Synthetic efforts towards the protoilludenes. A formal synthesis of Δ7-protoilludene

An improved route to 5,8,8-trimethylbicyclo[4.3.0]-4-nonen-3-one, a key intermediate for the synthesis of the protoilludane skeleton and in particular Δ7-protoilludene, is reported. Attempts on an alternative synthesis of Δ6-protoilludene based on a phenylsulfonyl allene cycloaddition reaction is also presented.