Synthesis of furan-bridged 10-membered rings through [8 + 2]-cycloaddition of dienylfurans and acetylenic esters.

[reaction: see text] The coupling of various dienylfurans with dimethyl acetylenedicarboxylate (DMAD) has been examined. In most cases this reaction proceeds via [8 + 2]-cycloaddition to afford furan-bridged 10-membered ring systems as a single diastereomer. Dienylfuran intermediates were generated using either a chromium carbene-based method or aldol-based methods. Reaction of [8 + 2]-cycloadducts with electrophilic reagents occurred selectively at the enol ether alkene.