1991 Fiscal Year Final Research Report Summary
Development of Novel Synthetic Reactions Using Cationic Reagents
| Project/Area Number |
02650619
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
Synthetic chemistry
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| Research Institution | University of Tokyo |
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Principal Investigator |
HASHIMOTO Yukihiko University of Tokyo, Faculty of Engineering Assistant, 工学部合成化学科, 助手 (50201710)
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| Project Period (FY) |
1990 – 1991
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| Keywords | Cation / The Michael Reaction / The Diels-Alder Reaction / The Claisen Condensation / Stereoselective / Regioselective / Lewis Acid |
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| Research Abstract |
2, 2-Dimethoxyethyl esters are easily transformed into 1, 3-dioxolan-2-ylium cations in situ on the action of Lewis Acid. Thus selectively monoprotected unsymmetrical 1, 3-diketones were obtained by the reaction of 2, 2-dimethoxyethyl esters with enamines in the presence of dichlorobis(trifluoromethanesulfonato)titanium. And 2, 2-dimethoxyethyl acrylate, which is easily prepared by the Mitsunobu reaction, reacts with dieties at -78ﾟC in the presence of a Lewis acid such as titanium(IV)chloride to afford the corresponding Diels-Alder adducts in high yields. Furthermore, 2-(I-alkenyl)-I, 3-dioxolan-2-ylium cations derived from 2, 2-dimethoxyethyl 2alkenoates react with enamities to predominantly give syn Michael adducts in good yields. This is the first example of such a high syn-selectivity for the Michael reaction of alpha, beta-unsaturated ester derivatives with ketone enelate equivalents.
An alpha-Sulfenyl group is known to participate to the neighboring cationic center and synthetic methodologies using sulfenyl group participation was also investigated. alpha-Sulfenyl acetals reacted smoothly with silylated carbon nucleophiles such as silyl enol ether, ketene silyl acetal, and allylsilane in the presence of a catalytic amount of Lewis acid mainly to give anti-Cram adducts with high diastereoselectivity by the asymmetric induction of the alpha-sulfur atom of the acetals. As well, (alpha-Sulfenylmethyl)allyl acetates reacted with silylated carbon nucleophiles in the presence of a catalytic amount of a Lewis acid to give mainly alpha-adducts at the sulfenylmethyl group in moderate to good yields with high regioselectivity. The reaction may proceed via episulfonium ion intermediates.
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