Enantioselective oxidative coupling

The enantioselective oxidative coupling of 2-naphthol itself was achieved by the aerobic oxidative reaction catalyzed by the photoactivated chiral ruthenium(II)-salen complex 73. 2 it reported that the (/ ,/ )-chloronitrosyl(salen)ruthenium complex [(/ ,/ )-(NO)Ru(II)salen complex] effectively catalyzed the aerobic oxidation of racemic secondary alcohols in a kinetic resolution manner under visible-light irradiation. The reaction mechanism is not fully understood although the electron transfer process should be involved. The solution of 2-naphthol was stirred in air under irradiation by a halogen lamp at 25°C for 24 h to afford BINOL 66 as the sole product. The screening of various chiral diamines and binaphthyl chirality revealed that the binaphthyl unit influences the enantioselection in this coupling reaction. The combination of (/f,f )-cyclohexanediamine and the (R)-binaphthyl unit was found to construct the most matched hgand to obtain the optically active BINOL 66 in 65% ee. 

ENANTIOSELECTIVE OXIDATIVE COUPLING OF 2-NAPHTHOLS CATALYZED BY A NOVEL CHIRAL VANADIUM COMPLEX... 

Recently, Chi and co-workers reported a highly enantioselective oxidative coupling reaction of aldehydes 14 with tertiary amines 13 under cooperative... 

Scheme 9.10 Catalytic and enantioselective oxidative coupling of 2-naphthol derivatives using vanadium(iv) complexes, independently reported by Chen and Uang. "...

Scheme 9.11 Enantioselective oxidative coupling of 2-naphthols using a-ketopinic acid and an (S)-amino acid-derived vanadium(iv) catalyst, reported ly Chen. ...

Scheme 9.17 Enantioselective oxidative coupling of 2-anthracenol (39) and 9-phe-nanthrol (41) catalysed by a chiral dinuclear vanadium complex, reported by Sasai and Takizawa. ...

Copper(II)-amine complexes are widely used and very effective phenolic oxidative coupling reagents. Since the reaction proceeds within the copper coordinative sphere, chiral amine ligand does induce the enantioselective oxidative couplings of phenols such as 2-naphthol [39-41], or 9-phenanthrol [42,43] to form respective atropisomeric... 

Apart from copper-based complexes, Katsuki s group reported that rathenium complex of chiral salen 648 readily effects the enantioselective oxidative couplings of 2-naphthols in air under very mild reaction conditions and irradiation of visible light [44], In this fashion, 6-bromo-2-naphthol (649) was converted to binaphthol 650 in 82% yield and 68% e.e. [44], Scheme 22. 

In the same year, Chi et al. developed an enantioselective oxidative coupling of tertiary amines with ahphatic aldehydes by combination of copper catalysis and aminocatalysis (Scheme 2.6) [31]. Both A -Aryl tetrohydroisoquinolines and simple A-Aryl tertiary amines can undergo this enantioselective alkylation reaction. Soon afterwards, organocatalytic enantioselective CDC reaction of ethers with aliphatic aldehydes [32] and Cu-catalyzed asymmetric CDC reaction of iV-carbamoyl tetrahydroisoquinohnes with terminal alkynes [33] were reported. 

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