Wittig double, ring closure

For a review of these double ring closures, see Vollhardt, K.P.C. Synthesis, 1975, 765. For a review of applications of the Wittig reaction to the synthesis of natural products, see Bestmann, H.J. Vostrowsky, O. Ref. 722. 

Furans having a double bond at position 2 can be obtained by a phosphine-initiated cyclization of enyne ketones in the presence of an aldehyde. The reaction may involve the 1,6-addition of the phosphine toward the enyne, ring closure and Wittig reaction of the ylide with the aldehyde <99TL3753>. 

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