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Journal of Organic Chemistry

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https://www.readbyqxmd.com/read/28748700/wittig-cyclization-of-%C3%AF-hydroxy-hemiacetals-synthesis-of-aspicilin
#1
René Schmidt, Michael Ostermeier, Rainer Schobert
The polyhydroxylated 18-membered lichen macrolide (+)-aspicilin was synthesized in 12 steps and 17% yield (longest linear sequence) starting from D-mannose and (S)-propylene oxide as the source of the stereogenic centers. Key steps were a palladium-catalyzed Csp3X-Csp3ZnX Negishi cross-coupling affording an ω-hydroxy hemiacetal which was macrocyclized via a domino addition-Wittig olefination reaction with the cumulated ylide Ph3PCCO. This synthetic approach also allowed a regioselective glycosylation of 6-OH of aspicilin with D desosamine, a quick entry to chimeric macrolides with potential antibiotic activity...
July 27, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28748699/1-3-syn-diaxial-repulsion-of-typical-protecting-groups-used-in-carbohydrate-chemistry-in-3-o-substituted-derivatives-of-isopropyl-d-idopyranosides
#2
Bozhena Sergeyevna Komarova, Alexey G Gerbst, Anastasiia M Finogenova, Andrey S Dmitrenok, Yury Evgenievich Tsvetkov, Nikolay E Nifantiev
The strength of 1,3-syn-diaxial repulsion was evaluated for main types of protecting groups (alkyl, silyl and acyl) usually used in carbohydrate chemistry. As molecular probes for this study, derivatives of isopropyl 2-O-benzyl-4,6-O-benzylidene-α-D-idopyranoside bearing allyl, acetyl and tert-butyldiphenylsilyl (TBDPS) protecting groups at O-3 were prepared from p-methoxyphenyl D-galactopyranoside. The equilibrium between (O)S2 and (4)C1 conformations in these compounds was investigated using (3)JH,H and (3)JС,H coupling constants that were determined from 1D (1)H-NMR and 2D J-resolved HMBC spectra in various solvents...
July 27, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28748692/reductive-activation-of-c70-equatorial-carbons-and-structurally-characterized-c70-%C3%AE-adduct-with-closed-5-6-ring-fusion
#3
Wei-Wei Yang, Zong-Jun Li, Shu-Hui Li, Sheng-Li Wu, Zujin Shi, Xiang Gao
The C70 δ-adducts with closed [5,6]-ring fusion are an important type of compounds in classifying the bond delocalization in the equatorial belt of C70. However, the formation of such compounds is severely restricted due to the low reactivity of the carbon atoms in the flat equatorial region. Such a restriction is lifted when reduced anionic C70 species are used, where the inert equatorial carbon atoms are activated.
July 27, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28721732/radical-addition-insertion-cyclization-cascade-reaction-to-assemble-phenanthridines-from-n-arylacrylamide-using-cyano-as-a-bridge-under-photoredox-catalysis
#4
Yulan Yu, Zhiqiang Cai, Weiwen Yuan, Ping Liu, Peipei Sun
A radical addition/nitrile insertion/homolytic aromatic substitution (HAS) cascade reaction to prepare 6-quaternary alkylated phenanthridines was developed. The addition of the active methylene radicals which were generated from 2-bromoacetonitrile, ethyl 2-bromoacetate, 2-bromo-N,N-dimethylacetamide, or 2-bromo-1-phenylethan-1-one to carbon-carbon double bonds of N-arylacrylamides followed by the cyano-participating sequential cyclization produced a series of phenanthridines in moderate to good yields under photoredox catalysis...
July 27, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28745886/sulfoximidoyl-containing-hypervalent-iodine-iii-reagents-1-sulfoximidoyl-1-2-benziodoxoles
#5
Han Wang, Duo Zhang, He Sheng, Carsten Bolm
Treatment of NH-sulfoximines with pseudocyclic benziodoxole triflate results in N-I bond formation leading to a new type of sulfoximidoyl-containing hypervalent iodine(III) reagents in high yields. Degradation studies revealed a pronounced stability in both the solid state and in solution.
July 26, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28745884/on-the-origins-of-small-proton-chemical-shift-differences-in-monodeuterated-methyl-groups
#6
O Maduka Ogba, Stuart J Elliott, David A Kolin, Lynda J Brown, Sebastian Cevallos, Stuart Sawyer, Malcolm H Levitt, Daniel J O'Leary
We have recently shown that the small proton chemical shift difference in 2-methyl-1-(methyl-d)piperidine supports a long-lived nuclear spin state. To identify additional candidate molecules with CH2D groups exhibiting accessible long-lived states, and to investigate the factors governing the magnitude of the shift differences, we report a computational and experimental investigation of methyl rotational dynamics and proton chemical shifts in a variety of 2-substituted 1-(methyl-d)piperidines. The polarity and size of the 2-substituent affect the 1,2-stereoisomeric relationship and consequently the strength of the rotational asymmetry within the CH2D group...
July 26, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28745505/iron-catalyzed-direct-c3-benzylation-of-indoles-with-benzyl-alcohols-through-borrowing-hydrogen
#7
Giovanni Di Gregorio, Michele Mari, Francesca Bartoccini, Giovanni Piersanti
We present the coupling of primary and secondary benzyl alcohols with indoles to form 3-benzylated indoles and H2O that is catalyzed, for the first time, by a complex of earth-abundant iron. This transformation accommodates a variety of substrates and is distinguished by its operational simplicity, sustainability, high functional-group tolerance, and amenability to gram-scale synthesis. On the basis of the preliminary experimental observations, we propose that the reaction proceeds through a borrowing hydrogen process...
July 26, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28745048/tautomerism-induced-cis-trans-isomerization-of-pyridylethenyl-n-confused-porphyrin
#8
Ryuichi Sakashita, Yasutaka Oka, Hisanori Akimaru, Praseetha E Kesavan, Masatoshi Ishida, Motoki Toganoh, Tomoya Ishizuka, Shigeki Mori, Hiroyuki Furuta
Pyridylethenyl-substituted N-confused porphyrins (NCPs) were synthesized and their cis-trans isomerization was studied. Among 4 possible isomers, trans-3H and cis-2H types of structures, of which aromaticity and absorption/emission properties differ largely, were isolated. The cis-isomer was largely stabilized by the intramolecular hydrogen bonding between the pyrrolic-NH and the pyridinic-N in the vicinity. The thermal cis-trans isomerization proceeded even at 30 °C, which was significantly accelerated by the pyridine added to the system...
July 26, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28742360/chiral-br%C3%A3-nsted-acid-catalyzed-enantioselective-aza-friedel-crafts-reaction-of-cyclic-%C3%AE-diaryl-n-acyl-imines-with-indoles
#9
Danijel Glavač, Chao Zheng, Irena Dokli, Shu-Li You, Matija Gredičak
Asymmetric addition of indoles to α-diaryl-substituted ketimines, which are generated in situ from 3-aryl 3-hydroxyisoindolinones, is described. The transformation proceeds smoothly with a broad range of indoles and isoindolinone alcohols using a SPINOL-derived chiral Brønsted acid catalyst to afford α-tetrasubstituted (3-indolyl)(diaryl)methylamines in excellent yields and enantioselectivities (up to 98 % yield, up to >99:1 e.r.). The origin of stereochemical induction is elucidated by DFT calculations and experimental data...
July 25, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28742352/stereocontrolled-nucleophilic-addition-to-five-membered-oxocarbenium-ions-directed-by-the-protecting-groups-application-to-the-total-synthesis-of-varitriol-and-of-two-diastereoisomers-thereof
#10
Alma Sánchez-Eleuterio, William Hernán García-Santos, Howard Díaz-Salazar, Marcos Hernández-Rodríguez, Alejandro Cordero-Vargas
A stereodivergent C-glycosidation of carbohydrate-derived lactones can be mediated by the protecting groups, and applied to the total synthesis of (+)-varitriol and of two diastereoisomers thereof, which represent an unprecedent use of the protecting groups in the synthesis of a naturally occurring compound. In particular, the stereoselective nucleophile attack for 2,3-trans substituted five-membered ring oxocarbenium ions is strongly influenced by the presence of aromatic rings in the protecting groups. According to quantum chemical calculations, the stereoselectvity depends on the π-π interactions between the aromatic ring of the C-2 protecting group with the exocyclic triple bond and the oxocarbenium ion...
July 25, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28741947/a-domino-azidation-c-h-amination-approach-towards-trifluoromethylsubstituted-imidazoles
#11
Haichao Ma, Xiaoyan Zhang, Liangliang Chen, Wei Yu
N-Alkyl enamines can be transformed into 2,4,5-trisubsituted imidazoles by reacting with (diacetoxyiodo) benzene and TMSN3 under the catalysis of a copper salt such as Cu(OAc)2. Tetrabutyl ammonium iodide was also capable of promoting the reaction. The transformations from N-alkyl enamines into 2,4,5-trisubsituted imidazoles took place in a domino azidation/intramolecular C(sp3)H amination pattern. The present reaction provides a new efficient method for the preparation of 5-(trifluoromethyl) imidazoles.
July 25, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28741945/copper-catalyzed-oxidative-coupling-of-%C3%AE-keto-esters-with-n-methylamides-for-the-synthesis-of-symmetrical-2-3-5-6-tetrasubstituted-pyridines
#12
Yizhe Yan, Hongyi Li, Zheng Li, Bin Niu, Miaomiao Shi, Yanqi Liu
A copper-catalyzed oxidative formal [2+2+1+1] cycloaddition for the synthesis of symmetrical tetrasubstituted pyridines was first demonstrated. The reaction is involved in a domino CDC of β-keto esters and N-methylamides, C-N cleavage, Michael addition, condensation and oxidative aromatization process. Multiple C-C and C-N bonds were constructed in one pot via C-H and C-N cleavage of N-methylamides, which was employed as carbon source of pyridines. The preliminary mechanistic studies revealed that C(sp3)-H bond cleavage of N-methylamides was the rate-determining step...
July 25, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28741357/modular-construction-of-protected-1-2-1-3-diols-amino-alcohols-and-diamines-via-catalytic-asymmetric-dehydrative-allylation-an-application-to-synthesis-of-sphingosine
#13
Shinji Tanaka, Ramachandran Gunasekar, Tatsuya Tanaka, Yoko Iyoda, Yusuke Suzuki, Masato Kitamura
A new enantioselective catalysis has been developed for the one-step construction of methylene-bridged chiral modules of 1,2- and 1,3-OH and/or NH function(s) from δ- or λ-OH/NHBoc-substituted allylic alcohols and "H2C=O"/"H2C=NBoc." A protonic nucleophile, either in situ generated CH2OH or CH2NHBoc, is intramolecularly allylated to furnish eight possible 1,2- or 1,3-O,O, -O,N, -N,O, and -N,N chiral modules equipped with an ethenyl group in high yields and enan-tioselectivities. The utility of this method has been demonstrated in the five-step synthesis of sphingosine...
July 25, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28741354/stereocontrolled-synthesis-of-left-halves-of-halichondrins
#14
Kenzo Yahata, Ning Ye, Kentaro Iso, Yanran Ai, Jihoon Lee, Yoshito Kishi
A stereocontrolled synthesis of the left halves of halichondrins was reported. An intramolecular oxy-Michael reaction under basic conditions was used to construct the [6,6]-spiroketal in a stereocontrolled manner. With this approach, the left halves of halichondrins, homohalichondrins, and norhalichondrins were synthesized.
July 25, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28741352/unified-synthesis-of-right-halves-of-halichondrins-a-c
#15
Kenzo Yahata, Ning Ye, Kentaro Iso, Santhosh Reddy Naini, Shuji Yamashita, Yanran Ai, Yoshito Kishi
Right halves of halichondrins A-C were synthesized by coupling the common C20-C37 building block 9 with the C1-C19 building blocks 10a~c, respectively. Catalytic, asymmetric Ni/Cr-mediated coupling was used for three C-C bond formations. For all the cases, the stereochemistry was controlled with the Cr-catalyst prepared from the chiral sulfonamide identified via the toolbox approach. For (3+4)-, (6+7)-, and (9+10)-couplings, the stereoselectivity of 28:1, >40:1, and ~20:1 was achieved by the Cr-catalysts prepared from (S)-H, (S)-I, and (R)-L, respectively...
July 25, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28703582/organocatalytic-asymmetric-mannich-aza-michael-cascade-reaction-of-%C3%AE-formyl-%C3%AE-%C3%AE-unsaturated-ketones-with-cyclic-n-sulfimines-enantioselective-synthesis-of-benzosulfamidate-fused-pyrrolidines
#16
Hanna Kim, Yerin Kim, Sung-Gon Kim
A catalytic highly enantioselective Mannich/aza-Michael cascade reaction of δ-formyl-α,β-unsaturated ketones with cyclic N-sulfimines, promoted by diphenylprolinol TMS ether as an organocatalyst, has been developed for the synthesis of chiral benzosulfamidate-fused pyrrolidines, which generated in good yields and with high diastero- and enantioselectivities. Further chemical transformations have been performed with chiral benzosulfamidate-fused pyrrolidines.
July 25, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28738152/natural-products-and-their-mimics-as-targets-of-opportunity-for-discovery
#17
Stephen F Martin
Diverse structural types of natural products and their mimics have served as targets of opportunity in our laboratory to inspire the discovery and development of new methods and strategies to assemble polyfunctional and polycyclic molecular architectures. Furthermore, our efforts toward identifying novel compounds having useful biological properties led to the creation of new targets, many of which posed synthetic challenges that required the invention of new methodology. In this Perspective, selected examples of how we have exploited a diverse range of natural products and their mimics to create, explore, and solve a variety of problems in chemistry and biology will be discussed...
July 24, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28738149/supported-and-unsupported-chiral-squaramides-as-organocatalysts-for-stereoselective-michael-additions-synthesis-of-enantiopure-chromenes-and-spirochromanes
#18
Jose Maria Andres, Jorge Losada, Alicia Maestro, Patricia Rodríguez-Ferrer, Rafael Pedrosa
Novel supported chiral bifunctional squaramides have been easily prepared starting from diamines derived from natural amino acids and commercially available aminoalkyl polystyrene resins. These squaramides behave as excellent stereoselective recoverable organocatalysts in different Michael additions, in neat conditions at room temperature. The reaction on 2-(2-nitrovinyl) phenol as electrophile lead, in excellent yields and enantioselectivities, to intermediates that can be easily transformed into 4H-chromenes, and spirochromanones...
July 24, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28737944/in-situ-generated-glycinyl-chloroaminals-for-a-one-pot-synthesis-of-non-proteinogenic-%C3%AE-amino-esters
#19
Shyam S Samanta, Stephane P Roche
An acetyl chloride-mediated cascade transformation involving a primary carbamate, ethyl glyoxylate and various types of nucleophiles is reported for the synthesis of orthogonally protected α-amino esters. These reactions proceeded rapidly to afford the pivotal α-chloroglycine intermediate in excellent yields which can be directly functionalized in situ with various types of nucleophiles. A mild and unique AcOH(cat.)/AcCl system was found to promote an autocatalytic-like condensation and facilitate the multicomponent assembly of non-proteinogenic α-amino esters...
July 24, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28737943/t-buok-mediated-oxidative-c-sp3-h-arylation-of-2-alkylazaarenes-with-nitroarenes
#20
Shuai-Shuai Li, Shiheng Fu, Liang Wang, Lubin Xu, Jian Xiao
The first transition-metal free and regioselective C(sp3)-H arylation of 2-alkylazaarenes with nitroarenes has been achieved via t-BuOK-mediated dehydrogenative C(sp3)-C(sp2) coupling. This reaction provides an efficient access to the biologically important and synthetically useful 2-benzyl-substituted azaarenes under mild conditions without the need of prefunctionalization of 2-alkylazaarenes or using the specialized arylating agents.
July 24, 2017: Journal of Organic Chemistry
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