Anionic [4+2] cycloaddition strategy to linear furocoumarins: Synthesis of 8 methoxypsoralen and its isoster

Article abstract of DOI:10.1016/S0040-4020(98)00387-1

The surfoxide esters 14 and 20d are successfully annulated with bicyclic enone 8 in the presence of (t)BuOLi to provide the pentacyclic ketones 9a and 21a respectively in good yields (≤70%). Flash vacuum pyrolysis of O-methyl derivatives 9b and 21b at - 500⁰ C/. 1 mm provide furoindacenones 16b and 22b respectively, which in turn are convertible to furocoumarins 1 and 3.