Chiral C2-Symmetric CuII Complexes as Catalysts for Enantioselective Hetero-Diels–Alder Reactions

Air-stable and recyclable , the Cu^II–(bis)oxazoline complex 1 efficiently catalyzes diastereo- and enantioselective hetero-Diels–Alder reactions between β,γ-unsaturated α-keto acid derivatives 2 and vinyl ethers for the synthesis of substituted dihydropyrans 3 [Eq. (1)]. Results of the crystal structure analysis of 1 in combination with calculations on model compounds indicate the formation of a reactive intermediate through replacement of the two H₂O ligands with a chelating substrate. X=OEt, N(OMe)Me; R=alkyl, aryl, alkoxy, thiobenzyl.     

Self-Assembling Sieves

A modular strategy has been applied to synthesize large, porous, self-assembling capsules. The coupling of tricyclic building blocks incorporating glycoluril hydrogen-bonding units and derivatives of triethylbenzene produces monomers which readily form homo- and heterodimeric assemblies (calculated structure is shown). Large guests can be trapped while small solvent molecules flow freely through the pores of the capsules.     

Symmetrization of organomercury(II) chlorides using basic alumina

The symmetrization reaction of organomercury(II) chlorides (RHgCl) to R₂Hg and HgCl₂ in toluene solution under identical conditions using a basic alumina column has been studied­in order to compare the effect of the nature of the R groups on the extent of symmetrization. The efficiency of symmetrization depends markedly on the electron-withdrawing nature of­R, varying from 90–94% for R = trichlorovinyl or phenyl to 11% for R = 2,6-dimethylphenyl.© 1998 John Wiley & Sons, Ltd.     

Molecular Self Assembly: Solvent Guests Tune the Conformation of a Series of 2,6-Bis(2-anilinoethynyl)pyridine-Based Ureas

The conformations of 2,6-bis(2-anilinoethynyl)pyridine-based urea receptors were studied by single crystal X-ray diffraction methods and revealed a rich conformational flexibility influenced by solvents. Whereas receptor L(1) in DMSO prefers an "S" conformation, receptor L(1) crystallizes in an "O" conformation from DMSO/CH(3)OH binary solvent system, and a "W" conformation in the ternary solvent mixture DMSO/toluene/1,4-dioxane. In the case of L(2), the molecule adopts an "S" conformation where water molecules are sandwiched between two molecules of L(2) to form a dimer. Similar to L(2), L(3) also forms a dimer where water molecules are sandwiched between L(3) molecules, which are capped with two molecules of DMSO. Such a capping DMSO solvate is lacking in the case of L(2). Taken together, these results demonstrate that the conformation of 2,6-bis(2-anilinoethynyl) pyridine-based urea receptors can be dramatically manipulated and tuned by the choice of crystallization solvents.     

9,12‐Di­iodo‐1,2‐dicarba‐closo‐dodecaborane(12)

The title compound, C₂H₁₀B₁₀I₂, has a pseudo‐icosahedral cluster geometry. The crystal structure features an intermole­cular C—H⋯I—B hydrogen bond with a normalized H⋯I distance of 3.00 Å.