AB-INITIO STUDY OF ENDO EXO AND DIASTEREOFACIAL SELECTIVITIES IN DIELS-ALDER REACTIONS BETWEEN CHIRAL BUTENOLIDES AND CYCLOPENTADIENE/

Diels-Alder reactions of cyclopentadiene with crotonolactone and beta- angelica lactone have been studied using ab initio methods at the MP3/ 6-31G//RHF/3-21G and MP2/6-31G*//RHF/6-31G* levels. The transition st ates corresponding to the formation of different stereoisomers and dia stereoisomers have been located. The results obtained show that the co rrect endo/exo selectivity is only obtained when polarization function s are included in the basis set. However, syn/anti selectivity is corr ectly described at all levels of calculation.