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

International audienceTwo equivalents of boron trifluoride-diethyl ether complex or 1 equiv of trifluoromethanesulfonic acid reacts with C-[bis(diisopropylamino)phosphino]-C,P-bis(diisopropylamino)phosphaalkene 1, cleaving one of the diisopropylamino substituents at the <r3-phosphorus atom. This affords the corresponding 1 2,3 a2-diphosphaallylic cation 4,which is isolated as the four-membered-heterocycle 3. Addition of a catalytic amount of base to 3 leads to a 1 *,3 3-diphosphaallylic cation 5, which is isolated as the diphosphirenium salt 2. Mesityllithium and the lithium salts of diisopropylamine or dicyclohexylamine react at the