SYNTHESIS AND REARRANGEMENT OF INTRAMOLECULARLY STABILIZED 1-SIGMA(2),3-SIGMA(2)-DIPHOSPHAALLYLIC CATIONS INTO INTRAMOLECULARLY STABILIZED 1-SIGMA(1),3-SIGMA(3)-DIPHOSPHAALLYLIC CATIONS

Two equivalents of boron trifluoride-diethyl ether complex or 1 equiv of trifluoromethanesulfonic acid reacts with sopropylamino)phosphino]- C,P-bis(diisopropylamino) phosphaalkene 1, cleaving one of the diisopr opylamino substituents at the sigma(3)-phosphorus atom. This affords t he corresponding 1 sigma(2),3 sigma(2)-diphosphaallylic cation 4, whic h is isolated as the four-membered-heterocycle 3. Addition of a cataly tic amount of base to 3 leads to a 1 sigma(1),3 sigma(3)-diphosphaally lic cation 5, which is isolated as the diphosphirenium salt 2. Mesityl lithium and the lithium salts of diisopropylamine or dicyclohexylamine react at the sigma(2)-phosphorus atom of the cationic heterocycles 2 and 3, affording the corresponding phosphaalkenes 8, 1, and 6, respect ively. All the results demonstrate the high electrophilicity of low-co ordinated diphosphaallylic cations, which are only isolable as intramo lecular donor-acceptor complexes.