2- und 6-Methyl-8-oxa-bicyclo[5.1.0]octa-2,4-dien. Über den Verlauf der Ringöffnung bei der Thermolyse in der Gasphase
✍ Scribed by Peter Schiess; Peter Fünfschilling
- Publisher
- John Wiley and Sons
- Year
- 1976
- Tongue
- German
- Weight
- 489 KB
- Volume
- 59
- Category
- Article
- ISSN
- 0018-019X
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✦ Synopsis
2‐ and 6‐Methyl‐8‐oxabicyclo[5.1.0]octa‐2,4‐diene. Ring cleavage reaction upon flash pyrolysis.
6‐Methyl‐8‐oxa‐bicyclo[5.1.0]‐octa‐2,4‐diene (1 a) has been subjected to flash pyrolysis with the aim to elucidate the course of its thermal ring cleavage reaction. At 100° equilibrium between 1a (6%) and its 2‐methylisomer 1 b (94%) is reached through a remarkably facile [1,5]‐hydrogen shift. Above 200° methyl‐bicyclo[3.2.0]hept‐2‐ene‐7‐ones (3), dihydrotolualdehydes 5 and 6 and their aromatization products 7 are isolated. It is concluded that these products arise from 2‐, 3‐ and 7‐methyl‐hepta‐2,4,6‐trienal 2a, 2b and 2f which are formed from 1a/1b by path C and D in Scheme 2 involving a formal [2+6]‐cycloreversion reaction of 1a/1b and of its valence isomer, 1,2‐homooxepine 11. Two alternate pathways, A and B, involving cleavage of the C,C bond common to both rings in 1 concomitant or followed by hydrogen shifts are not operative.