Please explain about Reduction of ether( R-O-R’ )

Please explain about Reduction of ether( R-O-R’ )


1 Answers

879 Points
13 years ago


Dear student,

When substituents are present, they may influence the regioselectivity of the Birch reduction. The product is determined by the site of the first protonation, since the second protonation is nearly always opposite (para to) the first. Electron-donating substituents such as ethers and alkyl groups favor protonation at an unoccupied site ortho to the substituent; whereas electron-attracting substituents such as carboxyl favor para protonation. The influence of a carboxyl group dominates poly substituted rings, and alkoxy groups have a greater directing influence than alkyl substituents. An oxy anion group, as in the conjugate base of phenol, prevents reduction from occurring. Two examples of such Birch reductions are shown below. Although the substrate molecule in the first reaction may appear very complex, it is essentially a rigid framework with a benzene ring at each end. The phenolic function on the left hand ring becomes a phenolate anion under the reduction conditions, and does not react further. The right hand aromatic ring is an ether, and it reduces as expected. The carboxylic acid in the second example is immediately converted to its conjugate base. Although this carboxylate anion is negatively charged, it still has an electrophilic carbon atom which acts to stabilize an adjacent negative charge as shown. After protonation of the para carbanion by ammonia, the carboxylate dianion remains unchanged until it is doubly protonated by a strong acid, such as NH4(+) or H3O(+).

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