Aiqiao Mi

Novel Achiral Biphenol‐Derived Diastereomeric Oxovanadium(IV) Complexes for Highly Enantioselective Oxidative Coupling of 2‐Naphthols

Optically pure 1,1’-binaphthol and its derivatives have been evaluated as versatile chiral auxiliaries and ligands in asymmetric transformations. Research in this area has provided many efficient and useful methods for the preparation of key chiral building blocks, some of which have been used for the construction of complex natural products.[1] They have also been extensively applied to the preparation of chiral organic materials.[2] The wide-ranging and important applications of such compounds in organic synthesis have stimulated great interest in developing efficient methods for their preparation.[3] Compared to the well-established resolution of racemic binaphthol for the preparation of optically pure BINOL,[3a±f] catalytic asymmetric preparation of chiral binaphthols has developed much more slowly. The discovery of efficient catalysts for the highly enantioselective formation of optically active binaphthol and its derivatives is an attractive target. The oxidative coupling of 2-naphthols in the presence of a catalytic amount of a copper complex of a chiral amine has provided several promising results, but high enantioselectivity has been achieved only for the coupling of 3carboalkoxyl-2-naphthols (93% ee).[4] A photo-activated chiral [RuII(salen)(NO)] complex catalyzes the aerobic oxidative coupling of 2-naphthols with 33±71% ee.[5] Chen et al. and Uang et al. independently designed similar oxovanadium(iv) complexes of chiral Schiff bases for the asymmetric oxidative coupling of 2-naphthols with moderate enantioselectivities of up to 62% ee.[6] We developed the catalyst (R,S)-1c for the oxidative coupling of 2-naphthol with high enantioselectivity, and found that the chiral centers on the amino acid part and the axially chiral binaphthyl unit are both crucial to stereocontrol by the catalyst.[7] However, a drawback is that the chiral oxovanadium complex must be prepared from an optically pure 3,3’diformyl-2,2’-dihydroxy-1,1’-binaphthol and (S)-amino acid. The catalyst is only highly enantioselective when the two COMMUNICATIONS

Palladium-catalyzed allylic alkylation of tert-butyl(diphenylmethylene)-glycinate with simple allyl esters under chiral phase transfer conditions

Abstract The first example of palladium-catalyzed allylic alkylation of an imino ester with simple allyl esters in the presence of a chiral quaternary ammonium salt is reported. The presence of molecular sieves was found to have a beneficial effect on the enantioselectivity of the reaction by scavenging water from the system. Alkylated products with e.e.s of up to 61% were obtained.

Salen-Ti(OR)4 complex catalysed trimethylsilylcyanation of aldehydes

Abstract Chiral salen-titanium complexes were found to be efficient catalysts for the enantioselective trimethylsilylcyanation of aldehydes. An enantioselectivity up to 87.1% e.e. was obtained by using 10mol% Ti(IV)-salen 2d as catalyst. The reaction mechanism was proposed and proved experimentally.

REDUCTION OF AZIDES TO AMINES OR AMIDES WITH ZINC AND AMMONIUM CHLORIDE AS REDUCING AGENT

ABSTRACT Alkyl azides and acyl azides were reduced to the corresponding amines and amides with zinc and ammonium chloride as reducing agent under mild conditions in good to excellent yield.

L-Prolinamide-catalyzed direct nitroso aldol reactions of α-branched aldehydes: a distinct regioselectivity from that with L-proline

The first direct enantioselective N-nitroso aldol reaction of aldehyde with nitrosobenzene catalyzed by an L-prolinamide derivative is presented; the reactions proceed smoothly furnishing the -hydroxyamino carbonyl compounds, the otherwise disfavored products, in good yields with up to 64% ee.

Novel C–C bond formation through addition of ammonium ylides to arylaldehydes: a facile approach to β-aryl-β-hydroxy α-amino acid frameworks

Ammonium ylides generated in situ from α-diazo esters and amines in the presence of catalytic Rh2(OAc)4, undergo an aldol-type reaction with aldehydes affording highly substituted amino acid frameworks in a convergent, three-component reaction.

Asymmetric synthesis. Part 29: Asymmetric hydroformylation of styrene catalyzed by chiral spiro diphosphite–rhodium(I) complexes

Abstract Chiral diphosphite ligands L 1 –L 3 were prepared by the reaction of (1 S ,5 S ,6 R )-( cis , trans )-spiro[4.4]nonane-1,6-diol with chlorophosphites. These ligands were tested in the rhodium catalyzed hydroformylation of styrene and enantioselectivities up to 69% were achieved. High regioselectivities (97%) to 2-phenylpropanal and high yields (98%) were obtained under mild reaction conditions. The influence of reaction conditions is also discussed.

Highly enantioselective hydrogenation of α-dehydroamino acids by rhodium complex with H8-MonoPhos

Abstract H 8 -MonoPhos, a new stable and easily prepared monodentate phosphoramidite ligand, has been synthesized from H 8 -BINOL. The ligand showed extremely highly enantioselectivity of higher than 99.9% e.e. in the asymmetric Rh-catalyzed hydrogenation of α-dehydroamino acids. Our study further supports the new concept that there is no gap in efficiency and enantioselectivity between monodentate and chelating ligands for asymmetric catalysis.

The first use of chiral oxazoline ligands in the highly enantioselective diethylzinc addition to diphenylphosphinoyl imines

Abstract A series of chiral oxazolines, which had been conveniently prepared from commercially available (1S,2S)-2-amino-1-phenylpropane-1,3-diol, was applied in the diethylzinc addition to diphenylphosphinoyl imines to give high yields of 68–84% and excellent e.e. values of 90–93%.

A HIGHLY EFFECTIVE RHODIUM SPIROCYCLIC PHOSPHINITE CATALYST FOR THE ASYMMETRIC HYDROGENATION OF ENAMIDES

Abstract A rhodium complex of the phosphinite ligand spirOP was found to be an effective catalyst for the asymmetric catalytic hydrogenation of α-substituted enamides with ee values ranging from 85.1% to 97.4%.