Methoxybenzene Birch reduction

The Y appendage of 2-cyclohexenone 191 cannot be directly disconnected by an alkylation transform. (y-Extended enolates derived from 2-cyclohexenones undergo alkylation a- rather than y- to the carbonyl group). However, 191 can be converted to 192 by application of the retro-Michael transform. The synthesis of 192 from methoxybenzene by way of the Birch reduction product 193 is straightforward. Another synthesis of 191 (free acid) is outlined in... 

For the Birch reduction of mono-substituted aromatic substrates the substituents generally influence the course of the reduction process. Electron-donating substituents (e.g. alkyl or alkoxyl groups) lead to products with the substituent located at a double bond carbon center. The reduction of methoxybenzene (anisole) 7 yields 1-methoxycyclohexa-1,4-diene 8 ... 

Reduction of aryl ethers is a particularly useful application of the Birch reduction. Thus, methoxybenzenes are reduced to 1,4-dienes, as expected, but one of the double bonds is enol ether and is readily hydrolyzed, followed by rearrangement to give the corresponding a,P-unsaturated-ketone h Li, NH,... 

A very useful method to prepare carbocyclic enol ethers is the Birch reduction of aryl ethers. In the simplest example, metal ammonia reduction of methoxybenzene gives methoxycyclohexadiene (21). The reaction has been applied to numerous aryl ethers of complex structures. 

Anacardic acid 8(Z),1 l(Z)-diene has been prepared by the Diels-Alder addition of 1-methoxycyclohexa- 1,4-diene to an homologous propiolic ester [241] with elimination of ethylene. The methoxydiene intermediate was prepared by the Birch reduction of methoxybenzene and this approach represents a link between the use of an aromatic and a derived acyclic precursor. 

There are a wide variety of synthetic applications of this chemistry, making it one of the most powerful reactions in organic chemistry (sec. 10.5.B.vi). An example is the Birch reduction of the methoxybenzene portion of 514, which gave 515.Subsequent treatment with methanolic HCl converted the vinyl ether moiety in 515 to the ketone unit (via the enol) found in 516. Note that Birch reduction formed a trans ring juncture in 515 from the conjugated C=C unit in 514. Initial hydrolysis of 515 led to a nonconjugated ketone, but under the acidic conditions the conjugated systems found in 516 was formed. However, it is... 

Substituent groups on the benzene ring influence the course of the reaction. Birch reduction of methoxybenzene (anisole) leads to the formation of 1-methoxy-1,4-cyclohexadiene, a compound that can be hydrolyzed by dilute acid to 2-cyclohexenone. This method provides a useful synthesis of 2-cyclohexenones ... 

Draw the radical anion intermediate formed when methoxybenzene (anisole see Chapter 21, Section 21.2) is treated with sodium in ethanol and ammonia (Birch reduction), and draw all resonance structures. Based on stability of the radical anion product, suggest the final product of this reduction. 

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See also in sourсe #XX -- [ , ]

See also in sourсe #XX -- [ ]

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