Hydroxylation enantioselective reactions with alkenes

The tra x-[Ru (0)2(por)] complexes are active stoichiometric oxidants of alkenes and alkylaro-matics under ambient conditions. Unlike cationic macrocyclic dioxoruthenium I) complexes that give substantial C=C bond cleavage products, the oxidation of alkenes by [Ru (0)2(por)] affords epoxides in good yields.Stereoretentive epoxidation of trans- and cw-stilbenes by [Ru (0)2(L)1 (L = TPP and sterically bulky porphyrins) has been observed, whereas the reaction between [Ru (0)2(OEP)] and cix-stilbene gives a mixture of cis- and trani-stilbene oxides. Adamantane and methylcyclohexane are hydroxylated at the tertiary C—H positions. Using [Ru (0)2(i)4-por)], enantioselective epoxidation of alkenes can be achieved with ee up to 77%. In the oxidation of aromatic hydrocarbons such as ethylbenzenes, 2-ethylnaphthalene, indane, and tetrahydronaphthalene by [Ru (0)2(Z>4-por )], enantioselective hydroxylation of benzylic C—H bonds occurs resulting in enantioenriched alcohols with ee up to 76%. ... 

In oxidation reactions, however, osmium is significantly more selective than catalysts derived from other transition metals. Osmium-based catalysts for the hydroxylation and amination of alkenes are very widely used in organic synthesis.With alkaloid-derived ligands, the hydroxylation and amination reactions are highly enantioselective see Enantioselectivit. The use of bleach, hydrogen peroxide, ferric cyanide, and oxygen have been reported as secondary oxidants for some of these reactions. 

Terminal epoxides of high enantiopurity are among the most important chiral building blocks in enantioselective synthesis, because they are easily opened through nucleophilic substitution reactions. Furthermore, this procedure can be scaled to industrial levels with low catalyst loading. Chiral metal salen complexes have also been successfully applied to the asymmetric hydroxylation of C H bonds, asymmetric oxidation of sulfides, asymmetric aziridination of alkenes, and the asymmetric alkylation of keto esters to name a few. 

An alternate synthesis of enantiopure (—)-diversonol was recently reported by Tietze et al. using an enantioselective transition-metal-catalyzed domino process (Scheme 14.48). Key step in the synthesis is the formation of a chromane with concomitant introduction of the quaternary stereocenter at C-4a with 96% ee using a domino Wacker/carbonylation/methoxylation reaction in the presence of (S,S)-Bn-BOXAX (310) as ligand [73]. In this reaction phenol 308, containing an alkene moiety, was treated with catalytic amounts of Pd(tfa)2 and 310 in MeOH in the presence of CO and p-benzoquinone the latter is necessary to reoxidize Pd to Pd". One can assume that the first step is an enantiofacial coordination of the Pd" species, which is attacked by the phenolic hydroxyl group to give intermediate... 

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