Abstract: The CFF method is used on the conformational analysis of the title complex. Eight possible isomers are treated, their minimum energies are given and equilibrium conformations are compared with recent crystal structure determination. Futhermorethe influences of the two five-membered chelate rings on the conformational change of the four-membered ring from puckered form to planar form are discussed in detail and the reproduction of the initia1 stage in the formation of four-membered ring is attempted.