Are any non-stereospecific 1,3-dipolar cycloadditions known? A revision

The cycloaddition of 1-benzylidenepyrazolid-3-one betaine to (E)-β-nitrostyrene, which has been claimed to furnish 15–30% non-stereospecific product, revealed stereospecificity up to 99.92% in a renewed study; (Z)-β-nitrostyrene stereoisomerizes under the influence of the 1,3-dipole.     

Asymmetric synthesis of (R)-reticuline. A new strategy for the asymmetric synthesis of isoquinolines via enantioselective epoxidation or dihydroxylation

A new strategy for the asymmetric synthesis of 1-benzyl-1,2,3,4-tetrahydroisoquinolines7 − 9 has been developed. The route involves introduction of asymmetry via enantioselective epoxidation or dihydroxylafion of corresponding stilbene precursors followed by aminolysis and Pomeranz-Fritsch cyclization. The strategy has been successfully applied to the asymmetric synthesis of (R)-reticuline (9), the key-intermediate in the synthesis of morphine alkaloids on the biomimetic route.     

Blockcopolymers in microemulsions differential heats of solution and shift of the percolation temperature in W/O microemulsions

Solutions of blockcopolymers (POE-b-PI-b-POE) in fluids of interacting aqueous nanodroplets (W/O microemulsions) are studied. The interaction strength between the (pseudo) two components is measured by the shift of the percolation temperature relative to that of the pure microemulsion. A quantitative measure of the interaction, the differential heat of solution, is thermodynamically related to the slopes of the equilibrium temperature of the system with varying monomeric nanodroplet concentration and the experimental percolation line in the presence of copolymer.     

Phanes with Three- and Four-Membered Rings as Building Elements

The systematic integration of the small 2π- and 4π-electron systems cyclopropenylium ion, cyclopropenone, oxo-cyclobutenylium ion, and cyclobutadiene into phane chemistry was initiated only a few years ago. [n₂]Cyclopropenylophanes, [n₂]cyclopropenonophanes, metal-capped [n₄]cyclobutadienosuperphanes, and other new families of double-decker phane species became available from cycloalkydiynes through special methods of double [2+1]cycloaddition with carbenes and metal complex induced dimerization by double [2+2]cycloaddition. Phane-specific structural features were elucidated by X-ray structural analyses. Cyclic voltammetry and PE spectroscopy as well as MO calculations reealed considerable interactions between closely spaced π-electron systems. Decapping cyclobutadienosuperphanes formally extended the synthetic principle to threefold [2+2]cycloadditions resulting in [n₄]-bridged tricyclo-[4.2.0.0^{3, 5}]octa-3,7-dienes, which represent a new type of cage compounds. Moreover, completion to fourfold [2+2]addition was achieved with the photoinduced transformation of [3₄]bridged tricyclo[4.2.0.0^{3, 5}]octa-3,7-diene into propella[3₄]cubane.     

Cycloalkadiynes—From Bent Triple Bonds to Strained Cage Compounds

The synthesis of Cycloalkadiynes with medium-sized rings may be accomplished by a number of ring-closing and elimination reactions. Information concerning the conformation of the rings as well as the extent of transannular interaction between the triple bonds is obtained by analysis of X-ray crystallographic data and by photoelectron spectroscopy. The diacetylene complexes of Ag¹ and Cu¹ show hardly any structural change compared to the uncomplexed compounds while the bis(hexacarbonyldicobalt) complexes differ significantly in their structural parameters. Reaction of Cycloalkadiynes with dicarbonyl(η⁵-cyclopentadienyl)cobalt yields inter- and intramolecular cyclobutadiene complexes. The superphane of cyclobutadiene formed by the intermolecular reaction can be transformed into a number of highly strained cage compounds in few steps. In addition, the variety of such cage compounds can be increased if the reaction of a cyclic diacetylene is carried out with dimethylacetylenedicarboxylate in the presence of aluminum chloride. The intermediate bridged Dewar benzenes eventually lead to propellaprismanes.     

On the exceptional reactivity of the norbornene double bond

The anomalous reactivity of the bicyclo [2.2.1] heptene double bond is interpreted in terms of hyperconjugative effects, leading to an exceptionally low endo out-of-plane deformation potential.