The fate of the external methylene Carbon atom of tetrahydrofurfuryl alcohol in the rearrangement to dihydropan.
McLeod, Gerald Louis
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When tertrahydrofurfuryl alchohol is passed over alumina at temperatures between 300 and 360 degrees celcius a unique rearrangement occurs. Instead of a simple dehydration of the alcohol, a ring expansion is observed. The product is dihydropyran. If it is assumed that the first step involves the removal of the hydroxyl group from the tetrahydrofurfuryl alcohol by the alumina to give a carbonium ion, then shift of the heterocyclic oxygen atom followed by loss of a proton would give the six-membered ring product, dihydropyran. It is also possible that instead of the oxygen atom migrating the carbon atom at the 3-position of the tetrahydrofurfuryl alcohol might shift to the external methylene carbon. Loss of a proton would also give dihydropyran. The path of the rearrangement can be followed if tetrahydrofurfuryl alcohol labeled with carbon-14 in the external methylene group is utilized. If the heterocyclic oxygen shifts the resulting dihydropyran will be labeled at the 2-position. On the other hand, if the 3-carbon atom shifts the dihydropyran will be labeled at the 3-position. It was considered possible that both paths might be operativen, so that the dihydropyran would be labeled at the 2- and 3-positions.[TRUNCATED] Summarizing, it can be stated that the rearrangement of tetrabydrofurfuryl alcohol to dihydropyran over activated alumina at 300-360° can be explained by a shift of the heterocyclic oxygen atom. It can be further stated that during or after the formation of dihydropyran a step occurs that places the labeled carbon at the 6- as well as the 2-position.
Thesis (Ph.D.)--Boston University