ISSN:
0947-3440
Keywords:
Ketene N,N-acetals, cyclic
;
Imidazole, derivatives of
;
Benzimidazole, derivatives of
;
Azides, electrophilic
;
Cycloaddition, 1,3-dipolar, nonconcerted
;
Zwitterions
;
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Cyclic ketene N,N-acetals derived from imidazolidine (4a, c) and 2,3-dihydrobenzimidazole (6a-c) add methanesulphonyl azide (2a) or picryl azide (2f) to afford the zwitterions 5 and 7, respectively. The structure of 7d is elucidated by X-ray crystallography. Reversibility of formation and thermal stability of the N-sulphonyl zwitterions depend on the substitution pattern at the carbon atom to which the triazenide moiety is attached: In the case of a pair of geminal methyl groups (5a, 7a) formation is irreversible and decomposition by cyclisation and subsequent reactions occurs above -20°C, while in presence of a single alkyl group (7c, d) these processes require heating to 80°C and are accompanied by partial reversion to 2a and ketene N,N-acetals (6b, c). Cyclisation of the zwitterions yields intermediate spirocyclic [3 + 2] cycloadducts, which may undergo [3 + 2] cycloreversion into N-sulphonylimine 13 and diazo compound 14 or extrude molecular nitrogen to furnish ring-expanded 2-(sulphonylimino)piperazine derivatives (9, 11).
Additional Material:
2 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jlac.199619961009
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