Radical Trifluoromethylation, Cyclization, and Iodination of 1,6-Enynes

Radical Trifluoromethylation, Cyclization, and Iodination of 1,6-Enynes

Author: Domenique Herbstritt

Upon light excitation, electron donor–acceptor (EDA) complexes can generate radical intermediates, which can be useful in organic synthesis. Such EDA-complex-mediated approaches have an advantage over photoredox catalysis processes because they do not need a separate photocatalyst, toxic reagents, or transition metals. EDA complexes can, for example be used for the cyclization of 1,n-enynes (n = 5,6,7), giving five- and six-membered heterocyclic molecule.

Jinhui Yang and Dianjun Li, Ningxia University, Yinchuan, China, and colleagues have found that triphenylphosphine and lithium iodide can promote a visible-light-induced radical cascade of trifluoromethylation/5-exo-dig cyclization/iodination of 1,6-enynes (general product structures pictured; top: X = NTs, O; bottom: X = C, CO). The well-known Togni’s reagent II (1-(trifluoromethyl)-1,2-benziodoxol-3(1H)-one) was used as a CF3 source, and lithium iodide functions as an iodine source.

Mechanistically, the researchers expect a radical mechanism since the addition of radical inhibitors such as TEMPO (2,2,6,6-tetramethylpiperidin-1-oxyl) leads to lower yields. The reaction shows good regioselectivity and functional group tolerance and proceeds under ambient conditions. The products are highly functionalized and could be useful for further transformations.


 

Leave a Reply

Kindly review our community guidelines before leaving a comment.

Your email address will not be published. Required fields are marked *