Thc introduction of an ethylene bridge between the nitrogens of 2, 2, 5, 5- tetramethylpiperazine, homopiperazinc arld 22-dimethylhomopiperazine to form the bicyclo compounds XIX, XX and XXI has been effected by the pyrolysis of the hpdrobromide salts of the l-(2-bromoethyl) derivatives (VIII, XV, XVII) of these monocyclic compounds. The presence of thc gem-dimethyl groups in VI11 severely hinders this bridging reaction so ...