Contributors: Kamath, Prashantha, Rajan, Ramya, Deshpande, Sudhindra, Montgomery, Mark, Lal, Mukul
... Abstract A simple, fast and efficient synthesis of 3-phosphorylated benzoxaboroles using the Pudovik reaction is reported. A number of diverse 3-(dialkoxyphosphoryl)-1-hydroxy-3H-2,1-benzoxaboroles were synthesised in 70–86% yield. Interesting hydrogen bond features were observed in the crystal lattice of the 5-chlorinated 3-bis(benzyloxy)phosphoryl derivative with both inter- and intramolecular C–H···O hydrogen bonds. Additionally, linear chains of intermolecular O–H···O hydrogen bonds were observed.
Allylic Azide Rearrangement in Tandem with Intramolecular Huisgen Cycloaddition for Iminosugar and Glycomimetic Synthesis: Functionalized Piperidine, Pyrrolidine, and Pyrrolotriazoles from d-Mannose
Contributors: Chadda, Rekha, McArdle, Patrick, Murphy, Paul
... Abstract Intramolecular Huisgen azide-alkene cycloaddition reaction of 7-azido-hepta-1,5-diene-3,4-diols, prepared from methyl α-d-mannopyranoside, were carried out. Allylic azide rearrangement to secondary azides occurred in tandem with triazoline formation and this intermediate was then decomposed in the presence of nucleophilic reagents to give pyrrolidines, piperidines, or azepanes depending on whether cyclic constraint was incorporated or not, on diol stereochemistry and on the nucleophile. The tandem reaction worked best when aziridine formation from the triazoline was efficient, and this efficiency improved on removal of cyclic constraint. Proposals to account for the observed diastereoselectivities are provided. The allylic azide rearrangement in tandem with the intramolecular Huisgen azide-alkyne cycloaddition was also investigated from azidoheptaenyne diols and gave dihydropyrrolotriazoles. All reactions were diastereoselective, and this was high in some cases. Two X-ray crystal structural determinations, 13C NMR data, and 1D and 2D NOESY experiments were used for stereochemical assignments.
Contributors: Markovič, Martin, Koóš, Peter, Gracza, Tibor
... Abstract A short and efficient asymmetric synthesis of natural sauropunols A, B, and C/D has been accomplished in 6 steps from divinylcarbinol with overall yield of 19%, 7% and 32%, respectively. The key synthetic steps include effective Sharpless asymmetric epoxidation of penta-1,4-dien-3-ol and a highly diastereoselective Pd-catalysed oxycarbonylation of pentene-1,2,3-triol. The structures of sauropunols A and B have been confirmed.
Contributors: Ribar, Peter, Šolomek, Tomáš, Le Pleux, Loïc, Häussinger, Daniel, Prescimone, Alessandro, Neuburger, Markus, Juríček, Michal
... Abstract The synthesis and optoelectronic properties of five donor–acceptor molecules, featuring an electron-acceptor unit made of six fused benzenoid rings that resembles an equilateral triangle, are described. These molecular ‘triangles’ were synthesized in eight steps from simple building blocks such that the electron-donor substituents could be installed in the last step by means of the Suzuki cross-coupling reaction. All molecules absorb and emit visible light in the region of around 450–650 and 550–850 nm, respectively, exhibit solvatochromism, and possess up to four redox states.
Contributors: Bao, Xuefei, Liu, Ziao, Liang, Xinjie, Song, Dake, Shi, Tao, Zhao, Xuan, Bao, Changshun, Chen, Guoliang
... Abstract A synthetic route to 3-formylbenzenesulfonyl chloride derivatives from the corresponding benzaldehydes has been developed. The key step in this procedure is the conversion of aldehyde bisulfite adducts to target compounds via a two-stage reaction in the presence of Na2SO4. A series of 3-formylbenzenesulfonyl chloride derivatives were prepared by this method and identified by chemical derivatization method.
Intermolecular [2+2] Photocycloaddition of β-Nitrostyrenes to Olefins upon Irradiation with Visible Light
Contributors: Mohr, Lisa-Marie, Bach, Thorsten
... Abstract The title compounds were found to undergo a [2+2] photocycloaddition with olefins at λ = 419 nm in CH2Cl2 as the solvent. The resulting cyclobutanes were isolated in yields of 32–87% (11 examples) and showed a defined relative configuration at C1/C4 in the major diastereoisomer (nitro and aryl trans). The analysis of side products and triplet sensitization experiments support a mechanistic scenario in which a 1,4-diradical is formed as a key intermediate.
Contributors: Chen, Xiang-Xiang, Wang, Jia-Xin, Ren, Jiang-Tao, Xie, Hu, Zhao, Yanxia, Li, Ya-Min, Sun, Meng
... Abstract A highly efficient and convenient strategy has been developed for remote C–H bond halogenation of 8-aminoquinolines in good to excellent yields under transition-metal-free conditions. The reaction tolerates a variety of functional groups and can potentially be scaled up.
Copper-Catalyzed Base-Controlled Diastereoselective Synthesis of Tetraarylethanes from 2-Benzylpyridines
Contributors: Chandrasekar, Selvaraj, Karthikeyan, Iyyanar, Sekar, Govindasamy
... Abstract A highly efficient and base-controlled diastereoselective synthesis of tetraarylethanes through copper-catalyzed dehydrogenative homocoupling of readily available 2-benzylpyridines is reported. Various dl- and meso-tetraarylethanes were diastereoseletively synthesized by this new protocol, where base plays the role of the principle modulator: Grignard reagents selectively provide the C2 isomers, whereas KOt-Bu promotes the formation of the meso-tetraarylethanes. Interestingly, the presence of excess KOt-Bu generates the (E)-tetraarylethenes as the only product.
Contributors: Tang, Xiaohang, Tong, Le, Yao, Mengyi, Liang, Qiaoli, Wang, Xiaolong, Yu, Haitao
... Abstract A novel and simple route was developed that gives sparstolonin B in high yields from affordable commercial compounds. A Diels–Alder strategy was used for the facile construction of the multisubstituted diphenyl ether. The xanthenone segment was obtained by cyclization in an intramolecular Friedel–Crafts reaction, followed by selective reduction of a ketone group and a transformation from a hydroxy group into a cyano group. The final part of the lactone was directly derived by the reduction of the cyano group with Raney nickel.
Contributors: Mayr, Florian, Mohr, Lisa-Marie, Rodriguez, Elsa, Bach, Thorsten
... Abstract Four different 1-aminocyclohexanes bearing a tethered thioxanthone group in the 2-position were prepared. The synthesis commenced with the respective N-protected β-amino acids, the carboxyl group of which was employed for the introduction of the thioxanthone moiety. After construction of the thioxanthone and protecting group removal, the conversion of the amino group into the respective thiourea was accomplished by treatment with N-3,5-bis(trifluoromethyl)phenyl isothiocyanate and yielded the title compounds in which the thioxanthone resides in different spatial positions relative to the thiourea motif. Overall yields varied between 20–35%.