Olefin osmium-based reagents

Osmium(VIII) tetraoxide (0s04) is an effective reagent for the cis hydroxylation of olefins under stoichiometric conditions as well as in a variety of catalytic variants.213 Under both catalytic and stoichiometric conditions, the critical step is the formation of an osmium(VI) cycloadduct, the formation of which is dramatically accelerated in the presence of amine bases such as pyridine,214 i.e.,... 

The regioselectivity of this new procedure toward terminal olefins is considerably better than that realized with the earlier catalytic oxyami-nation procedures based on chloramine-T.3 However, the catalytic procedure cannot compete with the regiospecificity exhibited by the stoichiometric ferr-alkyl imido osmium reagents.3... 

Oxidation systems based on osmium have been extensively researched for the hydroxylation of olefins. Hydrogen peroxide/Os04 (Milas reagent) will hydro-... 

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. 

The initial work on the reaction of osmium tetroxide with olefins was carried out by Hofmann early in the last century [3,4]. In the 1930s, Criegee [5] showed that the addition of a base, such as pyridine, accelerates the reaction rate. Later on, catalytic variations of the reaction were developed employing relatively inexpensive reagents for the reoxidation of the osmate species [6]. More recently, several advances were achieved to immobilize the catalyst and to improve the catalytic oxidation chain. In particular, recent work couples the oxidation of the osmium(VI) compound to a green terminal oxidant such as air or hydrogen peroxide [7-9]. 

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