%0 Journal Article
%A Afarinkia, Kamyar
%A Bearpark, Michael J.
%A Ndibwami, Alexis
%D 2005
%T An Experimental and Computational Investigation of the
Diels−Alder Cycloadditions of Halogen-Substituted
2(H)-Pyran-2-ones
%U 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
%R 10.1021/jo048213k.s002
%2 https://acs.figshare.com/ndownloader/files/5138137
%K pyran
%K stereochemical preferences
%K reactivity patterns
%K isolable bridged bicyclic lactone cycloadducts
%K Computational Investigation
%K cycloaddition
%K stereoisomeric cycloadducts
%K Diel
%K transition states
%K B 3LYP
%K regio
%K stereoselectivity
%K CO 2
%X Diels−Alder reactions of 3- and 5-halo-subsituted 2(H)-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(H)-pyran-2-ones afford cycloadducts which
are very prone to loss of bridging CO2 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(H)-pyran-2-ones and 4-halo-subsituted
2(H)-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(H)-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.
%I ACS Publications