2,4-Cyclohexadien-1-ones in Organic Synthesis. Further Studies of Molecular Rearrangements Occurring from Products of Intramolecular Azide-Olefin Cycloadditions

Article abstract of DOI:10.1021/jo00390a002

Thermolyses of 6-(3-azidopropyl)-2,4-cyclohexadien-1-ones 7a and 7b provide triazolines 8a and 8b, respectively.Photolysis of 8b (366nm) in methanol solution gives 2-azatricyclo<4.4.0.0^2,8>dec-9-en-7-one 9, but photolysis of 8a gives the pyrrole malonic ester 10a.The inability to isolate the corresponding azatricycle 11 is explained by the operation of a retro-Mannich reaction of 11 to give zwitterion 12, from which fragmentation occurs to give pyrrole ketene 13.Reaction of 13 with methanol generates pyrrole malonic ester 10a.Photolysis of 7a (366nm) in methanol solution gives azido diene 15; thermolysis of 15 at 80 deg C gives a mixture of diastereomeric vinylaziridines 16.Acid-catalyzed rearrangement of 16 gives the butadiene carboxylic ester 17, while thermolysis of 16 at 80-140 deg C provides vinylogous urethane 20.The rearrangement of 16 to 20 is suggested to occur by zwitterionization of 16 to give carbonyl-stabilized azomethine ylide 19, followed by hydrogen atom rearrangement.Cycloadduct 21 is obtained on thermolysis of 16 in the presence of excess dimethyl acetylenedicarboxylate (DMAD).Vinylaziridine 23 (obtained from 2,4-cyclohexadienone 7b via azido diene 22) is stable to p-toluenesulfonic acid in THF at room temperature and attempted thermolysis at 140 deg C