Reactivity of pyrimidinylphosphazenes with acetylenic esters: Competitive [4 + 2] and [2 + 2] tandem cycloaddition or retro‐cycloaddition approaches

This is the authors' abstract. We don't add key points for this paper.

In the search for new intermediates for heterocyclic synthesis, the reactivity of 6‐iminophosphoranepyrimidines against dimethyl acetylenedicarboxylate (DMAD) and ethyl propiolate as dienophiles, was studied in this work. The presence of a viable 2‐azadienic moiety in pyrimidin‐4‐one rings (oxo derivatives) favored reaction of DMAD by [4 + 2]/retro‐[4 + 2] sequence, in addition to the expected [2 + 2] cycloaddition/retrocycloaddition involving phosphazene moiety. In contrast, pyrimidine derivatives lacking a viable 2‐azadienic residue reacted only through phosphazene group by the aforementioned [2 + 2]/retro‐[2 + 2] tandem process. Ethyl propiolate (non‐symmetric dienophile) proved less reactive in the study, giving rise to undesired side reactions.