title: Theoretical Study of the Diels-Alder Reaction of Selenoaldehydes and Selenoketones.
abstract: The Diels-Alder reaction of a series of substituted selenoaldehydes (Se=CHR; R = H, F, Me, OMe, CH(2)F, CF(3), and CN) or selenoketones (Se=CR(2); R = Me and CN) with 1,3-butadiene or 2-methoxy-1,3-butadiene to yield 3,6-dihydro-2H-selenopyrans were examined using B3LYP with a modified 6-31G basis set. This method is compared with results from a number of standard ab initio procedures and compares well with post-HF results. The Diels-Alder reaction of the selenocarbonyl compounds proceeds through a concerted, though asynchronous, transition state. Strong electron-withdrawing groups alter the mechanism; a charge-transfer complex is first formed, followed by a concerted TS before reaching the heterocyclic product. The transition state geometry, regiochemistry, and dependence of the activation barrier on substituents can be understood in terms of FMO theory.
authors.affiliation: Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, Illinois 60115.
authors.forename: Steven M.
authors.initials: SM
authors.lastname: Bachrach
authors.forename: Sulin
authors.initials: S
authors.lastname: Jiang