Efficient Syntheses of Novel Cryptands Based on Bis(m-phenylene)-26-crown-8 and Their Complexation with Paraquat

High-yielding syntheses of two novel cryptands based on bis(m-phenylene)-26-crown-8 are reported. One-step [2+2] cyclization of methyl 3,5-dihydroxybenzoate with tri(ethylene glycol) ditosylate under pseudo-high-dilution conditions gave BMP26C8 (1) in 28 % yield. Reduction of 1 with LAH, followed by deprotonation (NaH) and alkylation with propargyl bromide, afforded the dialkynated BMP26C8 (3) in high yield (two-step 84 %). Unimolecular macrocyclization of 3 through copper(II)-mediated Eglinton coupling generated the diacetylene-containing cryptand 4 in 97 % yield. Pd/C-catalyzed hydrogenation of 4 yielded the cryptand 5 (93 %). Their structures were confirmed by NMR, ESI-MS, and Xray analysis. The complexation behavior of these new cryptands with paraquat was also studied, and it was found that these cryptands bind paraquat more strongly than the corresponding BMP26C8. The association constants (K-1 and K-2) in acetone solution were determined to be K-1 = 914 M-1, K-2 = 229 M-1 for complex 4(2).6 and K-1 = 758 M-1, K-2 = 190 M-1 for complex 5(2).6. Moreover, the two new [3]pseudorotaxane-like complexes 4(2).6 and 5(2).6 were also obtained in the solid state, as confirmed by X-ray analysis.