Naphthyl-substituted carbocations: From peri interaction to cyclization

Article abstract of DOI:10.1002/ejoc.200800124

The peri interaction of 1-functionalized naphthalenes equipped with a triarylmethyl cation at the 8-position has been studied because of the reversibility of the ring-closing reaction, which was monitored closely by NMR spectroscopy in the case of the cyclic ammonium salt 5b. Carbocycle 4a and N-heterocycle 5b did not exhibit any tendency for ring cleavage under various conditions, whereas the naphtho-annulated furan 4c underwent reversible ring cleavage under strongly acidic conditions. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejoc.200800124

FULL PAPER
DOI: 10.1002/ejoc.200800124
Naphthyl-Substituted Carbocations: From peri Interaction to Cyclization
Gerald Dyker,*[a] Marcel Hagel,[a] Gerald Henkel,[b] and Martin Köckerling[c]
Keywords: Carbocations / Cyclization / Triarylmethyl cations / peri interactions / Ring strain / para-Quinonoid compounds
The peri interaction of 1-functionalized naphthalenes
equipped with a triarylmethyl cation at the 8-position has
been studied because of the reversibility of the ring-closing
reaction, which was monitored closely by NMR spectroscopy
in the case of the cyclic ammonium salt 5b. Carbocycle 4a
and N-heterocycle 5b did not exhibit any tendency for ring
cleavage under various conditions, whereas the naphtho-an-
nulated furan 4c underwent reversible ring cleavage under
strongly acidic conditions.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
In order to evaluate the equilibria of Scheme 2, we syn-
thesized some naphtho-annulated compounds of the type 4
as well as triarylmethyl salts of type 6 with carbon-, nitro-
gen- and also oxygen-centred functional units G.
Introduction
Triarylmethyl compounds have found widespread appli-
cation as functional dyes, as exemplified by the prominent
indicators phenolphthalein (1) and thymol blue (2). In
structurally related naphthalene derivatives, such as the
moderately thermochromic naphthofurans 3,[1] the ring
strain elongates the peri bond, classified by Schiemenz and
co-workers as the peri stress (Scheme 1).[2]
Scheme 2. General concept of a peri sensor; Ar = aryl group, A+
= cationic agent, X– = corresponding anion, G = functional unit
able to coordinate a cationic agent.
Results and Discussion
For the synthesis of the donor–acceptor-substituted
acenaphthene 4a, we chose a one-step transformation of the
stabilized triarylmethyl salt 7 that involved a nucleophilic
attack of malononitrile followed by an Ullmann-type cop-
per-induced cyclization.[4] Indeed, we obtained a reasonable
yield of the target compound 4a; however, the formation
of the para-quinoid compound 8 by nucleophilic aromatic
substitution was the main reaction pathway, as observed
previously with sterically hindered triarylmethyl salts
(Scheme 3).[5]
Scheme 1. Examples of classical indicator molecules and thermo-
chromic compounds with a triarylmethyl moiety.
We became interested in naphthyl-substituted triarylme-
thyl compounds because of their potential as indicators.
Compounds with the general structure 4, equipped with a
functional group G with free electron pairs, should be able
to coordinate a cationic agent, whereupon the resulting
structure 5 could enter an equilibrium with the deeply col-
oured triarylmethyl salt 6, depending of course on the
strength of the peri interaction.[3]
The X-ray crystal analysis[6] of 4a (Figure 1) clearly re-
veals a 6% elongation of the central strained C–C bond
(164.0 pm compared with the standard bond length of
154 pm of an unstrained C–C bond between sp3-hybridized
centres and even surpasses the elongation of related pro-
pellanes).[7] However, despite the impressive bond elong-
ation, 4a withstands heterolytic bond cleavage under vari-
ous conditions, as proved by the absence of any change in
colour, for instance, when heating the melt to 300 °C in the
presence of silver tetrafluoroborate in DMF at reflux tem-
[a] Fakultät für Chemie, Ruhr-Universität Bochum,
Universitätsstrasse 150, 44780 Bochum, Germany
E-mail: gerald.dyker@ruhr-uni-bochum.de
[b] Fakultät für Chemie, Universität Paderborn,
Warburger Str. 100, 33098 Paderborn, Germany
[c] Institut für Chemie, Universität Rostock, Abteilung Anorgani-
sche Chemie-Festkörperchemie,
Albert-Einstein-Str. 3a, 18059 Rostock, Germany
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G. Dyker, M. Hagel, G. Henkel, M. Köckerling
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Scheme 3. Synthesis of model compound 4a. Reagents: (a) ma-
lononitrile, NaH, CuBr.
perature or with trifluoroacetic acid in DMSO at reflux
temperature, whereas the addition of trifluoromethanesul-
fonic acid leads to polymeric material. The unreactivity of
compound 4a resembles that of the related push–pull-sub-
stituted dihydrophenanthrenes and indanes reported pre-
viously by Suzuki and co-workers.[8]
Scheme 4. Intramolecular C–N bond formation at a suberenyl cat-
ion, as monitored by 1H NMR spectroscopy (CDCl3); the chemical
shifts (δ [ppm]) of the diagnostic signals are given.
Figure 1. Structure of the strained acenaphthene 4a in the crystal.[6]
pernatant, the NMR signals progressively losing intensity.
Within another 21 h, the precipitate dissolved again: the
slow deprotonation of 12 presumably leads to the short-
lived intermediate 6b. As CIDNP effects are missing from
the NMR spectra, we assume that the ring closure to the
colourless product 5b (Figure 2) does not involve radical
intermediates. The naphthopyrrolium salt 5b has been fully
We described the preparation and X-ray crystal analysis
of the nitrogen-centred model cationic compound 5b in an
earlier publication.[2] In this work we monitored closely the
formation of 5b by NMR spectroscopy starting from the
triarylmethyl alcohol 9 (Scheme 4). The N-methyl groups[9]
and the olefinic hydrogen atoms of the suberenyl moiety
exhibit diagnostic signals throughout the transformation,
allowing identification of the reactive intermediates. A sam-
ple of 9 in deuteriochloroform at –45 °C was successively
treated with 6 equiv. of HBF4–diethyl ether, whereupon a
downfield-shift of 0.4 ppm for the methyl signal was ob-
served, diagnostic of the protonation of the amino group
and best described by structure 10 with an intramolecular
hydrogen bond and as having a proton-sponge character.[10]
Because of the excess acid, we assumed a dynamic equi-
librium with the double salt 11. The solution was stable in
the cold and had a pale-red colour. Above 0 °C, the colour
changed to deep-violet, and a second set of signals evolved
in the 1H NMR spectrum: a singlet at δ = 9.46 ppm charac-
teristic of the aromatic dibenzosuberenyl cation and a new
N-methyl signal at δ = 2.71 ppm confirming the cationic
character of the amino function, sufficiently explained by
structure 12. Within 4 h at room temperature, this double
Figure 2. Structure of 5b in the crystal. Left: Molecular structure
of the cation with atom numbering scheme; right: view along the
salt formed a dark precipitate with an almost colourless su- naphthyl moiety.[2]
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Naphthyl-Substituted Carbocations
characterized by spectroscopic means and by X-ray crystal the naphthofuran 4c by an unusual intramolecular nucleo-
analysis.[2] In acetone and in DMSO, the same acid-driven philic aromatic substitution, profiting from the release of
transformation to 5b takes place, but without detection of steric strain. Attempts to alkylate 4c to 5c with trimethylox-
12 as an intermediate, simply because these solvents are onium tetrafluoroborate or with methyl trifluoromethane-
more basic than the dimethylamino group in close proxim- sulfonate as an alternative route failed. An equimolar
ity to the carbocation. Thus, 12 is immediately deproton- amount of trifluoromethanesulfonic acid (in CDCl3) trans-
ated in acetone and DMSO, if formed at all.
formed 4c quantitatively by ring cleavage to the suberenyl
1
The nucleophilicity of an anionic malononitrile group or salt 6c, as revealed by the diagnostic 2-H singlet in the H
a dimethylamino group is clearly too high to detect an equi- NMR spectrum at δ = 9.10 ppm. In contrast, trifluoroacetic
librium between structures of type 5 and 6, thus preventing acid is not acidic enough for this transformation. This suc-
ring cleavage, as proven by our tests with compounds 4a cessful C–O bond cleavage under strongly acidic conditions
and 5b. Therefore, we decided to target the corresponding is of some interest with respect to the recent discussion
O-heterocycles, as ether and alcohol moieties are far less about the formation of intramolecular triarylmethane/triar-
nucleophilic.[11] The synthesis of model compound 14 by
deprotonation of 1-methoxynaphthalene in the peri posi-
tion failed with nBuLi/TMEDA (Scheme 5).[12] Compound
16, derived from ortho-metallation, was exclusively isolated
instead, in accordance with recent publications.[13] There-
fore, we chose an alternative route to 14:[14] lithiation of the
peri-substituted iodonaphthalene 15 and subsequent ad-
dition to suberenone was successful and gave a moderate
yield of 14. Transformation to the suberenyl salt 6c pro-
ceeded cleanly. No equilibrium with 5c was detectable in
1
the H NMR spectrum: just one singlet of the olefinic pro-
tons at δ = 9.38 ppm, typical of the suberenyl cation. Con-
sequently, we decided to try the reverse transformation: syn-
thesis of the naphthofuran 4c and subsequent ring cleavage
to a structure of type 6 (see Scheme 6).
The sterically crowded suberenol 18 was easily synthe-
sized from 1,8-diiodonaphthalene by initial monolithiation.
The corresponding suberenyl tetrafluoroborate 19 was
quantitatively obtained by the standard procedure
(Scheme 6). Its X-ray crystal analysis revealed that there is
no bonding interaction between the suberenyl cation and
Scheme 6. Reagents: (a) HBF4–diethyl ether, dichloromethane,
the iodide in the peri position (Figure 3). We synthesized 99%, (b) NaH, THF, reflux, 32%.
Scheme 5. Reagnets: (a) 1. nBuLi, TMEDA; 2. suberenone, 82% of 16; (b) 1. nBuLi, 2. suberenone, 43% of 14; (c) HBF4–diethyl ether,
97% of 6c.
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G. Dyker, M. Hagel, G. Henkel, M. Köckerling
FULL PAPER
by flash chromatography on Kieselgel 60 (Merck, 0.030–0.60 mm).
All commercially available products were used without further pu-
rification. Compound 7 was synthesized in two steps starting from
1,8-dichloronaphthalene by initial monolithiation with tert-butyl-
lithium in THF at –70 °C and subsequent reaction with 4,4Ј-di-
methoxybenzophenone at room temperature (66% yield), followed
by treatment with HBF4–diethyl ether and crystallization from
dichloromethane/diethyl ether (97% yield). Preparative procedures
for compounds 9 and 5b have been described earlier.[2]
ylmethylium complexes with the naphthalene-1,8-diyl skel-
eton,[15] although the presence of the basic heteroatom in
4c should make a fundamental difference.
1,1-Dicyano-2,2-bis(4-methoxyphenyl)acenaphthene (4a) and 2-{4-
[(8-Chloro-1-naphthyl)(4-methoxyphenyl)methylene]cyclohexa-2,5-
dienylidene}malononitrile (8): A 60% sodium hydride/mineral oil
mixture (32 mg, 0.8 mmol) was added to a deep-red solution of
tetrafluoroborate 7 (200 mg, 0.421 mmol; see comment above), ma-
lononitrile (55 mg, 1.0 mmol) and CuBr (6 mg, 10 mol-%) in dry
THF (12 mL), and the mixture was stirred at room temperature
for 2 d. A deep-red suspension of tetrafluoroborate 8a (300 mg,
0.742 mmol) in dry THF (9 mL) was added, and the reaction mix-
ture was stirred at room temperature for 21 h. After hydrolysis with
a saturated aqueous (NH4)2HPO4 solution (20 mL), the water layer
was extracted with diethyl ether (3ϫ 20 mL), and the combined
organic layers were dried with sodium sulfate and the solvents
evaporated to dryness with a rotary evaporator. The residue was
fractionated by flash chromatography (TLC: silica; diethyl ether/n-
hexane, 2:3; Rf = 0.27, 0.21). First Fraction: 50 mg (29%) of acen-
aphthene derivative 4a as colorless crystals; m.p. 222 °C (from
Figure 3. Structure of the cation 19 in the crystal. Left: with atom
numbering scheme; right: view along the almost planar 5H-di-
benzo[a,d]cycloheptenylium unit.[6]
CH Cl /n-pentane, 1:3). IR (KBr): ν = 3037 (w), 2934 (w), 2839
˜
2
2
Conclusions
(w), 1608 (m), 1581 (w), 1510 (s), 1461 (w), 1442 (w), 1298 (m),
1257 (s), 1183 (s), 1124 (w), 1031 (m), 820 (m), 811 (m), 801 (w),
790 (w), 776 (m) cm–1. UV (acetonitrile): λmax (logε) = 203 (4.80),
219 (4.69, sh), 254 (3.88, sh), 284 (3.85), 308 (3.55, sh) nm. 1H
NMR (500 MHz, CDCl3): δ = 3.78 (s, 6 H, OCH3), 6.84 (d, J =
9.0 Hz, 4 H, 3Ј-H, 5Ј-H, 3ЈЈ-H, 5ЈЈ-H), 7.30–7.32 (m, 5 H), 7.59
(“dd”, “J” = 8.2, 7.1 Hz, 1 H), 7.74 (“dd”, “J” = 8.3, 7.1 Hz, 1 H),
Among the naphtho-annulated structures 4 and 5
studied, we found acidic reaction conditions for reversible
ring cleavage exclusively for the O-heterocycle 4c, which was
monitored by NMR spectroscopy and also noticed directly
by the intense colour of the corresponding suberenyl cation
of 6c. Unfortunately, carbocycle 4a and N-heterocycle 5b 7.79 (d, J = 8.0 Hz, 1 H), 7.85 (d, J = 7.0 Hz, 1 H), 7.95 (d, J =
7.9 Hz, 1 H) ppm. 13C NMR (125.8 MHz, CDCl3): δ = 54.81 (s),
did not exhibit any clear tendency for ring cleavage under
55.26 (q, OCH3), 72.59 (s), 113.97 (d), 114.30 (s), 120.91 (d), 123.99
a variety of conditions. Future preparative work for the
(d), 124.72 (d), 127.59 (d), 128.85 (d), 129.44 (d), 132.42 (s), 133.13
construction of indicators or sensors based on the struc-
(s), 134.67 (s), 134.84 (s), 144.47 (s), 159.52 (s) ppm; one missing d
tural motifs shown in Scheme 2 should focus either on func-
is superimposed. MS (EI, 70 eV): m/z (%) = 417 (31) [M + 1]+, 416
tionalizing the hydroxy group of 6c or on replacing the
methyl groups of 5b by electron-withdrawing groups such
as 2-pyridyl or isoxazolyl groups, thus diminishing the nu-
(100) [M]+, 385 (13), 309 (16), 284 (19). C28H20N2O2 (416.48):
calcd. C 80.75, H 4.84, N 6.73; found C 80.97, H 4.77, N 6.82.
Second Fraction: 66 mg (40%) of p-quinodimethane 8 as a green-
cleophilicity of the amino group and simultaneously offer-
ing coordination sites for transition-metal salts as objects
to be sensorily detected.
gold shining solid with m.p. 106 °C. IR (KBr): ν = 3061 (w), 2932
˜
(w), 2841 (w), 2207 (s), 1607 (m), 1589 (s), 1503 (w), 1452 (m), 1432
(s), 1412 (s), 1260 (s), 1194 (m), 1174 (s), 1025 (w), 840 (m), 821
(m), 765 (m) cm–1. UV (acetonitrile): λmax (logε) = 195 (4.63), 213
(4.60, sh), 226 (4.66), 278 (3.85, sh), 308 (4.19), 372 (3.69, sh), 390
1
(3.84), 522 (4.55) nm. H NMR (300 MHz, CDCl3): δ = 3.85 (s, 3
Experimental Section
H, OCH3), 6.79 (dd, J = 9.6, 2.0 Hz, 1 H, 6-H), 6.90 (d, J = 9.0 Hz,
2 H, 3ЈЈ-H, 5ЈЈ-H), 6.99 (dd, J = 9.6, 2.0 Hz, 1 H, 5-H), 7.19–7.30
(m, 4 H), 7.42–7.55 (m, 2 H), 7.57–7.62 (m, 2 H), 7.90 (dd, J =
8.0, 1.4 Hz, 1 H), 8.03 (dd, J = 8.3, 1.1 Hz, 1 H) ppm. 13C NMR
(125.8 MHz, CDCl3): δ = 55.58 (q, OCH3), 69.29 (s), 114.10 (d),
115.12 (s), 115.22 (s), 123.47 (d), 123.98 (d), 125.37 (d), 126.86 (d),
128.40 (d), 129.87 (d), 130.64 (s), 131.41 (d), 132.13 (s), 132.14 (s),
132.86 (d), 134.92 (d), 135.98 (s), 136.44 (s), 137.21 (d), 137.64 (d),
155.77 (s), 162.32 (s), 164.09 (s) ppm; one missing s is superim-
posed, presumably at δ = 129.87 ppm. MS (EI, 70 eV): m/z (%) =
422 (36) [M + 1]+, 421 (30) [M]+, 420 (100), 386 (8), 385 (26), 384
(9), 341 (10), 314 (11), 312 (13), 279 (11), 276 (12), 143 (13), 138
(11). C27H17ClN2O (420.90): calcd. C 77.05, H 4.07, N 6.66; found
C 76.93, H 4.30, N 6.54.
General: Melting points (uncorrected) were determined with a
Kofler-Heizmikroskop, Modell Reichert Thermovar. Elemental
analyses were carried out with a Carlo Erba Elemental Analyser
1106 or a Vario EL instrument. IR spectra (KBr) were recorded
with a Bruker Vector 22, a Bruker Equinox 55, a Perkin-Elmer
983G or a Perkin-Elmer 841 spectrometer. UV/Vis spectra were
recorded with a Perkin-Elmer Lambda 40 or a Varian Carey 1 spec-
trophotometer (ε measured in cm2 mmol–1). 1H and 13C NMR spec-
tra were recorded with a Bruker DPX 200, WM 300, DRX 400 or
DRX 500 spectrometer. Mass spectrometry was performed with a
Varian MAT 311 A, AMD 604, MAT CH5 or a VG Autospec
spectrometer. For TLC, SiO2 plates (Polygram SIL G/UV 254)
from Macherey & Nagel were used. All compounds were purified
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Naphthyl-Substituted Carbocations
1-Iodo-8-methoxynaphthalene (15):[14] 1,8-Diiodonaphthalene 1384 (m), 1337 (w), 1256 (w, sh), 1124 (s), 1084 (s, br), 819 (w), 770
(500 mg, 1.32 mmol)[16] and CuBr (38 mg, 20 mol-%) were added to
a methanolic solution of sodium methoxide, prepared from sodium
(50 mg, 2.18 mmol) and dry methanol (13 mL), and the mixture
(w), 733 (w) cm–1. UV (acetonitrile): λmax (logε) = 211 (4.64), 237
(4.66), 307 (5.08), 376 (3.80), 406 (3.79), 512 (3.62), 542 (3.67) nm.
1H NMR (300 MHz, CDCl3): δ = 2.81 (s, 3 H, OCH3), 6.73 (d, J
was stirred at reflux temperature for 4 h. After hydrolysis with = 7.7 Hz, 1 H, 7-H), 7.26 (d, J = 6.8 Hz, 1 H, 2-H), 7.59 (“t”, “J”
water (20 mL) and extraction with diethyl ether (3ϫ 20 mL), the
combined organic layers were filtered through a pad of silica and
concentrated to dryness; TLC (silica; n-pentane): Rf = 0.30, 0.12.
The crude product was fractionated by flash chromatography. First
Fraction: 60 mg (12%) of recovered 1,8-diiodonaphthalene. Second
Fraction: 216 mg (58%) of 15 as a pale-yellow solid with m.p. 61–
= 8.0 Hz, 1 H, 6-H), 7.75 (“t”, “J” = 7.9, 7.2 Hz, 1 H, 3-H), 7.76
(d, J = 8.2 Hz, 1 H, 5-H), 7.91–7.97 (m, 2 H, 3Ј-H, 7Ј-H), 8.14 (d,
J = 8.8 Hz, 2 H, 4Ј-H, 6Ј-H), 8.22 (d, J = 8.1 Hz, 1 H, 4-H), 8.50
(“t”, “J” = 7.1 Hz, 2 H, 2Ј-H, 8Ј-H), 8.87 (d, J = 7.7 Hz, 2 H, 1Ј-
H, 9Ј-H), 9.38 (s, 2 H, 10Ј-H, 11Ј-H) ppm. 13C NMR (75.5 MHz,
CDCl3): δ = 55.68 (q), 107.70 (d, C-7), 121.80 (d, C-3), 124.09 (s),
125.37 (d, C-5), 128.08 (d, C-2), 128.47 (d, C-6), 130.32 (d, C-4),
132.48 (d, C-3Ј, C-7Ј), 134.75 (s), 135.82 (s), 136.56 (d, C-1Ј, C-9Ј),
138.34 (s), 138.41 (d, C-4Ј, C-6Ј), 140.31 (d, C-2Ј, C-8Ј), 144.86 (d,
C-10Ј, C-11Ј), 145.94 (s), 153.94 (s), 187.35 (s, C-5Ј) ppm. MS (EI,
70 eV): m/z (%) = 348 (40) [M + 1 – BF4]+, 347 (13) [M – BF4]+,
334 (18), 331 (10), 318 (10), 207 (16), 205 (10), 196 (9), 194 (15),
193 (17), 191 (21), 179 (11), 178 (12), 131 (11), 129 (14), 117 (40),
115 (18), 105 (23), 104 (28), 103 (16), 92 (18), 91 (93), 78 (18), 77
(16), 44 (100). C26H19BF4O (434.24): calcd. C 71.92, H 4.41; found
C 71.73, H 4.46.
1
62 °C. H NMR (300 MHz, CDCl3): δ = 3.93 (s, 3 H, OCH3), 6.89
(“dd”, “J” = 8.9, 6.1 Hz, 1 H), 7.01 (“dd”, “J” = 8.1, 7.4 Hz, 1 H),
7.34–7.41 (m, 2 H), 7.73 (dd, J = 8.2, 1.2 Hz, 1 H), 8.17 (dd, J =
7.4, 1.2 Hz, 1 H) ppm. 13C NMR (125.8 MHz, CDCl3): δ = 54.85
(q, OCH3), 85.42 (s), 106.54 (d), 121.53 (d), 125.23 (s), 126.26 (d),
127.00 (d), 128.76 (d), 136.13 (s), 140.96 (d), 154.30 (s) ppm.
5-Hydroxy-5-(8-methoxy-1-naphthyl)-5H-dibenzo[a,d]cycloheptene
(14): A 15 % solution of n-butyllithium in n-hexane (0.5 mL,
0.8 mmol) was added to a solution of 1-iodo-8-methoxynaphtha-
lene (15) (200 mg, 0.704 mmol) in dry diethyl ether (10 mL) at
–70 °C within 10 min. After 30 min of stirring, 5H-dibenzo[a,d]cy-
clohepten-5-one (150 mg, 0.704 mmol) in dry diethyl ether (8 mL)
was added at –50 °C. The yellow solution was stirred at room tem-
perature for 1 d. After hydrolysis with a saturated aqueous (NH4)2-
HPO4 solution (20 mL), the water layer was extracted with diethyl
ether (3ϫ 20 mL), and the combined organic layers were dried with
sodium sulfate and the solvents evaporated to dryness with a rotary
evaporator. The crude product (242 mg) was fractionated by flash
chromatography (TLC: silica; toluene; Rf = 0.82, 0.49, 0.35). First
Fraction: 34 mg (28%) of 1-methoxynaphthalene (13). Second Frac-
tion: 110 mg (43%) of the tertiary alcohol 14 as colourless crystals
5-Hydroxy-5-(1-methoxy-2-naphthyl)-5H-dibenzo[a,d]cycloheptene
(16): 1-Methoxynaphthalene (13) (3.49 mL, 23.6 mmol) was added
dropwise to a mixture of a 15% solution of n-butyllithium in n-
hexane (16.2 mL, 25.9 mmol), additional n-hexane (30 mL) and
TMEDA (3.88 mL, 25.9 mmol) at 0 °C. After 30 min of stirring at
40 °C, the deep-red suspension was cooled to –20 °C, and a solu-
tion of 5H-dibenzo[a,d]cyclohepten-5-one (5.33 g, 25 mmol) in dry
diethyl ether (40 mL) was added dropwise. After stirring at room
temperature for 1 d, the reaction mixture was hydrolyzed with a
saturated aqueous (NH4)2HPO4 solution (20 mL), the water layer
was extracted with diethyl ether (3ϫ 20 mL), and the combined
organic layers were dried with sodium sulfate and the solvents
with m.p. 232 °C (crystallized from toluene). IR (KBr): ν = 3505
˜
(s), 3053 (w), 3019 (w), 2935 (w), 1616 (w), 1571 (m), 1481 (m), evaporated to dryness with a rotary evaporator. The brown crude
1459 (s), 1435 (m), 1375 (m), 1331 (m), 1259 (s), 1222 (m), 1174 product was purified by flash chromatography (TLC: silica; diethyl
(m), 1157 (m), 1127 (s), 1070 (s), 1036 (w), 1011 (s), 817 (s), 778
(m), 764 (s), 748 (s), 635 (w), 628 (m), 614 (m) cm–1. UV (acetoni-
trile): λmax (logε) = 194 (4.56), 222 (4.76), 243 (4.47, sh), 287 (4.07),
331 (3.50, sh) nm. 1H NMR (300 MHz, CDCl3): broad signals were
observed due to dynamic effects; δ = 3.45 (s, 3 H), 5.20 (s, 1 H,
OH), 6.15 (br. s, 1 H), 6.42 (br. s, 1 H), 6.43 (d, J = 7.7 Hz, 1 H),
6.82–7.57 (br. m, 11 H), 8.23 (m, 2 H) ppm. 13C NMR (125.8 MHz,
CDCl3): only sharp signals are listed; δ = 54.44 (q, OCH3), 79.24
(s), 104.22 (d), 121.55 (d), 123.85 (s), 124.36 (d), 125.04 (d), 127.85
ether/n-hexane, 1:3; Rf = 0.38) to give 7.0 g (82%) of the tertiary
alcohol 16 as colourless crystals with m.p. 187 °C (crystallized from
diethyl ether/n-hexane, 1:2). IR (KBr): ν = 3061 (m), 3020 (m),
˜
2941 (w), 2844 (w), 1931 (w, br), 1624 (w), 1594 (w), 1565 (w), 1501
(w), 1482 (m), 1434 (m), 1369 (s), 1332 (s), 1260 (m), 1226 (m),
1172 (m), 1158 (m), 1115 (m), 1086 (s), 1022 (s), 984 (m, sh), 815
(s), 796 (s), 771 (m), 752 (s), 708 (w), 665 (w) cm–1. UV (acetoni-
trile): λmax (logε) = 204 (5.23), 230 (4.93), 283 (4.27) nm. 1H NMR
(300 MHz, CDCl3): δ = 3.01 (s, 3 H), 3.77 (s, 1 H, OH), 6.67 (d, J
(d), 128.32 (d), 135.78 (s), 139.21 (s), 153.87 (s) ppm. MS (EI, = 8.8 Hz, 1 H), 6.79 (s, 2 H), 7.25 (d, J = 8.7 Hz, 1 H), 7.29–7.32
70 eV): m/z (%) = 364 (28) [M]+, 348 (12), 347 (23), 335 (9), 333 (m, 4 H), 7.38 (“dd”, “J” = 6.4, 3.3 Hz, 2 H), 7.49–7.55 (m, 2 H),
(10), 332 (15), 331 (30), 207 (17), 186 (49), 185 (100), 179 (22), 178
(72), 171 (22), 170 (14), 155 (20), 151 (11), 150 (11), 127 (14), 115
(19). C26H20O2 (364.44): calcd. C 85.69, H 5.53; found C 85.72, H
5.48. Third Fraction: 52 mg (35%) of 5H-dibenzo[a,d]cyclohepten-
5-one as recovered starting material.
7.71 (“dd”, “J” = 6.1, 3.4 Hz, 1 H), 7.86 (“dd”, “J” = 6.3, 3.4 Hz,
1 H), 8.22 (d, J = 8.0 Hz, 2 H) ppm. 13C NMR (75.5 MHz, CDCl3):
δ = 61.68 (q), 77.99 (s, C-OH), 122.28 (d), 122.47 (d), 123.99 (d),
125.61 (d), 126.05 (d), 126.33 (d), 126.61 (d), 128.02 (d), 128.26 (d),
128.53 (d), 128.78 (s), 131.50 (d), 133.01 (s), 133.07 (s), 134.86 (s),
142.92 (s), 154.44 (s) ppm. MS (EI, 70 eV): m/z (%) = 365 (28) [M
+ 1]+, 364 (100) [M]+, 349 (10), 333 (10), 332 (10), 331 (22), 315
(12), 207 (16), 194 (14), 185 (21), 179 (14), 178 (30), 171 (10), 158
(8), 151 (9), 143 (9). C26H20O2 (364.44): calcd. C 85.69, H 5.53;
found C 85.64, H 5.59.
5-(8-Methoxy-1-naphthyl)-5H-dibenzo[a,d]cyclohepten-5-ylium Tet-
rafluoroborate (6c): HBF4–diethyl ether (0.09 mL, 0.66 mmol) was
added to the tertiary alcohol 15 (60 mg, 0.17 mmol) in dry CH2Cl2
(2 mL) at room temperature. After 5 min, stirring was stopped, and
a layer of diethyl ether (13 mL) was carefully placed on top of the
reaction mixture. After 1 d at room temperature, the precipitate was
isolated by filtration, washed with diethyl ether (2ϫ 2 mL) and
dried at 50 °C/0.04 mbar. Tetrafluoroborate 6c (69 mg, 97%) was
obtained as violet needles with m.p. 204–206 °C. The deep-violet
solution in CDCl3 did not show any change in colour intensity
5-Hydroxy-5-(8-iodo-1-naphthyl)-5H-dibenzo[a,d]cycloheptene (18):
A 15% solution of n-butyllithium in n-hexane (0.81 mL, 1.3 mmol)
was added to a solution of diiodonaphthalene (500 mg, 1.32 mmol)
in dry diethyl ether (20 mL) at –70 °C within 20 min. After 30 min
of stirring, 5H-dibenzo[a,d]cyclohepten-5-one (280 mg, 1.32 mmol)
in dry diethyl ether (10 mL) was added at –50 °C. The yellow solu-
tion was stirred at room temperature for 2 d. After hydrolysis with
when cooled to –170 °C. IR (KBr): ν = 3053 (w), 3020 (w), 2938
˜
(w), 1603 (w), 1571 (w, sh), 1517 (w, sh), 1463 (w, sh), 1428 (m),
Eur. J. Org. Chem. 2008, 3095–3101
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3099

G. Dyker, M. Hagel, G. Henkel, M. Köckerling
FULL PAPER
a saturated aqueous (NH4)2HPO4 solution (20 mL), the water layer
was extracted with diethyl ether (3ϫ 20 mL), and the combined
organic layers were dried with sodium sulfate and the solvents
evaporated to dryness with a rotary evaporator. The crude product
(645 mg) was fractionated by flash chromatography (TLC: silica;
toluene; Rf = 0.74, 0.35). First Fraction: 368 mg (66%) of the terti-
ary alcohol 18 as reddish crystals with m.p. 179 °C (crystallized
thofuran 4c as colourless needles with m.p. 171 °C (from dichloro-
methane/n-hexane, 1:3). IR (KBr): ν = 3063 (w), 3024 (w), 1633
˜
(m), 1615 (m), 1587 (s), 1491 (s), 1463 (m), 1434 (w), 1370 (s), 1252
(s), 1224 (m), 1174 (w), 1117 (m), 946 (s), 885 (w), 809 (s), 798 (s),
767 (s), 730 (m) cm–1. UV (acetonitrile): λmax (logε) = 217 (4.65),
243 (4.49), 304 (4.20), 328 (3.95, sh) nm. 1H NMR (500 MHz,
CDCl3): δ = 6.94 (d, J = 7.3 Hz, 1 H, 7-H), 7.20 (s, 2 H, 10Ј-H,
11Ј-H), 7.24 (d, J = 8.1 Hz, 1 H, 5-H), 7.25–7.32 (m, 4 H, 2Ј-H,
from toluene). IR (KBr): ν = 3449 (s), 3055 (w), 3019 (w), 1626
˜
(m, br), 1481 (w), 1434 (w), 1319 (w), 1187 (w), 1167 (w), 1156 (w), 3Ј-H, 7Ј-H, 8Ј-H), 7.36 (“dd”, “J” = 8.1, 7.2 Hz, 1 H, 3-H), 7.42
1116 (w), 1067 (w), 1034 (m), 995 (w), 914 (w), 812 (s), 793 (m),
760 (s), 629 (m) cm–1. UV (acetonitrile): λmax (logε) = 232 (4.69),
272 (4.11, sh), 296 (4.02, sh), 320 (3.84, sh) nm. 1H NMR
(500 MHz, CDCl3): δ = 4.73 (s, 1 H, OH), 5.81 (br. s, 1 H), 5.98
(1 H, 6-H), 7.43 (dd, J = 7.2, 1.3 Hz, 2 H, 4Ј-H, 6Ј-H), 7.60 (d, J
= 8.0 Hz, 1 H, 4-H), 8.00 (d, J = 7.1 Hz, 1 H, 2-H), 8.01 (dd, J =
7.8, 1.5 Hz, 2 H, 1Ј-H, 9Ј-H) ppm. 13C NMR (75.5 MHz, CDCl3):
δ = 96.25 (s, C-5Ј), 100.94 (d, C-7), 116.07 (d, C-5), 119.45 (d, C-
(br. s, 1 H), 6.89 (“d”, “J” = 7.5 Hz, 2 H), 6.93–7.06 (br. m, 3 H), 2), 124.35 (d, C-4), 125.05 (d, C-1Ј, C-9Ј), 126.19 (s), 127.58 (d),
7.17 (dt, J = 7.5, 1.3 Hz, 2 H), 7.39 (br. s, 1 H), 7.45 (“dd”, “J” = 128.42 (d, C-3), 128.87 (d), 129.34 (d, C-6), 130.40 (d, C-4Ј, C-6Ј),
6.4, 2.9 Hz, 2 H), 7.65 (m, 2 H), 8.34 (br. m, 2 H) ppm. 13C NMR
132.07 (s), 132.73 (d, C-10Ј, C-11Ј), 132.93 (s), 139.53 (s), 144.17
(125.8 MHz, CDCl3): δ = 79.42 (s), 90.04 (s), 124.43 (d), 125.28 (s), 158.34 (s, C-8) ppm. MS (EI, 70 eV): m/z (%) = 333 (30) [M +
(d), 125.85 (d), 127.48 (br. d), 128.66 (d), 128.91 (d), 132.91 (br. d),
135.34 (s), 136.77 (s), 139.27 (d), 142.88 (s) ppm. MS (EI, 70 eV):
1]+, 332 (100) [M]+, 331 (99), 330 (5), 329 (10), 313 (7), 303 (8),
302 (16), 301 (7), 300 (13), 252 (7), 178 (6), 166 (10), 155 (6), 152
m/z (%) = 460 (5) [M]+, 333 (18), 332 (30), 331 (11), 316 (12), 315 (8), 151 (10), 144 (7), 126 (14). C25H16O (332.40): calcd. C 90.34,
(27), 313 (16), 304 (15), 303 (40), 302 (35), 300 (18), 282 (29), 281
(100), 254 (15), 216 (14), 215 (73), 207 (13), 179 (23), 178 (63), 155
(21), 151 (12), 127 (11), 126 (16). C25H17IO (460.31): calcd. C 65.23,
H 3.27; found C 65.27, H 3.75. Second Fraction: 35 mg (13%) of
5H-dibenzo[a,d]cyclohepten-5-one as recovered starting material.
H 4.85; found C 90.33, H 4.86.
NMR Experiment. 5-(8-Hydroxy-1-naphthyl)-5H-dibenzo[a,d]cy-
clohepten-5-ylium Trifluoromethanesulfonate (6c): Trifluorometh-
anesulfonic acid (6.7 µL, 11.5 mg, 0.075 mmol) was added to naph-
thofuran 4c (22 mg, 0.068 mmol) in CDCl3 (0.7 mL) in an NMR
tube at room temperature. The deep-violet solution was homoge-
nized in a sonicator. The 1H NMR spectrum showed exclusively
one data set that was in accord with the cycloheptenylium salt 6c.
1H NMR (CDCl3, 500 MHz): δ = 6.75 (br. s, 1 H), 7.25 (br. “d”,
“J” = 5.0 Hz, 1 H), 7.57 (br. s, 1 H), 7.77 (br. s, 2 H), 8.01 (“t”,
“J” = 7.7 Hz, 2 H, 3Ј-H, 7Ј-H), 8.26 (d, J = 8.1 Hz, 1 H), 8.31 (d,
J = 8.7 Hz, 2 H, 4Ј-H, 6Ј-H), 8.51 (“t”, “J” = 7.7 Hz, 2 H, 2Ј-H,
8Ј-H), 8.71 (d, J = 8.1 Hz, 2 H, 1Ј-H, 9Ј-H), 9.10 (s, 2 H, 10Ј-H,
11Ј-H) ppm.
5-(8-Iodo-1-naphthyl)-5H-dibenzo[a,d]cyclohepten-5-ylium Tetra-
fluoroborate (19): HBF4–diethyl ether (0.06 mL, 0.44 mmol) was
added to the tertiary alcohol 18 (100 mg, 0.22 mmol) in dry CH2Cl2
(3 mL) at room temperature. After 2 min, stirring was stopped, and
a layer of diethyl ether (18 mL) was carefully placed on top of the
reaction mixture. After 1 d at –10 °C, the precipitate was isolated
by filtration, washed with diethyl ether (2ϫ 2 mL) and dried at
room temperature/0.04 mbar to give 114 mg (99%) of the tetrafluo-
roborate 19 as deep-red needles with m.p. 208–212 °C. IR (KBr):
ν = 3042 (w), 3011 (w), 1602 (w), 1516 (w), 1432 (m), 1388 (s),
˜
1337 (w), 1194 (w), 1124 (m), 1084 (s, br), 814 (w), 765 (w), 733
(w) cm–1. UV (acetonitrile): λmax (logε) = 233 (4.65), 310 (4.75),
383 (3.72), 421 (3.61), 566 (3.55, sh) nm. 1H NMR (500 MHz,
CDCl3): δ = 7.36 (“dd”, “J” = 8.1, 7.5 Hz, 1 H, 6-H), 7.49 (dd, J
= 7.2, 1.2 Hz, 1 H, 2-H), 7.78 (“dd”, “J” = 8.1, 7.3 Hz, 1 H, 3-H),
7.99 (“ddd”, “J” = 8.6, 5.5, 1.4 Hz, 2 H, 3Ј-H, 7Ј-H), 8.08 (1 H, 7-
H), 8.09 (2 H, 4Ј-H, 6Ј-H), 8.26 (dd, J = 8.3, 1.0 Hz, 1 H, 5-H),
8.34 (dd, J = 8.2, 1.2 Hz, 1 H, 4-H), 8.53 (“ddd”, “J” = 8.1, 5.7,
1.1 Hz, 2 H, 2Ј-H, 8Ј-H), 8.84 (dd, J = 8.3, 1.1 Hz, 2 H, 1Ј-H, 9Ј-
H), 9.47 (s, 2 H, 10Ј-H, 11Ј-H) ppm. 13C NMR (75.5 MHz,
CDCl3): δ = 91.59 (s, C-8), 125.23 (d, C-3), 128.92 (d, C-6), 131.06
(d, C-5), 131.84 (s), 132.54 (d, C-4), 133.01 (d, C-2), 133.12 (d, C-
3Ј, C-7Ј), 135.65 (s), 136.79 (d, C-1Ј, C-9Ј), 138.22 (d, C-4Ј, C-6Ј),
138.37 (s), 140.40 (d, C-2Ј, C-8Ј), 141.42 (s), 143.02 (d, C-7), 145.72
(s), 146.33 (d, C-10Ј, C-11Ј), 182.17 (s, C-5Ј) ppm. MS (EI, 70 eV):
m/z (%) = 443 (31) [M + 1 – BF4]+, 442 (96), 316 (31), 315 (84),
314 (54), 313 (100), 312 (11), 311 (28), 300 (15), 158 (27), 157 (27),
157 (34). C25H16BF4I (530.11): calcd. C 56.64, H 3.04; found C
56.68, H 3.07.
X-ray Structure Determinations: Crystallographic data were col-
lected with a Siemens P4RA diffractometer, equipped with a rotat-
ing anode (4a) and with a conventional Siemens P4 diffractometer
(19). Graphite-monochromated Mo-Kα radiation (λ = 0.71073 Å)
was used in both cases. Data sets were collected at T = 150 (4a)
and 293(2) K (19). Empirical absorption corrections based on ψ
scans were applied to both data sets. The structures were solved by
direct methods and refined with full-matrix least-squares tech-
niques against F2 (SHELXL-97).[17] The positions of the hydrogen
atoms were calculated by assuming idealized geometries and were
refined by using riding models. 4a: C28H20N2O2,
M =
–1
¯
416.46 gmol , triclinic, space group P1 (No. 2), a = 10.091(1), b
= 11.121(1), c = 19.396(2) Å, α = 88.49(1), β = 85.21(1), γ = 80.54°,
V = 2139 Å3, Z = 4, Dx = 1.293 gcm–3, µ(Mo-Kα) = 0.080 mm–1,
transmission range 0.953–0.821, 2θmax = 54°, ω scans, crystal di-
mensions approx. 0.26ϫ0.19ϫ0.17 mm, 9224 unique reflections,
R1 (wR2) = 0.0391 (0.0978), 580 variables. 19: C25H16BF4I, M =
530.09 gmol–1, monoclinic, space group C2/c (No. 15), a =
28.995(5), b = 8.220(1), c = 22.340(4) Å, β = 128.95(1)°, V =
4141 Å3, Z = 8, Dx = 1.701 gcm–3, µ(Mo-Kα) = 1.592 mm–1, trans-
mission range 0.970–0.774, 2θmax = 50°, ω scans, crystal dimen-
sions approx. 0.52ϫ0.33ϫ0.30 mm, 3316 unique reflections, R1
(wR2) = 0.0733 (0.1510), 281 variables.
5H,2ЈH-Spiro[dibenzo[a,d]cycloheptene-5,2Ј-naphtho[1,8-bc]furan]
(4c): A suspension of tertiary alcohol 18 (459 mg, 1.00 mmol) and
NaH (120 mg, 3.00 mmol, 60% in mineral oil) in dry THF (30 mL)
was heated under reflux for 1 d. After hydrolysis with a saturated
aqueous (NH4)2HPO4 solution (20 mL), the water layer was ex-
tracted with diethyl ether (3ϫ 20 mL), and the combined organic
layers were dried with sodium sulfate and the solvents evaporated
to dryness with a rotary evaporator. Column chromatography (sil-
ica; toluene) of the residue resulted in 117 mg (32%) of the naph-
Acknowledgments
This work was supported by the Fonds der Chemischen Industrie.
3100
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 3095–3101

Naphthyl-Substituted Carbocations
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[6] CCDC-676419 (4a) and -666352 (19) contain the supplemen-
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Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
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[8] a) T. Suzuki, K. Ono, H. Kawai, T. Tsuji, J. Chem. Soc. Perkin
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Received: February 1, 2008
Published Online: May 6, 2008
Eur. J. Org. Chem. 2008, 3095–3101
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3101