Reactions Catalyzed by Silver or Gold

3 REACTIONS CATALYZED BY SILVER OR GOLD 12.3.1 Cyclization of V- Propargylcarboxam ides 

A 2008 publication by Harmata and Huang32 revealed that for a number of propargyl amide derivatives, 5 mol% of AgSbF6 at room temperature can achieve the same conversion to alkylidene oxazoles in 89-98% yield in minutes In the case of disubstitution at the propargylic position, the reactions proceeds in DCM without the 

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REACTIONS CATALYZED BY COPPER, SILVER, OR GOLD 12.2.1 Aldehyde-Alkyne-Amine Coupling... 

Interestingly, the aldol-type condensation of tosyhnethyl isocyanide 15 with aldehydes is catalyzed by the silver(I)/ferrocenylphosphine 2c or 2e catalyst more selectively than it is catalyzed by the chiral gold catalyst (about 20% ee) under the standard reaction conditions (Scheme 5) [30]. Oxazoline 16 can be converted to optically active a-alkyl-P-(N-metylamino)ethanols by reduction with LiAlH4. 

The cycloisomerization of allenyl ketones was initially described as being catalyzed by rhodium(I) or silver(I) by Marshall et al.21 The activity of copper, silver, and gold for this reaction was first compared in two papers published later (Scheme 12.7).22 In the case of copper and silver, only a cycloisomerization was observed (Table 12.4, entries 1 and 2) with gold, a dimer is obtained as well (entry 3). 

Cr(II) may be used to carry out all the reactions of Ti(III), but usually under milder conditions. Applications of Cr(II) as a reductant have been reviewed. The applications include Sn(IV) chloride in the presence of catalysts such as Sb(V) or Bi(III), Sb(V) in 20% HCl at elevated temperatures, Cu(II), silver, gold, mercury, bismuth, iron, cobalt, molybdenum, tungsten, uranium, dichromate, vanadate, titanium, thallium, hydrogen peroxide, oxygen in water and gases, as well as organic compounds such as azo, nitro, and nitroso compounds and quinones. Excess Cr(II) in sulfuric acid solution reduces nitrate to ammonium ion. The reduction is catalyzed by Ti(IV), which is rapidly reduced to Ti(III). 

Hayashi and Ito have shown that the reaction of methyl isocyanoacetate (MeOCOCH2NC) with aldehydes is catalyzed by gold [339, 408, 752, 1060] or silver [951] complexes. In the presence of ferrocenyl bisphosphines 3.41 (R = CH2CH2NMe2 or CH2CH2N(CH2)5) the reaction is diastereo- and enantio-selective, and provides trans oxazolines 6.131. These oxazolines are precursors of... 

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