In recent years, the synthesis and structural properties of phos- phaalkenes have been investigated with increasing intensity'. In contrast, their chemical reactivity is less well known. We are en- gaged in a systematic study of the chemical behaviour of triaryl- phosphaalkenes and wish to report on progress in three areas. ... 2, - 2' - While Te shows no reaction, the other rea- 2 2' gents attacked phosphorus at the lone pair to give the "phospha- alkene oxide" (= ...