5 jul. 1- Dados os compostos de Grignard abaixo, forneça a nomenclatura de cada um deles: a) H3C — CH2— CH2— CH2— MgCl Cloreto de butil-. Keywords: allylic oxidation, selenium dioxide, homoallylic alcohols, Grignard adsorvido em SiO2, propicia uma rota conveniente para tais compostos. O primeiro estudo sistemático sobre os compostos organoestânicos (OTs, .. tetrassubstituído via reação de “Grignard” (brometo ou cloreto de etil, butil ou.
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Preparation of aromatic geraniol analogues via a Cu I -mediated Grignard coupling. Difunctional allylic terpenes are important synthetic building blocks. The chosen protecting groups clearly influence the oxidation process.
Also, an efficient synthesis of 2-geranylphenol derivatives via a Cu I -mediated Grignard coupling of 2-lithiophenols and geranyl substrates was developed.
A wide variety of phenolic natural products contain isoprenoid residues. C -geranyl and C -farnesyl phenols have been prepared by reaction of geranyl or farnesyl bromide with the sodium salt of the phenol.
Alkylation of sodium salts, however, invariably leads to complex mixtures containing both ring and oxygen substituted products.
The Sharpless conditions for oxidation of geranyl acetate employs 0. Using lower molar quantities of SeO 2 should reduce selenium by-products, facilitating the purification of selenium-free products. Geranyl bromide 4 was necessary in the next steps dde its preparation although it is commercially available was achieved after some attempts in order to optimize the conditions for getting high yield.
Bromination of geraniol 15 with phosphorus tribromide 0. Our target was to obtain 2-[ 2 E ,6 E -3,7-dimethylhydroxy-2,6-octadienyl]phenol 9 by optimizing the coupling of geranyl acetate derivatives with more appropriate reagent O -protected 2-iodophenol.
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Scheme 2 shows the first attempt. To improve the low yield that was obtained for the oxidation of 8we investigated a new route to reach 9. A new sequence was investigated with another substrate in an attempt to improve the yield of the desired phenol-alcohol 9 Scheme 4.
This result was still not satisfactory so we tried a different approach. After allowing the reaction mixture to reach ambient temperature, CuI was added followed by the addition of allylic alcohol 2. In brief, we optimized a selective oxidation of allylic methyl groups in geraniol derivatives over a solid support to the corresponding trans- ab -unsaturated alcohols and aldehydes, using selenium dioxide and t -butylhydroperoxide adsorbed on silica gel as oxidants.
Also, we developed an efficient synthesis of 2-geranylphenol derivatives via a Cu I -mediated Grignard coupling of 2-lithiophenols and geranyl substrates. Further studies on phenolic oxidation of these synthetic intermediates to achieve grignzrd synthesis of cyclic isoprenoids will be reported in due course.
Preparative column chromatography was carried using silica gel ed Merckmesh. Completion of the reactions was established by TLC analysis. Geraniol was purchased from Aldrich Chem. A suspension of selenium oxide 0. The mixture was stirred for 48 h. The extracts were washed with a saturated aqueous solution of Grigbard 4.
To stirred solution of 1. The mixture was treated drop wise with cold metanol 1 mL and extracted with hexane. A solution of 2. The mixture was stirred at ambient temperature for 8 h and then diluted with 30 mL of ether. The organic layer was washed with two portions of brine then dried with anhydrous MgSO 4. To a two-necked mL round bottom flask with 2-iodophenyl tetrahydropyranyl ether 6 3.
After 30 min, geranyl bromide 2. Tetrahydro-2 H pyranyl ether 7 3.
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The solvent was removed under vacuum and the residue was diluted in ether 50 mL and water 30 mLthen extracted with ether 2×30 mLdried over MgSO 4 and filtered, and then the solvent was removed under reduced pressure. The same procedure as employed for the oxidation of 1 was used, starting with 7 ccomposto. To a solution of 2-iodophenol grigard.
After stirring for 15 min at room temperature, cold pentane 25 mL was added, and the organic layer was domposto with cold water, extracted with pentane 2×25 mL and then washed with brine. The organic layer was then dried over MgSO 4filtered and the solvent was removed under reduced pressure. In a three necked round bottom flask, tert -butyldimethylsilyl 2-iodophenol ether 11 3. Then BuLi in hexane 2. After the temperature reached room temperature, CuI 1. Then a solution of 2 E – 3,7-dimethyl-2,6-octadienyl tetrahydro-2 H pyranyl ether 12 The reaction was cooled, a saturated solution of NH 4 Cl was added, the solutions was fomposto with ether 3×50 mLdried over MgSO 4filtered and the solvent was removed under reduced pressure by rotatory evaporation.
The same procedure as employed for allylic oxidation of 1 was used ; compound 13 3. The same procedure as employed for the coupling of 11 and 12 was usedstarting with tert -butyldimethylsilyl 2-iodophenol ether 11 3.
The same procedure employed for the allylic oxidation of 1 was used; compound 8 2. To a solution of 10 3. The solvent was removed under reduced pressure commposto the residue was diluted with ether 50 mL and water 30 mL and extracted with ether 2×50 mL.
The ether phase was washed with water 30 mLthen with brine 2×30 mLdried over MgSO 4filtered and the solvent was removed under reduced pressure by rotatory evaporation.
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To a stirred solution of 14 3. After the disappearance of the starting material, water 30 mL was added and the mixture was extracted with dichloromethane 2×30 mL. The extracts were dried over MgSO 4filtered and the solvent was removed under reduced pressure by rotatory evaporation. New York,p. Naturstoffe22 S February 4, Published on the web: Kascheres on occasion of his 60 th birthday.
All the contents of this journal, except where otherwise noted, is licensed under a Creative Commons Attribution License. Services on Demand Journal. Introduction A wide variety of phenolic natural products contain isoprenoid residues. Results and Discussion The Sharpless conditions for oxidation of geranyl acetate employs 0. Conclusion In brief, we optimized a selective oxidation of allylic methyl groups in geraniol derivatives over a solid support to the corresponding trans- acompostto -unsaturated alcohols and aldehydes, using selenium dioxide and t -butylhydroperoxide adsorbed on silica gel as compposto.
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