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Abstract: A number of transition metal catalysts have been developed for transfer hydrogenation of organic molecules. This method provides a useful process for the reduction of unsaturated molecules without the need for explosive hydrogen gas. An important development in this area is the design of new ligands that improve activity and selectivity under mild reaction conditions. Polydentate ligands are good candidates for producing high performance metal catalysts. This digest describes recent developments in transfer hydrogenation as well as asymmetric reactions using metal catalysts containing polydentate ligand systems. [Copyright &y& Elsevier]

Abstract: A combination of a catalyst derived from ferrous acetate and sodium thiophene-2-carboxylate efficiently promoted hydrosilylation of aromatic and aliphatic ketones to give the corresponding secondary alcohols in high yields with extremely high selectivity. [Copyright &y& Elsevier]

Abstract: The conjugate reduction of α,β-unsaturated esters such as acrylates, crotonate, and cinnamates followed by Mannich-type coupling toward aldimines was efficiently promoted by rhodium-bis(oxazolinyl)phenyl catalyst and alkoxyhydrosilanes to show high anti-selectivity up to 99. [Copyright &y& Elsevier]

Abstract: The catalytic reductive aldol coupling of 2-phenylpropionaldehyde and acrylate derivatives with rhodium-bisoxazolinyl catalysts resulted in high Felkin–Anh selectivity (β,γ-syn) up to 98% accompanied by α,β-anti diastereoselectivity and high enantiomeric excesses up to 99%. [Copyright &y& Elsevier]

Abstract: The catalytic intermolecular cyclotrimerization of alkynylboronates, propargyl alcohols, and terminal alkynes was accomplished by means of the ruthenium catalysis and the temporary tethering approach with the C–B–O linkage to give rise to highly substituted arylboronates with excellent selectivity. The resultant arylboronates were further converted to highly substituted biaryls via the Suzuki–Miyaura coupling with various aryl iodides using Pd2(dba)3/PCy3 as a catalyst precursor in aqueous toluene. As a consequence, the four-component coupling approach to highly substituted biaryls was successfully established by combining these two operations into a sequential one-pot process. [Copyright &y& Elsevier]

Asymmetric diboration of N -acyl-protected allylamines such as substituted imides, amides, and carbamates catalyzed by chiral rhodium[bis(oxazolinyl)phenyl] complexes followed by oxidation in one-pot was realized to produce optically active 3-amino-1,2-propanediol derivatives in high enantioselectivities up to 99%. [ABSTRACT FROM AUTHOR]

Abstract: Chiral rhodium[bis(oxazolinyl)phenyl] complexes exhibited high catalytic activity for the β-boration of α,β-unsaturated esters, ketones, and amides with bis(pinacolato)diboron in the presence of sodium tert-butoxide to attain high enantioselectivity of up to 97%. The substrate scope and catalytic mechanism were discussed. [Copyright &y& Elsevier]

Abstract: A series of chiral 4,5-bis(2-oxazolinyl)-(2,7-di-tert-butyl-9,9-dimethyl)-9H-xanthenes (xabox) and their transition-metal complexes were synthesized. The X-ray analysis of xabox–RhCl3 complex shows a unique facial type structure. Xabox–Bn–Mn(II) and xabox–Bn–Mg(II) complexes were found to be efficient catalysts in nitrone 1,3-dipolar cycloaddition (1,3-D.C.) reaction resulting in good to excellent enantioselectivities ranging from 96:4 to >99:1of endo/exo ratio and 91–96% ee for the endo adduct. The correlation between enantiomeric excess of the ligand and the product in the nitrone 1,3-D.C. reaction shows a clear linear relationship, which suggests xabox–metal catalyst worked as a single molecular catalyst. In addition, xabox–i-Pr–Mn(II) complex was also found to be an active catalyst for Diels–Alder (D–A) reaction of acryloyloxazolidinone and cyclopentadiene affording the corresponding cycloadduct in quantitative yield along with 82% ee and 98:2 endo/exo ratio. [Copyright &y& Elsevier]

Abstract: Chiral bis(oxazolinyl)phenyl–rhodium complexes act as catalysts in the combination of AgOTf for direct aldol reaction of ketones and aromatic aldehydes to give the corresponding β-hydroxyketones in high anti-selectivity and a good to high enantioselectivity up to 91% ee. [Copyright &y& Elsevier]

Abstract: Optically active dihydrocinnamate derivatives bearing the chiral carbon center at α-position were synthesized by Rh(Phebox)-catalyzed asymmetric reductive aldol coupling reaction with substituted cinnamates and benzaldehyde derivatives and subsequent dehydroxylation reaction. [Copyright &y& Elsevier]

Abstract: Bis(oxazolinyl)phenyl–palladium(II)(Phebox–Pd) complexes were found to be efficient catalysts for Suzuki–Miyaura coupling reactions of aryl boronic acids and their derivatives with aryl halides to give the corresponding biaryl products in high yield along with moderate enantioslectivities in the case of axially chiral induction. The catalytic activity was attained more than 900,000 of TON and 45,000 of TOF. The catalyst can be recovered quantitatively and could be reused for Suzuki–Miyaura reactions. [Copyright &y& Elsevier]

Abstract: In the presence of 5–10mol% Cp*RuCl(cod), 1,6- and 1,7-diynes were allowed to react with an ethynylboronate at ambient temperature to give rise to bicyclic arylboronates in 64–93% isolated yields. 1,6-Diynes bearing a boronate terminal also underwent cycloaddition with monoalkynes to give the corresponding bicyclic arylboronates. [Copyright &y& Elsevier]

Chiral 4,5-bis(2-oxazolinyl)-(2,7-di-tert-butyl-9,9-dimethyl)-9H-xanthenes (xabox) were synthesized and the chiral environments were evaluated in catalytic asymmetric 1,3-dipolar cycloaddition reactions of nitrones resulting in good to excellent enantioselectivities. 1,3-Dipolar cycloaddition reactions of nitrones with 3-crotonoyl-2-oxazolidinone in the presence of a bis(2-oxazolinyl)xanthene (4c; xabox-Bn) and Mn(II) or Mg(II) complex as a chiral Lewis acid catalyst proceeded smoothly to give the corresponding cycloadducts ranging from 96:4 to >99:1 of endo:exo ratio and ranging from 91% to 98% ee for the endo adduct. [Copyright &y& Elsevier]

As a C2 symmetric hydrophilic chiral ligand, a series of 2,6-bis(oxazolinyl)-pyridines (pyboxs) bearing a hydroxyalkyl group on the oxazoline ring has been synthesized from readily available amino acid derivatives. Catalytic asymmetric intermolecular cyclopropanation of electron rich terminal alkenes with diazoesters in the presence of hydrophilic pybox ligand, pybox-hm and Ru(II) complex proceeded smoothly in protic or biphasic media to give the corresponding cyclopropanation products in 97:3 to 99:1 trans/cis ratios and 90 to 97% ee. In the case of the intramolecular cyclopropanation reaction of trans-cinnamyl diazoester using Ru(II)(pybox-he) complex in biphasic medium gave the corresponding cyclopropane ring fused lactone in 52% ee. Steric tuning of the chiral environment of pybox ligands was simply achieved by using a weak interaction between the solvent and the hydroxyl groups of the chiral ligand. The solubility of the new hydrophilic pybox and Ru(II) complexes in protic solvents is dramatically increased; hence, the efficiency of these catalysts enhanced the rate of cyclopropanation. Furthermore, the active catalyst in the water phase can be re-used several times for the cyclopropanation reaction. [Copyright &y& Elsevier]

From the viewpoint of environmentally friendly reaction conditions, catalytic asymmetric nitrone 1,3-dipolar cycloaddition (DC) reactions in protic media have been investigated. DC reaction of nitrones with alkenoyl oxazolidinone and pyrrolidinone derivatives in t-BuOH in the presence of sterically tuned bis(oxazolinyl)pyridine (pybox-tipsom 1d) and Ni(II) complex as a chiral Lewis acid catalyst proceeded smoothly to give the corresponding cycloadducts ranging from 90:10 to >99:1 of endo/exo ratio and ranging from 90 to 98% ee for the endo adduct. The use of sterically hindered alcohols such as t-BuOH and s-BuOH as a non-halogenated solvent was shown to effect rate acceleration for the DC reaction compare to CH2Cl2 at the same temperature. Furthermore, no solvolysis products of nitrones and cycloadducts were observed in these protic media despite the possible formation of Brønsted acid. [Copyright &y& Elsevier]

[Ir(I)(coe)2Cl]2 (2 mol%)-catalyzed hydrogen peroxide oxidation of hydroxamic acids in the presence of cyclopentadiene gave the corresponding cycloadducts up to 97% yield. With a catalyst loading of 0.05 mol%, a maximum TON was attained to 740. [Copyright &y& Elsevier]