Aryl-2-bromo-3,3-difluorocyclopropanes were prepared from the reaction of 2',2'-difluorostyrene and dibromocarbene instead of from 1-aryl-2-haloacetylenes and difluorocarbene. These results are rationalised by the energy gap between HOMO (styrene) , HOMO (acetylene) and LUMO (CX2) . The title compounds were converted to methyl arylpropynoate in MeOH solution in quantitative yield.
The electron ionization (EI) fragmentation of nitro-beta,beta-dihalostyrenes depends strongly on the specific halogens present as well as on the position of the nitro group. Beta,beta-difluorostyrenes yielded mainly fluoroacetylene ions as the base peaks and o-nitro-beta,beta-dihalostyrene possibly furnished the ion with a structure similar to that of benzo[a]isoxazole (11). The structural identity of the ion was verified by comparing the collision-induced dissociation (CID) spectra of m/z 119 ions from p- and o-nitro-beta,beta-difluorostyrene, o-nitro-beta,beta-dibromostyrene and compound 11.
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