Synthesis of series of 1- and 3-differently substituted xanthines from imidazoles

A new and general method is described for the synthesis, in three steps and in good overall yields, of tetrasubstituted xanthines from an easily prepared imidazole precursor. The method is especially useful for the preparation in standardized conditions of series of xanthines combining a broad variety of primary or secondary alkyl, benzyl or aryl groups at N1 and of alkyl or arylmethyl groups at N3, that are not readily available by other methods.     

An unprecedented surface oxidation of polystyrene substrates by wet chemistry under basic conditions

The surface of polystyrene substrates has been modified by wet chemistry consisting of a treatment with sodium hydroxide in a water-methanol solution at 50 degrees C for 15 h, under air atmosphere. The resulting samples were analyzed by XPS and AFM. The surface functional groups (hydroxyl and carboxyl functions) were assayed by radiolabeling. All the results are consistent with a surface oxidation process.     

Retrosynthetic analysis of fullerene C(60): structure, stereochemistry, and calculated stability of C(30) fragments.

The total number of possible retrosynthetic bisections of C(60) leads to nine different isometric C(30) fragments. These molecules include five chiral units, four of which derive from partitions corresponding to four distinct "Coupes du Roi". The energies, curvatures, and homodesmotic stabilization energies of the C(30) fragments are evaluated at the ab initio 6-31G level.     

Asymmetric 1,3-dipolar cycloaddition of N-metalated azomethine ylides to methyl (S)-2-(p-tolylsulfinyl)acrylate. Synthesis of optically pure 2,4,5-trisubstituted 2,5-dihydro-1H-pyrroles

The first 1,3-dipolar reaction of azomethine ylides with optically pure vinyl sulfoxide are reported. The presence of the sulfinyl group increase the reactivity of the acrylate moiety as a dipolarophile, and the reactions evolve with complete regio- and endo-selectivities. Nevertheless, mixtures of the two diastereoisomers 4 and 5 (75-88% de) resulting from the anti dipole/s-cis dipolarophile and syn dipole/s-trans dipolarophile approaches, respectively, are obtained. The stereoselectivity can be controlled by using THF or MeCN as solvents or by changing the reaction temperature in MeCN. After separation of the cycloadducts, optically pure 2,5-dihydro-1H-pyrroles are easily obtained by pyrolytic desulfinylation.     

Synthesis of 1,2,7,7a-tetrahydro-1aH-cyclopropa[b]quinoline-1a-carboxylic acid derivatives, doubly constrained ACC derivatives, by a remarkable cyclopropanation process

Reaction of N-benzoyl-1,2,3,4-tetrahydroquinoline-2-carboxylic acid with acetic anhydride resulted in 1H,3H,5H-oxazolo[3,4-a]quinolin-3-one derivative 13. Different cyclopropanation processes were applied to 13, but only diazomethane in the presence of water furnished the hitherto unknown methyl 1,2,7,7a-tetrahydro-1aH-cyclopropa[b]quinoline-1a-carboxylate 14, which can be considered as a doubly constrained 1-aminocyclopropane-1-carboxylic acid system. The mechanism of the cyclopropanation was studied in detail. The new ACC ester 14 was transformed into fused tetracyclic hydantoin derivatives, which comprised a new type of heterocyclic system.     

Novel acid-catalyzed rearrangement of tetrahydro-1,2,3,4-tetrazines: unexpected formation of glycosazones

The present contribution discloses a simple and unexpected acid-catalyzed cleavage of tetrahydrotetrazines leading to 1,2-bis(hydrazones). Incorporation of a chiral fragment derived from carbohydrates enables the rapid preparation of glycosazones, a family of compounds employed by Emil Fischer to elucidate the configuration of sugars. In addition, a mechanistic proposal accounts for experimental observations.     

Synthetic applications of o- and p-halobenzyl sulfones as zwitterionic synthons: preparation of ortho-substituted cinnamates and biarylacetic acids

The synthetic applications of o-halobenzyl and p-halobenzyl sulfones as precursors of 1,3- and 1,5-zwitterionic synthons, respectively, are described. Their alpha-sulfonyl carbanions, generated by means of the phosphazene base P2-Et or BuLi or K2CO3 under PTC conditions, reacted with different electrophiles such as alkyl halides, aldehydes, and electrophilic olefins. Palladium-catalyzed cross-coupling processes such as Heck, Suzuki, and Sonogashira reactions can be efficiently performed at the halogen atom. These two sequential functionalization processes are applied to the synthesis of ortho-substituted cinnamates and pharmaceuticals belonging to the family of p-biarylacetic acids such as 4-biphenylacetic acid, namoxyrate, xenyhexenic acid, and biphenylpropionic acid.     

1,1',3,3',6,6',8,8'-Octachloro-9,9'-bifluorenylidene and perchloro-9,9'-bifluorenylidene,two exceedingly twisted ethylenes

The syntheses of 1,1',3,3',6,6',8,8'-octachloro-9,9'-bifluorenylidene (1), its precursors, and the byproduct 3,3',5,5'-tetrachloro-4-(trichloromethyl)biphenyl (5) are described. Accurate structural X-ray data on 1 and on perchloro-9,9'-bifluorenylidene (2) are reported and discussed. Because of chlorine overcrowding, the dihedral angles between their two identical fluorenylidene moieties are abnormally large, the central-ethylene twist angles being 55 and 66 degrees, respectively. Significant out-of-plane carbon-chlorine bond bending is likewise exhibited. Their ESR spectra and magnetic measurements prove that they are singlet species. The exceptionally large bathochromic displacements of their UV-vis absorption spectrum with respect to that of their parent hydrocarbon are mainly attributed to bond bending and molecular warping.     

Productive trapping of NAD-type radicals. Non-biomimetic reduction of pyridinium salts

One-electron reduction of pyridinium salts (NAD+ analogues) generates dihydropyridyl radicals which may then be engaged in radical addition processes to regioselectively form gamma-substituted dihydropyridines.     

Synthesis and characterization of [Cu(Me2oxpn)Ni(NO2)(tmen)](ClO4): a single ferrimagnetic dinuclear CuII-NiII complex acting as weak molecule-based magnet

The new heterodinuclear complex [Cu(Me2oxpn)Ni(NO2)(tmen)](ClO4), that exhibits strong antiferromagnetic intramolecular coupling between CuII and NiII ions (ferrimagnetic behavior), shows ferromagnetic ordering at low temperature, due likely to a small canting phenomenon; it is one of the very few compounds made from isolated molecules that lead to cooperative magnetic behavior.