- Catalytic and metal-free intramolecular hydroalkoxylation of alkynes
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Benzyltrimethylammonium hydroxide act as an efficient metal-free catalyst for the intramolecular hydroalkoxylation of alkynes. Notably, the use of microwave irradiation allowed reaction to operate in only two minutes. Under optimized reaction conditions, linear alkynes bearing aryl and heteroaryl substituents were successfully cyclized with good level of stereoselectivity.
- Jean, Alexandre,Rouden, Jacques,Maddaluno, Jacques,De Paolis, Micha?l,Blanchet, Jér?me
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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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- ALKYLATION REACTIONS OF ANIONS DERIVED FROM 2-BENZENESULPHONYL TETRAHYDROPYRAN AND THEIR APPLICATION TO SPIROKETAL SYNTHESIS
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Reaction of 3,4-dihydro-2H-pyran or 2-methoxytetrahydropyran with benzenesulphinic acid gave 2-benzenesulphonyl tetrahydropyran (1).Deprotonation of (1) followed by alkylation with carbonyl compounds or halides gave cyclic enol ether addition products by
- Ley, Steven V.,Lygo, Barry,Sternfeld, Francine,Wonnacott, Anne
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p. 4333 - 4342
(2007/10/02)
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- WITTIG AND HORNER-WITTIG COUPLING REACTIONS OF 2-SUBSTITUTED CYCLIC ETHERS AND THEIR APPLICATION TO SPIROKETAL SYNTHESIS
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Wittig and Horner-Wittig coupling reactions of tetrahydropyran or tetrahydrofuran 2-triphenylphosphonium salts or 2-diphenylphosphine oxides with aldehydes and lactols affords good yields of the corresponding enol ethers.In selected examples these enol ether products may be further converted to spiroketals some of which are natural pheromones derived from Dacus oleae and Paravespula vulgaris.
- Ley, Steven V.,Lygo, Barry,Organ, Helen M.,Wonnacott, Anne
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p. 3825 - 3836
(2007/10/02)
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