- Gas-phase Protonation of Unsaturated Ethers: Experimental and Theoretical Study of 2,3- and 2,5-Dihydrofuran and Related Compounds
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The protonation of 2,3- and 2,5-dihydrofuran is examined in gas-phase equilibrium proton transfer reactions conducted in an ion cyclotron resonance spectrometer.The thermodynamically favoured site of protonation in the two compounds is seen to be different: whereas the first isomer forms a carbocation upon protonation, the second isomer protonates on the oxygen atom an oxonium ion.The results obtained with substituted derivatives and with linear analogues confirm these conclusions.Molecular orbital calculations on the various structures for protonated bases are performed at the 4-31G level with correction for configuration interaction effects and at the 4-31G* level.The latter basis set provides the best results owing to the introduction of d-type orbitals on the oxygen atom.The calculation results substantiate the experimental observations and provide details on the molecular structure of the protonated species.
- Bouchoux, Guy,Djazi, Faycal,Hoppilliard, Yannik,Houriet, Raymond,Rolli, Eric
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- Palladium-Catalyzed Enantioselective Intermolecular Carboetherification of Dihydrofurans
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A novel enantioselective Pd-catalyzed intermolecular carboetherification of dihydrofurans is reported. The in situ generation of chiral bis-phosphine mono-oxide ligands is crucial, and a general catalytic system has been identified based on this approach. It provides access to a variety of fused tetrahydrofurobenzofurans in consistently high yield and enantiomeric excess.
- Borrajo-Calleja, Gustavo M.,Bizet, Vincent,Mazet, Clément
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supporting information
p. 4014 - 4017
(2016/05/02)
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- METHOD FOR PRODUCING COMPOUND HAVING ACID-LABILE GROUP
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The present invention provides a process for producing a compound having a group represented by general formula (II): (wherein R1, R2, and R3 may be the same or different, and each represent a substituted or unsubstituted alkyl, a substituted or unsubstituted aryl, or a substituted or unsubstituted aralkyl, or R1 and R2 may bind to each other to form an alicyclic hydrocarbon ring together with the adjacent carbon atoms, or R2 and R3 may bind to each other to form a alicyclic heterocyclic ring together with the adjacent O-C-C that may have a substituent), which comprises allowing a compound having a hydroxyl group to react with halogenated alkyl ether represented by general formula (I): (wherein R1, R2, and R3 are the same as those defined above, respectively and X represents a halogen atom).
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- Process for producing 3-methyltetrahydrofuran, and process for producing an intermediate thereof
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A process for producing 3-methyltetrahydrofuran, and processes for producing 3-hydroxy-3-methyltetrahydrofuran and 3-methyldihydrofuran, which are intermediates thereof, are provided.
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- Highly Enantioselective Intermolecular Cu(I)-Catalyzed Cyclopropanation of Cyclic Enol Ethers. Asymmetric Total Synthesis of (+)-Quebrachamine
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A set of cyclic enol ethers derived from 2,3-dihydrofuran 35 and 3,4-dihydropyran 8 with a varying substitution pattern at the olefinic system were synthesized. Evans's ligand 5 with Cu(I)OTf was found to be an effective catalyst in the cyclopropanation reaction between cyclic enol ethers 14, 19, 28-31, and 33 and ethyl diazoacetate 6 to give diastereoselectivities up to exo/endo = 95:5 and enantioselectivities higher than 95% in nearly all cases. Because of the selective building of a quarternary carbon center and good yields in the formation of bicyclic structures 34c-h, the reaction was used as a key step in the asymmetric synthesis of (+)-quebrachamine 7, an indole alkaloid of the Aspidosperma family. After acid-induced ring opening of bicyclic compound 34f to lactone 40 followed by LiAlH4 reduction to the masked aldehyde 41, a reaction with tryptamine gave intermediate 42. This alcohol was efficiently converted into the indole alkaloid (+)-quebrachamine 7 in an overall yield of 37% starting from the chiral synthon 34f. Moreover it revealed the absolute configuration of the quarternary center of the cyclopropanation product 34f to be S.
- Temme, Oliver,Taj, Shabbir-Ali,Andersson, Pher G.
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p. 6007 - 6015
(2007/10/03)
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- Ring-size ans Substituent Effects in Intramolecular Reactions of Alkylidenecarbenes (Carbenoids)
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Intramolecular reaction of methylenecarbenes (carbenoids), derived by reaction of 1,1-dibromoalkenes and methyllithium, with 5,6-related C-H bonds leads to cyclopentenes when there is an alkoxy or amino substituent on C-5, but no reaction occurs at a 4,5-related C-H bond when there is a heteroatom on C-4; when there is an alkylthio group either on C-4 or C-5 attack occurs on sulphur and the alkyl group is lost, leading to a 2,3-dihydrothiophene or a 3,4-dihydro-2H-thiopyran respectively.If a heteroatom-hydrogen bond is present at the 5,6-position a formal insertion occurs at that bond leading to 2,3-dihydropyrroles, 2,3-dihydrofuranes or 2,3-dihydrothiophenes.
- Baird, Mark S.,Baxter, Anthony G. W.,Hoorfar, Alireza,Jefferies, Ian
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p. 2575 - 2582
(2007/10/02)
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