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Free keywords:
McMurry reaction; Macrocyclization reactions; Template effect; Crown ethers; Ag(+1) complexation
Abstract:
A set of tethered bis-benzophenone or -benzaldehyde derivatives was subjected to intramolecular McMurry reactions, thus affording hybrids with cyclophane and crown ether substructures (“crownophanes”). All macrocycles were formed in reasonable yields even at rather high concentrations. A comparative study showed that low-valent titanium [Ti] exerts a strong template effect whereas alkali metal salts accumulating during its preparation have only little influence upon the preorganization of the substrates in a favorable podand-like conformation. Ester linkages in the tethers turned out to be only partly compatible with the reaction conditions. Crystal structures of crownophanes 7, 8, and 12 are described. A 1H- and 13C-NMR study on the complexation of Ag(+1) by 8 and 10 revealed that the endocyclic arene entities rather than the polyether chains are the major sites of interaction of the cation with its host.
