Osmyl compounds

These compounds give characteristic osmyl IR bands (840 cm 1 in 0s02Cl2(PPh3)2) [151]. 

Next is the construction of the D ring. The TMS enol ether of compound 111 undergoes oxidation with m-CPBA, providing the C-5a trimethylsilyloxy ketone 112. Addition of methyl Grignard reagent to the ketone group and subsequent dehydration provides compound 113. Osmylation of the C=C double... 

Many ruthenyl and osmyl complexes with O donor ligands are known. The ruthenium compounds are usually prepared from [RuOJ, which can be generated by the oxidation of RuCl3 xH20 or [RUO2] with [104] . The osmium compounds are usually prepared from [OSO4] or K2[0s(0)2(0H)4]. 

In the event, osmylation of compound 16 in pyridine, followed by the usual workup, afforded a 92% yield of an 18 1 mixture of two diols. That the major one, mp 136-139° C, has the stereochemistry implied in 20 need not be debated in light of a single crystal determination of its 7,8-bis-3,5-dinitrobenzoate derivative 21, mp 114.5-115.5° C (see Figure 5). ... 

It is of interest to consider in retrospect the logic of the chirality transfers involved in this synthesis. In essence stereochemical information was passed from the stereogenic center of SS to control the sense of emergence of the pyranose ring in compound 8. Eventually, at the stage of Z-enoate IS, stereochemical information is pass from the ring back to the double bond in the all critical osmylation reaction (9). 

Bis-osmylation of C60 is feasible but the positions of each of the second osmate groups has yet to be determined (Hawkins 19926). If octahedral locations (figure 6) are involved, two disubstituted and three trisubstituted derivatives are possible. These intermediates can readily be converted into hydroxy compounds and hence, in principle, into polymers by reaction with chlorides of dicarboxylic acids. 

A similar compound, [0s206(py)4], prepared by the reaction of Os04 with pyridine in the presence of ethanol, originally formulated as 0s03(py)2 has been confirmed to be a dimer by single-crystal X-ray studies (184). The osmium is octahedral with trans osmyl linkages... 

When present in various compounds or alloys, osmium is conveniently estimated by ignition in a current of oxygen, collection in alcoholic alkali of the volatile tetroxide, and reduction with formaldehyde. The reduction product first forms a colloid, but is gradually precipitated and converted in metallic osmium by reduction in hydrogen at 230° to 250° C.3 Or the alcoholic solution may be treated with ammonium chloride and the precipitated osmyl diammine chloride reduced to metal in hydrogen. 

Similar to the case of C60,105,223 some exploratory work on the regio-chemistry of single and double osmylation of C70 was done by Hawkins and co-workers.224 A major and a minor mono-adduct were assigned the Cs-symmetric C(l)-C(2)- and C(5)-C(6)-adduct structures (cf. Figure 1.6), respectively. After re-submission of the mono-adducts to osmylation, a total of nine compounds was reported, but no individual structural assignments were made.224... 

Enantioselective total syntheses of (-)-6-epitrehazolin and (+)-trehazolin were achieved by the synthesis of 275, which began with an asymmetric heterocycloaddition between [(benzyloxy)methyl]cyclopentadiene (263),108 prepared from thallous cyclopentadienide, and the acylnitroso compound arising from in situ oxidation of (,S )-mandelohydroxamic acid (264) with tetrabutylammonium periodate. Cycloaddition led to a mixture of 265 and its diastereomer (Scheme 35).109 The inseparable mixture was reduced to afford cyclopentenes 266 and 268 in 40% and 11 % overall yields, respectively, from thallous cyclopentadienide. Catalytic osmylation of 266 favored syn addition, while the osmylation of diacetate 267 was more selective and nearly quantitative, affording, after acetylation, compounds 270 and 269 in >5 1 ratio. 

Osmylation afforded a mixture of two cis glycols 255, which was cleaved into the corresponding hydroxyaldehydes 256. Subsequent oxidation with chromic trioxide in methanol afforded a mixture of two hydroxy esters 257 and 258 that were separated. Contrary to the result in the model compounds (56), dehydration of both hydroxy esters 257 and 258 afforded the identical... 

A. The bis-osmyl ester C6o[Os04L2]2 has been prepared as a mixture of five isomers and probable structures for all five compounds have been deduced from H and NMR studies of the separated components. ... 

The asymmetric cis dihydroxylation of alkenes covalently bound to chiral fragments, which can be cleaved after the osmylation step, has been the subject of several reports2-5. The subsequent removal of the chiral auxiliary can be effected by various methods and allows the preparation of enantiomerically pure hydroxylated compounds. 

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