4.2.1 Synthesis of C2-3,9-diazatetraasterane 1a and 1b
The synthesis of compounds 1 was performed according to our previous reported procedures [17]. To be specific, γ-cyclodextrin (0.5 mmol) aqueous solutions were added to the diethyl 1,4-dihydropyridine-3,5-diicarboxylate (3 or 4, 1 mmol) in 100 mL tetrahydrofuran. The resulting mixture was sonicated at 60 ℃ for 2 h and a clear homogeneous solution was obtained, which was subjected to irradiation of 250 W medium-pressure mercury lamp under nitrogen atmosphere for 8 h until complete conversion of the reactant (monitored by TLC). Subsequently, the reaction solution was concentrated under reduced pressure to remove organic solvents, the residues were recrystallized with dichloromethane/methanol (V:V = 4:1) and afforded white solids as the target product.
Tetraethyl 6,12-diphenyl-3,9-diazahexacyclo [6.4.0.0 2,7 .0 4,11 .0 5,10 ] dodecane-1,5,7,11-tetracarboxylate (1a). Yield 80%, M.P: 208.5-211.2 ℃. 1H NMR (400 MHz, CDCl3): δ (ppm) 7.60–7.46 (m, 4H), 7.19 (t, J = 7.2 Hz, 4H), 7.15 (d, J = 7.1 Hz, 2H), 4.32 (s, 4H), 4.01–3.87 (m, 10H), 3.02 (brs, 2H), 0.98 (t, J = 7.1 Hz, 12H).13C NMR (100 MHz, CDCl3) δ (ppm) 173.22, 137.43, 130.90, 127.80, 126.84, 60.84, 55.10, 48.82, 43.82, 13.89. HRMS (ESI), m/z calcd 603.2701 for C34H39N2O8 [M + H]+, found 603.2705. (CCDC: 1484747)
Tetraethyl 3,6,9,12-tetraphenyl-3,9-diazapentacyclo [6.4.0.0 2,7 .0 4,11 .0 5,10 ] dodecane − 1,5,7,11-tetracarboxylate (1b). Yield 82%, M.P: 255.8-256.6℃ 1H NMR (400 MHz, CDCl3) δ (ppm) 7.37 (d, J = 3.9 Hz, 8H), 7.08 (q, J = 3.3, 2.4 Hz, 10H), 7.01–6.92 (m, 2H), 5.23 (s, 4H), 4.05–3.93 (m, 10H), 0.97 (t, J = 7.1 Hz, 12H). 13C NMR (100 MHz, CDCl3) δ (ppm) 172.8, 149.7, 136.6, 130.2, 129.5, 128.0, 127.0, 120.4, 117.5, 61.2, 57.9, 51.8, 44.1, 13.7. HRMS (ESI), m/z calcd 755.3342 for C46H47N2O8 [M + H]+, found 755.3346.
4.2.2 Synthesis of non-C2-3,9-diazatetraasterane 2a and 2b
The synthesis of compounds 2 was performed according to our previous reported procedures [13]. Dissolved an equivalent mixture of two different 1,4-dihydropyridine (3 and 4, or 3 and 5, 10 mmol) in methanol, the solution was poured into a quartz cuvette, N2 was introduced as the protective gas. The ring-shaped internally illuminated LED lamp (365 nm, 120 W) was used as the light source. The reaction was completed about 10 hours (TLC monitoring). Then the reaction solution was concentrated, and purified by flash column chromatography (silica gel), recrystallized with ethyl acetate/n-hexane (V:V = 1:4) to obtain the white solid.
Tetraethyl 3,6,12-triphenyl-3,9-diazapentacyclo [6.4.0.0 2,7 .0 4,11 .0 5,10 ] dodecane-1,5,7,11-tetracarboxylate (2a). Yield 30%, M.P: 199.5-201.3 ℃. 1H NMR (400 MHz, CDCl3): δ (ppm) 7.57–7.29 (m, 6H), 7.24–7.03 (m, 8H), 6.92–6.96 (m, J = 4.2 Hz, 1H), 5.21 (d, 2H), 4.35 (d, 2H), 4.03–3.91 (m, 8H), 3.91 (d, J = 10.2 Hz, 2H), 3.02 (brs, 1H), 1.00 (t, J = 7.1 Hz, 6H), 0.95 (t, J = 7.0 Hz, 6H). 13C NMR (100 MHz, CDCl3) δ (ppm) 173.04, 172.95, 130.82, 130.23, 129.40, 128.07, 127.80, 126.96, 126.90, 120.22, 117.38, 61.10, 61.00, 58.04, 54.73, 50.60, 49.97, 44.28, 43.58, 13.92, 13.76. HRMS (ESI), m/z calcd 679.3025 for C40H43N2O8 [M + H]+, found 679.3028.
Tetraethyl 6-phenyl-12-(3,4,5-trimethoxyphenyl)-3,9-diazapentacyclo [6.4.0.0 2,7 .0 4,11 .0 5,10 ] dodecane-1,5,7,11-tetracarboxylate (2b). Yield 28 %, M.P: 255.2-256.8 ℃. 1H NMR (400 MHz, CDCl3): δ (ppm) 7.53 (d, J = 7.2 Hz, 2H), 7.15–7.23 (m, 3H), 6.88 (s, 2H), 4.33–4.34 (d, 4H), 3.95–4.04 (m, 8H), 3.91 (s, 1H), 3.87 (s, 1H), 3.81 (s, 6H), 3.80 (s, 3H), 3.04 (brs, 2H), 1.05 (t, 6H), 1.00 (t, 6H). 13C NMR (100 MHz, CDCl3) δ (ppm) 173.2, 152.3, 137.3, 136.8, 133.0, 130.9, 127.8, 126.9, 108.5, 60.9, 60.8, 56.0, 55.2, 55.0, 48.9, 48.7, 44.0, 43.9, 14.0, 13.9. HRMS (ESI), m/z calcd 693.3018 for C43H49N2O11 [M + H]+, found 693.3021.(CCDC: 1537245)