- Unified enantioselective total syntheses of (?)-scholarisine G, (+)-melodinine E, (?)-leuconoxine and (?)-mersicarpine
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A unified strategy enabled the enantioselective syntheses of (?)-scholarisine G, (+)-melodinine E, (?)-leuconoxine and (?)-mersicarpine from a common 2-alkylated indole intermediate bearing an all-carbon quaternary stereogenic center. The Smith-modified Madelung indole synthesis was used to couple simple o-toluidine with chiral lactone (+)-8, incorporating the key elements for further cyclizations. Lactone (+)-8 was prepared via a palladium-catalyzed intermolecular asymmetric allylic alkylation. The unified and protecting-group-free reaction sequences allowed the synthesis of these alkaloids in a maximum of 10 steps and with high efficiency.
- Liu, Yao,Wang, Honggen
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- A photochemical route to carbapenems from pyrazolidin-3-ones. Formal synthesis of PS-5
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Photochemical ring contraction of a cis disubstituted pyrazolidin-3-one, prepared by hydrazinolysis of an α,β-unsaturated δ-lactone, gave the corresponding azetidinone which has been converted previously to the carbapenem antibiotic PS-5.
- White, James D.,Toske, Steven G.
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- Asymmetric Total Synthesis of Kopsiyunnanine K, a Monoterpenoid Indole Alkaloid with a Rearranged Skeleton
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A new monoterpenoid indole alkaloid, kopsiyunnanine K, was isolated from Kopsia arborea. Its intriguing rearranged structure and absolute configuration, which were inferred from spectral data and a possible biosynthetic pathway, were determined on the bas
- Tokuda, Ryoko,Okamoto, Yoshiki,Koyama, Tetsuya,Kogure, Noriyuki,Kitajima, Mariko,Takayama, Hiromitsu
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- Enantioselective Construction of Quaternary Carbon Stereocenter via Palladium-Catalyzed Asymmetric Allylic Alkylation of Lactones
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An efficient and practical method for the synthesis of α,α-disubstituted six-membered lactones was developed. Enantioselective construction of quaternary carbon centers by utilizing Pd-catalyzed asymmetric allylic alkylation proved its feasibility.
- Li, Xiao-Hui,Wan, Shi-Li,Chen, Di,Liu, Qing Rong,Ding, Chang-Hua,Fang, Ping,Hou, Xue-Long
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supporting information
p. 1568 - 1572
(2016/05/24)
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- Highly enantioselective iridium-catalyzed hydrogenation of α,β-unsaturated esters
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α,β-Unsaturated esters have been employed as substrates in iridium-catalyzed asymmetric hydrogenation. Full conversions and good to excellent enantioselectivities (up to 99 % ee) were obtained for a broad range of substrates with both aromatic- and aliphatic substituents on the prochiral carbon. The hydrogenated products are highly useful as building blocks in the synthesis of a variety of natural products and pharmaceuticals. Asymmetric hydrogenation: A variety of α,β-unsaturated esters were hydrogenated with high enantioselectivities (see scheme). The hydrogenated products have been used in synthetic transformations as well as in formal total syntheses. Copyright
- Li, Jia-Qi,Quan, Xu,Andersson, Pher G.
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p. 10609 - 10616
(2012/11/07)
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- Branched-regioselective hydroformylation with catalytic amounts of a reversibly bound directing group
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(Chemical Equation Presented) Phosphinites do the trick and work as reversibly bound catalyst-directing groups in catalytic amounts to allow for the highly regioselective hydroformylation of homo-allylic alcohols with terminal and internal alkene functions in favor of the branched product.
- Gruenanger, Christian U.,Breit, Bernhard
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supporting information; experimental part
p. 7346 - 7349
(2009/04/07)
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- Novel photolactonisation from xanthenoic esters
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In the context of our work on photocleavable fragrance precursors, we have discovered a new photo-fragmentation of xanthenoic esters into xanthene- and formyl radicals. This homolytic cleavage has not been reported previously. Thus, unsaturated formyl radicals cyclise to lactones of various ring size.
- Plessis, Caroline,Derrer, Sam
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p. 6519 - 6522
(2007/10/03)
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- Enantioselective synthesis of 2-substituted 6- and 7-membered lactones via α-alkylation of lactone hydrazones
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2-Alkyl-substituted lactones 4 were synthesized in good overall yields and high enantiomeric purities (ee = 90-94%) by deprotonation and alkylation of the corresponding lactone SAMP-hydrazones 2 and subsequent oxidative cleavage of the product hydrazones 3 by ozonolysis. The lactone hydrazones 2, in turn, were prepared in good yields by silver promoted cyclization of ω-chloroalkanohydrazides 1.
- Enders,Grobner,Runsink
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p. 947 - 951
(2007/10/02)
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- Synthesis of γ- and δ-Lactones by Free-Radical Annelation of Se-Phenyl Selenocarbonates
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A general method for the synthesis of γ- and δ-lactones through the intramolecular addition of alkoxycarbonyl radicals, formed by reaction of Se-phenylselenocarbonates with n-Bu3SnH, onto carbon-carbon multiple bonds is described.This free-radical cyclization is characterized by high regioselectivity favoring exo addition and by a high ratio of cyclization to reduction.Monocyclic, fused bicyclic, and spirocyclic lactones are formed in good to excellent yield.Use of allyltri-n-butyltin as a chain-transfer agent in the place of n-Bu3SnH affords the corresponding 3-butenyl lactones.
- Bachi, Mario D.,Bosch, Eric
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p. 4696 - 4705
(2007/10/02)
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- Homolytic cyclization of O-alkenyl-Se-phenylselenocarbonates. Synthesis of lactones
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O-Alk-3-enyl- and O-alk-4-enyl-Se-phenylselenocarbonates undergo regio-specific exo cyclization to the corresponding γ- and δ-lactones on treatment with tri-n-butylstannane and AIBN.
- Bachi, Mario D.,Bosch, Eric
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p. 579 - 582
(2007/10/02)
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- Total Synthesis of Ionophore Antibiotic X-14547A
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A highly stereocontrolled and convergent total synthesis of optically active ionophore antibiotic X-14547A (1) was designed and carried out.Degradative reactions led to the key intermediates 3 and 6, which served as convenient comparison stages.The tetrah
- Nicolaou, K. C.,Papahatjis, D. P.,Claremon, D. A.,Magolda, R. L.,Dolle, R. E.
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p. 1440 - 1456
(2007/10/02)
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- Ionophore Antibiotic X-14547A. Degradation Studies and Stereoselective Construction of the "Right Wing" (C11-C25 Fragment) by an Intramolecular Diels-Alder Reaction
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Studies directed toward the total synthesis of the ionophore antibiotic X-14547A are reported.Degradation methods led to a number of "left-wing" fragments, whereas synthetic operations led to a "right- wing" fragment, in a highly efficient and stereoselec
- Nicolaou, Kyriacos C.,Magolda, Ronald L.
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p. 1506 - 1508
(2007/10/02)
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- Asymmetric Synthesis of 2-Substituted Butyrolactones and Valerolactones
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The use of chiral oxazolines 1, 2, 5, and 8 under asymmetrically induced alkylation conditions gave α-substituted oxazolines 3, 6, 9, and 13 which were hydrolyzed to α-substituted butyro- and valerolactones 4 and 11.Either enantiomer of the lactones could be prepared in predictable absolute configuration by reversing the order of alkyl group introduction.The lactones were prepared in 60-86 percent enantiomeric excess which was determined by either chemical correlation or high-pressure liquid chromatography of the diastereomers 10.
- Meyers, A. I.,Yamamoto, Yukio,Mihelich, Edward D.,Bell, Richard A.
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p. 2792 - 2796
(2007/10/02)
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