Anionic [4+2]cycloaddition - Retro[4+2]cycloaddition strategy in the synthesis of psoralen and its isoster
Furan-1,4-dipolar agents 7 and 16e, prepared in few steps from commercially available furoates, have been annulated with bicyclopentadienone 2 to provide pentacyclic frameworks 8 and 17 respectively. Subsequent transformations of 8 and 17 through retro-Di