11 research outputs found
Remarkably Mild and Simple Preparation of Sulfenate Anions from b-Sulfinylesters: A New Route to Enantioenriched Sulfoxides
Is Homeopathy a Science?âContinuity and Clash of Concepts of Science within Holistic Medicine
Origin of a Large Temperature Dependence of Regioselectivity Observed for [2 + 2] Photocycloaddition (Paterno-Buchi Reaction) of 1, 3-Dimethylthymine with Benzophenone and Its Derivatives: Conformational Property of the Intermediary Triplet 1, 4-Diradicals
Modulation of the Reactivity, Stability and Substrate- and Enantioselectivity of an Epoxidation Catalyst by Noncovalent Dynamic Attachment of a Receptor Functionality - Aspects on the Mechanism of the Jacobsen-Katsuki Epoxidation Applied to a Supramolecular System
The synthesis of the components of the dynamic supramolecular hydrogen-bonded catalytic system 2 + 3 is described. The catalytic performance and substrate- and enantioselectivity of Mn(salen) catalyst 2 were investigated in the presence and absence of the Zn(porphyrin) receptor unit 3. The effects of pyridine and pyridine N-oxide donor ligands were also studied. Some aspects on the mechanism of the Jacobsen - Katsuki epoxidation, based on literature observations, are introduced as a means to analyse the behaviour of 2 and its modulation by the formation of macrocycle 1 with 3. A complete association model of the metal-free system 4 + 5 refutes the earlier assumption that macrocycle 1 is the predominant form of catalyst 2 under the standard epoxidation reaction conditions with 2 + 3. Evidence are provided that receptor-binding substrates and nonbinding substrates, respectively, are epoxidised by two different catalytic species, or two distinct distributions of species in competitive epoxidations using catalytic system 2 + 3. The two species are assigned to the endo and exo faces of the Mn( salen) catalyst in macrocycle 1, and to equivalently folded oligomeric structures with monomers 2 and 3 in adjacent positions