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DOI: 10.1055/s-0030-1258789
Phase-Transfer Catalysis in the Asymmetric Synthesis of Pyrazolines
O. Mahé, I. Dez, V. Levacher, J.-F. Brière*
Université de Rouen and Université de Caen, France
Publication History
Publication Date:
21 October 2010 (online)
Significance
The enantioselective synthesis of 3,5-diarylpyrazolines is accomplished by means of asymmetric phase-transfer catalysis. The authors found the cinchona-derived quaternary ammonium salt 1 bearing an ortho-methoxybenzyl group at the quinuclidine nitrogen to efficiently promote the enantioselective conjugate addition of Boc-protected hydrazine to various chalcones. The combination of catalyst 1, hydrazine, and an inorganic base leads to an efficient ammonium-amide ion pairing accounting for the high enantioselectivities obtained. Subsequent imine formation ensures the irreversible formation of the desired products in good yields and enantio-selectivities.