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Short Synthetic Routes (short + synthetic_route)
Selected AbstractsA Short Synthetic Route to the Calystegine Alkaloids.CHEMINFORM, Issue 29 2003Philip R. Skaanderup Abstract For Abstract see ChemInform Abstract in Full Text. [source] Facile Synthesis of Diastereoisomerically and Optically Pure 2-Substituted Hexahydro-1H -pyrrolizin-3-onesHELVETICA CHIMICA ACTA, Issue 8 2005Romain Siegrist We report a short synthetic route that provides optically active 2-substituted hexahydro-1H -pyrrolizin-3-ones in four steps from commercially available Boc (tert -but(oxy)carbonyl))-protected proline. Diastereoisomers (,)- 11 and (,)- 12 were assembled from the proline-derived aldehyde (,)- 8 and ylide 9via a Wittig reaction and subsequent catalytic hydrogenation (Scheme,3). Cleavage of the Boc protecting group under acidic conditions, followed by intramolecular cyclization, afforded the desired hexahydro-1H -pyrrolizinones (,)- 1 and (+)- 13. Applying the same protocol to ylide 19 afforded hexahydro-1H -pyrrolizinones (,)- 25 and (,)- 26 (Scheme,5). The absolute configuration of the target compounds was determined by a combination of NMR studies (Figs.,1 and 2) and X-ray crystallographic analysis (Fig.,3). [source] Complexation and Dynamic Switching Properties of Fluorophore-Appended Resorcin[4]arene CavitandsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 5 2010Laura D. Shirtcliff Abstract Fluorophore-appended resorcin[4]arene-based cavitands having pyrene (2) and anthracene (3) moieties attached to the rims were prepared by short synthetic routes. Both undergo reversible temperature- and acid- (CF3COOD) induced vase,,,kite switching as evidenced by 1H NMR spectroscopy. The 1H NMR spectra also suggest that suitably sized solvents, such as [D8]toluene, efficiently solvate the cavity, reducing the conformational flexibility. In [D12]mesitylene, both cavitands undergo remarkably stable host-guest inclusion complexation with cycloalkanes. The larger cavity of 3 preferentially hosts cyclohexane, whereas the smaller cavity of 2 forms the most stable complex with cyclopentane. The propensity for the cavitands to facilitate ,,, stacking between the chromophores was confirmed by both 1H NMR and fluorescence spectroscopy. The interchromophoric interaction is strongly solvent-dependent: ,,, stacking between the pyrene moieties of 2 is not as efficient in [D8]toluene, as it solvates the inner cavity and prevents the two chromophores from approaching each other. Fluorescence studies revealed an unexpectedly large conformational flexibility of the cavitand structures both in the vase and kite forms, which was further confirmed by molecular dynamics simulations. Excimer formation is most preferred in [D12]mesitylene when the cavities are empty, whereas efficient solvation or guest binding in the interior spaces reduces the propensity for excimer formation. The observed high conformational flexibility of the cavitands in solution explains previous differences from the behavior of related systems in the solid state. This study shows that the rigid, perfect vase and kite geometries found for bridged resorcin[4]arene cavitands in the solid state are largely a result of crystal packing effects and that the conformational flexibility of the structures in solution is rather high. [source] Towards the Synthesis of Highly Functionalized Chiral ,-Amino Nitriles by Aminative Cyanation and Their Synthetic ApplicationsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 1 2006Luca Bernardi Abstract The cyanobis(dibenzylamino)borane-mediated transformation of chiral aldehydes into the corresponding ,-amino nitriles is described. Starting from these compounds short synthetic routes can be envisaged for obtaining diastereomerically pure functionalized 1,2-diamines and hydroxylated ,-amino acids that are of interest as core key units of biologically active substances or as potential ligands for asymmetric catalysis. The stereochemical outcome of the aminative cyanation reaction is discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] | ||||||||||