Stereospecific [2+2] cycloaddition reactions of diphosphorus with alkenes

[2+2] Cycloaddition reactions of P2 with alkenes were predicted to have concerted paths, that is, pseudoexcitation, distorted 2πs+2πs, and 2πs+2πa processes without any interventions of intermediates. The pseudoexcitation and/or distorted 2πs+2πs paths with retention of configuration of alkenes are kinetically preferred to the 2πs+2πa path with inversion of configuration. The reactions were predicted from the appreciable difference in the calculated enthalpies of activation to be stereospecific.