High-Yielding Syntheses of Crown Ether-Based Pyridyl Cryptands

Pyridinium bis­(trifluoromethylsulfonyl)­imide (PyTFSI)-templated syntheses of 2,6-pyridyl cryptands of cis(4,4′)-dibenzo-30-crown-10 (3a), the p-bromobenzyloxy derivative 3b, bis­(m-phenylene)-32-crown-10 (5), cis(4,4′)-dibenzo-27S-crown-9 (7), cis(4,4′)-dibenzo-27L-crown-9 (9), and cis(4,4′)-dibenzo-24-crown-8 (11) are reported. Here we provide a fast (12 h), high-yielding (89%, 74%, 80%, and 62% for 3a, 3b, 5, and 9, respectively) templation method without the use of a syringe pump. The yields for 7 (19%) and 11 (26%) were lower than with the previous pseudo-high-dilution method, indicating ineffective templation in these cases. Coupled with our previously developed templated syntheses of dibenzo crown ethers, this protocol makes powerful cryptand hosts readily available in gram quantities in good yields from methyl 4­(or 3)-hydroxy-3­(or 4)-benzyloxybenzoate.