1992 Fiscal Year Final Research Report Summary
Study on [4+2]Type Annulation in Pyrone Derivatives and its Reaction Mechanisn
| Project/Area Number |
03453029
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
有機化学一般
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| Research Institution | HIROSHIMA UNIVERSITY |
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Principal Investigator |
OHKATA Katsuo Hiroshima University, Faculty of Science, Associate Professor, 理学部, 助教授 (50033882)
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| Project Period (FY) |
1991 – 1992
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| Keywords | Pyrone / [4+2]Cycloaddition / Asymmetric Reaction / Face Selectivity / Concerted Mechanism / Orbital Symmetry / Pyrylium Salt / Configuration |
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| Research Abstract |
1. [4+2]Cycloaddition in Pyrone Derivatives: The reaction of alpha-pyrone, coumarin, and chromone with various silyloxydienes in the presence of tert-butyldimethylsilyl triflate gave the [4+2]cycloadducts regio- and stereoselectively in moderate yield.
2. Asymmetric [4+2]Cycloaddition in Activated Coumarin: 3-Alkoxycarbonylcoumarin having a chiral auxiliary[(-)-8-phenylmethyl group] reacted with conjugated dienes in the presence of ZnCl2 to give [4+2]cycloaddition products with high diastereoselectivity (100 %). The absolute stereostructure of the product have been determined to be cis geometry and 3R,4R configuration by X-ray crystal analysis.
3. Asymmetric [4+2]Type Annulation in Activated Chromone: 3-Alkoxycarbonylchromone having a chiral auxiliary reacted with conjugated dienes in the presence of ZnCl2 to give [4+2]annulation products with high diastereoselectivity (100 %) in high yield (90 %).
4. Reaction Mechanism of [4+2]Type Annulation in Coumarin and Chromone: The reaction mechanism are considered by both trapping experiment of reaction intermediate and the conservation rule of orbital symmetry. The reaction of coumarin with diene proceeded via concerted mechanism (Diels-Alder reaction), while the same type annulation of chromone occurred by the stepwise mechanism via allyl cation intermediate.
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