Synthesis of Indolyl‐1,3‐dienes from β‐Sulphonyl Aldehydes through One‐Pot Sequential Brønsted Acid/Base Catalysis

• Published in: European journal of organic chemistry Vol. 2022; no. 18
• Main Authors: Karan, Ganesh, Sahu, Samrat, Sudan Maji, Modhu
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 13.05.2022
• Subjects: 1,3-Diene; Aldehydes; Brønsted acid; Catalysis; Conjugation; Dienes; Functional groups; Indoles; One-pot; Pyrroles; Sequential catalysis; Stereoselectivity
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.202200240

Introduction of a 1,3‐diene moiety at the C3‐position of pyrrole and indole bearing various aliphatic as well as aromatic functional groups with good stereoselectivity remains a challenging task. Keeping the synthetic applicability in mind, an eccentric strategy is developed to synthesize 1,3‐dienyl pyrroles and indoles from unprotected pyrroles and indoles employing β‐sulphonyl aldehyde as a dienylating agent. This method is developed by using a one‐pot sequential Brønsted acid/base catalysis strategy. The nucleophilicity of indole is transmitted through the conjugation to eliminate the sulfonyl groups in a step‐wise manner. Further, this developed protocol was extended to the incorporation of a 1,3,5‐triene moiety at the C3‐position of indoles through unprecedented successive three sulfonyl group elimination. As an application of this strategy, a Diels−Alder reaction and hydrothiolation of 1,3‐diene were demonstrated. Syntheses of dienyl pyrroles and indoles were achieved by using β‐sulfonyl aldehydes through transition‐metal‐free one‐pot sequential Brønsted acid/base catalysis. This transformation enables the access to various aliphatic as well as aromatic substituted 1,3‐dienes. Further, trienyl indole was also synthesized employing this strategy.