2 benzonitrile, rearrangement

The chemical behaviour of the mesoionic pyrazole (459) has been studied by Boyd et al (74JCS(P1)1028). Protonation and alkylation take place on the exocyclic nitrogen atom and a thermal rearrangement of a methyl group is observed when (459) is boiled in benzonitrile for several hours giving (460). 

Unfortunately, appearance energy measnrements become more complicated with larger substrates, where the cations are more prone to rearrangement during ionization. Eor example, numerous attempts have been made to measnre the energy for formation of o-benzyne cation, CgH4+ by using benzonitrile as a precursor (Eq. 5.6). 

Compound 384 derived from the reaction of two molecules of benzonitrile oxide (341) with one of BCP (3). Its formation can be explained with the cycloaddition of a second molecule of 341 to the isoxazoline Ml to give the isoxazolidine M5, which undergoes a thermal rearrangement to 384 (Scheme 54). 

Methylenecyclohexane oxide has been prepared by the oxidation of methylenecyclohexane with benzonitrile-hydrogen peroxide or with peracetic acid by treatment of 1-chlorocyclo-hexylmethanol with aqueous potassium hydroxide and by the reaction of dimethylsulfonium methylide with cyclohexanone. This reaction illustrates a general method for the conversion of ketones and aldehydes into oxiranes using the methylene-transfer reagent dimethyloxosulfonium methylide. The yields of oxiranes are usually high, and the crude products, in most cases, are of sufficient purity to be used in subsequent reactions (e.g., rearrangement to aldehydes) without further purification. 

It was suggested that benzonitrile (28) is formed from the Zf-conformer (31) in a Grob-type fragmentation <69AG543> and the isothiocyanate (27) is formed from the Z-conformer (32) in a Curtius rearrangement. 

An alternative approach to form a cyclobutylmethyl cation from a vinylcyclobutane uses organopalladium chemistry.25 For example, exposure of l-methyl-7-vinylbicyclo[4.2.0]octan-7-ol to 5mol% of bis(benzonitrile)palladium dichloride and 1,4-benzoquinone in boiling tetrahydrofuran gave the desired 6,9-dimcthylbicyclo[4.3.0]non-l(9)-en-8-one (7) in 67% yield.25 The mechanistic pathway of this transformation is shown. Further examples, showing the utility of the reaction, are shown for the rearrangement to 8.23... 

Note. Both the rearrangement In t-Butanol) and the double bond isomerization of (114) In Benzene) are quenched in a diffusion-controlled process by suitable triplet acceptors (e.g., naphthalene or 2,5-dimethylhexa-2,4-diene). The rearrangement (114) - (118) + (120) is also observed on irradiation in pyridine, the double bond isomerization (114) -> (122) in trifluorotoluene. In benzonitrile both types of processes occur in parallel with similar efficiencies. In hydrogen-donating solvents (toluene, ether, dioxane, ethanol), hydrogen abstraction processes prevail [toluene (114) - (123)]. 

When the reaction is carried out in boiling DMSO, no significant gain in the yield of benzamide (30%) is observed. Since under these conditions the primary dehydration of aldoximes is evident, the formation of benzamide is most likely to result from hydration of the intermediate benzonitrile rather than by the Beckmann rearrangement scheme. 

A rearrangement intermediate, protonated 4-hydroxy-3-(2-imino-propyl)benzonitrile (163) proved to be isolable (67TL2867). Analogously, from l-alkyl-4-nitrophenyloximinopiperidine (165) in ethanolic HC1, 2-methyl-6-nitro-l,2,3,4-tetrahydrobenzofuro[3,2-c]pyridine (167) was ob-... 

Similar rearrangements are observed with the nitrogen analogues l7). N, N-dimethylaniline isomerizes to ortho- and para-N-methyltoluidines and is partly fragmented to N-methylaniline, benzonitrile and methyleneaniline. When N-methylaniline is the starting material, the main products are toluidines and aniline. 

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