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Organic Letters

Jiaxin Xie, Jianchun Wang, Guangbin Dong
An efficient strategy to synthesize the western part of phainanoids is reported. The benzofuranone-based 4,5-spirocyclic motif is constructed diastereoselectively via a palladium-catalyzed intramolecular alkenylation. The computational study suggests that the remarkably high diastereoselectivity is attributed to the stabilizing interaction between the 2' carbonyl moiety and the palladium catalyst in the favored transition state.
May 19, 2017: Organic Letters
Sungjong Lee, Kyung-Hee Kim, Cheol-Hong Cheon
A new protocol for the synthesis of 2,2'-bisindole-3-acetic acid derivatives from aldimines derived from 2-aminocinnamic acid derivatives and indole-2-carboxaldehyde was developed via a cyanide-catalyzed imino-Stetter reaction. With this protocol, the divergent total syntheses of arcyriaflavin A, a representative indolocarbazole natural product, and calothrixin B, a representative indolo[3,2-j]phenanthridine natural product, were completed using a 2,2'-bisindole-3-acetic acid derivative as the common intermediate...
May 18, 2017: Organic Letters
Koichi Mitsudo, Yuji Kurimoto, Hiroki Mandai, Seiji Suga
The synthesis of 3-benzo[b]thienyl 3-thienyl ether and its dehydrogenative cyclization leading to benzodithienofuran (BDTF; [1]benzothieno[3,2-b]thieno[2,3-d]furan) are described for the first time. Further transformation of BDTF to more π-extended BDTF derivatives and their fundamental physical properties are also studied.
May 18, 2017: Organic Letters
Fan Yang, Jiaojiao Yu, Yun Liu, Jin Zhu
Aromatic heterocycles have been identified as effective directing groups (DGs) in C-H functionalization but can be retained as undesired bulky substituents in the final products. Herein, we report a Co(III)-catalyzed 1-aminoisoquinoline synthesis strategy based on oxadiazole-directed aromatic C-H coupling with alkynes and a subsequent redox-neutral C-N cyclization reaction. This labile N-O bond-based protocol has allowed the toleration of a broad range of functional groups.
May 18, 2017: Organic Letters
Jinhwan Shin, Jiyoun Lee, Donguk Ko, Nirupam De, Eun Jeong Yoo
A metal-catalyst-free, mild, and efficient synthetic protocol for polycyclic 1,4-benzodiazepines via cascade [5 + 2]/[2 + 2] cycloadditions between pyridinium zwitterions and arynes is reported. Mechanistic experiments revealed that pyridinium zwitterions act as 1,5-dipoles in [5 + 2] cycloadditions with arynes for the construction of 1,4-benzodiazepines, which further undergo [2 + 2] cycloaddition resulting in the one-pot formation of one C-N bond and three C-C bonds.
May 18, 2017: Organic Letters
Xi Wang, Armido Studer
A method for regio- and stereoselective anti-addition of the perfluoroalkyl and the triflate group of phenyl(perfluoroalkyl)iodonium triflates to alkynes is presented. The radical reaction uses cheap CuCl as a smart initiator and can be conducted in gram scale. The perfluoroalkyltriflated products are readily further functionalized, rendering this transformation valuable.
May 18, 2017: Organic Letters
Wanqing Wu, Songjian Yi, Wei Huang, Di Luo, Huanfeng Jiang
A convenient protocol for the synthesis of sulfonylated benzofurans via Ag-catalyzed oxidative cyclization has been established. Chemically stable and easily available sodium sulfinates were used as the sulfonylation reagents and building block for the heterocycle construction. With this novel strategy, various benzofurans bearing dual functional groups could be obtained in good yields with high chemo- and regioselectivities under mild conditions.
May 18, 2017: Organic Letters
Patrick S Fier, Kevin M Maloney
Parallel synthesis and mass-directed purification of a modular ligand library, high-throughput experimentation, and rational ligand evolution have led to a novel copper catalyst for the synthesis of phenols with a traceless hydroxide surrogate. The mild reaction conditions reported here enable the late-stage synthesis of numerous complex, druglike phenols.
May 18, 2017: Organic Letters
Zhen Long, Yudong Yang, Jingsong You
A rhodium-catalyzed regioselective C-H activation/cyclization of azoxy compounds with alkynes has been disclosed to construct a variety of 2H-indazoles. A [4 + 1]-cycloaddition rather than a normal [4 + 2] mode is observed in the process of cyclative capture along with an oxygen-atom transfer and a C≡C triple bond cleavage. This protocol features a broad substrate scope, a good functional group tolerance, and an exclusive regioselectivity.
May 17, 2017: Organic Letters
Zhen Long, Zhigang Wang, Danni Zhou, Danyang Wan, Jingsong You
A Rh(III)-catalyzed tandem C-H alkylation/intramolecular decarboxylative cyclization of azoxy compounds with diazoesters for the synthesis of 3-acyl-2H-indazoles is disclosed. The azoxy instead of the azo group enables a distinct approach for cyclative capture, leading to a [4 + 1]-annulation rather than a classic [4 + 2] manner. The azoxy oxygen atom is traceless after annulation, and further removal from the product is not required. This reaction features a complete regioselectivity for unsymmetrical azoxybenzenes and a compatibility of monoaryldiazene oxides...
May 17, 2017: Organic Letters
Long Liu, Liang-Wei Qian, Shaofeng Wu, Jianyu Dong, Qing Xu, Yongbo Zhou, Shuang-Feng Yin
Using O2 as the oxidant, the benzoxazole frameworks can be directly constructed from the readily available phenols and primary amines in the presence of NH4PF6 over copper under mild conditions. Mechanistic studies showed that a novel mechanism involving biphenyldiols and o-quinones very possibly takes effect in the reaction, because both can selectively give the benzoxazoles under the reaction conditions. An unprecedented unstrained Caryl-Caryl bond cleavage takes place in the reaction.
May 17, 2017: Organic Letters
Roberto Fanelli, Dorothée Berthomieu, Claude Didierjean, Abdelatif Doudouh, Aurélien Lebrun, Jean Martinez, Florine Cavelier
To evaluate the contribution of triethylsilyl α,α-di-n-propylglycine, namely TESDpg, to induce a defined secondary structure, we have prepared model tripeptides in which TESDpg was inserted in three different positions. Studies in solid state and in solution with adapted techniques showed that TESDpg was able to induce a nascent 310 helix in both crystal and solution states.
May 17, 2017: Organic Letters
Abhijit Sau, M Carmen Galan
Pd(MeCN)2Cl2 enables the α-stereoselective catalytic synthesis of 2,3-unsaturated O-glycosides from O(3)-acylated glycals without the requirement for additives to preactivate either donor or nucleophile. Mechanistic studies suggest that, unlike traditional (η3-allyl)palladium-mediated processes, the reaction proceeds via an alkoxy-palladium intermediate that increases the proton acidity and oxygen nucleophilicity of the alcohol. The method is exemplified with the synthesis of a range of glycosides and glycoconjugates of synthetic utility...
May 17, 2017: Organic Letters
Rachael Pittaway, José A Fuentes, Matthew L Clarke
Starting from readily available allylglycine, a tandem hydroformylation-hemiaminal formation reaction has been developed for the synthesis of chiral functionalized piperidines, with very good diastereoselectivity and branched regioselectivity using Rh/(S,S,S)-BOBPHOS catalysts. Tandem hydroformylation-hemiacetal formation also proceeds with good diastereoselectivity (88:12), with the hemiacetal product being hydrogenated with retention of stereochemistry to give a chiral intermediate used in the synthesis of the new antibiotic nemonoxacin...
May 17, 2017: Organic Letters
Xiao-Yan Ma, Xian-Tao An, Xian-He Zhao, Ji-Yuan Du, Yu-Hua Deng, Xiang-Zhi Zhang, Chun-An Fan
A novel Au-catalyzed [2 + 3] annulation reaction of enamides with propargyl esters has been developed, providing a new method for expeditious assembly of synthetically useful functionalized 1-azaspiro[4.4]nonane building blocks. Based on this key annulation, strategic installation of the pivotal azaspirocyclic core, followed by constructing the benzazepine unit via Witkop cyclization, led to the divergent total syntheses of cephalotaxine and cephalezomine H.
May 17, 2017: Organic Letters
Norihiko Hayase, Yuta Miyauchi, Yukimasa Aida, Haruki Sugiyama, Hidehiro Uekusa, Yu Shibata, Ken Tanaka
The synthesis of C4- and C2-symmetrical [8]cycloparaphenylene (CPP)-octacarboxylates has been achieved via macrocyclization by the rhodium-catalyzed intermolecular stepwise cross-cyclotrimerization and subsequent reductive aromatization. The C4-symmetrical octa-tert-butyl [8]CPP-octacarboxylate forms a dimer in which eight ester moieties face each other. The dimers are aligned so as to make a one-dimensional column with a channel structure inside. Both absorption and fluorescence maxima of [8]CPP-octacarboxylates in CHCl3 were significantly blue-shifted compared to those of [8]CPP due to the presence of eight electron-withdrawing ester moieties...
May 17, 2017: Organic Letters
Kengo Hyodo, Kosuke Togashi, Naoki Oishi, Genna Hasegawa, Kingo Uchida
The Brønsted acid-catalyzed synthesis of nitriles is described via transoximation under mild conditions using an O-protected oxime as a more stable equivalent of explosive O-protected hydroxylamines. The nitrile was generated via an O-protected aldoxime produced from the aldehyde and an O-protected oxime through transoximation. The reaction could be performed on a 1 g scale.
May 17, 2017: Organic Letters
Émilie Morin, Michaël Raymond, Amaury Dubart, Shawn K Collins
A synthesis of neomarchantin A has been achieved wherein key bond constructions involving C-O or C-C bond formations were augmented via continuous flow techniques. Of note, the synthesis of neomarchantin A represents the first demonstration of catalytic macrocyclic olefin metathesis as a key step for the synthesis of a macrocyclic bisbibenzyl natural product.
May 17, 2017: Organic Letters
Yuto Okugawa, Koji Hirano, Masahiro Miura
A Brønsted base mediated stereoselective diphosphination of terminal alkynes with diphosphanes proceeds to deliver the corresponding (E)-1,2-diphosphinoethenes in good yields. The reaction of aromatic alkynes occurs efficiently in the presence of a catalytic amount of LiO-t-Bu while MN(TMS)2 (M = Li or Na) gave better results in the case of aliphatic substrates. The Brønsted base mediated protocol can offer a good alternative to precedented transition-metal-catalyzed or radical-promoted approaches to the 1,2-diphosphinoethene framework of potent interest in catalysis and coordination chemistry...
May 17, 2017: Organic Letters
Alyssa M Hua, Duy N Mai, Ramon Martinez, Ryan D Baxter
We report a unique example of utilizing unprotected amino acids for benzylic C-H fluorination via a radical process. α-Aminoalkyl radicals are readily generated via oxidative decarboxylation of unprotected amino acids using a simple silver(I) catalyst and Selectfluor, which serves as both a mild oxidant and source of electrophilic fluorine. Mechanistic investigation shows that coordination of the unprotected amino acid plays a crucial role in lowering the oxidation potential of Ag(I), enabling oxidation under mild conditions...
May 17, 2017: Organic Letters
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