Trimethyl phosphite reacts with tetraphenylcyclopentadienone to give dimethyl 5-methyl-2,3,4,5-tetraphenylcyclopenta-1,3-dienyl phosphate (8), dimethyl 3-methyl-2,3,4,5-tetraphenylcyclopenta-1,4-dienyl phosphate (11) and 1,2,3,4-tetraphenylfulvene. The reaction proceeds by way of Arbuzov rearrangements of an intermediate zwitterion formed by attack of phosphorus at the carbonyl oxygen atom. The zwitterion may be trapped by carrying out in the reaction in methanol. An analogous zwitterion (17) may be isolated when phosphorus trisdimethylamide replaces the phosphite in the reaction and the chemistry of this stable 1 : 1 adduct is described. Pyrolysis affords a hydrocarbon (C58H40) which it is suggested is a benz[e]-as-indacene (26).
The involvement of 5-carbena-1,2,3,4-tetraphenylcyclopenta-1,3-diene in the reactions of the ketone–phosphorus amide adduct is discussed. Phosphorus trisdimethylamide adds to give a stable 1 : 1 adduct (34).
The mass spectra of a number of tetraphenylcyclopentadiene systems show only very weak M– 1 peaks.
