A General Method for Synthesis of Unclosed Cryptands via H-Bond Templated Macrocyclization and Subsequent Mild Postfunctionalization.

A practical four-step synthesis of a model 26-membered N-Boc-protected macrocycle, starting from commercially available and inexpensive materials, is reported. The crucial macrocyclization step does not require high-dilution conditions and is completed in a short time (8 h). The high yield of macrocyclization (61%) is achieved owing to templation by intramolecular H-bonds and a chloride anion, which both help to adopt a favorable folded conformation of the open-chain intermediate.

"Unclosed cryptands": a point of departure for developing potent neutral anion receptors.

Six macrocyclic lariat-type compounds, representing a new class of anion receptors, were synthesized in a simple approach. We identified the optimal macroring size and the position of the hydrogen bond donating center in the lariat arm offering the best affinities toward chloride and carboxylate anions. The anion-binding properties of such systems were investigated by applying (1)H NMR titrations in DMSO/water and methanol/DMSO mixtures.