2003
DOI: 10.1021/jo0265380
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Cyclic Allene Intermediates in Intramolecular Dehydro Diels−Alder Reactions:  Labeling and Theoretical Cycloaromatization Studies

Abstract: A comprehensive theoretical and experimental investigation of dehydro Diels-Alder reactions examining the evolution of the cyclic allene intermediates under conditions for intramolecular and ionic and radical intermolecular cycloaromatization processes is reported. Theoretical calculations showed that the most favored intramolecular path for cycloaromatization of 1,2,4-cyclohexatriene 4 and its benzoannulated derivative 14, strained cyclic allenes, consists of a pair of successive [1,2] H shifts rather than a … Show more

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Cited by 54 publications
(26 citation statements)
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“…19) A recent interesting study reported by Nakao, Shirakawa, Hiyama, and coworkers showed that a stannylative benzannulation occurred by the Pd-catalyzed reaction of enynes (or enynes and diynes) with hexabutyldistannoxane (Chart 11). 20) Since it has been postulated that the cyclic allene (1,2,4-cyclohexatriene) was converted to the benzene ring or reacted as a nucleophile, 21,22) their results (stannylative benzannulation), combined with our results (benzannulation), might indicate the intermediacy of a strained allene such as 20 (Chart 12). The reaction was further expanded by Gevorgyan, Yamamoto, and co-workers to the corss-benzannulation reaction between conjugated enynes and diynes.…”
Section: -7)supporting
confidence: 56%
“…19) A recent interesting study reported by Nakao, Shirakawa, Hiyama, and coworkers showed that a stannylative benzannulation occurred by the Pd-catalyzed reaction of enynes (or enynes and diynes) with hexabutyldistannoxane (Chart 11). 20) Since it has been postulated that the cyclic allene (1,2,4-cyclohexatriene) was converted to the benzene ring or reacted as a nucleophile, 21,22) their results (stannylative benzannulation), combined with our results (benzannulation), might indicate the intermediacy of a strained allene such as 20 (Chart 12). The reaction was further expanded by Gevorgyan, Yamamoto, and co-workers to the corss-benzannulation reaction between conjugated enynes and diynes.…”
Section: -7)supporting
confidence: 56%
“…The presence of DBU could probably not only accelerate the generation of acetylene silver and allenyl amide, but also stabilize the formed Ag intermediate . Then, C undergoes an intramolecular Diels‐Alder reaction to form the strained cyclic allene D , which isomerizes by intramolecular hydrogen shift to give the final product 3 a . For benzofuran‐pyrrole, the coordinating effect of the hydroxyl and alkynyl groups enables the formation of the silver complex E .…”
Section: Figurementioning
confidence: 99%
“…[17] Then, C undergoes an intramolecular Diels-Alder reaction to form the strained cyclic allene D, which isomerizes by intramolecular hydrogen shift to give the final product 3 a. [18] For benzofuran-pyrrole, the coordinating effect of the hydroxyl and alkynyl groups enables the formation of the silver complex E. [19] 5-Endo-dig cyclization of complex is occurred on E, generating the benzofuran F. The terminal alkyne in F undergoes a [3+ 2] cycloaddition with the isocyanide reactant, producing the intermediate G. [16,20] The oxidation of alcohol to carbonyl group gives the final product 6 a. [15a] In summary, we have developed a novel silvercatalyzed sequential cascade cyclization reaction of isocyanides with 1-(2-ethynyl-phenyl)-prop-2-yn-1-ols, which afforded either benzo [b]fluorenes or benzofuran-pyrrole in good to excellent yield, depending on the presence of a hydroxyl group on the aryl group of the substrate.…”
mentioning
confidence: 99%
“…Dehydro-Diels-Alder reactions between enynes and alkynes (type III) have been extensively established, since the first report in the 19th century. [19] Cycloadditiono fv inylacetylene with acetylene should give 1,2,4-cyclohexatriene, strained cyclic allenes that normally isomerize to give aromatic products (Scheme 16). In past years, mosto ft he DDA reactions of enyne-ynes reported featured ana romatic ring linker.T he linking group Xm ay be represented by as p 3 carbon atom, ac arbonyl group, an itrogen atom bearinga ne lectron-withdrawing group, an amide, or an ether moiety.…”
Section: Enyne-ene and Enyne-yne Cycloaddition(types II And Iii)mentioning
confidence: 99%