Cyclisation Reactions of Phenolic Ethers

Intramolecular cyclisations of phenolic ether derivatives often aided by an activating group at the 4-position have been used to obtain a variety of heterocycles. 

Dihenyl ether in the presence of palladous and cuprous acetates in acetic acid and oxygen (300psig) at 140°C was oxidatively converted to dibenzofuran in high yield after heating for 3 hours (ref. 143). 

The reaction of 5-methoxy-1-naphthol with cyclohexylamine (Imole) and aqueous formalin (2moles) at ambient temperature gave 3-cyclohexyl- 

The fluorophenoxyl ether, methyl 2-benzoylamino-4-(4-fluorophenoxy)-2-methoxybutyrate with methanesulphonic acid (or boron trifluoride etherate in chloroform) at 0°C followed by warming to ambient temperature gave the pyran, methyl 4-benzoylamino-2,3-dihydro-6-f luoro-4H-benzopyran-4- 

The loss of a methoxyl group from the ring of an aromatic ether occurred in the regioselective photocyclisation of 2-methoxystilbene to phenanthrene in a mixture of sulphuric acid and tert-butanol with elimination of methanol (ref. 146). Phenanthrenes are also obtained by treatment of 2,2 -dialkoxystilbenes with low valent titanium. The same pathway is involved as in the reduction of 2-methoxyacetophenone to 9,10-dimethylphenanthrene referred to earlier (ref.99). 

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