N-Methylmorpholine-JV-oxide

Alkenes can he dihydroxylated cw-selectively by reaction with a stoichiometric amount of N-methylmorpholine-jV-oxide (NMO), a catalytic amount of a suitable Os(VIII) reagent, and some water. From a preparative point of view, this reaction is closely related to oxidative cleavages, and for this reason it is introduced now (Figure 17.19). 

Extrusion of sulfur dioxide, by warming in ethanol in the presence of sodium hydrogen carbonate, is followed by hydroxylation at C-1 with sub-stoichiometric amounts of selenium dioxide and N-methylmorpholine JV-oxide as the oxidant. The stereoselectivity of the oxidation lies at a ratio of 7 1 in favour of the (S)-diastereomer. After sUylation with t-butyldimethylsUyl chloride and chromatographic purification, the desired diastereomer is obtained in a yield of 41 %. 

The osmium-catalyzed vicinal dihydroxylation of olefins with single oxygen donors, typically tert-butyl hydroperoxide or N -methylmorpholine-JV-oxide (NMO), has been known for three decades and forms the basis of the Sharpless asymmetric dihydroxylation of olefins. Recently, Sharpless and coworkers reported that particularly electron-deficient olefins are dihydroxylated more efficiently with NMO (Eq. 2) when the pH of... 

Because OSO4 is both very expensive and very toxic, the reaction is usually carried out using only a small, catalytic amount of OSO4 in the presence of a stoichiometric amount of a safe and inexpensive co-oxidant such as N-methylmorpholine JV-oxide, abbreviated NMO. The initially formed osmate intermediate reacts rapidly with NMO to yield the product diol plus... 

NMO NMP Nu PPA PCC PDC phen Phth PPE PPTS Red-Al SEM Sia2BH TAS TBAF TBDMS TBDMS-C1 TBHP TCE TCNE TES Tf TFA TFAA THF THP TIPBS-C1 TIPS-C1 TMEDA TMS TMS-C1 TMS-CN Tol TosMIC TPP Tr Ts TTFA TTN N-methylmorpholine N-oxide jV-methyl-2-pyrrolidone nucleophile polyphosphoric acid pyridinium chlorochromate pyridinium dichromate 1,10-phenanthroline phthaloyl polyphosphate ester pyridinium p-toluenesulfonate sodium bis(methoxyethoxy)aluminum dihydride (3-trimethylsilylethoxy methyl disiamylborane tris(diethylamino)sulfonium tetra-n-butylammonium fluoride f-butyldimethylsilyl f-butyldimethylsilyl chloride f-butyl hydroperoxide 2,2,2-trichloroethanol tetracyanoethylene triethylsilyl triflyl (trifluoromethanesulfonyl) trifluoroacetic acid trifluoroacetic anhydride tetrahydrofuran tetrahydropyranyl 2,4,6-triisopropylbenzenesulfonyl chloride 1,3-dichloro-1,1,3,3-tetraisopropyldisiloxane tetramethylethylenediamine [ 1,2-bis(dimethylamino)ethane] trimethylsilyl trimethylsilyl chloride trimethylsilyl cyanide tolyl tosylmethyl isocyanide meso-tetraphenylporphyrin trityl (triphenylmethyl) tosyl (p-toluenesulfonyl) thallium trifluoroacetate thallium(III) nitrate... 

Work has been done with salen catalysts to enable enantioselective epoxidations with m-CPBA. Highly enantioselective K.ochi-Jacobsen-K.atsuki epoxidation of unfunctionalized olefins with Mn(III)-(salen)-based chiral catalyst provides an efficient route to optically active epoxides. It has been noted that m-CPBA in the presence of JV-methylmorpholine N-oxide at low temperature (e.g., -78 °C) suppresses bond rotation leading to high enantioselectivity even when the substrate is acyclic.10,15... 

Some very mild oxidizing agents are being more and more widely used for the synthesis of very sensitive aldehydes. One of these is known as TPAP (tetra-n-propylammonium perruthe-nate, pronounced tee-pap ). TPAP can he used catalytically, avoiding the large amounts of toxic heavy metal by-products generated by most chromium oxidations. The stoichiometric oxidant in this reaction is NMO (JV-methylmorpholine-N-oxide), which is reduced to the amine, reoxidizing the ruthenium to Ru(VII). 

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