New adaptive chiral thiophene ligands for copper‐catalyzed asymmetric Henry reaction

Abstract

A new type of adaptive chiral thiophene-based ligands 3 has been designed and developed. The synthetic flexibility of the thienyl ring allowed for the preparation of polydendate C2-symmetric ligands in good yields, carrying simultaneously "hard" as well as "soft" coordinating atoms (i.e., N, S). The coordination attitude of 3 was then tested in the enantioselective base-free Cu(OAc)(2)-catalyzed addition of nitromethane to aromatic aldehydes, leading to the corresponding beta-nitro alcohols in excellent yields and enantiomeric excesses up to 86%.

Asymmetric Henry reactions of aldehydes with various nitroalkanes catalyzed by copper(II) complexes of novel chiral N‐monoalkyl cyclohexane‐1,2‐diamines

“…With i-PrOH as the solvent (entry 13), the nitroalcohol was isolated in 90% ee. A series of bases were also tested for the Henry reaction of benzaldehyde with nitromethane (entries [18][19][20]. Et 3 N turned out to be the best choice, with 91% ee and 99% yield (entry 18), while i-Pr 2 NEt induced almost the same result (entry 13).…”

“…This positioning of the reactants seems the most favorable orientation, taking into account steric and electronic considerations. [15] Subsequently, more secondary diamine-copper complexes with bulky aromatic substituents [16][17][18][19][20][21][22][23] (e.g. 2a, [16] Fig.…”

Synthesis of novel thiophene‐based chiral ligands and their application in asymmetric Henry reaction

“…Although many chiral ligands derived from amino alcohols have found applications as catalysts in asymmetric reactions, only a few thiophene‐based ligands have been employed in the Henry reaction or other asymmetric reactions . Bandini et al .…”

“…Bandini et al . [ a ] reported a new type of C 2 ‐symmetric diamino ligand ( 4 ), bearing oligothienyl groups, and their catalytic activity in the asymmetric Henry reaction (Scheme ).…”

Solvent‐free synthesis of chiral Schiff‐base ligands based on ferrocene under microwave irradiation and application to enantioselective nitroaldol (Henry) reaction

“…Chiral ligands based on ferrocene have been widely used in asymmetric catalysis of various reactions such as asymmetric allylation,30 enantioselective diketene addition to bezaldehyde,31 enantioselective addition of diethylzinc to N ‐diphenylphosphinoylimines,32 enantioselective addition of diethylzinc to aldehydes,33, 34 hydroformylation, allylic substitution, organometallic cross‐coupling,35 catalytic enantioselective reduction of prochiral ketones,36 hydrostlylation of olefins,37 and enantioselective hydroboration of 2,5‐dihydrofuran 38. Ferrocene offers a variety of properties when introduced to ligands due to appropriate rigidity, planer chirality, steric bulkiness and stability.…”