Rearrangement photochimique de 4h-pyrannes et de dienones en 2h-pyrannes

The photoreactivity of the 4H-pyrans 1 was studied in detail by fluorescence and phosphorescence, by deactivation measurements for the singlet state and by the determination of the accessible quantum yields and rate constants. The photochemical isomerisation of the 4H-pyrans 1 into 2H-pyrans 2 occurs with concerted migration of the benzyl group, in a singlet state as a sigmatropic 1, 3-transposition. The 2H-pyrans 2 are also obtained by irradiation of the nonconjugated dienone isomers 3 of the 2H-pyrans 2.     

Stereochemical study of hindered α-glycols by 1H and 13C NMR spectroscopy

Sterically hindered α-glycols, obtained from electrochemical hydrodimerization of polycyclic ketones (indanone, tetralone, chromanone, flavanone, xanthone and fluorenone), were studied by ¹H and ¹³C NMR. Evidence of conformational hindrance was deduced from the ¹H spectra; meso or racemic configurations and the conformational stereochemistry of these molecules in solution were assigned.     

Control of transient chaos in tent maps near crisis. I. Fixed point targeting

Combinatorial techniques are applied to the symbolic dynamics representing transient chaotic behavior in tent maps in order to solve the problem of Ott-Grebogi-Yorke control to the nontrivial fixed point occurring in such maps. This approach allows "preimage overlap" to be treated exactly. Closed forms for both the probability of control being achieved and the average number of iterations to control are derived. The results are discussed in relation to the work of Tel and shed new light on the transition to the control of permanent chaos.     

(Li/Ag)CoO2: a new intergrowth cobalt oxide composed of rock salt and delafossite layers

A new ordered (Li/Ag)CoO(2) layered compound with an unusual oxygen packing combining rock salt and delafossite layers is obtained during the (Li(+), Na(+))/Ag(+) ionic exchange from the OP4-(Li/Na)CoO(2) precursor. This compound is actually an intermediate step to the final D4-AgCoO(2) delafossite and can be isolated thanks to the kinetics difference between the Li(+)/Ag(+) and Na(+)/Ag(+) exchange processes. It crystallizes in the P6(3)/mmc space group with cell parameters a(hex.) = 2.848(3) ? and c(hex.) = 21.607(7) ?. The details of the structure as well as its thermal stability and transport properties are presented and discussed.     

Ruthenium‐Catalyzed α‐(Hetero)Arylation of Saturated Cyclic Amines: Reaction Scope and Mechanism

Transition‐metal‐catalyzed sp³ C? H activation has emerged as a powerful approach to functionalize saturated cyclic amines. Our group recently disclosed a direct catalytic arylation reaction of piperidines at the α position to the nitrogen atom. 1‐(Pyridin‐2‐yl)piperidine could be smoothly α‐arylated if treated with an arylboronic ester in the presence of a catalytic amount of [Ru₃(CO)₁₂] and one equivalent of 3‐ethyl‐3‐pentanol. A systematic study on the substrate and reagent scope of this transformation is disclosed in this paper. The effect of substitution on both the piperidine ring and the arylboronic ester has been investigated. Smaller (pyrrolidine) and larger (azepane) saturated ring systems, as well as benzoannulated derivatives, were found to be compatible substrates with the α‐arylation protocol. The successful use of a variety of heteroarylboronic esters as coupling partners further proved the power of this direct functionalization method. Mechanistic studies have allowed for a better understanding of the catalytic cycle of this remarkable transformation featuring an unprecedented direct transmetalation on a Ru^II? H species.     

ChemInform Abstract: Reinvestigation of the OP4-(Li/Na)CoO2-Layered System and First Evidence of the (Li/Na/Na)CoO2 Phase with OPP9 Oxygen Stacking.

The metastable 1:1 Li/Na-stacked OP4-Li_0.42Na_0.37CoO₂ phase is synthesized from a mixture of O3-LiCoO₂ and P2-Na_0.7CoO₂ in a molar ratio of 42:58 (sealed gold tubes, 920 °C, 24 h, very fast quenching).