Tandem catalytic epoxide opening

Titanocene-Catalyzed 5-exo Cydizations 443 Titanocene-Catalyzed Radical Tandem Reactions 444 Catalytic Enantioselective Epoxide Opening 445 Conclusion 448 References 449... 

Gansauer and coworkers have developed a tandem catalytic approach to reductive epoxide opening that employs H transfer from a dihydride complex (Scheme 1.2) [32, 33]. The carbonepoxide opening with Cp2TiCl abstracts H from the H2 adduct of Wilkinson s catalyst Manganese or zinc metal regenerates the active Ti" species and makes the reaction catalytic. 

The corresponding reaction of but-3-yn-l-ols or pent-4-yn-l-ols with primary or secondary alcohols in the presence of catalytic amounts of Ph3PAuBF4 and p-TsOH afforded tetrahydrofuranyl ethers (Scheme 4-76). This tandem 5-endo-cycloisomerization/hydroalkoxylation proceeds via 2,3-dihydrofurans, which then undergo an intermolecular Bronsted acid-catalyzed addition of the external alcohol. The transformation is not restricted to internal alkynols but can be applied to terminal acetylenes as well. Application of the method to the s thesis of bicyclic heterocycles with a P-lactam structure was reported recently.Under the same conditions, epoxyalkynes undergo a sequence of epoxide opening, 6-exo-cycloisomerization, and nucleophilic addition to afford tetrahydropyranyl ethers. In a closely related transformation, cyclic acetals were obtained from alk-2-ynoates bearing a hydroxy group in 6- or 7-position by treatment with AuCU and MeOH. ... 

Nemoto T, Kakei H, Gnanadesikan V, Tosaki S, Ohshima T, Shibasaki M. Catalytic asymmetric epoxidation of ,(3-unsaturated amides efficient s5mthesis of p-aryl a-hydroxy amides using a one-pot tandem catalytic asymmetric epoxidation-Pd-catalyzed epoxide opening process. J. Am. Chem. Soc. 2002 124(49) 14544-14545. 

Previously we pointed out that the oxidation of alkenes in water allows one-pot multi-step reactions to be carried out involving tandem epoxidation and ring-opening reactions. Further examples are the synthesis of optically active trifluorolactic acid by aqueous nitric acid ring-opening oxidation of (-)-l,2-epoxy-3,3,3-trifluoropropane [19] in the presence of a catalytic amount of copper metal ... 

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