Synthesis of Novel 3,4‐Dihydro‐2H‐pyrrolo[60]fullerene Derivatives Bearing an Alkylsulfanyl Substituent

Abstract

C₆₀ reacts thermally with azomethine ylides of glycine imines, in methyl ester and free acid form, bearing two alkylsulfanyl groups to give dihydro‐pyrrolo[60]fullerene derivatives 2 and 5a, respectively, in a 1,3‐dipolar cycloaddition reaction. The yields of products were found to depend strongly on acidic conditions applied and the size of the alkylsulfanyl substituent.

Keywords:

• Fullerenes
• Pyrrolidines
• Cycloaddition
• Azomethine

Acknowledgement

Financial support from the Research Committee of the University of Ioannina, (Program No: 607), is gratefully acknowledged. We also thank the NMR Center of University of Ioannina for NMR spectra, the Mass Spectrometry Service of Kings College, London, and the Laboratory of Peptide Chemistry at University of Ioannina for MS spectra. We also thank Professor C. S. Foote at UCLA for valuable discussions and comments.

Notes

^aThe FT‐IR spectra for 2a (KBr pellet) showed strong absorptions at 2924 cm⁻¹, 2859 cm⁻¹ (CH), 1743 cm⁻¹ (carbonyl group), and 1603 cm⁻¹ (imine group). UV‐VIS spectra for 2a (in hexanes) showed strong absorptions at 208, 255, 311, and 426 nm. Elemental analysis: calculated for C₆₅H₇NO₂S (2a): C, 90.26; H, 0.82; N, 1.62; S, 3.71%. Found: C, 90.74; H, 0.91; N, 1.92; S, 3.64%. The FT‐IR spectra for 2b (KBr pellet) showed strong absorptions at 2924 cm⁻¹, 2858 cm⁻¹ (CH), 1750 cm⁻¹ (carbonyl group), and 1603 cm⁻¹ (imine group). ¹H NMR for 2b (250 MHz, CDCl₃) δ (ppm): 6.54 (s, 1H), 3.87 (s, 3H, –OMe), 3.59 (m, 2H), 1.66 (t, 3H, J = 7.3 Hz). ESI‐MS for 2b showed a molecular ion at 880.7 (MH)⁺. The FT‐IR spectra for 2c (KBr pellet) showed strong absorptions at 2953 cm⁻¹, 2851 cm⁻¹ (CH), 1744 cm⁻¹ (carbonyl group), and 1602 cm⁻¹ (imine group). ¹H NMR for 2c (250 MHz, CDCl₃) δ (ppm): 6.56 (s, 1H), 3.88 (s, 3H, –OMe), 3.56 (m, 2H), 2.02 (sextet, 2H, J = 7.1 Hz), 1.20 (t, 3H, J = 7.3 Hz). ESI‐MS for 2c showed a molecular ion at 894.7 (MH)⁺.

The FT‐IR spectra for 2d (KBr pellet) showed strong absorptions at 2921 cm⁻¹, 2851 cm⁻¹ (CH), 1752 cm⁻¹ (carbonyl group), and 1602 cm⁻¹ (imine group). ¹H NMR for 2d (250 MHz, CDCl₃) δ (ppm): 6.56 (s, 1H), 4.36 (m, 1H), 3.88 (s, 3H, –OMe), 1.73 (d, 3H, J = 6.6 Hz), 1.67 (d, 3H, J = 6.8 Hz). ESI‐MS for 2d showed a molecular ion at 894.7 (MH)⁺.

^bGlycine 4a was prepared by saponification of 1a with Na₂CO₃ in MeOH/H₂O mixture followed by acidification with KHSO₄ to pH 5–6, and extraction of the water phase with CH₂Cl₂ (64% yield). ¹H NMR (250 MHz, CDCl₃) δ (ppm): 4.05 (s, 2H), 2.60 (s, 3H), 2.43 (s, 3H).

^cThe FT‐IR spectra for 5a (KBr pellet) showed strong absorptions at 2916 cm⁻¹ (CH) and 1605 cm⁻¹ (imine group). ¹H NMR (250 MHz, CDCl₃) δ (ppm): 5.83 (s, 2H), 2.93 (s, 3H). ESI‐MS for 5a showed a molecular ion at 808.6 (MH)⁺.