1,3-Dipolare Cycloaddition elektrophiler Azide an cyclische Keten-N,X-acetale. — Stickstoff-Extrusion und Ringerweiterung der [3 + 2]-Cycloaddukte
✍ Scribed by Quast, Helmut ;Ach, Manfred ;Peters, Eva-Maria ;Peters, Karl ;Peters, Karl ;von Schnering, Hans Georg
- Publisher
- John Wiley and Sons
- Year
- 1992
- Tongue
- English
- Weight
- 989 KB
- Volume
- 1992
- Category
- Article
- ISSN
- 0947-3440
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✦ Synopsis
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 ^1^H NMR time scale [19: Δ__G__^#^~c~ (285 K) = 54.8 kJmol^−1^, 29; Δ__G__^#^~c~ (301 K) = 61.4, Δ__G__^#^~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.