1,2,3,4,5,6-Hexamethylbicyclo(2,2,0)hexa-2,5-diene 2-Butin hexamethyl-dewar-benzol [German] 7641-77-2 BICYCLO(2.2.0)HEXA-2,5-DIENE, HEXAMETHYL- EINECS 231-576-3 Hexamethyl-bicyclo(2.2.0)hexa-2,5-dien [German]