Synthesis of novel 4,5‐diazafluoren‐9‐one derivatives and theoretical study of 3+2 cycloaddition reactions

Some novel salts of 4,5-diazafluoren-9-one N-monosubstituted have been obtained by using Krohnke method. The ability of 9-oxo-4,5-diazafluorenium phenacylides (as 1,3-dipoles) to react with activated symmetric dipolarophiles to give new heterocyclic compounds is presented. The new heterocyclic system of 10,10c-diazacyclopenta[c]fluoren-6-one is illustrated by a series of derivatives. The cycloaddition reaction proceeds, according to the semiempirical study, via a concerted nonsynchronous mechanism.