Gold Catalysis: Alkylideneoxazolines and ‐oxazoles from Intramolecular Hydroamination of an Alkyne by a Trichloroacetimidate

Abstract

Several propargylic trichloroacetimidates have been prepared and their reactions with gold catalysts studied. Only with the propargyl and the 1‐methylpropargyl substituent was a selective cyclization observed; with gold(III) chloride in acetonitrile only the product of a fast hydroamination to 4‐methylene‐4,5‐dihydrooxazoles was obtained, in chloroform the slower subsequent aromatization could not be prevented which delivered the oxazoles after long reaction times. Up to 3333 turnovers could be reached. With gold(I) catalysts in chloroform or dichloromethane selective hydroamination to 4‐methylene‐4,5‐dihydrooxazoles without subsequent aromatization was exclusively observed. The gold(I) catalysts also allowed chemoselective cycloisomerization of N‐propargylcarboxamides to 5‐methylene‐4,5‐dihydrooxazoles. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Gold‐Catalyzed Addition of Nitrogen and Sulfur Nucleophiles to CC Multiple Bonds

“…The 6-exo, but not the 5-exo, transformation tolerated substitution at the terminal alkyne carbon atom and both transformations tolerated a range of substitution at the oxygen-bound sp 3 carbon atom. Similar transformations were reported near the same time by Hashmi [11]. Carbamates are also effective nucleophiles for the gold(I)-catalyzed intramolecular hydroamination of alkynes [12].…”

Metal-free syntheses of oxazoles and their analogues based on λ3-iodane-mediated cycloisomerization/functionalization reactions or [2+2+1] cycloaddition type reactions

“…18 Recently, Hashmi et al reported an elegant synthesis of halogenated oxazoles via the gold-catalyzed formation of alkylideneoxazolines (path e) 19 followed by the halogenation of them (path f). 18 Such a method have been extended to oxazole synthesis with the introduction of heteroatomic or carbon functional groups 20,21 as well as the further oxidation of iodinated alkylideneoxazolines (path g) 22 by Hashmi's and other groups.…”

Regio‐ and Enantioselective Hydroamination of Dienes by Gold(I)/Menthol Cooperative Catalysis

“…In 2009, we found that, in presence of stoichiometric amounts of base, alkylgold(I) complexes could be formed by gold-promoted addition of nitrogen nucleophiles to unactivated alkenes [Eq. (1)]. [6,7] This result led us to posit that generation of an acidic species was important for catalytic turnover in the reported alkene hydroamination reactions.…”

“…[1,2] While significant progress has been made in the asymmetric hydroamination of allenes, enantioselective goldcatalyzed hydroamination of simple alkenes and dienes has been limited to reactions in which urea is employed as a nucleophile. [3] Furthermore, as simple Brønsted acids are also known to be effective catalysts for alkene hydroamination [4] and gold(I) triflates are often employed in olefin activation, [5] the role of gold in these reactions is unclear.…”