[reaction: see text] Partially protected thioglycuronic acids are prepared efficiently by chemo- and regioselective oxidation of the corresponding thioglycosides using the TEMPO/BAIB reagent combination. After esterification, the thioglycuronic acids proved to be useful as both donor and acceptor in sulfonium-mediated condensations toward acidic di- and trisaccharides.

No abstract

Diselenides are known precatalysts for catalytic oxidations. The use of these widely available compounds as catalysts for the oxidation of alcohols was investigated, still leaving many mechanistic questions to be answered. By using a range of analytical techniques, we found evidence for the unexpected involvement of seleninic anhydride in the catalytic mechanism. The activation time of the diselenide and its influence on the oxidation reaction itself was also investigated. On the basis of these findings, an improved protocol for the selective oxidation of activated alcohols was devised resulting in significantly decreased catalyst loadings (<1%).

A green strategy has been explored for olefin epoxidation which combines renewable solvents (derived from glycerol), aqueous hydrogen peroxide, and catalyst recycling (a seleninic acid derivative). The use of fluorinated glycerol derivatives allows good catalytic activity in the epoxidation of cyclooctene and cyclohexene with aqueous hydrogen peroxide, preventing epoxide hydrolysis to a great extent, which is particularly remarkable in the case of cyclohexene. Furthermore, recycling of the catalytically active phase is possible through distillation of the cyclohexene oxide from the reaction mixture, which can be subsequently recharged with fresh oxidant and substrate.

We have investigated the Ph2Se2‐catalysed oxidation of alcohols with tert‐butyl hydroperoxide (TBHP) by using a variety of spectroscopic techniques and reaction calorimetry. We showed that the active oxidant is benzeneseleninic anhydride (BSA), formed by reaction of Ph2Se2 with TBHP. The influence of aromatic substituents on the activity of a selection of nine aromatic diselenides involved in alcohol oxidations was studied. Calorimetric experiments showed that compounds that are activated more rapidly have higher initial activity in the catalytic oxidation of benzyl alcohol. An exception to this rule was observed when the diselenide contained a dimethylamino group in the ortho position, which can apparently compensate for its slow pre‐activation by a special ortho effect. An aliphatic alcohol, 1‐decanol was also used as a substrate. Besides diphenyl diselenide only three of the substituted diaryl diselenides studied showed reasonable activity after pre‐activation with TBHP. Dimesityl diselenide displayed the highest activity and selectivity for the oxidation of 1‐decanol. Specificity for a given aldehyde could be achieved by using an oxidant and substrate feed protocol.