Spiro[4,5]deca-2,7-diene-1,6-dione (2a) and spiro[5,5]undeca-2,8-diene-1,7-dione (2b) were prepared by a direct synthesis starting from diethyl malonate. The two-step 1,2-reductions (NaBH4/CeCl3) of the diones gave cis/trans-diols, which could be easily transformed into diacetates. Both diacetates were subjected to Pd(0)-catalyzed allylic alkylations, in which the relative stereochemistry was retained.