Copper Complex of Aminoisoborneol Schiff Base Cu₂(SBAIB‐d)₂: An Efficient Catalyst for Direct Catalytic Asymmetric Nitroaldol (Henry) Reaction

Abstract

A new bifunctional copper complex of the aminoisoborneol Schiff base -Cu 2 A C H T U N G T R E N N U N G (SBAIB-d) 2 -has been developed for the effective direct catalytic asymmetric Henry reaction. One mol% of this catalyst produces the expected Henry products in high yields (up to 99%) with excellent enantioselectivities (up to 98% ee). The utility of the present catalyst was also extended to the Henry reaction with nitroethane and 1-nitropropane that furnished the corresponding products in moderate to high yields (up to 99%) with moderate to high enantioselectivities of syn (up to 98% ee) and anti (up to 98% ee) diastereomers. The highlights of this catalytic system are easy manipulation, air and moisture tolerance, the need for 1 mol% of an easily synthesizable catalyst and the high enantioselectivities achieved for a wide range of substrates.

Solvent-Dependent Enantiodivergence inanti-Selective Catalytic Asymmetric Nitroaldol Reactions

“…The nitroaldol reaction is a synthetically advantageous carbon–carbon bond-forming reaction that produces vic -nitroalkanols from readily available starting materials under proton transfer conditions. , In particular, catalytic asymmetric variants offer streamlined access to chiral building blocks frequently used for synthesizing pharmaceuticals. We developed the first catalytic asymmetric nitroaldol reaction with nitromethane using heterobimetallic complex LLB (La-Li 3 -tris­(1,1′-bi-2-naphthoxide)) as an asymmetric catalyst in 1992, which later also proved effective for syn -selective and enantioselective reactions. , To achieve anti -diastereoselectivity, we disclosed a distinct Nd/Na heterobimetallic complex utilizing a diamide ligand prepared from α-amino acids. − The defining characteristic of the Nd/Na heterobimetallic catalyst is its heterogeneity, which expands the practical applicability of this asymmetric catalyst in continuous-flow reaction platforms. At the initial disclosure, NdO 1/5 (O i Pr) 13/5 , an expensive Nd salt with limited availability, was indispensable as the basic Nd source for catalyst preparation.…”

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

“…Anti ‐selective reaction in basic conditions is reported by Ooi and co‐workers and later reported by other researchers . Salen ligands are one of the most privileged ligands for the asymmetric catalysis, and Cu (II) complexes of salen and salan ligands were largely used for nitro‐aldol reaction and efficiently active at mild reaction conditions . ( S )‐Proline‐based single chiral center salalen and salan ligands were first reported by Katsuki and co‐workers for the asymmetric epoxidation of non‐functionalised alkenes .…”

“…[53][54][55][56][57][58][59][60][61] Salen ligands are one of the most privileged ligands for the asymmetric catalysis, and Cu (II) complexes of salen and salan ligands were largely used for nitro-aldol reaction and efficiently active at mild reaction conditions. [62][63][64][65][66][67][68][69][70][71][72] (S)-Proline-based single chiral center salalen and salan ligands were first reported by Katsuki and co-workers for the asymmetric epoxidation of non-functionalised alkenes. 73 These ligands were also used by Kol and co-workers for polymerisation of α-olefins and stereoselective polymerization of lactide.…”

Cu (II)-Catalyzed Asymmetric Henry Reaction with a Novel C1-Symmetric Aminopinane-Derived Ligand

“…Since then, extensive collection of organocatalysts [ 12 , 13 , 14 , 15 ] and transition metal based catalytic systems, i.e. , Zn [ 4 , 16 ], Co [ 17 , 18 ] Cr [ 19 , 20 ], Cu [ 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 ], have been developed with variable success. The majority of these metal-based catalysts reported involved the use of copper complexes with either a bi- or polydentate aza-containing chiral ligand (such as BOX-type [ 21 , 22 , 23 ], diamines [ 7 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 ...…”