Theoretical studies on the electrocyclic reaction mechanisms for s-cis butadiene and disilylbutadiene

The potential energy surfaces for electrocyclic reactions of s-cis butadiene, 1,4-disilylbutadiene and 1,3-disilylbutadiene were calculated by ab initio molecular orbital methods. The transition states of two reaction pathways (conrotatory and disrotatory) for butadiene and 1,4-disilylbutadiene were obtained. These mechanisms along the reaction pathways were analyzed by CI-LMO-CAS methods. The difference between the conrotatory and the disrotatory mechanisms was explained from the biradical character of the terminal carbon (or silicon) atoms. For the transition states on the conrotatory and the disrotatory pathways, the energy difference caused by the orbital phase by the orbital symmetry rule was also estimated for butadiene and 1,4-disilylbutadiene. (C) 1999 Elsevier Science B.V. All rights reserved.