Conjugate Addition of Grignard Reagents to N-(α,β-Unsaturated)acylpyrazoles. Diastereoselective β-Alkylation Using 3-Phenyl-l-menthopyrazole

Article abstract of DOI:10.1002/jhet.5570350303

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 diastereo-selectivities. 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.