Osmium tetroxide-Trimethylamine N-oxide-Pyridine

Osmium tetroxide-Trimethylamine N-oxide-Pyridine, 223 Oxymercuration 1,3-Propanedithiol, 261 Oxysulfenylation... 

Trimethylsilyldiazomethane, 327 Silyl substituted arenes Bis(trimethylsilyl)acetylene, 97 Chromium carbene complexes, 82 Titanium(IV) chloride-Diethylalu-minum chloride, 309 Other organosilanes Osmium tetroxide-Trimethylamine N-oxide-Pyridine, 223 Tributyltin chloride, 315 Di- x-carbonylhexacarbonyldicobalt, 99 Trimethylsilyl trifluoromethanesul-fonate, 329... 

Osmium tetroxide-N-Methyl-morpholine N-oxide, 222 Osmium tetroxide-Trimethylamine N-oxide-Pyridine, 223 Palladium Compounds Benzylchlorobis(triphenylphosphine)-palladium(II), 30 Bis (ace tonitrile) chloronitropalla-dium(II)-Copper(II) chloride, 33 Bis(acetonitrile)dichloropalladium(II), 33, 211, 236... 

Dihydroxylation of hindered double bonds.1 The tx-pinene derivative 1 (Nopol) is hydroxylated in low yield by osmium tetroxide and f-butyl hydroperoxide. Hydroxylation is effected in 62% yield by use of 0s04 in combination with trimethylamine N-oxide as oxidant and pyridine as base. This method is generally suitable for hindered alkenes (yields 78-93%). 

Pinanediol is the least expensive of the useful chiral directors. a-Pinene (13) reacts with trimethylamine N-oxide and osmium tetroxide catalyst in the presence of pyridine and water to produce pinanediol (14) (Scheme 8.3) [23, 24], A kinetic study has shown that the reaction is first-order in trimethylamine N-oxide, first-order in osmium tetroxide, and zero-order in a-pinene [25]. Trimethylamine N-oxide produced better yields than the less expensive N-methylmorpholine N-oxide [24,26]. Although the first reported solvent was tert-butyl alcohol [24], acetone can be used instead [26, 27], The reflux temperature of tert-butyl alcohol is a little too high, and some over-oxidation to hydroxyketone occurs above about 75 °C. Refluxing in acetone avoids over-oxidation but is slower. Two moles of pinene with a small excess of trimethylamine N-oxide and 1 g of osmium tetroxide produce pinanediol in 95-96% yield in 3-4 days in tert-butyl alcohol, or after about a week in acetone [24, 27]. 

For the oxidation of alkenes, osmium tetroxide is used either stoichiometrically, when the alkene is precious or only small scale operation is required, or catalytically with a range of secondary oxidants which include metal chlorates, hydrogen peroxide, f-butyl hydroperoxide and N-methylmorpholine A -oxide. The osmium tetroxide//V-methylmorpholine A -oxide combination is probably the most general and effective procedure which is currently available for the syn hydroxylation of alkenes, although tetrasubstituted alkenes may be resistant to oxidation. For hindered alkenes, use of the related oxidant trimethylamine A -oxide in the presence of pyridine appears advantageous. When r-butyl hydroperoxide is used as a cooxidant, problems of overoxidation are avoided which occasionally occur with the catalytic procedures using metal chlorates or hydrogen peroxide. Further, in the presence of tetraethylam-monium hydroxide hydroxylation of tetrasubstituted alkenes is possible, but the alkaline conditions clearly limit the application. 

---