Stereocontrolled Synthesis of Kelsoene by the Homo-Favorskii Rearrangement

2002-09-18T00:00:00Z (GMT) by Liming Zhang Masato Koreeda
(±)-Kelsoene (<b>4</b>) has been synthesized from 2,5-dihydroanisole in 16 steps in 12.5% overall yield. The key step involves a base-catalyzed reaction of γ-keto tosylate (<b>5</b>), which effects a homo-Favorskii rearrangement to <b>16</b> as well as the corresponding intramolecular S<sub>N</sub>2 product <b>15</b> from the enolate of <b>5</b>. Ketone <b>15</b> can efficiently be isomerized to cyclobutanone <b>17</b> having the kelsoene carbon skeleton upon acid treatment.