Ring opening of gem-dihalocyclopropanes: novel types of 1,4-elimination reactions

On treatment with Bu4N+ F-, cyclopropanecarboxylates I (R = Cl; R1 = Cl, F; R2 = OCMe3) undergo Cl-F exchange via cyclopropene intermediates. As a byproduct, H2C:CMeC.tplbond.CCO2CMe3 (II) is formed. I (R = R1 = Cl, R2 = CO2CMe3), II, and Me2CClC.tplbond.CCO2CMe3 are obtained when Me2C:CHCO2CMe3 is allowed to react with CHCl3 in strongly alk. medium. I (R = R1 = F, R2 = H) can be generated by oxidn. of the alc. In the presence of any base, however, instantaneous ring opening and dehydrofluorination occurs to give H2C:CMeCF:CHCHO. The solvolysis of 2,2-difluoro-3,3-dimethylcyclopropylmethyl p-toluenesulfonate in boiling aq. dioxane affords two ring opened products, 3,3-difluoro-2-methyl-1,4-pentadiene and 3,3-difluoro-2-methyl-4-penten-2-ol, besides 2,2-difluoro-3,3-dimethyl-1-cyclopropylmethanol. [on SciFinder (R)]