Photoaddition Reactions of Benzoxazole-2(3H)-thiones to Cycloalkenes and Heteroaromatics

✍ Scribed by Takehiko Nishio; Kiyoko Shiwa; Masami Sakamoto

• Publisher: John Wiley and Sons
• Year: 2003
• Tongue: German
• Weight: 184 KB
• Volume: 86
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.200390266

✦ Synopsis

Abstract

Photoaddition reactions of benzoxazole‐2‐thiones 1 with cycloalkenes 2 and heteroaromatics 3 were examined. Irradiation of N‐acylbenzoxazole‐2‐thiones 1a and 1b, and 3‐(methoxycarbonyl)‐ and 3‐(phenoxycarbonyl)benzoxazole‐2(3__H__)‐thiones (1f and 1h, resp.) in the presence of cycloalkenes 2a–2c, cyclohexa‐1,4‐diene (2d), and indene (2e) yielded 2‐substituted benzoxazoles 4–13, 18 and 19, and iminothietanes 14–17, by intramolecular trapping of the acyl or MeOCO and PhOCO groups by thiolate anion of the zwitterionic intermediate I and by the phenolate anion of the zwitterionic intermediate II, respectively, derived from the spirocyclic amino‐thietanes AT formed by [2+2] cycloaddition of the CS bond of 1 and CC bond of 2. Irradiation of 1 in the presence of heteroaromatics 3 gave the 2‐substituted benzoxazoles 20–33 exclusively.