Bergman and Myers-Saito cycloaromatizations of enediynes and enyne-allenes, respectively, are powerful ring-forming reactions that generate highly reactive diradical intermediates. Though the gain of aromaticity is a strong driving force, it is not required as competing Schreiner-Pascal and Schmittel cyclizations to non-aromatic diradicals are also possible for enediynes and enyne-allenes under appropriate conditions. Our research group is interested in the design and synthesis of new poly-unsaturated systems that may undergo similar diradical forming cyclizations. Toward this end, we have examined computationally the potential for cross-conjugated enyne-enones to undergo four possible diradical-forming cyclizations to produce 5-, 6-, or 7-membered rings. To gain experimental data, we have developed a synthetic route to prepare ethynyl-substituted chalcone derivatives (enyne-enones) containing electron-donating (OCH<sub>3</sub>) and electron-withdrawing (NO<sub>2</sub>) groups to examine thermal reactivity. Upon heating in the presence of 1,4-cyclohexadiene, we have observed C1-C6 and C1-C7 diradical cyclization of enyne-enone derivatives, though intramolecular Dehydro-Diels-Alder cyclization appears to be the major cyclization pathway. The syntheses and ongoing efforts to optimize diradical-forming cyclizations of enyne-enones will be presented.

Investigating cyclization channels of substituted enyne-enone derivatives

253rd National Meeting (2017)

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