Pierre Garcia

Gold‐Catalyzed Cross‐Couplings: New Opportunities for CC Bond Formation

Cross‐coupling is a powerful tool for the rapid construction of highly valuable compounds. In this area of chemical transformations, new catalysts have recently emerged. Combining both a π‐Lewis acid character and interesting redox properties, gold has proven to be an expedient choice for mediating such transformations. Recent developments in the use of gold to mediate a variety of CC coupling reactions are summarized, including Suzuki and Sonogashira cross‐coupling reactions, as well as the development of tandem processes and the combination of gold with palladium to enable CC bond formation via transmetalation.

Regioselective cobalt-catalyzed formation of bicyclic 3- and 4-aminopyridines.

Bimolecular cobalt-catalyzed [2 + 2 + 2] cycloadditions between yne-ynamides and nitriles afford bicyclic 3- or 4-aminopyridines in up to 100% yield. The high regioselectivity observed depends on the substitution pattern at the starting ynamide. Aminopyridines bearing TMS and Ts groups are efficiently deprotected in an orthogonal fashion.

Synthesis of aminopyridines and aminopyridones by cobalt-catalyzed [2+2+2] cycloadditions involving yne-ynamides: scope, limitations, and mechanistic insights.

An in-depth study of the cobalt-catalyzed [2+2+2] cycloaddition between yne-ynamides and nitriles to afford aminopyridines has been carried out. About 30 nitriles exhibiting a broad range of steric demand and electronic properties have been evaluated, some of which open new perspectives in metal-catalyzed arene formation. In particular, the use of [CpCo(CO)(dmfu)] (dmfu=dimethyl fumarate) as a precatalyst made possible the incorporation of electron-deficient nitriles into the pyridine core. Modification of the substitution pattern at the yne-ynamide allows the regioselectivity to be switched toward 3- or 4-aminopyridines. Application of this synthetic methodology to the construction of the aminopyridone framework using a yne-ynamide and an isocyanate was also briefly examined. DFT computations suggest that 3-aminopyridines are formed by formal [4+2] cycloaddition between the nitrile and the intermediate cobaltacyclopentadiene, whereas 4-aminopyridines arise from an insertion pathway.

Silver-Catalyzed Cycloisomerization of 1,n-Allenynamides

A variety of allenynamides can undergo cycloisomerization reactions in the presence of silver triflate thus leading to the formation of N-containing heterocycles incorporating cross-conjugated trienes. Access to new dienic 4-piperidinone and azepane motifs was achieved. An extension to one-pot tandem sequences involving silver-catalyzed cycloisomerization/Diels-Alder reaction was also examined.

Combination of gold catalysis and Selectfluor for the synthesis of fluorinated nitrogen heterocycles

Summary We herein report the synthesis of 3-fluoro-2-methylene-pyrrolidine (3a) and -piperidine (3b) from 1,5- and 1,6-aminoalkynes, respectively, using a combination of a gold-catalyzed hydroamination reaction followed by electrophilic trapping of an intermediate cyclic enamine by Selectfluor. Careful attention was paid to the elucidation of the mechanism and Selectfluor was suggested to play the double role of promoting the oxidation of gold(I) to a gold(III) active species and also the electrophilic fluorination of the enamine intermediates.

Solar Field Efficiency and Electricity Generation Estimations for a Hybrid Solar Gas Turbine Project in France

The production of electricity with gas turbine and solar energy project aims to install at the Themis site (Targasonne, France) a prototype of hybrid solar/fossil gas-turbine system for electricity generation. The system features a 3800 kW th pressurized air solar receiver combined with a fossil backup feeding a recuperated 1400 kW e Turbomeca gas turbine with an external combustion chamber.

Identification of a novel subfamily of bacterial AAT-fold basic amino acid decarboxylases and functional characterization of its first representative: Pseudomonas aeruginosa LdcA

Polyamines are small amino-acid derived polycations capable of binding negatively charged macromolecules. Bacterial polyamines are structurally and functionally diverse, and are mainly produced biosynthetically by PLP-dependent amino acid decarboxylases referred to as LAOdcs (Lysine-Arginine-Ornithine decarboxylases). In a phylogenetically limited group of bacteria, LAOdcs are also induced in response to acid stress. Here, we performed an exhaustive phylogenetic analysis of the AAT-fold LAOdcs which showcased the ancestral nature of their short forms in Cyanobacteria and Firmicutes, and emergence of distinct subfamilies of long LAOdcs in Proteobacteria. We identified a novel subfamily of lysine decarboxylases, LdcA, ancestral in Betaproteobacteria and Pseudomortadaceae {Gammaproteobacteria). We analyzed the expression of LdcA from Pseudomonas aeruginosa, and uncovered its role, intimately linked to cadaverine production, in promoting growth and reducing persistence of this multidrug resistant human pathogen during carbenicillin treatment. Finally, we documented a certain redundancy in the function of the three main polyamines - cadaverine, putrescine and spermidine - in P. aeruginosa by demonstrating the link between their intracellular level, as well as the capacity of putrescine and spermidine to complement the growth phenotype of the IdcA mutant.