title: Unexpected regioselective carbon-hydrogen bond activation/cyclization of indolyl aldehydes or ketones with alkynes to benzo-fused oxindoles.
abstract: Rhodium-catalyzed carbon-hydrogen bond activation has attracted great interest in the construction of carbon-carbon and carbon-heteroatom bonds. In recent years, transition metal-mediated oxygen transposition through a 'dehydration-rehydration' process has been considered as a promising strategy towards oxygen-functionalized compounds. Here we describe an unexpected rhodium-catalyzed regioselective carbon-hydrogen bond activation/cyclization of easily available indolyl aldehydes or ketones with alkynes to afford benzo-fused oxindoles, involving the sequential carbonyl-assisted carbon-hydrogen activation of the indole ring at the 4-position, [4+2] cyclization, aromatization via dehydration, nucleophilic addition of water to iminium and oxidation. Isotopic labelling experiments disclose the occurrence of apparent oxygen transposition via dehydration-rehydration from the indolyl-3-carbonyl group to the 2-position of pyrrole to forge a new carbonyl bond. The tandem reaction has been used as the key step for the concise synthesis of priolines, a type of alkaloid isolated from the roots of Salvia prionitis.
authors.affiliation: Key Laboratory of Green Chemistry and Technology of Ministry of Education, College of Chemistry, and State Key Laboratory of Biotherapy, West China Hospital, West China Medical School, Sichuan University, 29 Wangjiang Road, Chengdu 610064, China.
authors.forename: Xingyan
authors.initials: X
authors.lastname: Liu
authors.affiliation: Key Laboratory of Green Chemistry and Technology of Ministry of Education, College of Chemistry, and State Key Laboratory of Biotherapy, West China Hospital, West China Medical School, Sichuan University, 29 Wangjiang Road, Chengdu 610064, China.
authors.forename: Gaocan
authors.initials: G
authors.lastname: Li
authors.affiliation: Key Laboratory of Green Chemistry and Technology of Ministry of Education, College of Chemistry, and State Key Laboratory of Biotherapy, West China Hospital, West China Medical School, Sichuan University, 29 Wangjiang Road, Chengdu 610064, China.
authors.forename: Feijie
authors.initials: F
authors.lastname: Song
authors.affiliation: Key Laboratory of Green Chemistry and Technology of Ministry of Education, College of Chemistry, and State Key Laboratory of Biotherapy, West China Hospital, West China Medical School, Sichuan University, 29 Wangjiang Road, Chengdu 610064, China.
authors.forename: Jingsong
authors.initials: J
authors.lastname: You
mesh_terms: D000447:Aldehydes / Q000737:chemistry*; D000480:Alkynes / Q000737:chemistry*; D003500:Cyclization; D006860:Hydrogen Bonding; D007211:Indoles / Q000737:chemistry*; D007659:Ketones / Q000737:chemistry*; D015394:Molecular Structure; D010084:Oxidation-Reduction; D000078183:Oxindoles; D013237:Stereoisomerism
chemical_list: D000447:Aldehydes; D000480:Alkynes; D007211:Indoles; D007659:Ketones; D000078183:Oxindoles; C022960:2-oxindole