C. Kashima et al., SYNTHESIS OF OPTICALLY-ACTIVE BETA-LACTAMS BY THE REACTION OF 2-ACYL-3-PHENYL-L-MENTHOPYRAZOLES WITH C=N COMPOUNDS, Journal of heterocyclic chemistry, 34(5), 1997, pp. 1559-1565
The reaction of 1-acyl-3,5-dimethylpyrazoles 1 with C=N compounds was
kinetically controlled with syn stereoselectivity through a lithium en
olate intermediate using lithium diisopropylamide. In contrast, the an
ti stereoselective reaction of 1 was caused by the action of diisoprop
ylethylamine in the presence of magnesium bromide under the thermodyna
mic control. Reaction of 2-acyl-3-phenyl-l-menthopyrazoles 12 with C=N
compounds was observed in higher chemical and optical yields with the
predominant 2'S configuration. An especially diastereomerically pure
product was isolated in the reaction of 2-propanoyl-3-phenyl-l-menthop
yrazole (12a) with N-benzylidene-4-toluenesulfonamide (2). The product
s from N-acylpyrazoles and C=N compounds were further cyclized into be
ta-lactams directly or with short conversion steps.