bicyclo<3.3.0>-2-octen-6-one

3,3a,6,6a-tetrahydro-2H-pentalen-1-one semicarbazone

4-Hydroxy-5,6-dihydro-pentalene-1,2-dicarboxylic acid

2,3-dicarbomethoxy-6-pyrrolidinobicyclo(3,3,0)octa-1,3,5-triene