The fluorination of polyfluoroazabenzenes

Abstract

In this thesis the results of a series of fluorinations of polyfluoroazabenzenes with a 50:50 mixture of C0F3 and CaFg are described. Perfluoro-4-isopropyl, -2,4-di-isopropyl, -3-methyl and -4-methylpyridines reacted by the addition of two or four fluorine atoms to give high yields of -azacyclodienes and -monoenes. The observed products were thought to represent the thermodynamically more stable dienes and a mechanism is proposed for their formation. Pyrimidines exhibited a variety of behaviours in that a diene resulted from perfluoro-4,6-di-isopropylpyrimidine, 5-chlorotrifluoropyrimide behaved more like tetrafluoro- pyrmidine in that dimers were produced whilst perfluoro-4- isopropylpyrimidine gave a complicated mixture of fragmentation products. Perfluoro-4,5- aid 4,6-di-isopropyIpyridazines both gave products resulting from the loss of nitrogen whilst a diene was obtained in high yield upon fluorinating perfluoro-2,5-di-isopropylpyrazineo Cyanuric fluoride was resistant to fluorination. Some direct fluorinations have been performed but only tetrafluoropyrimidine and perfluoro-4,5-di-isopropylpyridazine were reactive, the former producing a dimer the latter products due to loss of nitrogen. Some of the new perfluoropolyazacyclodienes have been reacted with a variety of nucleophilic reagents and whilst imino fluorines were readily substituted imines bearing perfluoroisopropyl were resistant to reaction, Perfluoro-4- isopropyl-l-azacyclohexa-1,3-diene has a very labile fluorine at C-2 compared with the one at C-3 and it is thought that polarisation of the imine bond by nitrogen is responsible for this. Several of the new dienes have been subjected to photolysis and ring opening and fragmentation reactions were observed. Products with isolated double bonds were not reactive.