Application of the Novel Tandem Process Diels‐Alder Reaction/Ireland‐Claisen Rearrangement to the Synthesis of rac‐Juvabione and rac‐Epijuvabione

The novel tandem process Diels‐Alder reaction/Ireland‐Claisen rearrangement shows a high diastereoselectivity for the Ireland‐Claisen rearrangement starting from the endo‐product of the Diels‐Alder reaction. Based on this mechanistic knowledge, the novel tandem process could be applied to the synthesis of rac‐juvabione.     

Total Synthesis of Sanglifehrin A

The immunosuppressive agent sanglifehrin A has been prepared for the first time by total synthesis. The construction of the macrocyclic unit of the target molecule was achieved through a selective intramolecular Stille coupling, and the spirolactam unit by Paterson–aldol reactions. The final steps involve an intermolecular Stille coupling and the opening of the internal acetal unit. This convergent synthesis opens the way for the synthesis of libraries of novel sanglifehrin analogues for biological screening.     

Stereospecific Migration of P from N to C: Ring-Expansion Reaction of Chiral Diazaphospholidine Oxides

An addition-pseudorotation-elimination pathway is proposed for the first stereospecific ring-expansion reaction of chiral diazaphospholidine oxides by a 1,3-migration of P from N to C [Eq. (1)]. R=H, Ph; LDA=lithium diisopropylamide.     

Synthesis and chemistry of metallo poly(phenylene diacetylenes)

We describe the synthesis and characterization of metallopolymers comprising poly(phenylene diacetylenes) containing platinum and cobalt species coordinated to the triple bonds of the diacetylene moities. Thermal treatment of these polymers as thin films results in their conversion to hetero glassy carbon (HGC). The coordinated metals are retained within the matrices of the glassy carbons as small metallic clusters (∼10-30 Å for Pt and 50-1000 Å for cobalt). The platinum doped glassy carbon shows remarkable activity for the reduction of both H⁺ and O₂, a result that has important implications for the development of fuel cell electrodes. At both pH 0 and 7, the platinum Pt-HGC reduced the overpotential for O₂ reduction by ∼800 mV, and resulted in a voltammetric response similar to that of pure platinum.     

Cosserat continuum modelling of grain size effects in metal polycrystals

The global response of polycrystalline aggregates is investigated, in order to simulate grain size effects in IF ferritic steels. The mechanics of generalized continua is used to describe the studied phenomena. The polycrystal is regarded as a heterogeneous Cosserat medium, and the overall properties are estimated using a specific homogenization technique. To illustrate the capabilities of the model, some simple bidimensionnal computations are presented for different grain sizes. Afterwards tridimensionnal computations are shown in order to extract the global effect on the mechanical behaviour for grain sizes ranging from 5 µm to 120 µm. The finite element response is harder for the smallest grain size, but the model still underestimate the grain size effect on the tensile response. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

catena‐Poly[[bis[pentaaquaerbium(III)]‐μ‐benzenehexacarboxylato] tetrahydrate]

The title compound is composed of one‐dimensional polymeric {[Er₂(C₁₂O₁₂)(H₂O)₁₀]·4H₂O}_n chains containing Er in a slightly distorted antiprismatic eightfold coordination. The benzene­hexa­carboxyl­ate ion is located about an inversion centre. Water mol­ecules of crystallization, linked by hydrogen bonding to water mol­ecules of the rare earth coordination spheres or the carboxyl­ate groups of the organic ligands, fill the space generated by the packing of the separated chains.