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Organic Letters

Changqing Ye, Bo Qian, Yajun Li, Min Su, Daliang Li, Hongli Bao
This paper reports a new method for the generation of substituted 1,3-enynes, whose synthesis by other methods could be a challenge. The dehydrative decarboxylative cascade coupling reaction of propargyl alcohol with alkyl peroxides is enabled by an iron catalyst and alkylating reagents. Primary, secondary, and tertiary alkyl groups can be introduced into 1,3-enynes, affording various substituted 1,3-enynes in moderate to good yields. Mechanistic studies suggest the involvement of a radical-polar crossover pathway...
May 22, 2018: Organic Letters
Xiaoze Bao, Shiqiang Wei, Xingkai Qian, Jingping Qu, Baomin Wang, Liwei Zou, Guangbo Ge
A catalytic asymmetric [3 + 2] cyclization of novel 4-isothiocyanato pyrazolones and isatin-derived ketimines was developed, delivering a wide range of intriguing dispirotriheterocyclic products in high yield with excellent diastereoselectivity and enantioselectivity. A chiral sulfoxide derivative of this dispirocyclic product was identified to be a promising hit of the human carboxylesterase 1 inhibitor, and the significant difference of the activity between two enantiomers emphasized the importance of this asymmetric process...
May 22, 2018: Organic Letters
Hong-Xue Chen, Jie Kang, Rong Chang, Yun-Lai Zhang, Hua-Zhen Duan, Yan-Mei Li, Yong-Xiang Chen
A novel and facile synthetic strategy for α,α-difluorinated phosphonate mimetics of phosphoserine/phosphothreonine utilizing rhodium-catalyzed asymmetric hydrogenation was developed. The dehydrogenated substrate β-difluorophosphonomethyl α-(acylamino)acrylates were first prepared from protected serine/threonine followed by asymmetric hydrogenation using the rhodium-DuPhos catalytic system to generate the chiral center(s). These important phosphonate building blocks were successfully incorporated into phosphatase-resistant peptides, which displayed similar inhibition to the 14-3-3 ζ protein as the parent pSer/pThr peptides...
May 21, 2018: Organic Letters
Abigail Feceu, Lauren E Sangster, David B C Martin
An iterative cross-coupling approach to conjugated trienes was explored as part of a planned stereoselective synthesis of bicyclic terpenes. Using a bifunctional bromoboronate building block, sequential Suzuki coupling reactions were employed to provide a conjugated trienone target containing a tetrasubstituted alkene. During the final cross-coupling step, an unexpected alkene isomerization was observed to give less hindered trans products. Examination of different substrates determined that conjugation to a ketone withdrawing group was responsible for isomerization, rather than steric hindrance of the tetrasubstituted alkene...
May 21, 2018: Organic Letters
Yew Chin Teo, Zexin Jin, Yan Xia
The streamlined synthesis of a series of regioisomeric azaacene analogues containing fused phenazine and antiaromatic cyclobutadienoids (CBDs), using a catalytic arene-oxanorbornene annulation, followed by aromatization is reported. Controlling the fusion patterns allowed strong modulation of local antiaromaticity. Enhancing antiaromaticity in these regioisomeric azaacenes led to stabilized LUMO, reduced band gap, and quenched fluorescence. This synthetic strategy provides a facile means to fuse CBDs with variable degrees of antiaromaticity onto N-heteroarenes to tune their optoelectronic properties...
May 21, 2018: Organic Letters
Li Ren, Huan Cong
A decarboxylative alkylation of benzylic C(sp3 )-H bonds of N-aryl tetrahydroisoquinolines under the irradiation of blue light is reported, featuring a broad substrate scope, low cost, heavy-metal-free, and mild conditions. A preliminary mechanistic study indicated that radical intermediates are involved during the course of the reaction.
May 21, 2018: Organic Letters
Peizhong Xie, Jing Fan, Yanan Liu, Xiangyang Wo, Weishan Fu, Teck-Peng Loh
A Bronsted acid/organic photoredox cooperative catalytic system toward P-C bond formation from alcohols and P-H species is developed. With the assistance of visible light and TBHP, the reactions proceeded smoothly in an environmentally benign manner to give various alkenylphosphorus compounds in high efficiency.
May 21, 2018: Organic Letters
Wen Che, Danyang C Wen, Shou-Fei Zhu, Qi-Lin Zhou
A novel iterative protocol for the synthesis of polydeoxypropionates was developed based on iridium-catalyzed asymmetric hydrogenation of α-substituted acrylic acids. The catalyst loading can be as low as 0.01 mol %, and the overall yield for one iterative cycle is >76%. The reaction conditions are mild, and no organometallic reagents or chromatography steps are required. Using this protocol, (+)-phthioceranic acid and the polydeoxypropionate motifs of ionomycin and borrelidin were synthesized in high yield...
May 21, 2018: Organic Letters
Chengsen Cui, Wei-Min Dai
Total synthesis of (-)-(2 R,9 S)- and (+)-(2 S,9 S)-stereoisomers of laingolide B has been accomplished by using sequential ring-closing metathesis (RCM) and alkene isomerization to construct the macrocyclic trans- N-methyl enamide moiety. The Myers alkylation was used to secure the C2 stereochemistry of the two RCM precursors from a common (9 S)-C3-C9 alkyl iodide. The absolute configuration of laingolide B has been assigned as (2 S,9 R) by comparison of the optical rotation data.
May 21, 2018: Organic Letters
Hong-Xing Zheng, Xiang-Huan Shan, Jian-Ping Qu, Yan-Biao Kang
An intermolecular addition of carbon radicals enabled by a cascade radical coupling strategy is developed. It includes an intermolecular alkyl radical addition to a carbonyl group followed by an intramolecular alkoxy radical addition to haloarenes and produces substituted benzofurans in high yields. The radical nature of this reaction is explored by radical trapping experiments and EPR analysis. The mechanism is investigated by KIE experiments and control experiments. This method could provide rapid and practical access to the key intermediate of TAM-16, a safe and potent antibacterial agent for treating tuberculosis, and, therefore, is of great importance for organic synthesis and the pharmaceutical industry...
May 18, 2018: Organic Letters
Manthena Chaitanya, Pazhamalai Anbarasan
An efficient and chemodivergent palladium-catalyzed thiolation (C-S) and imidation (C-N) of directing group-assisted C-H bonds have been accomplished employing N-(arylthio)imides in combination with either Brønsted acid or Lewis acid, respectively. Notable features of the developed methodologies include excellent diversity, high functional group tolerance, wide substrate scope, and use of a single N-S reagent. Importantly, the developed hypothesis was also successfully extended to the amidation of C-H bonds...
May 18, 2018: Organic Letters
Ming-Hua Yang, Mei-Ling Gu, Chao Han, Xiao-Jiang Guo, Guo-Ping Yin, Pei Yu, Ling-Yi Kong
Aureochaeglobosins A-C (1-3), three novel [4 + 2] cycloaddition heterodimers of chaetoglobosin and aureonitol derivatives, were obtained from the culture of endophytic fungus Chaetomium globosum, representing the first adduct examples of chaetoglobosins. Their structures were elucidated by extensive spectroscopic analyses, single-crystal X-ray diffraction, and a modified Mosher's method. Compounds 2 and 3 showed significant cytotoxicities against human MDA-MB-231 cancer cells with IC50 values of 7.6 and 10...
May 17, 2018: Organic Letters
Xianqiang Huang, Nianxin Rong, Pengfei Li, Guodong Shen, Qiang Li, Nana Xin, Chuansheng Cui, Jichui Cui, Bingchuan Yang, Dacheng Li, Changqiu Zhao, Jianmin Dou, Bo Wang
A series of bibenzo[ b][1,4]thiazines with various functional groups has been synthesized by a free-radical condensation reaction. Bibenzo[ b][1,4]thiazines were obtained in moderate to good yield (up to 85%) through a one-step reaction of readily available 2,2'-dithiodianiline and methyl aryl ketones with AIBN as radical initiator in HOAc. Bibenzo[ b][1,4]thiazines exhibit diversiform solid-state packing.
May 17, 2018: Organic Letters
Tian-Ren Li, Mao-Mao Zhang, Bao-Cheng Wang, Liang-Qiu Lu, Wen-Jing Xiao
A copper-catalyzed Friedel-Crafts propargylation/hydroamination/aromatization sequence is described. In the presence of a catalytic amount of CuI, this sequential reaction can convert ethynyl benzoxazinanones and indoles into a diverse set of 3,3'-biindoles with high efficiency and selectivity. Moreover, the synthesis of other indole-heteroaryl molecules and the catalytic asymmetric formation of axially chiral 3,3'-biindoles are demonstrated.
May 17, 2018: Organic Letters
Pierre A Spreider, Bernhard Breit
A diastereoselective palladium-catalyzed cyclization of allenyl hemiacetals is described. It permits the selective synthesis of 1,3-dioxane derivatives, precursors for syn-configured 1,3-diols which make an appearance in all of the statin representatives. The reaction allows the total synthesis of Rosuvastatin and Pitavastatin in a straightforward fashion.
May 17, 2018: Organic Letters
Wei Xu, Gaonan Wang, Xin Xie, Yuanhong Liu
A gold-catalyzed cycloisomerization of ynamide-ynes via a formal dehydro-Diels-Alder reaction has been developed, providing an attractive route to diversely substituted benzo[ b]carbazoles. The reaction likely proceeds via regioselective attack of the pendant alkyne moiety to a keteniminium ion intermediate followed by benzannulation. The method offers several advantages such as high efficiency, mild reaction conditions, and wide functional group tolerance and serves as a highly useful complement to the thermal DDA reactions of ynamide-ynes...
May 16, 2018: Organic Letters
Julien Genovino, Yajing Lian, Yuan Zhang, Taylor O Hope, Antoine Juneau, Yohann Gagné, Gajendra Ingle, Mathieu Frenette
A metal-free photoredox C-H alkylation of heteroaromatics from readily available carboxylic acids using an organic photocatalyst and hypervalent iodine reagents under blue LED light is reported. The developed methodology tolerates a broad range of functional groups and can be applied to the late-stage functionalization of drugs and drug-like molecules. The reaction mechanism was investigated with control experiments and photophysical experiments as well as DFT calculations.
May 16, 2018: Organic Letters
Gianpiero Cera, Matteo Lanzi, Davide Balestri, Nicola Della Ca', Raimondo Maggi, Franca Bigi, Max Malacria, Giovanni Maestri
The combination of a Pd(0) complex with benzoic acid converts propargylic tryptamines to the corresponding tetrahydro-β-carbolines. The method uses unprotected indoles and affords the desired products with ample functional group tolerance. Detailed modeling studies reveal a close synergy between the organic and metal catalysts, which enables sequential alkyne isomerization, indole C-H activation, and eventual C-C reductive elimination to afford the target heterocycles.
May 16, 2018: Organic Letters
Yang Li, Jing Zhang, Defang Li, Yiyun Chen
The first aryl carboxyl radical generation by the donor-acceptor complex with N-acyloxyphthalimides and Hantzsch esters is reported. Regio- and chemoselective C(sp3 )-H bond allylation is enabled by aryl carboxyl radicals with visible light irradiation under mild and metal-free conditions.
May 16, 2018: Organic Letters
Elisa I León, Angeles Martín, Inés Pérez-Martín, Ernesto Suárez
The generation and fate of 2I-VII ,3I-VII ,6II-VII -icosa- O-methyl-β-cyclomaltoheptaos-6I - O-yl radical under reductive conditions is described. Two radical cascade reactions are involved: the main one is triggered by a 1,8-HAT of the hydrogen at 5VII C. The radical can reach the anomeric hydrogen at 1V C three sugar units ahead using a six-step sequence. The different hydrogen donor ability of the group 14 hydrides permits one to selectively stop the cascade at 5VII C, 2VI C, and 4VI C to obtain β-CD with a β-l-Ido p unit, acyclic hepta-, and hexa-saccharide structures, respectively...
May 16, 2018: Organic Letters
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