Enantioselective synthesis of α-aryl α-hydrazino phosphonates.

Catalysts generated by the combination of pyridine-hydrazone ,-ligands and Pd(TFA) have been applied to the addition of arylboronic acids to formylphosphonate-derived hydrazones, yielding α-aryl α-hydrazino phosphonates in excellent enantioselectivities (96 → 99% ee). Subsequent removal of the benzyloxycarbonyl (Cbz) -protecting group afforded key building blocks en route to appealing artificial peptides, herbicides and antitumoral derivatives. Experimental and computational data support a stereochemical model based on aryl-palladium intermediates in which the phosphono hydrazone coordinates in its -configuration, maximizing the interactions between the substrate and the pyridine-hydrazone ligand.

Asymmetric cross-aldol reactions of α-keto hydrazones and α,β-unsaturated γ-keto hydrazones with trifluoromethyl ketones.

α-Keto hydrazones and α,β-unsaturated γ-keto hydrazones are suitable pro-nucleophiles for asymmetric cross-aldol reactions with trifluoromethyl ketones aza-di(tri)enamine-type intermediates. A quinidine-derived primary amine catalyst affords tertiary trifluoromethylated alcohols in good-to-excellent yields and high enantioselectivities. Subsequent transformations of hydrazono moieties yield appealing fluorinated carboxylic acids, 1,4-dicarbonyls and γ-keto acids.

Catalytic enantioselective synthesis of α-aryl α-hydrazino esters and amides.

Catalysts generated by combinations of Pd(TFA) and pyridine-hydrazone ligands have allowed the asymmetric 1,2-addition of aryl boronic acids to N-carbamoyl (Cbz and Fmoc) protected glyoxylate-derived hydrazones, yielding α-aryl α-hydrazino esters/amides in high enantioselectivities. Subsequent removal of the carbamoyl moiety affords key building blocks en route to hydrazinopeptides, N-aminopeptides and peptidomimetics thereof.