- Formation of tetracyclo[10.2.n.02,11.04,9]pentadeca-2,4,5,7,13-pentaene-3,10 -diones and related systems induced by samarium diiodide
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The reaction of either endo or exo tetracyclo[10.2.n.02,11.04,9]penta deca-4,5,7,13-tetraene-3,10-diones with SmI2 led to efficient formation of oxidized title quinones.
- Pandey,Saravanan,Rao,Nagamani,Kumar
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- Asymmetric Diels-Alder Reactions of (S)-2-(p-Tolylsulfinyl)-1,4-naphthoquinones
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The asymmetric Diels-Alder reactions of (S)-2-(p-tolylsulfinyl)-1,4-naphthoquinones 1a-c with cyclic dienes have been explored.The high ? facial diastereoselectivity observed can be reversed in the presence of ZnBr2.Evidence is presented to show that the regiochemical outcome of these reactions is controlled only by the sulfinyl group.The in situ cycloaddition/pyrolytic sulfoxide elimination starting from chiral 1a-c offers a convenient new route for the construction of enantiomerically pure 1,4-dihydro-9,10-anthraquinones (+)-10 and (+)-12a-c.
- Carreno, M. Carmen,Ruano, Jose L. Garcia,Urbano, Antonio
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p. 6870 - 6876
(2007/10/02)
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- Electronic Control of Stereoselectivity. 6. Directionality of Singlet Oxygen Addition to 1,4-Dimethoxynaphthalenes Laterally Fused to Bridged Bicyclic Systems
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The photooxygenation in methanol solution of 1,4-dimethoxynaphthalene derivatives having bridged bicyclic systems fused at C2, C3 with rose bengal as sensitizer leads to formation of stereoisomeric epoxynaphthoquinone monoketals.These products, which are readily hydrolyzed in acid solution to the epoxynaphthoquinones, possess an epoxide oxygen which serves as a stereochemical marker for the directionality of singlet oxygen addition.For the norbornyl and norbornenyl cases, endo bonding by 1O2 is preferred; the reverse is true for the pair of bicyclooctenyl derivatives studied.This contrasting stereoselection was compared to the stereochemical consequences of alkaline hydroperoxidation of the corresponding naphthoquinones.In each instance, the reaction course was opposite to that observed with singlet oxygenation.Both processes are analyzed from the theoretical viewpoint, use being made of the photoelectron spectra of the substrate molecules, detailed evaluation of frontier orbital effects, and prevailing ?/? interactions.While the alkaline hydroperoxidation results can be interpreted in terms of standard kinetic and steric control, an understanding of the directionality of 1O2 capture appears dependent on our appreciation of the contributions made by the ? electrons of the bicyclic moieties upon the aromatic ? orbitals.The tilting caused by such interactions is thought to be source of the experimentally observed exo/endo ratios.
- Paquette, Leo A.,Bellamy, Francois,Boehm, Michael C.,Gleiter, Rolf
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p. 4913 - 4921
(2007/10/02)
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