Enediynes can cyclize via the Bergman Cyclization to form aromatic diradicals. These diradicals have significant importance in anti-cancer drug synthesis, as these diradicals are very efficient in abstracting hydrogen from cellular DNA. Although mechanistically similar to the Bergman Cyclization, Domino Cyclization instead leads into the formation of polyaromatic diradicals due the higher number of alkyne carbons in the starting structure. The goal of this study is to obtain an improved understanding of the reaction pathways that lead to the formation of these polyaromatic diradicals. Two possible domino cyclization mechanisms were hypothesized: concerted, where the alkyne carbons bonds break, cyclize, and form all of the aromatic rings at the same time, and step-wise, where individual alkyne bonds break and cyclize, forming one or two aromatic rings in each stage. Density Functional Theory (DFT) was used to study the domino cyclization pathway of ene-n-yne molecules. All reactants, transition states, intermediate structures and final structures of each ene-n-yne species were geometrically and energetically optimized using the B3LYP functional with basis sets 6-31g*, cc-pVDZ, and cc-pVTZ, implemented in the Gaussian09 software. Using these methods, the energetics of each reaction pathway was obtained, providing important insight into the mechanisms that lead to the formation of polyaromatic diradicals.

Quantum mechanics study of polyaromatic diradical formation through domino cyclization

2019 Spring National Meeting

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