HALOGEN-SUBSTITUTED AND PSEUDOHALOGEN-SUBSTITUTED PENTAMETHYLCYCLOPENTADIENE AND TETRAMETHYLCYCLOPENTADIENE

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. Copyright © 1990 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim