Osmium dehydration reactions

Decene complexes with gold, 12 348 Deformation density, 27 29-33 Degradation reactions, heteronuclear gold cluster compounds, 39 336-337 Dehydration reactions, osmium(II), 37 351 Delocalization, see also Valence delocalization added electron, reduced dimer, 38 447, 449 optical centers, interaction with surroundings, 35 380 Density... 

Triruthenium and triosmium complexes obtained from functionalized alkynes Complexes containing ligands with methoxycarbonyl (or acetato) groups Complexes obtained upon CO insertion into M-C bonds Hydration-dehydration reactions of alkynols promofed by silica or alumina Osmium derivafives obfained from oxygenafed ligands... 

Thus, Mathis et al. [1, 2] investigated oxidation reactions with 4-nitroperbenzoic acid, sodium hypobromite, osmium tetroxide and ruthenium tetroxide. Hamann et al. [3] employed phosphorus oxychloride in pyridine for dehydration. However, this method is accompanied by the disadvantages that the volume applied is increased because reagent has been added and that water is sometimes produced in the reaction and has to be removed before the chromatographic separation. 

Problems of acyl anion equivalents met above in the synthesis of similar TMs disappear if (25) is made from the alkene (26), A Wittig is the obvious method to make (26) and reaction between (27) and PhgCO will probably give (26), An alternative is the dehydration of (28), made by Grignard addition to ester (20), Osmium tetroxide was used for the hydroxylation. 

The bound peroxidase is visualized by reaction with a filtered solution of 0.05% DAB and 0.0005% hydrogen peroxide in PBS. After rinsing with 0.15 M sodium phosphate buffer (pH 7.4), the sections are postfixed with 0.25% osmium tetroxide in the same buffer for 1 hr and counterstained with 1% uranyl acetate in deionized water. The sections are dehydrated and flat-embedded in Epon according to standard procedures (Hayat, 2000a). Controls are processed as above, except that incubation in the absence of the primary antibody is carried out with PBS containing 2% normal serum and 0.015% Triton X-100. 

Further degradation of [n, R = H and R = CH3] has been achieved as follows. Oxidation of [ii, R = H] with osmium tetroxide afforded 6-y-hydroxy-13-(a /hdihydroxyethyl)-octahydromethyhnorphenol [iv, R = H] which was converted to 6-y-hydroxy-13-aldehydooctahydromethylmorphenol [v, R = H], which resisted all attempts at direct oxidation to the acid. However the oxime [vi, R = H] was dehydrated to 6-y -acetoxy-13 - cyano octahydromethylmorphenol [vii, R = Ac] hydrolysis of which afforded 6-y-hydroxy-13-carboxyoctahydromethylmorphenol [vni, R = H]. This sequence of reactions was repeated with [ii, R = CH3] giving [iv, R = CHS]-[vi, R — CH3] and with 6-a-hydroxy- and 6-a-methoxy- 13-vinyloctahydro-methylmorphenol obtained from a-tetrahydrocodeimethine. [vin, R = H] could not be lactonized. 

The approach used depends on the selective dehydration of hydroxy-isopropyldihydrofuroquinolines to produce terminal olefins. Acid-catalyzed dehydration resulted in the exclusive formation of the more stable isopropylfuroquinolines, e.g. 95. Although other conventional procedures were also largely unsuccessful, reaction of the hydroxy-isopropyldihydrofuroquinoline 93 with thionyl chloride and pyridine gave the terminal olefin 94, which was converted into O-methylptelefolonium salt (84). Triphenylphosphite dihalides in the presence of base, however, proved to be effective reagents. Thus, the phosphite dibromide and potassium carbonate reacted with platydesmine to give olefin 97 predominantly, which was converted into dubinidine (87) by treatment with osmium tetroxide. Ptelefolone was the only product formed when the 6,8-dimethoxy-4-quinolone 92 was treated successively with triphenylphosphite dichloride and with pyridine. 

Resolution of crystalline rac-29 (by means of brucine) gives 29, which, after conversion to 30, affords 15 Scheme 9) by Dieckmann condensation. The bicyclic hydroxy ketone 15 reacts with crotylmagnesium bromide to furnish 31a -I- 31b. On successive treatment with osmium tetroxide and lead tetraacetate the diastereoisomeric aldehydes arise which can be dehydrated to afford 16 -I- 32. The latter compound, obtainable by chromatography, on Wittig reaction leads to 33 which, on catalytic hydrogenation, gives 18 Scheme 9). Oxidation converts 18 to 19, and by successive Wittig reaction, followed by selective ozonolysis, unsaturated aldehyde 20 finally is formed. 

Pandit and coworkers also prepared a functionahzed tricyclic core (148) by a different version of the intramolecular Diels-Alder reaction (Scheme 13). For further introduction of an alkenyl group, the trisubstituted alkene in 148 was subjected to osmium dihydroxylation followed by dehydration imder... 

To our knowledge, there are no recent examples for hydration-dehydration processes involving osmium. However, the reactions of Os3(CO)io(NCMe)2 with HSi(OR)3 (R = Me, Et) lead to the trinuclear clusters ( -H)Os3(CO)9 -(RO)2SiOR) and (/r-H)Os3(CO)9 /r-(RO)2Si(OR)2, which could represent models for the interaction of metal clusters with silica. Similar reactions were performed by Ugo and co-workers during their work on surface organometallic chemistry . ... 

Dehydration of the tertiary alcohol (290) led to a miicture of approximately equal amounts of the A - and A -isomers (293) and (294) when it was oxidized with osmium tetroxide, all four theoretically possible isomers of the cis-diols (292) and (298) were obtained. At the same time, both in the case of the 16,17-diols (292) and in the case of the 17,17a-diols (298) the amount of the o -isomer was the greater. The cleavage of the first pair of diols (292) with periodic acid led to the ketoaldehyde (295), which, on being boiled in xylene with triethylammonium acetate, cyclized to form dl-5a-A -pregnen-3/S-ol-20-one acetate (296), identical in respect of its IR and UV spectra with the d-enantiomer obtained from natural sources. By a similar series of reactions, the second pair of diols (298) gave the keto-acetate (297) with an acetyl group at Cjg, isomeric with (296) [648, 649,... 

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