The Synthesis of 1,2-Bis(1,5,9-triazacyclododecyl)ethane: A Showcase for the Importance of the Linker Length within Bis(alkylating) Reagents

The synthesis of 1,2-bis(1,5,9-triazacyclododecyl)ethane (1) showcases how different bis(alkylating) reagents change the reaction from an
intra- to an intermolecular pathway. The isolation of the intermediate hexahydro-3a,6a-ethano-1H,4H,7H,9bH-9a-aza-3a,6a-diazoniaphenalene-3a,6a-diium (2) explained why initially the synthesis of 1 was not possible. Both isomers of 2 were found in solution. DFT calculations revealed
that isomer 2a is 4.6 kcal/mol lower in energy than 2b. Synthesis of 1 was finally achieved by using oxalyl chloride.