The Syntheses of new Camphorsulfonylated Ligands Derived from 2‐Amino‐2′‐Hydroxy‐1,1′‐Binaphthyl and Their Enantioselectivities in the Addition of Dialkylzinc Reagents to Aldehydes

Abstract

A series of new camphorsulfonylated ligands derived from chiral 2-amino-2'-hydroxy-1,1'-binaphthyl (NOBIN) and (+)-camphorsulfonic acid were synthesized by a short and simple synthetic sequence, and their enantioselective catalytic activities were assessed in the nucleophilic addition reaction of dialkylzinc reagents to aldehydes in the presence of titanium tetraisopropoxide. The most efficient ligand, N-hydroxycamphorsulfonylated (S)-NOBIN, gave (S)-addition products with good yields and up to 87% of ee value. The (1)H nuclear magnetic resonance (NMR) and (13)C NMR results of the titanium titration experiments on this ligand indicate that the most likely catalytic reactive species involved in this catalytic asymmetric addition is a bimetallic titanium complex. A possible catalytic reaction mechanism is proposed.

Highly Efficient Asymmetric Additions of Diethylzinc to Aldehydes Triply Activated by Chiral Phosphoramide‐Zn(II) Complexes Derived From Cinchona Alkaloids

“…[4][5][6][7][8][9] The design of catalysts for the asymmetric additions of organozinc reagents to aldehydes and ketones to give chiral alcohols has been the focus of intensive research and a large number of diverse catalysts have been developed. [10][11][12][13][14][15][16][17][18][19] Naturally occurring cinchona alkaloids and their derivatives have been widely used in a variety of asymmetric reactions with high catalytic efficiencies, [20][21][22][23][24][25][26][27][28] but they are less efficient [29][30][31][32] in the asymmetric organozinc addition reactions compared to other chiral ligands such as Walsh's HOCSAC [33][34][35][36][37][38][39] (a bis (hydroxycamphorsulfonamide) ligand derived from (R, R)-1,2-cyclohexyl diamine) and DAIB [40][41][42][43][44][45] (3-exo-dimethylaminoisoborneol). Herein, we report the development of a highly efficient trifunctional chiral phosphoramide-Zn(II) complex which can activate the asymmetric additions of diethylzinc with aldehydes to give desired alcohol products with excellent yields and enantiomeric excess (ee) values up...…”

“…Concerning this subject, the asymmetric additions of organometallic reagents to carbonyl groups have been extensively studied . The design of catalysts for the asymmetric additions of organozinc reagents to aldehydes and ketones to give chiral alcohols has been the focus of intensive research and a large number of diverse catalysts have been developed . Naturally occurring cinchona alkaloids and their derivatives have been widely used in a variety of asymmetric reactions with high catalytic efficiencies, but they are less efficient in the asymmetric organozinc addition reactions compared to other chiral ligands such as Walsh's HOCSAC (a bis (hydroxycamphorsulfonamide) ligand derived from ( R , R )‐1,2‐cyclohexyl diamine) and DAIB (3‐exo‐dimethylaminoisoborneol).…”