Subsequent Chemical Reactions of Photochromic 4,5‐Dibenzothienylthiazoles

Abstract

Abstract4,5‐Dibenzothienylthiazole derivatives having leaving groups at the reactive 2‐positions of benzothiophene rings have been synthesized, and their photochromic ring‐closing reaction followed by spontaneous elimination and substitution reactions have been studied. A 4,5‐dibenzothienylthiazole having an ethoxy group and a hydrogen atom at each 2‐position of the benzothienyl ring underwent elimination to generate a condensed aromatic structure upon the addition of acid. 4,5‐Dibenzothienylthiazoles having an ethoxy or methyl groups at the 2‐position of the benzothienyl rings showed photochromism both in hexane and in methanol solutions with photocyclization quantum yields as high as 60 %. Upon the addition of acid to the methanol solutions of closed‐ring isomers of dibenzothienylthiazoles, the substitution of the ethoxy group with a methoxy group occurred. The generation and rearrangement of the carbocation intermediate formed by elimination of the ethoxy group from the closed‐ring isomers were apparent from the chemical structure of methoxy‐substituted products.