TETRAKIS(DIMETHYLAMINO)ETHYLENE AS A USEFUL REDUCTANT OF SOME BROMODIFLUOROMETHYL HETEROCYCLES - APPLICATION TO THE SYNTHESIS OF NEW GEM-DIFLUORINATED HETEROARYLATED COMPOUNDS

The cyclic voltammetry of the reductive cleavage of some bromodifluoro methyl heterocycles and of the oxidation of the tetrakis(dimethylamino )ethylene was investigated in N,N-dimethylformamide and acetonitrile, at an inert electrode. The systematic investigation of the kinetics of the electrochemical reduction of this series of bromodifluoromethyl c ompounds provides clear evidence of a concerted electron-transfer-bond -breaking mechanism. Application of the theory of the dissociative ele ctron transfer allowed the estimation of the carbon-halogen bond disso ciation energy and the standard potential of the reaction. On the basi s of the electrochemical experiments, the tetrakis(dimethylamino)ethyl ene (TDAE) was found to be an effective reductant of the 2-(bromodiflu oromethyl)benzoxazole (1) and of the 5-(bromodifluoromethyl)-3-phenyl- 1,2,4-oxadiazole (4). A stepwise electron transfer with a difluorometh yl radical as intermediate is assumed to take place in this reaction. Under mild conditions, the generated difluoromethyl heterocyclic anion was efficiently trapped with aromatic and heterocyclic aldehydes 7-17 and ketones 18 and 19. In this way, the corresponding beta,beta-diflu oro-alpha-heteroarylated alcohols 20-38 were obtained in moderate to g ood yields and the compounds 20, 21, and 23-27 were tested against the HIV-1 virus.