A new stabilised form of isobenzofuran, rack-mounted on an alicyclophane

New stable, crystalline isobenzofurans 9a and 9b linked through the 1,3-positions and incorporated into alicyclophanes have been prepared from the related furano-alicyclophane 5 in three steps (i) addition of benzyne or 4,5-bis(trimethylsilyl)benzyne (ii) hydrogenation of the π-bond (iii) ejection of ethylene by flash vacuum pyrolysis, and shown to yet retain high 1,3-diene character and form adducts with dienophiles, e.g. dimethyl acetylenedicarboxylate or N-methyl maleimide; the corresponding off-rack 1,3-dimethylisobenzofurans were too unstable for isolation.