cis-Dihydroxylation of Olefins by a Non-Heme Iron Catalyst: A Functional Model for Rieske Dioxygenases

The first iron complex capable of olefin cis -dihydroxylation in combination with H₂O₂ provides a functional model for Rieske dioxygenases. Mechanistic studies on the model reaction suggest the participation of an Fe^III(η²-OOH) intermediate, with the oxygen atoms coming exclusively from H₂O₂ (see reaction scheme; L denotes a tris(6-methyl-2-pyridylmethyl)amine ligand, Solv=solvent). The similarities between the model and the enzymes strengthen the proposal that an Fe^III–peroxo intermediate is involved in the enzymatic reactions.     

Atom-Efficient Oxidation of Alkenes with Molecular Oxygen: Synthesis of Diols

Dihydroxylations of simple alkenes were carried out for the first time in excellent yields and selectivities with molecular oxygen as oxidant [(Eq. (a)]. Both oxygen atoms are used productively and are incorporated into the product in this transition metal catalyzed alkene oxidation.     

Selective Alkene Oxidation with H2O2 and a Heterogenized Mn Catalyst: Epoxidation and a New Entry to Vicinal cis-Diols

Covalent anchoring of 1,4-dimethyl-1,4,7-triazacyclononane on silica gel is the first step in the preparation of a heterogenized Mn catalyst. When H₂O₂ is used as the oxidant, this material can catalyze the vicinal cis-dihydroxylation of disubstituted olefins, as shown schematically here. Both enantiomers of the product are obtained.     

4,5-Unsubstituted 2,3-dihydroisoxazoles in the synthesis of racemic 4-substituted isoxazolidine-5-carbonitriles

The synthesis of novel types of the 4-hydroxy- and 4-bromosubstituted isoxazolidines is described. Dihydroxylation reactions of 4,5-unsubstituted 2,3-dihydroisoxazoles proceed from the less hindered side and provide the major 3,4-trans-isoxazolidine-4,5-diols in good yields. On the other hand, the hydroxybromination reaction of the model 3-phenyl-2,3-dihydroisoxazole predominantly proceeds with 3,4-cis selectivity. Isoxazolidine-5-carbonitriles have been prepared from isoxazolidines possessing a good leaving group at C5 by treatment with TMSCN in the presence of TMSOTf.     

Ansa Macrolides as Molecular Workbenches: Stereocontrolled syn Additions to E olefins

Fixed on an aromatic platform in a conformationally defined way, acyclic (E)-alkenes can be considered gripped on a molecular workbench. The olefinic ansa-macrolides formed in this way are shielded on one face. On epoxidation and dihydroxylation [Eq. (1)] the attack on the double bond takes place diastereoselectively from outside the ring, and the ansa chain can subsequently be cleaved from the workbench by mild hydrogenolysis. Bn=benzyl, NMO=N-methylmorpholin-N-oxide.     

Synthetic studies on amphidinolides C and F: synthesis of the C18-C29 segment of amphidinolide F

The C18-C29 segment of amphidinolide F is synthesised in 12 steps from 1,4-butanediol. Key steps include a mono-Sharpless dihydroxylation of a dienoate, iodocyclisation to construct the trans-THF ring and an E-selective Wittig reaction to introduce the C25-C26 olefin.