Vibrational predissociation induced by exciton trapping in inert-gas clusters

The dynamics of exciton trapping, vibrational energy transfer and vibrational predissociation in an electronically excited state of Ar₁₃ clusters was explored by classical molecular dynamics. Two distinct time scales were established for vibrational energy flow, which result in a molecular-type, reactive dissociation process of Ar atoms for this cluster.     

Palladium-catalyzed chemoselective direct α-arylation of carbonyl compounds with chloroaryl triflates at the C–Cl site

This study described palladium-catalyzed chemoselective direct α-arylation of carbonyl compounds with chloroaryl triflates in the Ar–Cl bond. The Pd/SelectPhos system showed excellent chemoselectivity toward the Ar–Cl bond in the presence of the Ar–OTf bond with a broad substrate scope and excellent product yields. The electronic and steric hindrance offered by the –PR₂ group of the ligand with the C2-alkyl group was found to be the key factor affecting the reactivity and chemoselectivity of the α-arylation reaction. The chemodivergent approach was also successfully employed in the synthesis of flurbiprofen and its derivatives (e.g., –OMe and –F).

Palladium-catalyzed chemoselective direct α-arylation of carbonyl compounds with chloroaryl triflates in the Ar–Cl bond is reported. The effects of –PR₂ and C2-alkyl groups of the ligands are investigated using experimental and computational methods.     

Synthese de fluoro-2 thiocyanates

2-Fluorinated thiocyanate compounds have been prepared by action of KSCN on an homologous series of 2-fluorotosylates in ethanol at about 100°C. The isomerization giving isothiocyanic derivatives does not take place under these conditions. The analysis of the NMR spectra on three members of the series has shown that the mechanism is of the SN₂ type.     

Further evidence for a metal-oxo intermediate in the olefin epoxidation by iron- or manganese-bleomycin complexes associated with KHSO5, an oxygen atom donor

The use of iodosylbenzene with the iron-bleomycin complex in the olefin epoxidation leads to the questionable role of iron-oxo in this oxygenation reaction (Tetrahedron Letters, 1985, 26, 4699-4702). Oxygenation of olefins is also observed when potassium hydrogen persulfate, KHSO₅, is used as oxygen donor and the reported data support a possible role of metal-oxo species in these oxygen transfers mediated by manganese- or iron-bleomycin complexes.     

Barriers to ring inversion in dibenzo[a,c]cyclooctene and its dihydro and tetrahydro derivatives by racemization and NMR bandshape studies

Dibenzo[a,c]cyclooctene and its 9,10-dihydro and 9,10,11,12-tetrahydro derivatives have been resolved by chromatography and their inversion barriers determined by thermal racemization. The 9,12-dihydro derivative has been studied by ¹H NMR bandshape technique.     

Conformational energies of trans-1,4-difluoro- and trans-1-chloro-4-fluorocyclohexane. The role of electrostatic interactions.

The conformational energies of the title compounds were extrapolated from solution ¹⁹F NMR measurements to vapour phase dielectric medium. Vapour phase values were satisfactorily reproduced by MM2 computations including electrostatic interactions between charges obtained by the PEOE method.     

Diastereoselective spiroannelation

The diastereoselection in the reaction of 1,4-di-(bromomagnesio) pentane with various structures of lactones and cyclic anhydrides is described.     

Synthesis of enantiomerically pure carbocyclic 3′-azido-2′, 3′-dideoxythymidine,a potential anti-aids drug

(+)-1-[(1R,3S,4S)-3-Azido-4-(hydroxymethyl)cylopentyl]-5-methyl- 2,4-(1H,3H)-pyrimidindione 7 (C-AZT) was synthesized starting from mesylated compound 1 in a six step sequence via urea derivative 5.     

Enzymatic oligomerisation versus lactonisation of ω -hydroxyesters

Porcine pancreatic lipase in anhydrous organic solvents catalyses almost exclusively the oligomerisation reaction of unsubstituted β, δ, and ε-hydroxyacid methyl esters. In Contrast, the substituted δ-methyl- δ-hydroxyester undergoes lactonisation.