5Transition metal-catalyzed C-H bond functionalizations of ferrocene derivatives have emerged in the last few years as a versatile tool in synthetic organometallic chemistry. These protocols offer significant advantages over more traditional approaches for the synthesis of functionalized ferrocene derivatives in terms of both atom-and step-economy. In this Perspective, we aim to showcase the state of the art in this field, with special emphasis on recent asymmetric methodologies.

A convenient process for the direct functionalization of ferrocene that exploits the high electrophilic character of gold-vinyl carbenoids catalytically generated from vinyldiazo compounds and gold complexes is reported. This process takes place with complete regioselectivity (vinilogous reactivity). The synthesis of the corresponding ruthenocene analogues has also been achieved. Preliminary studies on the reactivity of these new organometallic compounds seems to suggest that the presence of the adjacent ferrocenyl group confers a specific reactivity on the functionalized carbon chain manifested in the easy dry state aerobic allylic oxidation.More than sixty years after the discovery of ferrocene, 1 the chemistry of this organometallic compound continues to captivate chemists. This interest is based, mainly, on the huge number of applications of functionalized ferrocenes in several relevant areas including catalysis, material science and medicine. 2 Accordingly, the development of new and efficient methods for the synthesis of functionalized ferrocenes is highly desirable.In contrast to the situation found in other metallocenes, direct functionalization of the ferrocene is viable since its robust nature makes it compatible with the reaction conditions required for most common organic transformations. However, despite recent advances, 3 the number of currently available methodologies for the direct attachment of carbon chains bearing functional groups to the ferrocene remain very limited and can be classified into two general categories: a) initial Friedel-Crafts acylation followed by subsequent transformations of the resulting acylferrocene, 4 and b) initial formation of ferrocenyl lithium by treatment with alkyllithium reagents followed by coupling with a suitable carboelectrophile. 5 These classical methodologies have been successfully applied to the synthesis of many functionalized ferrocenes; however, these approaches also entail some limitations. Thus, in general, a multistep sequence is often required to install specific functionalities in remote positions. Moreover, these methodologies display a low functional group compatibility (particularly the second one, due to the high reactivity of ferrocenyl lithium).As expected, in general, Friedel-Crafts alkylation reactions of ferrocene do not represent a convenient synthetic method because mixtures of several alkylation products are formed. 6 On the other hand, the generation of electrophilic carbene species via transition-metal-catalyzed decomposition of -diazo carbonyl derivatives and their subsequent reactivity in addition and insertion reactions has become a powerful methodology in organic synthesis. 7 Surprisingly, in spite of the tremendous impact of gold catalysis in synthetic organic chemistry, 8 the use of gold complexes for the catalytic decomposition of -diazo carbonyl derivatives has been unexplored until recently. Indeed, in 2005 Nolan, Díaz-Requejo, Pérez et al reported the first gold-catalyzed decomposition of ethyl diazoacetate an...

Transition metal-catalyzed transformations of vinyldiazo compounds have become a versatile tool in organic synthesis. Although several transition metals have been investigated for this purpose, this field has been mainly dominated by dirhodium catalysts. Remarkable levels of chemo-, regio-, diastereo- and enantioselectivity have been reached in some of these rhodium-catalyzed transformations. In the last few years coinage metals have also emerged as useful catalysts in transformations involving vinyldiazo compounds. In some cases, highly efficient catalyst-dependent protocols arising from divergent mechanistic pathways have been reported. In this Personal Account, we aim to showcase recent advances in metal coinage catalyzed transformations of vinyldiazoacetates, an exciting field of research to which our group has actively contributed in the last few years.

Abstract:The reaction of vinylazides with alkenyldiazo compounds in the presence of [Cu(CH3CN)4][BF4] provided cyclopentene derivatives retaining the azide functionality. This process would involve a sequence comprising: 1) decomposition of the diazo component with generation of a copper alkenylcarbene species; 2) stepwise regioselective [3+2] cycloaddition; 3) allylic azide rearrangement. A broad range of substrates is compatible with this protocol. We have also shown that azide-containing cycloadducts can be efficiently converted to the corresponding amine and triazole derivatives.

A rhodium-catalyzed carbene transfer to alkynes is reported. Easily available enynones served as the carbene source replacing diazocompounds. The overall process involved a cyclization-cyclopropenation-ring enlargement sequence.

Coumarin and its derivatives have significantly attracted the attention of medicinal chemists and chemical biologists due to their huge range of biological, and in particular, pharmacological properties. Interesting families of coumarins have been found from marine sources, which has accelerated the drug discovery process by inspiring innovation or even by the identification of analogues with remarkable biological properties. The purpose of this review is to showcase the most interesting marine-derived coumarins from a medicinal chemistry point of view, as well as the novel and useful synthetic routes described to date to achieve these chemical structures. The references that compose this overview were collected from PubMed, Mendeley and SciFinder.

The reaction of ferrocene and ruthenocene with aryldiazo acetates in the presence of gold catalysts produced new functionalized metallocenes resulting from a C-H bond functionalization process. This process is believed to proceed through initial decomposition of the diazo component and formation of an electrophilic gold-carbene intermediate, which is subsequently involved in an electrophilic aromatic substitution. The gold-catalyzed functionalization of ruthenocene exhibited a broad scope and a notable functional-group tolerance. Interestingly, the functionalized ferrocene derivatives were found to react with molecular oxygen to yield α-aryl-α-ferrocenyl-α-hydroxyacetates. Adsorption on silica gel was found to be essential for this dioxygen activation/C(sp )-H bond functionalization sequence. The methodologies reported herein provide a simple and efficient approach to functionalized metallocene derivatives that are difficult to access through conventional organic functional group transformations.

Supporting information and the ORCID identification number(s) for the author(s) of this articlecan be found under: https://doi.