Cinncassiol D$\sb1$ is a diterpene isolated from water extracts of Cinnamomum cassia Blume. This and related diterpenes of the Cinncassiol series have exhibited in vitro anti-complement and anti-allergenic activity. The Cinncassiol D$\sb1$ ring system contains a polyhydroxy 5-6-5 cis fused ring system that is unique to this family of natural products. The synthesis of a model 5-6-5 ring system is accomplished through an intramolecular Diels-Alder reaction. Several routes directed towards the preparation of the model ring system are discussed. A short synthesis for preparing 5,5 disubstituted cyclopentene aldehydes in good yield is presented
