183 research outputs found
Dataset and R codes: Tools used to assess the quality of peer review reports: a methodological systematic review
No full textThis is the extracted data and R codes related to: Superchi C, González JA, Solà I, Cobo E, Hren D, Boutron I. Tools used to assess the quality of peer review reports: a methodological systematic review. BMC Med Res Methodol. 2019;19(48):1–14. DOI: https://doi.org/10.1186/s12874-019-0688-x</p
Asymmetric addition of dimethylzinc to malonates: a new synthetic strategy to valuable fragrances
No full textASYMMETRIC ADDITION OF DIMETHYLZINC TO MALONATES: A NEW SYNTHETIC STRATEGY TO VALUABLE FRAGRANCES
P. Scafato, V. Marchitiello, L. Pisani, S. Superchi, C. Rosini
Dipartimento di Chimica, Università degli Studi della Basilicata, via N. Sauro, 85; Potenza.
e-mail: [email protected]
The copper-catalyzed conjugate addition of organozinc reagent to α,β-unsaturated carbonyl compounds is a widely used strategy for the catalytic asymmetric C-C bond formation, with a large spectrum of substrates.1 Unfortunately, acyclic esters are not reactive in this reaction, in spite of the remarkable importance of chiral 3-alkylsubstituted esters both in asymmetric synthesis and as precursor of biologically active compounds. Recently, an efficient addition of dimethylzinc to unsaturated malonates, which can easily be transformed in monoesters by dealkoxycarbonylation, has been set up.2
We report herein the asymmetric addition of dimethylzinc to 3-phenylpropyliden malonate as a new route for the preparation of the valuable fragrances,3 Phenoxanol, Citralis and Nitrile Citralis, in optically active form.
References:
1) a) Feringa, B.L. Acc. Chem. Res. 2000, 33, 346. b) Alexakis, A.; Benhaim, C. Eur J. Org. Chem, 2002, 3221.
2) Schuppan, J.; Minnaard, A. J.; Feringa, B. L. Chem. Comm. 2004, 792.
3) Matteoli, U.; Ciappa, A.; Bovo,S.; Bertoldini, M.; Scrivanti, A. Tetrahedron:Asymmetry. 2007, 18, 797
Enantiopure p,p’-Disubstituted 1,2-Diphenylethane-1,2-diols as Chiral Inducers in the Ti-mediated Oxidation of Sulfides: a Case of Reversal of Asymmetric Induction by Fluorine Substitution
No full textIn the asymmetric oxidation of methyl p-tolyl sulfide, (2a), and benzyl phenyl sulfide (2b) by TBHP, mediated by a titanium complex with enantiopure (R,R)-p,p'-disubstituted-1,2-diphenylethane-1,2-diols, both the unsubstituted diol (R,R)-1a and the p-OMe substituted diol (R,R)-1b lead to sulfoxides of S configuration, with ee up to 99%. On the contrary the p-CF3 substituted ligand (R,R)-1c leads to significantly lower ee and in the case of 2a a reversal of asymmetric induction is observed
Regioselective Alkylation of N,N'-Diethylbenzamides via Lithiation and Copper Transmetalation Procedure
No full text
Regioselective ortho-Alkylation of N,N'-Diethylbenzamides via Lithiation and Copper Transmetalation
No full textOne-pot ortho-lithiation and copper transmetalation with CuCN·LiCl of N,N-diethylbenzamides afford the corresponding aryl cyanocuprate, which gives coupling with some aliphatic halides in fair to good yield
Diidrossilazione Enantioselettiva Stechiometrica di Olefine con Tetrossido di Osmio in Presenza di una Diammina 1,1’-Binaftilica
No full textInduction of Cholesteric Mesophases by Simple Cyclic Derivatives of p,p’-Disubstituted 1,2-Diphenylethane-1,2-diols: Importance of Shape and Polarizability Effects
No full textA systematic study of the cholesteric induction in nematic solvents (MBBA and E7) by some cyclic derivatives of unsubstituted and p,p'- disubstituted-1,2-diphenylethane-1,2-diols shows that the values of the twisting power are significantly dependent on the nature of the link connecting the two oxygen atoms and on the nature of the p,p'-substituents. This result has been interpreted considering that the nature of the bridge affects the overall molecular shape and the p,p'-substituents affect both the molecular polarizability and shape. This investigation points put that the polarizability of the solute and the solvent is the main parameter in determining the value of the twisting power while electrostatic arene-arene interactions contribute to a less extent. It has been also observed that solutes having the same structure and the same absolute configuration can induce cholesteric helix of opposite sign depending on the substituent on the aromatic ring. This finding indicates that configurational assignments by cholesteric induction are reliable only if high values of twisting power are measured
Biphenyl dioxolanes as circular dichroism probes for the assignment of absolute configuration to aliphatic diols: Extending the scope to anti 1,n-diols and cyclic syn 1,2-diols
No full textWe describe herein the use of a flexible biphenyl moiety as efficient chirality probe in the assignment of the absolute configuration (AC) of aliphatic, non-chromophoric diols. The diols are transformed in the corresponding biphenyl dioxolanes in which the biphenyl system has either a P or M torsion depending on the chirality of the diol. As the correlation between biphenyl torsion and diol AC has been established and the sense of torsion is revealed by the sign of the biphenyl A band at 250 nm in the CD spectrum of the dioxolane, then the diols AC can be assigned simply looking at the CD spectra of these derivatives. This approach proved to be general, straightforward, and reliable for anti 1,2- 1,3-, and 1,4-diols bearing both one and two stereogenic centers and for cyclic syn 1,2-diol
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