in tetrahydrofuran addn. of pyridinium salt (excess) to filtrated soln. of K salt in THF at ambient temp. under N2;; evapn. in vac. after 6 h; addn. of toluene; filtration through Celite; concn.; chromy. (silica, -15°C, toluene: isolation of Cr arenes, then ether); evapn. in vac. to dryness; addn. of ether; recrystn. from toluene/petroleum ether; elem. anal.;;