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The mechanism of the calcium-catalyzed coupling of alcohols with vinylboronic acids has been analyzed by means of density functional theory computations. This study reveals that the calcium and boron Lewis acids associate to form a superelectrophile able to promote a pericyclic group transfer reaction with allyl alcohols. With other alcohols, the two Lewis acids act synergistically to activate the OH functionality and trigger a S N i reaction pathway. These two mechanisms are affected by the nature of the counterions, which has been rationalized by electronic and steric factors.

Herein, we report the preparation of bridged tetrahydrobenzo[b]azepines, which was accomplished through an aza‐Piancatelli cyclization/Michael addition sequence in a one‐pot fashion from readily available precursors. It is noteworthy that a general method to access these scaffolds was hitherto unprecedented. Additionally, the multifaceted aspects of this process have been exemplified through its application to the synthesis of 2‐azabicyclo[3.2.1]octanes and bridged tetrahydrobenzo[b]oxepines, along with post‐derivatizations. [ABSTRACT FROM AUTHOR]

Abstract: Transformations of alkene and alkyne substrates relevant to π‐Lewis acid catalysis have been performed using low‐valent Ga(I) species for the first time. [Ga(I)(PhF)2]+[Al(ORF)4]− and gallium dichloride (i. e. [Ga(I)]+[GaCl4]−) proved to be efficient catalysts for cycloisomerizations, Friedel‐Crafts reactions, transfer hydrogenations, and reductive hydroarylations. Their activity is compared to more common Ga(III) complexes. This study shows that even the readily available and yet overlooked gallium dichloride salt can be a more active π‐Lewis acid catalyst than gallium trichloride or other Ga(III) species. [ABSTRACT FROM AUTHOR]

A compound that isomerizes into distinct products depending on the particular Lewis acid or Brønsted acid catalyst used is disclosed. One product can only be obtained with the softest π-acids, such as Au, Pt, Ga, or In complexes. Another is formed only with harder π-acids incorporating Ag or Cu salts. The formation of the third category requires even harder π-acids or protons. This simple benchmark reaction allows for prediction of the category of transformations that can be catalyzed by a new complex. It also informs whether protons have been unintentionally generated in the reaction mixture. [ABSTRACT FROM AUTHOR]

Cationic gold(I) complexes are soft Lewis acids that are able to trigger numerous types of nucleophilic attack onto alkenes, allenes, and alkynes (π-acid catalysis). In this account, we initially summarize the novel methods that we have developed to generate such catalysts by silver-free activation of ligated gold(I) chlorides. The advantages of this approach are the use of lower quantities of gold and the ability to scale-up transformations during which the standard gold/silver catalytic system is rapidly decomposed. In the second part, the synthesis and catalytic activity of original organogallium compounds is described. We have shown that (NHC)GaCl2 +-type complexes display a high affinity for alkenes and alkynes, and trigger tandem C–C/C–C or C–C/C–H bond formation processes. Thus, they also behave as π-acids. Practical applications of these different gold- and gallium-based catalytic systems for the synthesis of cyclic compounds are presented. 1 Introduction 2 Silver-Free Two-Component Approaches in Gold Catalysis 2.1 The Gold/Copper Catalytic System 2.2 Other Applications with Gold/Lewis Acid Systems 3 Gallium Catalysis 3.1 Cationic Gallium Complexes Supported by N-Heterocyclic Carbene Ligands 3.2 Catalytic Applications 4 Conclusions [ABSTRACT FROM AUTHOR]

[IPr·InBr2][SbF6] (2) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) has been synthesized and characterized in the solid state. This complex proved to be a very active catalyst for hydroarylations, transfer hydrogenations, and cycloisomerizations. [ABSTRACT FROM AUTHOR]

While the coordination chemistry of gallium is very rich, only a few applications of organo-gallium compounds as catalysts for molecular transformations have been reported. Nevertheless, some studies containing both families of X-ray characterized species and their catalytic activity allow the establishment of a structure–activity and a structure–stability relationship. They show that coordination compounds of gallium enable reactions that encroach upon the territory of transition metals. The interest of using specific ligands in gallium catalysis is also becoming clear in classical Lewis acid chemistry. In this review, the physical properties of gallium complexes are analyzed and related to their ability to activate alkynes toward nucleophilic additions, peracetic acid toward olefin epoxidation, and aldehydes toward hetero Diels–Alder reactions. [ABSTRACT FROM AUTHOR]

Complexes of type [LAuCl] (L=phosphine, phosphite, NHC and others) are widely employed in homogeneous catalysis, however, they are usually inactive as such and must be used jointly with a halide scavenger. To date, this role has mostly been entrusted to silver salts (AgSbF6, AgPF6, AgBF4, AgOTf, etc.). However, silver salts can be the source of deactivation processes or side reactions, so it is sometimes advisable to use silver-free cationic gold complexes, which can be difficult to synthesize and to handle compared with the more robust chloride. We show in this study that various Lewis acids of the transition and main group metal families are expedient substitutes to silver salts. We have tested CuI, CuII, ZnII, InIII, SiIV, BiIII, and other salts in a variety of typical AuI-catalyzed transformations, and the results have revealed that [LAuCl] can form active species in their presence. [ABSTRACT FROM AUTHOR]

Catalytically active species for a variety of transformations are obtained from stable gold complexes using non-silver metal-based activators. [ABSTRACT FROM AUTHOR]