Scope and Mechanism of "Double-Agent" Halogenation

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This research was initially conceived as a kinetic study of a recently reported1 acylmethylation reaction, schematically portrayed in eq 1, and was reported to produce good yields (62-94%) of exclusively para product in dry CHzClp as the solvent. Our preliminary studies suggest this reaction to be fur different than proposed by Lee and 0h.l For example, with 1-nitrocyclohexene, they reported 94% para product with toluene and 90% para product with anisole. With the same nitroalkene, we observed no acyl product with toluene and only modest amounts with anisole. Further, our GC/MS data suggest this to be an unusual reaction involving chlorination of the arene and a combination chlorination/NeF reaction of the nitro olefin resulting in an a-chloro ketone product. When toluene is used as the aryl component, the major products are 2-chlorocyclohexanone and monochlorinated toluenes; smaller amounts of 1-chlorocyclohexene and nitrosotoluenes are also produced. Because we apparently are seeing both electrophilic chlorination of arenes and nucleophilic chlorination of the nitro olefin, we call this reaction “double-agent” chlorination. Since this reaction appeared to be a promising method of producing a-halo ketones which are difficult to synthesize regioselectively,3 we have examined it with a variety of nitro olefins, metal halides, solvents, and arenes. These results are reported along with other mechanistic studies.