Choji Kashima

Stereoselective N-acylation of a new chiral auxiliary compound ; 3-phenyl-l-menthopyrazole

Abstract As a new chiral auxiliary compound having a pyrazole ring system, the synthetic utility of (4R,7S)-3-phenyl-4-methyl-7-isopropyl-4,5,6,7-tetrahydroindazole (3-phenyl-l-menthopyrazole), which was prepared from l-menthone, was discussed.

Enantiomerically enriched preparation of enolizable β-keto amides. Diastereoselective α-acylation and subsequent aminolysis of 2-acyl-3-phenyl-l-menthopyrazoles

Abstract After deprotonation with LDA, 2-acyl-3-phenyl-l-menthopyrazoles (13) were diastereomerically α-acylated to give N-(3-phenyl-l-menthopyrazolyl) β-keto amides (14–19). The subsequent amides were converted into the corresponding N-alkyl amides (21–24) retaining their enantiomeric enrichment on the α-position. These are the first examples of enolizable β-keto acid derivatives having only one chiral center at α-position. These chiral β-keto amides were surprisingly stable in dry benzene and their optical asymmetries were almost retained for two weeks at room temperature without any epimerization.

Restricted rotation about the carbon–nitrogen single bond of 1-aryl-4,6-dimethylpyrimidin-2(1H)-ones and the corresponding thiones

By recrystallizing the salts (3) and (4) with D-camphor-10-sulphonic acid, the rotational isomers due to restricted rotation about the carbon-nitrogen single bond in ortho-substituted-1-aryl-4,6-dimethylpyrimidin-2(1H)-ones (1) and the corresponding thiones (2) were separated. The activation energies for the racemization of the pyrimidin-2(1H)-ones (1c and f) were found to be 31.8 and 34.0 kcal mol–1, respectively and those of the pyrimidine-2(1H)-thiones (2c, d, and g) were 31.5, 30.1, and 31.1 kcal mol–1, respectively.

Aminolysis of N-acylpyrazoles

1-Acylpyrazoles reacted with amines having a tiny substituent to afford the corresponding amides. The aminolysis with bulky amines was control- led to be retarded by the steric factors. Due to this steric interac- tion, the stereoselective aminolysis was observed. This selectivity of aminolysis should increase the utility of pyrazoles as auxiliary com- pounds in the synthetic loop

Independent synthesis of three types of n-substituted dihydropyrimidines and their reactions with malachite green

Abstract Pyrimidine-2(1H)-thiones and their corresponding dihydro-derivatives were treated with Raney nickel to afford respectively three types of dihydropyrimidine isomers, which reacted with malachite green in similar rate constants to 1-benzyl-1,4-dihydronicotinamide.

Nuclear magnetic resonance spectral study of β-aminoenones

The n.m.r. spectra of the four geometrical isomers of β-aminoenones, trans-s-trans, trans-s-cis, cis-s-trans, and cis-s-cis, are discussed. It was found that the chemical shift of the α-proton of β-aminoenones depends on both anisotropic effects and the electron density: δ=δ0–Δδstruc=ΔδAr+K(q–q0). Thus the conformation of non-rigid β-aminoenones can be determined from the observed and the calculated chemical shifts of the α-proton.

The convenient and one-pot synthesis of N-substituted carbazoles

Abstract In spite of the very important compounds in the material sciences, conventional syntheses of carbazoles required severe and complicated reaction conditions. We can now report the convenient and one-pot synthesis of N-substituted carbazoles under mild conditions.

Trapping of dopachrome with 2,3-dihydro-1H-cyclopent[b]indole

Abstract Dopachrome ( 6 ) and related o-benzoquinones including dopaquinone (2d) were trapped, by treating each quinone from the corresponding catechol, with 2,3-dihydro-1H-cyclopent-[blindole (3) to afford [4.3.3]-propellane adduct.

Preparation of sterically more crowded 1,5-disubstituted imidazoles by the regioselective N-alkylation

4-Substituted 1-acetylimidazoles (6), which were derived from 4(5)-substituted imidazoles (1), were N-alkylated by the treatment with alkyl halides. During the work-up, the resulting N-alkylated products were easily hydrolyzed into 1,5-disubstituted imidazoles (3). These reactions were regarded to be the general method for the preparation of sterically more crowded 1,5-disubstituted imidazoles (3)

Formylation reaction using the ozonolysate of oxazole

The ozonolysis of oxazole (1) did not give formic anhydride (3), but gave N-formylformamide (5), which reacted with various nucleophiles to afford the corresponding formylated products in high yield. This formylating reaction should be useful in the organic syntheses.