Oximes ring opening

A -Pyrazolines and A -isoxazolines (302 Z = NH, O) are cyclic hydrazones and oximes, respectively. 2-Pyrazolines are quaternized at the 2-position (306 307) (64AHC(. ll). 1,3,4-Oxadiazolines (e.g. 308) are very easily ring-opened (66AHCi7 183). 

Base treatment of isoxazolin-5-ones produced the cyano aeids (70JOC3130), while ethoxide treatment of iV-alkyl-A -5-ones gave, after H2O treatment, a malonyl monoamide monoester (69JOC2981) and not an oximoacrylate as was reported earlier (Scheme 61) (23HCA102). The base treatment of a 4-bromoisoxazolin-5-one generated a ring-opened oxime (Scheme 62) (79JOC873). 

In a number of cases the intermediate oxime has been isolated in the reaction of hydroxylamine and /3-keto esters. The reaction of ethyl acetoacetate with hydroxylamine generated an oxime which cyclized on base treatment (Scheme 144) (70MI41600). Likewise, treatment of an analogous amide with hydroxylamine generated a ring opened material which cyclized on treatment with HCl (Scheme 144) (67T831). The presence of a minor contaminant in the standard reaction of ethyl acetoacetate with hydroxylamine was discovered and identified as an isomeric isoxazolin-3-one. The mechanism of product formation has been discussed (70BSF2685). 

If the carbonyl grou]) in the 3-position of N-methylisatin or tlii-ana])hthencquinone is blocked by formation of an oxime (cf. 112), A -methylation of the oxime group occurs instead of ring expansion on reaction with diazomethane. In methanol, thianaphthenequinone oxime iV-mcthyl ether (113) then undergoes ring opening catalyzed by diazoniethane (113 114). 

Bromination of 1,2-benzisoxazole 2-oxides (36) caused ring-opening to give dibromo-oximes (37), a scenario that was also followed in iodination, and contrasting with the nitration behavior, which led to 6-substitution [87JCS(P 1)695] (Scheme 23). 

Iodofurazans react with nucleophilic reagents differently from other halo- and nitrofurazans. For instance, treatment of 3-amino-4-iodofurazan 25 with sodium ethoxide at room temperature did not yield the expected ethoxy derivative 26 but led to the ring-open product, that is, the sodium salt of a-amino-a-hydroxyimino- acetonitrile 27 (Scheme 9). Acidification of salt 27 gave cyano oxime 28 <2004RCB1124>. 

Machiguchi, Nozoe and coworkers have very recently observed that in contrast to chemical reactivity of tropones, the tosylate of tropone oxime undergoes a facile ring-opening to 6-substituted (Z,Z,Z)-1,3,5-hexatriene nitriles on reaction with various nucleophiles305. For example, reaction of phenyl lithium results in the corresponding hexatriene carbonitrile (equation 183). 

On treatment with a base such as NaOMe or even LLAIH4, mono-cycloadducts of mesitonitrile oxide and polycyclic aromatic hydrocarbons have been cleaved to yield the corresponding oximes, which are oxidized to ketones by the Dess— Martin method. The same ketones have been obtained by reductive ring opening of the mono-cycloadducts with Raney Ni (438). 

Wordy Over the past few years, we have encountered numerous examples of water as the perfect solvent. We observed this first in osmium-catalyzed dihydroxylation reactions and also in nucleophilic ring-opening reactions of epoxides. We also observed this in cycloaddition reactions and in most oxime ether, hydrazone, and aromatic heterocycle condensation processes.Finally, we observed it in formation reactions of an amide from a primary amine and an acid chloride using aqueous Schotten-Baumann conditions. ... 

New azacyclic diterpenoid compounds were also prepared in good yields by ring expansion and only one isomer of the lactam 363 product was obtained (equation 142). However, when the oxime was tosylated, a nitrile compound resulting from ring opening was obtained in good yield (72%) as a result of the Beckmann degradation reaction. 

In general, the reaction of unsaturated 5(4//)-oxazolones 497 with nitrogen nucleophiles effects ring opening to give the corresponding unsaturated acylamino amides 498 (Scheme 7.158). Depending on the nucleophile, for example, amines, hydrazines, oximes, and so on, the products obtained can be cyclized and this process allows the synthesis of a wide variety of new heterocyclic compounds. 

Photolysis of 63 in methanol led to a ring-opened methoxy oxime, from attack of the solvent on the corresponding 92.71... 

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