THE CHEMISTRY OF VITAMIN E. XXVII.<sup>1</sup> OXIDATION OF HYDROQUINONES, p-HYDROXYCHROMANS AND p-HYDROXYCOUMARANS TO QUINONES WITH CERIC SULFATE

Smith, Lee Irvin; Ruoff, Peter; Wawzonek, S.

doi:10.1021/jo01202a007

Cited by 8 publications

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“…The other possible product of the oquinone methide 8 was not detected at all. Comparison of these results with those obtained for a-tocopherol and other 6-hydroxychromans, where in all cases the oxidation with silver nitrate 9 or silver oxide 11 occurred at the 5position, the previously proposed Mills-Nixon effect 12 of five-membered rings directing reactions into the 6-position was proved. This effect describes the directing ability of annulated rings in electrophilic aromatic substitution and was theoretically explained as a phenomenon of pbond localisation in aromatic rings annulated by strained saturated rings.…”

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Oxidation Reactions of 5-Hydroxy-2,3-dihydrobenzofurans and 5-Hydroxy-2,3-dihydronaphtho[1,2-b]furans

Schädel¹,

Habicher²

1998

Synthesis

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The oxidation of 5-hydroxy-2,2,4,6,7-pentamethyl-2,3-dihydrobenzofuran (1) and 5-hydroxy-2,2,4-trimethyl-2,3-dihydronaphtho[1,2-b]furan (2) in various systems was examined. For 1 the reaction mainly took place at the 6-position. On oxidation with silver nitrate we obtained 2,2,4,7-tetramethyl-2,3-dihydrobenzofuran-5,6-dione (4) and with silver oxide via 2,2,4,7-tetramethyl-6-methylene-2,3-dihydrobenzofuran-5(6H)-one (5), which can be trapped with ethyl vinyl ether, trimeric and dimeric products. Dimers are also the main products in the oxidation of 2.5-Hydroxy-2,3-dihydrobenzofurans and 5-hydroxy-2,3-dihydronaphtho[1,2-b]furans have been shown to be extremely effective antioxidants in various systems. 1-3 They became more interesting when they were found to be even more efficient than a-tocopherol, which was shown to be the major lipid-soluble chain-breaking antioxidant in human blood. 4 In addition, 5-hydroxy-2,3-dihydrobenzofurans have proved to be good free radical scavengers in biological systems, i.e. to work as lipoperoxidatio 5 inhibitors 2 or as inhibitors of leukotriene biosynthesis. Moreover, 5-hydroxy-2,3-dihydrobenzofuran is a widely occurring structural moiety in natural products. 6,7 Despite their promising biological and antioxidant activity, comparatively little work has been done on the synthesis and reactions of these compounds. At present the main research area of 5-hydroxy-2,3-dihydrobenzofurans is their antioxidation capability. Therefore, we considered it most interesting to investigate the oxidation reactions of these compounds in various chemical environments. For our work we chose 5-hydroxy-2,2,4,6,7-pentamethyl-2,3-dihydrobenzofuran (1) and 5-hydroxy-2,2,4-trimethyl-2,3-dihydronaphtho[1,2-b]furan (2) as model compounds. This choice was made to maintain the comparability of our results with those obtained for a-tocopherol and the corresponding 6-hydroxychromans. Analogous to 2,2,4,7,8-pentamethyl-2,3-dihydrochroman-6-ol, the model compound most frequently used instead of a-tocopherol, we chose the pentamethyl derivative of the 5-hydroxy-2,3-dihydrobenzofurans.The oxidation of 1 with iron(III) chloride in aqueous methanol yielded the p-quinoid product 3 (Scheme 1), as described earlier by Karrer and Jensen. 8 This product was also formed by treating 2 in this way (Scheme 5). Yellow needles of 9 were obtained which were unstable in air and decomposed into a black oil. By treating products 3 and 9 with zinc and acetic acid the substrates were recovered.The oxidation of 1 with silver nitrate in ethanol gave purple needles as described by Smith et al. 9 However, these needles do not have the structure 7 which was proposed by Smith but could be shown to have the o-quinoid structure 4. The latter is supported by data gained from 2D-NOESY spectra. While the 1 H NMR spectra shows only a very weak coupling of the H-4a protons with the H-3 protons the 2D-NOESY spectra shows a clear cross peak of the H-3 and the H-4a signals which should be possible for 4, but would not be expected for 7. Further s...

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“…The oxidation of 1 with silver nitrate in ethanol gave purple needles as described by Smith et al 9 However, these needles do not have the structure 7 which was proposed by Smith but could be shown to have the o-quinoid structure 4. The latter is supported by data gained from 2D-NOESY spectra.…”

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confidence: 76%

Oxidation Reactions of 5-Hydroxy-2,3-dihydrobenzofurans and 5-Hydroxy-2,3-dihydronaphtho[1,2-b]furans

Schädel¹,

Habicher²

1998

Synthesis

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Diseases of Nutrition

Butt¹

1943

Arch Intern Med (Chic)

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Synthesis of Benzoquinones by Oxidation*Present address: Department of Chemistry, University of California, Berkeley, Cal.

Cason

2011

Organic Reactions

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p‐Benzoquinone or quinone was discovered in 1838 as a product of the action of manganese dioxide in sulfuric acid on the natural product, quinic acid, However, benzoquinones generally prepared by the oxidation of disubstituted aromatic hydrocarbons derivatives having hydroxyl or amino groups in the ortho and para positions. The quinone results from the oxidation of hydroquinone, p‐aminophenol, or p‐phenylendiamine. Certain quinones are obtainable in moderate or fair yield by oxidation of starting materials containing only one hydroxyl or amino group as exemplified by the industrial production of quinine from aniline. Oxidation of phenols and amines constitutes the chief topic of discussion in this chapter.

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THE CHEMISTRY OF VITAMIN E. XXVII.¹ OXIDATION OF HYDROQUINONES, p-HYDROXYCHROMANS AND p-HYDROXYCOUMARANS TO QUINONES WITH CERIC SULFATE

Cited by 8 publications

References 3 publications

Oxidation Reactions of 5-Hydroxy-2,3-dihydrobenzofurans and 5-Hydroxy-2,3-dihydronaphtho[1,2-b]furans

Oxidation Reactions of 5-Hydroxy-2,3-dihydrobenzofurans and 5-Hydroxy-2,3-dihydronaphtho[1,2-b]furans

Diseases of Nutrition

Synthesis of Benzoquinones by Oxidation*Present address: Department of Chemistry, University of California, Berkeley, Cal.

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THE CHEMISTRY OF VITAMIN E. XXVII.1 OXIDATION OF HYDROQUINONES, p-HYDROXYCHROMANS AND p-HYDROXYCOUMARANS TO QUINONES WITH CERIC SULFATE

Cited by 8 publications

References 3 publications

Oxidation Reactions of 5-Hydroxy-2,3-dihydrobenzofurans and 5-Hydroxy-2,3-dihydronaphtho[1,2-b]furans

Oxidation Reactions of 5-Hydroxy-2,3-dihydrobenzofurans and 5-Hydroxy-2,3-dihydronaphtho[1,2-b]furans

Diseases of Nutrition

Synthesis of Benzoquinones by Oxidation*Present address: Department of Chemistry, University of California, Berkeley, Cal.

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THE CHEMISTRY OF VITAMIN E. XXVII.¹ OXIDATION OF HYDROQUINONES, p-HYDROXYCHROMANS AND p-HYDROXYCOUMARANS TO QUINONES WITH CERIC SULFATE