- The astounding chemistry of a 2-amino-1,2-dihydroisoquinoline derivative
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The cycloadducts of isoquinolinium N-phenyl imide 2 with C=C bonds are derivatives of 2-amino-1,2-dihydroisoquinoline. Their Nβ-vinylphenylhydrazine system is amenable to an acid-catalyzed [3,3]-sigmatropic shift; the formation of pentacyclic aminals is exemplified by 6 → 8. The dimethyl maleate adduct 11, C21H20N2O4, is exceptional by being converted on treatment with acid to bright-yellow crystals, C24H22N2O6 (additional C3H2O2). X-Ray crystal-structure analysis and NMR spectra reveal structure 13, and mechanistic studies indicated an initial β-elimination at the N-N bond of 11 to yield 18; this step is followed by a retro-Mannich-type cleavage that gives methyl isoquinoline-1-acetate (14) and methyl 2-(phenylimino)acetate (15), according to the sequence C21H20N2O4 (11) → 18 → C12H11NO2 (14)+C9H9NO2 (15). In the second act of the drama, electrophilic attack by 15-H+ on the ene-hydrazine group of a second molecule of 11 furnishes 13 by a polystep intramolecular redox reaction. All rate constants must be fine-tuned in this reaction cascade to give 13 in yields of up to 78% with an overall stoichiometry: 2 C21H20N2O4 (11) → C24H22N2O6 (13) + C12H11NO2 (14) + aniline. Interception and model experiments confirmed the above pathway. A by-product, C33H31N3O6 (62), arises from an acid-catalyzed dimerization of 11 and subsequent elimination of 15.
- Durst, Toni,Finke, Juergen A.,Huisgen, Rolf,Temme, Robert
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p. 2363 - 2382
(2007/10/03)
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