Asymmetric Henry reaction catalyzed by chiral Cu(II) salalen and salan complexes derived from ( S )-proline

Synthesis and structures of copper complexes bearing unsymmetric derivatives of (R,R)‐1,2‐diaminocyclohexane: An efficient catalyst for asymmetric Henry reaction

“…The reaction catalyzed by these catalytic species resulted in β ‐nitroalcohols with an ( S )‐conformation at the stereogenic center, which is attributed to the favorable orientation of the phenyl group of the aldehyde and aromatic moieties of the ligand architecture . The stereo‐chemical outcomes of the Henry reaction with diacetato Cu (II) complexes are in accord with the accepted model . In this model, a pentavalent copper species is generated for maximum activation, which should attach to the aldehyde in the equatorial plane; nitronate ion, deprotonated by i Pr 2 NEt, should coordinate at the axial location.…”

Synthesis of chiral salalen ligands and their in‐situ generated Cu‐complexes for asymmetric Henry reaction

“…Yield of the product 7 was found to be better in case of ligand 4e (R 1 = H and R 2 = H), but when bulky and electron donating group was attached to imine contained phenyl ring, yield of product 7 was decreased ( Table 1, In our recent report we have used ligand 4g (R 1 = -C (CH 3 ) 3 ) and product was obtained in a 66% ee (Table 1, entry 7). 79 Bulkiness of substituents R 1 = -C (CH 3 ) 2 Ph and R 2 = -C (CH 3 ) 3 in the ligands 4c also gave the product in 66% ee ( Table 1, entry 3 and 7). Enantiomeric excess of nitroaldol product was better in case of ligand 4b (R 1 = CH 3 , Table 1, entry 2) compared with other ligand (4a, 4c, 4d, 4f, and 4g) bearing bulky groups (Table 1, entries 1, 3, 4, 6, and 7).…”

“…Yield of the product 7 was found to be better in case of ligand 4e (R 1 = H and R 2 = H), but when bulky and electron donating group was attached to imine contained phenyl ring, yield of product 7 was decreased (Table , entries 2, 3, 4, 6, and 7). In our recent report we have used ligand 4g (R 1 = ‐C (CH 3 ) 3 ) and product was obtained in a 66% ee (Table , entry 7) . Bulkiness of substituents R 1 = ―C (CH 3 ) 2 Ph and R 2 = ―C (CH 3 ) 3 in the ligands 4c also gave the product in 66% ee (Table , entry 3 and 7).…”

“…Enantiomeric excess of nitroaldol product was better in case of ligand 4b (R 1 = CH 3 , Table , entry 2) compared with other ligand ( 4a , 4c , 4d , 4f , and 4g ) bearing bulky groups (Table 1, entries 1, 3, 4, 6, and 7). Product was obtained with ( S )‐absolute configuration which was determined by comparing the optical rotation of literature reports …”

“…These ligands were also used by Kol and co‐workers for polymerisation of α‐olefins and stereoselective polymerization of lactide . We have already reported Mn (III) and Cu (II) salalen and salan complexes of ligands derived from ( S )‐proline and derivatives of salicyaldehyde for asymmetric Strecker and Henry reactions . Herein, we wish to report the synthesis of salalen ligands and their in situ generated Cu (II) salalen complexes for diastereo‐ and enantioselective nitro‐aldol reaction.…”