We have focused our attention on cycloisomerization reactions involving silver-and gold-based homogeneous catalysis. This topic is divided into two parts: one relating to cycloisomerization with an allene group and the other with an alkyne group. In each case we have then studied different partners such as carbonyl/carboxy groups, imines, amides or alkenes. Reactions involving allene and alkyne systems as partners are also briefly reported, along with miscellaneous transformations. Our purpose is also to stimulate some dis-
The selective functionalization of carbon-carbon σ bonds is a synthetic strategy that offers uncommon retrosynthetic disconnections. Despite progress in C-C activation and its great importance, the development of asymmetric reactions lags behind. Rhodium(I)-catalyzed selective oxidative additions into enantiotopic C-C bonds in cyclobutanones are reported. Even operating at a reaction temperature of 130 °C, the process is characterized by outstanding enantioselectivity with the e.r. generally greater than 99.5:0.5. The intermediate rhodacycle is shown to react with a wide variety of tethered olefins to deliver complex bicyclic ketones in high yields.
An optimized ligand-controlled palladium-catalyzed allene synthesis starting from alkynes and aryl bromides giving rise to allene products in a simple and direct manner is described. The methodology is performed in an inter- and intramolecular fashion with unprecedented scope and excellent yields. Based on mechanistic investigations and on DFT calculations, the role played by the carboxylic additive (i.e., PivOH) in controlling the selectivity of the reaction is discussed, allowing us to propose an intramolecular base-assisted deprotonation (iBAD) mechanism for this process.
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