peri-Interaction between diarylmethyl and diarylmethylium units in 1,8-disubstituted naphthalenes: Preference of localized structure for the C-H bridged carbocation

Article abstract of DOI:10.1016/j.tetlet.2004.04.002

(8-Diarylmethyl-1-naphthyl)bis(4-dimethylaminophenyl)methyliums (aryl=C₆H₅, 4-IC₆H₄, and 4-MeOC ₆H₄) were generated by hydride shift from (4-dimethylaminophenyl)methyl group to the diarylmethylium unit at peri-positions of naphthalene. Successful isolation and low-temperature X-ray analysis indicated that they are novel C-H bridged carbocations, which prefer the localized structure with a short contact of C-H?C⁺ rather than the delocalized one with a three-centered-two-electron bond of (C?H?C)⁺.

Full text of DOI:10.1016/j.tetlet.2004.04.002

Tetrahedron
Letters
Tetrahedron Letters 45 (2004) 4553–4558
peri-Interaction between diarylmethyl and diarylmethylium units in
1,8-disubstituted naphthalenes: preference of localized structure
for the C–H bridged carbocationq
Hidetoshi Kawai, Takayuki Nagasu, Takashi Takeda, Kenshu Fujiwara, Takashi Tsuji,
Masakazu Ohkita, Jun-ichi Nishidaà and Takanori Suzuki*
Division of Chemistry, Graduate School of Science, Hokkaido University, Kita 10, Nishi 8, Kita-ku, Sapporo 060-0810, Japan
Received 9 March 2004; accepted 5 April 2004
Abstract—(8-Diarylmethyl-1-naphthyl)bis(4-dimethylaminophenyl)methyliums (aryl ¼ C6H5, 4-IC6H4, and 4-MeOC6H4) were
generated by hydride shift from (4-dimethylaminophenyl)methyl group to the diarylmethylium unit at peri-positions of naphthalene.
Successful isolation and low-temperature X-ray analysis indicated that they are novel C–H bridged carbocations, which prefer the
localized structure with a short contact of C–Hꢀ ꢀ ꢀCþ rather than the delocalized one with a three-centered-two-electron bond of
(Cꢀ ꢀ ꢀHꢀ ꢀ ꢀC)þ.
Ó 2004 Elsevier Ltd. All rights reserved.
The naphthalene-1,8-diyl skeleton has long been
attracting considerable attention in structural chemis-
try.1 By providing the unique opportunity to arrange the
two peri-substituents in a proximity, it serves as a special
scaffold to investigate the attractive or repulsive inter-
actions inbetween. A variety of 1,8-disubstituted naph-
thalenes have been prepared and studied in order to
clarify the nature of charge-transfer interaction,2 polar-p
interaction,3 and p-type complexation of a Lewis acid–
base pair.4
ment, which is also true in the 1,8-diborylnaphthalenes
with strong Lewis acidity.6;7 In contrast to the rich
chemistry for heteroatom analogues, it is still unclear
whether or not the C–H–C three-centered bond8 would
be formed at the peri-position of naphthalene as in 3 (X,
Y ¼ carbon substituents). It is of special interest to
H
X
X
X
Y
Y
Y
X
Y
Another characteristic endowed by this skeleton is the
cooperative enhancement of the electronic properties of
the substituents, for example, Lewis basicity of ‘proton-
sponge’ (1, X ¼ Y ¼ NMe2).5 Chelation or formation of
a three-centered bond can account for such enhance-
2
1
H
H
X
X
Y
Y
Keywords: peri-Interaction; Carbocation; Triarylmethylium; Hydride
shift; Three-centered-two-electron bond.
q Supplementary data associated with this article can be found, in the
online version, at doi:10.1016/j.tetlet.2004.04.002
* Corresponding author. Tel./fax: +81-11-706-2714; e-mail: tak@
sci.hokudai.ac.jp
3
3 '
Present address: Department of Applied Chemistry, Graduate
School of Engineering, Nagoya Institute of Technology, Nagoya
466-8555, Japan.
5
4
à
Department of Electronic Chemistry, Interdisciplinary Graduate
School of Science and Engineering, Tokyo Institute of Technology,
Yokohama 226-8502, Japan.
a: X = (4-Me2NC6H4)2C; Y = (4-Me2NC6H4)(HO)C
b: X = Y = (4-MeOC6H4)2C
0040-4039/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2004.04.002

4554
H. Kawai et al. / Tetrahedron Letters 45 (2004) 4553–4558
clarify whether the C–H bridged carbocations prefer the
localized structure (2) or the delocalized one (3).9 Very
obtained 6d15 and 6e15 in 18% and 34% respective
yield.18 The X-ray analysis19 of 6d showed that it adopts
the extended conformation with four aryl groups di-
rected outward (Fig. S1). Yet, it still suffers from severe
steric repulsion between the methine proton and hy-
droxy group around the peri-position, thus causing the
in-plane deviation of substituents at C1 and C8 directed
outward with a largest deviation of bond angles (a,b) of
5.7° from the ideal value (120°) (Table 1).
recently, we (a)4 and Gabbaı (b) postulated the
10
€
involvement of the C–H bridged cations 2a,b/3a,b as
reactive intermediates during the acid-catalyzed cleav-
age of the long C1–C2 bond in acenaphthenes 4a,b. In
our continuing studies on the novel electrochromic
systems based on the interconversion between the
hexaphenylethane derivatives 4 and the naphthalenediyl
dications 5 (X ¼ Y ¼ Ar2C),11 we have succeeded in
isolating a series of diaryl(8-diarylmethyl-1-naphthyl)-
methyliums 2 [X ¼ (4-Me2NC6H4)2C; Y ¼ (4-ZC6H4)2C;
Z ¼ H, I, OMe) for the first time. Here we report their
preparation and properties as well as the precise geo-
metrical features determined by the low-temperature X-
ray analysis. Preference of the localized structure 2 over
the delocalized one 3 is discussed based on the results
obtained for the present system.
Upon treatment of alcohols 6c–e with HBF4, deeply
colored cationic salts were obtained in 81%, 82%, and
62% yield, respectively. On the basis of high-resolution
mass spectra in a FABþ mode, each cation thus
obtained has the molecular formula identical to 2c–e,
respectively (Scheme 1). However, all the salts exhibit
strong absorption in the same region [kmax 627 (log e
4.86); 629 (4.83); 628 (4.91) nm, respectively] irrespective
to the substituent (Z ¼ H, I, or OMe) at the triaryl-
methanol moiety of precursors 6c–e. The close similarity
of these values to that of bis(4-dimethylaminophenyl)-
(1-naphthyl)methylium 8 (627 nm) indicates that the
salts in hand are not 2c–e with the positive charge on (4-
ZC6H4)2C unit but have the delocalized structures 3c–e
or the hydride-shifted structures 2c0–e0.
Diaryl(8-diarylmethyl-1-naphthyl)methanols 6 are the
promising precursors12 for the desired carbocations
(Scheme 1) since the monocation could not be obtained
upon treatment of the dication 5b [X ¼ Y ¼ (4-
MeOC6H4)2C)] with hydride reagents.10 The tert-alcohol
6c15 containing two 4-dimethylaminophenyl and two
phenyl groups was prepared by the reaction of methyl
8-[bis(4-dimethylaminophenyl)methyl]-1-naphthalene-
carboxylate 716 with PhLi in 52% yield. Similarly, by
using 4-iodo- and 4-methoxyphenyllithium were
1
Further information was given by the H NMR spectra
in CDCl3. Thus, the methoxy protons of 6e (d 3.78 ppm)
and those of the corresponding salt (3.72 ppm) resonate
nearly in the same region, which are not in accord with
the structure 2e for the cation. In contrast, the chemical
shifts of dimethylamino groups are largely down-field
shifted from 6c–e (2.85, 2.87, and 2.85 ppm, respectively)
to the salts (3.30, 3.34, and 3.30 ppm, respectively). The
close similarity of the latter values to that of 8
(3.33 ppm) again indicates the considerable amount of
positive charge on the (4-Me2NC6H4)2C moiety as in
hydride-shifted species 2c0–e0. In all salts, the methine
proton (6.14, 6.05, and 5.99 ppm) appears in the
expected region for triarylmethanes (e.g., 6c–e: 6.56,
6.55, and 6.66 ppm, respectively). When the contribution
from the delocalized structure 3 is important for these
cations, the methine protons must be shifted to the far
high-field since the typical values for the protons in the
C–H–C three-centered-two-electron bonds are in the
range of d )3 to )7 ppm due to the resonance structure
30 with a Cþ–Hꢁ–Cþ unit.8 Thus, the contribution from
delocalized form 3 should be marginal, if any, for the
present cations, and the hydride-shifted localized struc-
tures 2c0–e0 are finally assigned to them.20
NMe2
NMe2
Me2N
Me2N
O
OMe
H
8
7
4-Z-C6H4-Li
c: Z = H; d: Z = I; e: Z = OMe
NMe2
H
NMe2
H
Z
Z
Z
Me2N
acid
Z
Me2N
HO
6c - e
2c - e
(localized)
In order to determine the detailed structural features,
the X-ray analysis on 2c0BF4 was carried out at )120 °C.
The single crystal contains two crystallographically
independent molecules of 2c0 (mol-1 and-2), whose
structures are similar to each other. As shown in Figure
1 (mol-1), the methine proton determined by Fourier
NMe2
Z
NMe2
Z
Z
Me2N
Me2N
Z
H
H
ꢀ
Synthesis is bonded to the (C6H5)2C unit (1.00 A) in
accord with the structural assignment in solution. This
hydrogen is also close to the methylium carbon of (4-
hydride shift
Me2NC6H4)2Cþ unit. The nonbonded contact (2.26 A)
3c - e
ꢀ
2c' - e'
(localized)
(delocalized)
is significantly shorter than the sum of vdW radii
21
ꢀ
Scheme 1.
(Cꢀ ꢀ ꢀH, 2.90 A), showing that this is one of the rare

H. Kawai et al. / Tetrahedron Letters 45 (2004) 4553–4558
4555
Table 1. Listing of structural data in 6d, 2c0 and 9c determined by X-ray analyses at 153 Ka
d
X
Y
β
β'
α
α'
a, a0
b, b0
R(C–X–C)
R(C–Y–C)
d (A)
ꢀ
Compd
6d
117.2°, 115.7°
113.8°, 117.5°
112.4°, 118.0°
112.8°, 118.0°
123.3°, 125.7°
125.1°, 124.1°
127.0°, 123.5°
127.0°, 122.8°
333.9°
359.8°
359.6°
359.3°
330.7°
337.0°
337.7°
338.1°
3.27
3.02
3.02
3.00
2c0 (mol-1)
2c0 (mol-2)
9c
6d: X ¼ (4-Me2NC6H4)2CH, Y ¼ (4-IC6H4)2COH; 2c0: X ¼ (4-Me2NC6H4)2Cþ, Y ¼ (C6H5)2CH; 9c: X ¼ 4-Me2NC6H4C@C6H4@O, Y ¼ (C6H5)2CH.
a
0
ꢀ
ꢀ
Estimated standard deviations of distances and angles for nonhydrogen atoms are 0.005–0.007 A and 0.3–0.5° in 2c , 0.004–0.007 A and 0.3–0.5° in
6d, and 0.001–0.002 A and 0.08–0.1° in 9c, respectively.
ꢀ
examples of C–H bridged carbocations.8 The distance
ratios of Cꢀ ꢀ ꢀH/C–H in 2c0 (mol-1) is 2.26, which is
much larger than that in the isoelectronic hydride
adduct of 1,8-bis(dimethylboryl)naphthalene with a
three-centered-two-electron bond (1.24).6a Furthermore,
as shown in Table 1, the sum of bond angles defined by
C–C–C around the methylium carbon (RC–X–C:
359.8°) and the methine carbon (RC–Y–C: 337.0°) are
close to the expected values for pure Csp2 (360°) and Csp3
of triphenylmethane (339.1° and 336.4° for two crys-
tallographically independent molecules),22 respectively.
Such geometrical features of the solid-state structure for
2c0 clearly show negligible contribution from the delo-
calized structure 3c. As shown by the values of a and b
in Table 1, the in-plane deviations of two substituents at
Figure 1. Molecular structure of 2c0 (mol-1) determined by X-ray
C1 and C8 positions in 2c0 are as large as the highly
analysis of BFꢁ4 salt at )120 °C. The C–Hꢀ ꢀ ꢀCþ angle is 131.2°. The C–
congested alcohol 6d, suggesting that the attractive
H and Hꢀ ꢀ ꢀCþ distances and the C–Hꢀ ꢀ ꢀCþ angle in mol-2 are 1.10,
interaction through the C–Hꢀ ꢀ ꢀCþ contact observed
ꢀ
2.22 A, and 127.2°, respectively.
here is rather weak. Structural optimization of the cat-
ion by ab initio technique (B3LYP/6-31G*)23 converged
to the similar geometry to that of 2c0 in crystal (Table 2).
Ab initio calculation of (8-diphenylmethyl-1-naph-
thyl)diphenyl- methylium 2g indicated that the localized
structure is preferred even when the substituents on the
two diaryl units are identical. PM3 calculation suggested
that the delocalized structure 3g is the transition state
for the degenerate interconversion of 2g.
converted to the hexaphenylethane 4c (Scheme 2); yet,
this is not the case. Upon treatment of 2c0BF4 with
aqueous KOH was obtained quinonemethide 9c in 75%
yield, which is the hydrolyzed product of (4-
Me2NC6H4)2Cþ unit at the end group. According to the
X-ray analysis of 9c (Fig. S2),19 its geometry resembles
2c0 (Table 1). Lack of reactivity at the bridging hydrogen
nor the methylium carbon may be accounted for by the
sterically hindered structure of 2c0 as well as the higher
steric energies for the corresponding products (e.g., 4c
Finally, reactions of 2c0 with a few nucleophiles/bases
were investigated. When the bridging hydrogen is
abstracted as proton by the reagents, 2c0 would be
Table 2. Listing of structural data in 2c0 and 2g calculated by ab initio technique (B3LYP/6-31G*)a
H
γ
d"
d'
Y
d
X
β
β'
α
α
'
a, a0
b, b0
c
d, d0, d00 (A)
ꢀ
Compd
2c0
2g
113.0°, 118.1°
112.4°, 118.3°
126.4°, 123.0°
127.2°, 123.6°
125.0°
114.8°
3.15, 1.091, 2.390
3.20, 1.090, 2.585
2c0: X ¼ (4-Me2NC6H4)2C, Y ¼ (C6H5)2C; 2g: X ¼ (C6H5)2C, Y ¼ (C6H5)2C.
a Values of R(C–X–C) and R(C–Y–C) are 359.6°, 337.5° for 2c0, and 359.8°, 338.0° for 2g, respectively.

4556
H. Kawai et al. / Tetrahedron Letters 45 (2004) 4553–4558
tem. MS spectra were measured by Mr. Kenji Watanabe
and Dr. Eri Fukushi at the GC–MS & NMR Labora-
tory (Faculty of Agriculture, Hokkaido University).
(Ar = 4-Me2NC6H4)
Ar
Ar
Ph
Ph
H
H
Ar
H
Ar
Ph
Ph
NaBH4
References and notes
10c
2c'
KOH aq.
H+
Ph
1. Schweizer, W. B.; Procter, G.; Kaftory, M.; Dunitz, J. D.
Helv. Chem. Acta 1978, 61, 2783; Balasubramaniyan, V.
Chem. Rev. 1966, 66, 567.
O
Ar
Ph
H
Ar
Ph
2. (a) Komatsu, K.; Abe, N.; Takahashi, K.; Okamoto, K.
J. Org. Chem. 1979, 44, 2712; (b) Tsuji, R.; Komatsu, K.;
Inoue, Y.; Takeuchi, K. J. Org. Chem. 1992, 57, 636.
3. (a) Cozzi, F.; Cinguini, M.; Annunziata, R.; Dwyer, T.;
Siegel, J. S. J. Am. Chem. Soc. 1992, 114, 5729; (b) Cozzi,
F.; Cinguini, M.; Annunziata, R.; Siegel, J. S. J. Am.
Chem. Soc. 1993, 115, 3550; (c) Cozzi, F.; Siegel, J. S. Pure
Appl. Chem. 1995, 67, 683.
Ar
Ph
4c
9c
not observed
Scheme 2.
4. Suzuki, T.; Nagasu, T.; Kawai, H.; Fujiwara, K.; Tsuji, T.
Tetrahedron Lett. 2003, 44, 6095.
5. Review (a) Staab, H. A.; Saupe, T. Angew. Chem., Int. Ed.
Engl. 1988, 27, 865; (b) Llamas-Saiz, A. L.; Foces-Foces,
C.; Elguero, J. J. Mol. Struct. 1994, 328, 297.
6. (a) Katz, H. E. J. Am. Chem. Soc. 1985, 107, 1420; (b)
Katz, W. E. J. Org. Chem. 1985, 50, 5027; (c) Katz, H. E.
Organometallics 1987, 6, 1134.
€
7. Review (a) Gabbaı, F. P. Angew. Chem., Int. Ed. 2003, 42,
2218; (b) Hoefelmeyer, J. D.; Schulte, M.; Tschinkl, M.;
and the isomer of alcohol 6c) than for 9c. Upon treat-
ment of 2c0BF4 with NaBH4, hydride adduct 10c was
formed as a sole product and isolated in 45% yield,
which has the same skeleton to 1,8-bis[bis(4-dimethyl-
aminophenyl)methyl]-naphthalene 10f15 prepared from
1,8-dilithionaphthalene24 and (4-Me2NC6H4)2CHþBFꢁ4
salt in 20% yield. Although hydride addition to the
methylium carbon is quite common for triarylmethy-
lium dyes,25 this result disagrees with the recent proposal
€
Gabbaı, F. P. Cood. Chem. Rev. 2002, 235, 93.
10;26
€
by Gabbaı et al.,
cation 2b/3b might be converted to acenaphthene 4b by
who assumed that the bridged
8. (a) Kirchen, R. P.; Sorensen, T. S. J. Am. Chem. Soc. 1978,
100, 6761; (b) McMurry, J. E.; Hodge, C. N. J. Am. Chem.
Soc. 1984, 106, 6450; (c) McMurry, J. E.; Lectka, T. Acc.
Chem. Res. 1992, 25, 47; (d) Taeschler, C.; Parvez, M.;
Sorensen, T. S. J. Phys. Org. Chem. 2002, 15, 36.
9. Tantillo, D. J.; Hoffman, R. J. Am. Chem. Soc. 2003, 125,
4042.
hydride reagents.
In summary, we have succeeded in isolating and char-
acterizing the novel carbocations with a very short C–
Hꢀ ꢀ ꢀCþ contact. The first successful X-ray analysis on
the C–H bridged carbocation has proven that it prefers
localized structure rather than the delocalized one with a
three-centered-two-electron bond.27 Studies on other C–
H bridged carbocations are now underway.
€
10. Wang, H.; Gabbaı, F. P. Angew. Chem., Int. Ed. 2004, 43,
184.
11. Kawai, H.; Takeda, T.; Fujiwara, K.; Suzuki, T. Hokkaido
Winter Symposium, Abstract Paper (2B20), 2004, 87.
12. Another merit of using these precursors is that C–H
localized (2) and delocalized structures (3) in the isolated
cationic salts would be distinguished unambiguously by
X-ray analysis when two kinds of aryl substituents13
are placed at each of 1,8-positions (Z is not NMe2).
13. Hexaphenylethanes are notorious for giving the disor-
dered crystal structures around the inner C–C bond due to
the ‘globular’ molecular shape (Ref. 14). Since the
carbocations 2 possess the similar structural features,
there will be high possibility that the C–Hꢀ ꢀ ꢀC part in 2
with four aryl groups of a kind suffers from positional
disorder in crystal, thus preventing the chance to tell the
localized structure from the delocalized one by X-ray
analysis.
Supplementary material
Crystallographic data (excluding structure factors) for
the structures in this paper have been deposited with the
Cambridge Crystallographic Data Centre as supple-
mentary publication numbers CCDC 231949, 232245–
232247. Copies of the data can be obtained, free of
charge, on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK [fax: +44 (0)-1223-336033 or
e-mail: deposit@ccdc.cam.ac.uk]. ORTEP drawings of
alcohol 6d (Fig. S1), quinonemethide 9c (Fig. S2), and
conjugate adduct 12 (Fig. S3) were submitted as elec-
tronic supplementary material.
14. (a) Kahr, B.; Engen, D. V.; Mislow, K. J. Am. Chem. Soc.
1986, 108, 8305; (b) Suzuki, T.; Nishida, J.; Tsuji, T.
Angew. Chem., Int. Ed. 1997, 36, 1329.
15. Selected data for new compounds are as follows. 2c0þBF4ꢁ:
mp 270–275 °C (decomp.); 1H NMR (300 MHz, CDCl3) d
8.12 (br d, 1H, J ¼ 7:5 Hz), 7.92 (br d, 1H, J ¼ 7:5 Hz),
7.51 (dd, 1H, J ¼ 7:5, 7.5 Hz), 7.48 (dd, 1H, J ¼ 7:5,
7.5 Hz), 7.21–6.98 (m, 12H), 6.68 (AA0XX0, br, 4H), 6.44
(m, 4H), 6.14 (s, 1H), 3.30 (s, 12H); 13C NMR (75 MHz,
CDCl3) d 176.98, 156.64, 144.19, 140.10, 139.22, 136.88,
135.31, 134.44, 133.72, 132.82, 132.51, 129.37, 128.67,
128.04, 126.85, 126.53, 126.31, 123.99, 113.77, 53.61,
40.91; IR (KBr) 1585, 1368, 1170, 1083 cmꢁ1; UV/vis
(CH3CN) 627 (log e 4.86), 467 (sh, 3.73), 307 (4.06) nm;
Acknowledgements
This work was supported by the Ministry of Education,
Science, and Culture, Japan (No. 15350019 and
14654139). We thank Prof. Tamotsu Inabe (Hokkaido
University) for use of the X-ray structure analysis sys-

H. Kawai et al. / Tetrahedron Letters 45 (2004) 4553–4558
4557
HR-MS (FABþ) Calcd. for C40H37N2: 545.2957. Found:
545.2964. 2d0þBF4ꢁ: mp 166.0–168.0 °C (decomp.); 1H
NMR (300 MHz, CDCl3) d 8.12 (br d, 1H, J ¼ 7:5 Hz),
7.94 (br d, 1H, J ¼ 7:5 Hz), 7.53 (dd, 1H, J ¼ 7:5, 7.5 Hz),
7.48 (dd, 1H, J ¼ 7:5, 7.5 Hz), 7.35 (AA0XX0, 4H), 7.16 (br
d, 1H, J ¼ 7:5 Hz), 7.05 (br d, 1H, J ¼ 7:5 Hz), 7.40–7.00
(AA0XX0, br, 4H), 6.80–6.65 (AA0XX0, br, 4H), 6.21
(AA0XX0, 4H), 6.05 (s, 1H), 3.34 (s, 12H); 13C NMR
(75 MHz, CDCl3) d 175.98, 156.62, 143.43, 139.95, 137.99,
137.24, 136.58, 135.36, 134.52, 133.60, 132.54, 132.03,
131.41, 129.22, 126.96, 126.45, 124.26, 114.05, 92.02,
52.67, 41.14; IR (KBr) 2920, 1618, 1584, 1484, 1368,
J ¼ 8:0, 1.5 Hz), 7.08 (dd, 1H, J ¼ 8:0, 1.5 Hz), 6.83–6.77
(m, 4H), 6.65 (AA0XX0, 4H), 6.61 (s, 1H), 6.60 (AA0XX0,
4H), 6.22 (s, 1H), 2.89 (s, 12H); IR (KBr) 2922, 2852,
1611, 1517, 1492, 1347, 777, 701 cmꢁ1; HR-MS (FD)
Calcd for C40H38N2: 546.3035. Found: 546.3017. 10f: mp
257–261 °C (decomp.); 1H NMR (400 MHz, CDCl3) d 7.71
(dd, 2H, J ¼ 8:0, 1.5 Hz), 7.28 (dd, 2H, J ¼ 8:0, 8.0 Hz),
7.08 (dd, 2H, J ¼ 8:0, 1.5 Hz), 6.68 (AA0XX0, 8H), 6.58
(AA0XX0, 8H), 6.38 (s, 2H), 2.94 (s, 24H); IR (KBr) 2880,
2792, 1612, 1518, 1346, 1224, 1200, 1160, 1132, 948,
776 cmꢁ1; MS (FD) m=z 632 (Mþ).
16. This ester was obtained by treatment of the corresponding
carboxylic acid17 with CH2N2 in 69% yield: mp 147.5–
148.5 °C; 1H NMR (300 MHz, CDCl3) d 7.93 (dd, 1H,
J ¼ 7:5, 1.5 Hz), 7.74 (dd, 1H, J ¼ 7:5, 1.5 Hz), 7.56 (dd,
1H, J ¼ 7:5, 1.5 Hz), 7.41 (dd, 1H, J ¼ 7:5, 7.5 Hz), 7.39
(dd, 1H, J ¼ 7:5, 7.5 Hz), 7.25 (dd, 1H, J ¼ 7:5, 1.5 Hz),
6.87 (AA0XX0, 4H), 6.61 (AA0XX0, 4H), 6.13 (s, 1H), 3.67
(s, 3H), 2.89 (s, 12H); IR (KBr) 2948, 2888, 2804, 1718,
1614, 1518, 1480, 1446, 1346, 1278, 1228, 1196, 1164, 1144,
1076, 948, 826, 778 cmꢁ1; MS (FD) m=z 438 (Mþ).
1170, 1084, 1062, 1006, 940, 902, 832, 784, 728, 538 cmꢁ1
;
UV/vis (CH3CN) 629 (log e 4.83), 463 (sh, 3.80), 308 (4.16)
nm; HR-MS (FABþ) Calcd for C40H35N2I2: 797.0890.
Found: 797.0902. 2e0þBF4ꢁ: mp 115.0–120.0 °C (decomp.);
1H NMR (300 MHz, CDCl3)
d 8.10 (br. d, 1H,
J ¼ 7:5 Hz), 7.89 (br d, 1H, J ¼ 7:5 Hz), 7.50 (dd, 1H,
J ¼ 7:5, 7.5 Hz), 7.47 (dd, 1H, J ¼ 7:5, 7.5 Hz), 7.20
(AA0XX0, 4H), 7.15 (br d, 1H, J ¼ 7:5 Hz), 7.11 (br d, 1H,
J ¼ 7:5 Hz), 6.69 (AA0XX0, 4H), 6.37 (AA0XX0, 4H), 5.99
(s, 1H), 3.72 (s, 6H), 3.30 (s, 12H); 13C NMR spectrum
could not be measured due to its low solubility; IR (KBr)
1618, 1582, 1510, 1466, 1370, 1282, 1250, 1166, 1124, 1084,
522 cmꢁ1; UV/vis (CH3CN) 628 (log e 4.91), 462 (sh, 3.89),
307 (4.22) nm; HR-MS (FABþ) Calcd for C42H41O2N2:
605.3168. Found: 605.3155. 6c: mp 194.0–199.0 °C (de-
comp.); 1H NMR (300 MHz, CDCl3) d 7.75 (br d, 1H,
J ¼ 7:5 Hz), 7.75 (br d, 1H, J ¼ 7:5 Hz), 7.34 (dd, 1H,
J ¼ 7:5, 7.5 Hz), 7.23 (s, 10H), 7.19 (br d, 1H, J ¼ 7:5 Hz),
7.13 (dd, 1H, J ¼ 7:5, 7.5 Hz), 6.92 (br d, 1H, J ¼ 7:5 Hz),
6.56 (s, 1H), 6.45 (AA0XX0, 4H), 6.33 (AA0XX0, 4H), 3.58
(s, 1H), 2.85 (s, 12H); IR (KBr) 3416, 1614, 1516, 1478,
1448, 1344, 1202, 1160, 1142, 1032, 820, 774, 754,
702 cmꢁ1; HR-MS (FD) Calcd for C40H38ON2: 562.2984.
Found: 562.2973. 6d: mp 240.0–243.0 °C (decomp.); 1H
NMR (300 MHz, CDCl3) d 7.79 (br d, 1H, J ¼ 7:5 Hz),
7.77 (br d, 1H, J ¼ 7:5 Hz), 6.53 (AA0XX0, 4H), 7.34 (dd,
1H, J ¼ 7:5, 7.5 Hz), 7.15 (dd, 1H, J ¼ 7:5, 7.5 Hz), 7.14
(br d, 1H, J ¼ 7:5 Hz), 6.93 (AA0XX0, 4H), 6.87 (br d, 1H,
J ¼ 7:5 Hz), 6.55 (s, 1H), 6.49 (AA0XX0, 4H), 6.23
(AA0XX0, 4H), 3.65 (s, 1H), 2.87 (s, 12H); IR (KBr)
3536, 3052, 2884, 2796, 1738, 1608, 1566, 1518, 1480, 1444,
1392, 1344, 1224, 1204, 1162, 1126, 1062, 1042, 1016, 1004,
974, 946, 824, 810, 776, 568 cmꢁ1; HR-MS (FD) Calcd for
C40H36ON2I2: 814.0917. Found: 814.0940. 6e: mp 138.0–
17. Zsuffa, M. Chem. Ber. 1910, 43, 2915.
18. Many attempts to obtain pure alcohol 6f with four 4-
Me2NC6H4 groups are unfruitful due to the difficulty in
isolating the labile compound from the mixture contain-
ing the considerable amount of by-produced methyl
trans-1,2-dihydro-8-[bis(4-dimethylaminophenyl)methyl]-2-
(4-dimethylaminophenyl)-1-naphthalenecarboxylate
12
and methyl 8-[bis(4-dimethylaminophenyl)methyl]-2-(4-
dimethylaminophenyl)-1-naphthalenecarboxylate 13. The
former is the conjugate adduct of Me2NC6H4Li at the
naphthalene skeleton of the ester 7, whose structure was
unambiguously determined crystallographically (Fig.
S3).19 The latter seems the secondary product from 12
through aromatization by air oxidation. Low yields of
6c–e during the reactions of 7 and 4-ZC6H4Li are also
due to the similar by-production of such abnormal
adducts.
19. Crystal data for 2c0þBF4ꢁ: C40H37N2BF4, M 632.55,
monoclinic, P21/c, a ¼ 14:134 (3), b ¼ 19:579 (4),
3
ꢀ
ꢀ
c ¼ 23:353 (4) A, b ¼ 94:054 (1)°, U ¼ 6446:2 (1) A , Dc
ðZ ¼ 8; two independent moleculesÞ ¼ 1:303 g cmꢁ1
,
l ¼
0:91 cmꢁ1, T ¼ 153 K. The final R value is 0.066 for 5907
independent reflections with I > 3rI and 835 parameters.
For 6d: C40H36N2OI2,
M 814.55, triclinic, P1 bar,
ꢀ
a ¼ 9:298 (4), b ¼ 9:349 (4), c ¼ 20:290 (8) A, a ¼ 94:463
1
3
ꢀ
139.5 °C; H NMR (300 MHz, CDCl3) d 7.74 (br d, 1H,
(5), b ¼ 96:540 (4), c ¼ 109:370 (6)°, U ¼ 1640 (1) A , Dc
ðZ ¼ 2Þ ¼ 1:649 g cmꢁ1, l ¼ 19:53 cmꢁ1, T ¼ 153 K. The
final R value is 0.043 for 5600 independent reflections with
I > 3rI and 406 parameters. For 9c: C38H31NO, M
517.67, triclinic, P1 bar, a ¼ 10:847 (3), b ¼ 12:742 (2),
J ¼ 7:5 Hz), 7.74 (br d, 1H, J ¼ 7:5 Hz), 7.34 (dd, 1H,
J ¼ 7:5, 7.5 Hz), 7.22 (dd, 1H, J ¼ 7:5, 1.5 Hz), 7.13 (dd,
1H, J ¼ 7:5, 7.5 Hz), 7.09 (AA0XX0, 4H), 6.90 (br d, 1H,
J ¼ 7:5 Hz), 6.75 (AA0XX0, 4H), 6.66 (s, 1H), 6.46
(AA0XX0, 4H), 6.40 (AA0XX0, 4H), 3.78 (s, 6H), 3.49 (s,
1H), 2.85 (s, 12H); IR (KBr) 3428, 2948, 2832, 1610, 1580,
1514, 1444, 1344, 1302, 1250, 1202, 1178, 1034, 948, 820,
ꢀ
c ¼ 12:809 (3) A, a ¼ 61:36 (1), b ¼ 83:32 (2), c ¼ 64:49
3
(1)°, U ¼ 1393:1 (6) A , Dc ðZ ¼ 2Þ ¼ 1:234 g cmꢁ1, l ¼
ꢀ
0:73 cmꢁ1, T ¼ 153 K. The final R value is 0.046 for 4971
independent reflections with I > 3rI and 361 parameters.
For 12: C37H41N3O2, M 559.75, triclinic, P1 bar, a ¼ 9:651
798, 774, 586, 572 cmꢁ1
; HR-MS (FD) Calcd for
C42H42O3N2: 622.3195. Found: 622.3212. 9c: mp 257.0–
1
ꢀ
258.0 °C; H NMR (300 MHz, CDCl3) d 8.00 (br d, 1H,
(3), b ¼ 18:445 (5), c ¼ 19:640 (5) A, a ¼ 65:55 (2),
3
ꢀ
J ¼ 7:5 Hz), 7.85 (br d, 1H, J ¼ 7:5 Hz), 7.77 (dd, 1H,
J ¼ 7:5, 2.5 Hz), 7.48 (dd, 1H, J ¼ 7:5, 7.5 Hz), 7.40 (dd,
1H, J ¼ 7:5, 7.5 Hz), 7.17 (dd, 1H, J ¼ 7:5, 1.5 Hz), 7.05
(m, 8H), 6.98 (dd, 1H, J ¼ 7:5, 7.5 Hz), 6.59 (AA0XX0,
2H), 6.54 (m, 3H), 6.48 (dd, 1H, J ¼ 7:5, 2.5 Hz), 6.37 (dd,
1H, J ¼ 7:5, 2.5 Hz), 6.33 (AA0XX0, 2H), 5.80 (dd, 1H,
J ¼ 7:5, 2.5 Hz), 3.05 (s, 6H); IR (KBr) 2924, 1628, 1588,
1480, 1446, 1372, 1194, 1166, 776, 700, 534 cmꢁ1; MS (FD)
m=z 517 (Mþ). 10c: mp 72–73 °C; 1H NMR (300 MHz,
CDCl3) d 7.76 (dd, 1H, J ¼ 8:0, 1.5 Hz), 7.74 (dd, 1H,
J ¼ 8:0, 1.5 Hz), 7.30 (dd, 1H, J ¼ 8:0, 8.0 Hz), 7.28 (dd,
1H, J ¼ 8:0, 8.0 Hz), 7.24–7.15 (m, 6H), 7.08 (dd, 1H,
b ¼ 73:03 (2), c ¼ 79:57 (2)°, U ¼ 3037 (1) A , Dc
ðZ ¼ 4; two independent moleculesÞ ¼ 1:224 g cmꢁ1
,
l ¼
0:76 cmꢁ1, T ¼ 153 K. The final R value is 0.069 for
8195 independent reflections with I > 3rI and 757 para-
meters.
20. Resonances of the methylium carbon in 2c0 and 2d0 (dC 177
and 176 ppm, respectively) are close to that of 8 (175 ppm),
which is also in consonant with this structural assignment.
21. Pauling, L. The Nature of Chemical Bond, 3rd ed.; Cornell
University Press: Ithaca, NY, 1960; p 260.
22. Veldman, N.; Spek, A. L.; Schlotter, J. J. H.; Zwikker,
J. W. Acta Crystallogr. Sect. C 1996, 52, 174.

4558
H. Kawai et al. / Tetrahedron Letters 45 (2004) 4553–4558
23. GAUSSIAN98. Frisch, M. J.; Trucks, G. W.; Schlegel, H.
B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.;
Zakrzewski, V. G.; Montgomery, J. A.; Stratmann, R. E.;
Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels, A. D.;
Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.;
Barone, V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli,
C.; Adamo, C.; Clifford, S.; Ochterski, J.; Petersson, G.
A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.; Malick, D. K.;
Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.;
Cioslowski, J.; Ortiz, J. V.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.;
Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.;
Peng, C. Y.; Nanayakkara, A.; Gonzalez, C.; Challa-
combe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong,
M. W.; Andres, J. L.; Gonzalez, C.; Head-Gordon, M.;
Replogle, E. S.; Pople, J. A. Gaussian, Pittsburg, PA,
1998.
24. Letsinger, R. L.; Gilpin, J. A.; Vullo, W. J. J. Org. Chem.
1962, 27, 672.
25. Muthyala, R.; Lau, X. Chemistry and Applications of
Leuco Dyes; Plenum: New York, 1997; p 125.
26. Stability of cations 2c0–e0 under acidic conditions observed
here also conflicts with their view that 2b/3b might be
unstable against acid with forming dication 5b. We are not
sure that such drastic changes in reactivity come from the
different substituents on the aryl groups.
27. Similar unsymmetric structure was shown by the X-ray
analysis on the hydrogen-bonded complex of a carbene
with a Cꢀ ꢀ ꢀH–Cþ contact, that prefers the C–H local-
ized structure rather than the delocalized one with a three-
centered-four-electron bond Arduengo, A. J., III;
Gamper, S. F.; Tamm, M.; Calabrese, J. C.; Davidson,
F.; Craig, H. A. J. Am. Chem. Soc. 1995, 117,
572.