Isolation of the key intermediate in the formation of cis-bicyclo[3.3.0]octane-3,7-diones from dimethyl 3-ketoglutarate and 1,2-dicarbonyl compounds

SSZ-27: A Small-Pore Zeolite with Large Heart-Shaped Cavities Determined by Using Multi-crystal Electron Diffraction

The high-silica zeolite SSZ-27 was synthesized using one of the isomers of the organic structure-directing agent that is known to produce the large-pore zeolite SSZ-26 (CON). The structure of the as-synthesized form was solved using multi-crystal electron diffraction data. Data were collected on eighteen crystals, and to obtain a high-quality and complete data set for structure refinement, hierarchical cluster analysis was employed to select the data sets most suitable for merging. The framework structure of SSZ-27 can be described as a combination of two types of cavities, one of which is shaped like a heart. The cavities are connected through shared 8-ring windows to create straight channels that are linked together in pairs to form a one-dimensional channel system. Once the framework structure was known, molecular modelling was used to find the best fitting isomer, and this, in turn, was isolated to improve the synthesis conditions for SSZ-27.

Chiral Discrimination in Rhodium(I) Catalysis by 2,5-Disubstituted 1,3a,4,6a-Tetrahydropenatalene Ligands-More Than Just a Twist of the Olefins?

Chiral dienes are useful ligands in a number of asymmetric transition-metal-catalyzed reactions. Here, we evaluate the efficiency of 2,5-disubstituted 1,3a,4,6a-tetrahydropentalenes as ligands to rhodium(I). 2,5-Dibenzyl and diphenyl tetrahydropentalenes were synthesized in two steps and resolved, either chromatographically, or through fractional crystallization of diastereomeric rhodium(I) salts. When evaluated in a 1,4-arylation reaction, the 2,5-dibenzyl ligand gave up to 99% ee. The use of a well-defined rhodium complex as catalyst, Cs₂CO₃ as the base, and toluene/water as solvent was found to have a pronounced beneficial effect on the selectivity of the reaction. The homologous 2,5-diphenyl ligand on the other hand proved to be highly prone to racemization/loss of chirality during catalysis. Control experiments reveal that this rearrangement proceeds via a rhodium-mediated 1,3-hydride shift. Implications for ligand design and catalysis are discussed.

Recent applications of the divinylcyclopropane-cycloheptadiene rearrangement in organic synthesis

This review summarizes the application of the divinylcyclopropane–cycloheptadiene rearrangement in synthetic organic chemistry. A brief overview of the new mechanistic insights concerning the title reaction is provided as well as a condensed account on the biological relevance of the topic. Heteroatom variants of this rearrangement are covered briefly.