Compound I reacted readily also with hexachlorocyclopentadiene and yielded 5-t- butylpentachlorocyclopentadiene (X)(and di-t-butylphosphorochloridate,(tC, HgO), P (O) CI (XI), identified by P3I nmr The H1 and P31 nmr frequencies of the phosphorus compounds listed are presented in Table I.