MHEORETICAL STUDIES ON THE REACTION MECHANISMS OF CYCLOADDITION REACTIONS BETWEEN KETENE OR SUBSTITUTED KETENES AND CYCLOPENTADIENE

The cycloaddition reactions between ketene or substituted ketenes andcyelopentadiene have been studied theoretically by means of the semiempirical AMImethod.Three different substituted ketenes have been selected and tentransition states,corresponding to different approach geometries have beenlocated and characterized,The regioselectivity and stereoselectivity of thereactions are correctly predicted by the calculations and the reaction mechanismsare analyzed in terms of electronic and steric effects of the substitutents onthe reacting ketene and cyc-lopentadiene.