N-HALOGENO COMPOUNDS .12. SITE-SPECIFIC FLUORINATION OF CARBANIONS WITH PERFLUORO-N-FLUOROPIPERIDINE

Perfluoro-N-fluoropiperidine (1) acts as a site-selective electrophilic fluorinating agent towards carbanionic substrates [Me2CNaNO2 --> Me2CFNO2; PhMgBr --> PhF; PhCNa(CO2Et)2 --> PhCF(CO2Et)2; EtCNa(CO2Et)2 --> EtCF(CO2Et)2; activated CH2(CH2)2COCNaCO2Et --> activated CH2(CH2)2COCFCO2Et], but in doing so is converted to perfluoro-l-azacyclohexene (2). Unfortunately, this imidoyl fluoride (2) is highly electrophilic and competes with the N-F compound (1) for carbanionic species, as exemplified by the formation of the 2-substituted octafluoro-l-azacyclohexenes activated CF2(CF2)3N = CR, where R = Ph, CEt(CO2Et)2, and activated C(CO2Et)CO(CH2)2CH2 in the respective cases of the last three sodio derivatives listed above.