1 Recent Developments in the Osmium-catalyzed Dihydroxylation of Olefins Uta Sundermeier, Christian Döbler, and Matthias Beller 1.1 Introduction The oxidative functionalization of olefins is of major importance for both organic synthesis and the industrial production of bulk and fine chemicals [1]. Among the different oxidation products of olefins, 1,2-diols are used in a wide variety of applica- tions. Ethylene- and propylene-glycol are produced on a multi-million ton scale per annum, due to their importance as polyester monomers and anti-freeze agents [2]. A number of 1,2-diols such as 2,3-dimethyl-2,3-butanediol, 1,2-octanediol, 1,2-hexa- nediol, 1,2-pentanediol, 1,2- and 2,3-butanediol are of interest in the fine chemical industry. In addition, chiral 1,2-diols are employed as intermediates for pharmaceuti- cals and agrochemicals. At present 1,2-diols are manufactured industrially by a two step sequence consisting of epoxidation of an olefin with a hydroperoxide or a pera- cid followed by hydrolysis of the resulting epoxide [3]. Compared with this process the dihydroxylation of C=C double bonds constitutes a more atom-efficient and shorter route to 1,2-diols. In general the dihydroxylation of olefins is catalyzed by os- mium, ruthenium or manganese oxo species. The osmium-catalyzed variant is the most reliable and efficient method for the synthesis of cis-1,2-diols [4]. Using os- mium in catalytic amounts together with a secondary oxidant in stoichiometric amounts various olefins, including mono-, di-, and trisubstituted unfunctionalized, as well as many functionalized olefins, can be converted into the corresponding diols. OsO 4 as an electrophilic reagent reacts only slowly with electron-deficient ole- fins, and therefore higher amounts of catalyst and ligand are necessary in these cases. Recent studies have revealed that these substrates react much more efficiently when the pH of the reaction medium is maintained on the acidic side [5]. Here, citric acid appears to be superior for maintaining the pH in the desired range. On the other hand, in another study it was found that providing a constant pH value of 12.0 leads to improved reaction rates for internal olefins [6]. Since its discovery by Sharpless and coworkers, catalytic asymmetric dihydroxyla- tion (AD) has significantly enhanced the utility of osmium-catalyzed dihydroxylation (Scheme 1.1) [7]. Numerous applications in organic synthesis have appeared in re- cent years [8]. 1 Modern Oxidation Methods. Edited by Jan-Erling Bäckvall Copyright # 2004 WILEY-VCH Verlag GmbH & Co. KGaA,Weinheim ISBN: 3-527-30642-0