Triazolinediones. Conversion to Deaza Dimers by Electron-Transfer Catalysis. A Possible Radical Anion Diels-Alder Reaction

Article abstract of DOI:10.1021/jo00359a035

1,2,4-Triazolidines, 4-RTAD (1), are converted to dimeric products (deaza dimers 2) with loss of dinitrogen by a variety of agents of which the most effective are good single-electron donors (sodium naphthalenide, sodium iodide, sodium metal).The reaction is retarded by tetracyanoethylene or lead tetraacetate (electron acceptors).A radical anion chain reaction is proposed (Scheme IV and eq 9-12) in which the overall result is the reaction of two RTAD --> deaza dimer 2 + N2, catalyzed by electron donors.The sequence suggested includes the <4 + 2> cycloaddition of RTAD anion radical with the dienophile RTAD, the first example (of which we are aware) of a radical anion Diels-Alder reaction.In the presence of an alcohol (e.g., methanol) PhTAD is converted, again in a catalyzed reaction (e.g., sodium iodide), to a methanol addition product, formulated as 3a (eq 5a, 15, and 17 and Scheme V).