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Conjugate addition of grignard reagents to N ‐(α,β‐unsaturated)acylpyrazoles. Diastereoselective β‐alkylation using 3‐phenyl‐ l ‐menthopyrazole
Author(s) -
Kashima Choji,
Takahashi Katsumi,
Fukusaka Kiyoshi,
Hosomi Akira
Publication year - 1998
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.5570350303
Subject(s) - chemistry , magnesium bromide , conjugate , alkylation , reagent , protonation , grignard reagent , grignard reaction , halide , medicinal chemistry , bromide , addition reaction , lewis acids and bases , magnesium , asymmetric induction , organic chemistry , enantioselective synthesis , catalysis , ion , mathematical analysis , mathematics
The conjugate additions of N ‐(α,β‐unsaturated)acylpyrazoles were carried out by the treatment with Grignard reagents in the presence of cuprous halides. The reaction of 2‐(α,β‐unsaturated)acyl‐3‐phenyl‐ l ‐menthopyrazoles 3a‐h occurred in higher chemical yields and with asymmetric inductions on β‐position, where the addition of magnesium bromide as a Lewis acid influenced to the yields and the diastereoselectivities. In the case of α‐methylated 2‐(α,β‐unsaturated)acyl‐3‐phenyl‐ l ‐menthopyrazoles 3i‐n , the excellent asymmetric induction on the α‐position was also observed through the diastereofacial protonation.