- Stereodivergent Nucleophilic Additions to Racemic β-Oxo Acid Derivatives: Fast Addition Outcompetes Stereoconvergence in the Archetypal Configurationally Unstable Electrophile
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Additions of carbon nucleophiles to racemic α-stereogenic β-oxo acid derivatives that deliver enantiomerically enriched tertiary alcohols are valuable, but uncommon. This article describes stereodivergent Cu-catalyzed borylative cyclizations of racemic β-oxo acid derivatives bearing tethered pro-nucleophilic olefins to deliver highly functionalized cyclopentanols containing four contiguous stereogenic centers. The reported protocol is applicable to a range of β-oxo acid derivatives, and the diastereomeric products are readily isolable by typical chromatographic techniques. α-Stereogenic-β-keto esters are typically thought to have extreme or spontaneous configurational fragility, but mechanistic studies for this system reveal an unusual scenario wherein productive catalysis occurs on the same time scale as background substrate racemization and completely outcompetes on-cycle epimerization, even under the basic conditions of the reaction.
- Crawford, Evan T.,De Jesús Cruz, Pedro,Johnson, Jeffrey S.,Liu, Shubin
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p. 16264 - 16273
(2021/10/21)
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- Photocatalyzed Diastereoselective Isomerization of Cinnamyl Chlorides to Cyclopropanes
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Endergonic isomerizations are thermodynamically unfavored processes that are difficult to realize under thermal conditions. We report a photocatalytic and diastereoselective isomerization of acyclic cinnamyl chlorides to strained cyclopropanes. Quantum mechanical calculations (uM06-2X and DLPNO), including TD-DFT calculations, and experimental studies provide evidence for the energy transfer from an iridium photocatalyst to the allylic chloride substrate followed by C-Cl homolytic cleavage. Subsequent Cla¢ radical migration forms a localized triplet 1,3-diradical intermediate that, after intersystem crossing, undergoes ring-closing to form the desired product. The mild reaction conditions are compatible with a broad range of functional groups to generate chlorocyclopropanes in high yields and diastereoselectivities. A more efficient process is developed by addition of a catalytic amount of a nickel complex, and we propose a novel role for this cocatalyst to recycle an allyl chloride byproduct generated in the course of the reaction. The reaction is also shown to be stereoconvergent, as an E/Z mixture of cinnamyl chlorides furnish the anti-chlorocyclopropane product in high diastereoselectivity. We anticipate that the use of a visible light activated photocatalyst to transform substrates in combination with a transition metal catalyst to recycle byproducts back into the catalytic cycle will provide unique opportunities for the discovery of new reactivity.
- Dykstra, Ryan,Gutierrez, Osvaldo,Martin, Robert T.,Tambar, Uttam K.,Troian-Gautier, Ludovic,Xu, Bin
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supporting information
p. 6206 - 6215
(2020/04/27)
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- Asymmetric Cα-Alkylation of Proline via Chirality Transfers of Conformationally Restricted Proline Derivative: Application to the Total Synthesis of (-)-Amathaspiramide F
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An efficient strategy for the asymmetric synthesis of Cα-tetrasubstituted proline derivatives from proline has been established. A nitrogen-fused bicyclic system was devised to control the stereodynamics of proline. Through N-quaternizations with allylic electrophiles followed by [2,3]-rearrangements, the bicyclic proline system delivered enantioenriched Cα-tetrasubstituted prolines. This strategy was applied to the concise total synthesis of (-)-amathaspiramide F.
- Cho, Hyunkyung,Shin, Jae Eui,Lee, Seokwoo,Jeon, Hongjun,Park, Soojun,Kim, Sanghee
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p. 6121 - 6125
(2018/10/02)
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- Access to functionalized imidazolidin-2-one derivatives by Iron-catalyzed oxyamination of alkenes
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Functionalized imidazolidin-2-one were prepared by using an iron-catalyzed alkene oxyamination reaction. Hy-droxylamine derivatives were used in this atom-economical process, and the addition of an external oxidant was not required. The conditions developed were shown to be efficient for mono-, di-, and trisubstituted double bonds, and a large scope of diamino alcohol precursors were delivered in good yields with good diastereoselectivities. The mechanistic pathway was studied and appears to involve both a fused aziridine and a carbocationic species.
- Manick, Anne-Doriane,Aubert, Sidonie,Yalcouye, Boubacar,Prangé, Thierry,Berhal, Farouk,Prestat, Guillaume
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p. 11485 - 11492
(2018/10/20)
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- Highly-phosphorescent tungsten(0) carbonyl pyridyl-imidazole complexes as photosensitisers
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Photoluminescence data are reported for two W(CO)4L complexes (L = 2-(1H-imidazol-2-yl)pyridine and 2-(2′-pyridyl)benzimidazole) in room-temperature solutions. The bidentate ligands consist of a pyridine and an imidazole moiety connected by a C-C bond. The complexes have been found to exhibit enhanced phosphorescence from the metal-to-ligand charge transfer (MLCT) excited state with quantum yields in the order of 10-3, almost two orders of magnitude higher than those reported for W(CO)4(diimine) complexes. One of the complexes W(CO)4(2-(2′-pyridyl)benzimidazole) can serve as an efficient visible-light photosensitiser for the isomerisation of aromatic alkenes with efficiency comparable to and even exceeding that of the well-studied ruthenium tris-bipyridine complex, Ru(bpy)Cl2.
- Lee, Jia Jin,Yap, Chew Pheng,Chwee, Tsz Sian,Fan, Wai Yip
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p. 11008 - 11012
(2017/08/30)
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- A mild and efficient method for bromination of alcohols using α,α-dibromo-β-dicarbonyl compounds as halogen sources
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Exploration of α,α-dibromo-β-dicarbonyl compounds as novel bromine agents for the conversion of alcohols to alkyl bromides under neutral conditions has been achieved. This method can be used for acid-sensitive substrates and allows the bromination of various primary and secondary alcohols to proceed at room temperature within a very short period of time.
- Cui, Xiao-Meng,Guan, Yong-Hong,Li, Na,Lv, Hao,Fu, Lin-An,Guo, Kun,Fan, Xiaohui
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supporting information
p. 90 - 93
(2014/01/06)
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- Expedient access to branched allylic silanes by copper-catalysed allylic substitution of linear allylic halides
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An unprecedented copper-catalysed allylic transposition enables the regioselective synthesis of branched allylic silanes from linear allylic halides through direct C-Si bond formation.
- Vyas, Devendra J.,Oestreich, Martin
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supporting information; experimental part
p. 568 - 570
(2010/05/01)
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- γ-Spiroketal γ-Lactones from 2-(γ-Hydroxyalkyl)furans: Syntheses of epi-Pyrenolides D and crassalactone D
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Photooxygenation of 2-(γ-hydroxyalkyl)furans followed by dehydration affords, in one synthetic operation and in high yield, γ-spiroketal γ-lactones. This newly developed technology was successfully applied to the synthesis of three different epimers of pyrenolide D, as well as to the first synthesis of the anticancer natural product crassalactone D and its C4-epimer.
- Pavlakos, Ellas,Georglou, Thomas,Tofi, Maria,Montagnon, Tamsyn,Vassilikogiannakis, Georgios
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supporting information; experimental part
p. 4556 - 4559
(2009/12/08)
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- Pericyclic cascade reactions of (bicyclo[1.1.0]butylmethyl)amines
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(Chemical Equation Presented) Direct access: Phase-transfer N-allylation and N-propargylation of (bicyclo[1.1.0]butylmethyl)amines initiate diastereoselective pericyclic cascade reactions that culminate in novel spirocyclic and tricyclic pyrrolidine heterocycles through formal ene or [2+2] pathways.
- Wipf, Peter,Walczak, Maciej A. A.
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p. 4172 - 4175
(2007/10/03)
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- Asymmetric intramolecular cyclopropanation of diazo compounds with metallosalen complexes as catalyst: Structural tuning of salen ligand
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Intramolecular cyclopropanation of alkenyl α-diazoacetates and alkenyl diazomethyl ketones was examined by using optically active (ON+)Ru(II)(salen) and Co(II)(salen) complexes as catalysts. For the cyclization of 2-alkenyl α-diazoacetates, Co(II)(salen) complexes 9 and 10 were found to be superior catalysts to the corresponding (ON+)Ru(II)(salen) complexes 4 and 5. On the other hand, (ON+)Ru(II)(salen) complex 2 was found to be the catalyst of choice for the cyclization of 3-alkenyl diazomethyl ketones, and complex 4 was found to be a good catalyst for the cyclization of (E)-4-alkenyl diazomethyl ketones. The present study demonstrates that metallosalen complexes, especially optically active (ON+)Ru(II)(salen) and Co(II)(salen) complexes, can serve as efficient catalysts for the cyclization of alkenyl diazocarbonyl compounds, if a suitable salen ligand is used as the chiral auxiliary.
- Saha, Biswajit,Uchida, Tatsuya,Katsuki, Tsutomu
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p. 823 - 836
(2007/10/03)
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- Mechanism of oxygen transfer in the epoxidation of an olefin by molecular oxygen in the presence of an aldehyde
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(formula presented) The reaction pathway for peroxide-initiated aldehyde-mediated oxidation of olefins to epoxides by molecular oxygen has been studied. The pathways of reaction via a peroxy acid or an acyl peroxy radical have been differentiated by investigation of the reaction of 4 with oxygen to provide 6 via 8.
- Jarboe, Stephen G.,Beak, Peter
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p. 357 - 360
(2007/10/03)
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- Ring-closing metathesis in methanol and water
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The ring-closing metathesis (RCM) of acyclic dienes in both methanol and water has been achieved through the use of water-soluble ruthenium alkylidenes. These alkylidenes react readily with acyclic olefins in protic solvents, but they do not cyclize α,ω-dienes because of the instability of the resulting methylidene. Successful cyclization has been achieved through simple substrate modification - incorporation of an olefin substituent allows cyclization to proceed in good yield. A methyl-substituted substrate was cyclized in 60% conversion in methanol, and the incorporation of a phenyl substituent resulted in nearly quantitative cyclization. Phenyl-substituted substrates are best suited for the reaction, as a more stable, active catalyst is regenerated upon each catalyst turnover. Using this methodology, 90% conversion of a water-soluble substrate to a substituted cyclopentene has been achieved in aqueous solution. This methodology has also been successfully applied to increase RCM yield in organic solvents.
- Kirkland, Thomas A.,Lynn, David M.,Grubbs, Robert H.
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p. 9904 - 9909
(2007/10/03)
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