Toward an understanding of the mechanisms of the intramolecular |
| |
Authors: | Domingo Zaragoza |
| |
Institution: | Departamento de Quimica Organica, Universidad de Valencia, Dr Moliner 50, 46100-Burjassot, Valencia, Spain. |
| |
Abstract: | The molecular mechanism for the intramolecular 5 + 2] cycloaddition reaction of beta-silyloxy-gamma-pyrones bearing tethered alkenes has been characterized using ab initio methods. A comparative study for this sort of cycloaddition carried out at different computational levels points out that the B3LYP/6-31G calculations give similar barriers to those obtained with the MP3/6-31G level. Analysis of the energetic results shows that the reaction takes place along a stepwise process: first, the migration of the neighboring silyl group to the carbonyl group of the gamma-pyrone takes place to give a weak oxidopyrylium ylide intermediate, which by a subsequent concerted intramolecular 5 + 2] cycloaddition affords the final cycloadduct. The cycloaddition process is very stereoselective due to the constraints imposed by the tether. The 5 + 2] cycloaddition reaction has a large barrier, and the presence of the silyloxy group and the intramolecular character of the process are necessary to ensure the thermodynamic and kinetic feasibility of these cycloadditions. |
| |
Keywords: | |
本文献已被 PubMed 等数据库收录! |
|