Phosphorus heterocycle synthesis by RPX2·AlX3 addition to [1,n]dienes VI : RPX2·AlX3 phosphorylations in the presence and absence of water

The electrophilic addition of RPX₂·AlX₃ (1) (R=Ph or Me; X=Cl or Br) to 1,n]dienes was found to be an efficient and useful reaction for the synthesis of a variety of new phospha-heterocycles such as substituted phospholanes, dihalophosphorinanes, phosphorinenes, 3-phosphabicyclo3.1.0]hexanes, 2-phosphabicyclo2.2.1] heptanes, 2-phosphabicyclo3.2.1]octanes and substituted phosphetanes. An ionic multistep mechanism, governed by the stability of the intermediate carbonium ions, is suggested. The phosphorylation reaction was found to be most sensitive to water and in its presence (even 0.1 eq.) it takes a different course. The products, results from hydrogen and RP(O)X addition to the double bond. The phosphorylation is initiated by an unusual protonation process which employs the specific catalytic properties of the AlCl₃·H₂O complex (HX + RPX₂ in the presence or absence of AlCl₃ do not give any defined phosphorylation products but polymers). Some of the examined dienes give with water-doped RPX₂·AlX₃ phosphorylations and/or HX additions, involving in several cases participation of both double bonds to give intramolecular cyclisation products. These products may explain the substances obtained following phosphorylation of simple n-alkenes. Compound 16, one of the new addition compounds, was found to cyclise to the 2-oxaphospholane system (19).