2.5- Cyclohexadienone oximes Cyclohexadienones

Substrates with doubly bonded nitrogen-atom functionalities, e.g. the C=N-R (imino, oxime) group, are usually cleaved by dioxirane to give the corresponding carbonyl product" . A particular case represents the DMD oxidation of the nitronate ions, generated from nitroalkanes" or nitroarenes. For example, the nitronate anion 16 (equation 13) affords initially the cyclohexadienone on oxidation with DMD, which subsequently tau-tomerizes to the phenol as the final product. An exception is the DMD oxidation of an... 

Ramamurthy et al. have examined enantioselective and diastereoselective ODPM rearrangements of cyclohexadienone and naphthalenone derivatives within MY zeolites, where M is an alkali ion [38, 39]. For example, in Scheme 4.27, in NaY in the presence of several chiral inductors such as ephedrine, pseudoephedrine, and camphorquinone-3-oxime, an enantioselective ODPM rearrangement of 65 and 66 took place to afford 68 in 30% ee yield. In the frame of the chiral auxiliary approach, the compound 67 linked to (S)-ephedrine was irradiated within NaY to give 68 in moderate diastereoselective excess (de) (59%). Interestingly, the reaction media of KY, RbY, and CsY reverse the diastereoselectivities. The cation-dependent diastereo-meric switch has been discussed with respect to the N- or O-functional group in 67 [39]. Recently, Arumugan reported that the irradiation of naphthalenones 65 linked chiral auxiliaries (R3 = COO(—)-Ment or (S)-NHCH(Me)Ph) in Li+ or Na + Nafion resulted in chiral products ( 14% de) [40],... 

Sterically hindered phenols react with nitric oxide under basic conditions to give either cyclohexadienone diazenium diolates or oximates. Phenols with 2,6-di-tert-butyl and 4-methyl (butylated hydroxytoluene, BHT), 4-ethyl or 4-methoxymethyl substituents yield the corresponding 2,6-di-tert-butyl-2,5-cyclohexadienone-4-alkyl-4-diazenium diolate salts (equation 58)". ... 

Silver oxide Nitrobenzenes from 2,5-cyclohexadienone oximes with preferential C-de-r rr-butylation Ag O <-... 

Cyanomethylene-2,5-cyclohexadienone oximes from ar. nitro compounds... 

Isonitrile 19 was detected in ultraviolet (UV) and infrared (IR) studies at low temperatures. They speculated that azirine intermediate 21 may precede the formation of 19 and, indeed, LFP studies on 18 performed by Richard and co-workers allowed observation of an intermediate which was assigned to 21 on the basis of the similarity of its UV absorption spectra to that of the cyclohexadienone chro-mophore. The reaction was not quenchable by piperylene and is presumed to occur via the singlet manifold. The authors did not put forward a mechanism for the formation of 21, although it may be formed by initial ESIPT from the phenol to the cyano group to give tautomer 22, which can then rearrange to give 21. Similar products (substituted benzoxazoles) were observed via presumed initial ESIPT in structurally related o-hydroxy substituted aromatic oximes and oxime ethers. ... 

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