Summary Starting with the unsaturated 8-ketoesters of type I, a vinyl group is introduced into the P-position by 1, 4-addition of vinyl magnesium chloride to give I1 (Scheme 3). Treatment of the P-ketoester TI with phenyl vinyl sulfoxide in the presence of sodium hydride yields the sulfoxides 111, which on thermolysis lead to the a, P-divinyl ketoesters of type IV via elimination of sulfinic acid (Scheme 3). The Cope-System IV undergoes rearrangement to ...