Methano[60]fullerenes
SHORT COMMUNICATION
Scheme 2 for numbering) and a weaker 4-bond correlation Table 1. 2D-INADEQUATE NMR analysis (200 MHz, CDCl3) of
to the fullerenyl sp3 carbon at δ = 81.2 (C-9). The full-inten-
bis-adduct 6.
sity signal at δ = 69.8 was assigned to the malonic cyclopro-
pyl sp3 carbon atoms (C-16 and C-17).[13] Similar corre-
lations were observed in the HMBC spectra of 12.
C atom
δ [ppm]
Single-bond correlation
1
number[d]
(C atom number) JC–C/Hz[e]
1
82.92
(2) 36.0
As further confirmation of the e-edge-regiochemistry, 2,5
146.71
141.99
139.55
137.49
155.68
81.19
137.80
145.49
142.94
69.84
144.21
141.80
144.91
141.32
146.07
142.93
142.66
145.28
143.01
139.44
145.45
144.26
144.26
144.16
146.81
146.85
144.35
148.51
147.84
144.19
147.14
(1) 36.0, (3) 59.5, (6) 70.5
(2) 59.5, (15) 71.5
(2) 70.5, (7) 56.5, (13) 56.5
(6) 56.5, (8) 71.5, (22) 59.0
(7) 71.5, (9) 40.5, (25) 60.0
(8) 40.5
(6) 56.5, (14) 69.0, (21) 55.0
(13) 69.0, (15) 57.5
(3) 71.5, (14) 57.5, (16) 54.0
(15) 54.0, (34) 54.0
compound 6 was synthesized starting from 20–30% 13C-
3,4
6,12
enriched fullerene, and 2D-INADEQUATE NMR experi-
ments were conducted. Assignment of the carbon sphere
was achieved on the basis of one-bonded 13C-13C connectiv-
7,11
8,10
9
13,20
14,19
15,18
16,17
21,30
ities and examination of the carbon–carbon coupling (1JCC
)
values knowing typical values for C (sp2)-C (sp3) bonds (Ϸ
48 Hz), the longer 5,6 ring-fused bonds (53–59 Hz) and the
shorter 6,6 ring-fused bonds (65–71 Hz).[11–13] This analysis
(13) 55.0, (22) 56.0,(31) 71.0
(7) 59.0, (23) 70.0, (21) 56.0
(42) 55.0, (22) 70.0, (24) 56.5
(23) 56.5, (25) 69.0, (44) 58.0
(8) 60.0, (24) 69.0
facilitated the unambiguous characterisation of the entire 22,29
23,28
fullerene sphere (Figure 1 and Table 1). For example, a four
24,27
bond sequential connectivity was observed from the sp3
25,26
carbon at δ = 69.8 (C-16/17, malonate site) to the sp3 car-
bon at δ = 82.9 (C-1, dihydropyrrole site). These results
confirmed that the second addition occurred at the e-edge
position (Figure 1) and allowed the subsequent analysis of
the entire sphere (Table 1). The UV/Vis spectra of 6 and 12
showed two absorbance bands in DCM solution at 424 and
31,40
32,39
33,38
34,37
35,36
41,48
(42,47)[a]
(21) 71.0, (32),[b] (41) 59.0
(31),[b] (33) 67.5, (50) 59.0
(32) 67.5, (34) 57.5
(16) 54.0, (33) 57.5, (35) 72.0
(34) 72.0, (51) 59.0
(42) 70.0, (31) 59.0, (49) 58.0
(23) 55.0, (41) 70.0
451 nm and 424 and 455 nm, respectively, consistent with (43,46)[a]
[c]
an e-edge-[60]fullerene bis-adduct.[10a]
44,45
(24) 58.0
49,55
We previously demonstrated that mono- and bis[60]ful-
50,54
(41) 58.0, (56) 69.0
(32) 59.0, (51) 70.0
(50) 70.0, (52) 59.0
(51) 59.0, (60) 69.0
(57) 59.5, (60) 53.5
(56) 59.5
lerenyldihydropyrroles undergo reductive ring-opening re-
51,53
actions upon treatment with boron trifluoride–diethyl ether,
and sodium cyanoborohydride to give novel dihydrometh-
ano[60]fullerene derivatives.[8] Treatment of 12 with boron
trifluoride–diethyl ether, acetic acid and an excess of so-
dium cyanoborohydride for 15 min accomplished a re-
ductive ring-opening reaction to provide 13 in 40% yield,
as well as the known methanofullerene, C60C(CO2Me)2.
52
56,59
57,58
60
(52) 69.0, (56) 53.5
[a] Coincidental peaks. [b] Unable to obtain coupling constant due
to peak proximity. [c] Unable to obtain correlations due to peak
proximity. [d] The shift assignments for several very closely spaced
peaks may be reversed as they become overlapped in the 13C-lab-
eled sample. Specifically this applies to the following combinations:
21,30/42,47/43,46/57,58/44,45; 50,54/49,55; 14,19/41,48; 15,18/
31,40. Reversing any or all of these shift assignments never leads to
a different structure however. [e] J Values measured to +/– 0.5 Hz.
1
The H NMR spectrum of 13 revealed a two-proton-cou-
pled spin system at δ = 3.41 (d, J = 12 Hz, 1 H, NH) and
4.66 (d, J = 12 Hz, 1 H, Hα) with a singlet resonance at δ
= 5.16 ppm for Hγ to the fullerene cage (Scheme 4). The
singlet resonance at δ = 6.36 ppm corresponded to the ful-
lerenyl proton. The 13C NMR spectrum of 13 revealed 56
Reductive ring-opening of 6 required a larger excess of
sp2 resonances indicative of a fullerenyl bis-adduct pos- sodium cyanoborohydride (30 equiv.) and longer reaction
sessing no plane of symmetry. The addend and the fullerene times (18 h) and yielded 14 and 15 in yields of 50% and
sp3 carbon atoms were assigned by HSQC and HMBC ex- 10%, respectively (Scheme 4). Compound 14 exhibited no
1
periments with the former allowing the assignments of the plane of symmetry with the H NMR spectrum of 14 re-
1H-13C coupling for the fullerenyl proton and the sp3 fuller- vealing a single fullerenyl proton at δ = 6.10 and two sets
enyl carbon at δ = 58.7 ppm. Other correlations allowed the of diastereotopic benzyl methylene resonances at δ = 5.74
assignment of the dihydropyrrole carbon atoms, Cα and Cγ and 5.69 ppm (J = 11 Hz) and at δ = 4.80 and 4.68 ppm
at δ = 71.3 and 66.5 ppm, respectively. The HMBC spec- (J = 11 Hz). A singlet resonance corresponding to Hγ was
trum reveals a strong 2-bond correlation from Hα to the observed at δ = 5.18 ppm. A two-proton-coupled spin sys-
fullerene sp3 carbon bearing the glycine substituent at δ = tem was identified as Hα (δ = 4.53 ppm, d, J = 13 Hz) and
67.3 ppm. There were also three moderately strong 3-bond the NH (δ = 3.37 ppm, d, J = 13 Hz).
correlations; i) from the fullerenyl proton to Cα, ii) from Hα
In conclusion, a novel e-edge-[60]fullerenylmethanodihy-
to the sp3 fullerenyl methine carbon; and iii) from Hγ to Cα. dropyrrole adduct 6 has been prepared in an exclusive man-
The remaining two sp3 fullerenyl carbon atoms appeared at ner using a mixed-tethered system. The regiochemical out-
δ = 69.9 and 70.0 ppm and were identified as part of the come was found to be independent of the order of addition
cyclopropane ring. The bridgehead carbon of the malonate of either the N-(diphenylmethylene)glycinate or the malon-
site was not observed due to overlap with the three methoxy ate moieties. Ring-opening of the dihydropyrrole function-
signals.
ality of the bis-adduct under reductive conditions gave a
Eur. J. Org. Chem. 2005, 5158–5162
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
5161