Sunlight‐Driven, Catalyst‐Free Synthesis of Cyclobutanes by [2 + 2] Cycloaddition of Fluorinated Heterochalconoids in Solution

A cyclobutane ring constitutes an interesting scaffold for the development of new materials and drugs. Herein, the [2 + 2] cycloaddition of chalconoid precursors bearing fluorinated and heterocyclic moieties is described to produce cyclobutane derivatives in solution. The reaction is promoted by sunlight and does not require any added photocatalyst. The regio‐ and stereoselectivity output depends on the heteroaromatic system and the number of fluorine atoms. Experimental results and density functional theory calculations support a mechanism through the formation of an electron donor–acceptor complex between two molecules of the chalconoid.