Tetra-«-propylammonium perruthenate

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>. 

A milestone in the routine employment of perruthenate in the oxidation of alcohols was established with the publication by Griffith, Ley et al. in 1987 on the catalytic use of tetra- -propylammonium perruthenate (TPAP).11 The presence of the tetra- -propylammonium cation renders this compound soluble in apolar media and allows the existence of a high concentration of perruthenate ion in organic solvents. The tetra- -propylammonium perruthenate is easily prepared and can be employed catalytically in CH2CI2 solution in the oxidation of alcohols to ketones and aldehydes, using /V-methyl morpholine A-oxide (NMO) as the secondary oxidant. 

Recently two heterogeneous TPAP-catalysts were developed, which could be recycled successfully and displayed no leaching In the first example the tetra-alkylammonium perruthenate was tethered to the internal surface of mesopor-ous silica (MCM-41) and was shown [153] to catalyze the selective aerobic oxidation of primary and secondary allylic and benzylic alcohols. Surprisingly, both cyclohexanol and cyclohexenol were unreactive although these substrates can easily be accommodated in the pores of MCM-41. The second example involves straightforward doping of methyl modified silica, denoted as ormosil, with tetra-propylammonium perruthenate via the sol-gel process [154]. A serious disadvantage of this system is the low-turnover frequency (1.0 and 1.8 h-1) observed for primary aliphatic alcohol and allylic alcohol respectively. 

Tetra- -propylammonium perruthenate (TPAP, tetrapropyl tetraoxoruthenate) [114615-82-6] M 351.4, m 160 (dec). It is a strong oxidant and may explode on heating. It can be washed with aqueous -propanol, then H2O and dried over KOH in a vacuum. It is stable at room temperature but best stored in a refrigerator. It is soluble in CH2CI2 andMeCN. [Dengelet al. Transition Met Chem 10 98 1985, Griffith et al. J Chem Soc, Chem Commun 1625 1987.]... 

CH3CH2CH2)4N+ RUO4-tetra- -Propylammonium perruthenate (TPAP)... 

A remarkable multicatalytic relay system consisting of tetra-propylammonium perruthenate/N-methylmorpholine iV-oxide (TPAP/NMO) as oxidant, and chiral diarylprolinol trimethylsilyl ethers as organocatalysts, has recently been developed by Rueping et al. and applied in the efficient construction of various valuable chiral molecules through domino reactions. The latter were all based on the in situ generation of ot,p-unsaturated... 

Tetramethylpiperidine tetra-n-Propylammonium perruthenate Tolyl Trityl... 

Figure 5.1 The alcogels shown are ORMOSIL doped with the ruthenium species tetra-M-propylammonium perruthenate (TPAP). Upon a mild heat treatment these materials become more active than TPAP in solution.

R. Ciriminna and M. Pagliaro, Tailoring the Catalytic Performance of Sol-Gel-Encapsulated Tetra-n-propylammonium Perruthenate (TPAP) in Aerobic Oxidation of Alcohols, Chem. Eur. J., 2003, 9, 5067. 

Tetra-n-propylammonium perruthenate also oxidizes sulphides to sulphones [45]. Yields are generally high for dialkyl sulphides and alkyl aryl sulphides, but lower for diaryl sulphides. 

Secondary nitro compounds are oxidized to the corresponding ketones in moderate yields by a catalytic amount of tetra-n-propylammonium perruthenate in the presence of N-methyImorpholine-A-oxide and a silver salt [46]. Oxidation with a stoichiometric amount of the ammonium perruthenate has also been reported [47]. 

Secondary amines and A /V-dialkylhydroxylamines are rapidly oxidized by tetra-rt-propylammonium perruthenate to imines and nitrones, respectively (Scheme 10.5) [48,49]. Chiral centres are unaffected during the oxidation. 

Reductive y-lactone ring opening, with concomitant desilylation at the tertiary position by LiAlH4, gave triol 17 in 80% yield. Finally, acetonide formation followed by oxidation with tetra-n-propylammonium perruthenate/A-methylmorpholine / /-oxide oxidation, led to the target aldehyde 19 in 80% overall yield. 

After desilylation with tetra-n-butylammonium fluoride and oxidation with tetra-n-propylammonium perruthenate the dialdehyde 23 was obtained in 32% overall yield. 

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. 

TPAP Tetra-n-Propylammonium Perruthenate Pr4N+Ru04 ... 

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