- Une synthese hautement stereoselective de dienes conjugues (E)
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A general method for the preparation of (E) terminal conjugated dienes was developed by the flash thermolysis of 2-substituted 2,5-dihydrothiophene-1,1-dioxides generated by a retro Diels-Alder reaction.This process allows the obtention of conjugated dienes, bearing or not a functionality (alcohols, esters), with an excellent stereoisomeric purity (in general higher than 98percent).An application to the synthesis of (E)-9,11-dodecadien-1-yl acetate, the major component of the sex pheromone of Diparopsis castanea, shows the generality and the efficacy of this method.
- Bloch, R.,Abecassis, J.,Hassan, D.
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p. 2019 - 2024
(2007/10/02)
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- The Diels-Alder Route to Allylsilanes from 1-Trimethylsilylbutadienes
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The synthesis and Diels-Alder reactions of 1-trimethylsilylbutadiene (3) and its 3-methyl (17), 3-trimethylsilyloxy (20), 4-methyl (4), and 4-trimethylsilyl (6) derivatives are reported.The silyl group reduces somewhat the rate of the Diels-Alder reactions, and has, if anything, a small 'ortho'-directing effect on the regioselectivity in the reactions of (3) with methyl acylate, methyl propiolate, citraconic anhydride, and 2,6-dimethylbenzoquinone.The other substituent in the dienes (17), (20), and (4) is therefore the major influence on the regioselectivity in the reactions of these dienes with methyl acrylate and methyl propiolate.The products of the Diels-Alder reactions of (3), (17), and (4) are allylsilanes, which undergo clean protodesilylation with acid, and, with the acid and ester derived from the maleic anhydride adduct of (3), undergo epoxidation and sulphenylation reactions giving an allyl alcohol (33) and an allyl sulphide (37), respectively.The adducts from (20) can be hydrolysed to β-silylketones, which can be converted into enones by bromination. 1-Pentamethyldisilylbutadiene (15) is no more reactive and no more regioselective than (3).The 'ortho'-adduct (42) from the reaction of (3) and methyl propiolate aromatises with DDQ to give methyl m-trimethylsilylbenzoate (53) in high yield, in a reaction involving rearrangement of the silyl group, even though a direct dehydrogenation is an available pathway.
- Carter, Martin J.,Fleming, Ian,Percival, Alan
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p. 2415 - 2434
(2007/10/02)
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