Synthesis of Aromatic Compounds by Kenneth E. Maly

Author:Kenneth E. Maly
Language: eng
Format: epub
Publisher: De Gruyter
Published: 2022-05-18T18:33:38.826000+00:00

Figure 6.80: Stereoselective synthesis of (S)-(+)-gossypol [135].

Chiral auxiliaries have also been used to prepare axially chiral biaryls via Suzuki coupling. For example, Broutin and Colobert used a chiral β-hydroxy sulfoxide auxiliary appended to aryl halides to achieve diastereoselective biaryl formation (Figure 6.81) [136].

Figure 6.81: Diastereoselective Suzuki coupling using a β-hydroxy sulfoxide auxiliary [136].

Oxidative coupling reactions described in Section 6.2.3 can in some cases be carried out asymmetrically in the presence of metal salts and chiral ligands. For example, the oxidative coupling of 2-naphthol to prepare enantiomerically enriched 2,2ʹ-BINOL has been reported using CuCl2 and an excess of (S)-amphetamine (Figure 6.82) [137]. This reaction achieved a good yield and a 96% ee, with the high enantioselectivity being explained by a dynamic kinetic resolution. In a related example, a cross-coupling of 2-naphthol with the methyl ester of 3-hydroxy-2-naphthoic acid using CuCl2 and sparteine as the chiral ligand proceeded in good yield, but with only a 41% ee (Figure 6.82) [138]. These reactions have the disadvantage of using stoichiometric amounts of copper and an excess of the chiral ligand.

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