Oxolanes dehydration

The most studied area in this held is the dehydration of oxolanes to butadiene. This type of dehydration is catalyzed by various acidic heterogeneous catalysts. For example, 2,2,5,5-tetramethyloxolane can be dehydrated on Pt/Al203 to 2,5-dimethyl-2,4-hexadiene in good yield (Scheme 5.3).34... 

The ring-closure (cyclodehydration) of dihydroxy compounds affords five-, six-, seven-, and eight-membered cyclic ethers. The reaction can efficiently and conveniently be carried out with Nafion-H.687,688 Even diphenols (2,2 -dihydroxybiphenyls) undergo dehydration to afford oxolane derivatives276 [Eq. (5.244)]. The low yields of the fc/T-butyI-substituted compounds result from trans-terf-butylation (see Section 5.2.6). Cyclodehydration of stereoisomeric... 

The dehydration of oxolanes yields dienes. 2,5-Dimethylcyclohexadienes are selectively formed by ring-opening dehydration of 2,2,5,5-oxolane over platinum/Al203, AI2O3 or NaY zeolite. Bartok and Molnar found that ( )-2,2,3,4,5,5-hexamethyl oxolane (I) is converted mainly into 2,3,4,5-tetramethylhexa—1,5-diene (IV), whUe its meso-isomer (II) reacts at a higher rate than (I) to rive 2,3,4,5-tetramethylhexa— 2,4-deiene (III) with high selectivity on 7-alumina.Mutual isomerization of the dienes is not observed. 

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