| Co-Investigator(Kenkyū-buntansha) |
ITO Hajime Institute for Molecular Sciences, Assistant, 分子化学研究所, 助手 (90282300)
MIURA Katsukiyo University of Tsukuba, Chemistry, Lecturer, 化学系, 講師 (20251035)
HOJO Makoto University of Tsukuba, Chemistry, Lecturer, 化学系, 助教授 (50229150)
TATEIWA Jun-ichi University of Tsukuba, Chemistry, Assistant, 化学系, 助手 (30302350)
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| Research Abstract |
The following results are obtained in this research project.
1. Silicon-directed Cyclization of Vinylysilanes : Stereoselective Synthesis of Tetrahydrofurans and Tetrahydropyrans
Silicon-directed stereoselective syn addition of hydroxy group to olefinic double bond occurs intramolecularly in an acid-catalyzed cyclization of vinylsilanes bearing hydroxy group. The cyclization proceeds by stereospecific syn addition of the hydroxy group. Vinylsilanes, (Z)-5-silyl-4-penten-1-ols bearing a substituent on the methylene tether, smoothly undergo the acid-catalyzed cyclization to give trans-2,5-, cis-2,4-, and trans-2,3-disubstituted tetrahydrofurans, respectively, with moderate to high stereoselectivity.
2. Acid-Catalyzed Cyclization of Vinylsilanes Bearing an Amino Group. Stereoselective Synthesis of Pyrrolidines
In the presence of an acid catalyst, vinylsilanes bearing an amino group protected by an electron-withdrawing group were smoothly cyclized to 2-(silylmethyl) pyrrolidines. This cyclizat
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ion was utilized for the stereoselective synthesis of 2, n-disubstituted pyrrolidines (n=3-5).
3. Unprecedented Manganese-Mediated Reactions : Generation of Non-Stabilized Carbonyl Ylids
Activated manganese generates nonstabilized carbonyl ylides from bis (chloromethyl) ethers as a precursor, and using this system with manganese as a reductant, the reactions of the ylides with electron-deficient dipolarophiles can be attained without the direct reduction of dipolarophiles by the reductant.
4. Manganese Ate Species : Generation and Reactions with Electrophiles
Trialkylmanganese (II) ate reagents, "R_3MnLi" reacted with iodomethylsulfides to produce thiomethylmanganese reagents, where the manganate serves as a reductant not an alkylation agent.
The reductive behavior of trialkylmanganese (II) ate reagents provides aprotocol for the direct generation of a new class of reagents, thiomethylmanganese reagents with structural variety, and the generated thiomethylmanganese reagents reacted with allyl bromides, enones and aldehydes.
5. Radical Cyclization of 1,6-Enynes Using Allylstannanes and New Radical Reactions Using Stannyl Enolates as Radical Transfer Agents
In the presence of AIBN, allyltributylstannanes bearing a radical-stabilizing group at the β-position smoothly reacted with 1,6-enynes to give cyclized products incorporated with the stannyl and allyl groups in moderate to good yields. This cyclization is valuable for the synthesis of highly functionalized 5-membered carbocycles and heterocycles. The reactions with β-cyanoallylstannane formed a certain amount of bicyclo [4.3.0] non-1-enes along with monocyclized products. The radical-initiated reactions of α-halo-esters, -nitriles, and -ketones with stannyl enolates gave the corresponding γ-keto derivatives in moderate to high yields. This homolytic process was applied to the three-component coupling reaction among stannyl enolates, haloalkanes, and electron-deficient alkenes.
6. New Method for Introduction of a Silyl Group into α, β-Enones Using a Disilane Catalyzed by a Copper (I) salt.
The reaction of a disilane with a Cu (I) salt efficiently induces cleavage of the Si-Si bond to generate a silyl nucleophile in an aprotic polar solvent and its 1,4-addition to α, β-unsaturated enones smoothly proceeds with a catalytic amount of a Cu (I) salt were found. This reaction is successfully applied to hexamethyldisilane to generate a trimethylsilyl nucleophile, hitherto not easily accessible. Less
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