Palladium-catalyzed cross-coupling of five-membered heterocyclic silanolates.
The preparation of pi-rich 2-aryl heterocycles by palladium-catalyzed cross-coupling of sodium heteroarylsilanolates with aryl iodides, bromides, and chlorides is described. The cross-coupling process was developed through extensive optimization of the following key variables: (1) identification of stable, isolable alkali metal silanolates, (2) identification of conditions for preformation and isolation of silanolate salts, (3) judicious choice in the palladium catalyst/ligand combination, and (4) selection of the protecting group on the nitrogen of indole. It was found that the alkali metal silanolates, either isolated or formed in situ, offered a significant rate enhancement and broader substrate scope over the use of silanols activated by Brønsted bases such as NaOt-Bu. In addition, the optimized conditions for the cross-coupling of 2-indolylsilanolates were readily applied to the cross-coupling of 2-pyrrolyl-, 2-furyl-, and 2-thienylsilanolates.
Denmark
Scott E
SE
Department of Chemistry, University of Illinois Urbana-Champaign, Urbana, Illinois 61801, USA. denmark@scs.uiuc.edu
Baird
John D
JD
Regens
Christopher S
CS
D002384:Catalysis; D006571:Heterocyclic Compounds / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D010165:Palladium / Q000737:chemistry*; D012821:Silanes / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization; D013056:Spectrophotometry, Ultraviolet
D006571:Heterocyclic Compounds; D012821:Silanes; D010165:Palladium