(±)-<i>trans</i>,<i>cis</i>-4-Hydroxy-5,6-di-<i>O</i>-isopropylidenecyclohex-2-ene-1-one: Synthesis and Facile Dimerization to Decahydrodibenzofurans

An efficient synthesis of (±)-<i>trans</i>,<i>cis</i>-4-hydroxy-5,6-di-<i>O</i>-isopropylidenecyclohex-2-ene-1-one (<b>3</b>) has been developed from acetonide-protected <i>meso</i>-1,2-dihydrocatechol derivative <b>1</b> via photooxygenation, then Kornblum−DeLaMare rearrangement. The product is unstable unless its 4-hydroxy group is protected, as it undergoes facile dimerization in solution to a 1:1 mixture of diastereoisomeric decahydrodibenzofurans <b>8</b> and <b>9</b>. A new synthesis of the dihydrocatechol <b>1</b> from 1,3-cyclohexadiene has also been developed.