Reactions of phenyltriazolinedione with alkenes. Stereochemistry of methanol adducts to aziridinium imide intermediates

Article abstract of DOI:10.1021/ja00132a006

The addition of 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD) and the stereochemistry of methanol/PTAD adduct formation with cis- and trans-2-butenes, 1-methylcyclopentene, (E)-2-methyl-2-butene-1,1,1-d₃ and substituted indenes (indene, 2-methylindene, 2,3-dimethylindene) have been investigated. There is no loss of stereochemistry in the addition of MeOH and PTAD to butenes, 1-methylcyclopentene, 2-methyl-2-butene, and indene. However, in methyl-substituted indenes 9 and 14, loss of stereochemistry at the reaction center is observed. An aziridinium imide (AI) is proposed as an intermediate in all these systems. The stability of the AI intermediate and its equilibration with an open zwitterion depend on the particular system. Only in the benzylically-stabilized tertiary indenes is the open zwitterion stable enough to cause loss of stereochemistry.