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On the Reaction of 1‐Aza‐2‐azoniaallene Salts with Isocyanates
Author(s) -
Wang Quanrui,
Mohr Susanne,
Jochims Johannes C.
Publication year - 1994
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19941270524
Subject(s) - chemistry , pericyclic reaction , geminal , intramolecular force , medicinal chemistry , lewis acids and bases , sigmatropic reaction , intramolecular reaction , organic chemistry , stereochemistry , catalysis
1‐Aza‐2‐azoniaallene salts 3 , prepared in situ from geminal chloroalkylazo compounds 2 with Lewis acids, react with isocyanates 4 to give 4,5‐dihydro‐5‐oxo‐3 H ‐1,2,4‐triazolium salts 6 and 4,5‐dihydro‐5‐oxo‐1 H ‐1,2,4‐triazolium salts 7 , respectively. The intramolecular cyclization of 3u opens a new route to cinnolinium salts 11 . Allenes 3 react with isobutene to give pyrazolium salts 8 . According to AM1 calculations the cycloadditions of 3 to isocyanates proceed in two steps via acylium salts 5 as intermediates. Mechanistically, the rearrangements 6 → 7 resemble Wagner‐Meerwein rearrangements rather than pericyclic [1,5]‐sigmatropic shifts.