ZnCl2‐Catalyzed [4+1] Annulation of Alkylthio‐Substituted Enaminones and Enaminothiones with Sulfur Ylides

• Published in: Chemistry : a European journal Vol. 26; no. 22; pp. 4941 - 4946
• Main Authors: He, Yuan, Lou, Jiang, Zhou, Yong‐Gui, Yu, Zhengkun
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 16-04-2020
• Subjects: Acetals; annulation; Bioactive compounds; Chemical reactions; Chemistry; enaminones; enaminothiones; Functional groups; Functional materials; Furans; Lewis acid; Organic chemistry; Pesticides; Substitutes; Substrates; Sulfur; sulfur ylides; Thiophenes; zinc; Zinc chloride
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201905483

Concise construction of furan and thiophene units has played an important role in the synthesis of potentially bioactive compounds and functional materials. Herein, an efficient Lewis acid ZnCl2 catalyzed [4+1] annulation of alkylthio‐substituted enaminones is reported, that is, α‐oxo ketene N,S‐acetals with sulfur ylides to afford 2‐acyl‐3‐aminofuran derivatives. In a similar fashion, [4+1] annulation of the corresponding enaminothiones, that is, α‐thioxo ketene N,S‐acetals, with sulfur ylides efficiently proceeded to give multisubstituted 3‐aminothiophenes. This method features wide substrate scopes as well as broad functional group tolerance, offering a concise route to highly functionalized furans and thiophenes.
An efficient Lewis acid catalyzed protocol has been developed for the synthesis of 2‐acyl‐3‐amino‐substituted furan and thiophene derivatives from enaminones and enaminothiones. The [4+1] annulation allows for broad substrate scopes, high efficiency, and good functional‐group tolerance.