CROWN-CONTAINING STYRYL DYES .8. CATION-DEPENDENT CONCERTED [2+2]-AUTOPHOTOCYCLOADDITION OF PHOTOCHROMIC 15-CROWN-5 ETHER BETAINES

Styryl dyes containing a crown ether group and a heteroaromatic moiety with a sulfoalkyl N-substituent (1a,b) undergo photocyclodimerization in acetonitrile in the presence of Mg(ClO4)2 to give only the type A isomer of cyclobutane derivative (2a,b). The photochemical regio- and stereoselectivity of the cycloaddition is explained by self-organization of the trans-isomers of the styryl dyes upon complexation with the Mg2+ cations into dimers with a fixed mutual arrangement of multiple bonds.