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Reaction of 4-phenyl-1,2,4-triazoline-3,5-dione with substituted butadienes. A nonconcerted Diels-Alder reaction

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  • F. Jensen
  • Christopher S. Foote, University of California
The reaction of 4-phenyl-1,2,4-triazoline-3,5-dione with substituted 1,3-butadienes (1,3-butadiene, (E,E)-, (Z,E)-, and (Z,Z)-2,4-hexadiene, and 2,5-dimethyl-2,4-hexadiene) has been investigated. In CHCl, 1,3-butadiene, (E,E)-2,4-hexadiene, and (Z,E)-2,4-hexadiene give the expected Diels-Alder products with high stereospecificity (>200:1). Surprisingly, (Z,-Z)-2,4-hexadiene gives a mixture of two Diels-Alder products, with the major isomer having the "wrong" stereochemistry. 2,5-Dimethyl-2,4-hexadiene gives mainly (∼70%) the ene product. For both (Z,Z)-2,4-hexadiene and 2,5-dimethyl-2,4-hexadiene, the reactions proceed via observable intermediates to which we assign diazetidine structures. In MeOH, (Z,Z)-2,4-hexadiene and 2,5-dimethyl-2,4-hexadiene give mainly solvent adducts. (Z,E)-2,4-Hexadiene gives ∼12% MeOH adduct together with the expected Diels-Alder product, while (E,E)-2,4-hexadiene and 1,3-butadiene give less than 0.05% of the solvent adducts. A mechanism involving initial formation of an aziridinium imide which subsequently opens to a 1,4-zwitterion can account for all the observations and is consistent with force-field calculations. The proposed mechanism may also hold for reactions of other electrophilic reagents such as O and polycyanoethylenes.
Original languageEnglish
JournalJournal of the American Chemical Society
Pages (from-to)6376-6385
Number of pages10
Publication statusPublished - 1987
Externally publishedYes

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