The ability of 2-phosphabicyclo[2.2.2]oct-5-ene 2-oxides to undergo fragmentation of the bridging P-moiety

Abstract

New 2-phosphabicyclo[2.2.2]octene 2-oxides ( 2 and 3) were synthesized by the Diels–Alder reaction of 1,2-dihydrophosphinine oxides ( 1) and dienophiles, such as N-phenyl maleimide and maleic anhydride. The X-ray structure of one of the products ( 2Ab) suggests that the phosphabicyclooctenes have a less strained framework than the phosphabicyclooctadienes described earlier. As a consequence of this, also confirmed by thermal examinations and semiempirical calculations, thermal fragmentation of the phosphabicyclooctenes requires more forcing conditions, than that of the bicyclooctadienes. The methylenephosphine oxide ( 10) ejected could be utilized in the phosphorylation of hydroquinone in moderate yield. Mass spectral fragmentation of cycloadducts 2 and 3 under electron-impact conditions seems to be in agreement with the preparative experiences.