Synthesis of photochromic 2,3-bis(5-methyl-2-phenyl-4-thiazolyl)-1,4-naphthoquinone derivatives

2,3-Bis(5-methyl-2-phenyl-4-thiazolyl)-1,4-naphthoquinone 1-O, its monoethylene acetal 2-O and methylated derivatives 3-O and 4-O were synthesized and their photochromic properties were investigated. While bisarylnaphthoquinone 1-O was nonphotochromic, its monoacetal 2-O and methylated derivatives 3-O and 4-O displayed good photochromism. Among them, the isomer 4-O recorded a remarkable diastereomeric excess (98.40%) with high conversion ratio (96.20%) upon UV irradiation.