Effect of Lewis acid catalysts on Diels-Alder and hetero-Diels-Alder cycloadditions sharing a common transition state.

摘要: The thermal and Lewis acid catalyzed cycloadditions of beta,gamma-unsaturated alpha-ketophosphonates nitroalkenes with cyclopentadiene have been explored by using density functional theory (DFT) methods. In both cases, only a single highly asynchronous bis-pericyclic transition state yielding Diels-Alder hetero-Diels-Alder cycloadducts could be located. Stepwise pathways were found to higher in energy. On the potential energy surface, cycloaddition is followed Claisen rearrangement state. No intermediates located between these states. states are also asynchronous, but bond lengths skewed opposite direction compared relative positions may control periselectivity due shape surface corresponding dynamical influences. Inspection (PES) indicates that majority downhill paths after lead cycloadducts, whereas smaller number reach products no intervening barrier. catalysts alter shifting directions. This topographical change qualitatively affects branching ratio ultimately reverses giving preference for cycloadducts.