Oliver Weichold

Biotransformations with Peroxidases

Enzymes are chiral catalysts and are able to produce optically active molecules from prochiral or racemic substrates by catalytic asymmetric induction. One of the major challenges in organic synthesis is the development of environmentally acceptable chemical processes for the preparation of enantiomerically pure compounds, which are of increasing importance as pharmaceuticals and agrochemicals. Enzymes meet this challenge! For example, a variety of peroxidases effectively catalyze numerous selective oxidations of electron-rich substrates, which include the hydroxylation of arenes, the oxyfunctionalizations of phenols and aromatic amines, the epoxidation and halogenation of olefins, the oxygenation of heteroatoms and the enantioselective reduction of racemic hydroperoxides. In this review, we summarize the important advances achieved in the last few years on peroxidase-catalyzed transformations, with major emphasis on preparative applications.

Titanium-catalysed oxidation of thianthrene 5-oxide in heterogeneous (zeolites) versus homogeneous media : electrophilic versus template-mediated oxygen transfer

Abstract Large differences in the ratio of sulfide versus sulfoxide oxidation of thianthrene 5-oxide ( SSO ) have been observed for heterogeneous versus homogeneous Ti IV catalysts; whereas the Ti-doped zeolites (heterogeneous) oxidise by means of an electrophilic species, sulfoxide coordination (template effect) for Ti(O i Pr) 4 (homogeneous) masks the true electrophilic character of the metal oxidant.

Structure, Reactivity, and Selectivity of Metal-Peroxo Complexes Versus Dioxiranes

Dioxiranes, MTO/H2O2, and MTO/UHP are becoming increasingly important as efficient and selective oxidants in organic chemistry and numerous publications have appeared on each of them. Here we present a comprehensive review, comparing the chemistry of these reagents with particular emphasis on the oxidation of π bonds, heteroatoms, and σ bonds. We will discuss structural aspects and on this basis, will outline the reactivity and selectivity of these oxidants, along with the mechanistic aspects of the oxygen-transfer process.

The selective catalytic oxidation of silanes to silanols with H2O2 activated by the Ti-beta zeolite

Ti-beta catalyses the oxidation of small- and medium-sized silanes to the corresponding silanols by aqueous (30%) H2O2 as oxygen donor with high conversions and excellent selectivity (no disiloxane).