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Organic Letters

Yanchi Chen, Guobin Ma, Hegui Gong
This work illustrates a reductive cross-electrophile coupling protocol for trifluoromethylation of alkyl iodides under Cu-catalyzed/Ni-promoted reaction conditions. The use of diboron esters as the terminal reductant allows the effective generation of the alkyl-CF3 products with excellent functional group tolerance and broad substrate scope. A mechanism involving a reaction of alkyl-Cu with Togni's reagent was proposed.
July 19, 2018: Organic Letters
Shan Lu, Shinichi Nishimura, Kei Takenaka, Masashi Ito, Taira Kato, Hideaki Kakeya
The highly reactive precursor molecule, presaccharothriolide X, was successfully isolated from the rare actinomycete Saccharothrix sp. A1506. The comparable biological activity of presaccharothriolide X and its Michael addition product saccharothriolide B unveils a unique masking/activating property of 2-aminophenol. Unexpectedly, 2-aminophenol in saccharothriolide B was eliminated through a retro-Michael reaction, to yield presaccharothriolide X under physiological conditions. 2-Aminophenol might be developed into a useful protecting group for bioactive small molecules with an α,β-unsaturated ketone...
July 19, 2018: Organic Letters
Jing-Hao Li, Qi Huang, Shun-Yi Wang, Shun-Jun Ji
S3 •- -mediated [1 + 2 + 2] and [1 + 3 + 1] cycloaddition reactions of aromatic alkynes to give tetraphenylthiophene and 2-benzylidenetetrahydrothiophene derivatives via two C-S bond formations are developed. These two protocols provide new, simple, and straightforward strategies to construct tetraphenylthiophene and 2-benzylidenetetrahydrothiophene derivatives under transition-metal-free conditions. This study also expands the application of S3 •- in organic reactions.
July 19, 2018: Organic Letters
Jian Yang, Chaoqi Ke, Dong Zhang, Xiaohua Liu, Xiaoming Feng
An efficient asymmetric intramolecular trapping of ammonium ylides of α-diazoketones with enones to synthesize indoline derivatives was realized. A Rh(II)/chiral N,N'-dioxide-Sc(III) complex bimetallic relay catalytic system was established. A series of optically active 2,2,3-trisubstituted indolines were obtained in high yields (up to 99%), good enantioselectivities (up to 99% ee), and excellent diastereoselectivities (up to >19:1 dr) under mild reaction conditions.
July 19, 2018: Organic Letters
Xuan-Hui Ouyang, Chao Hu, Ren-Jie Song, Jin-Heng Li
Straightforward access to various substituted naphthalenones by copper-catalyzed [4 + 2] annulation cascades of 2-bromo-1-arylpropan-1-ones with terminal alkynes is presented. Employing a Cu(MeCN)4 PF4 catalyst and 1,10-phenanthroline (1,10-Phen) ligand enables the formation of three new C-C bonds in a single reaction via [4 + 2] annulation of a 2-bromo-1-arylpropan-1-one with an alkyne followed by α-alkylation with the other 2-bromo-1-arylpropan-1-one with excellent functional group tolerance and step efficiency...
July 19, 2018: Organic Letters
Liting Yu, Mei-Lin Tang, Chang-Mei Si, Zhi Meng, Yongxi Liang, Jilai Han, Xun Sun
An efficient and mild zinc-mediated decarboxylative alkylation of gem-difluoroalkenes with N-hydroxyphthalimide (NHP) esters, to give monofluoroalkenes in moderate to excellent yields with high Z-selectivity is reported. The reaction tolerates a broad range of functional groups and can be easily scaled up, which thus may pave the way for its further applications in medicinal chemistry and materials science.
July 19, 2018: Organic Letters
Jing-Feng Zhao, Xin-Hua Duan, Yu-Rui Gu, Pin Gao, Li-Na Guo
An iron-catalyzed redox-neutral, decarboxylative olefination of cycloketone oxime esters with α,β-unsaturated carboxylic acids has been developed. This reaction involves an iminyl radical mediated C-C bond cleavage/radical addition/decarboxylation cascade. This protocol is highlighted by its low-cost catalytic system and readily accessible starting materials, as well as broad substrate scope, thus providing facile access to structurally diverse cyano-containing alkenes.
July 19, 2018: Organic Letters
Xin-Yi Liu, Chuang-Jun Li, Fang-You Chen, Jie Ma, Shuo Wang, Yu-He Yuan, Li Li, Dong-Ming Zhang
Three triterpene saponins, nototronesides A-C (1-3), possessing an unprecedented 6/6/9 fused tricyclic tetranordammarane core, were isolated from the leaves of Panax notoginseng. Their structures were elucidated on the basis of spectroscopic data, and the structure of sapogenin (1a) was further confirmed by X-ray crystallography. The existence of 1-3 adds a new dimension to the diversity of the triterpene family. Moreover, compound 2 showed a moderate neuroprotective effect on serum deficiency-induced cellular damage in PC12 cells...
July 18, 2018: Organic Letters
Chen Li, Shi-Meng Wang, Hua-Li Qin
The first Rh-catalyzed activation of ortho sp2 C-H bonds of aldehydes (ketones) for monoselective coupling with ethenesulfonyl fluoride was accomplished without covalent or transient preinstallation of imines. The 42 examples revealed that the developed method has the advantage of a wide scope and functional-group tolerability. Application of this method for complicated natural product modification was also accomplished.
July 18, 2018: Organic Letters
Dinesh N Sawant, Dattatraya B Bagal, Saeko Ogawa, Kaliyamoorthy Selvam, Susumu Saito
Tetrakis(dimethylamido)diboron and tetrahydroxydiboron are herein reported as new catalysts for the synthesis of aryl amides by catalytic condensation of aromatic carboxylic acids with amines. The developed protocol is both simple and highly efficient over a broad range of substrates. This method thus represents an attractive approach for the use of diboron catalysts in the synthesis of amides without having to resort to stoichiometric or additional dehydrating agents.
July 18, 2018: Organic Letters
Ryosuke Yamada, Tohru Fukuyama, Satoshi Yokoshima
During the course of synthetic studies of the Daphniphyllum alkaloids, an unusual reaction of a rhodium carbenoid was observed. The bicyclic substrate, in which an α-diazo-β-ketoester moiety was present at the 3-position of a 1,4-diene moiety, was treated with rhodium pivalate to produce an intermediate having diene and ketene moieties. This intermediate underwent an intramolecular [4 + 2] cycloaddition reaction to form a tetracyclic compound.
July 18, 2018: Organic Letters
Jia-Nan Mo, Wan-Lei Yu, Jian-Qiang Chen, Xiu-Qin Hu, Peng-Fei Xu
Direct visible-light-mediated aminofluorination of styrenes has been developed with high regioselectivity. Shelf-stable N-Ts-protected 1-aminopyridine salt was used as the nitrogen-radical precursor, and the commercially available hydrogen fluoride-pyridine was used as the nucleophilic fluoride source. The synthesis of an analogue of LY503430 was performed to demonstrate the synthetic value of this strategy.
July 18, 2018: Organic Letters
Zhengshen Wang, Luxin Chen, Yuan Yao, Zhigang Liu, Jin-Ming Gao, Xuegong She, Huaiji Zheng
An efficient method to build various multisubstituted polycyclic indoline-annulated normal to medium-size rings through dearomatization of indole via a tandem 1,2-acyloxy migration/intramolecular [3 + 2] cycloaddition process is described. The pentacyclic skeleton of strychnine could be synthesized via this tandem cycloaddition and a further Mannich reaction. This approach would provide a novel strategy to the synthesis of strychons alkaloids.
July 17, 2018: Organic Letters
Duk Yi, Feng Zhu, Maciej A Walczak
A series of cyclic C-glycosides were synthesized using the palladium-catalyzed stereoretentive intramolecular glycosylation of aryl iodides by employing a bulky phosphine ligand. A variety of functional groups are tolerated in the reaction, and enantioenriched anomeric nucleophiles could be coupled without erosion of optical purity. This study offers a unified method to access both cis- and trans-fused rings by capitalizing on the stereoretentive nature of the Stille reaction. In addition, competition experiments for intermolecular and intramolecular cross-couplings revealed secondary KIEs of 1...
July 17, 2018: Organic Letters
Marissa Bylsma, Clay S Bennett
A synthetic route has been developed for constructing the d-saccharosamine-l-rhamnose-d-fucose (Sac-Rha-Fuc) trisaccharide fragment present in the antibacterial natural product saccharomicin B. The Sac monosaccharide was synthesized through a modified nine step procedure starting from d-rhamnal in 23% overall yield. 1- O-TBS Sac donors were used to construct the β-linked Sac-Rha disaccharide. This disaccharide was coupled to a Fuc acceptor under BSP/Tf2 O conditions to afford a trisaccharide properly functionalized for elaboration to saccharomicin B...
July 17, 2018: Organic Letters
Debobrata Paul, Sanu Saha, Rajib Kumar Goswami
A short and convergent strategy for the first asymmetric total synthesis of cytotoxic macrolides pestalotioprolides E and F has been developed. The key features of this synthesis include Takai olefination, Sonogashira coupling, Ni-assisted partial hydrogenation of alkyne, modified Steglich reaction to generate the ester moiety, and intramolecular Horner-Wadsworth-Emmons (HWE) olefination to complete the macrocycle. This synthetic study revised the proposed structure of pesralotioprolide F.
July 17, 2018: Organic Letters
Su Yong Go, Geun Seok Lee, Soon Hyeok Hong
Exclusively α- and highly E/ Z-selective hydroalkylation of ynone, ynoate, and ynamide was achieved via photoredox mediated Ni/Ir dual catalysis with high atom and step economy, producing trisubstituted enones, which are versatile synthetic building blocks. The developed reaction selectively delivered the α/ Z isomer, which is complementary to the previously reported β-alkylation processes. The trisubstituted enones could be transformed to more valuable compounds via post-functionalization.
July 17, 2018: Organic Letters
Pradheep Eradi, Samir Ghosh, Peter R Andreana
The tetrasaccharide repeating unit of zwitterionic polysaccharide A1 (PS A1) from Bacteroides fragilis ATCC 25285/NCTC 9343 has been synthesized using a linear glycosylation approach. One key step includes an α(1,4)-stereoselective [2 + 1] glycosylation of a 2,4,6-trideoxy-2-acetamido-4-amino-d-Gal p (AAT) donor with a poorly reactive axial C4-OH disaccharide acceptor. Mild acid-mediated deacetylation and a challenging [3 + 1] glycosylation are also highlighted. The strategy is inclusive of a single-pot, three-step deprotection affording PS A1 with alternating charges on adjacent monosaccharide units...
July 17, 2018: Organic Letters
Xu Han, Nidal Saleh, Pascal Retailleau, Arnaud Voituriez
A series of 1,2-dihydroquinolines were synthesized in good to excellent yields by reacting 2-aminobenzaldehyde derivatives and dialkyl acetylenedicarboxylates with catalytic amounts of phosphine. This reaction was rendered catalytic by the selective in situ phosphine oxide reduction with the use of phenylsilane. Furthermore, with the same starting materials and with an additional role of the reducing agent, a new olefination reaction was discovered. Hydrogen/deuterium (H/D) exchange experiments revealed the possible mechanism of this reaction...
July 17, 2018: Organic Letters
Jun-Liang Zeng, Zhen Chen, Fa-Guang Zhang, Jun-An Ma
Phenylsulfone difluorodiazoethane (PhSO2 CF2 CHN2 ), an easy-to-prepare and bench-stable masked CF2 -building block, has been developed. The synthetic utility of this reagent is demonstrated by a direct regioselective [3 + 2] cycloaddition with electron-deficient alkynes and alkenes. This protocol enables facile construction of an array of difluoromethyl-substituted pyrazoles in good to high yields under mild reaction conditions.
July 17, 2018: Organic Letters
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