Hidenori Chikashita

Lewis acid-promoted conjugate reduction of α,β-unsaturated carbonyl compounds by 2-phenylbenzothiazoline (2-phenyl-2,3-dihydrobenzothiazole)

Reduction of various α,β-unsaturated ketones (3a–g) and (4a–d) in methanol by the benzothiazoline (1) in the presence of aluminium chloride gives, in all cases, the corresponding saturated ketones (5a–g) and (6a–d) without any of the unsaturated or saturated alcohol. Reduction of α,β-unsaturated esters (7a,b) similarly gives the saturated esters (9a,b), while reaction of cinnamaldehyde (8) with compound (1) does not occur at all. Among the Lewis acids examined, aluminium chloride gives the best results. Reduction of 2′-azachalcone (21) with 2-phenyl[2-2H]benzothiazoline reveals that, in the reduction product, the deuterium atom is located at the β-position with respect to the carbonyl group. The result obtained from the reduction of the same substrate with compound (1) in methan[2H]ol shows that no incorporation of a hydrogen atom from the solvent takes place and suggests (indirectly) that the introduced hydrogen atom at the α-position of the product comes from the benzothiazoline (1). The reaction of (Z)-1,2-dibenzoyl-1,2-diphenylethylene (30) with compound (1) in the presence of aluminium chloride stereospecifically yields meso-1,2-dibenzoyl-1,2-diphenylethane (31). This shows that the transfer of two hydrogens from compound (1) to the carbon–carbon double bond of the enone proceeds via cis-addition. Experiments with ethyl phenylpropiolate (28) also support cis-reduction for the present conjugate reduction. These results are interpreted in terms of a mechanism involving synchronous transport of a pair of hydrogens from the benzothiazoline (1); i.e., a cyclic addition of the two hydrogens either in exact or nearly exact concurrence.

An Efficient Method for the Selective Reduction of 2-Aryl-1-Nitroalkenes to 2-Aryl-1-Nitroalkanes by 2-Phenylbenzimidazoline

Abstract Nitroalkanes have recently been demonstrated to be useful synthetic intermediates for a variety of trans- formations. They have, for example, been converted to carbonyl, la) nitrile oxide,lb) and amino compounds.1c) Especially, 2-aryl-1-nitroalkanes are important in connection with the synthesis of biochemically and pharmacologically interesting compounds. 2) They have also been used as synthetically equivalent to enamines and enolates.3) A widely employed method4) for the synthesis of nitroalkanes involves NaBH4 reduction of conjugated nitroalkenes. The NaBH4 reduction of nitro- alkenes derived from aliphatic aldehydes4b) or ketones5) usually proceeds smoothly in good yields. However, the reduction of 2-aryl-1-nitroalkenes with NaBH4 produces low yields of products due to undesired side reactions such as dimerization.4)

Transformation of Aromatic Nitroalkanes into Carbonyl Compounds by the Improved Nef Reaction

Abstract An improved two-layer method of the Nef reaction which is effective for the conversion of a variety of aromatic nitroalkanes into carbonyl compounds is described.

2-Phenylbenzimidazoline as a Reducing Agent in the Preparation of Malononitriles from α,β-Unsaturated Dinitriles

Abstract The development of methods applicable to the selective reduction of carbon-carbon double bonds conjugated with strong electronwithdrawing group such as cyano, nitro, ester or sulfonate group has been a synthetic subject. Although several procedures1) have been employed for such selective reduction, virtually no sufficient method is known. Recently we have found2) that benzylmalononitriles and 2-nitroethylbenzenes were obtained in good yields by the reactions of benzylidene-malononitriles and β-nitrostyrenes with a half molar amount of o-phenylenediamine (1), and showed that the products resulted from the reduction of the olefins by 2-phenylbenzimidazolines formed from equimolar amounts of the olefins and diamine (1). However, this reaction mode is not effective as a synthetic procedure for the reduction of the olefins because a half molar amount of the olefins is consumed to form 2-phenylbenzimidazolines.

Iterative and Stereoselective One-Carbon Homologation of 1,2-O-Cyclohexylidene-D-Glyceraldehyde to Aldose Derivatives by Employing 2-Lithio-1,3-Dithiane as a Formyl Anion Equivalent

Abstract 1,2-Polyol synthesis based on the iterative and diastereofacially selective carbonyl addition of 2-lithio-1,3-dithiane to chiral α-alkoxy aldehydes by starting from 1,2-O-cyclohexylidene-D-glyceraldehyde was studied in synthesizing aldose derivatives.

Synthesis of Poly=1={3-O-(1=(benzyl-L=alanyl Carboxylate)ethyl]-D-glucos=6-O-carbonyl}-1=methylethylene

Abstract Poly-1- {3-O-[1-(benzyl-L-alanyl carboxylate)ethyl]-D-glucos-6-O-carbonyl} -1-methylethylene was synthesized as the lipophilic and polymeric models of N-acetylmuramyl-L-alanyl-D-isoglutamine corresponding to the minimal structure required for the immunoadjuvant activity of bacterial cell wall. N-[2-(1,2-O-isoproplidene-6-O-methacryloyl-α-D-glucofuranos-3-O-yl)propionyl]-L-alanine benzyl ester was prepared from D-glucose through eight steps as a key monomer in the synthesis. The polymerization of that monomer was carried out in benzene at 50° C by using 2,2′-azobisisobutyronitrile as a radical initiator to give poly-1-{12-O-isopropylidene-3-O-[1-(benzyl-L-alanyl carboxylate)ethyl] -α-D-glucofuranos-6-O-carbonyl} -1-methylethylene. The removal of isopropylidene groups in this polymer was carried out by treatment with trifluoroacetic acid-water (6:l v/v) to give the intended polymer. Characterizations of the polymers obtained were carried out.

Novel Chiral Building Block: (2R,3S)-2-(1,3-Dithian-2-yl)-3-hydroxybutanoates. Highly Diastereo- and Enantioselective Baker's Yeast Reduction of 2-(1,3-Dithian-2-yl)-3-oxobutanoates

Abstract The bakers yeast reduction of 2-(1,3-dithian-2-yl)-3-oxobutanoates gave (2R,3S)-2-(1,3-dithian-2-yl)-3-hydroxybutanoates in good yiels and in high diastereo- and enantioselectivity.

Ketone-generating reaction of 3-methyl-2-(1'-hydroxydialkylmethyl)benzothiazolium iodide under basic conditions

En presence de bases diverses les sels de benzothiazolium conduisent a des alcanophenones et a des alcanones