Synlett, Table of Contents Synlett 2019; 30(18): 2068-2072DOI: 10.1055/s-0039-1690698 letter © Georg Thieme Verlag Stuttgart · New York [2+2] Photocycloaddition of 3-Alkoxycoumarins with C60 Mitsuhiro Ueda ∗ , Miho Hayama , Hiroyuki Hashishita Recommend Article Abstract Buy Article All articles of this category Abstract The [2+2] cycloaddition of 3-alkoxycoumarins with C60 proceeded stereoselectively under photoirradiation conditions to produce a new class of fullerene fused oligocyclic cyclobutane products. This reaction seems to progress via radical ion pair intermediates that arise from the SET processing of 3-alkoxycoumarins with the excited form of C60. Key words Key words[2+2] cycloaddition - 3-alkoxycoumarin - fullerene - photoreactions - oligocyclic cyclobutane Full Text References References and Notes For recent reviews, see: 1a Giacalone F, Martín N. Adv. Mater. 2010; 22: 4220 1b Roncali J. Acc. Chem. Res. 2009; 42: 1719 1c Chen J, Cao Y. Acc. Chem. 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Soc. 1993; 115: 8495 9 A similar reaction with use of 425 nm LED (6 W) also proceeded but the result was inferior (25% yield) and no reaction took place under heating (80 °C). 10 Further reducing the amount of 1a (5 equiv) resulted in low yield (31%). 11 We also investigated the [2+2] photocycloaddition of some 3- or 4-substituted coumarin derivatives, such as coumarin, coumarin-3-carboxylic acid, coumarin-3-carbonitrile, 2-oxo-2H-chromen-3-yl acetate, 4-propoxy-2H-chromen-2-one, and 7-methoxy-3-propoxy-2H-chromen-2-one, with C60 under the conditions of Table 2 . No reactions took place in all cases. 12a Harano K, Narita A, Nakamura E. Chem. Lett. 2014; 43: 877 12b Brites MJ, Santos C, Nascimento S, Gigante B, Berberan-Santos MN. Tetrahedron Lett. 2004; 45: 6927 13 The reaction of 1a with C60 was completely inhibited by the addition of 10 equiv of rubrene as a triplet quencher of C60. See: Akasaka T, Ando W. J. Am. Chem. Soc. 1993; 115: 10366 14a Montalti M, Credi A, Prodi L, Gandolfi MT. Handbook of Photochemistry, 3rd ed. CRC Press; Boca Raton: 2006 14b Arbogast JW, Darmanyan AP, Foote CS, Rubin Y, Diederich FN, Alvarez MM, Anz SJ, Whetten RL. J. Phys. Chem. 1991; 95: 11 15a Mikami K, Matsumoto S, Ishida A, Takamuku S, Suenobu T, Fukuzumi S. J. Am. Chem. Soc. 1995; 117: 11134 15b Tokuyama H, Isobe H, Nakamura E. J. Chem. Soc., Chem. Commun. 1994; 2753 15c Arbogast JW, Foote CS, Kao M. J. Am. Chem. Soc. 1992; 114: 2277 16 The reactions of photoexcited C60 thorough single-electron transfer process are well known. For recent reviews, see ref. 4. 17 Schuster and Wilson proposed the addition of triplet excited states of enones to fullerene, via triplet 1,4-biradical intermediate of enones in Ref. 8b. However, if our reaction proceeds to give the [2+2] cycloaddition products via 1,4-biradical intermediates of 3-alkoxycoumarins, the products should be given in a 1:1 diastereomixture. 18 Stereoselective [2+2] Photocycloaddition of 3-Alkoxycoumarins with C60; Typical Procedure A 50 mL Pyrex screw-capped test tube was charged with C60 (0.05 mmol), 3-alkoxycoumarin 1 (0.50 mmol), and ODCB (5 mL). The reaction mixture was bubbled through with argon gas for 10 min. Then, this test tube was purged with argon and sealed. The reaction mixture was irradiated by using a UV-LED (365 nm, 50 W). The reaction was monitored by analytical HPLC. After 16 h, the solvent was evaporated under reduced pressure, and then MeOH was added. The sediment was filtered and washed with MeOH. The residue was purified by silica-gel column chromatography (hexane/toluene, 2:1) to give 2 as a solid. Compound 2a: 14.3 mg, 31% yield as a brown solid. 1H NMR (500 MHz, CDCl3): δ = 0.89 (t, J = 7.6 Hz, 3 H), 1.60–1.69 (m, 2 H), 4.12–4.24 (m, 2 H), 5.46 (br, 1 H), 7.28–7.33 (m, 1 H), 7.46 (d, J = 4 Hz, 2 H), 7.70 (d, J = 6.8 Hz, 1 H). 13C NMR (125 MHz, CDCl3/CS2 = 5:1): δ = 10.47, 22.22, 55.87, 66.61 (two peaks overlap), 67.58, 96.20, 120.50, 125.05, 126.63, 128.43, 128.99, 129.15, 130.35, 138.58, 139.87, 141.42, 141.65, 142.03, 142.26, 142.40, 142.57, 142.80, 143.19, 143.55, 144.20, 144.86, 145.44, 145.56, 145.71, 145.78, 146.22, 146.34, 146.65, 146.83, 147.93, 148.55, 156.24, 169.81. HRMS (ESI): m/z calcd for C72H12O3 [M – CO + K]: 935.0474; found: 935.0670. Compound 2b: 16.5 mg, 16% yield as a brown solid. 1H NMR (500 MHz, CDCl3): δ = 2.03–2.05 (m, 2 H), 2.61–2.71 (m, 2 H), 4.31 (dt, J = 8.4, 4.8 Hz, 1 H), 4.41 (dt, J = 8.8, 5.2 Hz, 1 H), 5.48 (s, 1 H), 7.10 (d, J = 5.6 Hz, 2 H), 7.19 (t, J = 5.6 Hz, 1 H), 7.25–7.28 (m, 2 H), 7.45 (t, J = 6.0 Hz, 1 H), 7.56 (d, J = 6.0 Hz, 1 H), 7.62 (dt, J = 6.4, 1.2 Hz, 1 H), 7.81 (d, J = 6.0 Hz, 1 H). 13C NMR (125 MHz, CDCl3): δ = 30.38, 32.09, 55.57, 65.21, 66.56 (two peaks overlap), 96.20, 120.62, 125.18, 126.13, 128.47, 129.40, 130.53, 136.39, 136.90, 138.37, 139.34, 139.78, 139.86, 139.92, 139.98, 141.12, 141.47, 141.52, 141.69, 142.06, 142.17, 142.30, 142.44, 142.60, 142.74, 142.84, 142.90, 142.96, 143.09, 144.57, 144.71, 144.86, 144.91, 144.98, 145.23, 145.47, 145.51, 145.55, 145.60, 145.68, 145.82, 146.16, 146.23, 146.32, 146.36, 146.39, 146.54, 146.64, 146.69, 146.82, 146.88, 147.99, 148.26, 148.62, 152.34, 156.33, 169.92. HRMS (ESI): m/z calcd for C78H16O3 [M – CO + K]: 1011.0787; found: 1011.0247. Compound 2c: 11.8 mg, 24% yield as a brown solid. 1H NMR (500 MHz, CDCl3): δ = 2.04–2.09 (m, 2 H), 2.36–2.43 (m, 2 H), 3.67 (s, 3 H), 4.37 (dt, J = 8.8, 4.8 Hz, 1 H), 4.43 (dt, J = 8.4, 5.2 Hz, 1 H), 5.47 (s, 1 H), 7.43–7.45 (m, 1 H), 7.55 (d, J = 5.6 Hz, 1 H), 7.60–7.62 (m, 1 H), 7.79 (d, J = 6.0 Hz, 1 H). 13C NMR (125 MHz, CDCl3): δ = 23.97, 29.68, 51.73, 55.31, 64.74, 66.56 (two peaks overlap), 96.00, 120.43, 125.01, 127.69, 128.10, 129.16, 130.36, 130.50, 136.19, 136.74, 139.59, 139.74, 139.80, 141.34, 141.51, 141.90, 142.00, 142.12, 142.26, 142.42, 142.58, 142.67, 142.78, 142.91, 143.05, 144.33, 144.53, 144,68, 144.74, 144.79, 145.02, 145.30, 145.39, 145.45, 145.51, 145.62, 146.06, 146.22, 146.36, 146.48, 146.65, 146.70, 147.81, 148.06, 148.44, 152.05, 156.09, 169.65, 173.13. HRMS (ESI): m/z calcd for C74H14O5 [M – CO + K]: 993.0529; found: 993.0797. Compound 2d: 6.5 mg, 13% yield as a brown solid. 1H NMR (500 MHz, CDCl3): δ = 2.20–2.31 (m, 2 H), 3.40–3.48 (m, 2 H), 4.42–4.48 (m, 1 H), 4.53–4.60 (m, 1 H), 5.49 (s, 1 H), 7.44 (t, J = 7.0 Hz, 1 H), 7.56 (d, J = 8.5 Hz, 1 H), 7.62 (t, J = 7.5 Hz, 1 H), 7.79 (d, J = 7.0 Hz, 1 H). 13C NMR (125 MHz, CDCl3): not detected because of the low solubility of 2d in organic solvents. LRMS (APCI): m/z calcd for C72H11BrO3 [M – C]: 989; found: 989. Compound 2e: 2.9 mg, 16% yield as a brown solid. 1H NMR (500 MHz, CDCl3): δ = 1.42–1.45 (m, 2 H), 1.70–1.74 (m, 2 H), 2.02–2.07 (m, 2 H), 4.29–4.34 (m, 1 H), 4.39–4.43 (m, 1 H), 4.96 (d, J = 10.0 Hz, 1 H), 5.00 (d, J = 16.5 Hz, 1 H), 5.48 (s, 1 H), 5.71–5.78 (m, 1 H), 7.44–7.46 (m, 1 H), 7.55 (d, J = 7.5 Hz, 1 H), 7.62 (t, J = 7.0 Hz, 1 H), 7.79 (d, J = 7.0 Hz, 1 H). 13C NMR (125 MHz, CDCl3): δ = 25.17, 28.18, 29.85, 33.35, 51.04, 55.56, 64.60, 65.97, 115.06, 120.55, 125.11, 127.85, 128.41, 129.29, 130.43, 130.67, 136.34, 138.38, 139.29, 139.73, 139.86, 141.46, 141.50, 141.68, 142.10, 142.25, 142.31, 142.44, 142.60, 142.73, 142.84, 143.11, 143.20, 144.60, 144,77, 144.86, 144.97, 145.47, 145.60, 145.93, 146.20, 146.39, 146.53, 146.64, 146.87, 147.99, 148.31, 148.61, 152.22, 156.29, 169.99. LRMS (APCI): m/z calcd for C75H16O3 [M – C]: 951; found: 951. Compound 2g: 9.5 mg, 16% yield as a brown solid. 1H NMR (500 MHz, CDCl3): δ = 0.86–1.88 (m, 16 H), 4.00–4.02 (m, 2 H), 4.30–4.41 (m, 2 H), 5.49 (br s, 1 H), 6.81 (s, 1 H), 7.24–7.27 (m, 1 H), 7.30 (d, J = 6.0 Hz, 1 H), 7.36–7.39 (m, 2 H), 7.42 (t, J = 6.0 Hz, 1 H), 7.54 (d, J = 6.0 Hz, 1 H), 7.61 (t, J = 6.0 Hz, 1 H), 7.80 (d, J = 6.4 Hz, 1 H). 13C NMR (125 MHz, CDCl3): not detected because of the low solubility of 2g in organic solvents. HRMS (ESI): m/z calcd for C88H30O6 [M – CO + K]: 1193.1730; found: 1193.1783.
