Experimental and theoretical studies of Diels-Alder dimerization of 1,2,3,4,5-pentachlorocyclopentadiene and of Diels-Alder cycloaddition of polychlorinated cyclopentadienes to norbornadiene

摘要

Diels-Alder cyclodirnerization of 1,2,3,4,5-pentachlorocyclopentadiene (1) affords 2a as the exclusive reaction product. Diels-Alder cycloaddition of 1 to norbomadiene also proceeds stereoselectively to produce a single [4+2] cycloadduct, 4c. The structures of 2a and 4c were established unequivocally via application of single crystal X-ray crystallographic techniques. The origins of the observed diastereofacial selectivity in each of these cycloaddition processes have been investigated by application of semiempirical (AMI Hamiltonian) and ab initio (Hartree-Fock 3-21G*) calculations. The computational results thereby obtained, which are based upon consideration of the kinetically favored transition state for each of the two cycloaddition reactions studied, are consistent with experiment. These sermempirical and ab initio methods also have been used to investigate the mechanisms of the Diels-Alder reactions that have been used to prepare aldrin and isodrin (7 and 8, respectively). The results thereby obtained suggest that isodrin formation via Diels-Alder cycloaddition of cyclopentadiene to 1,2,3,4,7,7-hexachloronorbomadiene proceeds with kinetic control of product stereochemistry. (C) 2003 Published by Elsevier Science Ltd. [References: 24]