Synthetic studies towards Delta(6)-protoilludene. A formal synthesis

A synthetic strategy towards Delta(6)-protoilludene included an intramolecu lar allene-ene cycloaddition reaction as a key step; however, the thermal r eaction furnished a stereoisomeric mixture of 9-methyl-1,4,4,8-tetramethylt ricyclo[6.2.0.0(2,6)]decane, which has a ring assembly isomeric with that o f the target molecule. Another approach to Delta(6)-protoilludene required cis-4,4-dimethyl-2-isopropenylcyclopentylacetic acid, which was obtained fr om the mixture of stereoisomers by column chromatographic separation of the corresponding iodolactones. The cis-acid was further converted into cis-et hyl 4-(2-isopropenyl-4,4-dimethylcyclopentyl)-3-methyl-2-butenoate which ha s previously been transformed by others into Delta(6)-protoilludene. Hence, our approach constitutes formally a new synthesis of Delta(6)-protoilluden e.