Rhodium‐ and Platinum‐Catalyzed [4+3] Cycloaddition with Concomitant Indole Annulation: Synthesis of Cyclohepta[b]indoles

Abstract

Verschiedenartig substituierte Cyclohepta[b]indole wurden in einer Tandemreaktion aus Indolanellierung und [4+3]‐Cycloaddition aus Propargylethern und Dienen hergestellt (siehe Schema; Boc=tert‐Butoxycarbonyl). Acyclische sowie cyclische Diene können in der [4+3]‐Cycloaddition eingesetzt werden und liefern tri‐ bzw. tetracyclische Produkte. Elektronenarme Phosphan‐ oder Phosphitliganden erleichtern die Tandemreaktion.

Gold‐Catalyzed CH Annulation of Anthranils with Alkynes: A Facile, Flexible, and Atom‐Economical Synthesis of Unprotected 7‐Acylindoles

“…The control experiment without catalyst showed no reaction even at room temperature (entry 1). Among the screened gold catalysts,t he catalyst with an NHC ligand (entry 7) showed higher activity than those with phosphane and phosphite ligands (entries [3][4][5]. AuBr 3 was also less efficient (entry 6).…”

Nitrones as Trapping Reagents of α,β‐Unsaturated Carbene Intermediates – [1,2]Oxazino[5,4‐b]indoles by a Platinum‐ Catalyzed Intermolecular [3+3] Cycloaddition

“…[5] To our delight, with this ligand the reaction afforded 3a with a very respectable 86% yield in 3 h (entry 6). Tangs successful report of a Pt-catalyzed [4+3] cycloaddition reaction with PA C H T U N G T R E N N U N G (C 6 F 5 ) 3 as efficient ligand encouraged us to employ it to improve the yield of the desired product.…”

“…[5] Inspired by these intriguing studies and in continuation of our work on the synthesis of indole derivatives, [6] we attempted to explore novel [n + m] cycloaddition reactions by utilizing nitrones [7] as remarkable 1,3-dipole reagents for the trapping of the a,b-unsaturated carbene. [5] Inspired by these intriguing studies and in continuation of our work on the synthesis of indole derivatives, [6] we attempted to explore novel [n + m] cycloaddition reactions by utilizing nitrones [7] as remarkable 1,3-dipole reagents for the trapping of the a,b-unsaturated carbene.…”

“…[8] However, to the best of our knowledge, there are no examples of platinum-catalyzed [3+3] cycloaddition reactions of nitrones and a,b-unsaturated carbene intermediates generated from propargylic ethers. Based on the previous work of Iwasawa et al [4] and Tang et al, [5] we switched to the PtCl 2 as catalyst with Xphos as ligand, the yield of the target product 3a was increased to some extent (entry 3). [9] In order to achieve this novel intermolecular [3+3] cycloaddition reaction, our initial efforts focused on the model reaction of 1a and 2a with different gold catalysts.…”

Rhodium(I)‐Catalyzed Intermolecular Aza‐[4+3] Cycloaddition of Vinyl Aziridines and Dienes: Atom‐Economical Synthesis of Enantiomerically Enriched Functionalized Azepines

“…However,r elative to reactions to construct five-and sixmembered Nheterocycles,t he development of efficient methodologies for the construction of azepine skeletons is often much more difficult because of the unfavorable entropic factors and transannular interactions. [4][5][6] [4+ +3] cycloaddition reactions are particularly attractive for their remarkable efficiency and convergence in the synthesis of azepines, and diverse three-carbon (3C) and aza-3C dienophiles have been developed (Scheme 2). [3] The[ m + n]c ycloaddition has been established as ar eliable and atom-economical method for the synthesis of heterocycles from simple starting materials.…”