Importance of the role of secondary orbital interactions in the Diels–Alder reaction. Regioselectivity in the catalyzed and uncatalyzed reactions of juglone and aliphatic dienes
作者:Jiro Motoyoshiya、Tetsuo Kameda、Makiko Asari、Maki Miyamoto、Susumu Narita、Hiromu Aoyama、Sadao Hayashi
DOI:10.1039/a608273d
日期:——
The regioselectivities in the uncatalyzed and catalyzed
DielsâAlder (DA) reactions of juglone with piperylene
(penta-1,3-diene) or 2,3-dimethylpenta-1,3-diene have been investigated,
employing Lewis acids such as boron trifluoride (BF
3
) and
sterically hindered aluminium catalysts in order to verify the role of
the secondary orbital interactions (SOI). While the results of the
uncatalyzed and catalyzed reactions using BF
3
or aluminium
trimethoxide agree with the prediction made by the frontier molecular
orbital (FMO) theory considering SOI, steric repulsion of the aluminium
catalysts causes orderly changes to the ratios of the product
regioisomers, which could be interpreted by diminution of SOI. The
transition states are located by AM1 calculations and their energies are
estimated by CDNO/2-CI and ab initio 6-31G* calculations. The
regioselectivities observed in the experiments are explained by
comparison of their energies. A zwitterionic mechanism in the catalyzed
reaction was strongly supported and the molecular orbital feature
suggests the contribution of SOI which would stabilize the transition
state to control the reaction pathway.
研究了未催化和催化的核桃醌与派比烯(全烯-1,3)或2,3-二甲基全烯-1,3反应中的区域选择性,使用了路易斯酸如三氟化硼(BF₃)和空间位阻铝催化剂,以验证次级轨道相互作用(SOI)的作用。未催化和使用BF₃或铝三甲氧基催化剂的催化反应结果与考虑SOI的前沿分子轨道(FMO)理论的预测一致,而铝催化剂的立体排斥导致产物区域异构体比例的规律性变化,这可以通过SOI的减弱来解释。通过AM1计算定位过渡态,并通过CDNO/2-CI和从头计算6-31G*估算其能量。实验中观察到的区域选择性通过比较它们的能量来解释。催化反应中强烈支持了一种偶极子机制,并且分子轨道特征表明SOI的贡献,这将稳定过渡态以控制反应路径。