Enantioselective synthesis of binaphthyl polymers using chiral asymmetric phenolic coupling catalysts: oxidative coupling and tandem glaser/oxidative coupling.
A series of functionalized and optically active polybinaphthyls have been synthesized from achiral substrates by asymmetric oxidative phenolic coupling using a chiral 1,5-diaza-cis-decalin copper catalyst. In most cases, a copper tetrafluoroborate catalyst was found to be superior to the copper iodide catalyst, as ortho-iodination of the substrates could be prevented. Three methods for the formation of chiral polymers are described. In the first method, two 2-naphthols linked together at C-6 are subjected to the optimized asymmetric oxidative phenolic coupling conditions to form chiral polynaphthyls. A combination of NMR and HPLC measurements secured the selectivity of the asymmetric coupling. In the second method, substrates containing only one naphthalene were utilized. By incorporating a 2-naphthol and a terminal alkyne, the chiral copper catalysts effect both Glaser-Hay coupling of the alkyne and oxidative asymmetric coupling of the 2-naphthol with remarkable chemoselectivity. The relative reaction rates of various moieties with the chiral catalysts follows the order: benzyl cyanides > aryl alkynes > electron-rich 2-naphthols > electron-deficient 2-naphthols > alkyl alkynes. Because of high chemoselectivity, this approach is useful for the organized assembly of multifunctional substrates in a single operation. In all cases, no cross-coupling is observed between the alkyne and the 2-naphthol. This approach was thus applied to a set of highly functionalized precursors. In this third case, the biaryl coupling was performed first and a Glaser-Hay coupling was performed in a separate step to generate a highly functionalized polymer. In some cases, the resultant chiral polymers exhibit very large optical rotations.
Morgan
Barbara J
BJ
Department of Chemistry, Roy and Diana Vagelos Laboratories, University of Pennsylvania, Philadelphia, PA 19104, USA.
Xie
Xu
X
Phuan
Puay-Wah
PW
Kozlowski
Marisa C
MC
D002384:Catalysis; D002625:Chemistry, Organic / Q000379:methods*; D002626:Chemistry, Pharmaceutical / Q000379:methods*; D019281:Dimerization; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D009284:Naphthols / Q000737:chemistry; D010100:Oxygen / Q000737:chemistry*; D019800:Phenol; D010636:Phenols / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D013237:Stereoisomerism
D009284:Naphthols; D010636:Phenols; D011108:Polymers; D019800:Phenol; D010100:Oxygen