Rearrangement of indene skeletons under mild conditions

Article abstract of DOI:10.1021/jo070537w

(Chemical Equation Presented) Isomerization between two isomers of 1,2-disubstituted 3-aminoindenes occurs via the rearrangement of indene frameworks. In contrast to previous rearrangements of indene derivatives, which occur under high-temperature conditi

Full text of DOI:10.1021/jo070537w

Rearrangement of Indene Skeletons under Mild Conditions
Yoichiro Kuninobu,* Hirokazu Ueda, Atsushi Kawata, and Kazuhiko Takai*
DiVision of Chemistry and Biochemistry, Graduate School of Natural Science and Technology,
Okayama UniVersity, Tsushima, Okayama 700-8530, Japan
kuninobu@cc.okayama-u.ac.jp; ktakai@cc.okayama-u.ac.jp
ReceiVed March 23, 2007
Isomerization between two isomers of 1,2-disubstituted 3-aminoindenes occurs via the rearrangement of
indene frameworks. In contrast to previous rearrangements of indene derivatives, which occur under
high-temperature conditions or the irradiation of light, this rearrangement proceeds at room temperature
without UV light irradiation. An amino group at the 3-position plays an important role to accelerate the
rearrangement under mild conditions.
Introduction
photochemical or transition-metal-promoted isomerization of
cyclopropenes and cyclopentadienes under UV irradiation.7
Some examples of the isomerization of indene derivatives have
also been reported, although the reaction needs harsh conditions8
or irradiation of UV light.9 We report herein on a rearrangement
of aminoindene derivatives that proceeds even at room tem-
perature without UV irradiation. Investigations on the isomer-
ization mechanism of the aminoindene derivatives are also
described.
Rearrangement of carbon frameworks is one of the funda-
mental reactions in organic chemistry. Some well-known
examples utilizing rearrangement include the pinacol-pina-
colone rearrangement,1 Wagner-Meerwein rearrangement,2
Beckmann rearrangement,3 Cope rearrangement,4 rearrangement
of vinylcyclopropane,5 rearrangement of di-π-methane,6 and
(1) (a) Fitty, R. Ann. 1860, 114, 54. (b) Blicke, F.; Azuara, J.; Doorenbos,
N.; Hotelling, E. J. Am. Chem. Soc. 1953, 75, 5418. (c) Mundy, B. P.;
Srinivasa, R.; Otzenberger, R. D.; Debernardis, A. R. Tetrahedron Lett.
1979, 2673. (d) Olah, J. A. J. Org. Chem. 1997, 62, 6666. (e) Shinohara,
T.; Suzuki, K. Tetrahedron Lett. 2002, 43, 6937.
(2) (a) Wagner, G. J. Russ. Phys. Chem. Soc. 1899, 31, 690. (b)
Meerwein, H. Ann. 1914, 405, 129. (c) Sorensen, T. S. Acc. Chem. Res.
1976, 9, 257. (d) Fitjer, L.; Wehle, D.; Noltemeyer, M.; Egert, E.; Sheldrick,
G. M. Chem. Ber. 1984, 117, 203. (e) Paquette, L. A.; Waykole, L.;
Jendralla, H.; Cottrell, C. E. J. Am. Chem. Soc. 1986, 108, 3739.
(3) (a) Beckmann, E. Ber. 1886, 19, 988. (b) Beckmann, E. Ber. 1887,
20, 1507. (c) Ruzicka, L.; Kobelt, M.; Hafliger, O.; Prelog, V. HelV. Chim.
Acta. 1949, 32, 544. (d) Meth-Cohn, O.; Narine, B. Synthesis 1980, 133.
(e) Sharghi, H.; Hosseini, M. Synthesis 2002, 1057. (f) Tanaka, M.; Oba,
M.; Tamai, K.; Suemune, H. J. Org. Chem. 2001, 66, 2667.
(4) (a) Cope, A. C.; Hardy, E. M. J. Am. Chem. Soc. 1940, 62, 441. (b)
Rhoads, S. J.; Raulins, N. R. Org. React. 1975, 22, 1. (c) Lutz, R. P. Chem.
ReV. 1984, 84, 205. (d) Corey, E. J.; Guzman-Perez, A. Angew. Chem., Int.
Ed. Engl. 1998, 37, 388. (e) Nubbemeyer, U. Synthesis 2003, 961.
(5) (a) Neureiter, N. P. J. Org. Chem. 1959, 24, 2044. (b) Hudlicky, T.;
Kutchan, T. M.; Naqvi, S. Org. React. 1985, 33, 247. (c) Zimmerman, H.
E.; Fleming, S. A. J. Am. Chem. Soc. 1983, 105, 622. (d) McGaffin, G.; de
Meijere, A.; Walsh, R. Chem. Ber. 1991, 124, 939.
(6) (a) Zimmerman, H. E.; Grunewald, G. L. J. Am. Chem. Soc. 1966,
88, 183. (b) Zimmerman, H. E. Angew. Chem., Int. Ed. Engl. 1969, 8, 1.
(c) Hixson, S. S.; Mariano, P. S.; Zimmerman, H. E. Chem. ReV. 1973, 73,
531. (d) Paquette, L. A.; Bay, E.; Yeh, Ku, A.; Rondan, N. G.; Houk, K.
N. J. Org. Chem. 1982, 47, 422. (e) Demuth, M.; Mikhail, G. Synthesis
1989, 145. (f) Zimmerman, H. E.; Armesto, D. Chem. ReV. 1996, 96, 3065.
Results and Discussion
We have already reported on a rhenium complex ([ReBr-
(CO)3(thf)]2) catalyzed synthesis of aminoindene derivatives by
the reactions of aromatic aldimines with internal acetylenes.10
In the case of using dissymmetric acetylenes, two aminoindene
isomers were obtained (eq 1). In this reaction, the ratio of the
(7) (a) Zimmerman, H. E.; Hovey, M. C. J. Org. Chem. 1979, 44, 2331.
(b) Zimmerman, H. E.; Kreil, D. J. J. Org. Chem. 1982, 47, 2060. (c)
Hughes, R. P.; Trujillo, H. A.; Egan, J. W., Jr.; Rheingold, A. L. J. Am.
Chem. Soc. 2000, 122, 2261.
(8) (a) Koelsch, C. F.; Johnson, P. R. J. Am. Chem. Soc. 1943, 65, 567.
(b) Miller, L. L.; Boyer, R. F. J. Am. Chem. Soc. 1971, 93, 650.
(9) (a) Padwa, A.; Loza, R.; Getman, D. Tetrahedron Lett. 1977, 33,
2847. (b) Palensky, F. J.; Morrison, H. A. J. Am. Chem. Soc. 1977, 99,
3507. (c) Padwa, A.; Blacklock, T. J.; Getman, D.; Hatanaka, N.; Loza, R.
J. Org. Chem. 1978, 43, 1481. (d) Giacherio, D.; Morrison, H. J. Am. Chem.
Soc. 1978, 100, 7109. (e) Padwa, A.; Goldstein, S.; Loza, R.; Pulwer, M.
Tetrahedron Lett. 1979, 51, 4895. (f) Morrison, H.; Giacherio, D.; Balensky,
F. J. J. Org. Chem. 1982, 47, 1051. (g) Duguid, R. J.; Morrison, H. J. Am.
Chem. Soc. 1991, 113, 3519.
(10) (a) Kuninobu, Y.; Kawata, A.; Takai, K. J. Am. Chem. Soc. 2005,
127, 13498. (b) Kuninobu, Y.; Tokunaga, Y.; Kawata, A.; Takai, K. J. Am.
Chem. Soc. 2006, 128, 202.
10.1021/jo070537w CCC: $37.00 © 2007 American Chemical Society
Published on Web 08/03/2007
J. Org. Chem. 2007, 72, 6749-6752
6749

Kuninobu et al.
TABLE 1. Solvent Effect on the Yields of Aminoindenes
% yielda
% recova
two aminoindene derivatives was reversed as the reaction time
increased (eq 1). For example, the treatment of aromatic
aldimine 1a with 1-phenyl-1-propyne (2a) in toluene under
reflux conditions for 10 min gave only aminoindene derivative
3a in 50% yield. In contrast, after 24 h, 3a disappeared and
only aminoindene derivative 4a was obtained quantitatively.
These results indicate that 3a was isomerized to 4a under the
reaction conditions. In fact, by refluxing the solution of the
isolated aminoindene derivative 3a in the absence of the rhenium
complex [ReBr(CO)3(thf)]2 in toluene for 24 h, aminoindene
isomer 4a was formed in 35% yield and 3a was recovered in
65% yield.11
entry
solvent
toluene
4a
3a
1
2
3
4
5
6
40
57
55
>99
83
60
43
45
0
17
0
THF
1,2-dichloroethane
DMFb
acetonitrile
DMSOc
>99
a The yield was determined by H NMR with 1,1,2,2-tetrachloroethane
1
as an internal standard. b N,N-Dimethylformamide. c Dimethylsulfoxide.
formed. This result also indicates that the isomerization of
aminoindenes is an intramolecular version.12
Next, we carried out the isomerization reaction using 13C-
labeled aminoindene derivative 5a to investigate the reaction
mechanism (eq 3). By heating 5a at 135 °C for 24 h,
isomerization of 5a proceeded and isomer 6a was obtained in
82% yield. As a result of 13C NMR measurements, not only
We examined the solvent effect on the isomerization rates
of aminoindene derivative 3a (Table 1). In toluene, the rate of
isomerization from 3a to 4a was slow (Table 1, entry 1). The
rate of isomerization increased slightly with rather polar solvents,
such as tetrahydrofuran and 1,2-dichloroethane (Table 1, entries
2 and 3). When N,N-dimethylformamide (DMF), acetonitrile,
or DMSO was used as the solvent, the rate of isomerization
increased substantially (Table 1, entries 4-6). The results show
that the rate of isomerization of aminoindene derivative 3a to
4a becomes faster with polar solvents, and thus the isomerization
proceeds via a polar intermediate.
The next question is whether the isomerization proceeds via
an intra- or intermolecular reaction. The isomerization reaction
of aminoindene derivative 3a was carried out in toluene at
115 °C for 24 h in the presence of 10 equiv of 1-phenyl-1-
propyne-d3. Although isomerization of 3a afforded 4a, deute-
rium atoms were not incorporated into 4a, and 1-phenyl-1-
propyne-d3 was recovered completely. This result indicates that
this reaction is an intramolecular isomerization. To elucidate
the reaction mode more clearly, we heated a mixture of
aminoindene 3b and deuterated aminoindene 3a′ (eq 2). As a
did the interconversion of two substituents, hexyl and phenyl
groups, take place but also the interconversion of carbon atoms
of the indene framework. This result shows that the carbon-
carbon bonds between the indene framework and the substituted
groups were not cleaved, and aminoindene derivative 6a was
formed by the rearrangement of the indene framework.
By investigating the reaction temperature in DMF for 24 h,
aminoindene 3a was isomerized even at 25 °C (4a: 12% yield;
3a: 88% recovery).13 Since isomerizations of indene derivatives
via the rearrangement of an indene skeleton usually need harsh
conditions or UV irradiation,9 the fact that the isomerization of
3a to 4a proceeds even at room temperature without UV
irradiation deserves special mention.
One of the possible mechanisms is that the isomerization of
aminoindene 3a is promoted by light (a fluorescent light or
sunlight). By heating aminoindene 3a in DMF at 50 °C for 24
h in the dark, aminoindene 4a was formed in 17% yield. This
yield is the same as that obtained by heating 3a at 50 °C for 24
h without shading. The result shows that the isomerization did
not proceed by light. Another possible mechanism is that the
(12) The isomerization rates of 3a to 4a in N,N-dimethylformamide at
100 °C for 3 h were changed when the reactions were carried out under
different concentrations (4a: 43% (0.40 M); 38% (0.20 M); 27% (0.10
M); 18% (0.050 M).). One possible explanation of this result is that 4a
was formed via intramolecular isomerization, which was influenced by the
amino group of another molecule. In fact, by adding a base (1.0 equiv) in
the reaction mixture, the accelerating effect of the base was observed (0.20
M, none: 38%; aniline: 61%; piperidine: >99%).
result, aminoindenes 3b and 3a′ were isomerized to 4b and 4a′.
In this reaction, aminoindene derivatives 4b′ and 4a, which
could be produced by intermolecular isomerization, were not
(11) In the presence of a catalytic amount of a rhenium complex, [ReBr-
(CO)3(thf)]2, the rate of isomerization was increased and indene isomer 4a
was obtained in 92% yield.
(13) 80 °C (4a: 90%; 3a: 10%); 50 °C (4a: 17%; 3a: 82%).
6750 J. Org. Chem., Vol. 72, No. 18, 2007

Indene Skeletal Rearrangement under Mild Conditions
TABLE 2. Effect of Substituents of Aminoindenes on
Isomerization Rate
Summary
We have found that aminoindene derivatives isomerize to the
isomers of the aminoindenes under mild reaction conditions.
Previously reported indene isomerizations have needed harsh
conditions or UV irradiation. From this viewpoint, the fact that
the rearrangement proceeds even at room temperature without
UV irradiation deserves special mention. The 13C-labeled
experiment shows that this isomerization is not just the exchange
of two substituents on the indene skeleton; this reaction proceeds
via the rearrangement of the indene framework. Since the
rearrangement of the indene framework usually occurs under
UV irradiation, an amino group is important to promote the
rearrangement under mild conditions, and so the rearrangement
looks like a thermal version of a UV light-promoted valence
isomerization of an indene framework.
R1 ) H
recov [%]
R1 ) MeO
time/
h
yield [%]
yield [%]
4c
recov [%]
4a
3a
3c
0.5
1
3
8
24
16
17
53
87
>99
84
83
47
12
0
4
12
35
58
>99
96
88
65
42
0
Experimental Section
SCHEME 1. Proposed Mechanism of the Isomerization of
Aminoindene Derivative 3
General Procedure for the Isomerization of Aminoindene
Derivatives. The mixture of an aminoindene derivative (0.200
mmol) and DMF (1.0 mL) was heated at 100 °C for 24 h. After
the solvent was removed in vacuo, the product was isolated by
silica gel column chromatography.
sec-Phenethylalcohol-methyl-13C.15 A solution of iodomethane-
13C (10 atom % 13C) in anhydrous ether (93.0 mL) was added
dropwise to a stirred suspension of dry magnesium turnings
(2.62 g, 107 mmol) in anhydrous ether (7.00 mL) (Scheme S1).
The resulting mixture was stirred at reflux for 1 h, and a solution
of benzaldehyde (10.9 mL, 107 mmol) in anhydrous ether (70.0
mL) was added dropwise at -5 °C. The reaction mixture was
gradually warmed to 25 °C, and the reaction mixture was stirred
for 2 h. After the mixture was quenched with aq NH4Cl, washed
with brine, and dried with MgSO4. The solution was concentrated
in vacuo to give sec-phenetylalcohol-methyl-13C in 99% yield.
Acetophenone-methyl-13C.16 The mixture of H5IO6 (6.48 g, 28.4
mmol) and acetonitrile (160 mL) was stirred vigorously at 25 °C
for 15 min (Scheme S1). Then, sec-phenetylalcohol-methyl-13C
(3.14 g, 25.5 mmol) was added to the above mixture at 0 °C,
followed by the addition of pyridinium chlorochromate (PCC) (115
mg, 0.538 mmol) in acetonitrile (15 mL) in three portions. After
being stirred for 2 h, the reaction mixture was diluted with ethyl
acetate (100 mL) and was washed with brine, saturated aq Na2-
SO3, and brine. After the mixture was dried with anhydrous Na2-
SO4 and concentrated, acetophenone-methyl-13C was obtained in
65% yield.
isomerization proceeds via a radical pathway.14 Addition of such
radical inhibitors as 1-dodecene, butyl vinyl ether, 1,4-benzo-
quinone, and galvinoxyl to the isomerization from aminoindene
3a to 4a did not disturb the reaction. This result indicates that
the isomerization of 3a did not proceed via a radical pathway.
We investigated a substituent on the aromatic ring of
aminoindenes (Table 2). By heating an aminoindene derivative
3c that has an electron-donating methoxy group at the para-
position in DMF at 100 °C, the corresponding aminoindene
isomer 4c was formed. However, the rate of isomerization of
3c was slightly slow. This result indicates that destabilization
by the electron-donating group at the position indicated with
sharps (#) in Scheme 1 decreased the reaction rate.
Phenylacetylene-r-13C.17 To a solution of lithium diisopropy-
lamide (which was prepared at 0 °C from diisopropylamine (3.70
mL, 26.4 mmol) and n-butyllithium in hexane (1.57 M, 17.0 mL,
26.7 mmol)) in dry THF (30 mL) was added dropwise acetophe-
none-methyl-13C (3.01 g, 25.0 mmol) in THF (13 mL) at -78 °C
(Scheme S1). After the mixture was stirred for 1 h, diethyl
chlorophosphate (3.99 mL, 27.6 mmol) was added at this temper-
ature. After warming to room temperature gradually, the mixture
was added dropwise to a solution of LDA (56.3 mmol) in THF
(60 mL), which was prepared at -78 °C as described above. The
mixture was warmed to room temperature over 3 h and was
quenched with water. The mixture was extracted with pentane, was
washed with 1 M HCl, water, and aq NaHCO3, and was dried with
MgSO4. After distillation, phenylacetylene-R-13C was obtained in
43% yield.
Compared with the previous reports on the indene isomer-
ization, the rearrangement of aminoindene derivatives proceeded
under mild conditions. The existence of a nitrogen atom
accelerates the rearrangement. By considering the above inves-
tigations, the proposed mechanism of isomerization is as follows
(Scheme 1): (1) formation of bicyclo[2.1.0]pentenamine inter-
mediate A by the flow of electrons from a nitrogen atom and
dearomatization; (2) rearrangement of the intermediate A to give
bicycle[2.1.0]pentane intermediate B by rearomatization; (3)
production of aminoindene derivative 4, which is the isomer of
3, by a ring opening reaction and the rearrangement of a proton.
In the last step, the reaction does not proceed in a reverse manner
because 4 is thermodynamically more stable than 3, owing to
the conjugation in 4.
Phenyl-1-octyne-r-13C.18 To a solution of n-butyllithium in
hexane (1.57 M, 7.62 mL, 12.0 mmol) was added phenylacetylene-
(15) Fieser, M.; Fieser, L. F. Org. Synth. 1972, 3, 26.
(16) Hunsen, M. Tetrahedron Lett. 2005, 46, 1651.
(17) Negishi, E.-i.; King, A. O.; Klima, W. L. J. Org. Chem. 1980, 45,
2526.
(14) For the theoretical calculations of the isomerization of indene
derivatives via radical intermediates, see: Dubnikova, F.; Lifshitz, A. Isr.
J. Chem. 2003, 43, 325.
(18) Crandall, J. K.; Michaely, W. J. J. Org. Chem. 1984, 49, 4244.
J. Org. Chem, Vol. 72, No. 18, 2007 6751

Kuninobu et al.
R-13C (1.02 g, 9.97 mmol) in THF (4.0 mL) (Scheme S1). The
solution was heated at reflux until gas evolution ceased (3.5 h).
Iodohexane (1.62 mL, 11.0 mmol) was added, and the mixture was
heated at reflux for 12 h. After cooling, the mixture was quenched
with water, was extracted with ether, and was washed with brine.
After the mixture was dried with MgSO4 and distilled, phenyl-1-
octyne-R-13C was obtained in 73% yield.
143.7 (1C), 148.4 (1C); IR (nujol, ν/cm-1) 2721 (w), 1598 (m),
1464 (w), 1377 (w), 1220 (w), 1198 (s), 1156 (w), 1072 (w), 888
(s), 840 (m), 759 (m), 725 (m), 710 (w), 673 (s), 659 (s). Anal.
Calcd for C26H27N: C, 88.34; H, 7.70; N, 3.96. Found: C, 88.26;
H, 7.76; N, 3.84.
N-tert-Butyl-5-methoxy-2-phenyl-3-metheyl-3H-inden-1-
1
amine (4c). H NMR (400 MHz, CDCl3) δ 1.05 (s, 9H), 1.16 (d,
N-tert-Butyl-2-hexyl-3-phenyl-3H-inden-1-amine (5a).10 The
mixture of aldimine 1a (0.500 mmol), phenyl-1-octyne-R-13C (0.500
mmol), and [ReBr(CO)3(thf)]2 (12.7 mg, 0.0150 mmol) in toluene
(1.0 mL) was heated at 135 °C for 1 h (eq S1). After the solvent
was removed in vacuo, aminoindene 5a was isolated in 57% yield
by silica gel column chromatography.
J ) 7.6 Hz, 3H), 3.79-3.88 (m, 1H), 3.85 (s, 3H), 6.85 (dd, J )
8.4, 2.4 Hz, 1H), 7.00 (s, 1H), 7.23-7.25 (m, 1H), 7.33-7.43 (m,
5H); 13C NMR (100 MHz, CDCl3) δ 17.0 (1C), 30.9 (3C), 44.0
(1C), 54.7 (1C), 55.5 (1C), 109.1 (1C), 111.4 (1C), 120.5 (1C),
126.1 (1C), 128.3 (2C), 128.8 (2C), 136.9 (1C), 137.2 (1C), 137.3
(1C), 140.6 (1C), 149.6 (1C), 157.9 (1C); IR (nujol, ν/cm-1) 3853
(w), 3750 (w), 3734 (w), 3675 (w), 3648 (w), 2724 (s), 1549 (m),
1457 (s), 1376 (s), 1217 (w), 722 (w). HR-MS Calcd for C21H26-
ON ([M + H]+): 308.2014; Found: 308.2021.
N-tert-Butyl-3,5-diphenyl-2-methyl-3H-inden-1-amine (3b). 1H
NMR (400 MHz, CDCl3) δ 1.04 (s, 9H), 2.08 (s, 1H), 4.76 (s,
1H), 7.29-7.34 (m, 4H), 7.38-7.45 (m, 6H), 7.61-7.63 (m, 3H);
13C NMR (100 MHz, CDCl3) δ 11.3 (1C), 30.8 (3C), 50.8 (1C),
62.5 (1C), 118.0 (1C), 123.7 (1C), 124.7 (1C), 127.0 (1C), 127.2
(2C), 128.0 (2C), 128.7 (1C), 129.8 (3C), 134.3 (1C), 140.7 (1C),
N-tert-Butyl-2-hexyl-3-phenyl-3H-inden-1-amine (5a). 1H NMR
(400 MHz, CDCl3) δ 0.83 (t, J ) 7.0 Hz, 3H), 0.99 (s, 9H), 1.19-
1.30 (m, 4H), 1.50-1.60 (m, 4H), 2.41 (t, J ) 7.8 Hz, 2H), 4.64
(s, 1H), 7.17-7.23 (m, 1H), 7.27-7.32 (m, 5H), 7.37-7.40 (m,
2H), 7.53-7.55 (m, 1H); 13C NMR (100 MHz, CDCl3) δ 14.0 (1C),
22.6 (1C), 25.9 (1C), 28.8 (2C), 29.5 (2C), 30.6 (3C), 31.5 (1C),
50.7 (1C), 63.1 (1C), 119.5 (1C), 123.6 (1C), 125.3 (1C), 126.9
(1C), 127.1 (1C), 128.0 (1C), 129.7 (2C), 136.7 (1C), 138.9 (1C),
144.1 (1C) 145.7 (1C) 148.4 (1C); IR (nujol, ν/cm-1) 3853 (m),
3750 (m), 3744 (m), 3675 (m), 3648 (m), 3057 (m), 2857 (w),
1733 (m), 1700 (m), 1652 (m), 1609 (s), 1521 (s), 1558 (m), 1465
(m), 1419 (s), 1362 (w), 1225 (m), 1113 (m), 1027 (w), 757 (w),
737 (s) 700 (s). Anal. Calcd for C25H33N: C, 86.40; H, 9.57; N,
4.03. Found: C, 86.15; H, 9.60; N, 4.10.
141.8 (1C), 145.7 (1C), 146.2 (1C), 147.0 (1C); IR (nujol, ν/cm-1
)
3058 (w), 2724 (w), 1601 (m), 1465 (w), 1377 (w), 1301 (s), 1226
(w), 1155 (m), 1106 (w), 1074 (w), 1022 (w), 880 (w), 760 (s),
721 (m), 697 (s). Anal. Calcd for C26H27N: C, 88.34; H, 7.70; N,
3.96. Found: C, 88.26; H, 7.82; N, 3.89.
N-tert-Butyl-5-methoxy-2-methyl-3-phenyl-3H-inden-1-
1
amine (3c). H NMR (400 MHz, CDCl3) δ 1.01 (s, 9H), 2.02 (s,
3H), 3.84 (s, 3H), 4.67 (s, 1H), 6.73-6.75 (dd, J ) 8.0, 2.3 Hz,
1H), 6.81 (d, J ) 2.0 Hz, 1H), 7.30-7.32 (m, 3H), 7.37-7.45 (m,
3H); 13C NMR (100 MHz, CDCl3) δ 11.2 (1C) 30.8 (3C), 50.8
(1C), 55.5 (1C), 62.1 (1C), 105.5 (1C), 110.3 (2C), 124.1 (1C),
126.9 (1C), 128.0 (2C), 129.7 (2C), 134.1 (1C), 136.3 (1C), 140.0
(1C), 146.7 (1C), 159.7 (1C); IR (nujol, ν/cm-1) 3055 (w), 1604
(w), 1584 (s), 1473 (w), 1440 (w), 1361 (s), 1343 (s), 1285 (s),
1214 (w), 1175 (s), 1067 (w), 1035 (m), 917 (s), 858 (m), 842
(m), 803 (w), 738 (s), 700 (s), 665 (w). Anal. Calcd for C21H25-
NO: C, 82.04; H, 8.20; N, 4.56; O, 5.20. Found: C, 81.87; H,
8.25; N, 4.55.
Acknowledgment. Financial support by a Grant-in-Aid for
Scientific Research on Priority Areas (No. 18037049, “Ad-
vanced Molecular Transformations of Carbon Resources”), and
for Young Scientists (B) (No. 18750088) from the Ministry of
Education, Culture, Sports, Science, and Technology of Japan.
N-tert-Butyl-2,5-diphenyl-3-methyl-3H-inden-1-amine (4b). 1H
NMR (400 MHz, CDCl3) δ 1.07 (s, 9H), 1.20-1.22 (d, J ) 7.6
Hz, 3H), 3.90-3.92 (m, 1H), 7.25-7.33 (m, 4H), 7.37-7.54 (m,
6H), 7.63-7.66 (m, 3H); 13C NMR (100 MHz, CDCl3) δ 16.8 (1C),
31.0 (3C), 44.3 (1C), 54.8 (1C), 120.2 (1C), 121.4 (1C), 125.4 (1C),
126.4 (1C), 126.8 (1C), 127.2 (3C), 128.3 (1C), 128.7 (3C), 128.9
(1C), 137.1 (1C), 138.0 (1C), 139.6 (1C), 140.1 (1C), 141.7 (1C),
Supporting Information Available: Scheme for the preparation
of 13C-labeled aminoindene derivative 5a, 13C NMR spectra of the
13C-labeled aminoindene derivatives 5a and 6a, and copies of NMR
spectra for all products. This material is available free of charge
via the Internet at http://pubs.acs.org.
JO070537W
6752 J. Org. Chem., Vol. 72, No. 18, 2007