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Organic Lab Reactions 21 - 16 THE CLAISEN REARRANGEMENT by...

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16 ' THE CLAISEN REARRANGEMENT by ring closure of the initial product. Compounds with substituted allyl groups seem to form the dihydrobenzofurans more readily than the unsubstituted allyl compounds; 43 - M - 68 thus 2-G8-methylallyl)-phenol* 6 forms the corresponding dihydrobenzofuran on heating or even on stand- ing in petroleum ether solution over anhydrous magnesium sulfate. Mechanism of the Rearrangement * TheClaisen rearrangement to the ortho position is a first-order reac- tion, 87 ' 68 and the process does not require catalysis by acids and bases. • The rearrangement is intramolecular, since rearrangement of mixtures of ethers such as allyl /3-naphthyl ether and cinnamyl phenyl ether, 60 or cinnamyl 4-methylphenyl ether and allyl 4-aminophenyl ether, 68 yields none of the cross products which would result from an intermolecular reaction. The process is best represented by the cyclic mechanism, in which the following processes take place, with the electronic shifts during reaction indicated by the arrows.
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