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

The reactions of kinetically stabilized 9-anthryldiphosphene <b>1b</b> with 2,3-dimethyl-1,3-butadiene and electron-deficient olefins <b>3</b> were found to afford the corresponding [4+2] cycloadducts <b>2</b> and <b>4</b>, respectively. The transformation of <b>1b</b> into alkylaryldiphosphene derivatives <b>4</b> 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 <b>4</b> support their PP double-bond character. Furthermore, unique <i>E</i>−<i>Z</i> isomerization of fumaronitrile (<b>3c</b>) was found to occur in the reaction with a diphosphene such as BbtPPBbt.