Transformation of substituted 2H-pyran-5-carboxylates into 3R*-vinyl-1,2R*-cyclopropanedicarboxylates

Substituted alkyl 2H-pyran-5-carboxylates, 1, have been condensed with meth yl 2-(triphenylarsoranylidene) ethanoate, 14a, to form substituted 3-vinyl- 1,2-cyclopropanedicarboxylates, 15, and, in a number of cases, 2,3-dihydro- 3-vinyl-2,4-furandicarboxylates, 16. NMR experiments showed that for the ma jority of cyclopropane products formed, the cyclopropane ring hydrogen atom s have the trans configuration. This was validated by molecular orbital cal culations. Biological screening tests revealed that these compounds showed some ectoparasiticidal activity.