Photodimerization reactions of olefins continue to attract great attention in organic chemistry for the synthesis of four-membered rings. Although photochemical [2+2] cycloaddition reactions of cinnamic acid derivatives provide a promising synthetic protocol to attain β-truxinic acids, a complex mixture of products is obtained in the solution phase due to cis-trans isomerization, and a general protocol for selective heterodimerization of two different cinnamic acids still remains elusive. In this work, a novel methodology is presented which enables homo- and heterodimerization of cinnamic acid derivatives in solid state, and provides disubstituted symmetrical and unsymmetrical cyclobutane products with full regio- and diastereocontrol by utilizing 1,8-naphthalenediol as a covalent template molecule. Utilization of this template ensures that two different alkene groups of cinnamic acid derivatives align in the same direction as parallel to each other and having adequate distance between them, facilitating the synthesis of [2+2] cycloadducts under UV-light in high yields and as single diastereomers. Hydrolysis reactions of the cycloaddition products under basic conditions give β-truxinic acid derivatives in quantitative yield and with complete recovery of the template. The facts that this reaction is carried out in solid-state without using solvent, without the formation of any side product, and with full recovery of the template molecule greatly contribute to developments in green chemistry.

Template-directed photochemical [2+2] cycloaddition reactions of cinnamic acid derivatives

ACS Fall 2021

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