AbstractSolvolysis of Δ1,9‐10‐hydroxymethyl‐octaline benzenesulfonate (XIII) yields as the chief product [0,1,4,4]‐Δ1‐tricyclo‐undecene (XV), the structure of which was subsequently proven by chemical means. In a competing reaction involving molecular rearrangement some bicyclic compound XVI is also found. Similarly Δ12‐18, 28‐cyclo compounds have been isolated in the solvolysis of Δ13,18‐28‐mesylates or benzenesulfonates of the oleanane series, thus supporting the view that homoallylic ring closure is the major reaction occurring in the solvolysis of compounds which contain the Δ1,9‐10‐h