Butenolides furan syntheses from

A concise synthesis of highly substituted furans, pyrroles, butenolides, and 2-butene-4-lactam esters starts from alkynyl adducts of a Fischer carbene complex 21 (Scheme 27) < 1998JOC3164>. Incorporation of an aldehyde yields a reactive vinyl tungstencarbonyl complex 22 that can be oxidatively transformed to an ester group, furnishing the furan carboxylic ester 23. 

Takei utilized a furan as the synthetic equivalent of a 1,4 dicarbonyl compound in his synthesis of pyrenophorin as described in Scheme 4.6. ° Thus butenolide 28, obtained by Michael addition of butenolide 27 to methyl vinyl ketone, was silylated to provide the silyloxyfuran. Treatment with lead tetraacetate followed by aqueous hydrolysis gave 29 in 55% yield. Protection of the ketones as dimethyl ketals followed by selective removal of the C-7 ketal and reduction gave seco acid 30. Dimerization and hydrolysis gave a mixture of 9 and 18 (17% from 29). 

Several butenolide natural products of terpenoid origin have been synthesized from furan precursors. On the other hand furan natural products are synthesized from butenolide precursors, e.g. ancistrofuran (133) (Scheme 75). The synthesis of two members of the drimane class of sesquiterpenes containing a butenolide ring have been reported. The first synthesis provides a route to racemic cinnamodial, and the second describes the synthesis of optically active confertifolin (134) from the natural product manool. A rather doubtful mechanism is proposed for the most important reaction in this sequence (Scheme 76). ... 

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