Catalysis, rearrangement

If, in an attempt to obtain free 6-amino-6-deoxy-L-xt/Io-hexulose, the isopropylidene compound 80 is hydrolyzed at 65° with 2 M hydrochloric acid, an almost quantitative yield of 3-hydroxy-2-pyrldinemeth-anol (86) hydrochloride is obtained instead. The formation of 86 can result only through the intermediate 6-amino-6-deoxy-L-xyfo-hexulo-pyranose (83). The furanose (81) first formed is in equilibrium with the pyranose (83). The latter is dehydrated in acid solution to 82 which, under acid catalysis, rearranges to the intermediate 84. In the following steps, the allylic hydroxyl groups on C-4 and C-5 are readily removed, and aromatization to the pyridine derivative (86) ensues. 

Carbonylation of tertiary alcohols is effective using strong acid catalysis rearranged tertiary carboxylic acids are obtained [54] ... 

Boiling spiro-quinoxalin-2,5 -pyrazol-3-ones 134a-f in an acetic acid solution for 8 h results in the acid catalysis rearrangement with the release of water and the formation of corresponding 2-(pyrazol-3 -yl)benzimidazoles in quantitative yields (Table 6.15). 

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