Oxidation with tetrapropylammonium

Hydroboration occurred from the less hindered top face of rac-29 and resulted in the formation of alcohol rac-30. After a three-step sequence which included oxidation with tetrapropylammonium perruthenate (TPAP), methyl lithium addition and repeated oxidation with TPAP, ketone rac-31 was isolated. Finally, epimerization of the stereogenic center at C-7 to the correct configuration and methylenation with the Lombardo reagent led to the formation of racemic kelsoene (rac-1). 

Reductive alkylation of -caprolactone (1 equiv) with a 2 0.25 mixture of Grignard reagent and Zn(BH4)2 affords monoalkylated diols, which can be further selectively oxidized with tetrapropylammonium perruthenate (TPAP) into the expected monoalkylated lactones <2002CR571>. 

Most compounds of this type are derived from methyl hexosides methyl 2,6 3,4-dianhydro-a-D-altropyranoside309 398 400 516 and methyl 2,5 3,6-dianhydro-a- and /J-n-mannol iiranosides.517 From hexuloses, the synthetically useful l,5 3,6-dianhydro-D-<2raZ)i o-hex-2-ulose (172) has been prepared by regioselective monobenzylation of l,5 3,6-dianhydro-D-mannitol at C-4 (171a — 171b) followed by oxidation with tetrapropylammonium perruthenate.518... 

The oxidation of alcohols with (l,l-dimethylethyl)benzene-sulfenamide is extremely mild and many sensitive functional groups such as epoxides and alkenes are tolerated hy the reaction conditions (eq 5). In the case of alcohol 1, oxidation with tetrapropylammonium perruthenate (TPAP) resulted in only 58% yield and Swern oxidation was unsuccessful. Epimerizable aldehydes such as the protected phenylglycinol 2 do not undergo racemization when oxidized (eq 6). ... 

When 125 was subjected to a two-step sequence, reductive cleavage of the 0-0 bond and subsequent oxidative dehydration, by treatment with zinc in AcOH, the allylic diol 135 and the 1,2-oxazocine 126, as minor product, were isolated. Oxidation of the diol 135 under several different reaction conditions (pyridinium chlorochromate (PCC), 2-iodoxybenzoic acid (IBX)/EtOH, IBX/DMSO, Pyr/SOj) gave 126 in high yield (68-92%), while with tetrapropylammonium perruthenate/Wmethylmorphaline Ar-oxidc (TPAP/NMO) as oxidizing agent 126 was the minor product and the a,/3-unsaturated 7-butyrolactone 136 was obtained in 68% yield (Scheme 28) <2005JOC6995>. 

Chiral nitrosoureas can be easily prepared starting from disubstituted pyrrolidines possessing C2 symmetry. Thus (27 , 57 l-dimcthyI pyrrolidine can be smoothly converted, by reaction with phenoxyhydroxamic acid in pyridine solution to the corresponding (V-hydroxyurea 1. Oxidation of 1 with tetrapropylammonium periodate in dichloromethane gives the short-lived nitroso dienophile 2 which reacts with 1,3-cyclohexadiene to give the bicyclic 3,6-dihydro-2//-1,2-ox-azine 3 in 81% yield and d.r. 99 1, The absolute configuration of the reaction product was ascertained unequivocally by synthetic methods as (17 ,45)107. 

Another ruthenium-catalyzed oxidation uses tetrapropylammonium permthenate (TRAP) [24]. Being a ruthenium(VII) oxide, the permthenate ion is a less powerful oxidant than rutheni-um(VIII) oxide and more functional groups are stable to the oxidation conditions, including alkenes, alkynes, amines, amides, benzyl, trityl and silyl ethers [24]. However, alcohols and lactols still undergo oxidations in high yield with W-methyl-morpholine A-oxide (NMO) as the stoichiometric oxidant. The reactions are usually carried out in dichloromethane, acetonitrile, or mixtures of both in the presence of molecular sieves [24]. 

Oxidation of diene-containing hydroxamic acids has been reported to give acylnitroso species which undergo spontaneous hetero-IMDA reactions to give heterobicyclic ketones. (E,E)-N-Hydroxy-5,7-dodecadienamide, upon treatment with tetrapropylammonium periodate, gave the pyrido[l,2-b][l,2]oxazine structure in high yield88. 

Oxidative isomerization of vinylidenecyclopropanes gives dimethylenecyclopropane aldehydes using tetrapropylammonium perruthenate (TPAP)/4-methylmorpholine A-oxide (NMO) as a catalytic system. A Witkop-Winterfeldt oxidation with ozone has been reported to convert tetrahydropyridoindoles into pyrroloquinolones and cinnolines. Activation of phenol derivatives with a hypervalent iodine reagent has been reported to promote the formation of bicycUc and tricyclic products via a cationic cyclization process (Scheme 64). ... 

A series of homo-allylic steroidic alcohols were oxidized with N-methyl morpholine N-oxide (NMO) in the presence of tetrapropylammonium perrhutenate (TPAP) (Eq. 70, see Ch. 9, p. 358).The mechanism probably implies the preliminary oxidation of the alcohol. A labile silyl enol ether is preserved under the conditions specified. 

The THP protective group was removed with NH4CI in refluxing methanol (24), The 1,4-diol 25 was oxidized directly to the lactone 21 with tetrapropylammonium pemithinate (TPAP) and 4-methylmorpholine-N-oxide as co-oxidant in CH2CI2 (25),... 

Acylnitroso-compounds are extremely reactive because the lowest unoccupied molecular orbital (LUMO) is very low because of the acyl electron-withdrawing group. Thus, they have to be generated in situ by oxidation from the corresponding hydroxamic acid in the presence of the diene. Therefore, oxidation of enantiopure dienic hydroxamic acid 185 with tetrapropylammonium periodate in chloroform at 0°C delivered the two diastereomeric cycloadducts 187a and 187b in 1.7 1 ratio (81% yield. Scheme 41.39). The use of methanol as a solvent increased the ratio to 2.6 1. Finally, aqueous conditions resulted in an improvement of the ratio to 6.6 1 as a result of the hydrophobic effect on a reactant... 

The isomorphous substitution of T atoms by other elements produces novel hybrid atom molecular sieves with interesting properties. In the early 1980s, the synthesis of a zeolite material where titanium was included in the MFI framework of silicalite, that is, in the aluminum-free form of ZSM-5, was reported. The name given to the obtained material was titanium silicalite (TS-1) [27], This material was synthesized in a tetrapropylammonium hydroxide (TPAOH) system substantially free of metal cations. A material containing low levels (up to about 2.5 atom %) of titanium substituted into the tetrahedral positions of the MFI framework of silicalite was obtained [28], TS-1 has been shown to be a very good oxidation catalyst, mainly in combination with a peroxide, and is currently in commercial use. It is used in epoxidations and related reactions. TS-1, additionally an active and selective catalyst, is the first genuine Ti-containing microporous crystalline material. 

Tetrapropylammonium perruthenate (0.027 mmol) was added to a mixture of (15,4/ )-4-(f-butyldimethylsilanyloxy)cyclopent-2-enol (0.54 mmol), 4-methylmorpholine IV-oxide (0.81 mmol), and 270 mg crushed 4 A molecular sieves dissolved in 10 ml CH2C12. The mixture was stirred 30 minutes at ambient temperature, then filtered through a plug of silica gel with CH2C12, concentrated, and the product isolated in 86% yield. 

There are problems associated with the expensive disposal of toxic waste from metal-based oxidations of alcohols. Thus, the focus has been largely on catalytic reactions as typified by Ley and Griffith s tetrapropylammonium perruthenate oxidant (section 7.1.6). Completely metal-free oxidations have much potential for environment-friendly oxidations, particularly if the reagent can be recovered and recycled. The most common metal-free oxidation of alcohols are TEMPO/oxone or TEMPO/N-chlorosuccinimide oxidation, Dess-Martin periodane oxidation (section 7.1.5) and Swern oxidation (section 7.1.4) and its several variants. 

Hasan, M., Musawir, M., Davey, P. N., Kozhevnikov, I. V. Oxidation of primary alcohols to aldehydes with oxygen catalyzed by tetrapropylammonium perruthenate. J. Mol. Catal. A Chemical 2002, 180, 77-84. 

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