Claudia Lalli

Highly enantioselective electrophilic α-bromination of enecarbamates: chiral phosphoric acid and calcium phosphate salt catalysts.

Metal-free chiral phosphoric acids and chiral calcium phosphates both catalyze highly enantio- and diastereoselective electrophilic α-bromination of enecarbamates to provide an atom-economical synthesis of enantioenriched vicinal haloamines. Either enantiomer can be formed in good yield with excellent diastereo- and enantioselectivity simply by switching the catalyst from a phosphoric acid to its calcium salt.

Exploiting the Divergent Reactivity of α‐Isocyanoacetate: Multicomponent Synthesis of 5‐Alkoxyoxazoles and Related Heterocycles

A novel multicomponent synthesis of 5-alkoxyoxazoles, based on a new reactivity profile of α-isocyanoacetates, is described. Thus, simply heating a solution of amine, aldehyde, and α-(EWG-phenyl)-α-isocyanoacetate or α-(4-pyridyl)-α-isocyanoacetate (EWG=electron-withdrawing group) in toluene provided 5-alkoxyoxazoles in good to excellent yields. Reaction of the 5-alkoxyoxazoles with various α,β-unsaturated acyl chlorides led to the formation of epoxytetrahydropyrrolo[3,4-b]pyridin-5-ones by a domino N-acylation/Diels-Alder cycloaddition sequence. Subsequent fragmentation under basic conditions provided 6,7-dihydro-5H-pyrrolo[3,4-b]pyridin-5-ones. A four-component synthesis of the pyridin-5-one compounds, without isolation of the 5-alkoxyoxazole, was subsequently developed.

Chiral Calcium Organophosphate-Catalyzed Enantioselective Electrophilic Amination of Enamides

Highly enantioselective direct amination of enamides catalyzed by chiral nonracemic calcium bis(phosphate) complex 3g afforded optically active 1,2-hydrazinoimines 4. Following a subsequent in situ hydrolysis or reduction, 2-hydrazinoketones 5 or syn-1,2-disubstituted 1,2-diamines 6 were obtained in high yields and excellent enantiomeric excess.

Chiral Calcium–BINOL Phosphate Catalyzed Diastereo- and Enantioselective Synthesis of syn-1,2-Disubstituted 1,2-Diamines: Scope and Mechanistic Studies

A highly enantioselective, chiral, Lewis acid calcium-bis(phosphate) complex, Ca[3 a]n, which catalyzes the electrophilic amination of enamides with azodicarboxylate derivatives 2 to provide versatile chiral 1,2-hydrazinoimines 4 is disclosed. The reaction gives an easy entry to optically active syn-1,2-disubstituted 1,2-diamines 6 in high yields with excellent enantioselectivities, after a one-pot reduction of the intermediate 1,2-hydrazinoimines 4. The geometry and nature of the N-substituent of the enamide affect dramatically both the reactivity and the enantioselectivity. Although the calcium-bis(phosphate) complex was a uniquely effective catalyst, the exact nature of the active catalytic species remains unclear. NMR spectroscopy and MS analysis of the various calcium complexes Ca[3]n reveals that the catalysts exist in various oligomer forms. The present mechanistic study, which includes nonlinear effects and kinetic measurements, constitutes a first step in understanding these calcium-bis(phosphate) complex catalysts. DFT calculations were carried out to explore the mechanism and the origin of the enantioselectivity with the Ca[3]n catalysts.

Synergistic Effect of the TiCl4/p-TsOH Promoter System on the Aza-Prins Cyclization

A novel aza-Prins cyclization promoted by a synergistic combination between a Lewis acid and a Brønsted acid to efficiently afford piperidines is described. Contrary to what has been previously reported in the literature, the generality of the reaction employing N-alkyl, N-aryl, and nonprotected homoallylamines has been demonstrated. The reaction is highly diastereoselective depending on the homoallylic amine used, N-PMP homoallyl amine leading preferentially to the trans diastereomer, and free homoallylamine affording the deprotected piperidine as single cis diastereomer.

One-pot sequential Ti-/Cu-catalysis for tandem amidation/Ullmann-type cyclization: synthesis of model benzodiazepine(di)ones promoted by microwave irradiation

The application of sequential Ti-/Cu-catalysis in the model one-pot synthesis of benzodiazepine(di)ones promoted by microwave irradiation demonstrates the expediency of dual catalysis in coupling-cyclization methods useful for diversity-oriented synthesis.

Enantioselective Brønsted Acid Catalysis as a Tool for the Synthesis of Natural Products and Pharmaceuticals

Synthesis of biologically active molecules (whether at laboratory or industrial scale) remains a highly appealing area of modern organic chemistry. Nowadays, the need to access original bioactive scaffolds goes together with the desire to improve synthetic efficiency, while reducing the environmental footprint of chemical activities. Long neglected in the field of total synthesis, enantioselective organocatalysis has recently emerged as an environmentally friendly and indispensable tool for the construction of relevant bioactive molecules. Notably, enantioselective Brønsted acid catalysis has offered new opportunities in terms of both retrosynthetic disconnections and controlling stereoselectivity. The present report attempts to provide an overview of enantioselective total or formal syntheses designed around Brønsted acid-catalyzed transformations. To demonstrate the versatility of the reactions promoted and the diversity of the accessible motifs, this Minireview draws a systematic parallel between methods and retrosynthetic analysis. The manuscript is organized according to the main reaction types and the nature of newly-formed bonds.

Depsides: Lichen Metabolites Active against Hepatitis C Virus

A thorough phytochemical study of Stereocaulon evolutum was conducted, for the isolation of structurally related atranorin derivatives. Indeed, pilot experiments suggested that atranorin (1), the main metabolite of this lichen, would interfere with the lifecycle of hepatitis C virus (HCV). Eight compounds, including one reported for the first time (2), were isolated and characterized. Two analogs (5, 6) were also synthesized, to enlarge the panel of atranorin-related structures. Most of these compounds were active against HCV, with a half-maximal inhibitory concentration of about 10 to 70 µM, with depsides more potent than monoaromatic phenols. The most effective inhibitors (1, 5 and 6) were then added at different steps of the HCV lifecycle. Interestingly, atranorin (1), bearing an aldehyde function at C-3, inhibited only viral entry, whereas the synthetic compounds 5 and 6, bearing a hydroxymethyl and a methyl function, respectively, at C-3 interfered with viral replication.