Redox-photosensitized aminations of 1,2-benzo-1,3-cycloalkadienes, arylcyclopropanes, and quadricyclane with ammonia

Article abstract of DOI:10.1021/jo030053+

1,2,4-Triphenylbenzene and 2,2′-methylenedioxy-1,1′ -binaphthalene successfully photosensitized the aminations of 1,2-benzo-1,3-cycloalkadienes, arylcyclopropanes, and quadricyclane with ammonia and primary amines in the presence of m- or p-dicyanobenzene, which gave the 4-amino-1,2-benzocycloalkenes, 3-amino-1-arylpropanes, and 7-amino-5-(p-cyanophenyl)bicyclo[2.2.1]hept-2-ene, respectively. A key pathway for the photosensitized amination is the hole transfer from the cation radicals of the sensitizers that were generated by photoinduced electron transfer to the electron acceptors to the substrates. Therefore, it was found that the relationships in oxidation potentials between the sensitizers and the substrates and the positive charge distribution of the cation radicals of the substrates were important factors for the efficient amination.

Full text of DOI:10.1021/jo030053+

Red ox-P h otosen sitized Am in a tion s of
1,2-Ben zo-1,3-cycloa lk a d ien es, Ar ylcyclop r op a n es, a n d
Qu a d r icycla n e w ith Am m on ia
Masahide Yasuda,* Ryuji Kojima, Hiroshi Tsutsui, Daigo Utsunomiya, Kazuaki Ishii,
Koutaro J innouchi, and Tsutomu Shiragami
Department of Applied Chemistry, Faculty of Engineering, Miyazaki University,
Gakuen-Kibanadai, Miyazaki 889-2192, J apan
Toshiaki Yamashita*
Department of Chemical Science and Engineering, Miyakonojo National College of Technology,
Miyakonojo, Miyazaki 885-8567, J apan
yasuda@cc.miyazaki-u.ac.jp; photoya@cc.miyakonojo-nct.ac.jp
Received February 13, 2003
1,2,4-Triphenylbenzene and 2,2′-methylenedioxy-1,1′-binaphthalene successfully photosensitized
the aminations of 1,2-benzo-1,3-cycloalkadienes, arylcyclopropanes, and quadricyclane with am-
monia and primary amines in the presence of m- or p-dicyanobenzene, which gave the 4-amino-
1,2-benzocycloalkenes, 3-amino-1-arylpropanes, and 7-amino-5-(p-cyanophenyl)bicyclo[2.2.1]hept-
2-ene, respectively. A key pathway for the photosensitized amination is the hole transfer from the
cation radicals of the sensitizers that were generated by photoinduced electron transfer to the
electron acceptors to the substrates. Therefore, it was found that the relationships in oxidation
potentials between the sensitizers and the substrates and the positive charge distribution of the
cation radicals of the substrates were important factors for the efficient amination.
In tr od u ction
these sensitizers by ammonia and amines. Redox pho-
tosensitization is a powerful method for achieving ef-
ficient reactions via photoinduced electron transfer.6
Recently, redox photosensitization by 2,2′-methylene-
dioxy-1,1′-binaphthalene (BN) and its derivatives has
been successfully applied to the photoamination of 1,2-
diarylcyclopropanes.7 Here, we will extensively apply
redox photosensitization by BN and polyphenylben-
zenes to the amination of 1,2-benzo-1,3-cycloalkadienes
(1a -d ), arylcyclopropanes (3a -e),8 and quadricyclane
(3f), which have a weak absorption at >300 nm.
The photochemical synthetic method has received
much attention as an environmentally friendly synthetic
process. We have developed the direct amination with
ammonia by photoinduced electron transfer (photoami-
nation) without using an acid or an alkaline.1 So far, we
have investigated the photoamination of a variety of
arenes and aryl-substituted alkenes.2 However, the pho-
toamination has been restricted to the substrates that
have a strong absorption near the UV region (>300 nm),
since usual electron-transfer photosensitization by aro-
matic nitriles (e.g., 1-cyanonaphthalene,3 1,4-dicyano-
naphthalene,4 9,10-dicyanoanthracene5) could not be
applied to the photoamination due to the quenching of
Resu lts a n d Discu ssion
R ed ox P h ot osen sit izer . Previously, it has been
reported that the additions of alcohols and water to
indene (1a ) have been achieved by the electron-transfer
photosensitization with 1-cyanonaphthalene (CNN).9 In
(1) (a) Yasuda, M.; Yamashita, T.; Shiragami, T.; Shima, K. Recent
Res. Dev. Photochem. Photobiol. 1999, 3, 65-76. (b) Lewis, F. D. In
Advances in Electron Transfer Chemistry; Mariano, P. S., Ed.; J AI
Press, Inc.: London, 1996; Vol. 5, pp 1-39.
(2) For examples of photoamination, see. (a) Yasuda, M.; Yamashita,
T.; Shima, K.; Pac C. J . Org. Chem. 1987, 54, 753-759. (b) Yamashita,
T.; Shiomori, K.; Yasuda, M.; Shima, K. Bull. Chem. Soc. J pn. 1991,
64, 366-374. (c) Yasuda, M.; Isami, T.; Kubo, J .; Mizutani, M.;
Yamashita, T.; Shima, K. J . Org. Chem. 1992, 57, 1351-1354. (d)
Yamashita, T.; Yasuda, M.; Isami, T.; Tanabe, K.; Shima, K. Tetrahe-
dron 1994, 50, 9275-9286. (e) Yasuda, M.; Sone, T.; Tanabe, K.; Shima,
K. J . Chem. Soc., Perkin Trans. 1 1995, 459-464. (f) Yasuda, M.;
Wakisaka, T.; Kojima, R.; Tanabe, K.; Shima, K. Bull. Chem. Soc. J pn.
1995, 68, 3169-3173. (g) Kojima, R.; Yamashita, T.; Tanabe, K.;
Shiragami, T.; Yasuda, M.; Shima, K. J . Chem. Soc., Perkin Trans. 1
1997, 217-222. (h) Yasuda, M.; Kojima, R.; Ohira, R.; Shiragami, T.;
Shima, K. Bull. Chem. Soc. J pn. 1998, 71, 1655-1660.
(4) For example, see: Hirano, T.; Shiina, S.; Ohashi, M. J . Chem.
Soc., Chem. Commun. 1992, 1544-1545.
(5) For example, see: Mizuno, K.; Yoshioka, K.; Otsuji, Y. J . Chem.
Soc., Chem. Commun. 1984, 1665-1667.
(6) Majima, T.; Pac, C.; Nakasone, A.; Sakurai, H. J . Am. Chem.
Soc. 1981, 103, 4499-4508.
(7) Yasuda, M.; Kojima, R.; Tsutsui, H.; Watanabe, Louis A.; Hobo,
J .; Yamashita, T.; Shiragami, T.; Shima, K. Chem. Lett. 1999, 1269-
1270.
(8) (a) Hixson, S. S. In Organic Photochemistry; Padwa, A., Ed.;
Marcel Dekker: New York, 1979; Vol. 4, pp 191-260. (b) Rao, V. R.;
Hixson, S. S. J . Am. Chem. Soc. 1979, 101, 6458-6459. (c) Mizuno,
K.; Ogawa, J .; Otsuji, Y. Chem. Lett. 1981, 741-744.
(9) Yasuda, M.; Pac, C.; Sakurai, H. Bull. Chem. Soc. J pn. 1980,
53, 502-507.
(3) For example, see: (a) Arnold, D. A.; Shigemitsu, Y.; Arnold, D.
R. J . Chem. Soc., Chem. Commun. 1975, 407-408. (b) Maroulis, A. J .;
Shigemitsu, Y.; Arnold, D. R. J . Am. Chem. Soc. 1978, 102, 535-541.
10.1021/jo030053+ CCC: $25.00 © 2003 American Chemical Society
Published on Web 09/03/2003
7618
J . Org. Chem. 2003, 68, 7618-7624

Redox-Photosensitized Aminations
TABLE 1. Red ox-P h otosen sitized Am in a tion s of 1a -d a n d 3a -f w ith Am m on ia a n d Alk yla m in esa
conversion (%)
recovery (%)
DCB ArH
entry
substrate
RNH2
NH3
DCB
ArH
none
1,2,4-TPB
1,3,5-TPB
p-TB
m-TB
none
BN
1,2,4-TPB
none
1,2,4-TPB
none
1,2,4-TPB
1,2,4-TPB
1,2,4-TPB
none
BN
1,2,4-TPB
none
product yield (%)
substrate
1b
2
3
1a
1a
1a
1a
1a
1b
1b
1b
1c
1c
1d
1d
1a
1a
3a
3a
3a
3b
3b
3b
3c
3c
3c
3d
3e
3e
3e
3f
m-DCB
m-DCB
m-DCB
m-DCB
m-DCB
m-DCB
m-DCB
m-DCB
m-DCB
m-DCB
m-DCB
m-DCB
m-DCB
m-DCB
m-DCB
m-DCB
m-DCB
m-DCB
m-DCB
m-DCB
m-DCB
m-DCB
m-DCB
m-DCB
p-DCB
p-DCB
p-DCB
p-DCB
p-DCB
p-DCB
2a (5)
2a (79)
2a (12)
2a (76)
2a (34)
2b (31)
2b (58)
2b (83)
2c (16)
2c (63)
2d (31)
2d (57)
2e (52)
2f (49)
4a (14)
4a (40)
4a (71)
4b (27)
4b (90)
4b (54)
4c (32), 4c′(9)
4c (61), 4c′ (18)
4c (49), 4c′ (15)
no productd
5a (2)
4e (4), 5a (40)
4e (8), 5a (49)
5b (0)
54
99
54
99
88
84
100
92
93
97
89
98
77
66
17
53
81
29
100
100
52
100
100
65
54
95
97
0
61
90
83
72
88
92
70
77
98
96
100
100
87
85
85
90
92
90
76
58
93
95
80
97
50
60
70
95
38
50
NH3
NH3
NH3
NH3
NH3
NH3
NH3
NH3
NH3
NH3
NH3
i-PrNH2
t-BuNH2
NH3
NH3
NH3
NH3
NH3
NH3
NH3
NH3
NH3
NH3
NH3
NH3
NH3
NH3
NH3
NH3
83
30
66
47
4
5
6c
7
22
92
8
9c
10
11c
12
13
14
15c
16
17
18c
19
20
21c
22
23
24
25c
26
27
28c
39
30
92
94
96
92
87
66
BN
1,2,4-TPB
none
45
78
BN
82
82
78
1,2,4-TPB
1,2,4-TPB
none
BN
1,2,4-TPB
none
27
72
3f
3f
BN
1,2,4-TPB
5b (62)
5b (5)
85
20
70
62
a
In the cases of the photoamination of 1a -d , an MeCN-H2O (19:1, 50 mL) solution containing 1 (2 mmol), DCB (3.75 mol), and ArH
(0.75 mmol) was bubbled with ammonia and then irradiated for 5-13 h. In the cases of primary amines, an MeCN-H2O (9:1, 50 mL)
solution containing 1 (2 mmol), DCB (3.75 mol), and ArH (0.75 mmol) was bubbled with argon gas and then RNH2 (20 mmol) was added
and irradiated for 9 h (entries 13 and 14). In the cases of the photoamination of 3a -e, the irradiation was performed for an ammonia-
saturated MeCN-H2O (9:1, 70 mL) solution containing 3 (3 mmol), DCB (3.5 mmol), ArH (1 mmol), and Et4NBF4 (7 mmol) for 20 h. The
photoamination of 3f was performed by the irradiation of an ammonia-saturated MeCN-H2O (9:1, 70 mL) solution containing 3f (3.5
b
mmol), DCB (3.5 mmol), and ArH (1 mmol) for 8 h. Irradiation for an ammonia-saturated MeCN-H2O (19:1; 50 mL) solution containing
d
1a (27 mmol) and m-DCB (5 mmol). c Irradiation in the absence of ArH. Aminated products were not formed.
SCHEME 1. Red ox P h otosen sitiza tion
a similar way, we attempted the CNN-photosensitized
amination of 1a with NH3, but no photoamination oc-
curred. Moreover, irradiation of an ammonia-saturated
MeCN-H2O (v/v, 9:1, 50 mL) containing 1a (27 mmol)
and m-dicyanobenzene (m-DCB, 5 mmol) for 52 h gave
2-aminoindan (2a , 5%) and a dimer of 1a (18%) in low
conversion (54%) (Table 1, entry 1). To improve the
yield of 2a , we intended to apply a redox photosensiti-
zation.
At first, we attempted to find arenes acting as a
sensitizer, which are inert toward NH3 and amines,
because many arenes readily react with NH3 under the
conditions of the photoamination.2a Recently, we have
used 2,2′-methylenedioxy-1,1′-binaphthalene (BN) and
the related compounds as redox photosensitizers for the
photoamination of 1,2-diarylcyclopropanes.7 Although
these sensitizers are inert toward NH3 and amines, the
BN-photosensitization would be restricted to substrates
whose oxidation potentials were lower than that of BN
ox
(E1/2 ) 1.20 V). Indeed, the BN-photosensitized amina-
ox
tion of 1a (E1/2 ) 1.33 V) with NH3 gave the colored
in aqueous MeCN solutions. As sensitizers that were
moderately soluble in an aqueous MeCN solution, we
therefore selected 1,2,4-triphenylbenzene (1,2,4-TPB),
1,3,5-triphenylbenzene (1,3,5-TPB), m-terphenyl (m-TP),
and p-terphenyl (p-TP) (Scheme 1).
solution from which a trace of 2a and a large amount of
1a (65%) were isolated.
We have previously found that polyphenylbenzenes
have relatively high oxidation potentials and are inert
toward NH3 under the photoamination conditions.2d
However, many polyphenylbenzenes are poorly soluble
To find the more effective sensitizer among the above
polyphenylbenzenes, the control experiments were per-
J . Org. Chem, Vol. 68, No. 20, 2003 7619

Yasuda et al.
SCHEME 2
SCHEME 3
SCHEME 4
formed for the photoamination of 1a with NH3 (entries
2-5). Irradiation of an ammonia-saturated MeCN-H2O
(19:1, 50 mL) solution containing 1a (2 mmol), m-DCB
(3.75 mmol), and the polyphenylbenzene (0.75 mmol) for
5-13 h gave 2a (Scheme 2). When 1,2,4-TPB and p-TP
were used as the sensitizer, the photoamination of 1a
proceeded in good yields (entries 2 and 4). However, p-TP
was deposited during the irradiation because of the poor
solubility in an MeCN-H2O solution. Therefore, we
selected 1,2,4-TPB as the sensitizer for the photoamina-
tion. Moreover, the necessity of m-DCB was confirmed
by the control experiment where no reaction occurred in
the absence of m-DCB even upon prolonged irradiation.
18-20). In the case of the photoamination of unsymmet-
ric trans-1-(p-methoxyphenyl)-2-phenylcyclopropane (3c),
1-amino-1-(p-methoxyphenyl)-3-phenylpropane (4c) and
its regioisomer (4c′) were formed (entries 21-23). How-
ever, trans-1-(2,4-dimethoxyphenyl)-2-phenylcyclopro-
pane (3d ) was not aminated (entry 24). In the photoam-
ination of 1-(p-methoxyphenyl)-2,2-dimethylcyclopropane
(3e) sensitized by a pair of BN and p-DCB or 1,2,4-TPB
and p-DCB, the p-cyanophenyl group-incorporated ami-
nated product, 5a , was mainly obtained along with the
formation of 4e, while direct photoamination without the
sensitizer gave 5a in only 2% yield (entries 25-27). These
aminated products from arylcyclopropanes (3a -e) are
shown in Schemes 3 and 4 with the optimum yields. In
cases of 3a -e, the photoaminations were carried out in
the presence of Et4NBF4. Without Et4NBF4, the yields
of aminated products were decreased; for example, the
yields of 4c and 4c′ were 32%.7
Red ox-P h otosen sitized Am in a tion . The 1,2,4-TPB-
photosensitized amination of 2-methylindene (1b), 3,4-
dihydronaphthalene (1c), and 1,2-benzo-1,3-cyclohepta-
diene (1d ) with NH3 gave 2-amino-2-methylindan (2b),
2-amino-1,2,3,4-tetrahydronaphthalene (2c), and 4-amino-
1,2-benzocycloheptene (2d ), respectively, in high yields
compared with the photoamination without sensitizers
(entries 6-12). The 1,2,4-TPB-photosensitized amina-
tions of 1a with alkylamines, i-PrNH2 and t-BuNH2, were
carried out by the irradiation of an MeCN-H2O solution
(v/v, 19:1) containing 1a , m-DCB, 1,2,4-TPB, and the
amines to afford the corresponding 2-alkylaminoindan
(2e-f) along with a small amount of 2-indanol (entries
13 and 14). However, the photoamination of 1a with
t-BuNH2 in the absence of water proceeded to give 2f in
poor yield (12%). Scheme 2 summarizes the aminated
products with the optimum yields.
The redox photosensitization was applied to the ami-
nation of arylcyclopropanes (3a -e). The amination of 1,2-
diphenylcyclopropane (3a ) photosensitized by a pair of
1,2,4-TPB and m-DCB gave 1-amino-1,3-diphenylpropane
(4a ) in high yield compared with the BN-photosensiti-
zation and the photoamination without the sensitizer
(entries 15-17). Moreover, the direct irradiation of 3a
with NH3 in the absence of m-DCB did not form 4a ,
although it has been reported that the direct irradiation
of 3a with alkylamines (e.g., cyclohexylamine, piperidine,
n-BuNH2) gave the aminated products.10 When BN and
1,2,4-TPB were used as sensitizers, 1-amino-1,3-bis(p-
methoxyphenyl)propane (4b) from the photoamination of
trans-1,2-bis(p-methoxyphenyl)cyclopropane (3b) were
obtained in 90 and 54% yields, respectively (entries
The photosensitization by a pair of BN and p-DCB was
effective for the amination of quadricyclane (3f) with NH3
that gave 7-amino-5-(p-cyanophenyl)bicyclo[2.2.1]hept-
2-ene (5b) in 62% yield (Scheme 5), while the photosen-
sitization by a pair of 1,2,4-TPB and p-DCB was ineffec-
tive for the amination of 3f (entries 28-30). The structure
of the acetamide of 5b was confirmed by X-ray crystal-
lographic analysis.
Efficien cy a n d Regioch em istr y. From the compari-
son of absorption coefficiencies of 1a -d (ꢀ300 < 800 M-1
cm-1) and 3a -f (ꢀ300 < 300 M-1 cm-1) with those of the
sensitizers (ArH) (Table 2), it was found that most of the
incident light was absorbed by ArH under the reaction
conditions. Therefore, the initiation step should be an
electron transfer from the excited singlet states of ArH
(1ArH*) to DCB, resulting in the cation radicals of ArH
(ArH+•) and the anion radical of DCB. This mechanism
(10) Hixson, S. S. J . Am. Chem. Soc. 1974, 96, 4866-4871.
7620 J . Org. Chem., Vol. 68, No. 20, 2003

Redox-Photosensitized Aminations
SCHEME 5
the efficiency of the photoamination. The charge distribu-
tions in the cation radicals of 1a -d (1a -d +•) and 3a -e
(3a -e+•) were calculated by the ab initio method (Table
3). In 1a -d +•, the positive charge was distributed sub-
stantially over carbon C2 where the amination occurred
actually. Dinnocenzo et al. has reported that the photo-
induced nucleophilic addition of MeOH to the arylcyclo-
propanes proceeded via the nucleophilic attack on the
cation radicals of the ring-closed cyclopropanes.16 We
have also estimated that the photoamination of 3c
occurred by the nucleophilic attack on the ring-closed
cation radical of 3c, since the ab initio calculation of the
ring-opened cation radical of 3c showed that the positive
charge developed over the benzylic carbon (+0.11) of the
p-methoxyphenyl group but not over the benzylic carbon
(-0.04) of the phenyl group where the photoamination
actually occurred to give 4c′. Therefore, the calculations
of the charge distribution of 3a -e+• were performed for
the ring-closed cation radicals. The positive charge
develops over the methoxy-substituted aryl group, except
for the case of 3a . In the case of 3d having two methoxy
groups, the positive charge localized more highly on the
aryl group compared with the cases of the other cyclo-
propanes. This is one reason that the 3d +• did not allow
the nucleophilic attack of NH3 to cyclopropane moiety,
leading to no aminated products. Similar localization of
the positive charge by the methoxy group has been
previously observed in the cases of photoamination of stil-
benes and styrenes having two or three methoxy groups,
which underwent no amination to the olefinic moiety.2c,d
As shown in Scheme 1, the nucleophilic addition of NH3
at the ring-closed cation radicals of 3 gave the aminated
radicals, which were reduced by DCB-• after the depro-
tonation and then followed by the protonation to give the
aminated products (4). Therefore, the isomer ratio of 4
would depend on the relative stabilities of the aminated
radicals (‚D-NHR in Scheme 1).2g The stabilities of the
aminated radicals were estimated by the heats of the
formations calculated by the ab initio method, as shown
in Table 4. In the cases of the photoaminations of 1a -d ,
the radicals 6A-9A were much lower in energy than
radicals 6B-9B, as expected. In the case of 3e, the
radical 10A was more stable than 10B by ca. 127 kJ /
mol. This result of the calculation was in agreement with
the fact that the photoamination occurred selectively to
give 4e and 5a via the 10A intermediate. In the case of
3c, on the other hand, the heats of the formations of the
aminated radicals (11A and 11B) were nearly equal to
each other, thus giving a mixture of 4c and 4c′. Similarly,
the photoaminations of 1a -d proceeded according to
Scheme 1, and the regioselectivities of 2a -d were
consistent with the stabilities of the aminated radicals,
as shown in Table 4.
is confirmed from the following experiments: the fluo-
rescences of ArH were quenched by DCB at nearly
diffusion-controlled rates, and the free energy changes
(∆G) for the electron transfer were calculated to be
negative or slightly positive by the Rehm-Weller equa-
tion (Table 2).11 We have previously reported that the
addition of salts such as Et4NBF4 and Et4NOAc was
effective in preventing back-electron transfer from DCB-•.
to substrates+•.12 Therefore, the addition of Et4NBF4 was
effective in preventing the competitive back-electron
transfer in the cases of 3a -e.13
Moreover, the hole transfer from ArH+• to the sub-
strates is a key pathway for the efficient photoamination.
The efficiency of the hole transfer should depend on the
ox
difference in E1/2 between ArH and the substrates
(Figure 1). In the case of the ArH-photosensitized ami-
nation of substrates whose E1/2ox values were lower than
those of ArH, efficient hole transfer would occur. How-
ever, the hole transfer did not occur from ArH+• to
ox
substrates whose E1/2 values were much higher than
those of ArH. In the case of 1,2,4-TPB-photosensitized
amination of 3f, however, the yield of 5b was very low
(entry 30), although E1/2ox of 3f was much lower than that
of 1,2,4-TPB. Because the hole transfer process from the
cation radical of 1,2,4-TPB to 3f is a much more exergonic
process (0.89 eV ) 85.9 kJ /mol), this process lies in the
Marcus inverted region, resulting in slow hole transfer.14
In the case of 1,2,4-TPB-photosensitized amination of 3b,
4b was formed in 54% yield (entry 20), although the hole
transfer of this reaction lies on Marcus inverted region.
It is assumed that the nucleophilic attack of NH3 occurred
at the charge-transfer complex (1,2,4-TPB/3b)+• formed
between the cation radical of 1,2,4-TPB and 3b, which
have a π-chromophore.2d,6,15
The charge distribution of the resulting cation radicals
of the substrates (1 and 3) is another factor determining
Roth et al. has reported the detailed product analysis
for the p-DCB-photosensitized nucleophilic addition of
MeOH to 3f, which gave several types of the MeOH
adducts.17 On the other hand, the present photoamination
of 3f gave 5b as the sole product. Nucleophilic addition
of NH3 to 3f+• might be faster than competitive side
(11) Rehm, D.; Weller, A. Isr. J . Chem. 1970, 8, 259-271.
(12) (a) Yasuda, M.; Matsuzaki, Y.; Shima, K. Chem. Lett. 1989,
551-554. (b) Yamashita, T.; Tsurusako, T.; Nakamura, N.; Yasuda,
M.; Shima, K. Bull. Chem. Soc. J pn. 1993, 66, 857-862.
(13) (a) Santamaria, J . In Photoinduced Electron Transfer; Fox, M.
A., Chanon, M., Eds.; Elsevier: Amsterdam, 1988; Part B, pp 483-
540. (b) Mizuno, K.; Ichinose, N.; Otsuji, Y. Chem. Lett. 1985, 455-
458. (c) Mizuno, K.; Ichinose, N.; Otsuji, Y. J . Org. Chem. 1992, 57,
1855-1860. (d) Mizuno, K.; Ichinose, N.; Yoshimi, Y. J . Photochem.
Photobiol. C, Photochem. Rev. 2000, 1, 167-193.
(16) (a) Dinnocenzo, J . P.; Simpson, T. R.; Zuilhof, H.; Todd, W. P.;
Heinrich, T. J . Am. Chem. Soc. 1997, 119, 987-993. (b) Dinnocenzo,
J . P.; Zuilhof, H.; Lieberman, D. R.; Simpson, T. R.; McKechney, M.
W. J . Am. Chem. Soc. 1997, 119, 994-1004.
(14) (a) Marcus, R. A.; Sutin, N. Biochim. Biophys. Acta 1985, 811,
265-322. (b) Gould, I. R.; Ege, D.; Moser, J . E.; Farid, S. J . Am. Chem.
Soc. 1990, 112, 4290-4301.
(15) Arnold, D. R.; Snow, M. S. Can. J . Chem. 1988, 66, 3012-3026.
(17) Weng, H.; Roth, H. D. J . Org. Chem. 1995, 60, 4136-4145.
J . Org. Chem, Vol. 68, No. 20, 2003 7621

Yasuda et al.
TABLE 2. P r op er ties of Sen sitizer s, Ra te Con sta n ts for F lu or escen ce Qu en ch in g by DCB, a n d Ca lcu la ted F r ee-En er gy
Ch a n gesa
red
b
ArH
E1/2 (V)
ꢀ300 (M-1cm-1
)
τF (ns)
E0-0 (kJ /mol)
KSV (M-1
)
kqc (109 M-1 s-1
)
∆Gd (kJ /mol)
1,2,4-TPB
1,3,5-TPB
p-TP
m-TP
BN
1.54
1.52
1.51
1.52
1.20
5160
830
17 300
2300
2
42
2
4
2
369
346
369
368
303
28 (23)
14 (11)
2.6 (17)
16 (12)
9.5 (12)
13 (16)
-19 (-40)
+2 (-19)
-22 (-43)
-20 (-41)
14 ( -7)
108 (712)
33 (25)
38 (41)
26 (36)
12 000
a
b
Values in parentheses are values for p-DCB. Stern-Volmer constants for the fluorescence quenching of ArH by DCB. c Rate constant
d
for the fluorescence quenching by DCB determined by fluorescence quenching. Calculated by the Rehm-Weller equation using -1.93
and -2.15 V as E1/2 of p-DCB and m-DCB, respectively.
red
TABLE 4. Differ en ce in th e Hea t of F or m a tion (∆H) of
th e Am in a ted Ra d ica ls Ca lcu la ted by th e Ab In itio
Meth od a
F IGURE 1. Relationship between the oxidation potentials of
1a -d and 3a -f and those of ArH.
TABLE 3. Ab In itio Ca lcu la tion a on Ch a r ge
Distr ibu tion on th e Ca r bon Atom s in th e Ca tion Ra d ica ls
of 1a -d a n d 3a -eb
group
reaction site
1 and 3
Ar
Ph
C1
C2
1a
1b
1c
1d
3a
3b
3c
3d
3e
+0.07
0.00
+0.01
0.00
+0.01
0.00
+0.06
-0.04
-0.08
-0.08
-0.09
+0.07
+0.17
+0.06
+0.06
+0.06
-0.08
-0.04
-0.04
-0.03
+0.04
+0.03
-0.18
+0.18
+0.23
+0.35
+0.11
a
-0.18
-0.13c
-0.29
-0.28
Ab initio calculation was done on a Silicon Graphycs O2
workstation using the SPALTAN program.
ox
sensitizers were able to sensitize substrates whose E1/2
values were ca. 0.06 V higher and ca. 0.9 V lower than
those of the sensitizers. Thus, the redox-photosensitized
amination provides a useful synthetic tool. For example,
2-aminoindan, an intermediate for synthesis of com-
pounds with biological activities, was prepared by the
direct photoamination of indene without special reagents
such as acids and bases, whereas in general, it has been
prepared from indene in four steps using several re-
agents.18,19 The present photoamination provides an
environmentally friendly synthetic process to transform
simple alkenes and cyclopropanes into the corresponding
aminated compounds.
a
Calculated by the ab initio method on SPALTAN program.
Calculation for the ring-closed cation radicals. c For the
b
4-MeOC6H4- group.
reactions such as isomerization of 3f+• because of its
strong nucleophilicity. Also, the rate of coupling of the
aminated radical with the p-cyanophenyl anion radical
was faster than that of the p-DCB-photosensitized ad-
dition of MeOH, probably because the redox photosensi-
tization enhanced the concentration of the anion radical
of p-DCB, thus providing efficient formation of 5b.
Con clu sion
(18) Cannon, J . G.; Perez, J . A.; Pease, J . P.; Long, J . P.; Flynn, J .
R.; Rusterholz, D. B.; Dryer, S. E. J . Med. Chem. 1980, 23, 745-749.
(19) Horan, J . E.; Schiessler, R. W. Org. Synth. 1973, 5, 647-649.
Consequently, it was found that 1,2,4-TPB and BN
were suitable sensitizers for the photoamination. These
7622 J . Org. Chem., Vol. 68, No. 20, 2003

Redox-Photosensitized Aminations
103.94, 123.26, 125.48, 125.99, 126.11, 128.25, 143.21, 158.99,
159.16; HRMS calcd for C17H18O2 254.1307, found 254.1323.
Anal. Calcd for C17H18O2: C, 80.28; H, 7.13. Found: C, 80.07;
H, 7.04.
Exp er im en ta l Section
1,2,4-Tr ip h en ylben zen e (1,2,4-TP B). 1,2,4-TPB was pre-
pared by the coupling reaction of 1,2,4-tribromobenzene (12.6
g) with PhMgBr in the presence of bis(triphenylphosphine)-
nickel chloride (3 g) in Et2O (150 mL): mp 100-101 °C (from
MeOH, lit.20 99-100 °C); 1H NMR δ ) 7.14-7.20, (m, 9H),
7.31-7.50 (m, 5H), 7.61-7.68 (m, 4H); 13C NMR δ ) 126.11,
126.50, 126.58, 127.12, 127.42, 127.89, 127.89, 128.81, 129.41,
129.85, 129.85, 131.09, 139.52, 140.34, 140.56, 140.95, 141.08,
141.45; MS m/z 306 (M+).
1-(p-Meth oxyp h en yl)-2,2-d im eth ylcyclop r op a n e (3e).
1-(p-Methoxyphenyl)-3-methyl-1-propene (3.24 g) in CHCl3 (15
mL) was added to a CHCl3 solution (30 mL) containing 50%
aqueous NaOH solution (30 mL) and benzyltrimethylammo-
nium chloride (40% in MeOH; 0.1 mL), and the reaction
mixture was stirred for 1 day to give 1-(p-methoxyphenyl)-
2,2-dichloro-3,3-dimethylcyclopropene in 95% yield.23 The
resulting product (0.3 g) was treated with Na (1.0 g) in Et2O
(50 mL) at room temperature for 1 day to give 3e: 1H NMR δ
) 0.70-0.73 (m, 2H), 0.77 (s, 3H), 1.97 (s, 3H), 1.80 (dd, J )
7.6, 6.6 Hz, 1H), 3.78 (s, 3H), 6.80 (d, J ) 8.7 Hz, 2H), 7.07 (d,
J ) 8.7 Hz, 2H); 13C NMR δ ) 18.37, 20.43, 27.31, 28.88, 55.16,
2,2′-Meth ylen d ioxy-1,1′-bin a p h th a len e (BN). The prepa-
ration of BN was performed by the reaction of (()-2,2′-
dihydroxy-1,1-binaphthalene (35 mmol) with dibromomethane
(102 mmol) in the presence of K2CO3 (30 g) and NaI (0.5 g) in
acetone (150 mL) at refluxing temperature for 40 h:21 mp 82.5-
1
83.5 °C; H NMR δ ) 5.69 (s, 2H), 7.25-7.33 (m, 2H), 7.39-
113.38, 129.87, 132.40, 152.56; HRMS calcd for C12H16
176.1200, found 176.1234.
O
7.60 (m, 6H), 7.85-8.03 (m, 4H); 13C NMR δ ) 103.12, 120.92,
124.97, 126.03, 126.89, 128.37, 130.30, 131.78, 132.15, 151.23;
HRMS calcd for C21H14O2 298.1200, found 298.1014. Anal.
Calcd for C21H14O2: C, 84.54; H, 4.73; O, 10.73. Found: C,
84.37; H, 4.90; O, 10.73.
Gen er a l P r oced u r e of P h otoa m in a tion . In the cases of
1a -d , an ammonia-saturated MeCN-H2O (19:1, 50 mL)
solution of 1a -d (2 mmol), DCB (3.75 mmol), and ArH (0.75
mmol) was poured into a Pyrex glass tube, sealed with a rubber
septum, and irradiated with a high-pressure mercury lamp
for 5-13 h at ambient temperature. In the cases of primary
amines, an MeCN-H2O (9:1, 50 mL) solution containing 1 (2
mmol), DCB (3.75 mmol), and ArH (0.75 mmol) was bubbled
with argon gas, and then RNH2 (20 mmol) was added and
irradiated for 9 h. In the cases of 3a -e, the irradiation was
performed for an ammonia-saturated MeCN-H2O (9:1, 70 mL)
solution containing 3a -e (3 mmol), DCB (3.5 mmol), ArH (1
mmol), and Et4NBF4 (7 mmol) for 20 h. In the case of 3f, an
MeCN-H2O (9:1, 70 mL) solution containing p-DCB (3.5
mmol) and ArH (1 mmol) was bubbled with ammonia gas.
After 3f (3.5 mmol) was added, the solution was irradiated
for 8 h.
1,2-Ben zo-1,3-cycloh eptadien e (1d). The reaction of 1-ben-
zosuberone (5.6 mmol) and p-toluenesulfonylhydrazide (8.1
mmol) in EtOH (180 mL) at refluxing temperature for 3 h
gave a white precipitate, which was treated by butyllithium
(in hexane 15%, 40 mL) in Et2O (150 mL) at room temper-
ature for 6 h (yield 65%): bp 61 °C (4 mmHg); IR (neat) 781
1
cm-1 (lit.22 782 cm-1); H NMR δ ) 1.90-1.96 (m, 2H), 2.36-
2.37 (m, 2H), 2.61 (t, J ) 15.0 Hz, 2H), 5.63-5.91 (m, 1H), 6.39
(d, J ) 10.0 Hz, 1H), 7.05-7.31 (m, 4H); 13C NMR δ ) 26.90,
32.40, 36.05, 125.76, 126.46, 128.68, 129.77, 130.77, 132.09,
136.21, 141.56; HRMS calcd for
144.0947.
C11H12 144.0939, found
Gen er a l P r oced u r e of th e P r ep a r a tion of 1,2-Dia r yl-
cyclop r op a n es (3a -d ). The reaction of the substituted
benzaldehyde (100 mmol) with the substituted acetophenone
(100 mmol) in the presence of KOH (2.0 g) in EtOH (100 mL)
at room temperature gave the chalcone derivative.23 The EtOH
(50 mL) solution of the chalcone derivatives was refluxed with
H2N-NH2/H2O (12 mL) for 2 h, and then KOH (2.0 g) was
added to the solution and heated at 200 °C for 2 h to give cis/
trans mixtures of 3a -d . The trans isomers of 3b-d were
isolated by column chromatography on silica gel. Compound
3a was used as a cis/trans mixture.10
tr a n s-1,2-Bis(p-m eth oxyp h en yl)cyclop r op a n e (3b): mp
70.0-71.0 °C (lit.24 70.5-71.5°C); 1H NMR δ ) 1.32 (t, J )
7.1 Hz, 2H), 2.04 (t, J ) 7.1 Hz, 2H), 3.78 (s, 6H), 6.64 (d, J )
6.7 Hz, 4H), 7.07 (d, J ) 6.7 Hz, 4H); 13C NMR δ ) 17.35,
26.76, 55.31, 113.62, 126.62, 134.71, 157.76; HRMS calcd for
After the irradiation, the photolysates were treated by Ac2O.
The starting materials, DCN, ArH, and the aminated products
were separated by chromatography on silica gel. The formation
of 2a was confirmed by comparison with a commercially
available authentic sample.
2-Am in o-2-m eth ylin d a n (2b): the acetamide; mp 54.0-
1
56.0 °C; H NMR δ ) 1.55 (s, 3H), 1.92 (s, 3H), 3.00 (d, J )
15.8 Hz, 2H), 3.33 (d, J ) 15.8 Hz, 2H), 5.61 (brs, 1H), 7.15-
7.18 (m, 4H); 13C NMR δ ) 24.29, 25.62, 46.18, 61.37, 124.75,
126.54, 141.30, 169.80; HRMS calcd for C12H15NO 189.1107,
found 189.1152.
2-Am in o-1,2,3,4-tetr a h yd r on a p h th a len e (2c): the aceta-
mide; mp 107.0-107.5 °C; 1H NMR δ ) 1.64-1.79 (m, 1H),
1.98 (s, 3H), 1.93-2.07 (m, 1H), 2.65 (dd, J ) 16.2, 8.8 Hz,
1H), 2.80-2.85 (m, 2H), 3.04 (dd, J ) 16.2, 5.1 Hz, 1H), 4.04-
4.25 (m, 1H), 6.67 (brs, 1H), 6.96-7.13 (m, 4H); 13C NMR δ )
22.97, 27.22, 28.53, 35.27, 45.08, 125.41, 125.62, 128.34,
128.89, 133.91, 135.08, 169.52; HRMS calcd for C12H15NO
189.1154, found 189.1168. Anal. Calcd for C12H15NO: C, 76.16;
H, 7.99; N, 7.40; O, 8.45. Found: C, 76.18; H, 8.00; N, 7.37; O,
8.45.
C
17H18O2 254.1305, found 254.1322.
t r a n s-1-(p -Me t h oxyp h e n yl)-2-p h e n ylcyclop r op a n e
(3c): mp 82.5-83.5 °C (lit.23 82.5-83.5 °C); 1H NMR δ ) 1.24-
1.42 (m, 2H), 2.06-2.15 (m, 2H), 3.79 (s, 3H), 6.55-7.24 (m,
9H); 13C NMR δ ) 17.79, 23.84, 27.49, 55.31, 113.63, 125.40,
125.66, 126.88, 134.49, 142.49, 142.71, 157.82; HRMS calcd
for C16H16O 224.1200, found 224.1191.
4-Am in o-1,2-ben zocycloh ep ten e (2d ): the acetamide; mp
t r a n s-1-(2,4-Dim e t h oxyp h e n yl)-2-p h e n ylcyclop r o-
p a n e (3d ): mp 79.5-80.5 °C; 1H NMR δ ) 1.29-1.35 (m, 2H),
2.01-2.09 (m 1H), 2.29-2.37 (m 1H), 3.79 (s, 6H), 6.41-6.45
(m, 1H), 6.45 (s, 1H), 6.89 (d, J ) 8.6 Hz, 1H), 7.12-7.31 (m,
5H); 13C NMR δ ) 16.49, 21.46, 25.98, 55.39, 55.48, 98.50,
1
146.5-148.0 °C; H NMR δ ) 1.60-1.69 (m, 2H), 1.80-2.02
(m, 2H), 1.87 (s, 3H), 2.74-2.78 (m, 2H), 2.90 (dd, J ) 13.7,
8.2 Hz, 1H), 3.00 (dd, J ) 13.7, 1.8 Hz, 1H), 4.05-4.17 (m,
1H), 5.76 (brd, J ) 6.2 Hz, 1H), 7.07-7.15 (m, 4H); 13C
NMR δ ) 23.30, 24.40, 35.80, 37.20, 41.10, 46.80, 126.30,
126.90, 129.00, 129.30, 137.10, 143.20, 169.20; HRMS calcd
for C13H17NO 203.1309, found 203.1354. Anal. Calcd for
(20) Doss, R. C.; Solomon, P. W. J . Org. Chem. 1964, 29, 1567-
1574.
C
13H17NO: C, 76.81; H, 8.43; N, 6.89; O, 7.87. Found: C, 76.61;
(21) Deussen, H.-D.; Hendrickx, E.; Boutton, C.; Krog, D.; Clays,
K.; Bechgaard, K.; Persoons, A.; Bjørnholm, T. J . Am. Chem. Soc. 1996,
118, 6841-6852.
H, 8.27; N,6.85; O,8.27.
2-Isop r op yla m in oin d a n (2e): the acetamide; mp 137.0-
138.0 °C; 1H NMR δ ) 1.23 (d, J ) 6.6 Hz, 6H) and 1.35 (d, J
) 6.5 Hz, 6H), 2.11 (s, 3H) and 2.07 (s, 3H), 2.85 (dd, J ) 14.9,
8.6 Hz, 2H) and 3.03-3.19 (m, 2H), 3.03-3.19 (m, 1H) and
3.86-4.07 (m, 1H), 3.70 (dd, J ) 14.9, 9.9 Hz, 2H) and 3.86-
4.07 (m, 2H), 3.86-4.07 (m, 1H) and 4.49-4.64 (m, 1H), 7.07-
(22) Granger, R.; Orzalesi, H.; Chapat, J .-P. Bull. Soc. Chim. Fr.
1967, 1951-1956.
(23) Hixson, S. S.; Garret, D. W. J . Am. Chem. Soc. 1974, 96, 4872-
4879.
(24) Overberger, C. G.; Weishenker, N.; Anelme, J . P. J . Am. Chem.
Soc. 1965, 87, 4119-4124.
J . Org. Chem, Vol. 68, No. 20, 2003 7623

Yasuda et al.
7.18 (m, 8H); 13C NMR δ ) 21.00 and 20.24, 23.53 and 23.80,
36.13 and 37.25, 49.50 and 46.44, 53.31 and 56.71, 124.04 and
124.33, 125.74 and 126.65, 141.74 and 140.08, 169.17 and
169.17; HRMS calcd for C14H19NO 217.1467, found 217.1439.
Anal. Calcd for C14H19NO: C, 77.38; H, 8.81; N, 6.45; O, 7.36.
Found: C, 77.48; H, 8.82; N, 6.42; O, 7.28.
2-t-Bu tyla m in oin d a n (2f): the acetamide; mp 95.0-95.5
°C; 1H NMR δ ) 1.49 (s, 9H), 2.00 (s, 3H), 3.24 (d, J ) 9.2 Hz,
4H), 2.63 (quint, J ) 9.2 Hz, 1H), 7.13-7.25 (m, 4H); 13C NMR
δ ) 26.50, 30.00, 39.90, 53.80, 58.30, 124.70, 126.70, 140.80,
172.40; HRMS calcd for C15H21NO 231.1623, found 231.1659.
Anal. Calcd for C15H21NO: C, 77.88; H, 9.15; N, 6.05; O, 6.92.
Found: C, 77.79; H, 9.12; N, 6.07; O, 7.02.
3-Am in o-1-(p-m eth oxyph en yl)-3-m eth ylbu tan e (4e): the
acetamide; 1H NMR δ ) 1.35 (s, 6H), 1.89 (s, 3H), 2.00 (t, J )
7.0 Hz, 2H), 2.51 (t, J ) 7.0 Hz, 2H), 3.77 (s, 3H), 5.27 (brs,
1H), 6.81 (d, J ) 8.6 Hz, 2H), 7.10 (d, J ) 8.6 Hz, 2H); 13C
NMR δ ) 24.27, 26.99, 29.97, 41.81, 53.56, 55.13, 113.67,
129.14, 134.16, 157.59, 169.39; HRMS calcd for C14H21NO2
235.1567, found 235.1570.
3-Am in o-1-(p -cya n op h en yl)-1-(p -m et h oxyp h en yl)-3-
m eth ylbu ta n e (5a ): the acetamide; 1H NMR δ ) 1.26 (s, 3H),
1.31 (s, 3H), 1.56 (s, 3H), 2.58 (d, J ) 4.3 Hz, 2H), 3.74 (s,
3H); 4.06 (t, J ) 4.3 Hz, 1H), 5.16 (brd, 1H), 6.83 (d, J ) 8.7
Hz, 2H), 7.17 (d, J ) 8.7 Hz, 2H), 7.37 (d, J ) 8.3 Hz, 2H),
7.52 (d, J ) 8.3 Hz, 2H); 13C NMR δ ) 23.92, 27.76, 28.15,
43.50, 46.93, 53.53, 55.09, 109.46, 114.09, 116.80, 128.31,
128.58, 132.11, 135.71, 151.56, 158.14, 169.42; HRMS calcd
for C21H24N2O2 336.1835, found 336.1804.
1-Am in o-1,3-d ip h en ylp r op a n e (4a ). The structure was
1
determined by comparison of H and 13C NMR spectra with
the authentic sample prepared by reductive amination of
2-tetralone with NH4OAc and NaBCNH3.18 The acetamide; 1H
NMR δ ) 1.89 (s, 3H), 2.03-2.15 (m, 2H), 2.53-2.63 (m, 2H),
5.00 (q, J ) 7.7 Hz, 1H), 6.24 (brs, 1H), 7.10-7.33 (m, 10H);
13C NMR δ ) 23.27, 32.59, 37.68, 53.29, 125.80, 126.48, 127.22,
128.15, 128.26, 128.52, 141.26, 141.99, 169.15; HRMS calcd
for C17H19NO 253.3471, found 253.3440.
1-Am in o-1,3-bis(p-m eth oxyp h en yl)p r op a n e (4b): the
acetamide; 1H NMR δ ) 1.93 (s, 3H), 2.05-2.56 (m, 4H), 3.78
(m, 3H), 3.79 (m, 3H), 4.87-4.98 (m, 1H), 6.78-7.27 (m, 8H);
13C NMR δ ) 20.71, 31.54, 37.69, 52.69, 55.14, 113.74, 113.96,
127.72, 129.11, 133.36, 133.94, 158.72, 158.74, 169.71; HRMS
calcd for C19H23NO3 313.1677, found 313.1677.
7-Am in o-5-(p-cyan oph en yl)bicyclo[2.2.1]h ept-2-en e (5b):
1
the acetamide; mp > 200 °C, H NMR δ ) 1.52 (s, 3H), 1.70-
2.08 (m, 2H), 2.88-2.95 (m, 2H), 3.44 (d, J ) 2.5 Hz, 1H), 3.75
(d, J ) 7.5 Hz, 1H), 4.96 (brs, 1H), 6.18-6.29 (m, 2H), 7.45 (d,
J ) 7.5 Hz, 2H), 7.61 (d, J ) 7.5 Hz, 2H); 13C NMR δ ) 23.04,
30.46, 42.50, 44.41, 47.05, 64.23, 110.0, 119.0, 128.18, 132.04,
135.94, 136.04, 149.68, 170.0; HRMS calcd for C16H16N2O
252.1262, found 252.1203.
X-r a y Cr ysta llogr a p h ic An a lysis. X-ray crystallographic
analysis was performed on an Enraf-Nonius CAD-4 system
using Mo KR irradiation (λ ) 0.71069 Å). All of the calculations
were done on a DEC 3000 computer using the AXP Model 1300
program. Crystal data of the acetamide of 5b: M ) 250,
monoclinic, Cc, a ) 9.408 Å, b ) 17.344 Å, c ) 9.540 Å, â )
118.4°, V ) 1369 Å3, Z ) 4, Dm ) 1.15 g/cm3, Dc ) 1.22 g/cm3,
R ) 4.1%, Rw ) 4.9%, number of unique reflections ) 1790.
1-Am in o-1-(p-m eth oxyp h en yl)-3-p h en ylp r op a n e (4c):
1
the acetamide; H NMR δ ) 1.94 (s, 3H), 2.06-2.24 (m, 2H),
2.54-2.63 (m, 2H), 3.80 (s, 3H), 4.92-5.01 (m, 1H), 5.70 (d, J
) 8.2 Hz, 1H), 6.86-6.89 (m, 3H), 7.13-7.32 (m, 6H); 13C NMR
δ ) 22.92, 31.44, 37.84, 52.95, 54.95, 113.58, 126.37, 126.96,
128.31, 128.98, 133.23, 142.24, 157.54, 169.48; HRMS calcd
for C18H21NO2 283.1570, found 283.1541.
Su p p or t in g In for m a t ion Ava ila b le: 1H and 13C NMR
spectra for new compounds (2b, 3e, 4b, 4c, 4c′, 4e, 5a ) lacking
combustion data and tables of X-ray data for the acetamide of
5b involving the crystallographic parameters, positional pa-
rameters, bond distances, bond angles, and torsional angles.
This material is available free of charge via the Internet at
http://pubs.acs.org.
1-Am in o-3-(p-m eth oxyp h en yl)-1-p h en ylp r op a n e (4c′):
1
the acetamide; H NMR δ ) 1.94 (s, 3H), 2.06-2.24 (m, 2H),
2.54-2.63 (m, 2H), 3.80 (s, 3H), 4.92-5.01 (m, 1H), 5.70 (d, J
) 8.2 Hz, 1H), 6.68-6.89 (m, 3H), 7.13-7.32 (m, 6H); 13C NMR
δ ) 22.92, 32.41, 37.53, 52.44, 54.95, 113.69, 125.64, 127.55,
128.07, 128.13, 134.23, 141.27, 158.44, 169.36; HRMS calcd
for C18H21NO2 283.1570, found 283.1541.
J O030053+
7624 J . Org. Chem., Vol. 68, No. 20, 2003