ISSN:
0170-2041
Keywords:
[3 + 2] Cycloaddition
;
[3 + 2] Cycloreversion
;
Nitrogen extrusion
;
Ketene N,X-acetals, cyclic
;
Azides, electrophilic
;
Amidines, cyclic N-sulfonyl- and N-picryl-
;
Ring expansion of heterocycles
;
1,2-Shift of carbon, nitrogen or sulfur
;
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
1,3-Dipolar Cycloaddition of Electrophilic Azides to Cyclic Ketene N,X-Acetals. - Extrusion of Molecular Nitrogen and Ring Expansion of the [3 + 2] Cycloadducts.The electrophilic azides 2 react with cyclic ketene N,X-acetals of type 7, e.g. 13, 15, 18, 21, 23, 25, and with the alkylidene-dihydroindoles 28 as well, to produce, besides molecular nitrogen, ring-expanded products of type 11 and 12, e.g. 14, 16, 19, 22, 24, 26, and 29 (path A), and/or N-sulfonylimines 10, viz. 17, 20, 27, and 31, besides diazo compounds (path B). The configurations of 16b, 19, 24a, and 26a are elucidated by means of X-ray diffraction analyses. The envelope conformations of the hetero rings of 19, 29 undergo ring inversion with rates in the range of the 1H NMR time scale [19: ΔG#c (285 K) = 54.8 kJmol-1, 29; ΔG#c (301 K) = 61.4, ΔG#c (314 K) = 60.7]. The formation of the ring-expanded products 11 and 12 is interpreted in terms of an initial [3 + 2] cycloaddition leading to unstable spiro compounds 8. Opening of their dihydro-1,2,3-triazole ring generates the zwitterions 9 which lose molecular nitrogen with concomitant ring expansion by a 1,2-shift of the more soft one of the atoms N and X.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jlac.1992199201209
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