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

New stable, crystalline isobenzofurans 9a and 9b linked through the 1,3-pos itions and incorporated into alicyclo-phanes have been prepared from the re lated foranoalicyclophane 5 in three steps (i) addition of benzyne or 4,5-b is(trimethylsilyl)benzyne (ii) hydrogenation of the pi -bond (iii) ejection of ethylene by flash vacuum pyrolysis, and shown to yet retain high 1,3-di ene character and form adducts with dienophiles, e.g. dimethyl acetylenedic arboxylate or N-methyl maleimide; the corresponding off-rack 1,3-dimethylis obenzofurans were too unstable for isolation.