Few methods exist for the preparation of chiral 4,5-dihydro-1H-pyrazoles. Treatment of tosylhydrazones with DBU in the presence of a chiral 3-butenoate provides excellent isolated yields and stereoselectivity of the desired pyrazoles. A variety of reaction parameters were monitored for their influence on stereoselectivity. The menthol ester chiral inducing moiety is remote from the pyrazole ring, is relatively inexpensive and can be easily removed and recycled. 

Chiral induction in 1,3-dipolar cycloadditions: Preparation of 4,5-dihydro-1H-pyrazoles

244th National Meeting (2012)

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