Cleavage of the ring

The thiazolium is not acidic enough for observing directly solvation of the molecule (or an hydrolysis and subsequent cleavage of the ring) (24) without adding a base, as it is the case for benzoxazolium or benzothiazolium. With the same dilution (10 mole liter ), it is necessary to add sodium ethylate to the solution of 2-methyl-4.5-diphenylthiazolium to observe the equilibrium described above. A new band appears in the UV spectrum at 320 nm that is attributed to the ethoxy derivative by analogy to what has been observed with other benzothiazoliums (26),... 

Tetrahydrofurfuryl alcohol is surprisingly resistant to hydrogenolysis under vigorous conditions, however, cleavage of the ring or side chain occurs (126,127). 

Hydantoins can react with electrophiles at both nitrogen atoms and at C-5. The electrophilic carbonyl groups can be attacked by nucleophiles, leading to hydrolysis of the ring or to partial or total reduction of the carbonyl system. Other reactions are possible, including photochemical cleavage of the ring. 

Benzene undergoes substitution, addition, and cleavage of the ring substitution reactions are the most important for iadustrial appHcations. 

Tetracyanoethylene oxide [3189-43-3] (8), oxiranetetracarbonitnle, is the most notable member of the class of oxacyanocarbons (57). It is made by treating TCNE with hydrogen peroxide in acetonitrile. In reactions unprecedented for olefin oxides, it adds to olefins to form 2,2,5,5-tetracyanotetrahydrofuran [3041-31-4] in the case of ethylene, acetylenes, and aromatic hydrocarbons via cleavage of the ring C—C bond. The benzene adduct (9) is 3t ,7t -dihydro-l,l,3,3-phthalantetracarbonitrile [3041-36-9], C22HgN O. 

Attempts to prepare this substance by reduction of dioxotetrahydro-1,3,5-triazine with sodium amalgam,hydroiodic acid, or tin in acetic acid, were accompanied by hydrolytic cleavage of the ring. Only... 

Quatemization of the isoxazole nitrogen atom makes the ring particularly susceptible toward nucleophilic attack there is a certain analogy here with pyridine. The cleavage of the ring proceeds extremely readily in quaternary salts of isoxazole, even occurring by the action of such weak nucleophilic agents as the anions of carboxylic acids. 

Another group of reactions with the predominant cleavage of the ring comprises catalytic hydrogenation of isoxazole derivatives and has been investigated only recently. The most commonly used catalyst has been Raney nickel,but use has sometimes been made of platinum catalysts. Hydrogenolysis of the 0—N bond (172—>173) occurs in isoxazole, its homologs,and their functional derivatives, for example, isoxazole carboxylic acids- and 5-aminoisoxazoles. ... 

The oxidation of oxepins generally results in cleavage of the ring. An exception is the bridged oxepin derivative diethyl 3,6-hexanooxepin-4,5-dicarboxylate which is oxidized with potassium permanganate in the presence of potassium carbonate to give diethyl 8-hydroxy-9-oxo-10-oxabicyclo[6.3.2]trideca-l(ll),12-diene-12,13-dicarboxylate in 39% yield (mp 98 C).130... 

Thiadiazolidines cannot be prepared by reduction of the corresponding thiadiazoles or thiadiazolines because cleavage of the ring would occur in preference to reduction as a consequence of the harsh conditions required. No preparations of 1,2,4-thiadiazolidines have been reported. 

The pyran-2-one ring system 174 (Scheme 68) is a potentially aromatic species, due to the contribution of the pyrylium-2-olate structure 174b, but facile cleavage of the ring by nucleophiles makes it most likely a lactone rather than an aromatic system. 

Polycyclic aromatic hydrocarbons S,L,G Biooxidation and cleavage of the rings... 

Biooxidation by cometabobzation with methane or ammonium Biooxidation after reductive or oxidative biodechlorination Biooxidation after reductive or oxidative biodechlorination Biooxidation after reductive or oxidative biodechlorination Biooxidation and cleavage of the rings... 

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