Thermal and photochemical radical cyclizations of enediynes (Bergman cyclization) and enyne-allenes (Myers-Saito cyclization) are well known. In an effort to design new diradical-forming cyclizations, we have examined the thermal reactivity of ethynyl-substituted chalcone derivatives we refer to as enyne-enones. While multiple diradical-forming cyclization pathways are possible for enyne-enones, including formation of 5-, 6-, and 7-membered rings via diradical intermediates, for the parent ethynylchalcone ((E)-1-(2-ethynylphenyl)-3-phenylprop-2-en-1-one) an intramolecular Dehydro-Diels-Alder cycloaddition is the major reaction pathway. In an effort to prevent the intramolecular Dehydro-Diels-Alder reaction, we have replaced the phenyl substituent on the beta-carbon of the α,β-unsaturated ketone with an anthracen-9-yl group. With the Dehydro-Diels-Alder reaction effectively blocked, thermolysis of the anthracen-9-yl substituted enyne-enone leads to isolation of the C1-C7 diradical cyclization product in the presence of 1,4-cyclohexadiene. The synthesis of the anthracen-9-yl substituted enyne-enone, along with its thermal conversion to the dihydrobenzotropone derivative, will be presented.

C1-C7 Diradical cyclization of an anthracen-9-yl substituted enyne-enone

253rd National Meeting (2017)

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