Aromatization naphthoquinone ring

Potassium hy dr oxide oxygen Naphthoquinone ring by aromatization 904. O—j ... 

The introduction of a substituent, especially a free or methylated hydroxyl group, determines a bathochromic shift of band II in the visible region. The 1,4-naphthoquinone absorption bands are at 245, 257, and 335 nm and the bands are at 243, 263, 332, and 405 nm for anthaqninone. The introduction of a substituent (especially a hydroxyl group) in the aromatic ring of a naphthoquinone determines a strong bathochromic effect (up to 100 nm) and some UV bands are shifted into the visible (vis) region. 

The use of the stannylquinones 81 results in the regioselective formation of 1,4-naphthoquinones or 9,10-anthraquinones 82 [40]. Highly-oxygenated angularly-fused polycyclic aromatic compounds are prepared by the ring enlargement [41]. (Scheme 29)... 

Compounds showing vitamin K activity are substituted naphthoquinones. The parent compound, 2-methyl-1,4-naphthoquinone, does show some biological activity as do other similar but synthetic compounds. The production of the complete naturally active forms is thought to depend upon the addition of an isoprene chain at position 3 on the aromatic ring. Differences in this side chain produce the various K vitamins (Figure 12.10). A most important physiological role of vitamin K is in the synthesis of the blood clotting factors, II (prothrombin), VII, IX and X. 

As the final example of the simplified treatment of an aromatic ring, a novel potential energy calculation of a naphthoquinone derivative (36) with a program called EENY will be briefly mentioned (155). This program seems to resemble WMIN in that it calculates only van der Waals energy. The rotation around the cyclopropyl-quinonoid bonds is calculated to have a barrier of about 10 kcal/mol. In this and another case (156), the results could be considerably improved by full relaxation MM calculations. 

Oxidation Oxidation of naphthalene by oxygen in the presence of vanadium pentoxide (V2O5) destroys one ring and yields phthalic anhydride (an important industrial process). However, oxidation in the presence of CrOs and acetic acid (AcOH) destroys the aromatic character of one ring and yields naphthoquinone (a diketo compound). 

The formation of aromatic rings via rDA processes has found application in the synthesis of many natural products only a representative set can be presented here. Pyrenochaetic acid A (134), a phytotoxic metabolite, was synthesized by a process involving a rDA reaction as a key step. The DA reaction of pyrone (132) with ethyl propiolate gave, after isolation, benzoate (133) via a rDA reaction evolving carixin dioxide (equation 60). A synthesis of a-cartopterone (137) has been achieved that involves the rDA elimination of ethylene. The tey step is rDA decomposition of adduct (135) to naphthoquinone... 

Interest continues in the photoreactions of quinones, especially anthraquinones, in which substitution occurs in one of the aromatic rings. In the 1,4-naphthoquinone series, irradiation of an aqueous solution of sodium 1,4-naphthoquinone-2-sulphonate gives a mixture of products including the 5-hydroxy-compound the effects of pH, irradiation wavelength, solvents, and radical scavengers are described. Replacement of halogen by butylamino in anthraquinone (103) is... 

The biosynthesis of compounds derived from shikimic acid is closely linked to that of isomers of vitamin K (35) (Fig. 6.7). In plants and in microorganisms, die aromatic ring is formed via the shikimate pathway, which does not exist in animals. Only recently has it been established that vitamin K synthesis branches from wo-chorismic acid (36) and not from chorismic acid (37). fro-Chorismic acid (36) is derived from shikimic acid (see Chapter 7) (Leistner, 1986). Both of the cyclization steps leading to naphthoquinones and vitamin K are unusual in plants. 

Quinones aromatic dioxo compounds derived from benzene or multiple-ring hydrocarbons such as naphthalene, anthracene, etc. They are classified as Benzoquinones (see). Naphthoquinones (see), An-thraquinones (see), etc. on the basis of the ring system. The C = O groups are generally ortho or para, and form a conjugated system with at least two C = C double bonds hence the compounds are colored, yellow, orange or red. This type of chromo-phore is found in many natural and synthetic pigments. 

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