ethyl 2,3,3a,4,5,6-hexahydro-5,5-dimethyl-2-oxo-1-pentalenecarboxylate

4,4-dimethyl-2-(3'-carboethoxy-2'-oxo-propyl)-cyclopentanone

4,4-dimethyl-1-pyrrolidinocyclopentene

(2aR,4aR,7aR)-2a-Hydroxymethyl-6,6-dimethyl-2-methylene-hexahydro-cyclobuta[c]pentalen-3-one