Vanadium catalysts allylic alcohol asymmetric epoxidation

Another interesting asymmetric epoxidation technique using metal catalysis involves the vanadium complexes of A-hydroxy-[2.2]paracyclophane-4-carboxylic amides (e.g., 19), which serve as catalysts for the epoxidation of allylic alcohols with f-butyl hydroperoxide as... 

Katsuki-Sharpless asymmetric epoxidation. Since its introduction in 1980 [10], the Katsuki-Sharpless asymmetric epoxidation (AE) reaction of allylic alcohols has been one of the most popular methods in asymmetric synthesis ([11-14]). In this work, the metal-catalyzed epoxidation of allylic alcohols described in the previous section was rendered asymmetric by switching from vanadium catalysts to titanium ones and by the addition of various tartrate esters as chiral ligands. Although subject to some technical improvements (most notably the addition of molecular sieves, which allowed the use of catalytic amounts of the titanium-tartrate complex), this recipe has persisted to this writing. 

Epoxidations. Grafting tantalum onto silica to form a useful catalyst for the Sharpless asymmetric epoxidation of allyl alcohols is contrary to the ineffective titanium species on a similar support. Vanadium-complexed chiral hydroxamic... 

SCHEME 34.15. Asymmetric epoxidation of allyl alcohols 54 leading to enantioenriched epoxides 56 mediated by vanadium(V) catalysts with a chiral hydroxamic acid ligand 55 and t-butyl hydroperoxide as a terminal oxidant. 

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