Patrick Pale

The organic chemistry of silver acetylides

Silver acetylides are among the oldest organometallics known; however, their applications in organic chemistry remained scarce until very recently. Indeed, several reactions involving silver salts as catalyst or silver acetylides have been reported in the past five years. The extreme mildness and very low basicity of these nucleophilic reagents nicely complement the behavior of other alkynyl metals, rendering them very useful in various transformations, especially in the synthesis of complex molecules. Silver acetylides are now seen as promising tools in organic chemistry. This critical review focuses on this emerging field, and, with emphasis on mechanistic aspects, cover the synthesis of silver acetylides, their applications in organic chemistry and reactions involving silver salts as catalysts where silver acetylides are probable intermediates.

Copper(I) Zeolites as Heterogeneous and Ligand‐Free Catalysts: [3+2] Cycloaddition of Azomethine Imines

Copper(I)-exchanged zeolites were used as heterogeneous ligand-free catalysts for [3+2] cycloaddition of azomethine ylides, which allows versatile, efficient, and highly regioselective synthesis of pyrazolone derivatives. These cheap and easy-to-prepare catalysts exhibit wide scope and compatibility with functional groups. They are very simple to use, easy to remove (by simple filtration), and recyclable (up to six times without loss of activity).

Mechanistic Studies and Improvement of Coinage Metal-Catalyzed Transformation of Alkynyloxiranes to Furans: An Alcohol Addition−Cyclization−Elimination Cascade

In the presence of alcohol Ag or Au salts or complexes catalyze the conversion of alkynyloxiranes to substituted furans. Both catalysts are effective, and a large furan diversity can be obtained in high yield with one or the other catalyst. Mechanistic studies revealed that a cascade pathway and not the sometimes reported direct intramolecular nucleophilic addition of oxirane oxygen atom to intermediate acetylene-metal pi-complex occurs. Under the defined conditions, the intermediate formation of epoxide opening products has been identified. Depending on the catalyst, one or both of the latter cyclized to dihydrofurans, and further elimination of the alcohol led to the corresponding furans. These results highlight the duality between oxophilicity and alkynophilicity of Ag or Au salts.

Silver assisted heterocyclization of acetylenic compounds

Abstract Silver assisted heterocyclization of acetylenic alcohols or acids provides an easy and mild access to α-methylene oxygenated heterocycles.

Silver(I)-Catalyzed Cascade: Direct Access to Furans from Alkynyloxiranes

Functionalized furans are conveniently formed by a new silver(I)-catalyzed reaction of alk-1-ynyl oxiranes in the presence of p-toluenesulfonic acid and methanol. Evidence supported a cascade mechanism.

Targeting the dimerization initiation site of HIV-1 RNA with aminoglycosides: from crystal to cell.

The kissing-loop complex that initiates dimerization of genomic RNA is crucial for Human Immunodeficiency Virus Type 1 (HIV-1) replication. We showed that owing to its strong similitude with the bacterial ribosomal A site it can be targeted by aminoglycosides. Here, we present its crystal structure in complex with neamine, ribostamycin, neomycin and lividomycin. These structures explain the specificity for 4,5-disubstituted 2-deoxystreptamine (DOS) derivatives and for subtype A and subtype F kissing-loop complexes, and provide a strong basis for rational drug design. As a consequence of the different topologies of the kissing-loop complex and the A site, these aminoglycosides establish more contacts with HIV-1 RNA than with 16S RNA. Together with biochemical experiments, they showed that while rings I, II and III confer binding specificity, rings IV and V are important for affinity. Binding of neomycin, paromomycin and lividomycin strongly stabilized the kissing-loop complex by bridging the two HIV-1 RNA molecules. Furthermore, in situ footprinting showed that the dimerization initiation site (DIS) of HIV-1 genomic RNA could be targeted by these aminoglycosides in infected cells and virions, demonstrating its accessibility.

Silver-Catalyzed Cyclization of Acetylenic Alcohols: Synthesis of Functionalized 2-Methylene-oxolanes

Silver salts which have a basic counter-ion are efficient catalysts for the regiospecific intramolecular addition of various acetylenic alcohols. Silver carbonate in aromatic solvent proved to be the best catalyst. Alkynols in which the two reacting parts of the molecule are relatively close together in space required only catalytic amounts of silver ion, while others cyclize readily with stoichiometric quantities. This heterocyclization reaction provides a mild and convenient access to 2-methylene-oxolanes or oxanes.

Gold(I)-catalyzed rearrangement of alkynyloxiranes: a mild access to divinyl ketones.

Acyloxylated divinyl ketones are conveniently formed by a new gold(I)-catalyzed rearrangement of (3-acyloxyprop-1-ynyl)oxiranes.

The first direct coupling of 1-trialkylsilyl-1-alkynes with vinyl triflates; a new access to enynes

Abstract 1-Trialkylsilyl-1-alkynes can be directly coupled with vinyl triflates in the presence of TBAF, 3H 2 O and a catalytic amount of AgI and Pd(PPh 3 ) 4 . Functionalized enynes can thus be obtained in good to excellent yields without prior deprotection of the alkyne.

Gold(I)-catalyzed cycloisomerization of β-alkynylpropiolactones to substituted α-pyrones.

Substituted α-pyrones were straightforwardly synthesized in good to excellent yields by a new gold(I)-catalyzed rearrangement of β-alkynylpropiolactones.