2
S.H. Lim, D.W. Cho / Tetrahedron Letters xxx (xxxx) xxx
from these photoreactions were that reaction efficiencies (i.e., con-
version/product yields vs irradiation time) could be varied depend-
ing on reaction solvent system. Especially, reaction efficiencies
were improved when polar protic EtOH solvent was added to pure
toluene solvent [11a,13b]. It is worthy to mention that neither bis-
nor multi-pyrrolidine ring fused photoproducts were observed in
current reaction conditions.
In the photoreactions of O -purged solutions, both TMS and
2
cyano group containing trans-fulleropyrrolidines 14a-14c were
also produced more predominantly or exclusively. (Table 2)
Interestingly, the reactions of O
containing 13a-13c and C60 took place chemoselectively to give
4a-14c as a sole product. Here, it is worthy to mention that pho-
tochemical reaction conducted in O -purged condition required
less irradiation time to bring about high conversion of starting
fullerene C60 than those performed in N -purged condition did.
Under the nearly equal reaction conditions, photochemical
reactions of phenethyl (PhCH CH -) substituted -aminonitrile
analogs 13d-13f were also performed.
As described in Scheme 3 and Tables 3 and 4, the product distri-
bution profiles arisen from the reactions of 13d-13f with C60 were
quite comparable to those observed from the reactions of 13a-13c
with C60. Specifically, when either deoxygenated or oxygenated
solutions containing C60 and 13d-13f were irradiated, photoreac-
tions took place to give rise to formation of both TMS and cyano
group substituted trans-fulleropyrrolidines 14d-14f with a highly
chemo- and stereoselective manner. Equally interesting point
was that regardless of the presence of electron withdrawing group
2
-purged 10% EtOH-ODCB solutions
1
2
2
Scheme 1. Preparation of a-aminonitrile substrates 13a-13f.
2
2
a
Firstly, photoreactions of C60 with
11a], bearing both TMSCH and benzyl group, were performed.
-purged condition, as can be seen from Scheme 2 and
a-aminonitriles 13a-13c
[
2
In the N
2
Table 1, while the photoreactions of pure toluene solution
containing non (p-H, 13a)- and para-OMe (13b) substituted
benzylamines and C60 produced TMS group containing trans-
fulleropyrrolidines 14a-14b [11a] predominantly along with non-
TMS containing fulleropyrrolidines 15a-15b [11a] (entries 1–2),
the reaction of para-F substituted benzylamine 13c and C60 gave
rise to formation of a photoadduct 14c [11a] solely (entry 3)
Noticeably, the reaction of 13c with C60 required much longer
irradiation time to bring about high conversion yields [11,13a].
Similar product distribution patterns were observed in the pho-
(
EWG) (i.e., para-F) on phenyl ring in 13f, in which EWG generally
cause diminish reaction efficiencies [13a], reaction efficiencies for
all of 13d-13f were quite similar.
The structure of all of photoproducts, 14a-14f and 15a-15b,
toreactions of 13a-13c and C60 under the N
EtOH-toluene (entries 4–6) or 10% EtOH-ODCB solution (entries
–9), albeit yields are a little different. Interesting results made
2
-purged, either 10%
1
secured in these reactions were clearly assigned by using H- and
1
3
C NMR, HRMS and UV–visible spectroscopic methods as well
7
as by comparison of data to those of previously reported fulleropy-
rrolidine derivatives [7,9,11,14]. In addition, based upon the
nuclear overhauser enhancement spectroscopic technique (NOESY)
[
7a,8c,11a], stereochemistry of photoadducts could be successfully
determined as a trans-isomer.
As can be seen by viewing the data shown in Table 1–4, we
found that both the reaction condition and the structural nature
of a-aminonitriles play an important role in governing the irradia-
tion time required to bring about high-yielding conversion- and
chemical-yields (i.e., reaction efficiencies). Thus, in order to gain
quantitative information about the reaction efficiencies for these
photoreactions of 13a-13f with C60, relative quantum efficiencies
(U
rel) of the photoreactions were determined (see Experimental).
Specifically, by setting the rel for the reaction of 13c with C60
under the -purged 10% EtOH-ODCB solution to be unity
rel = 1), rel for all of amines 13a-13f was then determined.
U
N
2
Scheme 2. Photochemical reactions of C60 with a-aminonitriles 13a-13c.
(U
U
Table 1
Product and yields of photoreactions of C60 with
a-aminonitriles 13a-13c in deoxygenated (N
2
-purged) condition.a
Entry
Amine
Reaction condition
Irradiation time (h)
Conversion (%)b
Yield (%)c
1
2
3
4
5
6
7
8
9
13a
13b
13c
13a
13b
13c
13a
13b
13c
Toluene
Toluene
Toluene
10% EtOH-toluene
10% EtOH-toluene
10% EtOH-toluene
10% EtOH-ODCB
10% EtOH-ODCB
10% EtOH-ODCB
2
2
6
2
2
6
3
3
6
77
78
50
83
85
69
87
89
62
14a (32), 15a (2)
14b (24), 15b (3)
14c (15)
14a (42), 15a (11)
14b (44), 15b (15)
14c (41)
14a (40), 15a (3)
14b (47), 15b (1)
14c (30)
a
b
c
2
20 mL of solutions containing C60 (0.28 mmol) and a-aminonitriles (0.56 mmol) were irradiated during the given period time.
Conversion yield was determined by recovered C60
Isolation yields.
.
Please cite this article as: S. H. Lim and D. W. Cho, Photoaddition reactions of azomethine ylides generated from a-aminonitriles to fullerene C60: Formation