syn-(Methyl,methyl)bimane

2,3,5,6-Tetramethyl-pyrazolo[1,2-α]pyrazole-1,7-dione

2,3,5,6-Tetramethyl-pyrazolo[1,2-a]pyrazole-1,7-dione

3,4,6,7-Tetramethyl-1,5-diazabicyclo[3.3.0]octa-3,6-diene-2,8-dione

2,3,7,8-Tetramethyl-1,5-diaza-bicyclo(3.3.0)octa-2,7-dien-4,6-dione

3,4,6,7-Tetramethyl-1,5-diazabicyclo[3.3.0]octa-3,6-diene -2,8-dione