Fluorination and chlorination of nitroalkyl groups

Heterocycles substituted with a nitromethyl (CH2NO2) or phenyl-nitromethyl (CHPhNO2) group were prepared by reaction of a methyl- or phenylmethyl-substituted heterocycle, respectively, with lithium di-isopropylamide followed by quenching the intermediate carbanion with methyl nitrate. Conversion of CH2NO2 attached to an alkyl or aryl moiety into a dichloronitromethyl (CCl2NO2) group was achieved using N-chlorosuccinimide and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in dichloromethane. Similarly, CH2NO2 attached to an alkyl or aryl group was converted into difluoronitromethyl (CF2NO2) using either 1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate) (Selectfluor™) or N-fluorobenzenesulfonimide with DBU as base and dichloromethane as solvent. Reaction of ω-nitroacetophenone with Selectfluor/DBU in dimethylformamide followed by acidification and distillation gave the parent difluoronitromethane in a useful ‘one-pot’ procedure.