page_title: Tropocoronand ligand
section_title: Synthesis
hierarchical_section_title: Tropocoronand ligand / Synthesis
caption_attribution_description: English: Synthetic Route for Tropocoronand Ligands
context_page_description: The tropocoronand ligand is a macrocyclic ligand in which two aminotroponiminate rings are connected to one another via polymethylene linker chains of length m and n. Double deprotonation of the ligand yields a dianionic macrocylic species that is capable of binding divalent transition metal ions to form neutral complexes [M]. The 2-aminotroponeimine units are bridged by polymethylene linker chains with all four nitrogen atoms of the tropocoronand ligand bonded to a metal atom.
  Tropocoronand ligands ²⁻ are known for a range of methylene bridges, m and n, in the arms connecting the two aminotroponiminate rings. They represent a new class of molecules with potential to be modified with a chiral moiety and applied to enantioselective reactions.
context_section_description: Symmetrical tropocoronands where m =  n =  2 – 6 have been made in a four-step synthesis (Scheme 1) from tropolone.
  Either 2-tosyloxytropone (1) or 2-chlorotropone can be made from tropolone and then reacted with the appropriate diamine to give diaminodiketones 2. These diketones then give dialkoxydiimines 3 by treatment with dimethyl sulfate in refluxing toluene, or with triethyloxonium tetrafluoroborate in refluxing chloroform/hexamethylphosphoramide. The resulting dialkoxides can then undergo amine displacement and ring closure at 25 °C to form tropocoronands 4. Reported yields in the cyclization are generally in the range of 20 – 40%, but only 2% when m =  n =  2. In most of the cases decreasing the straight-chain linkages size results in lower yields however Nozoe has demonstrated yields of 55– 65% for m =  n =  3 using methylfluorosulfate in dichloromethane as the alkylating agent.
  Asymmetrical tropocoronands where the number of carbons of the simple straight-chain linkages is different (m ≠ n, but variability in the m,n lengths tends to be only by 1 methylene group) as well as chiral tropocoronands  can be synthesized using the method outlined in Scheme 1 with the modification of the last step where the straight-chain diamine can be substituted to the diamine with a different length of chain (m ≠ n) or to the chiral one. An alternative synthesis involves placing the chiral group in the sequence first to form a diaminoketone, followed by cyclization with a straight chain diamine in the last step.
caption: Synthesis of Tropocoronands
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