Ring destruction

Figure 9. Ring destructive pathway in Brevibacterium strain DO.

If the double bond is connected directly to the three-membered ring, i.e. if the substrate is a dihalo-vinylcyclopropane derivative, a vinylcyclopropylidene to cyclopentadiene isomerization, the so-called Skattebol rearrangement, takes place upon treatment with alkyllithium. Again, this ring-forming step competes with a ring-destruction process leading to allenic hydrocarbons (vinylallenes,... 

The aromatic ring is considered fairly stable at moderate cracking temperatures (350-500°C, 660-930°F). Alkyl aromatics, like the alkyl naphthenes, are more prone to dealkylation than to ring destruction. However, ring destruction of the benzene derivatives occurs above 500°C (930°F), but condensed aromatics may undergo ring destruction at somewhat lower temperatures (450°C, 840°F). 

Some oxygen functional groups do not react with water molecules and behave thus as neutral. Their fundamental structures are shown in Fig. 22. Some carbonyl groups can still react with sodium ethoxide. The ether or xanthene structure is fully inactive in aqueous media. Both neutral structures are believed to occur frequently due to their structural simplicity and the fact that in any oxidation reaction these structures have to occur as intermediates in ring destruction sequences. In quantitative studies where the oxygen content is compared to the sum of all neutralization reactions a significant excess of chemically unreactive oxygen is stated [149, 146] which is accounted for by these neutral functions. 

Fused 1,4-oxazepines 92a have also formed the basis for a ring destruction approach to the eleven-membered ring systems 93 <03H(60)887>. 

The oxidation was also carried out in the presence of lignite coal. The coal mineral did not make any hydroxylation, ring destruction, or other side... 

The reaction of AI with hydrazines follows a complex pathway. Thus 5-amino-isoxazoles react with hydrazine to furnish a mixture of pyrazolone 83, 4-amino-pyrazol-5-one 84, and l-aminopyrazol-5-one 85 (72JHC1219). Bipyrazole 86 and isoxazole ring destruction product 87 were obtained from the reactions of 5-AI with phenylhydrazine (53JPJ387) and semicarbazide (54JPJ138), respectively. This issue seems to require reinvestigation however, these reactions have a complex nature and... 

The fact that the alpha position of the aromatic compounds is the most reactive accounts for the formation of alpha-naplithaquinone to the practical exclusion of the two other naphtliaquinones theoretically possible. This structure is the only comparatively stable configuration before ring destruction. 

Ring destruction with the formation of olefins is shown in reaction (6.38) ... 

Chloro-l,3,5-triazine-2,4-diamine is one of the products of the oxidation of Atrazine with Fenton s reagent. In this case, no hydroxylated triazines can be observed. Trace amounts of carbon dioxide are generated, blit this is assumed to arise from side-chain degradation and not ring destruction.22... 

---