Theoretical exammation of the Diels–Alder reaction of 1,3-butadiene with cyclopentadiene and 2H-phosphole

Abstract

All Diels–Alder reactions between 1,3-butadiene and cyclopentadiene or 2H-phosphole have been examined at the MP4SDQ/6-31G*//HF/6-31G* level. There is remarkable similarity between the two systems. The thermodynamic product is the bicyclo[4.2.0]nonadiene while the kinetic product is the norbornene product. There is a slight kinetic preference for the endo addition and for the butadiene to be in the s-trans conformation. Except for the case where butadiene is the diene component and addition is endo, the reactions are concerted and synchronous. In these other two cases, the reaction is stepwise with a diradical intermediate.Key words: phosphole, Diels–Alder reaction, topological electron density analysis.