Theoretical Study of the Diels-Alder Reaction of Selenoaldehydes and Selenoketones.
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.
Bachrach
Steven M.
SM
Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, Illinois 60115.
Jiang
Sulin
S