Recently we reported the synthesis of desether-muscarine,1a compound of interesting cholinergic activity. The starting material for this synthesis was the 3-methyl-3-cyclopentene-l-carboxylic acid (II) already synthesized through photochemical addition of ethyl diazoacetate to isoprene and subsequent pyrolisis ofI2Following this synthetic route it was difficult to obtain such compound and mostly starting material was recovered together with a little photoaddition product. In order to have enough compound for the synthesis of desethermuscarine with the aim to separate its optical isomers, a new synthesis ofI, from isoprene and ethyl diazoacetateviacopper-catalized addition,3has been sought and is reported here.