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The Astounding Chemistry of a 2‐Amino‐1,2‐dihydroisoquinoline Derivative
Author(s) -
Durst Toni,
Finke Jürgen A.,
Huisgen Rolf,
Temme Robert
Publication year - 2000
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/1522-2675(20000906)83:9<2363::aid-hlca2363>3.0.co;2-4
Subject(s) - chemistry , intramolecular force , medicinal chemistry , crystal structure , electrophile , aniline , adduct , nmr spectra database , protonation , catalysis , stereochemistry , organic chemistry , physics , astronomy , spectral line , ion
The cycloadducts of isoquinolinium N ‐phenyl imide 2 with C=C bonds are derivatives of 2‐amino‐1,2‐dihydroisoquinoline. Their N β ‐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 , C 21 H 20 N 2 O 4 , is exceptional by being converted on treatment with acid to bright‐yellow crystals, C 24 H 22 N 2 O 6 (additional C 3 H 2 O 2 ). 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 C 21 H 20 N 2 O 4 ( 11 )→ 18 →C 12 H 11 NO 2 ( 14 )+C 9 H 9 NO 2 ( 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 C 21 H 20 N 2 O 4 ( 11 )→C 24 H 22 N 2 O 6 ( 13 )+C 12 H 11 NO 2 ( 14 )+aniline. Interception and model experiments confirmed the above pathway. A by‐product, C 33 H 31 N 3 O 6 ( 62 ), arises from an acid‐catalyzed dimerization of 11 and subsequent elimination of 15 .