Afarinkia, Kamyar Bearpark, Michael J. Ndibwami, Alexis An Experimental and Computational Investigation of the Diels−Alder Cycloadditions of Halogen-Substituted 2(<i>H</i>)-Pyran-2-ones Diels−Alder reactions of 3- and 5-halo-subsituted 2(<i>H</i>)-pyran-2-ones with both electron-rich and electron-deficient dienophiles afford stable and readily isolable bridged bicyclic lactone cycloadducts. These cycloadditions proceed with excellent regioselectivity and very good stereoselectivity. In contrast, Diels−Alder reactions of 4-halo-subsituted 2(<i>H</i>)-pyran-2-ones afford cycloadducts which are very prone to loss of bridging CO<sub>2</sub> and the subsequent formation of barrelenes ([2.2.2]cyclooctenes). Furthermore, these cycloadditions proceed with only moderate regio- and stereoselectivity. For both series of the 3- and 5-halo-subsituted 2(<i>H</i>)-pyran-2-ones and 4-halo-subsituted 2(<i>H</i>)-pyran-2-ones, the reactivity patterns do not significantly change between the halogens. The regio- and stereochemical preferences of the cycloadditions of halo-substituted 2(<i>H</i>)-pyran-2-ones are investigated computationally. Calculations were carried out on the transition states leading to the four possible regio- and stereoisomeric cycloadducts by using density functional theory (B3LYP/6-31G*). These studies allow prediction of the regio- and stereoselectivity in these reactions which are broadly in line with experimental observations. pyran;stereochemical preferences;reactivity patterns;isolable bridged bicyclic lactone cycloadducts;Computational Investigation;cycloaddition;stereoisomeric cycloadducts;Diel;transition states;B 3LYP;regio;stereoselectivity;CO 2 2005-02-18
    https://acs.figshare.com/articles/journal_contribution/An_Experimental_and_Computational_Investigation_of_the_Diels_Alder_Cycloadditions_of_Halogen_Substituted_2_i_H_i_Pyran_2_ones/3300403
10.1021/jo048213k.s002