The [2+2]-Cycloaddition Reaction of Bisallenes: A Dramatic Substituent Effect

The bisallenes 1 possessing a phenylsulfonyl or n-butyl substituent at the internal position of allene moieties could be smoothly transformed to the bicyclo[5.2.0] or bicyclo[6.2.0] derivatives 2 in moderate to excellent yields with good regioselectivity upon refluxing in toluene. This [2+2]-cycloaddition reaction shows an interesting substituent effect as unveiled by comparing with the results of unsubstituted substrates. However, further attention should be paid to the control of the regioselectivity of the [2+2]-cycloaddition involving different C-C bonds.