Dehydration of Alcohol with Ring Transformation

Dehydration of cycloalkylmethyl alcohol gives ring-expanded products via Wanger-Meewein rearrsmgement. Pines and Brown performed dehydration of cy-cloalkylmethanol with 4 to 7-membered rings.The dehydration at 573 K over fresh alumina of cyclobutane-, cyclopentane-, cyclohexane-, and cycloheptane-methanol yielded 99, 55, 7 and 6% of ring-expanded product. 

Dehydration of tetrahydrofurfuryl alcohol (tetrahydrofuran-2-methanol) over silica - alumina at 623 K gives dihydropyrane. The dehydration at higher temperatures (723-763 K) gives acrolein and ethylene as the main products.  

Dehydration of tetrahydropyran-2-methanol over high purity ij-alumina without any carrier gas produced cyclopentane carbaldehyde in a yield of 71 % at 603 K, while dehydration over copper-chromia oxide supported on kieselguhr with hydrogen carrier gas at 703 K yielded 2,3,4,5-tetrahydrooxepine and cyclopentanecarbaldehyde (44.8% and 4.7%, respectively).  

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