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101.
102.
Andrew J. Smaligo Jason Wu Nikolas R. Burton Allison S. Hacker Aslam C. Shaikh Jason C. Quintana Ruoxi Wang Changmin Xie Ohyun Kwon 《Angewandte Chemie (International ed. in English)》2020,59(3):1211-1215
Reported herein is a one‐pot protocol for the oxodealkenylative introduction of carbonyl functionalities into terpenes and terpene‐derived compounds. This transformation proceeds by Criegee ozonolysis of an alkene, reductive cleavage of the resulting α‐alkoxy hydroperoxide, trapping of the generated alkyl radical with 2,2,6,6‐tetramethylpiperidin‐1‐yl (TEMPO), and subsequent oxidative fragmentation with MMPP. Using readily available starting materials from chiral pool, a variety of carbonyl‐containing products have been accessed rapidly in good yields. 相似文献
103.
NaIO4/LiBr‐Mediated Direct Conversion of Benzylic Alcohols and Aromatic Aldehydes to Aromatic Esters
Aromatic aldehydes or benzylic alcohols are directly converted to the corresponding aromatic esters in high yields on treatment with methanol or ethanol mediated by sodium metaperiodate (NaIO4)/LiBr in an acidic medium. 相似文献
104.
Enantiomeric separation of a melatonin agonist Ramelteon using amylose-based chiral stationary phase
Sachin D. Patil Nandkumar Khandekar Gajanan B. Kasawar K.A. Shaikh 《Arabian Journal of Chemistry》2013,6(1):103-109
A new simple isocratic chiral liquid chromatographic method was developed for the enantiomeric purity of Ramelteon[(S)-N-[2-(1,6,7,8-tetrahydro-2H-indeno[5,4-b]furan-8-yl) ethyl]-propionamide], a melatonin agonist in bulk drugs. The chromatographic separation was achieved on Chiralpak AD-H, 250 mm × 4.6 mm, 5 μm column using a mobile phase system consisting of n-hexane, ethanol and methanesulfonic acid in the ratio of 900:100:0.1 (v/v/v). The mobile phase was pumped on the column at the flow rate of 1 mL min?1. Addition of methane sulfonic acid in the mobile phase enhanced chromatographic efficiency and resolution between the enantiomers. The resolution between the enantiomers was found to be more than four. The developed method was subsequently validated and proved to be accurate and precise. The experimentally established limit of detection and quantification of (R)-enantiomer were found to be 25.5 and 77.2 ng ml?1, respectively, for 20 μl injection volumes. The percentage recovery of (R)-enantiomer was ranged from 98.5 to 101.9 in bulk drug samples of Ramelteon. The stability of Ramelteon sample in analytical solution was checked for about 48 h at room temperature and was found to be stable for about 48 h. The proposed method was found to be suitable and accurate for the quantitative determination of (R)-enantiomer in drug substance. 相似文献
105.
Three compounds ( 1 – 3 ) were synthesized, where ethynylferrocene is substituted at different positions of anthracene and anthraquinone, and their biological properties were investigated. Compounds 1 – 3 were characterized using NMR and mass spectroscopies and confirmed by their single‐crystal X‐ray structure. They were also characterized from electronic and photophysical properties. All three crystal structures were optimized using density functional theory calculations. The presence of C–H???π interactions in 1 – 3 leads to the formation of two‐ and three‐dimensional networks. The bioactivity of 1 – 3 was expressed by molecular docking with various cancerous proteins, which participated in progression of cancer. Compound 2 displayed the best interaction with cancer‐related Aurora A protein in terms of both binding energy (?10.61 kcal mol?1) as well as inhibition constant (16.74 nM). The molecular docking result also coincides with cytotoxicity on cancer cell lines (A375, HeLa) and DNA/protein binding affinity. 相似文献
106.
Seema Yadav Ajeet Singh Isha Mishra Sriparna Ray Shaikh M. Mobin Chandrakanta Dash 《应用有机金属化学》2019,33(7)
Well‐defined and air‐stable PEPPSI (Pyridine Enhanced Precatalyst Preparation Stabilization and Initiation) themed palladium bis‐N‐heterocyclic carbene complexes have been developed for the domino Sonogashira coupling/cyclization reaction of 2‐iodophenol with a variety of terminal alkynes and C‐H bond arylation of benzothiazole with aryl iodides. The PEPPSI themed palladium complexes, 2a and 2b were synthesized in good yields from the reaction of corresponding imidazolium salts with PdCl2 and K2CO3 in pyridine. The new air‐stable palladium‐NHC complexes were characterized by NMR spectroscopy, X‐ray crystallography, elemental analysis, and mass spectroscopy studies. The PEPPSI themed palladium(II) bis‐N‐heterocyclic carbene complexes 2a and 2b exhibited excellent catalytic activities for domino Sonogashira coupling/cyclization reaction of 2‐iodophenol with terminal alkynes yielding benzofuran derivatives. In addition, the palladium complexes, 2a and 2b successfully catalyzed the direct C‐H bond arylation of benzothiazole with aryl iodides as coupling partners in presence of CuI as co‐catalyst. 相似文献
107.
Shaikh M. Shamid 《Liquid crystals》2013,40(1):130-136
Using Landau theory, it is shown that eight phenomenological parameters are needed to describe and distinguish the twelve viscosity coefficients of a biaxial nematic phase, or the five viscosity coefficients of a uniaxial nematic phase. The dependence of the coefficients on the macroscopic uniaxial and biaxial order parameters is established. Since these order parameters are determined by the anisotropies of the dielectric constant, we show that it should be possible to determine values for all eight of the phenomenological parameters of the theory from measurements of the temperature dependence of the five viscosities of a uniaxial phase. 相似文献
108.
A new, stereoselective formal synthesis of hirsutic acid and medium ring carbocyclic systems from salicyl alcohol is described. Cycloaddition between electron deficient partners such as cyclohexa-2,4-dienone and methylmethacrylate, triplet sensitized 1,2-acyl shift and ring-closing metathesis are the key features of our approach. 相似文献
109.
Tanveer Mahamadali Shaikh 《Tetrahedron letters》2009,50(23):2815-4239
A new facile procedure for the aminobromination of olefins in high yields has been described using p-toluene sulfonamide (p-TsNH2) and N-bromosuccinimide (NBS) as nitrogen and bromine sources, respectively, and titanium superoxide as a truly heterogeneous catalyst. The formation of anti-Markovnikov product exclusively in all the cases studied possibly proceeding through a free radical reaction pathway is remarkable. 相似文献
110.
Judit E. Puskas Sam W. P. Chan Kimberley B. Mcauley Gabor Kaszas Sohel Shaikh 《Journal of polymer science. Part A, Polymer chemistry》2007,45(9):1778-1787
The carbocationic copolymerization of isobutylene (IB) and styrene (St), initiated by 2‐chloro‐2,4,4‐trimethylpentane/TiCl4 in 60/40 (v/v) methyl chloride/hexane at ?90 °C, was investigated. At a low total concentration (0.5 mol/L), slow initiation and rapid monomer conversion were observed. At a high total comonomer concentration (3 mol/L), living conditions (a linear semilogarithmic rate and Mn–conversion plots) were found, provided that the St concentration was above a critical value ([St]0 ~ 0.6 mol/L). The breadth of the molecular weight distribution decreased with increasing IB concentration in the feed, reaching Mw/Mn ~ 1.1. St homopolymerization was also living at a high total concentration, yielding polystyrene with Mn = 82,000 g/mol, the highest molecular weight ever achieved in carbocationic St polymerization. An analysis of this system by both the traditional gravimetric–NMR copolymer composition method and FTIR demonstrated penultimate effects. IB enrichment was found in the copolymers at all feed compositions, with very little drift at a high total concentration and above the critical St concentration. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1778–1787, 2007 相似文献