Thiol Mediated Free Radical Cyclization of Alkenyl and Alkynyl Isocyanides
摘要:
Thiol-mediated free radical cyclizations of but-3-enyl and but-3-ynyl isocyanides of types 6-8 give new access to 3,5-disubstituted 2-(alkyl- and 2-(arylthio)pyrrolines 11, 12, and 18. When 2-mercaptoethanol is used with the same isocyanides the reaction results in pyroglutamates 16, 17, or 19. These cyclizations involve the formation of a new carbon-carbon bond through intramolecular addition of a carbon-centered thioimidoyl radical to a carbon-carbon multiple bond. Although cyclic products are usually obtained in high yields, in a few cases a competing radical degradation process leading to isothiocyanates was observed. Isocyanide 8a carrying an allyl(phenyl) sulfide moiety isomerizes to 2-(phenylthio)pyrroline 24 in a series of sequential steps.
Silver‐Catalyzed Asymmetric Dearomatization of Electron‐Deficient Heteroarenes via Interrupted Barton–Zard Reaction
作者:Qian Wan、Jia‐Hao Xie、Chao Zheng、Yao‐Feng Yuan、Shu‐Li You
DOI:10.1002/anie.202107767
日期:2021.9
Herein we report a catalytic asymmetricdearomatizationreaction of electron-deficient heteroarenes with α-substituted isocyanoacetates through an interrupted Barton–Zard reaction. A range of optically active pyrrolo[3,4-b]indole derivatives was obtained in good yields (up to 97 %) with high stereoselectivities (up to >20:1 dr and 97 % ee), using a catalytic system consisting of a cinchona-derived