Emanuela Licandro

A convenient procedure for the synthesis of tetrathia-[7]-helicene and the selective α-functionalisation of terminal thiophene ring

This paper describes a convenient preparation of tetrathia-[7]-helicene (TH[7]), the generation of the α-anion on the terminal thiophene ring, and the synthesis of the 2-formyl-tetrathia-[7]-helicene (2-CHO-TH[7]). The key intermediate trans-1,2-dibenzodithiophene-ethene, prepared in 97% yield by McMurry coupling of the 2-formyl-benzo[1,2-b;4,3-b′]dithiophene, was transformed into TH[7] using a known procedure. The described method affords TH[7] in 46% overall yield, which is more than four times the yield previously reported in the literature. The α-anion of TH[7], which is easily generated on the α-position of one of the terminal thiophene rings, reacts with electrophilic reagents such as D2O and DMF. The latter reaction proved to be the best way to prepare 2-CHO-TH[7], a key intermediate for the preparation of new substituted heterohelicenes.

Luminescent conjugates between dinuclear rhenium(I) complexes and peptide nucleic acids (PNA) for cell imaging and DNA targeting

New luminescent dinuclear rhenium(I) tricarbonyl complex-PNA conjugates have been synthesized through a reliable solid-phase synthetic methodology. Their photophysical properties have been measured. The most luminescent Re-PNA conjugate 7 showed interesting two-photon absorption (TPA) properties, that were exploited for imaging experiments, to demonstrate its easy uptake into living cells.

Phosphathiahelicenes: Synthesis and Uses in Enantioselective Gold Catalysis

Enantiomerically pure thiahelicenes displaying a terminal phosphole unit and a stereogenic phosphorus center have been prepared by oxidative photocyclization of a diaryl-olefin precursor. Starting from one of these phosphathiahelicene oxides, the corresponding trivalent phosphine-Au(I) complex is obtained with complete diastereoselectivity. It affords a new, excellent precatalyst for the enantioselective cycloisomerization of N-tethered enynes (up to 96 % ee).

Gold(I) complexes of tetrathiaheterohelicene phosphanes.

New tetrathia[7]helicene-based (7-TH-based) gold(I) complexes 6 and 7 have been readily prepared by reaction of the respective phosphine ligands 2 and 3 with Au(tht)Cl in a 1:1 and 1:2 molar ratio, respectively. These complexes have been fully characterized by analytical and spectroscopic techniques as well as quantum chemical calculations. The molecular structure of dinuclear complex 7 has been determined by single-crystal X-ray diffraction, showing a gold-gold interaction of 3.1825(3) Å and a significant contraction of the 7-TH total dihedral angle. Au(I) complex 7 displays luminescence emission at room and low temperature in diluted solution and in the solid state. Quantum chemical calculations show that the luminescence emission at room temperature is primarily due to slightly perturbed fluorescence emission from purely ππ* excited states of the conjugated helicene scaffold. At 77 K phosphorescence emission is displayed as well. Preliminary studies on the use of 6 and 7 as catalysts in typical Au(I)-catalyzed cycloisomerizations have demonstrated the reactivity of these systems in the intramolecular allene hydroarylations and the hydroxycarboxylation of allene-carboxylates.

Synthesis and non-linear properties of conjugated poly-unsaturated amino carbene complexes

A series of poly-unsaturated pyrrolidino carbene complexes have been synthesized and their first β hyperpolarizabilities evaluated using the Hyper Rayleigh Scattering (HRS) technique. Some of these complexes have good to high β values (up to 543×10−30 esu). A comparison of the non-linear responses of the complexes with those of the corresponding amides (their isolobal organic analogues) highlighted the potential usefulness of the pentacarbonylchromium carbene moiety as an electron-accepting group in the design of second order non-linear optical (NLO) materials.

Tricarbonyl(η6arene)Chromium(0) complexes as chiral auxiliaries: Asymmetric synthesis of β-aminoesters and β-lactams by Reformatsky condensation

Abstract Highly stereoselective syntheses (e.e. > 98%) of β-aminoesters and β-lactams were accomplished using enantiomerically pure tricarbonyl (η6benzaldimine)chromium complexes in a Reformatsky type reaction promoted by ultrasound. A correlation between the configuration of complexed imines and absolute configuration of β-lactam derivatives is reported.

The first chiral racemic Fischer-type aminocarbene complex bearing a C2 symmetry amine: stereochemical characteristics and application to Michael addition reactions

Abstract The synthesis of [ trans -methyl(2,6-dimethyl)morpholinocarbene]pentacarbonylchromium(0) complex ( 3 ) is reported, together with the stereoselective Michael addition of the conjugate base of complex 3 to enones.

Transition metal (‘Fischer-type’) carbene complexes as protein labelling reagents

Abstract The electrophilic property of metallocarbenes of Fischer-type was used to label amino acid derivatives and a model protein in a regio-specific manner with a transition heavy metal complex. Hence, the reaction of (CO) 5 WC(OMe)Me ( 1 ) was shown to involve exclusively the amino group of a series of α-amino esters whether this function was carried by the α-carbon or by the side chain, leading to stable aminocarbenes. With a model protein, namely bovine serum albumin, labelling also occurred involving solely the amine function of some of its lysine residues. Coupling yield was shown to depend both on the pH where the reaction was carried out, and on the quantity of carbene. This work could find an application in the field of protein X-ray crystallography.

Enantioselective synthesis of (R)-(−)-baclofen using Fischer-type carbene anions

Abstract The antispastic drug ( R )-(−)-baclofen has been synthesized enantioselectively using a diastereoselective Michael addition reaction of the conjugate base of an enantiopure Fischer-type amino carbene to p -chloro-nitrostyrene.

Michael addition of nitromethane to non-racemic chiral Cr(CO)3 complexes of ethyl cinnamate derivatives: stereoselective synthesis of (R)-(−)-baclofen

Abstract We carried out a highly stereoselective Michael addition (96% de ) of nitromethane to enantiomerically pure tricarbonyl(ethyl-4-chloro-2-trimethylsilylcinnamate)chromium(0). This reaction is the key step in the synthesis of ( R )-(−)-baclofen, a potent antispastic drug.