The hydration of alkynes has been extensively studied for more than 100 years. This reation allows the access to various carbonyl derivatives starting from alkynes. Nolan and coworkers reported the acid-free catalyzed alkyne hydration using a gold catalyst. Nolan has been one of the pioneer in the use of N-heterocyclic carbene (NHC) as ligands in various catalytic transformation using a variety of metals. Using a gold-NHC complex and silver hexafluoroantimonate, the authors demonstrated the outstanding activity of this catalyst in the hydration of various alkynes using 1,4-dioxane and methanol as reaction media. It is important to note that acid is not needed for this transformation and that catalyst loadings as low as 10 ppm were used for this reaction. 

Written by William Sommer, PhD

The development of gold catalysis has been an endeavor for the past 10 years.¹ One of the leaders in this field, professor Toste and coworkers, developed a new way to synthesize azepines via a gold catalyzed intermolecular [4+3]-annulation.² In this study, the authors demonstrated the efficiency of the transformation, catalyzed by PicAuCl₂, with a variety of substrates. It was noted that the substrates containing electron-rich N-aryl groups gave the highest yields. In a typical procedure, 2 to 10 mol% of the gold catalyst is needed in methylene chloride at room temperature. Good to excellent yields are obtained with good diastereomic ratios.

Written by William Sommer, Ph.D

The use of gold as a catalyst has been an ever expending research field for the past 10 years. It has been showed to catalyze a variety of transformations such as nucleophilic additions, oxidations or nucleophilic cyclization of allenes.¹ The latest transformation is of interest due to its potential applications in the synthesis of biologically active molecules. Watanabe et al. reports the hydroarylation of allenes derived from anilines and phenols.² These compounds are of importance because they are widely found as core structures of natural products.The researchers investigated the cyclization of various N-allenylaniline derivatives, using a gold complex having the Buchwald's JohnPhos ligand, 2-Dicyclohexylphosphino-2′,4′,6′-triisopropylbiphenyl gold(I) chloride, as a catalyst. The investigation showed that AgOTf was necessary for the reaction to give good yields. Disubstituted electron-rich aniline derivatives yielded the desired product with good yields. 

In summary, a new efficient route from allenic compounds to dihydroquinolines have been developed. This novel synthesis, give access to molecules that are essentials for the synthesis of natural products and drugs.

Reference: 1. Hashmi, A. S. K. Chem. Rev. 2007, 107, 3180.

                2. Watanabe T. et al. Org. Lett. 2007, 9, 4821.

Written by: William Sommer, Ph.D

The quest to synthesize biologically active building blocks has been ongoing for the past 40 years. Another area with growing interest is the use of gold in catalysis. For the past 10 years several reports demonstrated the ability of gold in catalytic reactions. It can be used as a Lewis acid to activate unsaturated C-C bonds for nucleophilic attacks.¹ Utilizing these properties, Zhou and Che catalyzed the intramolecular addition of β-ketoamide to unactivated alkenes to yield substituted lactams.² Several metals salts such as Au(PPh₃)Cl with AgOTf, were tested for this reaction. The best system for this reaction consisted of (2-Biphenyl)di-tert-butylphosphine gold(I) chloride and AgOTf. Optimizing the conditions for this reaction lead to a catalyst loading of 5 mol % in toluene at 50 ˚C. The scope of the reaction includes a variety of substrates with yields up to 99%.

1. Zhang, J. et al. J. Am. Chem. Soc. 2006, 128, 1798.

2. Zhou, C.-Y.; Che, C.-M. J. Am. Chem. Soc 2007, 129, 5828.