Synthesis of homoallylic chiral tertiary alcohols via chelation-controlled diastereoselective nucleophilic addition on alpha-alkoxyketones: application for the synthesis of the C(1)-C(11) subunit of 8-epi-fostriecin

[reaction: see text] Chiral beta-syn-alkoxyhomoallylic alcohols derived from alkoxyallylboration of aldehydes upon oxidation provided the corresponding chiral ketones. Chelation-controlled nucleophilic addition to these ketones occurred in a highly stereoselective manner to afford anti-homoallylic tertiary alcohols. This methodology has been applied for the synthesis of the C(1)-C(11) subunit of C(8)-epi-fostriecin.     

Infrared Study of Solid Dispersions of β-Cyclodextrin with Naphthalene Derivitaves

The inclusion complexes of β-cyclodextrin (β-CD) with naphthalene and some of its derivatives in the solid state have been studied by infrared spectroscopy. Digital subtraction, deconvolution and curve fitting have been used to investigate the interactions between the naphthalene derivatives andβ-CD. Several preparation methods for the solid dispersions have been tested, using FTIR as an effective tool to evaluate the interactions at the molecular level. The effects of temperature and humidity on the spectra have been also analyzed. A carbonyl moiety in the guest molecule can increase the stability of the complex by establishing specific interactions with the hydroxyl groups of the CD cavity rims. The stability of the complexes is higher for 2-naphthylacetate than that for 1-naphthyl acetate, andso is the degree of association of its carbonyl groups. On the other hand, 2-acetylnaphthaleneforms very stable inclusioncomplexes although its carbonyl groups appear to be significantly less associated.     

An effective enantioselective approach to the securinega alkaloids: total synthesis of (-)-norsecurinine

[reaction: see text] A highly versatile approach to the enantioselective synthesis of securinega alkaloids is presented. Crucial steps are a palladium-catalyzed enantioselective imide alkylation, a vinylogous Mannich reaction, and a ring-closing metathesis process. Through this strategy, the synthesis of (-)-norsecurinine has been accomplished in nine steps and 11% overall yield.     

Unique tautomeric properties of isoguanine

The tautomeric properties of isoguanine (also named 2-oxoadenine or 2-hydroxyadenine) have been studied in the gas phase, in different pure solvents, and in the DNA environment using state of the art theoretical methods. Our results show that isoguanine constitutes an unique example of how tautomerism can be modulated by the environment. Compared to the tautomeric preference in the gas phase, both polar solvents and the DNA microenvironment dramatically change the intrinsic tautomeric properties of isoguanine. Tautomers which are important in physiological conditions are less than 1/10(5) of the total population of isoguanine in the gas phase. The impact of the present findings in the understanding of spontaneous mutations and in the design of new nucleobases with multiple recognition properties is discussed.     

Degradation Kinetics of an Epoxy/Cycloaliphatic Amine Resin Under Isothermal and Non-isothermal Conditions

A study of an epoxy-cycloaliphatic amine system has been realized using a thermogravimetric technique (TG). Isothermal and non-isothermal (dynamic) methods were employed to determine the kinetic data of this system. Five methods were used for determining the activation energies of this system in the dynamic heating experiments. In two of them (Flynn-Wall-Ozawa, and Kissinger) it is not necessary to have a prior knowledge of the reaction mechanism of the degradation behaviour for this system. In the other ones (Coats and Redfern, Horowitz and Metzger, and Van Krevelen et al.) it is necessary to know this reaction mechanism, besides Criado et al. method was used for determining it. The results have shown that good agreement between the activation energies obtained from all methods can be achieved if it is assumed that the degradation behaviour of this system is of sigmoidal-rate type. This revised version was published online in August 2006 with corrections to the Cover Date.     

Copper(II) tetrafluoroborate as an extremely efficient catalyst for 1,3-dithiolane/dithiane formation from carbonyl compounds under solvent-free conditions at room temperature

Copper(II) tetrafluoroborate hydrate is a new and extremely efficient catalyst for 1,3-dithiolane/dithiane formation from aromatic, heteroaromatic and aliphatic aldehydes and cyclic saturated ketones in 1-5 min under solvent-free conditions at room temperature. The reaction is compatible with other functionalities such as ether, ester, hydroxyl, halide, nitro and cyano groups and exhibits excellent chemoselectivity. α,β-Unsaturated aldehydes/ketones lead to selective formation of 1,3-dithiolanes instead of Michael addition products. For substrates bearing an aldehyde and a ketone carbonyl group, chemoselective dithiolane formation takes place with the aldehyde.     

Surface tension measurements in the study of molecular complexes

Surface tension measurements can be used to investigate molecular complex formation in liquid solutions for strong and weak complexes. The association constant and epthalpy for triethylamine-iodine, hexamethylbenzene-tetracyanoethylene and ethanol-iodine in cyclohexane are 4·55×10³, 218 and 0.93M⁻¹ at 25° C and 12·5, 7·7 and 5·1 kcal/mol respectively. These values compare well with those reported in the literature by other methods.