Synthesis and characterisation of optically active spiro[4.5]decanes

The synthesis of spiro[4.5]decanes through a Diels–Alder cycloaddition between 5-methylenefuran-2(5H)-one (protoanemonin) 8, and chiral dienes 1-[(–)-menthyloxy]-3-trimethylsilyloxybuta-1,3-diene, 5, 1-[(–)-bornyloxy]-3-trimethylsilyloxybuta-1,3-diene, 6, and 1-[(+)-isopinocampheyloxy]-3-trimethylsilyloxybuta-1,3-diene, 7, is reported for the first time. Diastereofacial selectivity together with the preference for an endo/exo attack are examined. The effect on the diastereofacial selectivity of substituting dienophile 8 by 3-acetoxy-5-methylenefuran-2(5H)-one 18 is also discussed. The use of Lewis acids as catalysts to enhance selectivity has been attempted without success.