Oximes isomers

Methional reacts with PFBOA to form two oxime isomers. 

A mixture of benzothieno[2,3-d]- and benzothieno[3,2-d]-azocines (194 and 195) is produced in 43% overall yield by the Beckmann rearrangement of the mixture of oxime isomers 193 with phosphorus pentoxide in dichloromethane (90JCS(P1)1083 Scheme 53). 

The resulting estimated average polarizabilities for the hydroxylamines, oximes and hydroxamic acids that we have discussed are given in Table 8. (It should be noted that Miller s approach does not distinguish between oxime isomers.) As anticipated from the correlation between average polarizability and volume (equation 10), the a in Table 8 increase with molecular size. 

The formation of a very electrophilic intermediate 258 from 256 and 257 is proposed (equation 78). The hydroxyl group of the oxime adds to 259, giving a reactive cationic species 260 that rearranges and affords the nitrile 261 (in the case of aldoxime, equation 79), or the amide 262 upon hydrolytic workup (equation 80). The conversion of 260 to the nitrilium ion should occur through a concerted [1,2]-intramolecular shift. This procedure can be applied in the conversion of aldoximes to nitriles. It was observed that the stereochemistry of the ketoximes has little effect on the reaction, this fact being explained by the E-Z isomerization of the oxime isomers under the reaction conditions. 

Another chiral synthesis of the azepine nucleus of Balanol (397) was developed by Wu and Jacobsen, once again converting a cyclohexanone oxime tosylates 399 to a seven-membered lactam (equation 162). The use of a mixture of oxime isomers did not cause... 

Selected computed structural data on the three tautomeric forms of protonated NNtM, DNNtM and NDNtM are depicted in Figure 33. Only the most stable oxime isomers are presented. As long as only two functional groups are attached to the central methanide carbon, the entire molecule remains planar due to resonance stabilization, whereas introduction of a third group, either NO or NO2, results in rotation of at least one group, preferably the nitro group. Flowever, the CN3 moiety in the nonplanar species remains... 

Photoaddition of nitrosamines (carcinogens) to alkenes in the presence of oxygen gives quite good yields of 1 1 adducts as their oxime isomers.Nitronium tetiafluoroborate in acetonitrile adds to alkenes in Maricovnikov manner, giving acetamidonitro compounds, 38-84% (from arylalkenes) or... 

Intramolecular radical capture was observed when a 19-CH2 radical (17) was generated by irradiation of corticosterone 21-acetate ii nitrite (16 [14]. In addition to the i8-oxime (20 21% yield), the 4-oximinO 5j5,19-cyclo-steroids (19 two oxime isomers) were major products (45%). These arose through sr-electron attack on the 19-CH2 radical to form the... 

A regiospecific synthesis of A -substituted (aminopyridinyl)imidazole 1286 started with ketone 1282 (cf. Section 4.02.9.2(i)). a-Oximination of ketone 1282 with isoamyl nitrite under basic condition provides oxime isomers 1283. Both as- and /ra t-oximes 1283 participate in the cyclization process when treated with l,3,5-trimethyl-l,3,5-triazinane, leading to imidazole iV-oxide 1284 that is then reduced with 2,2,4,4-treta-methyl-cyclobutane-l,3-dithione to give 1285 (Scheme 326) <2003JOC4527, 1999JME2180> (see also Section 4.02.9.3(i)). 

In addition to providing hydroxy (alkoxy) amines, the reaction of oximes" or oxime ethers " with or-ganometallic reagents can generate additional products. The propensity for proton abstraction a to the carbon-nitrogen double bond, the existence of mixtures of ( )- and (Z)-oxime isomers, the lability of the nitrogen-oxygen bond coupled with the poor oxime reactivity all contribute to the variability of this reaction. 

Reaction with (172) and other aldoximes may require oxime activation, which can be achieved with the addition of 1 equiv. of BF3-OEt2." " Yields in the addition of organometallic reagents to substituted aldoximes are modest and are a function of the isomeric composition of the oxime ethers, as the (Z)-oxime isomers are reported to preferentially react with organolithium reagents (entries 1 and 2, Table 13). ° The reaction has been employed for the preparation of 6-aminoalkyl-substituted pencillins (entry 3, Table 13)."° Cyclic oxime ether additions have also been evaluated (entries 4 and 5, Table 13). ° With the lability of the nitrogen-oxygen bond, addition to S-substituted isoxazolines provides a potential avenue for stereospecific synthesis of substituted 3-aminoalcohols (entry 5, Table 13). 

The archival enthalpies of combustion for three nitrosonaphthol (naphthoquinone oxime) isomers are from a rather contemporary paper , while the earlier ones (reported... 

A further useful preparation consists in photoisomerization of oximes. As had often been supposed, oximes, especially a,) -unsaturated ones, isomerize with formation of oxaziridines 36 was formed in 50% yield from benzylideneacetone oxime on irradiation, and 37 could be prepared from both Z and E oxime isomers. 

Additional insight into the competition between the various cyclic transition states is provided by a recent study of the reactions of crotylboronates (22) and (23) with the two isomers of oxime silyl ether (24 Scheme 8). The stereoselectivities of these reactions were found to be independent of the geometry of (24), both isomers of which were shown to be conflgurationally stable under the reaction conditions. Since the oxime stereochemistry defines the site of coordination to the boron atom, it seems likely that the (Z)-oxime isomer reacts preferentially through the chair-like transition state (28), while the ( )-oxime reactions proceed preferentially via boat-like transition state (27). Evidently, the chair-like arrangement... 

Oxime (Isomer) Desazabrucidine 133-134 (CHaOH) Yellow plates 228... 

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