title: Counter ion effect in Au/Ag-catalyzed chemoselective 6-endo-dig N- and O-cyclizations of enyne-urea system: diversity-oriented synthesis of annulated indoles.
abstract: A two-step protocol for the diversity-oriented synthesis of annulated indoles following MCR-post MCR modification concept is described. The reaction initially proceeds through the annulation of 2-(2,2-dibromovinyl)aniline, an isocyanate, and a terminal alkyne in a three-component tandem format via Cu/Pd-catalyzed cross coupling to afford N-1 and C-2 functionalized indole. In the subsequent step, the enyne-urea derivative undergoes chemo- and regioselective 6-endo cyclization to afford O-cyclized product in the presence of Au(I)/AgNO3 and N-cyclized product in the presence of Au(I)/AgOTf under a post-MCR modification step. A mechanistic investigation following a recent pioneering work on the silver effect in gold catalysis (Shi, X. J. Am. Chem. Soc. 2012, 134, 9012) explains the role of counterion on Au/Ag-catalyzed regiodivergent pathways.
authors.affiliation: Medicinal and Process Chemistry Division, CSIR-Central Drug Research Institute, Lucknow 226001, India.
authors.forename: Sahaj
authors.initials: S
authors.lastname: Gupta
authors.forename: Dipankar
authors.initials: D
authors.lastname: Koley
authors.forename: Krishnan
authors.initials: K
authors.lastname: Ravikumar
authors.forename: Bijoy
authors.initials: B
authors.lastname: Kundu
mesh_terms: D000480:Alkynes / Q000737:chemistry*; D002384:Catalysis; D003500:Cyclization; D006046:Gold / Q000737:chemistry*; D007211:Indoles / Q000138:chemical synthesis* / Q000737:chemistry; D015394:Molecular Structure; D012834:Silver / Q000737:chemistry*; D014508:Urea / Q000737:chemistry*
chemical_list: D000480:Alkynes; D007211:Indoles; D012834:Silver; D006046:Gold; D014508:Urea