Diastereoselective 1,3-dipolar cycloaddition of 2-(α,β-unsaturated) acyl-3-phenyl-l-menthopyrazoles

Article abstract of DOI:10.3987/COM-96-S19

The 1,3-dipolar cycloadducts of N-(α,β-unsaturated) acylpyrazoles (2) with benzonitrile oxide or nitrones were afforded in good yield. In the cases of nitrones, the addition of MgBr₂ or ZnBr₂ promoted the stereoselectivity as well as the acceleration of the reaction rate. In the reaction of 2f and 2g, the big jump on the diastercoselectivity was accomplished by the addition of MgBr₂, and (3′S,4′R,5′S)-8 was obtained as optically pure form in over 90% yield. These isoxazolidinecarbonylpyrazoles were converted into azetidinones in moderate yield with the retention of their stereo structures.