1,10-phenanthroline 4,7-dimethoxy

The first synthesis of a derivative of 2,8-phenanthroline was reported by Merz, Weidlich, and Fink13 in 1964. They prepared 5,6-dimethoxy-2,8-phenanthroline (34) (isolated as the dipicrate) in very low yield by conducting a double Pomeranz-Fritsch isoquinoline synthesis on 4,5-dimethoxyisophthalaldehyde. The parent compound was prepared 2 years later12 in 25-35% yield, along with 1,9-phenanthroline (4%), by the photocyclization of trans-1 (3-pyridyl)-2-(4-pyridyl)ethylene in benzene. This reaction was used by Hiinig and his colleagues15 to prepare an N,N -dimethyl diquaternary salt of 2,8-phenanthroline by methylating the crude product from the irradiation reaction. 

Continuous irradiation at 400 nm of a solution of [Ru(bipy)3p and PhCHjS in dry oxygen-free MeCN has been observed to give a quantitative yield of [Ru(bipy)3]. In the presence of BU4NQO4, this same system can act as a two-compartment cell if coupled with the reduction of a weak electron-acceptor such as 9,10-anthraquinone, 1,3-dinitrobenzene, or 2,6-dimethoxy-p-benzoquinone. The temperature dependence of the reductive quenching of electronically excited [RuLj] (where L = bipy or 4,7-dimethyl-l,10-phenanthroline) by aromatic amines in MeOH has been studied and fitted by theoretical expressions. Activation parameters for a series of quenching reac-... 

Formation of the quaternary carbon center was also carried out by the reaction of ethyl 4-oxo-cycloheX"2-ene carboxylate with 3,4-dimethoxyphe-nyllead triacetate (403) in chloroform containing 1,10-phenanthroline at 55°C to give ethyl 4-[(3,4-dimethoxy)phenyl]-4-oxocyclohex-2-ene carboxylate (404) in 57% yield. Thus, 4-[(3,4-dimethoxy)phenyl]-4-oxo-cydlohex-... 

Dimethoxy-1,10-phenanthroline is a superior ligand for the arylation and heteroarylation of imidazoles using a cuprous oxide catalyst. 

A stoichiometric quantity of 1,10-phenanthroline (L13) was the first ligand used for copper-catalyzed arylation of imidazole with aryl iodides (Table 9.4, entry 1) [18]. As an ejctension of this methodology, Cu2O/4,7-dimethoxy-l,10-phenanthroline (LI4) was found to be more effective, the coupling reaction occur-ing at 80-110 °C in the presence of CS2CO3 and using n-PrCN as a solvent (entry 2 ) [19, 20]. 

The group of Buchwald has developed a copper/4,7-dimethoxy-l,10-phenanthroline system enabling the N-arylation of a various imidazole derivatives (Table 1, entry 5 L9, R = OMe) [51, 52]. Note that no general useful palladium catalytic systems have been described for this type of coupling. The use of a solid-liquid phase transfer catalyst, the polyethylene glycol (PEG), and a 2,000 times turnover achieved from iodobenzene and imidazole are interesting features of this procedure. 

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