Organphosphorus Compounds, Part 150; Imidovanadium(V)-Complexes as Reaction Partners for Kinetically Stabilized Phosphaalkynes. 1-Aza-2-phospha-4-vanada(V)-cyclobutenes: Precursors in the Synthesis of 1H-1,2-Azaphospholes

A new synthetic pathway to the 1H-1,2-azaphospholes 12a-m has been developed involving reactions of the 1-aza-2-phospha-4-vanada(V)-cyclobutenes 9a-g, generated in situ from the imidovanadium(V) complexes 7a-c and the phosphaalkynes 8a-e, with the acetylenes 10a-g. This synthesis affords the heterocyclic compounds 12a-m in good yields and allows variation of all substituents for the first time. The structure of the 1H-1,2-azaphosphole 12a has been confirmed by X-ray crystallographic analysis. A selective η¹-complexation of the azaphospholes 12a,b to afford the transition metal complexes 13a,b can be realized by reaction with diiron nonacarbonyl. While reactions of the alkyl trifluoromethanesulfonates 14a,b with the heterophosphole 12a result in the formation of the azaphospholium compounds 15a,b, the azaphosphole 12a reacts with the azo compound 16 to form the spirotricyclic betaine 17. Diels-Alder reactions occur when the heterophospholes 12a,b are treated with the electron-poor acetylenes 18a-e and furnish the 1,2-azaphosphanorbornadienes 19a-f, the structures of which have been confirmed by an X-ray crystallographic analysis of the bicyclic product 19e. The phosphorus atom of the azaphosphanorbornadiene 19a can be oxidized and sulfurized to form the bicyclic species 20 and 21 containing λ⁵σ⁴-phosphorus atoms.

1H-1,2-azaphospholes - 1,2-azaphosphanorbornadienes - heterophospholes - Diels-Alder reaction - phosphorus - organometallic reagents - azo compounds - heterocycles