Hexaphenylcarbodiphosphorane reacted with oxobutenyl-, and oxophenylpropenyl-pyrazolones to give oxaphosphinin, triphenylphosphaneylidenecyclobutenyl, (triphenylphosphaneylidene)-butadienyl and triphenyldihydrophosphetyl derivatives. Triphenylphosphane and triphenylphosphane oxide were also isolated and identified. Moreover, Japanese reagent reacted with the same pyrazolones to afford sulfido-oxathiaphosphinin products. Possible reaction mechanisms were considered and structured elucidations for the new products were based upon compatible microanalytical and spectroscopic measurements. Four newly synthesized compounds showed promising cytotoxicity against human myeloblastic leukemia HL60 cells with selectivity towards tumor cells when compared to non-tumor human fibroblasts BJ cells.