(1R,5S)-6,6-Dimethyl-3-azabicyclo[3.1.0]hexane-2,4-dione194421-56-2100 % similar (1R,5S)-6,6-Dimethyl-3-oxabicyclo(3.1.0)hexane-2,4-dione67911-21-144 % similar 5-Methylhydantoin616-03-531 % similar