The effect of the "inert" counteranions in the deprotonation of the dihydrogen complex trans-[FeH(eta 2-H2)(dppe)2]+: kinetic and theoretical studies

Kinetic studies indicate that trans-[FeH(H2)(dppe)2]+ reacts with an excess of NEt3 to form cis-[FeH2(dppe)2] in a single kinetic step. The second-order rate constant is strongly affected by the presence of added salts, an acceleration being observed with BF4- and PF6- salts and a deceleration with BPh4-. Theoretical calculations indicate that the role of the accelerating anions consists of the formation of ion pairs that provide a more effective reaction pathway for deprotonation. However, for the ion pair with the bulky BPh4- anion, steric crowding in the proximities of the dihydrogen ligand hinders the approach of the base, and the reaction is decelerated.     

Fullerohelicates: a new class of fullerene-containing supermolecules

A multicomponent array made of a bis-copper(I) helicate core and two peripheral fullerene subunits has been prepared and electron transfer from the photoexcited Cu(I)-complexed unit to C60 occurs.     

A copper- and amine-free sonogashira reaction employing aminophosphines as ligands

An efficient Pd-catalyzed Sonogashira coupling reaction was achieved in the absence of a copper salt or amine with an inorganic base and easily prepared, air-stable aminophosphine ligands in commonly used organic solvents; good to excellent yields were obtained. Under optimized reaction conditions, the Sonogashira coupling reaction occurred selectively when an enyne substrate was employed and no Heck reaction product was detected; acetone-masked acetylene and trimethylsilylacetylene can also be efficiently coupled, providing a method to make terminal alkynes.     

Photometric determination of aluminium with alizarin fluorine blue

In order to decide whether Alizarin Fluorine Blue (alizarin complexan, 3-amino-methylalizarin-N,N-diacetic acid) is a suitable reagent for the spectrophotometric determination of aluminium, values of the stability constants for some reactions of this reagent with aluminium(III) and iron(III) have been determined spectrophotometrically in a medium containing 20 % dioxan and 80 % water at ionic strength 0.1. The values of the constants that were determined are log K(Al)(AlHL) = 14.3, log K(2Al)(Al2L) = 25.3 and log K(Fe)(FeHL) = 19.6. These results were employed in the design of a method for the spectrophotometric determination of aluminium in the presence of iron and titanium. The Sandell sensitivity is 0.01 mug/cm(2) and the coefficient of variation for 34 determinations was 0.9 %.     

Synthesis of C-3' methyl taxotere (docetaxel)

Protected (3R,4S)-N-Boc-3-hydroxy-4-methyl-4-phenylazetidin-2-one has been synthesized stereoselectively and used to esterify protected 10-desacetylbaccatin III to give, following removal of the protecting groups, novel C-3' methyl taxotere (docetaxel).     

Synthesis of new dihydropyrazines with DNA strand-breakage activity

Treatment of 1,2-cyclohexanedione with 1,2-diamines, e.g. ethylenediamine and cis-(and trans-)1,2-diaminocyclohexane, caused [4+2] cyclocondensation to give the corresponding dihydropyrazine derivatives (compounds 1-6). They exhibited stronger DNA strand-breakage activity than that of dihydropyrazines, which has already been reported in previous papers.     

(+)- and (-)-2-aminocyclobutane-1-carboxylic acids and their incorporation into highly rigid beta-peptides: stereoselective synthesis and a structural study

[Chemical reaction: See text] Several derivatives of (+)- and (-)-2-aminocyclobutane-1-carboxylic acid, 1, have been prepared through enantiodivergent synthetic sequences. The stereoselective synthesis of free amino acid (+)-1 has been achieved, and this product has been fully characterized for the first time. Stereocontrolled alternative synthetic methodologies have been developed for the preparation of bis(cyclobutane) beta-dipeptides in high yields. Among them, enantio and diastereomers have been synthesized. beta,beta- and beta,delta-Dimers resulting from the coupling of a cyclobutane residue and a linear amino acid have also been prepared. The ability of the cyclobutane ring as a structure-promoting unit both in the monomers and in the dimers has been manifested. The NMR structural study and DFT theoretical calculations evidence the formation of strong intramolecular hydrogen bonds giving rise to cis-fused [4.2.0]octane structural units that confer high rigidity on these molecules both in solution and in the gas phase. The contribution of a cis-trans conformational equilibrium derived from the rotation around the carbamate N-C(O) bond has also been observed, the trans form being the major conformer. In the solid state, this equilibrium does not exist, and moreover, intermolecular hydrogen bonds are present.     

Copper reagents: a new and efficient solution for the selective addition of metallated propargylic amines to aldehydes

[reaction: see text] Anti alpha-amino-homopropargylic alcohols are prepared by addition of metallated propargylic amines to aldehydes. Among the four organometallic (LI, Zn, Ti, Cu) derivatives used, the most effective are the copper reagents.     

Voltammetric determination of buspirone

The electroanalytical chemical properties of buspirone are reported in this paper. A sensitive single sweep voltammetric procedure for trace buspirone determination was developed. The detection limit is 5.0 x 10(-9)M. The method has been applied to the determination of buspirone in blood serum by simple dilution in a buffer.