Paramagnetic adducts in the reaction of 4-substituted pyridines and phosphorus-centred radicals

The reactions of a number of 4-substituted pyridines with diethoxyphosphonyl, diphenylphosphonyl and diphenylphosphinyl radicals have been monitored by e.s.r. spectroscopy in the temperature range 293 to 403 K. Whereas with phosphonyl radicals the corresponding 1-phosphonyl pyridinyls were observed, the spectra detected with phosphinyl radicals proved to be those of the 4-substituted 1-hydropyridinyls. A comparison with data available for related pyridinyls indicates a marked electron withdrawing ability for the phosphonyl group. An analogous reactivity pattern has also been established for pyrazine and 2,6-dimethylpyrazine.