hydrogenation-Dynamic Kinetic Resolution of α-Alkoxy-Substituted β-Ketoesters

Asymmetric transfer hydrogenation was applied to a wide range of racemic aryl α-alkoxy-β-ketoesters in the presence of well-defined, commercially available, chiral catalyst Ru(II) -(N-p-toluenesulfonyl-1,2-diphenylethylenediamine) and a 5:2 mixture of formic acid and triethylamine as the hydrogen source. Under these conditions, dynamic kinetic resolution was efficiently promoted to provide the corresponding syn α-alkoxy-β-hydroxyesters derived from substituted aromatic and heteroaromatic aldehydes with a high level of diastereoselectivity (diastereomeric ratio (d.r.)>99:1) and an almost perfect enantioselectivity (enantiomeric excess (ee)>99 %). Additionally, after extensive screening of the reaction conditions, the use of Ru(II) - and Rh(III) -tethered precatalysts extended this process to more-challenging substrates that bore alkenyl-, alkynyl-, and alkyl substituents to provide the corresponding syn α-alkoxy-β-hydroxyesters with excellent enantiocontrol (up to 99 % ee) and good to perfect diastereocontrol (d.r.>99:1). Lastly, the synthetic utility of the present protocol was demonstrated by application to the asymmetric synthesis of chiral ester ethyl (2S)-2-ethoxy-3-(4-hydroxyphenyl)-propanoate, which is an important pharmacophore in a number of peroxisome proliferator-activated receptor α/γ dual agonist advanced drug candidates used for the treatment of type-II diabetes.

(R)-3,5-diCF3-SYNPHOS and (R)-p-CF3-SYNPHOS, electron-poor diphosphines for efficient room temperature Rh-catalyzed asymmetric conjugate addition of arylboronic acids

Two new atropisomeric electron-poor chiral diphosphine ligand analogues of SYNPHOS were prepared, and their electronic properties are described. These two ligands afforded high performance for the Rh-catalyzed asymmetric 1,4-addition of arylboronic acids to α,β-unsaturated carbonyl compounds at room temperature.

Enatiomerically pure hydroxycarboxylic acids: current approaches and future perspectives

The growing awareness of the importance of chirality in conjunction with biological activity has led to an increasing demand for efficient methods for the industrial synthesis of enantiomerically pure compounds. Polyhydroxyalkanotes (PHAs) are a family of polyesters consisting of over 140 chiral R-hydroxycarboxylic acids (R-HAs), representing a promising source for obtaining chiral chemicals from renewable carbon sources. Although some R-HAs have been produced for some time and certain knowledge of the production processes has been gained, large-scale production has not yet been possible. In this article, through analysis of the current advances in production of these acids, we present guidelines for future developments in biotechnological processes for R-HA production.

Chiral α-substituted allylboronates in a one-pot three-component asymmetric allylic alkylation/carbonyl allylation reaction sequence — Applications to the syntheses of (+)-(3R,5R)-3-hydroxy-5-decanolide and (–)-massoialactone

The use of different organomagnesium reagents in the copper-catalyzed allylic alkylation of 3-chloropropenyl boronates with chiral phosphoramidite ligands produces the desired α-substituted allylic boronate reagents in high regioselectivity and with modest to high enantioselectivities (up to 96% ee). The size of the incoming alkyl substituent from the organomagnesium reagent was found to impact the yield and selectivity of the allylic alkylation. A one-pot procedure for the preparation of these chiral allylic boronates followed by a Lewis acid (BF3) catalyzed addition to aldehydes delivers the desired allylboration products, homoallylic secondary alcohols, in good yields and very high diastereoselectivity. This three-component reaction methodology was applied to the syntheses of two lactone-containing natural products, (–)-massoialactone and (+)-(3R,5R)-3-hydroxy-5-decanolide. The key step of these syntheses involved the one-pot enantioselective copper-catalyzed allylic alkylation/allylboration reaction with a benzylic aldehyde, and afforded the desired product in 87% yield, 92% ee, and high E/Z selectivity in a ratio of 22:1. Remarkably, the allylic alkylation step of this sequential reaction was performed with a low catalyst loading of 2 mol% on a scale of >15 mmol that can provide multiple grams of the three-component product.

Synphos modified Pt nanoclusters, their heterogenization by silica sol-gel entrapment, and catalytic activity in hydrogenolysis of bicyclo[2.2.2]oct-7-enes and hydrogenation of ethyl pyruvate

Platinum (Pt) colloids modified by the chiral ligand synphos were prepared with the goal of obtaining a catalytic nanomaterial and were subsequently embedded in silica to form a heterogeneous catalyst. The systems were characterized by (31)P-NMR, x-ray diffraction, molecular modeling and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTs) measurements. These colloids, both as 'quasi-homogeneous catalysts' (or soluble heterogeneous catalysts) and embedded in silica (heterogeneous catalysts) were employed in the selective hydrogenolysis of highly sterically constrained bicyclo[2.2.2]oct-7-enes and hydrogenation of ethyl pyruvate.