Aerobic oxidation of alcohols using bismuth bromide as a catalyst

We developed an environmentally friendly method for aerobic oxidation of alcohols using a commercially available, relatively benign bismuth salt as a catalyst. We found that the catalytic combination of BiBr₃ with nitric acid is key for enhancing the reactivity. The reaction proceeds well under air, making the use of pure oxygen unnecessary. Each of the primary or secondary alcohols tested was oxidized to the corresponding aldehydes or ketones using this protocol.     

Synthesis of Enantiopure syn-beta-Amino Alcohols. A Simple Case of Chelation-Controlled Additions of Diethylzinc to alpha-(Dibenzylamino) Aldehydes

Enantiomerically pure syn-2-amino alcohols 6 are prepared by addition of diethylzinc to chiral alpha-(dibenzylamino) aldehydes 4. The addition is highly stereoselective, leading to syn-2-(dibenzylamino) alcohols 5 with excellent diastereomeric excesses (76-98%). Debenzylation of 5 by hydrogenolysis on Pearlman's catalyst yields quantitatively the amino alcohols 6.     

Acceleration effect of Lewis acid in allylboration of aldehydes: catalytic,regiospecific, diastereospecific,and enantioselective synthesis of homoallyl alcohols

The addition of pinacol allylboronic esters to aromatic and aliphatic aldehydes smoothly occurred at -78 degrees C in toluene in the presence of a catalytic amount of AlCl3 or Sc(OTf)3 (10 mol %) to give the corresponding homoallyl alcohols in high yields. The reactions proceeded regio- and diastereospecifically, yielding the isomerically pure syn- and anti-homoallyl alcohols from (Z)- and (E)-allylboronic esters, respectively. The protocol was also applied to enantioselective reactions by using a chiral Lewis acid catalyst.     

Synthesis and application of chiral spiro phospholane ligand in Pd-catalyzed asymmetric allylation of aldehydes with allylic alcohols

[reaction: see text] A novel chiral monodentate spiro phenylphospholane ligand 4 was prepared from a readily accessible, enantiomerically pure 1,1'-spirobiindane-7,7'-diol in high yield. This ligand has proven to be efficient for Pd-catalyzed enantioselective allylation of aldehydes with allylic alcohols. Aromatic, heteroaromatic, and aliphatic aldehydes gave homoallylic alcohols in good enantioselectivities (up to 83% ee) and excellent anti diastereoselectivities (up to 99:1 dr).     

tert-Butylnitrite as a convenient and easy-removable oxidant for the conversion of benzylic alcohols to ketones and aldehydes

The oxidation of primary and secondary benzylic alcohols was achieved by using tert-butyl nitrite (t-BuONO) as a stoichiometric oxidant. Various substrates were effectively converted into the corresponding ketones or aldehydes in good to excellent yields. The reaction presumably proceeded by a nitrosyl exchange and a subsequent thermal decomposition of benzylic nitrites. This process would realize an oxidation of alcohols with oxygen in theory by combining with a reproduction of alkyl nitrites from NO and alcohols under an O₂ atmosphere. In addition, almost pure oxidized products were readily obtained by simple evaporation of the reaction mixtures since t-BuONO produced only volatile side products.     

Synthesis of optically pure arylsilylcarbinols and their use as chiral auxiliaries in oxacarbenium ion reactions

A family of arylsilylcarbinols was synthesized and investigated as chiral auxiliaries for oxacarbenium ion reactions. The optically pure arylsilylcarbinols were prepared using Noyori's transfer hydrogenation catalyst 11. The transfer hydrogenation shows very good enantioselectivities and turnover efficiency for the aryl silyl ketones and is the method of choice for preparing these optically pure alcohols. The diastereoselective addition of allyltrimethylsilane to an in situ generated oxacarbenium ion was explored using Marko's conditions. The selectivity for a representative aliphatic aldehyde was very good, but the selectivity was significantly reduced with unsaturated and aromatic aldehydes. The range of selectivities with different auxiliaries was narrow, and the most practical auxiliary is the phenylsilylcarbinol 2.     

光学纯7,7′-二取代联二萘酚催化乙基锌对醛的对映选择性加成

合成了一类光学纯的7,7′-二取代联二萘酚, 并将其用在乙基锌对醛的对映选择性加成, 以54%～88%的产率和最高88%的对映选择性得到了光学活性的1-苯基-1-丙醇.     

A highly efficient and direct approach for synthesis of enantiopure beta-amino alcohols by reductive cross-coupling of chiral N-tert-butanesulfinyl imines with aldehydes

A highly efficient and practical approach for the synthesis of optically pure beta-amino alcohols by the SmI2-induced reductive cross-coupling of chiral N-tert-butanesulfinyl imines with aldehydes was developed. This method allows the preparation of a broad range of chiral beta-amino alcohols, including functionalized ones under mild conditions. It provides a straightforward access to enantiopure beta-amino alcohols that are widely applicable in asymmetric synthesis.     

Synthesis of new planar chiral [2.2]paracyclophane Schiff base ligands and their application in the asymmetric Henry reaction

A series of new planar and central chiral ligands based on [2.2]paracyclophane backbones were designed and prepared from enantiomerically pure 4-amino-13-bromo[2.2]paracyclophane and commercially available chiral amino alcohols. Their application in a copper-catalyzed asymmetric Henry reaction resulted in secondary alcohols with high yield and excellent selectivity for active aldehydes (up to 94% ee). This is a successful example of employing planar chiral [2.2]paracyclophane ligands in copper-catalyzed reaction.     

Barbier-type diastereoselective allylation of alpha-amino aldehydes with an enantiopure 2-sulfinylallyl building block.

An optimized procedure for the diastereoselective allylation under aqueous Barbier conditions of a series of alpha-amino aldehydes with our new chiral building block (S(s))-3-chloro-2-(p-tolylsulfinyl)-1-propene [(S(s))-1a] to afford enantiomerically pure sulfinylamino alcohols in good yields and diastereoselectivites is reported. High levels of diastereoinduction can be achieved from alpha-amino aldehydes configurationally related to natural alpha-amino acids.     

Use of S-pentafluorophenyl tris(2,4,6-trimethoxyphenyl)phosphonium acetate bromide and (4-hydrazino-4-oxobutyl) [tris(2,4,6-trimethoxyphenyl)phosphonium bromide for the derivatization of alcohols,aldehydes and ketones for detection by liquid chromatography/electrospray mass spectrometry

The synthesis of S-pentafluorophenyl tris(2,4,6-trimethoxyphenyl)phosphonium acetate bromide (TMPP-AcPFP) and the novel compound (4-hydrazino-4-oxobutyl) [tris(2,4,6-trimethoxyphenyl)phosphonium bromide (TMPP-PrG) is described and the use of these compounds as derivatizing reagents for alcohols, aldehydes and ketones evaluated. Methods have been developed for the pre-column derivatization of alcohols using TMPP-AcPFP and for aldehydes and ketones using TMPP-PrG. The reactions were investigated by the use of a variety of individual test compounds containing the target functional groups. The TMPP acetyl ester and TMPP propyl hydrazone derivatives formed with their respective target analytes produced an enhanced response in electrospray ionization mass spectrometry (ESI-MS), and reproducible chromatography. The use of these two reagents to derivatize and facilitate detection of alcohols (including sugars and steroids), aldehydes and ketones (including steroids) by LC/ESI-MS was investigated.     

Kinetics of catalytic Meerwein-Ponndorf-Verley reduction of aldehydes and ketones using boron triethoxide

Catalytic Meerwein-Ponndorf-Verley (MPV) reduction of various aliphatic, aromatic, and unsaturated aldehydes and ketones to corresponding alcohols (analyzed by GC-MS) in the presence of boron triethoxide (B(OEt)₃) were studied. Kinetics of this reduction reaction was also studied and the respective rate constants were determined. It was found that B(OEt)₃ catalyzes the reduction of aliphatic aldehydes and ketones to alcohols at room temperature while aromatic aldehydes and ketones were not reduced under the same conditions. In addition, MPV reduction using B(OEt)₃ was found to be chemoselective as unsaturated aldehydes and ketones afforded the corresponding alcohols without affecting unsaturated groups. The mechanism proposed involves a six-membered transition state in which both the alcohol and the carbonyl are coordinated to the same boron centre of a boron alkoxide catalyst.     

Solution- and solid-phase synthesis of 4-hydroxy-4,5-dihydroisoxazole derivatives from enantiomerically pure N-tosyl-2,3-aziridine alcohols

[reaction: see text] Enantiomerically pure N-tosyl-2,3-aziridine alcohols are directly converted into 4-hydroxy-4,5-dihydroisoxazole 2-oxides through oxidation to the corresponding aldehydes followed by in situ tandem nitroaldol-intramolecular cyclization. This study was concerned with (i) the selection of a suitable aziridine activation, (ii) the preparation of the target 4-hydroxy-4,5-dihydroisoxazole derivatives in solution, and (iii) the elaboration of a solid-phase process using hydroxy Merrifield-supported nitroacetic acid ester.     

Addition of a chiral copper reagent derived from propargylic oxazolidininone to aldehydes

[reaction: see text] The copper reagent arising from an optically pure propargylic oxazolidinone was found to react regio- and diastereoselectively with aldehydes, leading, in a one-pot procedure, to the anti homopropargylic amino alcohols derivatives in good yields.     

Catalytic diastereoselective petasis reactions

Multicomponent Petasis reactions: The first diastereoselective Petasis reaction catalyzed by chiral biphenols that enables the synthesis of syn and anti?β-amino alcohols in pure form has been developed. The reaction exploits a multicomponent approach that involves boronates, α-hydroxy aldehydes, and amines.     

Diastereoselective synthesis of polysubstituted tetrahydropyrans and thiacyclohexanes via indium trichloride mediated cyclizations.

Polysubstituted tetrahydropyrans and thiacyclohexanes were synthesized in high yields with excellent diastereoselectivities via indium trichloride mediated cyclizations between homoallyl alcohols and mercaptans with aldehydes. In the case of tetrahydropyran products, the stereochemistry of the product was found to be directly correlated with the geometry of the homoallyl alcohols; whereas the cross-cyclization of aldehydes with trans-homoallyl alcohols generated (up-down-up) 2,3,4-trisubstituted tetrahydropyran products exclusively, the reaction of aldehydes with cis-homoallyl alcohols provided mainly (up-up-up) 2,3,4-trisubstituted products. When a trisubstituted homoallyl alcohol was used, its cross-cyclization with aldehydes generated (up-down-up-down-up) pentasubstituted tetrahydropyran derivatives with simultaneous controlling of five stereogenic centers. On the other hand, a cyclization-decyclization equilibrium was observed in the formation of thiacyclohexanes. The reaction of both cis- and trans-homoallyl mercaptans with aldehydes provided the same major diastereomers.     

Diastereoselective aldolization of alpha-aminonitriles. Diastereoselective synthesis of beta-amino alcohols and beta,gamma-diamino alcohols

Aldolization performed by addition of lithiated N-benzyl-N-tert-butylaminoacetonitrile to aldehydes provides diastereomerically pure anti-beta-hydroxy-alpha-aminonitriles. They are transformed into syn,anti-protected beta,gamma-diamino alcohols by a two-step procedure, involving addition of a Grignard reagent and reduction. The cleavage of the N-tert-butyl group is achieved by a simple acidic treatment. The application of this methodology to chiral, nonracemic aldehydes is studied. Starting from D-isopropylideneglyceraldehyde, an anti, anti, syn, anti-(2R,3S,4S,5R,6R)-diaminotriol is prepared in acceptable yield and with a good level of diastereoselectivity.     

纳米尺度氧化石墨烯层作为高效碳催化剂用于苄醇与芳香醛的绿色氧化

合成了纳米尺度氧化石墨烯(NGO)层,用作碳催化剂高效催化苄醇与芳香醛的氧化反应.对于醇氧化反应,当80℃时H2O2存在下,NGOs(20 wt％)可高效催化醇选择性生成醛,其反应速率和产率取决于醇上取代基的性质.对于4-硝基苄醇,反应24 h后,只有10％可转换为相应羧酸.相反,4-甲氧基苄醇和二苯基甲醇分别反应仅9和3h则可完全转化为对应的羧酸和酮.NGO碳催化剂上芳香醛氧化速率高于醇氧化速率.对于所有的醛,采用7 wt％ NGO作催化剂,在70℃反应2-3 h后,就可完全转化为相应羧酸.我们讨论了NGO催化剂结构对苄醇和芳香醛氧化反应影响的可能机理.     

Synthesis of alpha-heteroarylpropanoic acid via asymmetric hydroformylation catalyzed by Rh(I)-(R,S)-BINAPHOS and the subsequent oxidation

The asymmetric hydroformylation of vinyl heteroarenes (vinylfurans and vinylthiophenes) was investigated by using Rh(I)-BINAPHOS derivatives as a catalyst. The hydroformylation of vinylthiophenes 1 gave the corresponding branched aldehydes 2 with high enantiopurities as major products. Oxidation of the aldehydes 2 successfully afforded alpha-heteroarylpropanoic acids 4 in good yields. In addition, the aldehydes 2 were reduced to alcohols 5 without loss of enantiomeric excess.     

Sodium cyanide‐promoted copper‐catalysed aerobic oxidative synthesis of esters from aldehydes

A simple and efficient copper‐catalysed procedure for oxidative esterification of aldehydes with alcohols and phenols mediated by sodium cyanide, using air as a clean oxidant, is described. A variety of aromatic aldehydes and structurally different alcohols and phenols reacted efficiently, and the product esters were obtained in good to excellent yields under normal atmospheric and solvent‐free conditions.