Oxotropic rearrangement

With acid, the above enol methyl ethers undergo an oxotropic rearrangement to 3,4-dideoxyaldopyranosulos-3-enes (m-unsaturated glycosones), which react further to give 2-furaldehydes (see Section IV, 2b p. 194). 

A more convenient method is the oxotropic rearrangement of 3-deoxy-2-O-methylhexos-2-enes, enolic forms of 3-deoxyhexosuloses. - The preparation of the starting material from 2-0-methylhexoses is described in Section IV, la (see p. 188). 

Allylic alcohols, esters, and ethers undergo acid-catalyzed isomerizations, and allylic alcohols and ethers isomerize at appreciable rates only in the presence of acids. The migrating groups in these reactions are uncharged molecules derived from the oxonium ion conjugate acids of the starting materials. For this reason, and because they are mechanistically related to anionotropic isomerizations, Braude named these reactions oxotropic rearrangements. 

Prototropic and oxotropic rearrangement s. 13, 223 Hydrazones from 2-ethylenealcohols via ketones s. 12, 215 a,j -Ethylenecarboxylic acid esters from alkoxyethynylalcohols s. 11, 223... 

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