Oximes from

The reaction of aliphatic and aromatic ketone oximes 97 with a dialkyl carbonate 98 in the presence of K2CO3 at 180-190 °C yields 3-alkyl-4,5-disubstituted-2(3//)-oxazolones 104 in 22-48% yields. Mechanistically, it is proposed that N-alkylation of the initially formed oxime O-carbonate 99 yields 100, which affords the enamine 101 in the presence of base. A [3,3] sigmatropic rearrangement ensues to produce 102, which then cyclizes to 104. In cases where 97 contains two methylene groups in proximity to the C=N bond, one of which is benzylic, the above reaction sequence is regioselective for the benzylic methylene group (Fig. 5.25 Table 5.6, Fig. 5.26).  

TABLE 5.6. 3-ALKYL-4,5-DISUBSTITUTED-2(3H)-OXAZOLONES EROM OXIMES AND DIAEKYECARBONATES  

The intramolecular base-induced ring transformation of 3-phenacyl-2,4-thiazol-idinediones 105 with sodium hydroxide or triethylamine smoothly proceeds to give 5-aryl-2(3/7)-oxazolones 108 (Fig. 5.27). 

Similarly, 6-methyl-3-phenacyl-l,3-oxazine-2,4(3/f)-diones 110 are transformed 

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By similar procedures diazirines were prepared not only from simple aliphatic ketones but also from hydroxyketones and )3-aminoketones (B-67MI50800), and so were a large number of diazirines from steroidal ketones (65JA2665). Permanganate, bromine, chlorine and hypochlorite were used as oxidants. A one-step preparation of diazirines from ketones like 3-nonanone, ammonia and chlorine has been claimed in a patent (66USP3290289). 3,3-Diazirinedicarboxylic acid derivatives like (286) were obtained directly from oxime tosylates by the action of two moles of O-ethoxyamine (81AG(E)200). 

FORSTER Diazo Synthesis Formation ol diazo denvatives from oximes... 

HOCH CAMPBELL Azindtna Synthesis Azindines from oximes or from a haioimines (via azinnes)... 

N2O4, -40 - 0°, CH3CN, THF, CHCI3, CCI4, 10 min, 75-95% yield. This method is also effective for the regeneration of ketones from oximes (45-95% yield). 

Imines are easily reduced and rarely accumulate (62,83). Hydroxylamines are reduced relatively slowly and can be obtained in good yield platinum in acidic media appears to be the preferred system (6,27,54,58,65). Best yields are obtained from oximes of aliphatic carbonyls aromatic oximes give amines. 

Azirines (three-membered cyclic imines) are related to aziridines by a single redox step, and these reagents can therefore function as precursors to aziridines by way of addition reactions. The addition of carbon nucleophiles has been known for some time [52], but has recently undergone a renaissance, attracting the interest of several research groups. The cyclization of 2-(0-tosyl)oximino carbonyl compounds - the Neber reaction [53] - is the oldest known azirine synthesis, and asymmetric variants have been reported. Zwanenburg et ah, for example, prepared nonracemic chiral azirines from oximes of 3-ketoesters, using cinchona alkaloids as catalysts (Scheme 4.37) [54]. 

Since diazoates can be considered to be derived from oximes by substitution of nitrogen for the methine group, Hantzsch (1894) put forward the hypothesis that configurational isomerism was also occurring here. He therefore represented the isomeric diazoates by the structures 7.1 and 7.2, assigning the syn structure (7.1) to the labile diazoate and the anti (7.2) to the stable isomer. Nowadays the description recommended by IUPAC (1979) for such configurational isomers, namely (Z) instead of syn and (E) instead of anti, should be used. 

Formation of cyclohexane fused isoxazolidine 237 from oxime 236 was less selective, providing a mixture of isomers in 51% yield (Eq. 26). On the other hand, citronellal oxime 238 led stereospecifically and in 80% yield to the fused cyclohexane 239 when heated at 190 °C for 5 h. 

Reagent (7) is made by the cc-functlonalisation strategy (p T 191 ). The amino group comes from oxime (12) which can be made by direct nitrosation of malonate,... 

DipolarCycloaddition Reactions. The 1,3-dipolar cyclization of nitrile oxide with dipolarophiles generates structurally important heterocycles. As shown by Lee,139 the reaction can be carried out in an aqueous-organic biphasic system in which the nitrile oxide substrates can be generated from oximes or hydrazones in situ. The method provides a convenient one-pot procedure for generating a variety of heterocyclic products. 

Oximinoimidazolides can be obtained from oximes and CDI with retention of stereochemistry heating in octane or nonane under anhydrous conditions leads to their conversion to imidazolylimidates [123]... 

Pyrazolo[4,3-e][l,2,4]triazine derivatives have been prepared from oximes of 5-aryl- and 5-formyl-l,2,4-triazines <06MI191 >. Novel pyrazolo[5,1 -c][ 1,2,4]triazines incorporating an Af-(2-oxoethyl)phthalimide moiety have been reported <06JCR(S)6>. 

Cages derived from oxime precursors. In the initial synthesis of a cage (Boston Rose, 1968), tris(dimethylglyoximato)cobalt(m) [where dimethylglyoximato (dmgH) = (147)] was reacted with boron trifluoride... 

Oximes are also good substrates for allylsamarium bromide addition.25 The Beckmann rearrangement product 44 was produced from oxime 43 in good yields when the ratio of allysamarium bromide to oximes was more than 3 1 (Equation (8)). This type of product was also obtained when the other allylic organometallic compounds were used. The reaction mechanism was proposed as shown in Scheme 13. 

Two general mechanisms exist for NO release from oximes 1. hydrolysis to hydrox-ylamine followed by hydroxylamine oxidation and 2. direct oxidation and decomposition of the oxime. 

Scheme 7.10 P450 Cytochrome-mediated nitric oxide formation from oximes.

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