Photochemical cyclization triggering

The enediyne structure in anticancer drugs, that act via DNA cleavage, is caused by a diradical formed in cyclo-aromatization. Thus a triggering mechanism was required to initiate the cyclization of stable precursors under physiological conditions (temperature about 37°C). Photochemical triggering is one approach used for this purpose. In some cases, it was achieved by photochemical synthesis of reactive enediynes that then readily undergo cyclo-aromatization [244]. 

Scheme 3.17 Triggering the Bergman cyclization by photochemical ring contraction.

Scheme 3.19 Photochemical triggering the Bergman and Myers-Saito cyclizations.

Karpov, G.V. and Popik, V.V. (2007) Triggering of the Bergman cyclization by photochemical ring contraction. Facile cycloaromatization of benzannulated cyclodeca-3,7-diene-l,5-diynes. Journal of the American Chemical Society, 129(13), 3792-3793. 

Polukhtine, A., Karpov, G., Pandithavidana, D.R., Kuzmin, A. and Popik, V.V. (2010) Photochemical triggering of the Bergman and Myers-Saito cyclizations. Australian Journal of Chemistry, 63(7), 1099-1107. 

Xing, X. and Demuth, M. (1999) An efficient formal total synthesis of ( )-stypoldione via photochemically triggered biomimetic cyclizations of terpenoid polyalkenes. Synlett, 987-990. 

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