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The mechanisms involved in the gold(I)-catalyzed annulations or cyclization of the different alkenylbenzene compounds are discussed. The application of the process in the synthesis of free gold carbenes is also explained.

The gold(I)-catalyzed intermolecular reaction of terminal alkynes with alkenes are used to obtain cyclobutenes. The sterically hindered cationic Au(I) complexes are used as key catalysts to achieve the reaction.

Palladium catalyzes the coupling of (E)-1,2-bis(tri-n-butylstannyl)ethene, C2H2(Bu3Sn)2, with acid chlorides (RCOCl) to form symmetric 1,4-diketones. beta-Stannyl enones, derived from the reaction of C2H2(Bu3Sn)2 with RCOCl, yield unsymmetric 1, 4-diketones. Carried out in refluxing 1,4-dioxane, the reactions involve the reduction of an olefiinic dicarbonyl intermediate by a palladium hydride obtained from the beta-hydrogen elimination of an n-butylpalladium intermediate. The yields are 47-100%.

The reaction at the cyclopropane or at the carbene carbons of the intermediate cyclopropyl gold carbenes were used to perform gold(I)-catalyzed addition of carbon nucleophiles to 1,6-enynes to give two different types of products. The newly obtained gold(I) complexes which are stable at room temperature could be used as valuable catalyst to perform reactions of enynes in the absence of silver salts.

The synthesis of NaB[(OMe).sub.4] (sodium tetramethoxyborate) by reaction of inexpensive sodium borohydride with methanol is described. The compound possesses an ideal combination of a Lewis base and Lewis acid to catalyze Michael additions of stabilized carbon nucleophiles.

A proton abstraction by the carbonate or a related basic ligand is the basic mechanism involved in the palladium-catalyzed intramolecular arylation, which is normally facilitated by the electron-withdrawing substituents on the aromatic ring. The results show that though the electron-withdrawing substituents are inconsistent with an electrophilic aromatic-substitution mechanism, it has the most important directing effect, when placed ortho to the reacting site.

The effect of substituents on substrates is studied, with an alkyl tether CH(R) between the two aryls, which should present minimum steric and/or electron bias in this reaction, in order to determine the mechanism of the Pd-catalyzed arylation. It is observed that the mechanism for Pd-catalyzed arylation involving a proton abstraction by a carbonate, or related ligand, provides a satisfactory explanation for the experimental data.

A novel synthesis of indanes and dihydronaphtalenes based on the intramolecular insertion into C(sp3)−H bonds of gold(I) carbenes generated by retro‐Buchner reaction (decarbenation) has been developed. Deuterium‐labeling and kinetic isotope effect experiments, DFT calculations, and generation of the proposed carbene intermediate from a well‐characterized gold(I) carbenoid support the involvement of a three‐center concerted mechanism for the C(sp3)−H functionalization process. [ABSTRACT FROM AUTHOR]

The goal of this short review is to provide an overview of the different synthetic methodologies applied along the years for the synthesis of bullvalenes, prototypical fluxional molecules that were key in the understanding of valence tautomerism phenomena. Some interesting applications of these unique shapeshifting compounds are also presented. 1 Introduction 2 Classical Syntheses of Bullvalenes 3 Recent Developments in the Synthesis of Bullvalenes 4 Applications of Bullvalenes 5 Conclusion [ABSTRACT FROM AUTHOR]

The gold(I)‐catalyzed retro‐Buchner (decarbenation, retrocyclopropanation) reaction of 7‐substituted cycloheptatrienes has emerged as a safe and powerful alternative for the generation of gold(I) carbenes. These carbenes can cyclopropanate alkenes, take part in intramolecular reactions, or engage in higher cycloadditions with different partners, giving rise to a wide range of relevant structures. This review covers the developments made on the generation of gold(I) carbenes via decarbenation reactions, and the applications of these reactions in organic synthesis. Gold is still shining: The gold(I)‐catalyzed retro‐Buchner (decarbenation, retrocyclopropanation) reaction of 7‐substituted cycloheptatrienes has emerged as a safe and powerful alternative for the generation of gold(I) carbenes. This review covers the developments made on the generation of gold(I) carbenes via decarbenation reactions, and the applications of these reactions in organic synthesis. [ABSTRACT FROM AUTHOR]