[1.1]meta-Stilbenophanes as calixarene analogs: preparation, crystal structure, and cis–trans photoisomerization

Three isomers of [1.1]meta-stilbenophane were synthesized by the McMurry reaction of diarylmethane dialdehyde and their crystal structures and photochemical properties were investigated. X-ray crystallographic analyses of these isomers revealed that they were assigned to a trans–trans (t–t) form with a 1,3-alternate conformation, a cis–trans (c–t) form with a distorted-cone conformation, and a cis–cis (c–c) form with a 1,2-alternate conformation. A 1H NMR study indicated that a t–t isomer could be completely transformed into a 35:65 mixture of c–t and c–c isomers by photoirradiation at 254 nm.