Crown ether styryl dyes 18. Synthesis, anion-"capped" complexes, and ion-selective stereospecific [2+2] autophotocycloaddition of photochromic 18-crown-6 ethers

Article abstract of DOI:10.1007/BF01435800

New crown ether styryl dyes (trans- 1c,d) containing the 18-crown-6 ether fragment were synthesized. Interaction of trans-1c,d dyes, as well as their analogs, trans-1a,b containing the 15-crown-5 ether fragment, with Ca(ClO₄)₂ in MeCN afforded supramolecular structures (dimeric complexes). Competing reactions, trans-cis-photoisomerization with the formation of anion-"capped" complexes of cis-1a-d and [2+2] autophotocycloaddition with the formation of cyclobutane derivatives 8a-d and 9c, were observed on photolysis of solutions of complexes of trans-1a-d with Ca²⁺. Preorganization of trans-isomers in dimeric complexes with Ca²⁺ determined the regio- and stereoselectivity of each of the two directions of the photocycloaddition and the efficiency of the reaction.