Vinyl quinone

Zanarotti, A. Synthesis and reactivity of vinyl quinone methides. J. Org. Chem. 1985, 50, 941-945. 

Zanarotti, A. Preparation and reactivity of 2,6-dimethoxy-4-allylidene-2,5-cyclohexa-dien-l-one (vinyl quinone methide). A novel synthesis of sinapyl alcohol. Tetrahedron Lett, 1982, 23, 3815-3818. 

The vinyl quinones (248) undergo different photochemistry. When these are irradiated a quantitative yield of dimers (249) is obtained. A report has been published dealing with the photocyclisation reactions of benzoyl benzo-1,4-quinones. A laser flash study at 248 nm of vitamin K3 has been reported and... 

A direct access to the synthesis of dihydroquinolines (eq 22) was developed. The vinyl quinone mono- or di-SES-imide, accessible by oxidation of the corresponding aminophenol or phenylenediamine, undergoes a thermal 67r-electrocyclization in the presence of a polar nonprotic additive. Dehydrodesulfinylation of the SES group will lead to the quinoline. The vinyl quinone monoimide substrate can also provide the protected indole by photochemical cyclization. 

Ldbennaim, F., Mayer, P., and Trauner, D. (2010) Biomimetic synthesis of (—)-pycnanthuquinone C through the Diels-Alder reaction of a vinyl quinone. Angew. Chem. Int. Ed., 49, 6199-6202. 

Uses. About 35% of the isophthahc acid is used to prepare unsaturated polyester resins. These are condensation products of isophthahc acid, an unsaturated dibasic acid, most likely maleic anhydride, and a glycol such as propylene glycol. The polymer is dissolved in an inhibited vinyl monomer, usually styrene with a quinone inhibitor. When this viscous hquid is treated with a catalyst, heat or free-radical initiation causes cross-linking and sohdification. A range of properties is possible depending on the reactants used and their ratios (97). 

Quinone Methides. The reaction between aldehydes and alkylphenols can also be base-cataly2ed. Under mild conditions, 2,6-DTBP reacts with formaldehyde in the presence of a base to produce the methylol derivative (22) which reacts further with base to eliminate a molecule of water and form a reactive intermediate, the quinone methide (23). Quinone methides undergo a broad array of transformations by way of addition reactions. These molecules ate conjugated homologues of vinyl ketones, but are more reactive because of the driving force associated with rearomatization after addition. An example of this type of addition is between the quinone methide and methanol to produce the substituted ben2yl methyl ether (24). 

Hydrogen bromide adds to acetylene to form vinyl bromide or ethyHdene bromide, depending on stoichiometry. The acid cleaves acycHc and cycHc ethers. It adds to the cyclopropane group by ring-opening. Additions to quinones afford bromohydroquinones. Hydrobromic acid and aldehydes can be used to introduce bromoalkyl groups into various molecules. For example, reaction with formaldehyde and an alcohol produces a bromomethyl ether. Bromomethylation of aromatic nuclei can be carried out with formaldehyde and hydrobromic acid (6). 

One potentially important example of CIDNP in products resulting from a radical pair formed by electron transfer involves a quinone, anthraquinone j5-sulphonic acid (23). When irradiated in the presence of the cis-syn dimer of 1,3-dimethylthymine (24), enhanced absorption due to vinylic protons and emission from the allylic methyls of the monomer (25) produced can be observed (Roth and Lamola, 1972). The phase of the polarizations fits Kaptein s rules for intermediate X... 

FIGURE 6.9 Confirmed heterolytic formation pathway for 5a-a-tocopheryl benzoate (11) without involvement of 5a-C-centered radicals and its proof by trapping of ortho-quinone methide 3 with ethyl vinyl ether to pyranochroman 13. Shown are the major products of the reaction of a-tocopherol (1) with dihenzoyl peroxide. 

Hemmingson, J. A. Leary, G. The chemistry of reactive lignin intermediates. Part II. Addition reactions of vinyl-substituted quinone methides in aqueous solution. J. Chem. Soc., Perkin Trans. 1975, 2, 1584-1587. 

Feldman and Eastman have suggested that the kinamycins may by reductively activated to form reactive vinyl radical (25) and orf/to-quinone methide (26) intermediates (Scheme 3.2c) [16]. The authors provided convincing evidence that the alkenyl radical 25 is generated when the model substrate dimethyl prekinamycin (24) is exposed to reducing conditions (tri-n-butyltin hydride, AIBN). Products that may arise from addition of this radical (25) to aromatic solvents (benzene, anisole, and benzonitrile) were isolated. The ort/io-quinone methide 26 was also formed,... 

The chemical sensitization effect was 0.006 (calculated from the quantum yield of the photochemical transformation of 130 to 131, the yield of 131 obtained with the oxalate/hydrogen peroxide reaction, and the moles of oxalate employed). Higher chemical sensitization efficiencies (about 0.04) were observed when the oxalate/hydrogen-peroxide system was used in the addition of ethyl vinyl ether onto phenanthrene quinone... 

Waldmann et al. used tyrosinase which is obtained from Agaricus bisporus for the oxidation of phenols to give ortho-quinones via the corresponding catechols in the presence of oxygen (scheme 33).1881 A combination of this enzymatic-initiated domino process with a Diels-Alder reaction yields the functionalized bicyclic components 164 and 165 as a 33 1 mixture starting from simple p-methyl-phenol 160 in the presence of ethyl vinyl ether 163 as an electron rich dienophile via the intermediates 161 and 162 in an overall yield of 77%. 

For the cracking of catechol and 3-methylcatechol in the presence of iron oxide, reaction pathways for the secondary products appeared to follow the same trend based on the assumption that the possible identities of the products we proposed above were correct. As presented in Scheme 12.1, catechol and 3-methylcatechol were oxidized to their corresponding quinones, 1,2-benzoquinone, and methylbenzoquinone, respectively. This was followed by an expulsion of CO to form cyclopentadienones and further followed by one more CO expulsion to form possibly vinyl acetylene from catechol and pentenyne from 3-methylcatechol. These products were eventually converted to the tertiary products. The formation of quinones was also observed in other studies where the oxidation of catechols was carried out. The formation of secondary products I in our study is in agreement with the previous studies (e.g., Wornet et Therefore, it is reasonable to propose the reaction pathways de-... 

The reactivity trend in terms of the ring-opening reaction for the series 43, 47, and 53 can be analyzed in terms of the geometries of imino and vinyl radicals. Most of the spin density in imino radicals is concentrated in the p-orbital on nitrogen, but vinyl radicals have a nonlinear, vp -like structure, where the spin density is in the i /j -orbital of the carbon. In the o-quinone diradicals 43,47, and 53, the / -orbitals of the nitrogens (accomodating the odd electrons) are better... 

Shimao M, Tamogami T, Nishi K, Harayama S (1996) Cloning and characterization of the gene encoding pyrroloquinoline quinone-dependent poly(vinyl alcohol) dehydrogenase of Pseudomonas sp. strain VM15C. Biosci Biotechnol Biochem 60 1056-1062... 

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