ISSN:
0947-3440
Keywords:
[3 + 2] Cycloaddition
;
Ketene N,X-acetals, cyclic
;
Azides, electrophilic
;
Amidines, cyclic N-sulphonyl-
;
Ring expansion of heterocycles
;
1,2-Shift of carbon, nitrogen, sulphur, or selenium
;
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Methanesulphonyl azide (2) reacts readily with isolated cyclic ketene N,X-acetals of type 1, viz. 10a, d, 15b, d, and 22a-c, or those that are generated in situ by deprotonation of the corresponding 2-alkylbenzazolium tetrafluoroborates, i.e. 14a → 15a, 14b → 15b, and 18 → 19. Ring-expanded products are formed by extrusion of molecular nitrogen from intermediate labile [3 + 2] cycloadducts 3 with concomitant 1,2-shift of N (route A1 → 12, 24) or X (route A2 → 16, 20, 21). In addition, 3 may undergo [3 + 2] cycloreversion into N-sulphonylimine 5 and diazoalkane 6 (route B → 13, 17, 25). The configurations of the cyclic N-sulphonylamidines 16b and 21b, the N-sulphonylimine 24 and the N-sulphonylamine 27 are elucidated by means of X-ray diffraction analyses. The ratio of the (useful) ring-expansion reactions vs. the unwanted formation of 5 + 6 is hardly influenced by the solvent employed and temperature of the experiment but strongly by the nature of the potential migrating atom and the substituents at the α-carbon atom.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jlac.199619961008
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