[4+2] Cycloaddition of 9-Anthryldiphosphene with Electron-Deficient Olefins: Transformation of a Diaryldiphosphene to Alkylaryldiphosphenes

The reactions of kinetically stabilized 9-anthryldiphosphene 1b with 2,3-dimethyl-1,3-butadiene and electron-deficient olefins 3 were found to afford the corresponding [4+2] cycloadducts 2 and 4, respectively. The transformation of 1b into alkylaryldiphosphene derivatives 4 via the Diels−Alder reactions should be noteworthy as a unique example of the transformation of a diphosphene into other diphosphenes with keeping the highly reactive diphosphene unit. Both the spectral features and the results of X-ray crystallographic analyses of 4 support their PP double-bond character. Furthermore, unique E−Z isomerization of fumaronitrile (3c) was found to occur in the reaction with a diphosphene such as BbtPPBbt.