Platinum-catalyzed intramolecular alkylation of indoles with unactivated olefins.
Reaction of 1-methy-2-(4-pentenyl)indole (1) with a catalytic amount of PtCl2 (2 mol %) in dioxane that contained a trace of HCl (5 mol %) at 60 degrees C for 24 h led to the isolation of 4,9-dimethyl-2,3,4,9-tetrahydro-1H-carbazole (2) in 92% yield. Platinum-catalyzed cyclization of 2-(4-pentenyl)indoles tolerated substitution at each position of the 4-pentenyl chain. Furthermore, the protocol was applicable to the synthesis of tetrahydro-beta-carbolinones and was effective for cyclization of unprotected indoles. 2-(3-Butenyl)indoles underwent platinum-catalyzed cyclization with exclusive 6-endo-trig regioselectivity. Mechanistic studies established a mechanism for the platinum-catalyzed cyclization of 2-alkenyl indoles involving nucleophilic attack of the indole on a platinum-complexed olefin.
Liu
Cong
C
P. M. Gross Chemical Laboratory, Duke University, Durham, North Carolina 27708-0346, USA.
Han
Xiaoqing
X
Wang
Xiang
X
Widenhoefer
Ross A
RA
D000475:Alkenes / Q000737:chemistry*; D000478:Alkylation; D002384:Catalysis; D003500:Cyclization; D007211:Indoles / Q000737:chemistry*; D015394:Molecular Structure; D010984:Platinum / Q000737:chemistry*
D000475:Alkenes; D007211:Indoles; D010984:Platinum