Oxime as intermediates

Cyanogenic glucosides and glucosinolates are related groups of natural plant products, as both are derived from amino acids and have oximes as intermediates. 

HALKIER, B.A., OLSEN, C.E., M0LLER, B.L., The biosynthesis of cyanogenic glucosides in higher plants. The ( )- and (Z)-isomers of p-hydroxyphenylacetaldehyde oxime as intermediates in the biosynthesis of dhurrin in Sorghum bicolor (L.) Moench, J. Biol. Chem., 1989, 264, 19487-19494. 

The industrial e-caprolactam processes with cyclohexanone oxime as intermediate product were recently reviewed . The catalytic gas-phase Beckmann rearrangement has great industrial interest. Since the process proposed by DuPont in 1938 the investigation on catalytic gas-phase Beckmann rearrangement has been investigated, and a large variety of catalysts have been tested for the reaction. 

A catch and release synthesis of tetrazoles and cyclic amidines has been reported making use of solid-supported oximes [94]. When bound sulpho-nyloximes, obtained by reacting polymer supported sulfonyl chloride with oximes, were reacted with nucleophiles, tetrazoles or cychc amidines were obtained (Scheme 19). Alternatively, the use of TMS-CN affords imino nitriles, which have been used as intermediates for the preparation of indoles, 1,2,3,4-tetrahydropyridines, quinoxalines and benzimidazoles. 

Iminomethyl-l-phenyl-l,2,3-triazoles (106, R = CH3) and their structural isomer 4-(iminophenyl)-l-methyl-l,2,3-triazole (108, R = CH3) are interconvertible when they are heated in DMSO at 80°C (Scheme IV.43) (84JHC627 89JHC701 90JHC2021). The equihbrium position is dependent on the electronic properties of the substituent R. When R is alkyl, a benzyl or anisyl compound 108 is favored when R is p-chlorophenyl or p-nitrophenyl, 106 is the favored isomer. The hydrazone 106 R = NH2) or oxime 106 R = OH) do not rearrange. A diazoimine 107 can be postulated as intermediate, a species whose structure is similar to the one proposed... 

The reaction of a-halo ketone oximes 204 with isocyanides leads to formation of 5-aminoisoxazole derivatives 205. The reaction involves formation of nitrosoalkenes as intermediates (equation 89) ". ... 

Enehydroxylamines (102) are invoked as intermediates in the rearrangement of O-vinyl, acyl or aryl oximes (101) (equation 31). Varlamov and coworkers demonstrated that the heterocyclization of ketoximes (103) with acetylene in snper basic medium and in the presence of metal hydroxides proceeds by a [3,3]-sigmatropic rearrangement of the enehydroxylamine 105 of the corresponding oxime vinyl ethers 104 (equation 32). The unreactivity of 3-methyl-2-azabicyclo[3.3.1]nonan-9-one oxime (106) in the same reaction conditions was explained by its inability to isomerize to the corresponding enehydroxylamine. 

The rearrangement was done in similar ways by different caprolactam producers, and the differences can only be found in the purification processes. With the formation of ammonium sulfate being the most important problem for the producers of e-caprolactam, and due to the rising costs of its removal, many companies searched for new possibilities to produce caprolactam. There are some important industrial processes avoiding the cyclohexanone oxime as an intermediate product. 

In conclusion, oximes are produced in nature mostly, but not exclusively, as intermediates of secondary metabolites by enzymic oxidation of an amine function. The oxygenation is mediated by cytochrome P450 complex enzymes and FMOs. However, their formation via condensation of a carbonyl moiety with HA cannot be excluded. 

Over the last 30 years an ever increasing amount of information on the biosynthesis of oxime intermediates in plant metabolism and on interactions of oximes with enzymes has accumulated. Enzymatic reactions that were characterized with respect to oximes as products, substrates or inhibitors are listed in Table 2. 

The principal sources of nitrile oxides are oximes, hydroximoyl halides, and nitromethyl compounds. They have, however, also been identified as intermediates in various other reactions, and these could be used for the preparation of furoxans. In the following paragraphs the most preparatively useful methods are identified. 

The photochemistry of certain A-substituted heterocycles has also been studied. As part of a continuing investigation of the photolysis of A-nitroso compounds in solution, the conversion of A-nitroso-3-azabicyclo[3.2.2]nonane (65) into the oxime (66) by photolysis in the presence of acid was reported.58 N-Nitrosopyrrolidine is similarly transformed. The mechanism of this reaction is said58 to involve elimination of NOH with the formation of an imine as intermediate, and, in fact, in the photolysis of 2-ethyl-A-nitrosopiperidine (67), the tetrahydropyridine (68) is the major product. This mechanism certainly does not operate in the photolysis of iV-nitroso-2-azacyclo-octanone, which can be rationalized on the basis of an intramolecular hydrogen transfer [Eq. (16)].59 Acyclic iV-nitrosoamides behave in a similar fashion to IV-nitrosoamines.60... 

The C=N bonds of imines, oximes and hydrazones can be hydrogenated to form the corresponding amines even under ambient conditions on Pt, Pd, Rh and Raney Ni catalysts in acidic, neutral or basic media (equation 42). The imines, furthermore, are intermediates in the hydrogenation of nitro compounds, nitriles and oximes, and likewise play a key role as intermediates in the reductive amination of carbonyl compounds. 

An iron-catalyzed reaction of an a,P-unsaturated oxime such as 68 with a P-oxo ester also gave pyridine derivatives such as nicotinic acid 69 [99]. Under the reaction conditions (150-160 °C, without solvent) first Michael adducts such as intermediate 70 are presumably formed, which further condense via intermediate 71. This method is not restricted to a centric symmetry in the substitution pattern, which is an advantage compared with the Hantzsch synthesis. Moreover, the method starts with hydroxylamine being two oxidation stages above ammonia therefore, no oxidation in the final stage from dihydro- to pyridine is necessary (Scheme 8.31). 

Oximes can be formed by the iV-hydroxylation of imines and primary amines. Imines have been suggested as intermediates in the formation of oximes from primary amines (Figure 7.6). 

The Griesbaum Coozonolysis allows the preparation of defined, tetrasubsituted ozonides (1,2,4-trioxolanes) by the reaction of O-methyl oximes with a carbonyl compound in the presence of ozone. In contrast to their traditional role as intermediates in oxidative alkene cleavage, 1,2,4-trioxolanes with bulky substituents are isolable and relatively stable compounds. 

Pseudonitrosites and a-nitro ketone oximes were identified as intermediates in this process. This route has since been developed to provide access to mono- and poly-cyclic furoxans from readily-available alkenes and cycloalkenes. Treatment of the alkene with dinitrogen trioxide affords the nitro-nitroso adduct, which is readily isolated as its nitroso dimer (pseudonitrosite) thermal isomerization to the a-nitro ketone oxime, followed by dehydration with cyclization leads to the furoxan (Scheme 19). 

This procedure has been used by Grigg as well as by other authors to synthesize nitrones as intermediates in the preparation of more complex molecules. An example is reported in Scheme 29. The oxime 192 was treated with PhSeBr and... 

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