Complications in the Castagnoli-Cushman reaction: An unusual course of reaction between cyclic anhydrides and sterically hindered indolenines. Issue 35 (30th August 2017)

• Record Type: Journal Article
• Authors: Chizhova, Maria; Dar'in, Dmitry; Krasavin, Mikhail
• Is Part Of: Tetrahedron letters. Volume 58:Issue 35(2017)
• Page Start: 3470
• Page End: 3473
• Publication Date: 2017-08-30
• Subjects: Castagnoli-Cushman reaction -- Side-reaction -- Steric hindrance -- Cyclic imines -- Indolenines -- N-acyliminium species -- Mannich reaction -- Medium-sized rings; Chemistry, Organic -- Periodicals; 547.005
• DOI: 10.1016/j.tetlet.2017.07.077
• Languages: English
• ISSNs: 0040-4039

Abstract

Graphical abstract: Highlights: Reaction of sterically hindered indolenines with cyclic anhydrides has been studied. Unlike with homophthalic anhydride, it did not deliver the expected products. Hydrolytically prone 16-membered 2:2 adducts were isolated instead. The reaction outcome is thought to be characteristic of sterically hindered imines. Additionally, less enolizable anhydrides prefer to react via initial N -acylation. Abstract: Attempted reaction of indolenines (which represent rather sterically hindered cyclic imines) with a series of dicarboxylic acid anhydrides yielded no expected product, the Castagnoli-Cushman lactam. Instead, products presumably formed via N -acyliminium species trapping by a carboxylate anion. Among them, hydrolytically labile 2:2 adducts of an indolenine and a cyclic anhydride, containing a 16-membered cyclic core, are particularly intriguing. This result contradicts the recently reported successful Castagnoli-Cushman reaction of indolenines with homophthalic anhydride suggesting a mechanistic switch in the course of the reaction.