The Cope Rearrangement, a Reaction for Repeatable Ring Expansions - Starting with the unsaturated beta-ketoesters of type I, a vinyl group is introduced into the beta-position by 1,4-addition of vinyl magnesium chloride to give II (Scheme 3). Treatment of the beta-ketoester II with phenyl vinyl sulfoxide in the presence of sodium hydride yields the sulfides III, which on thermolysis lead to the alpha,beta-divinyl ketoesters of type IV via elimination of sulfinic acid (Scheme 3). The Cope-System IV undergoes rearrangement to V, which is again an unsaturated beta-ketoester. The latter is suitable for a further ring expansion sequence. These reaction steps were carried out with the nine-, twelve- and fifteen-membered ketoesters 32, 33 and 34, as well as with the open-chain compound 35 (Table 1). With the cyclohexane derivative 31, ring expansion could not be achieved with the described sequence.