Synthesis of Substituted THF Rings

Similar 5-exo cyclization procedures have been widely utilized by Evans in his total syntheses of complex natural compounds, such as the synthesis of ionomycin [12a] and polyether antibiotic X-206 [12b]. A 5-exo cyclization of a y-epoxy alcohol has also been observed under basic conditions [12c]. 

A novel epoxide cydization approach to the formation of compound 23, contain- 

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