Ring scission

Ring Scission.—Aminolysis of 5-arylidene-3-phenylthiazolidine-2,4-diones 

The hydrolytic ring-opening of suitable thiazolidine derivatives in 20% aqueous acetonitrile catalysed by mercuric chloride provides a route to 

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The kinetics of this type of polymerization are the same as for simple condensation for this reason, the use of the term polycondensation is perhaps more appropriate. Unless kinetic evidence suggests otherwise, polymerizations involving the formation of chain polymers from cyclic compounds, following ring scission, are classed as condensation polymerizations. Some important con-... 

Thermal decompositions of di-Z fZ-cycloalkyl peroxides produce Z fZ-cycloalkoxy radicals which undergo ring -scission to give acycHc ketones,diketones, and other products (44) ... 

Oxazoles give acylamino ketones (158) by acid-catalyzed ring scission, although they are somewhat more stable than furans. The oxazole ring is also moderately stable to alkali (74AHCU7)99) as expected, reaction with hydroxide ions is facilitated by electron-with-drawing substituents and fused benzene rings. 

Oxygen-containing azoles are readily reduced, usually with ring scission. Only acyclic products have been reported from the reductions with complex metal hydrides of oxazoles (e.g. 209 210), isoxazoles (e.g. 211 212), benzoxazoles (e.g. 213 214) and benzoxazolinones (e.g. 215, 216->214). Reductions of 1,2,4-oxadiazoles always involve ring scission. Lithium aluminum hydride breaks the C—O bond in the ring Scheme 19) 76AHC(20)65>. 

Similarly, von Braun and Schmitz found that A-benzoylconiine, on distillation with phosphorus pentachloride, underwent ring scission with elimination of the nitrogen atom and formation of the dichlorooctane, CH2CI. (CH2)3. CHCl. CHa. CH. CH3. 

Ring contraction to 3 6 fused, e.g. 17, rather than 4 5 fused ring systems, accompanied by phenylation, occurs on treating l//-azepine-l-carboxylates, e.g. 16. with pailadium(II) acetate in benzene solution.242 In solvents other than benzene, ring-scission products result (see Section... 

Kassahun, K. Pearson, P. G. Tang, W. McIntosh, I. Leung, K. Elmore, C. Dean, D. Wang, R. Doss, G. Baillie, T. A. Studies on the metabolism of troglitazone to reactive intermediates in vitro and in vivo. Evidence for novel biotransformation pathways involving quinone methide formation and thiazolidinedione ring scission. Chem. Res. Toxicol. 2001, 14, 62-70. 

The use of phenylpiperidinols rather than the meperidine-related piperidines as the basic component in antidiarrheal compounds results in retention of activity. The fact that the base is not directly related to a narcotic presumably leads to greater selectivity of action on the gut. Ring scission of butyrolactone 98 (obtainable by alkylation of a diphenylacetate ester with ethylene oxide) with hydrogen bromide gives the bromo acid 99. This is then converted to the dimethylamide by successive treatment with thionyl chloride and dimethylamine. 

Boron trifluoride in aqueous dioxane was being evaporated with nitric acid treatment (3 portions) for analysis. Final addition of perchloric acid with continued heating led to an explosion while unattended. Ring scission of dioxane to diethylene glycol and formation of diethylene glycol nitrate and/or perchlorate may have been involved. 

Unstirred mixtures of sulfinyl chloride and tetrahydrofuran may react extremely exothermally and with gas evolution when heated to 60°C, the products of ring-scission being bis(4-chlorobutyl) ether, 1,4-dichlorobutane and sulfur dioxide. Some ratios of the two reactants enhance the tendency, and relatively confined mixtures may explode. Sufficient heat to initiate the reaction may arise from selfmixing of the layered liquids, the chloride being twice as dense as THF. 

Most investigations of the mechanism of ring scission have been made by studying the action of alkali on ethylene oxide anhydro sugars. These investigations will now be reviewed. 

An approach to derivatives of polyhydroxylated cyclooctane from D-ribose was proposed by Paquette.47 The crucial step involved a ring scission induced with zirconocene (Fig. 32). 

The formation of anhydro-glycitols and the investigation of their structure and that of the products of their ring scission provide fascinating problems in structural organic chemistry and this structural aspect of the chemistry of anhydrides of polyhydric alcohols forms the mainstay of this article. 

Overend, Montgomery and Wiggins60 noted an interesting reaction between isomannide and phosphorus tribromide. None of the expected 2,5-dibromo-2,5-didesoxy-l,4 3,6-dianhydro-D-mannitol (LIX) was isolated instead, ring scission took place and l,6-dibromo-l,6-didesoxy-D-mannitol (LX) was formed. Since no such ring scission occurs with hydrobromic acid under similar conditions it was probable that the phosphorus tribromide itself had effected the ring breakdown by direct attack on the oxide rings. 

The 5,6-anhydro derivatives of D-sorbitol and D-mannitol41 69 behave in like manner to the 5,6-anhydro-l,2-isopropylidene-D-glucofuranose of Freudenberg and coworkers.70 Thus, 5,6-anhydro-l,3 2,4-diethyli-dene-D-sorbitol (LXXXV) readily suffers ring scission with ammonia to give 6-amino 6-desoxy-l,3 2,4-diethylidene-D-sorbitol (LXXXVI)69 or with sodium methoxide to form 6-methyl-l,3 2,4-diethylidene-D-sorbitol.42 l,2 3,4-Diisopropylidene-5,6-anhydro-D-mannitol gives rise... 

Studies on the metabolism of troglitazone to reactive intermediates in vitro and in vivo. Evidence for novel biotransformation pathways involving quinone methide formation and thiazolidinedione ring scission. Chemical Research in Toxicology, 14 (1), 62—70. 

The high-pressure reaction of A-methylpiperidine with 4-chloronitrobenzene yields A-(4-nitrophenyl)piperidine (equation 117) 2-chloronitrobenzene and chloro-2,4-dinitrobenzene behave analogously. A-Methylpyrrolidine and 4-chloronitrobenzene afford a mixture of A-(4-nitrophenyl)pyrrolidine and the product 342 of ring scission (equation 118)385. 

The kinetics and mechanism of pyrrole pyrolysis were investigated by ab initio quantum-chemical calculations. It was revealed that pyrrole undergoes tautomerization to form 2H- and 37/-pyrroles prior to any thermal decomposition. It has been shown that the major product, HCN, arises from a hydrogen migration in pyrrole to form a cyclic carbene with the NH bond intact. Ring scission of the carbene leads to an allenic imine of HCN and propyne which is the lowest energy pathway. The 277-pyrrole... 

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