1,3‐Dipolar cycloadditions of 9‐diazofluorenes and diphenyldiazomethane to 2‐acyl‐2 H ‐1,2,3‐diazaphospholes

A series of 2‐acyl‐2 H ‐1,2,3‐diazaphospholes 3 underwent ready 1,3‐dipolar cycloaddition reactions with 9‐diazofluorenes as the 1,3‐dipole, yielding the respective bicyclic phosphiranes 5 or trimers 7 depending on the reaction conditions employed. The reaction is believed to proceed via the formation of the [3+2]‐cycloaddition adducts followed by elimination of nitrogen from the cyclic azo moiety. In the case of 3c , the phosphatetraazabicyclooctadiene compound 6 has been isolated with no loss of nitrogen. Likewise, the dipolar cycloaddition reaction of diphenyldiazomethane with the >CP‐ moiety as the 1,3‐dipolarophile gave phosphadiazabicyclohexenes 8 in 32–68% yields.