Oximes elimination reactions

Photolysis of the oxime group in the pyrazole miticide fenpyroximate resulted in the formation of two principal transformation products the nitrile via an elimination reaction and the aldehyde by hydrolysis (Swanson et al. 1995). 

After the elimination of water, the carbonyl oxygen has been substituted for the =NOH group in the final product. This compound is called an oxime. This reaction can also be performed with base catalysis. This type of tetrahedral substitution reaction may be performed with many nitrogen derivatives, such as hydrazine, NH2NH2. Write down the product that is formed from the reaction of... 

Oximes from alcohols. Primary and secondary alcohols are directly converted into oximes on reaction with A-tosyUiydroxylamine TBS ether in a conventional Mitsunobu reaction, with succeeding elimination of TsH and desilylation by heating with CsF in MeCN. The reaction conditions are sufficiently mild and many functional groups are left unscathed. 

Anti See torsion angle syn, anti. Also used to describe antarafacial addition or elimination reactions [74]. Formerly used to describe the configuration of azomethines such as oximes and hydrazones (See E, Z). 

While most reducing agents lead to the expected bornylamines as products of the reduction of camphor oxime (see above), diisobutylaluminum hydride is a notable exception, as a ring-enlarged amine, (1/ ,47 )-1.8,8-trimethyl-2-azabicyclo[3.2.1]octane (67) is obtained in high yield when starting with the oxime of (+ )-camphor16, It has been used as the lithium salt in enantioselective deprotonation and elimination reactions (Section C.). 

See Chapter 2 for a discussion of anti- and synperiplanar requirements in E2 elimination reactions.) In each diastereomeric diazonium ion in the example, the bond that is antiperiplanar to the C—N2 bond migrates selectively. (Draw a Newman projection or make a model if you have trouble seeing this.) The same phenomenon is observed in the Beckmann rearrangement, in which an oxime is converted into an amide after a 1,2-alkyl shift and addition of H2O. The group that is trans to the OH group (i.e., antiperiplanar) shifts selectively. 

FIGURE 2. The Jencks-More O Ferrall energy surface diagram for the elimination reaction of (E)-0-aryl benzaldehyde oximes promoted by OH in 60% aqueous DMSO... 

Purpose. The aromatic nitrile, piperonylonitrile, is obtained via a multistep synthesis that does not depend on potentially dangerous diazonium intermediates. The selective oxidation of a primary alcohol to an aldehyde is investigated. You will explore, at the same time, the use of resin-bound reagents that simplify the isolation of products.You will carry out a novel elimination reaction using an oxime to obtain the target nitrile. 

Treatment of the oxime intermediate with alcoholic KOH causes an elimination reaction that yields the target nitrile product, piperonylonitrile ... 

Purpose. You wiU carry out the second step in the sequence of synthetic reactions leading to an aromatic nitrile, piperonylonitrile.You wiU prepare a specific oxime derivative of the aldehyde obtained in Experiment [El].This oxime derivative is derivatized on oxygen so as to allow the oxygen to function as a good leaving group, which wUl allow an elimination reaction to form a nitrile in the final step of the synthetic sequence leading to piperonylonitrile. 

The preparation of this oxime is the second step in this sequence to obtain the aromatic nitrile target molecule. In Experiment [E2] you are going to convert the aromatic aldehyde formed in Experiment [El] into an 0-phenylated oxime, which on treatment with base in Experiment [E3] yields the desired nitrile via an elimination reaction. Oxime formation is also involved in the well-known Beckmann rearrangement (see Experiment [6adv])/ which is used for the synthesis of amides. 

Purpose. Tbe piperonal 0-(2,4-dinitropbenyl)oxime intermediate, prepared in the previous experiment (Experiment [E2]), is converted into the target molecule, piperonylonitrile. This completes the set of Sequence E reactions for the conversion of a substituted benzyl alcohol into an aromatic nitrile. You will investigate the use of a novel elimination reaction to convert an oxime derivative to a nitrile. 

In the present reaction, treatment of an 0-phenylated oxime with base yields the nitrile by an elimination reaction. The role of the dinitrophenyl group is to enhance the oxime oxygen to function as a good leaving group. Thus, the phenoxy system departs as the conjugate base of the relatively acidic 2,4-dinitrophenol. The mechanistic sequence is outlined below ... 

Since the base-promoted elimination reactions of E- and Z-benzoyloximes 1 and 2 exhibit second-order kinetics (first order in base and oxime), the kinetic law would have the form of Eq. 12.1 ... 

SET-sensitized irradiations of 39c, 39d, and 40b also afforded, in addition to the corresponding cyclopropanes, the nitriles 53a, 53b, and 54, respectively, resulting from ehmination of acetic acid. This elimination reaction cannot be considered a thermal process because it does not occur in the triplet-sensitized irradiation of oxime acetates. The mechanism shown in Scheme 13 for compound 39d is proposed to account for the formation of these nitriles. It involves the generation of a radical-cation centered on the CN double bond 55, followed by elimination of acetic acid to afford the radical-cation 56, which yields the nitrile 53b by back electron transfer (Scheme 13). 

Diels-Alder reaction of 2-bromoacrolein and 5-[(ben2yloxy)meth5i]cyclopentadiene in the presence of 5 mol % of the catalyst (35) afforded the adduct (36) in 83—85% yield, 95 5 exo/endo ratio, and greater than 96 4 enantioselectivity. Treatment of the aldehyde (36) with aqueous hydroxylamine, led to oxime formation and bromide solvolysis. Tosylation and elimination to the cyanohydrin followed by basic hydrolysis gave (24). 

The pharmacological versatility of this general substitution strategy is further illustrated by diazonium coupling of 14 with 2-nitrobenzenediazonium chloride to produce biarylal-dehyde 18. Formation of the oxime with hydroxylamine is followed by dehydration to the nitrile. Reaction with anhydrous methanolic hydrogen chloride leads to imino ether and addition-elimination of ammonia leads to the antidepressant amid-ine, nitrafudam (20). ... 

The reaction is thought to occur by nucleophilic addition of the N-alkyl-hydroxylamine to the keto acid as if forming an oxime (Section 19.8), followed by decarboxylation and elimination of wrater. Show the mechanism. 

It is believed that SCR by hydrocarbons is an important way for elimination of nitrogen oxide emissions from diesel and lean-burn engines. Gerlach etal. [115] studied by infrared in batch condition the mechanism of the reaction between nitrogen dioxide and propene over acidic mordenites. The aim of their work was to elucidate the relevance of adsorbed N-containing species for the F>cNOx reaction to propose a mechanism. Infrared experiments showed that nitrosonium ions (NO+) are formed upon reaction between NO, NOz and the Brpnsted acid sites of H—MOR and that this species is highly reactive towards propene, forming propenal oxime at 120°C. At temperatures above 170°C, the propenal oxime is dehydrated to acrylonitrile. A mechanism is proposed to explain the acrylonitrile formation. The nitrile can further be hydrolysed to yield... 

The chemistry of O-acyl derivatives of trinitromethane was studied in more detail. By analogy with O-silyl ethers of trinitromethane, for intermediate (120) (Scheme 3.103, Eq. 1) it was suggested (222a) that the reaction involves elimination of acetyl nitrate to form the very unstable N-oxide A, which adds acetyl chloride to give derivative (121). Saponification of the latter affords isolable oxime (122). 

For example, BENA (336) can be detected only by NMR spectra of the reaction mixture. At higher temperature, this nitroso acetal is transformed in solution into a mixture of oxime (334a) (the rearrangement product) and enoxime (337) (the elimination product of trimethylsilanol) (469) (Scheme 3.198). 

N,C Elimination The reactions of standard BENAs with bases were considered in the previous section. As a rule, these reactions proceed at the silicon atom of the nitroso acetal fragment. However, if a EWG-group is adjacent to the y-C atom of BENA, the ally lie proton (Hy) at this carbon atom becomes so labile that it can be eliminated already in the presence of bases at room temperature (504), thus initiating the transformation of such BENA into conjugated en oximes (Scheme 3.227). 

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