Reduction of anisole

Scheme 158 Mercury-catalyzed Birch reduction of anisole.

The Birch-type electrochemical reduction (460) (461) has been shown to proceed through the action of tetra-butylammonium amalgam in the steps (460)— (462)— (463), in contrast to a direct electron transfer from the electrode to the aromatics (Scheme 158) [548]. The preparative-scale reduction of anisole, of l,2,3,4-tetrahydro-6-methoxynaphthalene, and several aromatic steroids is performed in an H20-Bu4N0H-(Hg) system. The unique aspect of the reduction is the proposed formation of a tetrabutylammo-nium amalgam complex, BU4N (Hg) (465)... 

In the actual synthesis, Birch reduction of anisole (10, R = CH3) affords the... 

As a further illustration of the regiochemistry associated with the Birch reduction of anisole derivatives, 11 p-acetoxy-O-methylestrone [274] offers an interesting case. 

The Birch reduction of anisole, followed by reaction with acid, provides a... 

Formation of Cyclohexenones. Hydrolysis of the initial enol ether (vinyl ether) formed from Birch reduction of anisole or substituted anisoles under mild acidic conditions leads to P,y-unsaturated cyclohexenones. Under more drastic acidic conditions, these isomerize to the conjugated a, 3-cyclohexenones. Birch reduction of anisoles followed by hydrolytic workup is one of the best methods available for preparing substituted cyclohexenones. ... 

Zimmerman s explanation for the regioselectivity of the Birch reduction of anisole. The Birch reduction on a aromatic system with an electron-withdrawing group should have a similar reaction process but a different position for the solvated electron to attack. 

Birch reduction of anisole (Chapter 21, Section 21.6.1) leads to 1-methoxycyclohexa-l,4-diene. Heating this with aqueous acid leads to cyclohex-2-en-l-one. Draw all of these products and provide a mechanism for the formation of cyclohexanone. Why should this product form ... 

For aromatic compounds containing electron-donating alkoxy or alkyl groups, the substituent is found in a non-reduced position in the product. Thus, reduction of anisole results in the formation of 1-methoxycyclohexa-1,4-diene and not 3-methoxycyclohexa-l,4-diene. The following protocol for the synthesis of l-methoxy-4-methylcyclohexa-l,4-diene 28 by Birch reduction of 4-methylanisole 27 is representative. 

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