Einfach überbrückte <i>cis</i>‐Oxa‐ und <i>cis</i>‐Aza‐tris‐σ‐homobenzol‐Systeme; Synthese und 3σ→3π‐Isomerisierung

Oxa-bis-and Oxa-tris-u/n-homobenzenes Syntheses and a + n-IsomerhitionsAddition of diazomethane to the benzene oxides 13a-d yields -under the cis-directing influence of the oxirane oxygen atom often stereoselcciively -the cis-mono- (16% c, d), the cis-bis-(17a-c) and the rr.utis-bis-l-pyrazolines 19b. Photolysis of 16a.c.d. of 17b.c. and of 19b proceeds exclusively to the oxa-bis-a-homohenzenes 20a, c, d and the cislrrans-oxa-tris-a-homobenzenes 24b, c and 30b, respectively. In the case of the diester 17a formation of 24. faces competition by H-migration (20e) upon direct excitation, by transannular C -C-bridging (25a) upon acetone-sensitized excitation. The cis-oxa-bis-a-homobenzenes 20a -e thermally isomerize rapidly -and with the exception of 20c -reversibly to the 4H-oxocines 21a-e, the cis-oxatris-a-homobenzenes 24a-c irreversibly to the 4,7-dihydrooxonines 31a-c. In contrast, the equally strained rrans-isomers 30a, b are thermally much more stable and decompose above 180-200°C in an unspecific way. Kinetic and thermodynamic parameters for these 20 + 2n-and 30 + 3n isomerization reactions as well as the spectroscopic data typical of the oxa-bisand oxa-tris-ain-homobenzene structures are presented, the classification of the transformations 24a -c -, 31a-c as [02s + a2s + a2s]-cycloreversions is discussed.

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Einfach überbrückte cis‐Oxa‐ und cis‐Aza‐tris‐σ‐homobenzol‐Systeme; Synthese und 3σ→3π‐Isomerisierung

Cited by 8 publications

References 10 publications

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Oxa‐bis‐ und Oxa‐tris‐σ/π‐homobenzole Synthesen und σ → π‐Isomerisierungen

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