Cw-dihydroxylation

The first attempt to effect the asymmetric cw-dihydroxylation of olefins with osmium tetroxide was reported in 1980 by Hentges and Sharpless.54 Taking into consideration that the rate of osmium(VI) ester formation can be accelerated by nucleophilic ligands such as pyridine, Hentges and Sharpless used 1-2-(2-menthyl)-pyridine as a chiral ligand. However, the diols obtained in this way were of low enantiomeric excess (3-18% ee only). The low ee was attributed to the instability of the osmium tetroxide chiral pyridine complexes. As a result, the naturally occurring cinchona alkaloids quinine and quinidine were derived to dihydroquinine and dihydroquinidine acetate and were selected as chiral... 

There is a rich chemistry of alkene and alkyne oxidation by RuO. The main application lies in alkene cleavage, bnt there is growing interest in cw-dihydroxylation by the reagent. In the sections below we first consider oxidations which do not sever the C=C bond (epoxidation, ctT-dihydroxylation, ketohydroxylation), and then alkene cleavage reactions. 

For the cw-dihydroxylation of protected lL-l,2 3,4-di-0-isopropylidenecyclohex-5-ene-l,2,3,4-tetrol (22g) to the diol lD-l,2 3,4-di-0-isopropylidene-a/to-inositol by RuClj/aq. Na(IO )/EtOAc-CH3CN/0°C cf. 3.1.2.1 and Fig. 3.3 [347]. Oxygen insertion by stoich. RuO /CCl occurred in addition to the secondary alcohol oxidation of the five-membered ring 5-0-benzoyl-l,2-0-isopropylidene-a-D-xylofnranose, giving the six-membered ring l,2-0-isopropylidene-6-0-benzoyl-3-oxa-a-D-e/7fftro -4-hexulopyranose-a-D-xylofuranose [325]. 

The system RuCl3/aq. Na(IO )/CeCl3.7H3O/EtOAc-CH3CN/0°C was used to cw-dihydroxylate 3-benzyloxy-2,2-difluoro-cyclo-oct-4Z-en-l-one to 3R -benzyloxy-2,2-difluoro-9-oxa-15, 5R -bicyclo[3.3.1]nona-15, 45 -diol and the... 

Asymmetric cw-dihydroxylations of a,p-unsaturated carbonyl compounds have been achieved using RuClj/aq. NaCIO yCH CN-EtOAc, using N-enoyl sultams as chiral auxiliaries [173]. 

DihydroxylationJ The cw-dihydroxylation of cycloalkenylsilanes with this inexpensive reagent in aqueous f-BuOH or dichloromethane at room temperature is obviously more advantageous than using the toxic osmium tetroxide. 

The Rieske dioxygenases (so-called because they contain a Rieske [2Fe—2S] cluster in addition to the mononuclear iron centre) catalyse cw-dihydroxylation of arene double bonds using NADH as the source of two electrons again, both dioxygen atoms are incorporated into the cA-diol product. 

The enantioselective ctT-dihydroxylation of benzothiophenes and benzofnrans in the heterocyclic ring, by Pseudomonas putida, is analogous to well-known conversions of simple benzenoid compounds, bnt in the heterocyclic context, hydroxyl groups introduced at an a-carbon easily epimerise. Indole gives indoxyl probably via dehydration of an intermediate 2,3-diol. In contrast, cw-dihydroxylation of quinolines, or of 2-phenylpyridines, takes place selectively in the benzene ring. ... 

Enantioselective cw-dihydroxylation of olefins using osmium catalyst in the presence of cinchona alkaloid ligands. 

Scheme 2 Benzylic hydroxylation and aromatic cw-dihydroxylation reactions catalyzed by Rieske oxygenases (toluene monooxygenase and naphthalene-1,2-dioxygenase, respectively)...

Beginning with furan (15), exposure to bromine in a suspension of potassium carbonate in methanol gave the dimethoxy furan 16. Next, treatment of 16 with potassium permanganate yielded cw-dihydroxylated acetal 17. The acetal functionality was converted to the transient dialdehyde 18, which underwent the title reaction upon exposure to acetonedicarboxylic acid and methylamine under simulated physiological conditions to give teloidinone (19). 

The familiar cw-dihydroxylation of alkenes with OSO4 or KMn04 creates two new stereogenic centres. Normally, this is of no consequence since in most applications the diol is cleaved or the alkene has a plane of symmetry. 

The humble soil bacteria of Pseudomonas species are capable of effecting a variety of enantiospecific cw-dihydroxylations of alkenes and aromatics, some of which have no equivalent in ordinary organic... 

---