Over the past decades, the biological activity of enediyne antitumor antibiotics has been established to arise from their ability to form carbon-centered para-benzyne biradical intermediates via Bergman cyclization. Unfortunately, these drugs are cytotoxic. In order to rationally design less cytotoxic synthetic drugs,it is essential to obtain a better understanding on the reactivity of these biradical intermediates in solution. However, the study of the reactivity of para-benzynes has proven to be challenging due to the difficulties of generating them cleanly in solution. In the past decades, para-benzynes have been generated in solution primarily via Bergman cyclization at temperatures higher than 155 oC. Recently, para-benzynes have been successfully generated in the gas phase by collision-activated cleavage of two iodine atoms from diiodoprecursors. However, little is still known about the reactivity of para-benzynes.In this study, a para-benzyne analog, the 5,8-didehydroquinoline, was successfully generated in solution via photon-induced Bergman cyclization. The para-benzyne reacts with dimethyl disulfide and allyl iodide via abstraction of two SCH3 groups and two iodine atoms, respectively, which demonstrates the presence of two radical sites. Its reactivity has been examined under different pH in order to examine the importance of polar effects on its reactivity.

Generation of para-benzyne biradicals in solution via photon-induced Bergman cyclization

248th National Meeting (2014)

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