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Organic Letters

Séverine Amand, Marine Vallet, Laura Guedon, Grégory Genta-Jouve, Frank Wien, Stéphane Mann, Joëlle Dupont, Soizic Prado, Bastien Nay
Two sesquiterpenes, 4-epi-microsphaeropsisin (1) and a dihydrofurano-2(1H)-naphthalenone (variabilone, 2) which represents a new skeleton, were isolated from endophytic fungus Paraconiothyrium variabile. Reactivity studies showed that eremophilane 1 is a precursor of 2 through acid-promoted methyl 1,2-migration and aromatization. An electrophilic intermediate of this transformation was intercepted by N-acetylcysteamine, a biomimetic nucleophile. Only compound 2 was antibacterial against endophytic bacterium Bacillus subtilis (coisolated with P...
July 24, 2017: Organic Letters
Jiawei Tang, Paramasivam Sivaguru, Yongquan Ning, Giuseppe Zanoni, Xihe Bi
A silver-catalyzed tandem carbon-carbon triple bond hydroazidation, radical addition, and cyclization of biphenyl acetylene is described under mild conditions, leading to the formation of 6-methyl sulfonylated phenanthridines in good yields. In this novel cascade reaction, most of the atoms are incorporated into the product without cleavage of the C≡C bond. Mechanistic studies suggest the reaction should proceed through an iminyl radical reactive intermediate.
July 24, 2017: Organic Letters
Kinthada Ramakumar, Tapan Maji, James J Partridge, Jon A Tunge
A new method is developed for the synthesis of spirooxindoles from amines and isatins via C-H functionalization. The reaction leverages the tert-amino effect to form an enolate-iminium intermediate via [1,5]-hydride shift followed by cyclization. Interestingly the hydride migrates to the N atom of a C═N, which is atypical for hydride additions to imines.
July 24, 2017: Organic Letters
Abhishek A Kadam, Arkady Ellern, Levi M Stanley
We report enantioselective, palladium-catalyzed conjugate additions of arylboronic acids to β-aryl, β,β-disubstituted enones to generate ketones containing bis-benzylic quaternary stereocenters. A catalyst generated from palladium trifluoroacetate and (S)-4-tert-butyl-2-(2-pyridyl)oxazoline ligand ((S)-t-BuPyOx) promotes conjugate additions of a wide range of arylboronic acids to a variety of β-aryl, β,β-disubstituted enones. Iterative addition of the arylboronic acid to minimize undesired protodeboronation pathways leads to efficient formation of the corresponding ketones containing bis-benzylic quaternary stereocenters in up to 92% yield and up to 93% enantioselectivity...
July 24, 2017: Organic Letters
Venubabu Kotikam, Eriks Rozners
Internucleoside amide linkages are excellent mimics of phosphodiesters in RNA and may be used to optimize the properties of short interfering RNAs. Herein we report a remarkably straightforward, efficient and step economic synthesis of C3'-homologated uridine and adenosine amino acids starting from nucleosides in six steps (31% overall yield) and eight steps (16% overall yield), respectively. The key enabling step is a one-pot multifunctional group transformation including a stereoselective hydrogenation, termed "Global Hydrogenation"...
July 21, 2017: Organic Letters
Maria Pérez, Carlos Ramos, Lucia Massi, Silvia Gazzola, Chiara Taglienti, Nihan Yayik, Elies Molins, Antonio Viayna, F Javier Luque, Joan Bosch, Mercedes Amat
A three-step procedure for the enantioselective synthesis of spiro[indolizidine-1,3'-oxindoles], consisting of a stereoselective cyclocondensation reaction between (S)-tryptophanol and a prochiral or racemic δ-oxoester, bromination of the resulting oxazolopiperidone lactam, and a final stereoselective spirocyclization, is reported.
July 21, 2017: Organic Letters
Ya-Ni Wang, Bao-Cheng Wang, Mao-Mao Zhang, Xiao-Wen Gao, Tian-Ren Li, Liang-Qiu Lu, Wen-Jing Xiao
The palladium-catalyzed branch- and enantioselective allylic amination of vinyl benzoxazinones was accomplished through controlling the hydrogen bond direction. This protocol provides a rapid and efficient route for synthesizing an important building block, chiral amino alkene, from widely available aliphatic amines in 64 → 99% yields with up to 99% ee. Furthermore, this transformation and the accompanying products were utilized to develop one-pot reactions through dual catalysis, affording chiral indolines with good synthetic efficiency and excellent enantiocontrol...
July 21, 2017: Organic Letters
Yi Zhao, Vijaybabu Mandadapu, Hasti Iranmanesh, Jonathon E Beves, Anthony I Day
Two new glycoluril diethers have been prepared, bearing strained cyclobutene and cyclobutane rings at the fused junction of the two imidazolidinone rings. The wide angle of the concave face of the cyclobutano derivative enabled the synthesis of cyclobutanocucurbit[5-8]uril, the largest member being the most significant achievement. A limited binding affinity study compared the new substituted family to classical cucurbit[5-8]uril. Surprisingly lower affinities were found, except for cyclobutanocucurbit[6]uril, which was 3...
July 21, 2017: Organic Letters
Ravi P Singh, Jayanta Das, Muhammed Yousufuddin, Delphine Gout, Carl J Lovely
Treatment of propargyl ureas or guanidines with iodosobenzene diacetate results in an oxidative tandem amination/etherification dearomatizing spirocyclization. This transformation leads directly to the complete framework of the Leucetta alkaloids, spirocalcaridine A and B.
July 21, 2017: Organic Letters
Mehdi Makrerougras, Romain Coffinier, Samuel Oger, Arnaud Chevalier, Cyrille Sabot, Xavier Franck
The first synthesis of the proposed structures of chaetoviridins A 1-4 has been achieved in 10 steps by controlling the syn- or anti-aldol side chain. The angular lactone has been regioselectively introduced by condensation of a chiral dioxin-4-one to cazisochromene. Comparison of the NMR and circular dichroism data of the synthesized and reported natural products led to the complete reassignment and renaming of the chaetoviridins.
July 21, 2017: Organic Letters
Shuangjiang Li, Merfat Aljhdli, Haresh Thakellapalli, Behzad Farajidizaji, Yu Zhang, Novruz G Akhmedov, Carsten Milsmann, Brian V Popp, Kung K Wang
A synthetic pathway to a functionalized [9]cycloparaphenylene bearing three indeno[2,1-a]fluorene-11,12-dione-2,9-diyl units in the macrocyclic ring structure ([3]CIFO) has been developed. The (1)H and (13)C NMR spectra show that only the anti rotamer (anti-[3]CIFO) is produced. DFT calculations indicate that the anti rotamer is thermodynamically more stable than the syn rotamer by 4.3 kcal/mol, and the rotational barrier from the anti to syn rotamer is estimated to be 23.3 kcal/mol. The UV-vis and fluorescence spectra and cyclic voltammogram of anti-[3]CIFO were investigated...
July 20, 2017: Organic Letters
Kyung Hwan Oh, Jin Gyeong Kim, Jin Kyoon Park
A copper-catalyzed regiocontrolled three-component reaction afforded diversified 4-aminoquinolines using nitriles, diaryliodoniums, and ynamides. The C7-substituted regioisomers were formed regioselectively when meta-substituted phenyliodonium salts were used. [1,3] N-to-C rearrangement of the products to quinolin-4-ylmethanesulfonamides and simultaneous deprotection of benzyl and sulfonamide group were newly developed. Finally, antimalarial CK-2-68 was successfully prepared.
July 20, 2017: Organic Letters
Renjie Chen, Sunliang Cui
A Rh(III)-catalyzed C-H activation/cyclization of benzamides and diazonaphthalen-2(1H)-ones for synthesis of lactones has been developed. In the presence of Rh(III) catalysis, the benzamides would form rhodacycle species and could be trapped by diazonaphthalen-2(1H)-ones for arylation, and the following intramolecular lactonization would rapidly furnish the products. Thus, the diazonaphthalen-2(1H)-ones were first revealed as a lactonization component in Rh(III)-catalysis, while the kinetic isotope effect study was conducted and a plausible reaction mechanism was proposed...
July 20, 2017: Organic Letters
Su-Lei Zhang, Yong Lu, Yuan-He Li, Kuang-Yu Wang, Jia-Hua Chen, Zhen Yang
Novel oxazaborolidines activated by the strong acid triflimide or AlBr3 form cationic chiral catalysts. These are effective catalysts for highly regio- and enantioselective Diels-Alder reactions using substituted (E)-4-oxopent-2-enoates as dienophiles.
July 20, 2017: Organic Letters
Anup Mandal, Harekrishna Sahoo, Suman Dana, Mahiuddin Baidya
An efficient Ru(II)-catalyzed hydroarylation of maleimides with ready-stock aryl carboxylic acids has been developed based on weak carboxylate-directed ortho-C-H alkylation and concomitant decarboxylation processes, fabricating 3-aryl succinimides, a recurrent scaffold in drug molecules, in high yields (up to 97%). The protocol features operational simplicity, avoids the need for precious metal additives/oxidants, and offers broad substrate scope with formal meta- and para-selectivities. It represents the first example of Ru(II)-catalyzed direct arylation of maleimides with unbiased benzoic acids...
July 20, 2017: Organic Letters
Niklas B Heine, Armido Studer
A method for facile difluoromethylation of various thiols using (difluoromethyl)triphenylphosphonium bromide under mild reaction conditions is presented. The transformation proceeds in the absence of any transition metal using a bench-stable and readily accessible phosphonium salt. Deuterium labeling experiments and cyclic voltammetry measurements reveal that the difluoromethylation occurs via a SRN1-type mechanism. Substrate scope is broad, and various functional groups are tolerated (OH, NH2, amide, ester)...
July 20, 2017: Organic Letters
Kai Huang, Guorong Sheng, Ping Lu, Yanguang Wang
Trifluoroboron-promoted cascade reactions between tryptophols and propagylic alcohols furnished three types of skeletons, including carbazoles, cyclopenta[b]furo[2,3-b]indoles, and allenyl furo[2,3-b]indoles, with excellent selectivity based on the substrate structure. Tryptophols without a substituent on the 2-position of the indole ring reacted with 1,1,3-triphenylprop-2-yn-1-ol and 9-(phenylethynyl)-9H-fluoren-9-ol to give carbazoles and cyclopenta[b]furo[2,3-b]indoles, respectively, while the reaction of 2-substituted tryptophols afforded allenylfuro[2,3-b]indoles...
July 20, 2017: Organic Letters
Marie-Gabrielle Braun, Georgette Castanedo, Ling Qin, Patrick Salvo, Samir Z Zard
A direct and efficient introduction of a trifluoroethylamine motif into various heteroaromatic structures, using a readily available xanthate S-[1-(N-acetylamino)-2,2,2-trifluoroethyl]-O-ethyl dithiocarbonate (5), is reported. Medicinally relevant trifluoroethylaminated heteroarenes containing a wide range of functional groups were successfully synthesized under mild conditions. This amide isostere could be introduced into both electron-rich and -poor heteroarenes to give the desired products in one step. The beneficial effect of camphorsulfonic acid (CSA) was also demonstrated with electron-deficient heteroarenes...
July 20, 2017: Organic Letters
Michael Eisold, Dorian Didier
Alkylidenecyclobutanes (ACBs) containing all-carbon quaternary stereocenters were simply and efficiently synthesized by combining boron-homologation and γ-selective cross-coupling strategies. This unique sequence led to excellent regio- and diastereoselectivities in the generation of targeted four-membered rings with up to 99% enantiomeric excess using chiral substrates. In addition to the original synthesis of ACBs, the first asymmetric catalytic formation of quaternary stereocenters based on γ-selective cross-coupling reactions is finally shown...
July 20, 2017: Organic Letters
Junnosuke Otaka, Daisuke Hashizume, Yui Masumoto, Atsuya Muranaka, Masanobu Uchiyama, Hiroyuki Koshino, Yushi Futamura, Hiroyuki Osada
Hitoyol A (1), an unprecedented norsesquiterpenoid with an exo-tricyclo[,6)]decane skeleton, was isolated from the culture broth of Basidiomycete Coprinopsis cinerea along with a novel skeletal hitoyol B (2) containing 4-cyclopentene-1,3-dione. Their structures and absolute configurations were analyzed by single-crystal X-ray diffraction and electronic circular dichroism spectroscopic methods. Compound 1 is possibly biosynthesized through decarboxylation-induced cyclization of lagopodin B, a known cuparene-type sesquiterpenoid...
July 20, 2017: Organic Letters
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