Selectivity switch in the synthesis of vinylgold(I) intermediates
AuthorsHashmi, A. Stephen K
Schuster, Andreas M.
Nolan, Steven P.
KAUST DepartmentBiological and Environmental Sciences and Engineering (BESE) Division
KAUST Catalysis Center (KCC)
Physical Sciences and Engineering (PSE) Division
Chemical Science Program
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AbstractAn unexpected regioselectivity reversal was observed in the synthesis of vinylgold(I) complexes from propargyl carboxamides. The use of [Au(IPr)(OH)] affords preferentially vinylgold(I) complexes resulting from a 5-exo-dig cyclization, whereas the use [Au(IPr)]+ species, generated in situ starting from [Au(IPr)(Cl)] and AgOTf, leads to vinylgold(I) complexes which form via a 6-endo-dig cyclization, This unexpected "selectivity switch" for this cyclization led us to propose two different reaction pathways enabling the formation of the two different products. One mechanism involves the [Au(IPr)]+ species with "classical" I activation of the alkyne framework of the carboxamides, and the second represents an "unusual" use of the basic Brønsted character of [Au(IPr)(OH)]. Mechanistic and DFT studies support the mechanistic hypotheses. © 2011 American Chemical Society.
SponsorsThe ERC (FUNCAT to SPN) and the EPSRC are gratefully acknowledged for support of this work. A.P. thanks the Spanish MICINN for a Ramon y Cajal contract (RYC-2009-04170). Umicore AG and Chemetall AG are thanked for their generous gifts of materials. S.P.N. is a Royal Society Wolfson Research Merit Award holder. We thank Dr. Pierrick Nun for valuable discussions.
PublisherAmerican Chemical Society (ACS)