Buchanan J Grant, Ruggiero Giuseppe D, Williams Ian H
Department of Chemistry, University of Bath, Bath, UKBA2 7AY.
Org Biomol Chem. 2008 Jan 7;6(1):66-72. doi: 10.1039/b714118a. Epub 2007 Nov 13.
Transition structures have been optimised using the B3LYP/6-31+G* density functional level method, in vacuum and in implicit (PCM) and explicit (DFT/MM) aqueous solvation, for the degenerate rearrangement of the alpha-lactone derived by the formal addition of Cl(+) to acrylate anion and for the dyotropic rearrangement of this to the beta-lactone. Despite being lower in energy than the alpha-lactone, there is no direct pathway to the beta-lactone from the acrylate chloronium zwitterion, which is the transition structure for the degenerate rearrangement. This may be rationalised by consideration of the unfavorable angle of attack by the carboxylate nucleophile on the beta-position; attack on the alpha-position involves a less unfavorable angle. Formation of the beta-lactone may occur by means of a dyotropic rearrangement of the alpha-lactone. This involves a high energy barrier for the acrylate derived alpha-lactone, but dyotropic rearrangement of the beta,beta-dimethyl substituted alpha-lactone to the corresponding beta-lactone involves a much lower barrier, estimated at about 46 kJ mol(-1) in water, and is predicted to be a facile process.
使用B3LYP/6-31+G*密度泛函水平方法，在真空、隐式（PCM）和显式（DFT/MM）水溶剂化条件下，对通过向丙烯酸根阴离子正式添加Cl(+)得到的α-内酯的简并重排以及其向β-内酯的亲核重排的过渡结构进行了优化。尽管能量比α-内酯低，但从丙烯酸氯鎓两性离子（简并重排的过渡结构）到β-内酯没有直接途径。这可以通过考虑羧酸根亲核试剂对β-位的进攻角度不利来解释；对α-位的进攻涉及的角度较有利。β-内酯的形成可能通过α-内酯的亲核重排发生。这对于丙烯酸衍生的α-内酯涉及高能垒，但β,β-二甲基取代的α-内酯向相应β-内酯的亲核重排涉及的能垒要低得多，在水中估计约为46 kJ mol(-1)，预计是一个容易的过程。
