Potassium osmate .dihydrate

In a 50 mL round-bottomed flask equipped with a magnetic stirrer bar were placed tert-butyl carbamate (545 mg) and n-propanol (6 mL). A solution of sodium hydroxide (183 mg) in water (12.2 mL) and tert-butyl hypochlorite (0.53 mL) were added to the solution. The resulting solution was stirred for 5 minutes and cooled to 0°C. Then a solution of DHQ2PHAL (71 mg) in n-propanol (6mL), a solution of 4-methoxystyrene in //-propanol (12.2 mL) and potassium osmate dihydrate (22.5 mg) were added sequentially to give a green solution. After 1 hour at 0 °C, the reaction mixture had turned from green to yellow. 

The potassium ferricyanide was Spectrum technical grade. Methane-sulfonamide (97%), (DHQ)2PHAL (95%), potassium osmate dihydrate and tert-butyl alcohol (99.3%) were obtained from Aldrich Chemical Company, Inc. 1-Phenylcyclohexene (98%) was obtained from Acros Organics. 

The Sharpless group is best known for development of a method for the asymmetrical dihydroxylation of olefins.104 A typical oxidation uses 1 mol% of potassium osmate dihydrate, 1 mol% ligand, potassium carbonate, potassium ferricyanide, and methylsulfonamide in aqueous tert-butyl alcohol. Other oxidants such as A-melhylmor pholine N oxide can be used in place of the potassium ferricyanide. One of the preferred ligands is a bis(dihydro-quinidine ether) of phthalazine (10.46). 

Potassium osmate (VI) dihydrate [19718-36-6] M 368.4. Hygroscopic POISONOUS crystals which are soluble in H2O but insol in EtOH and Et2O. It decomposes slowly in H2O to form the tetroxide which attacks the eyes. The solid should be kept dry and in this form it is relatively safe. [5 610 7972],... 

In the currently preferred variant of this reaction, one introduces a mixture of dipotassium osmate dihydrate (K20s04 2Hd)) as a nonvolatile source of osmium (rather than osmium tetroxide), along with potassium hexaeyannferrate(III) (Ki[Fe(CN)6J) as cooxidizing... 

Alternate sources of osmium can be used and should be considered, as they offer advantages in ease of handling. Both osmium(III) chloride hydrate [OsCl xHjO] [30] and potassium osmate(VI) dihydrate [K2OsO2(0H)4] [31] have been used as replacements for osmium tetroxide, and the latter reagent is specified in the preceding standard set of conditions for catalytic AD. 

Methyl cinnamate (30) served as starting material for both routes. The AD was carried out with only 0.5 mol % of the (DHQ)2PHAL ligand and 0.2 mol % of potassium osmate(VI) dihydrate, which renders this process extremely cost-effective. Enantiomerically pure bis-hydroxyester 86 was obtained in 72% yield after one recrystallization. Conversion of 86 into A7-benzoyl-(2i ,3S)-3-phenylisoserine (88) was accomplished in only three steps giving the paclitaxel C-13 side chain in 23% overall yield. 

Potassium osmate(Vl) dihydrate Osmic acid, dipotassium salt (8,9) (19718-36-3)... 

DHQ)2PHAL and (DHQD)2PHAL are commercially available—packaged as a mixture with dipotassium osmate dihydrate, potassium ferricyanide, and K2CO3—and are known by the trade names AD-mix-a mdAD-mix-P, respectively. With the exception... 

---