Synthesis of optically active β‐lactams by the reaction of 2‐acyl‐3‐phenyl‐l‐menthopyrazoles with CN compounds

The reaction of 1‐acyl‐3,5‐dimethylpyrazoles 1 with CN compounds was kinetically controlled with syn stereoselectivity through a lithium enolate intermediate using lithium diisopropylamide. In contrast, the anti stereoselective reaction of 1 was caused by the action of diisopropylethylamine in the presence of magnesium bromide under the thermodynamic 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‐menthopyrazole (12a) with N‐benzylidene‐4‐toluenesulfonamide (2). The products from N‐acyl‐pyrazoles and CN compounds were further cyclized into β‐lactams directly or with short conversion steps.