Boron, Trichloride as a Selective Demethylating Agent for Hindered Ethers: a Synthesis of the Phytoalexins α- and Β-Pyrufuran, a Synthesis of Tri-O-methylleprolomin and its Demethylation

Carvalho, CF; Russo, A. V.; Sargent, Melvyn V.

doi:10.1071/ch9850777

Cited by 28 publications

(17 citation statements)

References 3 publications

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“…Clearly the hydroxy group flanked by two ortho-bromo substituents exhibits enhanced nucleophilicity toward the methylating agent. This result is analogous to the formation of 3-methoxy-2,4-dibromophenol from 2,4-dibromoresorcino1 and dimethyl sulfate, as reported by Rice (12b), and parallels the enhanced reactivity of orthodisubstituted anisoles toward dealkylating agents (7,30). In the presence of hydrogen bromide, 4 d rearranges to the more stable 2,6-dibromo isomer (4e), and both compounds were found to undergo slow debromination as well as H/D exchange at the unsubstituted ring carbon after several days of exposure to hydrochloric acid in acetone-d6 solution (monitored by nmr).…”

Section: Introductionmentioning

confidence: 56%

Bromophloroglucinols and their methyl ethers

Kiehlmann¹,

Lauener²

1989

Can. J. Chem.

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All 16 bromination products of phloroglucinol and its methyl ethers, as well as five bromoresorcinols and three of their dimethyl ethers, were synthesized and analyzed by nuclear magnetic resonance spectroscopy. Two or three equivalents of bromine convert phloroglucinol to di-and tribromophloroglucinol, 5-methoxyresorcinol to the tri-and 2,4-dibromo, 3,s-dimethoxyphenol to the tri-and 2,6-dibromo, and 1,3,5-trimethoxybenzene to the dibromo compound. With one equivalent of bromine, 3,s-dimethoxyphenol reacts preferentially at C-2 while 5-methoxyresorcinol gives both monobromo isomers. Partial debromination with sodium sulfite yields successively 2,4-dibromo-and 2-bromo-5-methoxyresorcinol from the tribromo compound but fails with brominated 3,s-dimethoxyphenol. In the resorcinol series, C-2 is invariably the least reactive position.4,6-Dibromo-5-methoxyresorcinol and 2,4-dibromo-3,s-dimethoxyphenol are accessible by methylation of dibromophloroglucinol, obtained from 3,s-dibromo-2,4,6-trihydroxybenzoic acid by decarboxylation. In contrast to resorcinol and tribromoresorcinol, the partial bromination of phloroglucinol and debromination of tribromophloroglucinol are not selective. The 13cmr spectra of bromophloroglucinol methyl ethers show characteristic downfield shifts for methoxy groups orthogonal to the aromatic ring plane.Key words: bromophloroglucinols, synthesis, nmr, and debromination; bromo-5-methoxyresorcinols, synthesis, nmr, and debromination; bromo-3,s-dimethoxyphenols, synthesis and nmr. On a effectuC la synthtse des 16 produits de bromination du phloroglucinol et de ses Cthers mCthyliques ainsi que de cinq bromorCsorcinols et de trois de leurs Cthers dimCthyliques et on a pu effectuer une analyse de tous ces dCrivCs par spectroscopie en rksonance magnttique nuclCaire. Deux ou trois Cquivalents de brome transforment le phloroglucinol en di-et en tri-bromophloroglucinols, le mCthoxy-5 rtsorcinol en dCrivCs tribromo et dibromo-2,4, le dimCthoxy-3,s phCnol en dCrivCs tribromo et dibromo-2,6 et le trimCthoxy-1,3,5 benzkne en composC dibromC. Avec un Cquivalent de brome, le dimtthoxy-3,s phtnol rCagit prCf6rentiellement en C-2 alors que le mCthoxy-5 rCsorcinol foumit les deux isomkres monobromCs. Si on soumet le dCrivC tribromC i une dCbromation partielle i I'aide de sulfite de sodium, on obtient successivement le dibromo-2,4 et le bromo-2 mCthoxy-5 rCsorcinol; toutefois, on ne peut effectuer de dkbromation partielle sur le dimCthoxy-3,s phCnol bromC. Dans la sCrie du rCsorcinol, la position C-2 est toujours la moins reactive. Les dibromo-4.6 mCthoxy-5 rCsorcinol et dibromo-2,4 dimCthoxy-3,s phCnol sont accessibles par mCthylation du dibromophloroglucinoI qui est obtenu par dCcarboxylation de l'acide dibromo-3,s trihydroxy-2,4,6 benzoi'que. Par opposition avec ce qui est observC avec le rCsorcinol et le tribromorCsorcinol, la bromation partielle du phloroglucinol et la dCbromation du tribromophloroglucinol ne sont pas sClectives. Dans les spectres rmn du I3c des Cthers mCthyliques des bromophloroglucinols,...

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Section: Introductionmentioning

confidence: 56%

Bromophloroglucinols and their methyl ethers

Kiehlmann¹,

Lauener²

1989

Can. J. Chem.

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“…In 10, the phenolic groups are protected as their methyl ethers, but we also chose to prepare the analogue 11 possessing isopropyl protecting groups, as it was hoped that these groups could be selectively removed when required to afford phenolic analogues of 6. 11 We elected to synthesise the desired isochromanes 10 and 11 from 1-allyloxy-2,4-dimethoxybenzene 13 and its isopropoxy analogue 14. The bromide analogue 12 was also prepared from 13.…”

Section: Resultsmentioning

confidence: 99%

“…The reaction mixture was allowed to warm up to room temperature and stirred under nitrogen for 55 h, during which time a pink precipitate formed. An additional portion of MMPP (10 g) was added and the reaction mixture was stirred for a further 15 h. The solvent was removed in vacuo and the residue was purified by column chromatography (20% ethyl acetate-hexane), to afford the phenol 16 as a dark red-brown oil (9.91 g, 64%) (Found: M (12), 69 (6), 65 (8) and 41 (11).…”

Section: -Allyloxy-3-methoxyphenol 16mentioning

confidence: 99%

Syntheses of isochromane analogues of the michellamines and korupensamines

Koning

Michael

Otterlo

2000

J. Chem. Soc., Perkin Trans. 1

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“…The common reagents for the cleavage of aryl methyl ethers are boron trichloride [8,9] or boron tribromide. [10] We hoped that these reagents might cleave the C-5 methyl ether in 5,8-dimethoxy-1,4-phenanthrenequinone (4) selectively by chelation with the C-4 carbonyl group.…”

Section: Chemistrymentioning

confidence: 99%

Novel 1,4,5,8‐Phenanthrenediquinones and Unusual Deoxygenation with Trimethylsilyl Iodide

et al. 2009

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Attempt for aryl methyl ether cleavage of 5,8-dimethoxy-1,4-phenanthrenequinone (4) with boron trichloride or tribromide resulted in the halogenation of the quinone double bond to form 5a,b. Surprisingly, reaction of dimethyl ether 4 with trimethylsilyl iodide afforded the phenanthrenediquinone 6, whereas deoxygenation to 8 and 9 occurred by reaction of trimethylsilyl iodide with derivative 7. The phen-

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Boron, Trichloride as a Selective Demethylating Agent for Hindered Ethers: a Synthesis of the Phytoalexins α- and Β-Pyrufuran, a Synthesis of Tri-O-methylleprolomin and its Demethylation

Cited by 28 publications

References 3 publications

Bromophloroglucinols and their methyl ethers

Bromophloroglucinols and their methyl ethers

Syntheses of isochromane analogues of the michellamines and korupensamines

Novel 1,4,5,8‐Phenanthrenediquinones and Unusual Deoxygenation with Trimethylsilyl Iodide

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