Methylmorpholine A-oxide

In a similar reaction, 2,3,6-trimethoxydibenz[6,/]oxepin gives 10,11-dihydro-2,3,6-trimeth-oxydibenz[/>,/]oxepin-cw-10,l 1-diol upon treatment with osmium(VIII) oxide in the presence of A-methylmorpholine A -oxide.262 When treated with acid the diol undergoes a pinacol rearrangement to the corresponding xanthene-9-carbaldehyde. 

A very mild oxidative transformation of nitro compounds into ketones using tetrapropylam-monium perruthenate (TPAP) has been developed. A stoichiometric amount of TPAP in the presence of A-methylmorpholine A-oxide (NMO) and 4 A molecular sieves (MS).18a As the reaction conditions are neutral and mild, this method is compatible with the presence of other sensitive functionalities (Eq. 6.11). This transformation can be carried out with 10 mol% of TPAP and 1.5 equiv of NMO in the presence of potassium carbonate, 4 A MS, and silver acetate (Eq. 6.12).18b... 

Method A The alcohol (0.5 mmol) and N-methylmorpholine-A-oxide (0.1 g, 0.75 mmol) are stirred in CH2Cl2 (10 ml) with 4A molecular sieves for 10 min. TPA-Ru04 (0.025 mmol) is then added and the reaction is monitored by TLC analysis. Upon comple-... 

The alcohol (0.5 mmol) is stirred with Y-methylmorpholine A -oxide (88 mg, 0.75 mmol),... 

After the "asymmetric epoxidation" of allylic alcohols at the very beginning of the 80 s, at the end of the same decade (1988) Sharpless again surprised the chemical community with a new procedure for the "asymmetric dihydroxylation" of alkenes [30]. The procedure involves the dihydroxylation of simple alkenes with N-methylmorpholine A -oxide and catalytic amounts of osmium tetroxide in acetone-water as solvent at 0 to 4 °C, in the presence of either dihydroquinine or dihydroquinidine p-chlorobenzoate (DHQ-pClBz or DHQD-pClBz) as the chiral ligands (Scheme 10.3). 

In the stoichiometric ADH of ( )-3-hexene the highest ee was achieved using the ligand 4b (88% ee). On the other hand, the catalytic process (Table 10.4, entries 1-3) was carried out by slow addition of ( )-3-hexene (1 equiv.) to a mixture of 4a (0.25 equiv.), A-methylmorpholine A-oxide (NMO, 1.5 equiv.) and OSO4 (0.004 equiv.) in acetone-water (10/1, v/v) at 0 °C, followed by working-up with Na2S205. Although the catalytic reaction was slow and required a slower addition... 

The next important steps to the key intermediate 30 are outlined in Scheme 13.6.5. Monoacetylation of 24 followed by oxidation with tetra-n-propylammonium perruthenateW-methylmorpholine A -oxide, afforded regioselectively in 88% overall yield, ketoacetate 21. ... 

Unambigous structural confirmation was obtained by converting 53a to diol carbonate 56, which was independently synthesised from baccatin III. Selective deprotection of 53a with TBAF gave alcohol 54, which was oxidised with tetra-n-propylammonium perruthenate/)V-methylmorpholine A -oxide (CH2CI2, molecular sieves, 25 °C, 1.5 h) to ketone 55 in 86% overall yield from 53a. Deprotection (HF, pyridine, CH3CN, 96%) of gave diol carbonate 56, identical to the compound prepared from baccatin III. 

Af-methylmorpholine A-oxide or 4-phenylpyridine A-oxide as cocatalysts. The yields and enantioselectivities obtained with HgOg or urea hydrogen peroxide were comparable, with slightly better yields for the epoxidation with HgOg (73% versus 68% for the epoxide of 1,2-dihydronaphthalene in the presence of NH4OAC). 

From the study of a microbially mediated oxidation of arteether 28b, sufficient quantities of 7a-hydroxy 180 and 15-hydroxy derivatives 182 were obtained to employ them as intermediates for the preparation of fluorinated compounds. The hydroxyl groups were oxidized to the corresponding aldehyde 187, or ketone 188, with catalytic quantities of tetra- -propylammonium perruthenate (TPAP) in the presence of excess iV-methylmorpholine A -oxide. On reaction with DAST, 187 and 188 were converted into the corresponding geminal difluoro derivatives, 189 (63%) and 190 (42%). In addition to 190, a monofluoro olefin 191 was obtained in 25% yield from 188 on reaction with DAST <1995JME4120>. 

All of the usual chromium-based oxidation reagents that have been used for the oxidation of cyclobutanols to cyclobutanones, for example, chromium(VI) oxide (Jones reagent),302 pyri-dinium chlorochromate,304 pyridinium dichromate,307 and chromium(YI) oxide/pyridine (Collins),303 are reported to do so without any serious problems. Alternatively, tetrapropylam-monium perruthenate in the presence of A-methylmorpholine A -oxide. oxalyl chloride in the presence of triethylamine in dimethyl sulfoxide (Swern),158,309,310 or phenyl dichlorophos-phate in the presence of triethylamine and dimethyl sulfoxide in dichloromethane (Pfitzner-Moffatt),308 can be used. The Pfitzner-Moffatt oxidation procedure is found to be more convenient than the Swern oxidation procedure, especially with respect to the strict temperature control that is necessary to achieve good yields in the latter, e.g. oxidation of 1 to give 2.308... 

Treatment of MFA (1) with cyanogen bromide [6] opened ring G to yield the bromo derivative 3 [7]. Attempts to dehydrobrominate 3 in one step via a base-catalyzed elimination with DBU/CH3CN, KOH/MeOH, or terr-BuOK/DMSO were unsuccessful. However, the required methylene entity could be introduced by converting 3 first to a selenide, then oxidation with periodate, followed by thermolysis in benzene to provide compound 4. Hydrolysis of the cyano group with NaOH in ethylene glycol [8] produced 5 (50% yield). Osmium catalyzed oxidation of 5 in the presence of 4-methylmorpholine A-oxide (NMO) gave a diol, which was cleaved to an aldehyde upon treatment with periodate. Treatment of the aldehyde with sodium cyanoborohydride resulted in an intramolecular reductive animation to yield the desired product PHB (6). 

Ru(II) halosulfoxide complexes catalyse the oxidation of secondary alcohols by N-methylmorpholine-A-oxide (NMO) via a proposed Ru(TV)oxo species.92 Ruthenium (VI) catalyses the oxidation of diethylene glycol by alkaline solution of potassium bromate.93 Acid bromate oxidation of butylethylene glycol is catalysed by ruthenium(III).94 Ruthenium(III) catalyses DMF oxidation by periodate in alkaline... 

The oxidation to the enone was realized with catalytic amounts of tetra-n-propylammonium perruthenate (TPAP)21 (46), which is a mild oxidant for conversion of multifunctionalized alcohols to aldehydes or ketones. Catalytic TPAP oxidations are carried out in the presence of stoichiometric or excess A-methylmorpholine-A-oxide (NMO)22 (47) as cooxidant. Other common reagents for oxidation of alcohols are e.g. DMS0/C202C1223, Dess-Martin periodinane24, PCC25, PDC26 or the Jones reagent27. 

An older paper <1971MI873> reported that ozonolysis of alkenes in the presence of tertiary amines resulted in the formation of aldehydes. A recent reinvestigation <20060L3199> has shown that amine oxides were responsible for this reductive ozonolysis . Indeed, pretreatment of the tertiary amines with ozone, giving rise to amine oxides, accounted for this phenomenon. A preparative method emerged, by treating the alkene (e.g., 1-decene) at 0 °C with a solution of 2% 03/02 in dichloromethane (2 equiv of ozone relative to the alkene) in the presence of an excess (about threefold molar excess) of A-methylmorpholine A-oxide, pyridine A-oxide, or l,4-diazabicyclo[2.2.2]octane A-oxide (DABCO A-oxide). Yields of aldehydes (nonanal in the above example) were 80-96%, and the excess of amine oxide ensured the absence of residual ozonide (Scheme 21). 

Dihydroxylation with catalytic osmium tetroxide and stoichiometric oxidant such as NMO (TV -methylmorpholine-A -oxide) gives diols that can be cleaved to the same aldehydes with sodium periodiate or lead tetra-acetate. It is also possible to combine either KMnC>4 or catalytic OSO4 with an excess of NaIC>4 and complete the operation in one pot. 

Abbreviations AD, asymmetric dihydroxylation BPY, 2,2 -bipyridine DMTACN, 1,4-dimethyl-l,4,7-triazacyclonane EBHP, ethylbenzene hydroperoxide ee, enantiomeric excess HAP, hydroxyapatite LDH, layered double hydroxide or hydrotalcite-type structure mCPBA, meta-chloroperbenzoic acid MTO, methyltrioxorhenium NMO, A-methylmorpholine-A-oxide OMS, octahedral molecular sieve Pc, phthalocyanine phen, 1,10-phenantroline PILC, pillared clay PBI, polybenzimidazole PI, polyimide Por, porphyrin PPNO, 4-phenylpyridine-A-oxide PS, polystyrene PVP, polyvinylpyridine SLPC, supported liquid-phase catalysis f-BuOOH, tertiary butylhydroperoxide TEMPO, 2,2,6,6-tetramethyl-l-piperdinyloxy TEOS, tetraethoxysilane TS-1, titanium silicalite 1 XPS, X-ray photoelectron spectroscopy. 

If no iV-methylmorpholine-iV-oxidc were added the ruthenium(V) acid would be converted into RuOz. In that case, Ru(VII) would be a three-electron oxidizing agent just like Cr(VI) (Figure 14.10). Such a conversion of Ru(V) into Ru(IV) could in principle occur, since Ru(V) also oxidizes alcohols. This oxidation presumably would proceed via an a-hydroxylated radical as discussed for the Cr(IV) oxidation of alcohols (Fig 14.10, center). Yet, there is no indication for such a radical pathway to occur when the reaction is carried out in the presence of A-methylmorpholine-A-oxide. Hence, it appears that A-methylmorpholine-A-oxide reoxidizes the ruthenium(V) acid to per-ruthenate faster than the ruthenium(V) acid could attack an alcohol molecule. 

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