No abstract

Unprecedented silanol-based bifunctional HBD catalysts with tetraalkylammonium units directly incorporated into their structures were prepared from tailor-made silanols and used in the preparation of cyclic carbonates.

The diastereoselectivity of diazomethane addition to the conjugated double bond of α,β-unsaturated sesquiterpene lactones was explored using zaluzanin A (1) as a model. Thus, the absolute configuration of 1 was assured by X-ray diffraction analysis including evaluation of Flack and Hooft parameters, and by vibrational circular dichroism spectroscopy of its diacetyl derivative 2, while the absolute configuration of the diazomethane addition product, zaluzanin A pyrazoline (3), was determined by evaluation of the 1 H NMR chemical shift changes with respect to 1, and confirmed by X-ray diffraction analysis, again including evaluation of Flack and Hooft parameters.

The synergy between porosity and soft properties in metal−organic frameworks (MOFs) can result in materials with adaptability of the pore size/shape to the adsorbate. Herein, we present a new guest-responsive flexible MOF: CCIQS-1. This material consists of threefold interpenetrated subnetworks comprising] nodes interconnected by 4,4′-(9,10-anthracenediyl)dibenzoate ligands. This arrangement gives rise to the formation of hydrophilic and hydrophobic channels. Although the activated material is permanently porous, a crystal-to-crystal phase transition takes place upon solvent removal, leading to the contraction of the hydrophobic pores while 1D hydrophilic channels remain open. As a result, CCIQS-1 exhibits a higher affinity for guests with moderate polarity [tetrahydrofuran (THF), MeOH, and acetone] than for non-polar ones (toluene, cyclohexene, and hexane). X-ray diffraction studies on the contracted-pore phase (cp-CCIQS-1) after exposure to different solvents indicate that only adsorbates with a suitable polarity and molecular size trigger the recovery of the open-pore phase (op-CCIQS-1) via the combination of a breathing effect and subnetwork displacement.