Memory Effect and Crystallization of (R, S)-2-Chloromandelic Acid Glass.

(R, S)-2-Chloromandelic acid, which can crystallize in racemic crystals (forms α and ß) or a conglomerate (form γ), has been studied for its glass-forming behavior. Below the glass transition temperature, samples of the title compound crack into pieces. Correlation plots of DSC results have been used to investigate what determines the cracking and its occurrence temperature. We found that the latter is influenced by the polymorph from which the melt state has been obtained, showing that a certain memory of the previous crystalline phase persists in the undercooled melt. Moreover, this residual structure could be eliminated by elongating the annealing period or increasing the annealing temperature. Investigation using broadband dielectric spectroscopy confirmed such a memory effect. Finally, we studied the role of cracking in the control of the crystallization. In contrast with previous literature on other glass-forming molecular systems, we verified that the crystallization upon reheating is not impacted by the occurrence of cracks in the glassy state. This observation challenges the current views on polymorphic crystallization from organic glasses.

Direct aerobic oxidation of alcohols into esters catalyzed by carbon nanotube-gold nanohybrids.

Gold nanoparticles supported on carbon nanotubes were shown to efficiently catalyze the oxidation of alcohols to methyl esters under mild and selective reaction conditions. The reaction works with low catalyst loadings and the nanohybrid could be readily recycled and reused.

Combination of Aryl Diselenides/Hydrogen Peroxide and Carbon-Nanotube/Rhodium Nanohybrids for Naphthol Oxidation: An Efficient Route towards Trypanocidal Quinones.

This work reports a combination of aryl diselenides/hydrogen peroxide and carbon-nanotube (CNT)/rhodium nanohybrids (RhCNT) for naphthol oxidation towards the synthesis of 1,4-naphthoquinones and evaluation of their relevant trypanocidal activity. Under a combination of (PhSe)2 /H2 O2 in the presence of O2 in iPrOH/hexane, several benzenoid (A-ring)-substituted quinones were prepared in moderate to high yields. We also studied the contribution of RhCNT as co-catalyst in this process and, in some cases, yields were improved. This method provides an efficient and versatile alternative for preparing A-ring-modified naphthoquinonoid compounds with relevant biological profile.

Synthesis of fused cyanopyrroles and spirocyclopropanes via addition of N-ylides to chalconimines.

Addition of N-ylides derived from DABCO to chalconimines takes place through a Michael addition-cyclization pathway to afford fused cyanopyrroles and/or spirocyclopropanes. The product profile depends heavily on the nature of chalconimines. While 6-membered cyclic chalconimines provide a mixture of pyrrole and spirocyclopropane, 5-membered chalconimines furnish exclusively spirocyclopropane. Cyclopropane was the only product in the case of a representative open chain chalconimine as well. On the other hand, chalcones provide only spirocyclopropanes which is in contrast to the previously reported reactivity of enones. The complementary nature of the reactivity of the tetralone derived chalcone and its corresponding imine in providing spirocyclopropane and pyrrole, respectively, has also been demonstrated.

Imidazoles from nitroallylic acetates and α-bromonitroalkenes with amidines: synthesis and trypanocidal activity studies.

Cascade reactions of amidines with nitroallylic acetates and α-bromonitroalkenes provide potentially bioactive imidazoles in good to excellent yields in most cases. While 2,4-disubstituted imidazol-5-yl acetates are formed in the first case, 2,4-disubstituted imidazoles, bearing no substituent at position 5, are the products in the second case. These two series of imidazoles, viz. 2,4,5-trisubstituted and 2,4-disubstituted, were screened for their activity against the protozoan parasite Trypanosoma cruzi which is responsible for Chagas disease. As many as three compounds were as active as the standard benznidazole and two others were 2-3-fold more active highlighting the potential of substituted imidazoles, easily accessible from nitroalkenes, as possible anti-parasitic agents.

One-pot regioselective synthesis of meta-terphenyls via [3 + 3] annulation of nitroallylic acetates with alkylidenemalononitriles.

A highly efficient one-pot method has been developed for the synthesis of meta-terphenyls via a regioselective [3 + 3] annulation-elimination sequence involving Morita-Baylis-Hillman (MBH) acetates of nitroalkenes and alkylidenemalononitriles. The reaction takes place in a regioselective manner under mild conditions (Et3N, room temperature) to afford a wide variety of meta-terphenyls bearing aryl, heteroaryl and styrenyl groups. This novel [3 + 3] annulation takes advantage of the 1,3-bielectrophilic character of MBH acetates and 1,3-binucleophilic character of alkylidenemalononitriles and proceeds in a cascade fashion comprising an SN2' substitution, intramolecular 6-endo-trig Michael addition and double elimination. Representative synthetic transformations of the products, for instance, to meta-terphenyl derived isoindolinones have also been demonstrated.

Synthesis of α-tribromomethylamines via Mg-mediated addition of bromoform to imines.

Mg-mediated addition of bromoform to electron deficient imines such as N-sulfonylimines affords α-tribromomethylated N-sulfonylamines in good to excellent yields. The procedure could be further simplified by transforming the imine precursors, α-sulfonyl-N-tosyl- and Boc-amines, in one pot to the corresponding α-tribromomethyl derivatives. Facile removal of the Boc protecting group in nearly quantitative yield and a silver carbonate mediated monodebromination have also been demonstrated.

Synthesis of fused bromofurans via Mg-mediated dibromocyclopropanation of cycloalkanone-derived chalcones and Cloke-Wilson rearrangement.

A convenient two-step sequence for the conversion of alkylidenecycloalkanones to bromofurans is reported. The steps involve Mg-mediated diastereoselective dibromocyclopropanation of alkylidenecycloalkanone followed by acidic alumina-mediated regioselective ring expansion of the cyclopropyl ketone. The scope of the reaction was investigated using alkylidenecycloalkanones derived from tetralone, indanone, and benzosuberone to afford 2-aryl-3-bromofurans fused to various benzocycloalkanes. Representative examples of stereoconvergent dibromocyclopropanation and total aromatization of the furobenzocycloalkane are also reported.