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Organic Letters

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https://www.readbyqxmd.com/read/28636402/a-chiral-pentenolide-based-unified-strategy-toward-dihydrocorynantheal-dihydrocorynantheol-protoemetine-protoemetinol-and-yohimbane
#1
Changmin Xie, Jisheng Luo, Yan Zhang, Lili Zhu, Ran Hong
An organocatalytic cross-aldol reaction of formaldehyde (formalin) with alkyl aldehydes, followed by the Z-selective Horner-Wadsworth-Emmons (HWE) reaction and immediate lactonization, afforded γ-alkylated pentenolides in good overall yields and excellent enantioselectivities. Based on this scalable sequence, five quinolizidine alkaloids were synthesized in a unified and concise manner. The development of an in situ activation of a tertiary amide to improve the efficiency of the Bischler-Napieraiski (B-N) reaction was also noteworthy due to the generality to sensitive substrates for a variety of target molecules...
June 21, 2017: Organic Letters
https://www.readbyqxmd.com/read/28636396/copper-catalyzed-asymmetric-protoboration-of-%C3%AE-amidoacrylonitriles-and-%C3%AE-amidoacrylate-esters-an-efficient-approach-to-functionalized-chiral-%C3%AE-amino-boronate-esters
#2
Lili Chen, Xiaoliang Zou, Haonan Zhao, Senmiao Xu
A copper-catalyzed asymmetric protoboration of both Z-β-amidoacrylonitriles and ethyl E-β-amidoacrylates using bis(pinacolato)diboron has been developed for the first time. The process tolerates a vast array of substrates, delivering a series of stable functionalized chiral α-amino boronate esters in good yields and enantioselectivities under mild reaction conditions. The current method is also applicable for gram-scale synthesis without erosion of enantioselectivity. This work provides an attractive and complementary approach to synthesizing enantioriched chiral α-amino boronate esters...
June 21, 2017: Organic Letters
https://www.readbyqxmd.com/read/28636394/synthesis-of-rna-5-azides-from-2-o-pivaloyloxymethyl-protected-rnas-and-their-reactivity-in-azide-alkyne-cycloaddition-reactions
#3
Marcin Warminski, Joanna Kowalska, Jacek Jemielity
Commercially available 2'-O-pivaloyloxymethyl (PivOM) phosphoramidites were employed in an SPS protocol for RNA 5' azides. The utility of the N3-RNAs in CuAAC and SPAAC was demonstrated by RNA 5' labeling, chemical ligation including fragment joining and cyclization, and bioconjugation. As a result, several new RNA conjugates that may be valuable tools for studies on biological events such as innate immune response (cyclic dinucleotides), post-transcriptional gene regulation (circular RNAs), or mRNA turnover (m(7)G capped RNAs) were obtained...
June 21, 2017: Organic Letters
https://www.readbyqxmd.com/read/28636391/copper-catalyzed-direct-nitration-on-aryl-c-h-bonds-by-concomitant-azidation-oxidation-with-tms-azide-and-tbhp-under-aerobic-conditions
#4
Botla Vinayak, Malapaka Chandrasekharam
An unprecedented copper-catalyzed in situ azidation-oxidation for the nitration of anilides and sulfonamides has been developed by direct CAr-H functionalization. This novel and efficient nitration protocol is achieved employing TMSN3 and TBHP without the exclusion of air or moisture. The synthetic applications of the 2-nitroanilides have been explored.
June 21, 2017: Organic Letters
https://www.readbyqxmd.com/read/28636390/application-of-a-heterogeneous-chiral-titanium-catalyst-derived-from-silica-supported-3-aryl-h8-binol-to-enantioselective-alkylation-and-arylation-of-aldehydes
#5
Junichiro Akai, Satoshi Watanabe, Kumiko Michikawa, Toshiro Harada
A 3-aryl H8-BINOL was grafted on the surface of silica gel using a hydrosilane derivative as a precursor, and the resulting silica-supported ligand (6 mol %) was employed in the enantioselective alkylation and arylation of aldehydes in the presence of Ti(O(i)Pr)4. The reactions using Et2Zn, Et3B, and aryl Grignard reagents all afforded the corresponding adducts in high enantioselectivities and yields. The silica-immobilized titanium catalyst could be reused up to 14 times without appreciable deterioration of the activity...
June 21, 2017: Organic Letters
https://www.readbyqxmd.com/read/28636385/sequential-catalysis-of-phosphine-oxide-for-stereoselective-synthesis-of-stereopentads
#6
Shunsuke Kotani, Kosuke Kai, Masaharu Sugiura, Makoto Nakajima
An efficient method for accessing enantiomerically pure stereopentads via a catalytic asymmetric sequential aldol reaction has been developed for the first time. The enantioselective sequential aldol reaction produces a wide range of chiral stereopentad precursors in good yields with excellent enantioselectivities. The key to success is the use of the sequential catalytic system involving a chiral phosphine oxide catalyst and trichlorosilyl triflate.
June 21, 2017: Organic Letters
https://www.readbyqxmd.com/read/28632391/transfer-hydrogenation-of-carbonyl-derivatives-catalyzed-by-an-inexpensive-phosphine-free-manganese-precatalyst
#7
Antoine Bruneau-Voisine, Ding Wang, Vincent Dorcet, Thierry Roisnel, Christophe Darcel, Jean-Baptiste Sortais
A very simple and inexpensive catalytic system based on abundant manganese as transition metal and on an inexpensive phosphine-free bidendate ligand, 2-(aminomethyl)pyridine, has been developed for the reduction of a large variety of carbonyl derivatives with 2-propanol as hydrogen donor. Remarkably, the reaction proceeds at room temperature with low catalyst loading (down to 0.1 mol %) and exhibits a good tolerance toward functional groups. High TON (2000) and TOF (3600 h(-1)) were obtained.
June 20, 2017: Organic Letters
https://www.readbyqxmd.com/read/28632389/chiral-selenide-catalyzed-enantioselective-construction-of-saturated-trifluoromethylthiolated-azaheterocycles
#8
Jie Luo, Yannan Liu, Xiaodan Zhao
An indane-based, bifunctional, chiral selenide catalyst has been developed. The new catalyst is efficient for the enantioselective synthesis of saturated azaheterocycles possessing a trifluoromethylthio group. The desired products were obtained in good yields with high diastereo- and enantioselectivities.
June 20, 2017: Organic Letters
https://www.readbyqxmd.com/read/28631488/synthesis-of-6-7-dideoxysqualestatin-h5-by-carbonyl-ylide-cycloaddition-rearrangement-and-cross-electrophile-coupling
#9
Younes Fegheh-Hassanpour, Tanzeel Arif, Herman O Sintim, Hamad H Al Mamari, David M Hodgson
An asymmetric synthesis of (-)-6,7-dideoxysqualestatin H5 is reported. Key features of the synthesis include the following: (1) highly diastereoselective n-alkylation of a tartrate acetonide enolate and subsequent oxidation-hydrolysis to provide an asymmetric entry to a β-hydroxy-α-ketoester motif; (2) facilitation of Rh(II)-catalyzed cyclic carbonyl ylide formation-cycloaddition by co-generation of keto and diazo functionality through ozonolysis of an unsaturated hydrazone; and (3) stereoretentive Ni-catalyzed Csp(3)-Csp(2) cross-electrophile coupling between tricarboxylate core and unsaturated side chain to complete the natural product...
June 20, 2017: Organic Letters
https://www.readbyqxmd.com/read/28631487/chemoselective-nitrile-oxide-alkyne-1-3-dipolar-cycloaddition-reactions-from-nitroalkane-tethered-peptides
#10
Rahi M Reja, Sereena Sunny, Hosahudya N Gopi
Synthesis and incorporation of a new amino acid with a nitroalkane side chain into peptides, in situ transformation of a nitroalkane side chain into nitrile oxide, and chemoselective 1,3-dipolar cycloaddition reactions between in situ generated nitrile oxide and different alkynes are reported. The nitroalkane-mediated nitrile oxide-alkyne cycloaddition was found to be orthogonal to the copper(I)-catalyzed azide-alkyne cycloaddition reaction. The combination of orthogonal nitrile oxide-alkyne and azide-alkyne cycloaddition reactions can be explored to tailor different 1,2,3-triazole and 3,5-isoxazoles, respectively, on the peptide backbone...
June 20, 2017: Organic Letters
https://www.readbyqxmd.com/read/28631486/melding-caged-compounds-with-supramolecular-containers-photogeneration-and-miscreant-behavior-of-the-coumarylmethyl-carbocation
#11
Nareshbabu Kamatham, José P Da Silva, Richard S Givens, V Ramamurthy
By merging well-established concepts of supramolecular chemistry, protecting group strategy, and photochemistry, we have solubilized in water hydrophobic organic molecules consisting of a photoactive protecting group and masked carboxylic acids, released the desired acid, and confined a reactive carbocation intermediate within a capsule. Confinement of the photogenerated carbocation brought out the latent radical-like behavior. This observation is consistent with the recent theoretical prediction of the 7-(diethylamino)coumarinyl-4-methyl carbocation having a triplet diradical ground-state electronic contribution...
June 20, 2017: Organic Letters
https://www.readbyqxmd.com/read/28631468/pyrene-tagged-ionic-liquids-separable-organic-catalysts-for-sn2-fluorination
#12
Abu Taher, Kyo Chul Lee, Hye Ji Han, Dong Wook Kim
We prepared pyrene-substituted imidazolium-based ionic liquids (PILs) as organic catalysts for the SN2 fluorination using alkali metal fluoride (MF). In this system, the PIL significantly enhanced the reactivity of MF due to the phase-transfer catalytic effect of the imidazolium moiety as well as the metal cation-π (pyrene) interactions. Furthermore, this homogeneous catalyst PIL was easily separated from the reaction mixture using reduced graphene oxide by π-π stacking with the pyrene of PIL.
June 20, 2017: Organic Letters
https://www.readbyqxmd.com/read/28627177/rhodium-iii-catalyzed-selective-c-h-acetoxylation-and-hydroxylation-reactions
#13
Yunxiang Wu, Bing Zhou
An efficient Cp*Rh(III)-catalyzed, chelation-assisted C(sp(2))-H acetoxylation and hydroxylation reaction has been developed for the first time. The reaction proceeds under mild conditions and allows for selective preparation of C-H acetoxylation and hydroxylation products, thus providing a good complement to previous C-H oxygenation reactions and expanding the field of Cp*Rh(III)-catalyzed C-H functionalizations.
June 19, 2017: Organic Letters
https://www.readbyqxmd.com/read/28621955/regioselective-three-component-reaction-of-pyridine-n-oxides-acyl-chlorides-and-cyclic-ethers
#14
D Heulyn Jones, Steven T Kay, Jayde A McLellan, Alan R Kennedy, Nicholas C O Tomkinson
A novel three-component reaction of pyridine N-oxides, acyl chlorides, and cyclic ethers is described. Treatment of an electron-deficient pyridine N-oxide with an acyl chloride in the presence of a cyclic ether at 25-50 °C leads to a substituted pyridine as a single regioisomer in up to 58% isolated yield. Isotopic-labeling experiments and substrate scope support the reaction proceeding through a carbene intermediate.
June 16, 2017: Organic Letters
https://www.readbyqxmd.com/read/28621951/bioinspired-total-synthesis-and-stereochemical-revision-of-the-fungal-metabolite-pestalospirane-b
#15
Sandhya Badrinarayanan, Christopher J Squire, Jonathan Sperry, Margaret A Brimble
The total synthesis of both enantiomers of pestalospirane B, 2, has been achieved using a bioinspired tandem dimerization-spiroketalization reaction. Electronic circular dichroism (ECD) and X-ray analysis were used to revise the absolute stereochemistry of the natural product pestalospirane B from 3S, 3'S, 12R, 12'R to its enantiomer 3R, 3'R, 12S, 12'S.
June 16, 2017: Organic Letters
https://www.readbyqxmd.com/read/28621545/rh-iii-catalyzed-carboamination-of-propargyl-cycloalkanols-with-arylamines-via-csp-2-h-csp-3-csp-3-activation
#16
Xinwei Hu, Xun Chen, Yong Zhu, Yuanfu Deng, Huaqiang Zeng, Huanfeng Jiang, Wei Zeng
A Rh(III)-catalyzed carboamination of alkynyl cycloalkanols with arylamines has been developed. This transformation involves a novel Csp(2)-H/Csp(3)-Csp(3) activation relay and provides an efficient approach to versatile 1,2,3-trisubstituted indoles with a broad range of functional group tolerance.
June 16, 2017: Organic Letters
https://www.readbyqxmd.com/read/28621539/dual-role-of-h2o2-in-palladium-catalyzed-dioxygenation-of-terminal-alkenes
#17
Jiuzhong Huang, Jianxiao Li, Jia Zheng, Wanqing Wu, Weigao Hu, Lu Ouyang, Huanfeng Jiang
A palladium-catalyzed, environmentally friendly dioxygenation reaction of simple alkenes has been developed that enabled rapid assembly of valuable α-hydroxy ketones with high atom economy. Notably, control experiments and (18)O isotope-labeling experiments established that H2O2 played a dominant dual role in this transformation.
June 16, 2017: Organic Letters
https://www.readbyqxmd.com/read/28617613/additions-of-organomagnesium-halides-to-%C3%AE-alkoxy-ketones-revision-of-the-chelation-control-model
#18
Jacquelyne A Read, Yingying Yang, K A Woerpel
The chelation-control model explains the high diastereoselectivity obtained in additions of organometallic nucleophiles to α-alkoxy ketones but fails for reactions of allylmagnesium halides. Low diastereoselectivity in ethereal solvents results from no chelation-induced rate acceleration. Additions of allylmagnesium bromide to carbonyl compounds are diastereoselective using CH2Cl2 as the solvent even though rate acceleration is still absent. Stereoselectivity likely arises from the predominance of the chelated form in solution...
June 15, 2017: Organic Letters
https://www.readbyqxmd.com/read/28617610/total-synthesis-of-the-cyclic-dodecapeptides-wewakazole-and-wewakazole-b
#19
Martyn Inman, Hannah L Dexter, Christopher J Moody
The cyclic dodecapeptides wewakazole and wewakazole B have been synthesized by a divergent strategy via a common tris-proline containing oxazole octapeptide and two separate bis-oxazole containing tetrapeptide units, followed by peptide coupling and macrocyclization. The three oxazole amino acid fragments are readily accessible by rhodium(II)-catalyzed amide N-H insertion of diazocarbonyl compounds, or by the cycloaddition of rhodium carbenoids with nitriles.
June 15, 2017: Organic Letters
https://www.readbyqxmd.com/read/28617609/transition-metal-free-photoinduced-intramolecular-annulation-of-2-3-di-hetero-arylchromen-4-one
#20
Jie Han, Tao Wang, Yong Liang, Ying Li, Chenchen Li, Rui Wang, Siqi Feng, Zunting Zhang
An efficient transition-metal-free photoinduced intracyclization of 4H-chromen-4-ones in EtOH-H2O (7:1, v/v) at ambient temperature for the construction of complicated fused-ring heteroaromatics is established. The reaction proceeds smoothly without requiring any catalysts/additives.
June 15, 2017: Organic Letters
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