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Dual Activation of Aromatic Diels-Alder Reactions.

08:00 EDT 21st May 2019 | BioPortfolio

Summary of "Dual Activation of Aromatic Diels-Alder Reactions."

We have analyzed the unusually fast Diels-Alder reactivity of [5]cyclophanes using density functional theory at the BLYP-D3(BJ)/TZ2P level. The computations were guided by an integrated activation strain and Kohn-Sham molecular orbital analysis. It is revealed why both [5]metacyclophane and [5]paracyclophane exhibit a significant rate enhancement compared to their planar benzene analog. The activation strain analyses reveal the enhanced reactivity to originate from (i) pre-distortion of the aromatic core resulting in a reduced activation strain of the aromatic diene and/or (ii) enhanced interaction with the dienophile through a distortion-controlled lowering of the HOMO-LUMO gap within the diene. Both of these physical mechanisms and thus the rate of Diels-Alder cycloaddition can be tuned via different modes of geometrical distortion (meta- versus para-bridging) as well as by heteroatom substitution in the aromatic ring. Judicious choice of the bridge and heteroatom in the aromatic core enables effective tuning of the aromatic Diels-Alder reactivity to achieve activation barriers as low as 2 kcal mol-1, which is an impressive 35 kcal mol-1 lower than that for benzene.

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Name: Chemistry (Weinheim an der Bergstrasse, Germany)
ISSN: 1521-3765
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