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Synthesis of optically active β‐lactams by the reaction of 2‐acyl‐3‐phenyl‐ l ‐menthopyrazoles with CN compounds
Author(s) -
Kashima Choji,
Fukusaka Kiyoshi,
Takahashi Katsumi
Publication year - 1997
Publication title -
journal of heterocyclic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.321
H-Index - 59
eISSN - 1943-5193
pISSN - 0022-152X
DOI - 10.1002/jhet.5570340529
Subject(s) - chemistry , lithium diisopropylamide , stereoselectivity , magnesium bromide , lithium (medication) , optically active , bromide , medicinal chemistry , stereochemistry , magnesium , organic chemistry , catalysis , medicine , ion , deprotonation , endocrinology
The reaction of 1‐acyl‐3,5‐dimethylpyrazoles 1 with CN 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 CN 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 CN compounds were further cyclized into β‐lactams directly or with short conversion steps.