Method for the synthesis of amine-functionalized fullerenes involving set-promoted photoaddition reactions of -silylamines

Article abstract of DOI:10.1021/jo501034t

A novel method for the preparation of structurally diverse fullerene derivatives, which relies on the use of single electron transfer (SET)-promoted photochemical reactions between fullerene C₆₀ and α-trimethylsilylamines, has been developed. Photoirradiation of 10% EtOH-toluene solutions containing C₆₀ and α-silylamines leads to high-yielding, regioselective formation of 1,2-adducts that arise through a pathway in which sequential SET-desilylation occurs to generate α-amino and C₆₀ anion radical pair intermediates, which undergo C-C bond formation. Protonation of generated α-aminofullerene anions gives rise to formation of monoaddition products that possess functionalized α-aminomethyl-substituted 1,2-dihydrofullerene structures. Observations made in this effort show that the use of EtOH in the solvent mixture is critical for efficient photoproduct formation. In contrast to typical thermal and photochemical strategies devised previously for the preparation of fullerene derivatives, the new photochemical approach takes place under mild conditions and does not require the use of excess amounts of substrates. Thus, the method developed in this study could broaden the scope of fullerene chemistry by providing a simple photochemical strategy for large-scale preparation of highly substituted fullerene derivatives. Finally, the α-aminomethyl-substituted 1,2-dihydrofullerene photoadducts are observed to undergo photoinduced fragmentation reactions to produce C₆₀ and the corresponding N-methylamines.

Full text of DOI:10.1021/jo501034t

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Article
Method for the Synthesis of Amine Functionalized Fullerenes
Involving SET Promoted Photoaddition Reactions of #-Silylamines
Suk Hyun Lim, Jinju Yi, Gyeong Min Moon, Choon Sup Ra, Keepyung Nahm, Dae Won Cho, Kyungmok
Kim, Tae Gyung Hyung, Ung Chan Yoon, Ga Ye Lee, Soojin Kim, Jinheung Kim, and Patrick S Mariano
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/jo501034t • Publication Date (Web): 01 Jul 2014
Downloaded from http://pubs.acs.org on July 5, 2014
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The Journal of Organic Chemistry is published by the American Chemical Society.
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Method for the Synthesis of Amine Functionalized Fullerenes Involving SET Promoted
Photoaddition Reactions of α-Silylamines
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1*
Suk Hyun Lim, Jinju Yi, Gyeong Min Moon, Choon Sup Ra, Keepyung Nahm, Dae Won Cho,
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2*
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Kyungmok Kim, Tae Gyung Hyung, Ung Chan Yoon, Ga Ye Lee, Soojin Kim , Jinheung
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Kim, Patrick S. Mariano
1
Department of Chemistry, Yeungnam University, Gyeongsan, Gyeongbuk 712-749, Korea
(dwcho00@yu.ac.kr)
2
Department of Chemistry and Chemistry Institute for Functional Materials,
Pusan National University, Busan 609-735, Korea
(
ucyoon@pusan.ac.kr)
3
Department of Chemistry and Nano Science, Global Top5 Research Program,
Ewha Womans University, Seoul 120-750, Korea
4
Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque,
New Mexico 87131, USA
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Graphical Abstract
R1
SiMe3
1. hv
H
+
N
R2
R
N
1
2. SET
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R2
3
. ~SiMe +
3
(R
1
,
R =
2
alkyl, Bn)
H+
SET
R1
~ SiMe +
3
SiMe3
R1
+
N
R2
N
C-C bond
forming
R2
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A novel method for the preparation of structurally diverse fullerene derivatives, which relies on
the use of single electron transfer (SET) promoted photochemical reactions between fullerene C60
and α-trimethylsilylamines, has been developed. Photoirradiation of 10% EtOH-toluene solutions
containing C and the α-silylamines leads to high yielding, regioselective formation of 1,2-adducts
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that arise through a pathway in which sequential SET-desilylation occurs to generate
intermediates α-amino and C anion radical pairs, which undergo C-C bond formation. Protonation
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of generated α-aminofullerene anions gives rise to formation of mono-addition products that possess
functionalized α-aminomethyl substituted 1,2-dihydrofullerene structures. Observations made in this
effort show that the use of EtOH in the solvent mixture is critical for efficient photoproduct
formation. In contrast to typical thermal and photochemical strategies devised previously for the
preparation of fullerene derivatives, the new photochemical approach takes place under mild
conditions and it does not require the use of excess amounts of substrates. Thus, the method
developed in this study could broaden the scope of the fullerene chemistry by providing a simple
photochemical strategy for large scale preparation of highly substituted fullerene derivatives. Finally,
the α-aminomethyl substituted 1,2-dihydrofullerene photoadducts are observed to undergo
photoinduced fragmentation reactions to produce C and the corresponding N-methylamines.
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Introduction
Since the time of the first report describing its preparation using laser vaporization of graphite
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by Kroto et al. and its large scale synthesis, fullerene (C ) has received intense interest owing to its
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12-20
chemical and physical properties, and broad applications in the material
and biological
sciences. Of specific interest are [6,6]-phenyl C -butyric acid methyl ester (PCBM) and
61
fulleropyrrolidine, which have found widespread applications as n-type organic conducting materials
in organic field effect transistor and organic photovoltaic devices. These applications are a
consequence of the unique and useful electronic properties of fullerenes, such as high electron
2
1-23
24-27
28
affinities,
small reorganization energies
and high electron transporting abilities, as well as
their interesting physical properties including high solubility in common solvents.
The commonly employed synthetic approaches for the preparation of fullerene C derivatives
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29-32
33,34
35-
involve 1,3-dipolar cycloadditions,
cyclopropanations,
addition of organometallic reagents,
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45-47
base-promoted nucleophilic additions,
transition metal mediated free radical reactions,
and
48-52
photoinduced single electron transfer (SET) reactions.
The latter approach in this group is of
particular interest because in comparison to the others it relies on the use of more environmentally
benign conditions. As mentioned above, fullerenes are excellent electron acceptors owing to the fact
that they have high electron affinities associated with high reduction potentials (for C E = -0.42
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red
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3-55
V vs. SCE in PhCN).
In addition, the singlet excited state of fullerenes, generated by direct
1
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irradiation, undergo highly efficient intersystem crossing (for C60 ΦISC = 1) to produce the
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corresponding triplet excited state. Importantly, the fullerene triplet has a relatively high reduction
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potential (for C Ered = 1.14 V vs SCE) and, as a result, it should participate in rapid (diffusion
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controlled) SET with a wide variety of ground state electron donors that possess oxidation potentials
lower than ca. 1.1 V.
Several reports already exist describing highly inefficient SET promoted excited state addition
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reactions of tertiary alkyl and aromatic amines to C60.
These processes follow pathways in which
-•
SET occurs to form amine cation radicals (aminium radicals) and the fullerene radical anion (C60 ).
55
The low oxidation potentials of tertiary amines (Eox <1 V vs.Ag/AgCl) and relatively high
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reduction potential of the triplet state of C ( E = 1.19 V vs Ag/AgCl), combine to make the free
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red
energy changes for SET in these cases negative (∆GSET <0 V) and, consequently, the rate constants
9
10
-1 -1 55,61
for these processes (kSET ) nearly equal to that of diffusion (1 x 10 - 10 M s ).
Subsequent α-
CH deprotonation of the formed aminium radicals takes place to form α−amino radicals that couple
-•
with C60 to form the anion precursors of adducts. This mechanistic pathway mimics those that drive
numerous excited state reactions occurring between amines and a variety of electron acceptors,
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63-65
66-67
68-72
including cyanoarenes, saturated
and α,β-unsaturated ketones,
and phthalimides.
Among the tertiary amines that participate in these types of SET promoted photochemical
processes, those that possess α-trialkylsilyl substitution have unique features that enable them to
67
undergo both highly regioselective and efficient SET photoadditions. Specifically, trialkylsilyl
substituted amines are readily oxidized by SET to corresponding aminium ions owing to the fact that
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they have ca. 0.4 V lower oxidation potentials than their non-silyl analogs. This property is a
consequence of radical cation stabilization by overlap of the high energy σC-Si orbital with the half-
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3-75
filled nitrogen p-orbital in these aminium radicals.
In addition, overlap of the σC-Si-p and N p-
orbital leads to weakening of the C-Si bond and an increase in the electron deficiency at Si in the α-
trialkylsilylaminium radical, which combine to facilitate rapid transfer of the trialkylsilyl groups to
silophiles forming carbon-centered α-amino radicals. Importantly, the results of earlier laser flash
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photolysis (LFP) investigations
show that water and alcohol promoted desilylation reactions of
α-trialkylsilylaminium radicals take place at much higher rates than do α-CH deprotonations of non-
silyl analogs, a feature that contribute to the high regioselectivities and efficiencies.
In early studies, we also demonstrated that SET promoted photochemical addition and
cyclization reactions of a number of α-trialkylsilyl substituted electron donors including allyl- and
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68,69,80
benzyl-silanes, and silyl-ethers, -thioethers and –amides
take place regioselectively and
efficiently and that these processes can be applied to the synthesis of interesting target
69b,79a,81
molecules.
Owing to the growing importance of need for functionalized fullerenes in current
strategies employed to design photovoltaic devices, we have initiated a broad program to explore
SET photoaddition reactions of a variety of α-trialkylsilyl substituted electron donors to fullerenes
with the aim of evaluating the scope and efficiencies of the processes. In the initial phase of this
long-range study, we explored photoaddition reactions of C60 with α-silyl tertiary amines. The
results of this effort, presented below, demonstrate that these processes, following the pathway
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depicted in Scheme 1, take place with high chemical and quantum efficiencies and, consequently,
they constitute a potentially powerful and general method to synthesize novel fullerene derivatives.
Scheme 1.
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9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
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0
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H
hv
R'
N
+
Me Si CH2 N R
3
R
R'
1
. hv
1. C-C bonding
+
2. SET
2.
~ H
Nu
H
CH2 N R
R'
Me Si Nu
H
3
Me Si CH2 N R
3
R'
Results and Discussion
Preparation of α-silyl tertiary amine donors. Photoaddition reactions of fullerene (C ) with a
6
0
wide variety of α-trimethylsilyl substituted tertiary amines were explored in this investigation. The
routes employed to prepare the amines are outlined in Schemes 2-4. For example, the known α-
8
2
69c
83
trimethylsilyl substituted secondary amines 1, 6, and 9 react with various types of alkyl halides
in the presence of K CO to yield the corresponding α-silyl tertiary amines 2-5, 7-8, and 10-14 in
2
3
high yields (55-90 %) (Scheme 2). α-Silyl amines 16, 19, 20 and 22 are synthesized by employing
base promoted substitution reactions of commercially available secondary amines 15, 17, 18, and 21
with iodomethyltrimethylsilane (Scheme 3).
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Scheme 2.
RX
H
N
Me Si
Me Si
3
N
3
R1
4CH3
K CO /CH CN
2
3
3
2
%, from 1
)
0
1
2
3
4
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7
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9
0
1
2
3
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0
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9
0
1
6
9
= CH2
(85
=
(
R
(R
1
1
(CH
2
)
)
= CH CH OCH CH
(RX Hexylbromide)
2
2
2
2
OH)
=
(
R1 Bn)
O
O
OEt
Me Si
N
Me Si
N
Me Si
N
3
3
3
Me Si
N
O
3
OH
4 (68 %, from 1)
5
=
%, from 1
7
from 6
)
3
=
%, from 1
)
(80
)
(57 %,
=
(62
(RX = 2-Methoxyethyl iodide) (RX Ethylbromoacetate)
(
RX 2-Ethylhexyl iodide)
(RX 2-Ethylhexyl
iodide)
Me Si
N
Me
3
Si
N
Me
=
3
Si
N
O
O
3
O
OH
10
%, from 9
(RX Hexylbromide)
11
(90 %,
from 9
)
(
81
)
8
%, from 6
RX BnBr)
(49
)
=
(RX 2-(2-methoxyethoxy)ethyl iodide)
=
(
O
O
N
OEt
n
O
N
N
SiMe3
O
SiMe3
12 =1, 52 %, from 9
14
%, from 9
(
n
)
(61
)
=
=
(RX Ethylbromoacetate)
(RX N-(2-iodoethoxy)ethyl phthalimide)
1
3
=
= 2, 44 %, from 9)
(n
(
RX Ethylbromopropionate)
Scheme 3.
Me SiCH I
R
R
N
3
2
N
H
K CO /CH CN
SiMe3
2
3
3
= CH2
2
4
16
19
20
(R
(R
(R
= CH2
= Me, 79
= Bn, 42
2
4OH, 45
(CH ) %)
1
1
1
5
7
8
(R
(R
(R
(CH
O
)
OH)
=
%)
%)
Me)
Bn)
=
O
O
O
Me SiCH I
H
3
2
N
N
EtO
OEt
EtO
OEt
K CO /CH CN
2
3
3
SiMe3
21
2
2
(69 %)
α-Silyl tertiary amine oxidation potentials. Prior to initiating studies of the photoaddition
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reactions of α-silyl tertiary amines with C , oxidation potential (E ) measurements were performed
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ox
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1
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1
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1
1
2
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5
5
5
5
5
6
3
*
in order to ensure that SET from the amine donors to excited state of C60 ( C ) is
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thermodynamically favorable. As can be seen by viewing the data displayed in Table S1 (See
Supporting Information), all α-silyl tertiary amine donors have E values in the range of 0.15-0.65
ox
3
*
V (vs. Ag/AgCl) that fall below the reduction potentials of C . As a result, free energies for
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3
*
o
electron transfer from the amines to C , calculated using the expression ∆G
= E (α-
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SET
ox
3
*
silylamine) - E ( C ) are negative. Thus, as has been shown by Foote and coworkers utilizing
red
60
5
5
3
*
other amine donors, the rates of SET (k ) from the α-silyl tertiary amines to C should be
SET
60
nearly equal to the diffusion controlled limit.
Photoreactions of C60 with α-silyl tertiary amines. Formation of aminomethylfullerenes.
Photoaddition reactions of C60 with the α-silyl tertiary amines were explored. As the results
displayed in Scheme 4 and Table 1 show, irradiation (450 W Hanovia medium pressure Mercury
lamp and Uranium glass filter (λ > 330 nm)) of 10 % EtOH-toluene solutions (220 mL, N purged)
2
containing C (0.28 mmol) and the α-silyl tertiary amines 2-4 (0.56 mmol) for 4 min leads to
6
0
production of the respective 1,2-adducts 23-25, as a sole products in high yields (54-94 %). No poly-
substituted photoadducts are generated in these processes even when high concentrations of the
amines or long irradiation times are employed (Table 1, entry 2).
Scheme 4.
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1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
O
OEt
H
Me Si
R1
N
hv
3
R1
C60
+
+
N R2
SiMe3
N
R2 10% EtOH-toluene
R2
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
3
3
8
9
=
2
3-37
(R2 Bn)
= CH CO
(R2
2
2Et)
Product
�
R1
R �
2
2
2
3
4
Hexyl
Hexyl
Hexyl
Hexyl
Hexyl
CH CH CH
3
CH
2CH(Et)CH2
CH CH OCH
3
2
2
25
26
2
2
CH CO Et
2
2
27
28
29
30
CH
CH CH CH
CH CH OCH CH OH
2CH(Et)CH2
2
2
3
2 2 2 2
Bn
CH CH OCH CH OH
2
2
2
2
Bn
CH CH OCH CH OCH
3
Hexyl
Bn
Bn
Bn
Bn
Bn
2
2
2
2
31
CH CO Et
CH CH CO Et
2 2 2
2 2
32
33
34
35
CH CH OCH CH -N-Phthalimide
2
2
2
2
CH CH CH CH CH OH
2
2
2
2
2
Bn
Bn
CH3
Bn
36
37
CH CO Et
CH CO Et
2
2
2 2
a
Table 1. Products and yields of photoaddition reactions of α-silyl tertiary amines with C .
60
Irradiation
Time (min)
b
c
Entry
Amine
Conversion (%)
Product (%)
1
2
3
4
5
6
7
8
9
2
4
4
100
100
93
23 (92)
23 (94)
24 (90)
25 (54)
26 (36)
26 (42)
27 (51)
28 (57)
29 (47)
30 (56)
31 (32)
d
2
3
4
4
4
69
5
8
85
5
60
8
85
7
100
88
8
8
10
11
12
8
100
93
1
0
1
8
1
16
62
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20
20
22
22
60
8
100
82
31 (76), 38 (12)
32 (54)
1
1
1
1
4
5
6
7
8
100
100
100
75
33 (67)
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
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35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
8
34 (43)
8
35 (86)
8
36 (64)
18
60
60
120
100
68
36 (91)
1
2
9
0
37 (23)
78
37 (36), 39 (4)
a
b
d
α-Silyl amine/C is 0.56/0.28 mmol in 220 mL of 10% EtOH-toluene.
60
c
Conversion was determined by recovered C . Isolation yields.
6
0
5
.6 mmol of 2 in 220 mL 10% EtOH-toluene
Irradiation of a solution of C and α-silylamine 5, which contains an N-carboxymethyl moiety,
6
0
gives rise to formation of photoadduct 26 in only a modest yield (36 %) that is not significantly
improved by using longer irradiation times (Table 1, entry 6). In reactions of the hydroxyl group
containing α-silylamines 7 and 8, 8 min irradiations bring about high conversion (100 % and 88%
respectively) of the starting amine and moderate yielding generation of the corresponding
photoproducts 27 (51 %) and 28 (57 %). Similarly, photoreaction of N-hydroxypentyl substituted α-
silylamine 16 with C (Table 1, entry 15) produces 34 in a modest yield (43 %).
6
0
66b
The photoreaction of C60 with α-silylamine 12,
which contains N-benzyl- and N-
carboxymethyl substituents (Table 1, entries 11 and 12), is interesting in that the distribution of
products formed is dependent on irradiation time. Specifically, while irradiation of a 10 % EtOH-
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1
1
1
1
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1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
toluene solution of C60 and 12 for a shorter time period of 16 min produces the expected 1-
aminomethyl-2-hydrofullerene 31 as a sole photoproduct (32 %), irradiation for 1 h gives rise to
formation of 31 (76 %) along with the fulleropyrrolidine 38 (12 %). In a similar manner,
photoreaction of C60 with N,N-dicarboxymethyl substituted α-silylamine 22 also displays an
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
84
irradiation time dependent product distribution (Table 1, entries 19 and 20), with adduct 37 being
formed solely at a shorter (1 h) irradiation time while 37 and fulleropyrrolidine 39 are produced at a
longer (2 h) time. In contrast, photoreaction of the N-carboxyethyl substituted α-silylamine 13
generates 1,2-photoadduct 32 as a sole product in modestly high yield (54 %, Table 1, entry 13). In
addition, photochemical reaction of C with N,N-dibenzyl tethered α-silylamine 20 produces adduct
6
0
3
6 exclusively even when a longer irradiation time is utilized (Table 1, entries 17 and 18).
Photoreaction of C with α-silylamine 14 was explored because the amine substrate possesses
6
0
a phthalimide group that also can serve as an electron acceptor (Table 1, entry 12). It was expected
that direct irradiation of a solution containing only 14 (λmax = 290 nm) would promote
intramolecular SET leading to formation of the zwitterionic radical 40 (Scheme 5), which would
undergo rapid desilylation followed C-C bond formation to generate cyclic amidol 41. In accord with
this expectation, irradiation of a solution of 14 in 10 % EtOH-toluene does produce 41 (39 %).
However, when the reaction mixture contains both 14 and C , irradiation leads to formation of
60
adduct 33 (67 %) exclusively (Table 1, entry 14).
Scheme 5.
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7
8
9
O
without C60
O
with C60
N
N
33
14
1
2
. hv 290
(>
. / SET
1. hv
(>290 nm)
nm)
SiMe3
O
2. SET
40
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
-
SiMe +
3
Me SiO
3
HO
O
C-C bond
O
N
N
N
O
O
N
42
4
1
1
13
Structural assignments of the photoproducts described above were made by using H and C
NMR, and UV-visible spectroscopy and HRMS (see Experimental and Supporting Information) as
well as by comparing the data to those previously reported for related compounds. Diagnostic
1
resonances are observed in the H NMR spectra of the 1,2-adducts 23-37 at 6.7-7.0 ppm, which
correspond to the proton in each that is directly bonded to the C core and consequently experiences
60
5
7-60
a characteristic deshielding effect.
In addition, the methylene protons on carbons that are bonded
1
3
to both the C60 core and nitrogen in the adducts resonate in the 4.3-4.7 ppm region. In C NMR
3
spectra, the sp fullerene core carbons of 23-37 appear at ca. 70 ppm and the adjacent methylene
1
3
carbons resonate at ca. 60 ppm. Importantly, the C NMR spectral features of 23-37 exhibit patterns
that correspond to mono-1,2-adducts of C arising by addition across the [6,6]- rather than [5,6]-ring
6
0
5
7-60
juncture.
Owing to the presence of stereogenic carbons adjacent to nitrogen atom in the fulleropyrrolidine
1
adduct 38, the methylene protons in its ester ethoxy moiety appear in the H NMR spectrum as an
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1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
AB quartet at 4.19 and 4.28 ppm and the benzylic protons appear as an AB quartet at 4.58 and 5.26
13
3
ppm. Analysis of the C NMR and DEPT spectra of 38 shows that the quaternary sp carbons in the
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
fullerene core resonate at 77.7 and 78.0 ppm, the benzylic and ester ethoxy methylenes resonate at
5
6.2 and 60.9 ppm, and the chiral methine carbons appear at 70.2 and 77.2 ppm. Unfortunately, no
information is available to aid the assignment of cis vs. trans stereochemistry to the
8
5a
85b
fulleropyrrolidine adducts. However, Gan and Jorgensen studies of the stereochemistry of 1,3-
dipolar addition reactions of ylides to maleimides showed that cis isomers are produced
predominantly. Finally, the UV-visible absorption spectra of photoproducts 23-37, 38, and 39 contain
maxima at ca. 435 nm, which are characteristic of 1,2-adducts generated by addition across the [6,6]-
5
7-60
juncture of C .
6
0
The unusual behavior of 12 and 22 in photoreactions with C60 is also displayed by ester
66b
86
containing, non-silylmethyl substituted amines 43 and 44 (Scheme 6). Irradiation of 10 % EtOH-
toluene solutions of C containing these amines, prepared by the routes shown in Scheme 8, leads to
6
0
exclusive formation of the respective fulleropyrrolidine adducts 46 and 47. These reactions require
substantially longer irradiation times (120 min, 44-53 % conversion) than those needed to promote
reaction with the silyl substituted analog 45 (30 min, 88 % conversion), which efficiently forms 1,2-
adduct 48 (64 %) and fulleropyrrolidine adduct 49 (9 %) (Scheme 6 and Table 2).
Scheme 6.
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7
8
9
O
R1
Br
OR2
O
hv/ C60
Bn
N
R1
H)
N
OR2
H
Bn
10% EtOH-toluene
K CO /CH CN
2
3
3
1
1
1
2
4
4
4
3
= H, R =
= H, R = Me
= SiMe , R =
= SiMe3,
R
(R
Et)
(
2
4
5
(
R
R
)
2
(
3
Me)
O
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
O
O
OR2
OMe
Bn
H
N
OMe
+
N Me
+
N
Bn
SiMe3
2
4
6
7
= Et, from 43
)
(R
48
45
(from )
49
45
from )
(
2
4
= Me, from 44
(R
)
a
Table 2. Products and yields of photoaddition reactions of amine 43-45 with C .
6
0
Reaction Time
b
c
Amine
Conversion (%)
Product (%)
(
min)
120
120
30
4
4
3
4
55
43
88
46 (30)
47 (39)
45
48 (64), 49 (9)
a
Amine/C is 0.56/0.28 mmol in 220 mL of 10% EtOH-toluene.
60
b
c
Conversion was determined by recovered C . Isolation yields.
6
0
Solvent Effects. Because solvent polarity and silophilicity are also important factors that
63,66,67a
influence the efficiencies of SET photoreactions of α-silylamines,
we have briefly explored
the effects of variations in the EtOH content in the mixed EtOH-toluene solvent system on the
57
58
59
efficiency of photoaddition of 20 to C . In earlier studies by Sun, Nishimura, and Cheng,
6
0
photoaddition reactions of C60 with non-silyl tethered aliphatic and aromatic tertiary amines were
conducted in pure toluene and produced 1-hydroxy-2-aminomethyl fullerenes in low yields (5-16 %).
In the current effort, solutions of 20 and C60 in toluene containing volume percentages of EtOH
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6
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8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
ranging from 0-40 % were simultaneously irradiated for 1 h. Product yields were then determined by
using UV-visible spectroscopy (Figure S1, Supporting Information) and HPLC. The results
summarized in the plot displayed in Figure S1, show that no photoproduct is generated in a 1 h (or
even 3 h) photoreaction of 20 carried out in pure toluene. In addition, as the EtOH content of the
EtOH-toluene solvent mixture is increased to 15 % the yield of photoadduct 36 increases and then
decreases when the EtOH content exceeds 15 %. The decrease in efficiencies taking place when high
concentrations of EtOH are present might be a consequence of an increasing polarity effect that
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
8
7
causes C complex formation.
6
0
These findings show that the presence of polar protic EtOH enhances the efficiencies of these
photoaddition reactions, which proceed through a mechanistic pathway involving sequential excited
state SET - aminium radical desilylation (see below). In this pathway, coupling of the α-amino
radical formed by desilylation with the anion radical of C60 generates the adduct anion which is
protonated by the oxonium ion arising by EtOH promoted desilylation. Evidence for this proposal
comes from the observation that deuterium comprises ca. 75 % of the fullerene core proton in the
1
,2-adduct 36 formed by photoreaction of C with 20 in toluene containing 10 % EtOD.
60
Another important observation related to solvent effects arises in studies of photoaddition
reactions of α-silylamines 12 and 22 with C . As can be seen by viewing the results displayed in
60
Scheme 7 and Table 3, photoaddition reactions of C with 12 and 22, carried out in toluene solutions
60
containing low (10 and 15 %) percent by volume contents of EtOH, produce the respective α-
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4
aminofullerenes 31 and 37 exclusively/predominantly. In contrast, irradiation of C60 and these
amines in solutions having high contents (40 %) of EtOH in toluene leads to formation of
fulleropyrrolidine adducts 38 and 39 predominantly.
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Scheme 7.
12
31 38
+
hv / 1 h / EtOH-toluene
C60
22
37 + 39
hv / 2 h / EtOH-toluene
Table 3. Relative ratios of products produced in photoaddition reactions of α-silylamines 12 and 22
a
with C .
6
0
Relative product ratios derived from 12
Content (by volume)
of EtOH in toluene
b
and 22
3
1 : 38
37 : 39
1
1
4
0%
5%
0%
1 : 0
1 : 0
16 : 1
1 : 2
17 : 1
1 : 6
a
-3
Ratio of reactants (α-silylamine/C ) is 3.47/1.74 (10 mmol) in 10 mL EtOH-toluene
6
0
b
Relative product ratios were determined by using HPLC.
Conversion dependence of photoreaction efficiencies. In one approach to exploring the
conversion dependencies of product distribution and yields, the progress of photoreaction of α-
silylamine 5 with C60 was monitored as function of time. For this purpose, deoxygenated, 10 %
EtOH-toluene solutions containing 5 (0.35 mM) and C (0.17 mM) were irradiated for varying time
60
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1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
periods ranging from 5-180 min while monitoring the formation photoproduct 26 by using UV-
visible spectroscopy (Figure S2, Supporting Information). The results, which show that the yield of
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
6 gradually increases during the irradiation period, are in accord with observations made in studies
of the preparative photoreaction of this amine substrate that show that a mono adduct is generated
exclusively (see above).
Next, a study was conducted to determine if 1,2-adducts 31, 36 and 37 undergo secondary
photochemical reactions to form pyrrolidine type products. Processes of this type have been invoked
earlier to rationalize the formation of fulleropyrrolidines in photoreactions of C60 with tertiary
5
7,59
amines.
Independent, 10 % EtOH-toluene solutions containing the three adducts and either
HClO , pyridine or no additive were irradiated while monitoring photolysate compositions using
4
UV-visible spectroscopy and HPLC. The results (Figure S3, Supporting Information) show that
photoreactions of these substrates under the different conditions in all cases lead to formation of C60
along with the respective amines N-methylamines (Scheme 8). In the absence of added acid or base,
the photoreaction of 36 is more efficient than those of 31 and 37. Moreover, the presence of 2 molar
equivalents of HClO in solutions of each adduct enhances their photoconversions to form C and
4
60
the corresponding amines but pyridine has little effect on the efficiencies of these processes.
Scheme 8.
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H
R1
Me
N
hv / EtOH-toluene
C60
+
R2
addivtive
N R1
R2
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
3
3
3
1
6
7
= Bn, R = CH CO
(R
1
2
2
2
Et)
= R =
(R
1
2
Bn)
= R = CH CO
(R
1
2
2
2
Et)
Oxygen effects on fulleropyrrolidine formation. To gain information about the mechanistic
pathway that is responsible for generation of fulleropyrrolidine adducts, photoaddition reactions of
C with α-silylamines 12, 22 and 45 in O saturated 10 % EtOH-toluene solutions were explored.
60
2
The results (Table 4) show that photoaddition reactions in O saturated solutions take place much
2
less efficiently than those taking place in N purged solutions. Secondly, in contrast to processes
2
occurring in N purged solutions, fulleropyrrolidines 38, 39, and 49 are generated exclusively in
2
photoreactions in O saturated solutions. These observations strongly indicate that oxygen is
2
involved in pathway that produces fulleropyrrolidines (see below).
Table 4. Products and yields of photoaddition reactions of α-silyl tertiary amines with C carried
60
a
out in O saturated 10 % EtOH-toluene solutions
2
Irradiation
b
c
Substrate
Conversion (%)
Product (%)
time (h)
C60 + 12
C60 + 22
C60 + 45
2
10
3
91
10
65
38 (70)
39 (8)
49 (47)
a
α-Silyl amine/C ) is 0.56/0.28 mmol in 220 mL 10 % EtOH-toluene.
60
b
c
Conversion was determined by recovered C . Isolation yields.
6
0
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2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Factors governing the efficiencies of photoaddition reactions of amines with C . As can be
6
0
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
seen by viewing the data given in Tables 1 and 2, the nature of the amine substrate plays a significant
role in governing the times required to bring about high yielding formation of the C photoadducts.
6
0
In order to gain more detailed information about factors governing the efficiencies of these processes,
relative quantum yields (Φ ) were determined by measuring product yields for simultaneous, fixed
rel
time, low conversion photoreactions. For this purpose, deoxygenated 10 % EtOH-toluene solutions
(10 mL) containing 0.17 mM C60 and 0.35 mM amine were simultaneously irradiated for a fixed
time period that promotes an average substrate conversion of ca. 10 %. Product yields were then
determined by utilizing HPLC analysis of crude photolysates and transformed into relative quantum
yields (Φ ) by setting the quantum yield for reaction of 22 to be unity.
rel
Inspection of the relative quantum efficiency data displayed in Table 5 clearly shows that
photoaddition reactions of the non-carboxymethyl substituted α-silylamines are higher than those of
counterparts that either contain N-carboxymethyl groups (5, 12 and 22) or lack α-silyl substituents
(
50-51). Importantly, the differences in the efficiencies of these processes do not appear to be a
3
*
consequence of varying rates of SET from the amines to C60 because in all cases, even those of the
non-silyl amines 50 (E (+) = 0.73 V vs. Ag/AgCl) and 51 (E (+) = 0.23 V vs. Ag/AgCl), the free
ox
ox
energy for electron transfer step is negative, ensuring that SET is diffusion controlled.
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8
9
R
N
Me
50
51
= Me, Eox(+) = 0.73 V vs Ag/AgCl)
= Bn, Eox(+) = 0.26 V vs Ag/AgCl)
(
(
R
R
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
a
Table 5. Relative quantum efficiencies (Φ ) of photoaddition reactions of tertiary amines with C .
rel
60
Substrate
Φrel
Substrate
Φrel
2
3
4
5
7
8
13.2
15.1
8.4
2.7
3.9
7.1
5.0
4.5
2.1
13
14
16
19
20
22
50
51
2.8
4.1
7.9
4.1
3.0
1
1
0
0.4
0.2
11
1
2
a
Fixed time irradiations of N purged, 10%EtOH-toluene solutions with reactant
2
concentration being [α-silyl amine] = 0.35 mM and [C ] = 0.17 mM.
6
0
Mechanism for 1,2-adduct and fulleropyrrolidine formation. The mechanism depicted in
Scheme 1 is responsible for formation of 1,2-adducts in photoreactions between the α-silyl tertiary
amines and C . The pathway is initiated by SET from the amine donors to the triplet excited state of
6
0
fullerene, which is followed by silophile (EtOH) induced desilylation to generate key α-amino
radical intermediates. This mechanism contrasts with an analogous route responsible for
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2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
photoreactions of C with unsymmetric tertiary amines, which do not possess α-silyl groups, where
6
0
SET is followed by proton transfer from the generated aminium radical. As a consequence of this
difference, photoreactions of trimethylsilyl substituted amines take place with higher efficiencies,
and exceptionally high and predictable levels of regioselectivity. Both of these outcomes are a result
of the much larger rates of silophile promoted desilylation compared to deprotonation of
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
6
5,66,67a
intermediate aminium radicals.
As a result of this factor, site selective formation of α-amino
radicals takes place with rates that are more competitive with that of energy wasting (excited state
quenching) back SET between the amine cation radicals and fullerene anion radical.
The source of the quantum efficiency diminishing effect of N-carboxymethyl substitution on the
α-silyl amines is not well understood at this point. However, it might not be a coincidence that the
low relative quantum yields are associated with the same substrates that undergo competitive
formation of fulleropyrrolidine photoadducts. Specifically, the low efficiencies of 1,2-adduct
formation in these cases might enable a typically inefficient, pyrrolidine ring forming reaction to
become competitive. It should be noted that the low efficiencies and fulleropyrrolidine formation
tendencies associated with photoreactions of N-carboxymethyl substituted amines is not likely to be
a consequence of a competition between deprotonation and desilylation of intermediate aminium
cations. Support for this prediction comes from both an earlier observation that shows that
carboxymethyl protons of the aminium cations are not more kinetically acidic (rapidly abstracted)
6
5,88
than those present in simple alkyl groups,
and the fact that the C radical anion formed by SET
60
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1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
3
*
21,89
to C60 is an extremely weak base basic.
Although little evidence has been accumulated in this effort to address the issue, a reasonable
mechanism for the fulleropyrrolidine forming process can be proposed based on earlier observations
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
3
2
made by Prato and Foote. In a seminal investigation, Prato and his coworkers showed that thermal
reaction of aziridine 52 with C leads to exclusive production of fulleropyrrolidine 54 (Scheme 9).
60
This process, which has gained great utility in the synthesis of fullerene derivatives that are
employed in photovoltaic devices, likely takes place by sequential formation and dipolar
9
0
cycloaddition of the intermediate azomethine ylide 53. In addition, Foote demonstrated that singlet
oxygen is involved in pyrrolidine ring forming reactions of tertiary amines with C .
60
Scheme 9.
Bn
N
CO
N
2
Me
C H Cl
6
4
2
Bn
N
+
C60
CO Me
2
Bn
OMe
o
150 C
O
52
53
54
(73 %)
When combined, the results of these earlier investigations suggest that fulleropyrrolidine
formation in photoreactions of N-carboxymethyl substituted tertiary amines takes place via a route
that involves singlet oxygen mediated formation of azomethine ylides that then participate in dipolar
3
cycloadditions to C (Scheme 10). Accordingly, in the presence of O the triplet excited state of C
6
0
2
60
9
-1 -1 56a,91
1
should undergo energy transfer (k (O ) = 2 x 10 M s )
to form O and ground state C , a
2 60
q
2
process that effectively quenches formation of 1,2-photoadducts. As suggested by Foote, reaction of
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2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
1
O with a N-carboxymethyl-N-α-silylmethyl amine (e.g., 12, Scheme 10) likely involves
2
α−hydrogen atom abstraction to form α-carbon radicals 55 and 56 along with the hydroperoxy
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
9
2
radical. Subsequent hydroperoxide forming reaction of either 55 or 56 through H-atom transfer
generates the key azomethine ylide 57 that then undergoes dipolar cycloaddition with C to produce
60
the fulleropyrrolidine adduct.
Scheme 10.
3
3O
2
+
(C
60
)
energy transfer
1O2
Bn
Bn
N
Bn
CO Et
N
CO Et
2
2
N
CO Et
2
+
Me Si
H
Me Si
3
3
Me Si
H
3
12
55
56
O-OH
CO Et
2
1,3-Dipolar
Cycloaddition
Bn
N
CO Et
2
N
Bn
C60
Me Si
3
SiMe3
57
38
Conclusion
In the study described above, a novel, efficient, highly regioselective and environmentally
benign method for the preparation of variously substituted α-aminofullerene derivatives has been
developed. The process, involving photoaddition of α-silyl tertiary amines to C , takes place via a
6
0
mechanistic pathway involving formation of aminium radicals by SET from the amine to the triplet
excited state of C followed by desilylation to generate α-amino radicals that couple with the C
60
60
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4
radical anion to form precursors of the 1,2-adducts. The high efficiencies of these reactions, which
enable large scale production of adducts in short time periods, are associated with the large rates of
aminium radical desilylation promoted by the silophile EtOH incorporated as a solvent component. It
is envisaged that this new strategy will find utility in the synthesis of new fullerene derivatives.
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Experimental
1
13
General Procedure H and C NMR spectra were recorded on CDCl solutions and chemical
3
1
13
shifts are reported in parts per million relative to CHCl (7.24 ppm for H and 77.0 ppm for C) as
3
an internal standard. High resolution (HRMS) mass spectra were obtained by using a quadrupole
mass analyzer and electron impact ionization unless otherwise noted. All starting materials used in
the photoreactions derived from commercial sources. All new compounds described were isolated as
oils in > 95 % purity (by NMR analysis as well as HPLC trace) unless noted otherwise.
α-Silyl tertiary amines 2-5. Individual solutions of N-trimethylsilyl-N-1-hexylamine 1 (3.0 g,
1
6 mmol) in acetonitrile (100 mL) containing K CO (5.0 g, 36 mmol) and 20 mmol of the alkyl
2 3
halide (3.3 g of 1-hexylbromide for 2, 4.8 g of 2-ethyl-1-hexyl iodide for 3, 3.7 g of 2-methoxy-1-
ethyl iodide for 4, and 3.34 g of ethyl 2-bromoacetate for 5) were stirred for 12 h at room
temperature and concentrated in vacuo to give residues which were triturated with CH Cl . The
2
2
triturates were dried and concentrated in vacuo to afford residues, which were subjected to silica gel
column chromatography (EtOAc: hexane = 1: 10) to yield 2 (3.69 g, 85 %), 2 (2.97 g, 62 %), 3 (2.67
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5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
g, 68 %), and 4 (3.5 g, 80 %).
1
2
: H-NMR 0.03 (s, 9H), 0.88 (t, 6H, J = 6.9 Hz), 1.16-1.30 (m, 12H), 1.32-1.44 (m, 4H), 1.90
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
13
(s, 2H), 2.32 (t, 4H, J = 7.2 Hz); C-NMR -1.2, 14.1, 22.7, 26.8, 27.2, 31.9, 45.9, 57.6; HRMS (FAB)
m/z 272.2768 (M+1, C H NSi requires 272.2774).
1
6
38
1
3
: H-NMR 0.00 (s, 9H), 0.79-0.88 (m, 9H), 1.23-1.35 (m, 17H), 1.82 (s, 2H), 2.06 (d, 2H, J =
13
5
.7 Hz), 2.23 (t, 2H, J = 6.6 Hz); C-NMR -1.2, 10.9, 14.1 (2C), 22.7, 23.2, 24.4, 26.8, 27.2, 29.0,
31.2, 32.0, 37.4, 46.7, 57.8, 62.5; HRMS (FAB) m/z 300.3088 (M+1, C H NSi requires 300.3087).
1
8
42
1
4: H-NMR 0.02 (s, 9H), 0.85 (t, 3H, J = 6.9 Hz), 1.23-1.28 (m, 6H), 1.34-1.41 (m, 2H), 1.95 (s,
1
3
2H), 2.34 (t, 2H, J = 7.5 Hz), 2.56 (t, 2H, J = 6.3 Hz), 3.31 (s, 3H), 3.41 (t, 2H, J = 6.3 Hz); C-
NMR -1.3, 14.0, 22.6, 26.8, 27.1, 31.8, 46.6, 56.6, 58.2, 58.8, 71.1; HRMS (FAB) m/z 246.2256
(
M+1, C H NOSi requires 246.2253).
13 32
1
5
: H-NMR 0.02 (s, 9H), 0.84 (t, 3H, J = 6.6 Hz), 1.21-1.25 (m, 6H), 1.34-1.41 (m, 2H), 2.11 (s,
13
2
H), 2.52 (t, 2H, J = 7.2 Hz), 3.26 (s, 3H), 4.11 (q, 2H, J = 6.9 Hz); C-NMR -1.8, 13.8, 14.0, 22.4,
6.6, 27.3, 31.6, 45.5, 57.3, 57.6, 59.5, 170.9; HRMS (FAB) m/z 274.2200 (M+1, C H NO Si
2
14
32
2
requires 274.2202).
α-Silyl tertiary amines 7-8. Individual solutions of N-trimethylsilylmethyl-N-
hydroxyethoxyamine 6 (2.0 g, 10.5 mmol) in acetonitrile (100 mL) containing K CO (5.8 g, 41.8
2
3
mmol) and 21 mmol of the alkyl halide (4.0 g of 2-ethyl-1-hexylbromide for 7, 3.54 g of
benzylbromide for 8) was stirred for 12 h at room temperature and concentrated of solution in vacuo
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3
4
to give residues which were triturated with CH Cl . The triturates were dried and concentrated in
2
2
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
vacuo to afford residues, which were subjected to silica gel column chromatography (EtOAc: hexane
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
=
1: 5) to yield 7 (1.8 g, 57 %) and 8 (1.44 g, 49 %).
1
7
: H-NMR 0.04 (s, 9H), 0.82-0.91 (m, 6H), 1.20-1.32 (m, 7H), 1.34-1.44 (m, 2H), 1.94 (s, 2H),
2
3
.18 (d, 2H, diastereotopic, J = 6.6 Hz , 1.8 Hz), 2.54 (t, 2H, diastereotopic, J = 6.0 Hz , 1.8 Hz),
1
3
.54 (t, 2H, J = 6.0 Hz), 3.56 (t, 2H, J = 4.5 Hz), 3.71 (t, 2H, J = 4.5 Hz); C-NMR -1.2, 10.8, 14.1,
23.2, 24.4, 28.9, 31.2, 37.5, 41.5, 57.3, 61.9, 63.2, 69.5, 72.2; HRMS (FAB) m/z 302.2520 (M-1,
C H NO Si requires 302.2521).
16
36
2
1
8: H-NMR 0.07 (s, 9H), 2.04 (s, 2H), 2.59 (t, 2H, J = 6 Hz), 3.50 (t, 2H, J = 4.7 Hz), 3.20 (s,
1
3
1
H), 3.56 (t, 2H, J = 6 Hz), 3.58 (s, 2H), 3.66 (t, 2H, J = 4.7 Hz), 7.22-7.35 (m, 5H); C-NMR -1.5,
4
6.5, 56.4, 61.5, 62.5, 69.1, 72.0, 126.7, 127.9, 128.0, 128.7, 139.2; HRMS (FAB) m/z 282.1891
(
M+1, C H NO Si requires 282.1889).
15 28 2
α-Silyl tertiary amines 10-14 and 45. Individual solutions of N-trimethylsilylmethyl-N-
benzylamine 9 (3.0 g, 15.5 mmol) in acetonitrile (100 mL) containing K CO (4.3 g, 31 mmol) and
2
3
3
0 mmol of the alkyl halide (4.95 g of 1-hexylbromide for 10, 6.9 g of 2-(2-methoxyethoxy)ethyl
iodide for 11, 5.0 g of ethyl 2-bromoacetate for 12, 5.43 g of ethyl 2-bromopropionate for 13, 10.35 g
of N-(2-iodoethoxy)ethylphthalimide for 14, 4.9 g of methylbromoacetate for 45) were stirred for 12
h at room temperature and concentrated in vacuo to give residues which were triturated with CH Cl .
2
2
The triturates were dried and concentrated in vacuo to afford residues, which were subjected to silica
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2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
gel column chromatography (EtOAc: hexane = 1: 8) to yield 10 (3.48 g, 81 %), 11 (4.12 g, 90 %), 12
(2.25 g, 52 %), 13 (2.0 g, 44 %), 14 (3.88 g, 61 %) and 45 (2.6 g, 63 %).
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
1
0: H-NMR 0.05 (s, 9H), 0.87 (t, 3H, J = 7.2 Hz), 1.24-1.30 (m, 6H), 1.32-1.44 (m, 2H), 1.93
1
3
(
s, 2H), 2.31 (t, 2H, J = 6.9 Hz), 3.48 (s, 2H), 7.19-7.35 (m, 5H); C-NMR -1.3, 14.0, 22.6, 26.9,
+
2
7.0, 31.8, 45.8, 57.2, 62.1, 126.5, 128.0, 128.6, 140.6; HRMS (EI) m/z 277.2227 (M , C H NSi
17 31
requires 277.2226).
1
11: H-NMR 0.05 (s, 9H), 2.03 (s, 2H), 2.60 (t, 2H, J = 6.3 Hz), 3.34 (s, 3H), 3.48-3.56 (m, 8H),
1
3
7.16-7.33 (m, 5H); C-NMR -1.6, 46.4, 56.0, 58.7, 62.6, 69.6, 70.0, 71.7, 126.4, 127.8, 128.4, 139.9;
HRMS (FAB) m/z 296.2042 (M+1, C H NO Si requires 296.2046).
1
6
30
2
1
1
2: H-NMR 0.01 (s, 9H), 1.20 (t, 3H, J = 7.2 Hz), 2.16 (s, 2H), 3.20 (s, 2H), 3.71 (s, 2H), 4.09
1
3
(
q, 2H, J = 7.2 Hz), 7.17-7.31 (m, 5H); C-NMR -1.6, 14.2, 45.5, 56.9, 59.8, 61.4, 126.9, 128.1,
1
28.7, 139.4, 171.2.
1
1
3: H-NMR 0.01 (s, 9H), 1.18 (t, 3H, J = 7.2 Hz), 1.90 (s, 2H), 2.41 (t, 2H, J = 7.5 Hz), 2.67 (t,
13
2
4
H, J = 7.2 Hz), 3.45 (s, 2H), 4.05 (q, 2H, J = 7.2 Hz), 7.17-7.22 (m, 5H); C-NMR -1.6, 14.0, 32.3,
5.6, 52.5, 60.1, 61.7, 126.7, 128.0, 128.5, 139.7, 172.5; HRMS (FAB) m/z 294.1885 (M+1,
C H NO Si requires 294.1889).
16
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2
1
1
4: H-NMR 0.04 (s, 9H), 1.93 (s, 2H), 2.51 (t, 2H, J = 6.0 Hz), 3.47 (s, 2H), 3.51 (t, 2H, J =
6.0 Hz), 3.63 (t, 2H, J = 5.7 Hz), 3.85 (t, 2H, J = 5.7 Hz), 7.14-7.7.24 (m, 5H), 7.66-7.69 (m, 2H),
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7.79-7.82 (m, 2H); C-NMR -1.6, 37.4, 46.3, 56.1, 62.6, 67.5, 69.3, 123.1, 126.5, 127.9, 128.5,
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The Journal of Organic Chemistry
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32.0, 133.7, 140.1, 168.1; HRMS (FAB) m/z 411.2106 (M+1, C H N O Si requires 411.2104).
23 31 2 3
5
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7
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9
1
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5: H-NMR 0.07 (s, 9H), 2.21 (s, 2H), 3.27 (s, 2H), 3.67 (s, 3H), 3.76 (s, 2H), 7.25-7.36 (m,
0
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9
0
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9
0
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0
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9
0
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9
0
13
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H); C-NMR -1.6, 45.6, 50.9, 56.7, 61.3, 126.9, 128.1, 128.7, 139.3, 171.6; HRMS (FAB) m/z
66.1578 (M+1, C H NO Si requires 266.1576).
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2
α-Silyl tertiary amines 16, 19, 20 and 22. Individual solutions of 15.5 mmol of N-5-
hydroxypentyl-N-benzylamine (3.0 g, for 16), N-benzyl-N-methylamine (1.89 g, for 19), and of
N,N,-dibenzylamine (3.06 g, for 20), and of N,N-bis-ethylcarboxymethylamine (2.93 g, for 22) in
acetonitrile (150 mL) containing K CO (4.3 g, 31 mmol) and Me SiCH I (4.28 g, 20.0 mmol) were
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stirred for 12 h at room temperature and concentrated in vacuo to give residues which were triturated
with CH Cl . The triturates were dried and concentrated in vacuo to afford residues, which were
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2
subjected to silica gel column chromatography (EtOAc: hexane = 1: 8) to yield 16 (1.95 g, 45 %), 19
(
2.54 g, 79 %), 20 (1.85 g, 42 %) and 22 (2.95 g, 69 %) respectively.
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6: H-NMR 0.03 (s, 9H), 1.26-1.34 (m, 2H), 1.41-1.54 (m, 4H), 1.92 (s, 2H), 2.31 (t, 2H, J =
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.9 Hz), 3.47 (s, 2H), 3.58 (t, 2H, J = 6.6 Hz); C-NMR -1.4, 23.2, 26.6, 32.4, 45.7, 56.9, 62.0, 62.5,
26.5, 127.9, 128.6, 140.1; HRMS (FAB) m/z 280.2094 (M+1, C H NOSi requires 280.2097).
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9: H-NMR 0.07 (s, 9H), 1.92 (s, 2H), 2.19 (s, 3H), 3.44 (s, 2H), 7.23-7.32 (m, 5H).
1
13
2
0: H-NMR 0.20 (s, 9H), 2.10 (s, 2H), 3.63 (s, 4H), 7.33-7.56 (m, 10H); C-NMR -1.3, 45.8,
61.9, 126.6, 128.0, 128.6, 140.2; HRMS (FAB) m/z 284.1831 (M+1, C H NSi requires 284.1835).
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22: H-NMR 0.00 (s, 9H), 1.19 (t, 3H, J = 7.2 Hz), 2.26 (s, 2H), 3.46 (s, 4H), 4.08 (q, 2H, J =
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