Synthesis of Norbornahemicucurbiturils

Abstract

Ethyleneurea fused with a norbornane ring was prepared. Acid-catalyzed polycondensation of the urea with paraformaldehyde yielded a new six-membered hemicucurbituril derivative. The presence of hemicucurbiturils containing from four to eight monomer units were also detected.

Key words

hemicucurbiturils - cucurbiturils - macrocycles - polycondensation - supramolecular chemistry

• References and Notes

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• 11 endo-3,5-Diazatricyclo[5.2.1.0^2,6]decane-4-one (1): A solution of 2 (0.27 g, 1.8 mmol) in MeOH–CH₂Cl₂ (12 mL, 4:1 v/v) was stirred under an atmospheric pressure of H₂ in the presence of 10% Pd/C (0.12 g) for 22 h. The resulting mixture was filtered through Celite, washed with MeOH (15 mL) and the combined filtrates were concentrated in vacuo to give 1 (0.26 g, 1.7 mmol, 95%) as a white solid; mp 235.7–236.1 °C (dec.). IR (KBr): 710 (m), 774 (m), 1131 (m), 1252 (m), 1351 (m), 1466 (m), 1690 (s), 2871 (m), 2949 (s), 3067 (br. m), 3218 (br. s) cm^–1. ¹H NMR (300 MHz, CDCl₃, 30 °C): δ = 1.36 (d, J = 8 Hz, 2 H, C(8,9)-H_A), 1.39 (d, J = 11 Hz, 1 H, C(10)-H_A), 1.48 (d, J = 11 Hz, 1 H, C(10)-H_B), 1.71 (d, J = 8 Hz, 2 H, C(8,9)-H_B), 2.32 (s, 2 H, C(1,7)-H), 3.96 (s, 2 H, C(2,6)-H), 4.75 (br s, 2 H, NH); ¹³C NMR (125 MHz, CDCl₃, 30 °C): δ = 21.7 (C(8,9)-H₂), 36.4 (C(10)-H₂), 40.8 (C(1,7)-H), 57.7 (C(2,6)-H), 163.6 (C=O). HRMS: m/z calcd. for [C₈H₁₂N₂O+H]⁺: 153.1022; found: 153.1022.
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• 15 Norbornahemicucurbit[6]uril (NorHmCB[6]): Compound 1 (0.25 g, 1.6 mmol) was dissolved in 4 M aq HCl (20 mL) at 70 °C. Paraformaldehyde (0.054 g, 1.8 mmol of CH₂O) was added and the resulting mixture was heated at 70 °C for 4 h (during this period a white precipitate formed). The solid material was collected by filtration, washed with H₂O (10 mL), and dried in vacuo. The desired macrocyclic product was separated from the crude mixture by silica gel column chromatography (acetone–CHCl₃, 1:4 v/v). Yield: 0.024 g (0.024 mmol, 8.9%); mp >250 °C. IR (KBr): 614 (m), 760 (m), 813 (w), 1216 (s), 1372 (s), 1441 (s), 1699 (s), 2871 (m), 2961 (m), 3437 (br m) cm^–1. ¹H NMR (300 MHz, CDCl₃, 30 °C): δ = 1.28 (d, J = 13 Hz, 6 H, C(10)-H_A), 1.34 (d, J = 11 Hz, 12 H, C(8,9)-H_A), 1.40 (d, J = 11 Hz, 12 H, C(8,9)-H_B), 1.57 (d, J = 13 Hz, 6 H, C(10)-H_B), 2.63 (s, 12 H, C(1,7)-H), 3.50 (s, 12 H, C(2,6)-H), 4.59 (s, 12 H, C(11)-H₂). ¹³C NMR (125 MHz, CDCl₃, 30 °C): δ = 21.9 (C(8,9)-H₂), 36.4 (C(10)-H₂), 39.4 (C(1,7)-H), 49.1 (C(11)-H₂), 57.0 (C(2,6)-H), 160.4 (C=O). HRMS: m/z calcd for [C₅₄H₇₂N₁₂O₆+H]⁺: 985.5771; found: 985.5777. Anal. Calcd for C₅₄H₇₂N₁₂O₆·2 H₂O: C, 63.51; H, 7.50; N, 16.46. Found: C, 63.55; H, 7.55; N, 15.75.
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