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Organic Letters

Santosh J Gharpure, Dharmendra S Vishwakarma, Santosh K Nanda
Lewis acid mediated 5/6/7-endo-dig hydroalkoxylation-reduction cascade on internal alkynols gave an expedient, stereoselective synthesis of cyclic ethers and 1,4-oxazepanes. The strategy has been extended to the first examples of hydroalkoxylation-alkyne Prins-type cyclization cascade of alkyne-tethered alkynols, giving access to oxa-bicyclic scaffolds. This method was used as the key step in the stereoselective total synthesis of calyxolane A-B, as well as (±)-centrolobine and its homologue.
November 22, 2017: Organic Letters
Heming Jiang, Tian-Yu Sun, Xiao Wang, Yaoming Xie, Xinhao Zhang, Yun-Dong Wu, Henry F Schaefer
2-Iodoxybenzoic acid (IBX) is an important species for the oxidation of alcohols to aldehydes or ketones. An often-cited mechanism involving a hypervalent twist as the rate-determining step (RDS) is inconsistent with kinetic isotope effect (KIE) experiments. The computations with larger basis sets reveal that the reductive elimination involving the C-H bond cleavage is the RDS (rate-determining step). Further computational/experimental studies suggest that the reactivity can be improved by adjusting the trans influence with Lewis acids...
November 22, 2017: Organic Letters
Hualong Ding, Zaibin Wang, Songlin Bai, Ping Lu, Yanguang Wang
A rhodium-catalyzed reaction between 3-diazoindolin-2-imines and 2H-azirines, followed by treatment with a base, furnishes 5H-pyrazino[2,3-b]indoles in excellent yields. A number of functional groups tolerate the reaction conditions, and the resulting 5H-pyrazino[2,3-b]indoles present strong photoluminecence in solutions, powders, and films.
November 22, 2017: Organic Letters
Meredith A Allen, Ryan A Ivanovich, Dilan E Polat, André M Beauchemin
Oxy-carbamate O-isocyanate precursors facilitate access to synthetically valuable N-oxyureas via substitution with amines. This work exploits the reactivity of suitable O-isocyanate precursors, identified by a thorough study highlighting the different reactivity of isocyanate masking groups. This led to bench-stable O-isocyanate precursors, offering improved versatility in the synthesis of N-oxyureas, and demonstrates the controlled reactivity of masked O-isocyanates. Suitable precursors also enabled the first example of Cope-type hydroamination of unsaturated hydroxyureas...
November 22, 2017: Organic Letters
Devulapally Mahesh, Vanaparthi Satheesh, Sundaravel Vivek Kumar, Tharmalingam Punniyamurthy
Copper(II)-catalyzed cross-coupling of anilines, methyl arenes, and TMSN3 in the presence of tert-butylhydroperoxide at moderate temperature produced 2-aryl benzimidazoles via a tandem C(sp(3)/sp(2))-H functionalization and C-N bond formations. The selectivity and multiple C-H functionalization of the simple substrates are significant practical features.
November 22, 2017: Organic Letters
Andreas N Baumann, Michael Eisold, Arif Music, Geoffrey Haas, Yu Min Kiw, Dorian Didier
No abstract text is available yet for this article.
November 22, 2017: Organic Letters
Janakiram Vaitla, Kathrin H Hopmann, Annette Bayer
A convenient strategy for the synthesis of sulfur ylides via rhodium-catalyzed coupling of in situ generated iodonium ylides with sulfides or sulfoxides has been developed. A wide range of sulfur ylides were obtained in moderate to good yields from inexpensive sulfur compounds and active methylene compounds with a short reaction time (MW, 5-10 min) or 12-16 h at rt. Furthermore, these sulfoxonium ylides were used as novel acceptor/acceptor carbenes for N-H insertion reactions.
November 22, 2017: Organic Letters
Songwei Wen, Caiyou Chen, Shuaichen Du, Zhefan Zhang, Yi Huang, Zhengyu Han, Xiu-Qin Dong, Xumu Zhang
The t-Bu-Wudaphos was successfully applied into Rh-catalyzed asymmetric hydrogenation of α,α-disubstituted terminal olefins bearing a carboxy-directed group with excellent reactivities and enantioselectivities via the ion pair noncovalent interaction (up to >99% conversion, 98% yield, 98% ee) under mild reaction conditions without base. In addition, control experiments were conducted, and the results demonstrated that the ion pair noncovalent interaction between ligand and substrate played an important role in achieving an outstanding performance in this asymmetric hydrogenation...
November 22, 2017: Organic Letters
Jianming Yan, Naohiko Yoshikai
A chromium/2,2'-bipyridine-catalyzed annulation reaction of 2-biarylmagnesium reagents with alkynes is reported. The reaction is applicable to a variety of aryl- and/or alkyl-substituted internal alkynes as well as 2-biaryl and related Grignard reagents, thus affording phenanthrene derivatives in moderate to good yields. The reaction proceeds at the expense of excess alkyne as a hydrogen acceptor and thus does not need an external oxidant. Deuterium-labeling experiments shed light on the reaction mechanism, which likely involves multiple intramolecular C-H activation processes on chromium...
November 22, 2017: Organic Letters
Jian-Ping Li, Guo-Feng Zhao, Hai-Xia Wang, Ming-Sheng Xie, Gui-Rong Qu, Hai-Ming Guo
An efficient route to construct chiral cyclopropyl purine nucleoside analogues has been established via the catalytic asymmetric Michael-initiated ring-closure reactions of α-purine acrylates with α-bromo-carboxylic esters. Using (DHQD)2AQN as the catalyst, various chiral cyclopropyl purine nucleoside analogues with a chiral quaternary stereocenter were obtained in 72-98% yields, excellent diastereoselectivities, and 93-97% ee. Through simple functional group transformations, diverse chiral cyclopropyl purine nucleosides with hydroxymethyl group or carboxyl group were obtained...
November 22, 2017: Organic Letters
Jia-Jia Suo, Juan Du, Qing-Rong Liu, Di Chen, Chang-Hua Ding, Qian Peng, Xue-Long Hou
An asymmetric [3 + 2] cycloaddition reaction of vinyl epoxides with α,β-unsaturated ketones, the single activated electron-deficient alkenes, has been achieved under Pd-catalysis in excellent diastereo- and enantioselectivity. The utilities of the protocol are demonstrated by transformation of the products into other useful chiral molecules. Density functional theory calculations rationalize the stereocontrol of the reaction.
November 22, 2017: Organic Letters
Tao-Yan Lin, Hai-Hong Wu, Jian-Jun Feng, Junliang Zhang
A useful synthesis of five-membered N-heterocycles has been developed through an iridium-catalyzed domino-ring-opening cyclization of vinylaziridines with β-ketocarbonyls. α-Substituted 1,3-dicarbonyls reacted with vinylaziridines to give 2-methylenepyrrolidines bearing two adjacent sp(3)-carbon centers with moderate to excellent diastereoselectivity, while the reaction of α-unsubstituted 1,3-dicarbonyls afforded 2-pyrrolines in good yield.
November 22, 2017: Organic Letters
Gabriel Schäfer, Muhamed Ahmetovic, Stefan Abele
A scalable synthesis of trifluoromethylated imidazo-fused N-heterocyles from heterocyclic benzylamines using TFAA as trifluoromethylating reagent is presented. The reaction proceeds via intermediate benzylic N-trifluoroacetamides followed by dehydrative cyclization to the products. To further broaden the scope and practicality, a new method for the preparation of benzylic N-trifluoroacetamides via alkylation of trifluoroacetamide with benzyl (pseudo)halides was developed. Both methods proceed under mild conditions, and their symbiosis provides access to a wide range of novel CF3-heterocycles...
November 21, 2017: Organic Letters
Jian Xu, Xiaoxia Yu, Jianxiang Yan, Qiuling Song
tert-Butyl hydroperoxide-initiated radical cyclization of 2-alkynylthioanisoles or -selenoanisoles with sulfinic acids has been developed. This reaction is applicable to a wide substrate scope via one C(sp(3))-S(Se) bond cleavage and two C(sp(2))-S(Se) bond formation, leading to the synthesis of 3-(arylsulfonyl)benzothiophenes or -benzoselenophenes under mild conditions.
November 21, 2017: Organic Letters
Biming Mao, Wangyu Shi, Jianning Liao, Honglei Liu, Cheng Zhang, Hongchao Guo
A phosphine-catalyzed [4 + 2] cycloaddition of cyclic α-substituted allenoates with sulfamate-derived cyclic imines has been reported. Using dibenzylphenylphosphine as the nucleophilic catalyst, the reaction worked efficiently to yield various fused multicyclic heterocyclic compounds in high yields with excellent diastereoselectivities. It undergoes a new reaction mode involving γ'-carbon of α-substituted allenoate.
November 21, 2017: Organic Letters
Jin-Shan Li, Yong-Jie Liu, Guang-Wu Zhang, Jun-An Ma
A catalytic enantioselective Mukaiyama-Mannich reaction of cyclic C-acylimines with difluoroenoxysilanes is reported. (S)-TRIP enables the enantioselective synthesis of a series of novel difluoroalkylated indolin-3-ones bearing a quaternary stereocenter in up to 97% yield and 98% ee. The synthetic utility of this protocol is highlighted by efficient conversion of the products to the corresponding indolin-3-one derivatives without any erosion of the enantiopurity.
November 21, 2017: Organic Letters
Fei Peng, Hua Tian, Pengxiang Zhang, Can Liu, Xudong Wu, Xi Yuan, Haijun Yang, Hua Fu
A highly efficient, enantioselective intramolecular allylation of (E)-4-(alkyl(4-oxo-3,4-dihydroquinazolin-2-yl)amino)but-2-en-1-yl methyl carbonates was developed, and the corresponding dihydroimidazoquinazolinones were prepared in high yields and enantiomeric excess. The allylation was performed under catalysis of iridium-chiral cyclic phosphoramidite complexes, in which the reactivity and enantioselectivity of the substrates were elaborately tuned by our developed chiral cyclic phosphoramidite ligands with adjustable sizes of rings...
November 21, 2017: Organic Letters
Taisuke Matsuno, Kanako Kogashi, Sota Sato, Hiroyuki Isobe
A sextuple helix molecule possessing four cove regions of helicene and two axes of biaryls was synthesized. The entropy-driven self-assembly in solution was determined by concentration- and temperature-dependent NMR spectra, which also revealed unique dynamics of isomerization involving structural changes at the cove regions. Unexpectedly, the assembly retarded the isomerization in solution, and the sextuple helix structure was rigidified.
November 21, 2017: Organic Letters
Javier Fernández-Valparis, Pedro Romea, Fèlix Urpí, Mercè Font-Bardia
Direct addition of a chiral N-azidoacetyl thiazolidinethione to a variety of dialkyl acetals catalyzed by a commercially available and structurally simple nickel(II) complex gives access in good yields and a highly stereocontrolled manner to anti-β-alkoxy-α-azido carboxylic derivatives which, in turn, can be easily converted into a wide array of enantiomerically pure compounds.
November 21, 2017: Organic Letters
Toshihiro Hirai, Kohki Shibata, Yohei Niwano, Masao Shiozaki, Yoshimitsu Hashimoto, Nobuyoshi Morita, Shintaro Ban, Osamu Tamura
The total synthesis of neodysiherbaine A was achieved via 1,3-dipolar cycloaddition of a chiral nitrone template with a sugar-derived allyl alcohol in the presence of MgBr2·OEt2. This cycloaddition constructed the C2 and C4 asymmetric centers in a single step. Then reductive cleavage, intramolecular SN2 reaction of the tertiary alcohol, and oxidation of the primary alcohol afforded neodysiherbaine A.
November 20, 2017: Organic Letters
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