Catalytic isomerization of 1-alkynyl-2,3-epoxy alcohols to substituted furans: Succinct routes to furanoid fatty acids and difurylmethanes

A versatile procedure for the preparation of synthetically valuable 2,5-disubstituted and 2,3,5-trisubstituted furans via mercury(II)-mediated isomerization of 1-alkynyl-2,3-epoxy alcohols is described. Mercury(II)-catalyzed isomerization of alkynyl epoxides 3a-k derived from cyclic Phi-alkynyl allylic alcohols furnishes 2,3,5-substituted furans bearing an aldehyde or keto group on the C-2 side chain. The reaction is used in a succinct and efficient synthesis of the furanoid fatty acid F-5. In contrast, the mercury(II)-catalyzed reaction of a series of alkynyl epoxides 3m-p lacking ring fusion affords difurylmethanes 5, presumably by the dimerization of intermediate 2-(alpha-hydroxyalkyl)furans 4.