Halogen‐ und Pseudohalogen‐substituierte Penta‐ und Tetramethylcyclopentadine

Halogen‐ and Pseudohalogen‐Substituted Penta‐ and Tetramethylcyclopentadienes The alkyl halides 5‐bromo‐1,2,3,4,5‐pentamethyl‐1,3‐cyclopentadiene ( 2 ), 5‐iodo‐1,2,3,4,5‐pentamethyl‐1,3‐cycloentadiene ( 3 ), and 5‐bromo‐1,2,3,4‐tetramethyl‐1,3‐cyclopentadiene ( 8 ) are formed in good yields by treatment of pentamethylcyclopentadienyllitium ( 1 ) and tetramethylcyclopentadienyllithium ( 7 ), respectively, with the corresponding cyanogen halides. Reaction of 1 with cyanogen chloride or cyanogen leads to 5‐cyano‐1,2,3,4,5‐pentamethyl‐1.3‐cyclopentadiene ( 4 ). Treatment of 1 with thiocyanogen yields 5‐isothiocyanato‐1,2,3,4,5‐pentamethyl‐1,3‐cyclopentadiene ( 5 ). 5‐Chloro‐1,2,3,4,5‐pentamethyl‐1,3‐cyclopentadiene ( 6 ) is obtained fro 1 and a mixture of tetrachloromethane and triphenylphosphane. Analogously, the halides 2 and 3 can be synthesized by the reaction of 1 with a mixture of triphenylphosphane and tetrabromomethane or tetraiodomethane. Treatment of 7 with tetrachloromethane and triphenylphosphane yields a mixture of isomers of chlorotetramethylcyclopentadiene.