With osmium tetraoxide

The blends are frozen in liquid nitrogen and then microtomed and stained with osmium tetraoxide, which stains only unsaturated elastomers. 

Hydroxylation of 16 with osmium tetraoxide and hydrogen peroxide, followed by acetylation, gave 5a-carba-/ -DL-gulopyranose pentaacetate... 

Analogously, for preparation of racemic carba-a-glucopyranose 49 from 52, esterification of (—)-52 furnished the ester 95, which was transformed into compound 96 by debromination with zinc dust and acetic acid. Stereoselective hydroxylation of 96 with osmium tetraoxide and hydrogen peroxide, followed by acetylation, gave compound 97. Lithium aluminum hydride reduction of 97, and acetylation of the product, gave pentaacetate 98, which was converted into 99 by hydrolysis. ... 

Starting from 149, novel carba-sugar pentaacetates of the P-L-allo (168) and a-u-manno (171) configuration have been synthesized. Reduction of 149 with diisobutylaluminum hydride (DIBAL-H) and acetylation gave a mixture of acetates 162 and 163. Hydroxylation of the mixture with osmium tetraoxide and hydrogen peroxide provided compounds 164 and 165 in the ratio of 9 1. Hydrolysis of 164 gave compound 166, which was transformed into 168 by a reaction analogous to that employed in the preparation of 157 from 153. 

Oxidation of alkenes with osmium tetraoxide is much more moderate than similar oxidations with permanganate. This makes OSO4 a very reliable reagent for cis dihydroxylation. 

Visualization of the micromorphology with transmission-electron microscopy (TEM) on ultrathin cuts after staining with osmium tetraoxide... 

In a novel synthetic route involving the transformation of a tetrahydroproto-berberine nucleus to a pavine skeleton (Scheme 10) 119), canadine methiodide (67), was subjected to Hofmann degradation to yield styrene 68. This compound was successively oxidized with osmium tetraoxide-sodium periodate and the... 

This problem may, however, be a special case because the oxidation of pteridine alkenes in the presence of sensitive substituents such as alkylthio was shown to be possible using ligand-assisted catalysis with osmium tetraoxide or DMDO (Scheme 10). In the case of pteridine 65, a clean series of transformations to afford the pterin 66 was possible <20030BC664, 2005PTR53004/04>. However, if oxidation was carried out under moist conditions, the corresponding 2-oxopteridine (lumazine) was always obtained as illustrated by the conversion of 67 into the epoxide 68. 

A base-catalyzed, elimination reaction was a key step in a synthesis of D-ribose from L-glutamic acid.188 In that work, L-glutamic acid was converted, by a series of reactions, into 5-0-benzyl-2,3-dideoxy-D-glycero-pentofuranose (157) from compound 157, a mixture of glycosides was obtained which, on treatment with bromine and calcium carbonate, gave the monobromo derivative 158 as a mixture of diastereoisomers. Base-catalyzed dehydrobromination of 158 afforded the unsaturated derivative 159. Hydroxylation of 159 with potassium permanganate or with osmium tetraoxide gave a mixture of methyl 5-0-benzyl-/3-D-ribofuranoside and methyl 5-O-benzyl-a-D-lyxofuranoside. 

Osmium tetraoxide-promoted reactions are stevically controlled that is, in all instances, the predominant formation of products having tram-oriented substituents at C-2 and C-3, and C-2 and CA, is ob-served, and, consequently, 277 and 279 preponderate over 278 and 280. However, for 2-0-acetyl-l,6-anhydro-3,4-dideoxy-/3-DL- n/t/iro-hex-3-enopyranose (281), reaction with osmium tetraoxide leads175 to 2-0-acetyl-l,6-anhydro-/3-DL-alloside (282 88%) and -galactoside (283 8%). Obviously, the 1,6-anhydro bridge creates greater steric... 

DL-Dihydrostreptose and its ribo isomer were similarly obtained. Birch reduction of 2-methyl-3-furoic acid, followed by addition of methanol, bromination, and dehydrobromination, gave 402 as a mixture of the isomers. Hydroxylation of 402 with osmium tetraoxide-so-dium chlorate, and subsequent treatment with acetone-sulfuric acid afforded three isomeric acetals (403-405). The structures of these compounds were assigned on the basis of their H-n.m.r. spectra. In addition, the relationship between 403 and 404 was established by hydrolysis and reglycosidation. The methyl esters 403-405 were quantitatively reduced to the corresponding alcohols. The mixture of alcohols obtained from 403 and 404 was converted into crystalline 5-deoxy-3-C-(hydroxymethyl)-l,2-0-isopropylidene-a-DL-ribofuran-ose (406), which was compared directly with a sample prepared from D-xylose. Methyl 5-deox y-3-C-(hydroxy methyl)-2,3-O-isopropy lidene-/3-DL-lyxofuranoside (407), obtained by reduction of 405 with lithium aluminum hydride, was hydrolyzed with dilute hydrochloric acid, to give a,/3-DL-dihydrostreptose.2,ifi... 

The addition reaction to branched glycoenopyranosides sometimes offers a stereospecific pathway to A-type, branched sugars. A stereospecific synthesis of the e valose (15) derivative (110) by cis-hy droxy lation of methyl 4-0-benzoyl-2,3,6-trideoxy-3-C-methyl-a-D-en/thro-hex-2-en-opyranoside (109), derived from 57a (R = Me), with osmium tetraoxide... 

Spiro acetals can also be stereoselectively hydroxylated, in high yield, with osmium tetraoxide and a catalyst. The resultant diol is formed by. vyw-hydroxylation from the least hindered side of the alkene moiety (equation 21)121. 

For the sake of maximizing efficiency, the decision was made to prove the preceding question concurrently with the further functionalization of ring C. As reflected in our earlier studies involving 68, the appreciably hindered Cl 1-C12 double bond located in the five-membered ring was not expected to be more reactive than its counterpart in ring B in other settings. Indeed, dihydroxylation with osmium tetraoxide furnished 76, epoxidation of which led in a... 

Hydroxylation of alkenes with osmium tetraoxide is a syn addition. A racemic mixture of the 2R,3S... 

An alternate entry to the narciclasine class of alkaloids has provided access to compounds related to isonarciclasine (263) (Scheme 24). In the event, the aryla-tion of p-benzoquinone with diazonium salts derived from the aryl amines 250 and 251 yielded the aryl-substituted benzoquinones 252 and 253, respectively (146). The selective hydroxylation of 252 and 253 with osmium tetraoxide provided the corresponding m-diols 254 and 255. Catalytic hydrogenation of 254 and 255 using Pd/C or Raney Ni and subsequent lactonization gave the triols 256 and 257 together with small amounts of the C-2 a-epimers 258 and 259. Aminolysis of 256 and 257 afforded the corresponding racemic tetrahydrophen-anthridones 260 and 261, whereas similar treatment of the a-epimers 258 and 259 led to the formation of ( )-isolycoricidine (262) and ( )-isonarciclasine (263), respectively. 

Reaction of the unsaturated bromoethyl glycoside 216 in the foregoing manner gives the bicyclic product 217,218 and similar treatment of the propargyl ether 219 with a tributyltin radical results in carbon-radical generation and cyclization to afford the tin-containing adduct 220 in 90% yield. On oxidation with osmium tetraoxide and periodate ion, the Sn-C bond is cleaved, and the corresponding ketone 221 is produced in excellent yield.219... 

A similar approach, but using hydroxylation with osmium tetraoxide, was applied for the preparation of 2-C-methyl-D-xylono-1,4-lactone (114), 2-C-methyl-D-arabinono-1,4-lactone (115), 2-C-methyl-DL-lyxono-1,4-lactone (116, for the D isomer), and 2-C-methyl-DL-ribono-1,4-lactone (112 for the D isomer).297... 

Viridifloric /3-lactone, 143, has been identified as one of the pheromone components of a complex mixture of volatiles released by the pheromone glands of the male Idea leuconoe butterfly during courtship <1996BMC341>. A racemic mixture of both diastereoisomers was synthesized in four steps from the dilithio salt of 3-methylbutyric acid 144 alkylation with ethanal, dehydration of the secondary alcohol with phosphorus pentoxide, dihydroxylation of the C-C double bond with osmium tetraoxide, and finally formation of the /3-lactone by cyclization with sulfonyl chloride. By comparison with the sample isolated from I. leuconoe, the absolute configuration was established to be (2V,3V)-2-hydroxy-2-(l-methylethyl)-3-butanolide 143. 

Compound 191 was transformed into the exo-alkene 193 via the respective spiro epoxide the enone 192 (11%) was obtained as a side product (Scheme 24).97 Compound 193 was deprotected, and the triol obtained was selectively mesylated at the allylic position to give, after acetylation, compound 194 (68%). Treatment of 194 with sodium acetate resulted in the inversion of configuration at C-l to give the tetra-N,O-acetyl derivative 195. Oxidation of 195 with osmium tetraoxide in aqueous acetone, followed by acetylation, afforded 196 (87%) and 197 (13%), whose acid hydrolysis provided the free bases 5 and 37, respectively. 

Treatment of 193 with osmium tetraoxide, followed by conventional decyclohex-ylidenation, deisopropylidenation, and acetylation, gave the two branched aminocy-clitols, 198 (49%) and 199 (51%), which afforded almost quantitatively the respective free amino alcohols 34 and 42, upon acid hydrolysis followed by purification over Dowex 50W-X2 (H+) resin (Scheme 25).97 98... 

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