REACTIONS OF PHOSPHINES WITH ACETYLENES .7. STRUCTURE REVISION OF A REARRANGED 1 - 2 ADDUCT OF TRIPHENYLPHOSPHINE AND DIMETHYL ACETYLENEDICARBOXYLATE . A STABLE 2H-PHOSPH(V)OLE

Triphenylphosphine and dimethyl acetylenedicarboxylate (2 equiv.) react to form a yellow adduct, which has been shown to be the stable 2H-phosph(V)ole (10a) rather than an open-chain phosphine as previously postulated. Tri-p-tolylphosphine gives a similar yellow adduct (10b). The temperature-dependent 1H n.m.r. spectra of the adducts in deuteriochloroform solution and in trifluoroacetic acid solution display features characteristic of phosphoranes stabilised by alkoxycarbonyl groups. Treatment of the adduct with zinc and acetic acid gave the open chain phosphine oxide (12). The infrared spectra of allylidenephosphoranes stabilised by methoxycarbonyl groups are discussed.