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The 1,3-dipolar cycloadditions of C-glycosyl nitrile oxides and acetylenes to an alkyne and an azide, respectively, bearing a masked glycinyl moiety furnished disubstituted isoxazoles and triazoles. Unveiling the glycinyl group in these cycloadducts afforded C-glycosyl alpha-amino acids in which the two bioactive entities were tethered through rigid five-membered heterocycles. Optimized entries to the same compounds involved the use of unmasked but protected alkyne- and azide-containing amino acids as the partners of 1,3-dipolar cycloadditions. 相似文献
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Olga Bortolini Dr. Alberto Cavazzini Pier Paolo Giovannini Roberto Greco Nicola Marchetti Dr. Alessandro Massi Luisa Pasti 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(24):7802-7808
The heterogeneous proline‐catalyzed aldol reaction was investigated under continuous‐flow conditions by means of a packed‐bed microreactor. Reaction‐progress kinetic analysis (RPKA) was used in combination with nonlinear chromatography for the interpretation, under synthetically relevant conditions, of important mechanistic aspects of the heterogeneous catalytic process at a molecular level. The information gathered by RPKA and nonlinear chromatography proved to be highly complementary and allowed for the assessment of optimal operating variables. In particular, the determination of the rate‐determining step was pivotal for optimizing the feed composition. On the other hand, the competitive product inhibition was responsible for the unexpected decrease in the reaction yield following an apparently obvious variation in the feed composition. The study was facilitated by a suitable 2D instrumental arrangement for simultaneous flow reaction and online flow‐injection analysis. 相似文献
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Alessandro Massi Alberto CavazziniOmar Pandoli Valentina CostaLuisa Pasti Pier Paolo Giovannini 《Tetrahedron letters》2011,52(5):619-622
The activity and stability under flow conditions of covalently and non-covalently silica supported proline and proline-like organocatalysts is herein described. The slow aldol reaction of cyclohexanone with p-nitro benzaldehyde and the fast α-amination of isovaleraldehyde with dibenzyl azodicarboxylate have been selected as model reactions for this study. Prospects and limitations of the disclosed continuous-flow organocatalytic approach are widely discussed. 相似文献
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Bortolini O Fantin G Fogagnolo M Giovannini PP Massi A Pacifico S 《Organic & biomolecular chemistry》2011,9(24):8437-8444
An efficient method for the N-heterocyclic carbene (NHC)-catalyzed conjugate addition of acetyl anions to various α,β-unsaturated acceptors (Stetter reaction) has been optimized by using 2,3-butandione (biacetyl) as an alternative surrogate of acetaldehyde. The disclosed procedure proved to be compatible with microwave dielectric heating for reaction time reduction and with the use of different linear α-diketones as acyl anion donors (e.g. 3,4-hexanedione for propionyl anion additions). Moreover, the unprecedented umpolung reactivity of cyclic α-diketones in the atom economic nucleophilic acylation of chalcones is herein presented. Mechanistic aspects of the thiazolium-based catalysis involving linear and cyclic α-diketone substrates are also discussed. 相似文献
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R. Cicchi L. Sacconi A. Jasaitis R.P. O’Connor D. Massi S. Sestini V. De Giorgi T. Lotti F.S. Pavone 《Applied physics. B, Lasers and optics》2008,92(3):359-365
We have built a custom-made multidimensional non-linear microscope equipped with a combination of several non-linear laser
imaging techniques involving fluorescence lifetime, multispectral two-photon and second-harmonic generation imaging. The optical
system was mounted on a vertical honeycomb breadboard in an upright configuration, using two galvo-mirrors relayed by two
spherical mirrors as scanners. A double detection system working in non-descanning mode has allowed both photon counting and
a proportional regime. This experimental setup offering high spatial (micrometric) and temporal (sub-nanosecond) resolution
has been used to image both ex-vivo and in-vivo biological samples, including cells, tissues, and living animals. Multidimensional
imaging was used to spectroscopically characterize human skin lesions, as malignant melanoma and naevi. Moreover, two-color
detection of two photon excited fluorescence was applied to in-vivo imaging of living mice intact neocortex, as well as to
induce neuronal microlesions by femtosecond laser burning. The presented applications demonstrate the capability of the instrument
to be used in a wide range of biological and biomedical studies.
PACS 87.64.mn; 78.47.Cd; 87.19.lw 相似文献
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After an initial period of validating asymmetric organocatalysis by using a wide range of important model reactions that constitute the essential tools of organic synthesis, the time has now been reached when organocatalysis can be used to address specific issues and solve pending problems of stereochemical relevance. This Review deals with selected studies reported in 2006 and the first half of 2007, and is intended to highlight four main aspects that may be taken as testimony of the present status and prospective of organocatalysis: a) chemical efficiency; b) discovery of new substrate combinations to give new asymmetric syntheses; c) development of new catalysts for specific purposes by using mechanistic findings; and d) applications of organocatalytic reactions in the asymmetric total synthesis of target natural products and known compounds of biological and pharmaceutical relevance. 相似文献
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Stoliar P Kshirsagar R Massi M Annibale P Albonetti C de Leeuw DM Biscarini F 《Journal of the American Chemical Society》2007,129(20):6477-6484
We investigate the role of self-assembly monolayers in modulating the response of organic field-effect transistors. Alkanethiol monolayers of chain length n are self-assembled on the source and drain electrodes of pentacene field-effect transistors. The charge carrier mobility mu exhibits large fluctuations correlated with odd-even n. For n < 8, mu increases by 1 order of magnitude owing to the decrease of the hole injection barrier and the improved molecular order at the organic-metallic interface. For n > or = 8, mu decays exponentially with an inverse decay length beta = 0.6 A(-1). Our results show that (i) charge injection across the interface occurs by through-bond tunneling of holes mediated by the alkanethiol layer; (ii) in the long-chain regime, the charge injection across the alkanethiol monolayer completely governs the transistor response; (iii) the transistor is a sensitive gauge for probing charge transport across single monolayers. The odd-even effect is ascribed to the anisotropic coupling between the alkanethiol terminal sigma bond and the HOMO level of ordered pentacene molecules. 相似文献