Electrocyclization of Phosphahexatrienes: An Approach to λ⁵-Phosphinines

We experimentally verified an assumption that the substitution of a carbon atom with a pentavalent phosphorus atom in 1-alkoxy (dialkylamino) hexatrienes will not hamper its ability to electrocyclize. A series of 1-, 3-, and 5-phosphahexatrienes were synthesized. It was shown that parent λ5-phosphinines could be synthesized by electrocyclization of the 3- and 5-phosphahexatrienes. The resultant electrocyclization is a convenient method for the synthesis of parent λ5-phosphinines bearing different substituents on the phosphorus atom.