Organophosphorus 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 develope d involving reactions of the 1-aza-2-phospha-4-vanada(V)-cyclobutenes 9a-g, generated in situ from the imidovanadium(V) complexes 7a-e and the phospha alkynes 8a-e, with the acetylenes 10a-g. This synthesis affords the heteroc yclic compounds 12a-m in good yields and allows variation of all substituen ts for the first time. The structure of the 1H-1,2-azaphosphole 12a has bee n confirmed by X-ray crystallographic analysis. A selective eta(1)-complexa tion of the azaphospholes 12a,b to afford the transition metal complexes 13 a,b can be realized by reaction with diiron nonacarbonyl. While reactions o f the alkyl trifluoromethanesulfonates 14a,b with the heterophosphole 12a r esult in the formation of the azaphospholium compounds 15a,b, the azaphosph ole 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-azaphosphanorb ornadienes 19a-f, the structures of which have been confirmed by an X-ray c rystallographic analysis of the bicyclic product 19e. The phosphorus atom o f the azaphosphanorbornadiene 19a can be oxidized and sulfurized to form th e bicyclic species 20 and 21 containing lambda(5)sigma(4)-phosphorus atoms.