Alessandra Farina

Resolution of Racemic 1,2-Dibromohexafluoropropane through Halogen-Bonded Supramolecular Helices.

Halogen bonds, attractive intermolecular interactions between perfluoroalkyl bromides and bromide ions, are present in cocrystals of (-)-sparteinium hydrobromide (1) and (S)-1,2-dibromohexafluoropropane (2; shown schematically), and result in enantiopure and infinite supramolecular helices. The perfluorocarbon-hydrocarbon self-assembly allows the resolution of racemic 2.

New fluorinated chiral synthons

Abstract the syntheses of new optically pure poly-halo and poly-fluoro oxiranes 5b-e by addition of diazomethane on the corresponding β-ketoγ-fluorosubstituted sulphoxide intermediates, both in keto 3 , hydrate 4 or in keto/ hydrate form are described. Syntheses of sulphur-free fluorinated oxiranes 18b-e , β-hydroxy-β-trifluoromethyl amine 21d , α- acid 25d and β,γ-dihydroxy-β-trifluoro- and -chlorodifluoromethyl amines 26c and 26d are shown as examples of their chemical versatility

Racematspaltung von 1,2‐Dibromhexafluorpropan über Halogen‐verbrückte supramolekulare Helices

Halogenbrucken, anziehende intermolekulare Wechselwirkungen zwischen Perfluoralkylbromiden und Bromidionen, liegen in Mischkristallen aus (−)-Sparteinhydrobromid 1 und (S)-1,2-Dibromhexafluorpropan 2 vor (schematisch dargestellt) und fuhren zur Bildung enantiomerenreiner, endloser supramolekularer Helices. Die Aggregatbildung durch Selbstorganisation von Perfluorkohlenwasserstoff und Kohlenwasserstoff ermoglicht die Racematspaltung von 2.

Stereoselective Total Synthesis of Enantiomerically Pure 1-Trifluoromethyl Tetrahydroisoquinoline Alkaloids

Enantiomerically pure 1-trifluoromethyl-tetrahydroisoquinoline alkaloid analogues, in which C-1 is a quaternary stereogenic centre, have been synthesized by stereoselective intramolecular Pictet-Spengler reaction of the N-arylethyl γ-trifluoro-β-iminosulfoxide (R)-3, and subsequent elaborations of the sulfinyl auxiliary. The absolute stereochemistry of the stereogenic centre was determined by X-ray diffraction on the α-phenylpropionic ester (1R,2′S)-10.

Polythiophenes with Unusual Electrical and Optical Properties Based on Donor Acceptor Alternance Strategy

The strategy of donor-acceptor alternation was adopted to reduce the energy gap in substituted polythiophenes; energy gaps down to 1.2 eV were obtained, which is a very low value in the class of polythiophenes. Alkoxy groups and dicyanoethenyl groups were used to prepare electron-rich and electron-poor thiphene units. The copolymers were obtained by coupling reaction methods (Suzuki) and by oxidative chemical and electrochemical polymerisation of an opportunely designed substituted therthiophene. X-ray studies and spectroscopic data on the copolymers evidenced that the dicyanoethenyl group as substitutent was rather steric demanding and susceptible of side reactions also preventing the n-doping of the material. The conductivity behaviour was unusual but compatible with localised charge carriers.

Tetrahexylsexithiophene: crystal structure and molecular mechanics calculations

SUMMARY: The synthesis, crystal structure and detailed molecular mechanics calculations, including crystal packing interactions, of tetrahexylsubstituted sexithienylene are presented. Unexpectedly the molecule, which arranges in the P-1 space group, displays no herringbone arrangement, thienylenic rings are far from coplanarity and the alkylic side chains present different conformations. Molecular mechanics fully accounts for these findings. From crystal packing computations it is derived that different arrangements are unable to lower the packing energy, due to the closeness of two alkyl chains on the same side of the thienylenic backbone, which prevents interspersion of non-parallel molecules.

Synthesis of optically pure fluorosubstituted isoxazolidines by 1,3-dipolar cycloaddition of nitrones to chiral methyl enol ethers of 3-fluoro-1-sulphinyl-2-propanones

Abstract Optically pure enol ether 4 undergoes 1,3-dipolar cycloaddition, with C , N -diphenylnitrone 5 to give the fluorosubstituted isoxazolidine 6 in a fully regio- and diastereoselective manner. The absolute configuration of 6 has been established by X-ray analysis. When changing the nitrone and/or the fluoro substitution pattern in compounds similar to 4 , the same reactivity is observed.

Oxidative dimerization of diethyl 3-thienylmalonate by high valent metal salts. Synthesis of benzo[1,2-b:4,5-b′]dithiophene derivatives

Abstract The oxidation of diethyl 3-thienylmalonate (1) by metal oxidants (Fe(ClO4)3, Mn(OAc)3, MnO2 and CuO) in various solvents at 60 °C affords dimerization products arising from side-chain and nuclear coupling of the intermediate delocalized malonyl radicals 6. Metal to sulphur binding is suggested to play a role in controlling the distribution of dimers 2 – 5. The higher thermodynamic stability of unsymmetric dimer 3, along with its oxidative intramolecular 1,6-cyclization to 4, allows to develop a new simple synthesis of benzo[1,2-b:4,5-b′]dithiophene derivatives 15–18.

Structure and Polymorphic Behavior of Poly(dipropylphosphazene).

Abstract X-ray diffraction and DSC investigations indicate that poly(dipropylphosphazene) is characterized by one ordered crystalline modification and a thermotropic mesophase, which is formed at temperatures higher than 248°C and appears to maintain a 2D order. The structure of the crystalline phase has been determined: the unit cell is monoclinic, space group P21/c, and the cell parameters are: a=9.10(5)xa0A, b=4.88(4)xa0A, c=19.05(10)xa0A, β=92.43(1)°. The refinement indicates a twofold helical conformation with a nearly planar (CT)2 backbone. The cyclic trimer was studied by DSC and single crystal X-ray diffraction: the unit cell is monoclinic, space group P2/c, cell parameters are a=10.0131(5)xa0A, b=7.8342(4)xa0A, c=15.1782(11)xa0A, β=95.844(7)°. The conformations of the side chains in the polymer and the trimer are closely related, as already found in polydiethylphosphazene. In the polymer, however, the side chains probably show some disorder yet to be characterized.

On the preparation of disymmetrized tris(hydroxymethyl) methanol equivalents

Abstract Synthetic equivalents, 1,1-bis-hydroxymethyl methylene oxides 7, 18 , of trisubstituted carbinol derivatives such as the disymmetrized tetrahedral tris(hydroxymethyl) methanol 17 have been obtained in enantiomerically pure form from ( R )-methyl- p -tolylsulfoxide, glycolic acid ethyl ester and diazomethane.