Thermal cyclization of N-[2-(2-propenyl)-1-naphthyl] ketenimines: Intramolecular Diels-Alder reaction versus [1,5] hydrogen migration. Synthesis of dibenz[b,h]acridines and benzo[h]quinolines

Article abstract of DOI:10.1016/j.tet.2005.05.092

The thermal treatment of N-(2-propenyl)-1-naphthylamines provided the expected aza-Claisen rearranged products, 2-(2-propenyl)-1-naphthylamines and benz[g]indoles, these last derived from an intramolecular hydroamination reaction on those primary products. The 2-(2-propenyl)-1-naphthylamines were converted into their triphenylphosphazene derivatives, which by aza-Wittig reaction with disubstituted ketenes yielded N-[2-(2-propenyl)-1-naphthyl] ketenimines. The heating of these ketenimines in boiling toluene induced their cyclization either via an intramolecular Diels-Alder reaction, to afford dibenz[b,h]acridines, or via [1,5] hydrogen migration from the sp³ carbon atom of the propenyl substituent to the central carbon atom of the ketenimine fragment, followed by a 6π electrocyclic ring closure, to give benzo[h]quinolines.

Full text of DOI:10.1016/j.tet.2005.05.092

Tetrahedron 61 (2005) 7613–7621
Thermal cyclization of N-[2-(2-propenyl)-1-naphthyl]
ketenimines: intramolecular Diels–Alder reaction versus [1,5]
hydrogen migration. Synthesis of dibenz[b,h]acridines and
benzo[h]quinolines
´
Mateo Alajarın, Angel Vidal and Marıa-Mar Ortın
*
*
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´
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Departamento de Quımica Organica, Facultad de Quımica, Universidad de Murcia, Campus de Espinardo, E-30100 Murcia, Spain
Received 18 April 2005; revised 30 May 2005; accepted 31 May 2005
Available online 22 June 2005
´
Dedicated to Professor Joaquın Plumet on the occasion of his 60th birthday
Abstract—The thermal treatment of N-(2-propenyl)-1-naphthylamines provided the expected aza-Claisen rearranged products, 2-(2-
propenyl)-1-naphthylamines and benz[g]indoles, these last derived from an intramolecular hydroamination reaction on those primary
products. The 2-(2-propenyl)-1-naphthylamines were converted into their triphenylphosphazene derivatives, which by aza-Wittig reaction
with disubstituted ketenes yielded N-[2-(2-propenyl)-1-naphthyl] ketenimines. The heating of these ketenimines in boiling toluene induced
their cyclization either via an intramolecular Diels–Alder reaction, to afford dibenz[b,h]acridines, or via [1,5] hydrogen migration from the
sp3 carbon atom of the propenyl substituent to the central carbon atom of the ketenimine fragment, followed by a 6p electrocyclic ring
closure, to give benzo[h]quinolines.
q 2005 Elsevier Ltd. All rights reserved.
1. Introduction
occurring potential Diels–Alderases established the Diels–
Alder reaction as a viable biosynthetic transformation.5
The Diels–Alder reaction is undoubtedly one of the most
valuable reactions for the synthetic organic chemists due to
its widespread utility and enormous synthetic potential.1
This pericyclic process represents a powerful and effective
methodology for the formation of carbon–carbon bonds,
which allows high regio and stereoselective constructions of
six-membered carbocyclic systems with up to four
contiguous new stereogenic centers.2 This reaction is of
particular interest in the total synthesis of naturally
occurring products,3 or structurally related compounds.
In the context of the synthesis of heterocyclic compounds
via Diels–Alder reactions, ketenimines [R1–N]C]
CR2R3] are valuable precursors for the construction of
six-membered heterocycles by means of inter or intra-
molecular variants of these reactions.6 These heterocumu-
lenes have the ability to act as 2-azadienes (R1Zvinyl or
aryl group) or as all-carbon dienes (R2 and/or R3Zvinyl or
aryl group), an even can serve as the dienophile component,
with either the N]C or the C]C bond of the ketenimine
being involved in the cycloaddition process. As a matter of
fact, as part of our research work directed towards the study
of the participation of ketenimines in pericyclic processes,
we have successfully applied the Diels–Alder strategy to the
synthesis of benzo[d,e][1,6]naphthyridines7 and pyr-
ido[2,3,4-d,e]quinazolines7 (ketenimines as 2-azadienes),
benzimidazo[1,2-b]isoquinolines8 and benz[b]acridines9
(ketenimines as all-carbon dienes) and pyrido[1,2-a]benz-
imidazoles10 (ketenimines as dienophiles by means of its
C]C bond).
The Diels–Alder strategy has likewise found application in
the preparation of six-membered heterocyclic compounds
by positioning heteroatoms at the diene or at the dienophile
(hetero Diels–Alder reaction), and, in its intramolecular
version, a heterocycle is also forged by locating a
heteroatom in the tether connecting diene and dienophile.4
On the other hand, the characterization of several natural
Keywords: Aza-Claisen; Hydroamination; Ketenimines; Diels–Alder;
Hydrogen migration.
Our method for preparing benz[b]acridines9 was based on a
thermally induced intramolecular Diels–Alder reaction on
*
Corresponding authors. Tel.: C34 968 367497; fax: C34 968 364149
(M.A.); e-mail: alajarin@um.es
0040–4020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2005.05.092

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M. Alajarın et al. / Tetrahedron 61 (2005) 7613–7621
7614
N-[2-(2-propenyl)phenyl]-C,C-diphenyl ketenimines, in
which the ketenimine function acts as an all-carbon diene
and the C]C bond of the 2-propenyl side-chain plays the
role of the dienophile. With the aim of extending the
versatility of this particular methodology we decided to try
its application for the synthesis of dibenz[b,h]acridines,11 by
combination of a C-aryl ketenimine fragment (diene) and a
2-propenyl group (dienophile) at the adjacent C1 and C2
carbon atoms of a naphthalene ring. We present herein the
results obtained in the thermally induced intramolecular
cyclization of N-[2-(2-propenyl)-1-naphthyl] ketenimines,
forming the expected Diels–Alder adducts, 7,7a,8,14-
tetrahydrodibenz[b,h]acridines, unexpectedly accompanied
by benzo[h]quinolines, whose formation should involve an
initial [1,5] hydrogen migration from the sp3 carbon atom of
the propenyl substituent to the central carbon atom of the
ketenimine function.
a total conversion in the transformations 2/3 we increased
the reaction time. Thus, when the N-(2-propenyl) derivative
2a (R1ZH) was heated at 260–270 8C for 4 h it was totally
consumed, and column chromatography of the reaction
mixture allowed the isolation of 2-(2-propenyl)-l-naphthyl-
amine 3a (R1ZH; 38% yield), and, surprisingly, of
2-methyl-2,3-dihydro-1H-benz[g]indole 4a (R1ZH; 35%
yield) and 2-methyl-1H-benz[g]indole 5a (R1ZH; 3%
yield) (Scheme 1). A similar thermal treatment of 2b
(R1ZCH3) for 6 h yielded only trans-2,3-dimethyl-2,3-
dihydro-1H-benz[g]indole 4b (R1ZCH3; 22% yield) and
2,3-dimethyl-1H-benz[g]indole 5b (R1ZCH3; 21% yield)
(Scheme 1).13
The analytical and spectral data of benz[g]indoles 4 and 5
are in accordance with the proposed structures. The trans
relative positioning of the two methyl groups of 4b was
unequivocally determined by a NOESY experiment. More-
over, the collected data for benzindoles 5 are totally
coincident with those previously reported for these
compounds.14
2. Results and discussion
2.1. Preparation of 2-(2-propenyl)-1-naphthylamines
The formation of the 2,3-dihydro-1H-benz[g]indoles 4
could be explained as occurring by an intramolecular
hydroamination reaction of the carbon–carbon double bond
of the 2-propenyl substitutent in amines 3 (Scheme 2).
Further spontaneous dehydrogenation of 4 under the
reaction conditions should give the aromatic derivatives 5.
The N-(2-propenyl)-1-naphthylamines 2a,b were both
prepared following the reaction conditions reported by
Sloviter12 for the preparation of 2a, but with a new and
simpler protocol that we have developed for the isolation
and purification of these two compounds. The reaction of an
excess of 1-naphthylamine 1 with 3-chloropropene and
1-chloro-2-butene, in refluxing ethanol for 5 h, yielded only
the monoalkylation products 2a (67% yield) and 2b (84%
yield), respectively. The thermal treatment of neat N-(2-
propenyl)-1-naphthylamines 2 in a sealed tube at 260–
270 8C for 3 h induced their aza-Claisen rearrangement
providing 2-(2-propenyl)-l-naphthylamines 3 in approxi-
mately 50% yield, whereas a considerable amount (20–
30%) of the starting material remained unaltered (Scheme
1). The transformations 2/3 were carried out under the
reaction conditions described by Marcinkiewicz12b and
Inada12c in their respective preparations of 3a and 3a,b, but
we used a different method in the purification step. We
purified the crude materials resulting from these thermal
treatments by column chromatography, instead of by
distillation or conversion of compounds 3 into their
N-tosylamines as reported. With the objective of obtaining
The intramolecular hydroamination of aminoalkenes is a
well-known reaction, which is usually accomplished by
mediation of alkali metals, transition-metals, and actinide
and lanthanide complexes.15 On the other hand, it has been
reported that N-allylanilines undergo aromatic 3-aza-Cope
rearrangement in the presence of HY-Zeolite, HEMT or
HZeolite beta, in solution at 80 8C, to afford mixtures of
ortho-allylanilines and indolines,16 and in the presence
of ZnC2 montmorillonite, under microwave irradiation in
the absence of solvent, to yield indolines.17 By contrast, the
intramolecular hydroamination occurring in compounds 3
takes place under thermal conditions and in the absence of
any catalyst.18
2.2. Thermal cyclization of N-[2-(2-propenyl)-1-
naphthyl] ketenimines
Triphenylphosphazenes 6 were prepared by reaction of
amines 3, in acetonitrile solution, with triphenylphosphane,
carbon tetrachloride and triethylamine (Scheme 3).
Treatment of a toluene solution of triphenylphosphazene 6a
(R1ZH) with diphenylketene at room temperature afforded
N-[2-(2-propenyl)-1-naphthyl]-C,C-diphenylketenimine 7a.
The formation of ketenimine 7a was established by IR
spectroscopy: the IR spectrum of the reaction mixture
Scheme 1. Reagents and conditions: (a) CH2]CHCH2Cl or CH3–CH]
CH–CH2Cl, ethanol, reflux, 5 h; (b) 260–270 8C, sealed tube, 3–6 h.
Scheme 2. Intramolecular hydroamination in the aminoalkenes 3.

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M. Alajarın et al. / Tetrahedron 61 (2005) 7613–7621
7615
spectrum of compound 9a shows two signals in the aliphatic
region: one at dZ49.9 ppm due to the methine carbon C4,
and the other one at dZ52.3 ppm associated to the
quaternary carbon atom C3. The methylene carbon of the
vinyl group resonates at dZ116.9 ppm, and the signal of
the iminic carbon C2 appears at dZ164.6 ppm.
Scheme 3. Reagents and conditions: (a) PPh3, CCl4, Et3N, acetonitrile, rt,
16 h.
The transformation of the C,C-diphenyl ketenimine 7a into
the tetrahydrodibenz[b,h]acridine 8a can be explained by an
intramolecular Diels–Alder reaction, the ketenimine frag-
ment acting as all-carbon diene with the participation of its
cumulated C]C bond, followed by hydrogen shift. On the
other hand, we believe that the conversion of ketenimine 7a
into benzo[h]quinoline 9a takes place by initial [1,5]
migration of a hydrogen atom from the benzylic methylene
to the central carbon atom of the ketenimine function. This
sigmatropic rearrangement may lead to the stereoisomeric
intermediates (E)-11 and (Z)-11, in which the carbon–
carbon double bond exocyclic to the naphthalene core is of
E and Z configuration, respectively (Scheme 5). In these
intermediates the atoms of the original ketenimine grouping
and the 2-propenyl substituent now form part of a
conjugated 3-aza-1,3,5,7-octatetraene system. The cycliza-
tion of intermediates (E)-11 and (Z)-11 via a 6p
electrocyclic ring closure (6p-ERC) involving the
showed a strong absorption at 2004 cmK1, characteristic of
the N]C]C grouping. Next, the toluene solution contain-
ing ketenimine 7a was heated under reflux up to the total
dissapearance of the cumulenic band in its IR spectrum,
approximately 1 h. The crude material obtained from this
thermal treatment was chromatographed, giving as result
the isolation of the expected Diels–Alder cycloadduct 13-
phenyl-7,7a,8,14-tetrahydrodibenz[b,h]acridine (8a), in
40% yield, along with a 37% of an unexpected reaction
product which was identified as 3,3-diphenyl-4-vinyl-3,4-
dihydrobenzo[h]quinoline (9a) (Scheme 4).
The analytical and spectral data of the dibenz[b,h]acridine
8a are essentially similar to those of the benz[b]acridines
previously prepared by us.9 The IR spectrum of compound
8a exhibits a strong absorption at 3428 cmK1 due to the
1
vibration of the amino group. In its H NMR spectrum the
protons of the two methylene groups appear overlapped in a
complex signal at dZ2.92–3.23 ppm. The proton H–C7a is
observed as a multiplet, at dZ3.44–3.54 ppm. The 13C
NMR spectrum of 8a shows the signals corresponding to the
sp3 hybridized carbon atoms at dZ33.4, 34.9 (C7a) and
36.0 ppm.
1
In the H NMR spectrum of the benzo[h]quinoline 9a the
vinyl substituent is clearly observed, its protons appearing at
the following chemical shifts: 4.66 (CH]CHAHB), 4.78
(CH]CHAHB) and 5.54 (CH]CH2), all showing the
expected multiplicities and coupling constants. In this
spectrum, the proton H–C2 appears at 8.71 ppm as a
doublet, due to a small coupling constant (4JZ1.2 Hz,
W-type) with H–C4, as revealed by a COSY experiment.
This last proton appears at dZ4.22 ppm as a broad doublet,
as result of its coupling with the vinylic methine proton
(3JZ8.4 Hz), with the two methylene protons (4JZ1.0,
0.6 Hz, allylic-type) and with H–C2. The 13C NMR
Scheme 4. Reagents and conditions: (a) Ph2C]C]O, toluene, rt, 10 min;
(b) Toluene, reflux, 1 h.
Scheme 5. Proposed mechanism for the conversion 7a/8aC9a.

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M. Alajarın et al. / Tetrahedron 61 (2005) 7613–7621
7616
3-azatriene fragment19 of the 3-aza-1,3,5,7-octatetraene
system should provide the 3,4-dihydrobenzo[h]quinoline
9a. Intermediate (Z)-11 has also the appropriate geometry to
undergo cyclization by means of an alternative 6p-ERC
mode, that involving the 1-azatriene fragment of the 3-aza-
1,3,5,7-octatetraene system, affording the benzo[h]quino-
line 12. This is not the case, as this compound was not
This result suggests that in N-[2-(2-propenyl)-1-naphthyl]
ketenimines 7 the presence of one alkyl substituent at their
terminal carbon atom is enough to bring about their
cyclization periselectively via the consecutive [1,5] hydro-
gen migration/6p electrocyclic ring closure path.
Expecting a similar chemical behavior to that observed for
the C,C-diphenyl ketenimine 7a we prepared the methyl
substituted analogue 7c (Scheme 7), although it emerged not
to be the case. The difference between these two
ketenimines is the presence in 7c of a methyl group at the
sp3 carbon atom of the side chain. Two different fractions
were collected when the crude material that resulted from
the heating of ketenimine 7c in toluene at reflux temperature
for 1 h was chromatographed. The first one consisted on a
1:1 mixture of the two possible diastereoisomers of
7-methyl-13-phenyl-7,7a,8,14-tetrahydrodibenz[b,h]acri-
dine (8b), along with a small amount of an unidentified
impurity we were not able to separate chromatographically.
Compound 8b was separated from the impurity by crystal-
lization from diethyl ether. This is the reason why pure 8b
was obtained in low yield (14%). The crystalline product
still consisted on both diastereoisomers of 8b in a 1:1 ratio.
From the second chromatographic fraction 3-(2,2-diphenyl-
ethyl)-4-methylbenzo[h]quinoline (13) was isolated in
17% yield.
1
detected in the H NMR spectrum of the crude material
obtained from the thermal treatment of ketenimine 7a,
before the purification step.
Examples of sigmatropic [1,5]-H shifts to the electrophilic
central carbon atom of ketenimines have been occasionally
reported. Goerdeler20 has described that C-imidoyl keteni-
mines underwent, at room temperature, [1,5] hydrogen
migration followed by 6p-ERC to yield dihydropyrimi-
dines, whereas Foucaud21 has demonstrated that, in
refluxing dichloromethane, N-imidoyl ketenimines con-
verted into pyrrolotriazines by [1,5]-H shift followed by
intramolecular [4C2] cycloaddition. More recently,
Wentrup22 has reported that N-phenyl ketenimines bearing
methyl groups at the ortho position to the nitrogen atom,
under very mild flash vacuum thermolysis conditions
(350 8C), suffer a facile [1,5] hydrogen migration and
subsequent electrocyclization to dihydroquinolines.
The generation of N-[2-(2-propenyl)-1-naphthyl] keten-
imines bearing one or two alkyl substituent at the terminal
carbon atom of the ketenimine moiety instead of phenyl
groups should, respectively, decrease or prevent the
probability of occurring the [4C2] cyclization mode.
Thus the evolution of such ketenimines via the sequence
[1,5]-H/6p-ERC should be favoured. A major limitation
that we found in the preparation of ketenimines by the aza-
Wittig reaction of phosphazenes with ketenes is that only
ketenes that are stable enough to be isolated under usual
working conditions could be employed successfully.23
Thus, we carried out the reaction of triphenylphosphazene
6a (R1ZH), in toluene solution at room temperature, with
the isolable methylphenylketene to generate the C-methyl-
C-phenyl ketenimine 7b (Scheme 6). When this ketenimine
was heated in refluxing toluene it experienced cyclization to
3-methyl-3-phenyl-4-vinyl-3,4-dihydrobenzo[h]quinoline
(9b), which was obtained as a 1:1 mixture of cis and trans
diastereoisomers in good yield (73%).
The structures of compounds 8b and 13 were confirmed by
their analytical and spectroscopic data. The main features of
the 1H NMR spectrum of benzo[h]quinoline 13 are the
following: a singlet at dZ2.46 ppm, associated with the
methyl group CH3–C4, a doublet and a triplet at dZ
3.61 ppm and dZ4.27 ppm, respectively, assigned to the
methylene and methine protons of the diphenylethyl
substituent at C3, and a singlet at dZ8.49 ppm attributed
to the proton H–C2. The positions of the diphenylethyl and
methyl substituents at the benzoquinoline ring were
determined by performing NOESY and NOE difference
experiments. These experiments associated the signals of
the diphenylethyl group with those of H–C2 and CH3–C4.
H–C2 and CH3–C4, in turn, did not show any effect on each
other. Also NOE effect was observed between H–C5 and the
methyl group.
Scheme 6. Reagents and conditions: (a) Ph(CH3)C]C]O, toluene, rt,
10 min; (b) Toluene, reflux, 1 h.
Scheme 7. Reagents and conditions: (a) Ph2C]C]O, toluene, rt, 10 min;
(b) Toluene, reflux, 1 h.

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7617
The formation of the dibenzacridine 8b is easily understood
as occurring by an intramolecular Diels–Alder reaction in
ketenimine 7c, whereas the formation of benzoquinoline 13
should occur by a new, more complex, mechanistic
pathway. Probably, the conversion 7c/13 is initiated by
an [1,5] hydrogen migration from the sp3 carbon of the
propenyl substituent to the central carbon of the ketenimine
function, as it could be ascertained by the presence of an
hydrogen atom at carbon 2 of compound 13. After this first
hydrogen shift the resulting intermediate could undergo
evolution to the benzoquinoline 13, for example, either by
means of a sequence of shifts or by a mechanistic pathway
involving the formation of birradical species, as it is shown
in Scheme 8.
Scheme 9. Reagents and conditions: (a) Pd/C, ortho-xylene, reflux, 3 h.
2.3. Preparation of aromatic dibenz[b,h]acridines
Finally, the 7,7a,8,14-tetrahydrodibenz[b,h]acridines 8
could be easily oxidized in refluxing ortho-xylene in the
presence of Pd/C to give the fully aromatic dibenz[b,h]-
acridines 14 (Scheme 9). Compounds 14 were thus obtained
in almost quantitative yields (82–97%).
The aza-Wittig reaction of triphenylphosphazene 6b with
methylphenylketene, and the subsequent thermal treatment
of the resulting C-methyl-C-phenyl ketenimine only gave,
in our hands, very complex reaction mixtures.
3. Conclusion
In summary, in this work we have reported that under
thermal conditions, and in the absence of any catalyst, 2-(2-
propenyl)-1-naphthylamines undergo a formal intra-
molecular hydroamination reaction to yield 2,3-dihydro-
benz[g]indoles. We have also described how N-[2-(2-
propenyl)-1-naphthyl] ketenimines undergo cyclization
either by a Diels–Alder cycloaddition or by an [1,5]
hydrogen migration followed by a 6p electrocyclic ring
closure, providing new routes to dibenz[b,h]acridines and
benzo[h]quinolines. The mode selectivity, Diels–Alder
cycloaddition versus [1,5] hydrogen migration, found in
the cyclization of the N-[2-(2-propenyl)-1-naphthyl] keten-
imines prepared depends basically on the nature of the
substituents at the terminal carbon atom of the ketenimine
function.
4. Experimental
4.1. General method
All mps were determined on a Kofler hot-plate mp apparatus
and are uncorrected. IR spectra were obtained as films or
Nujol emulsions on a Nicolet Impact 400 spectropho-
tometer. NMR spectra were recorded on a Bruker Avance
300 (300, 75 MHz for 1H and 13C, respectively) or a Bruker
Avance 400 (400 and 100 MHz for 1H and 13C,
respectively), in CDCl3 as solvent, and the chemical shifts
1
are expressed in ppm relative to Me4Si at dZ0.00 for H
and to CDCl3 at dZ77.1 for 13C. Mass spectra were
recorded on a Hewlett-Packard 5993C spectrometer or on a
VG-Autospec spectrometer. Microanalyses were performed
on a Carlo Erba EA-1108 instrument.
4.2. Materials
Diphenylketene24 and methylphenylketene25 were prepared
according to literature procedures.
Scheme 8. Two mechanistic proposals for explaining the conversion of 7c
into 13.

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M. Alajarın et al. / Tetrahedron 61 (2005) 7613–7621
7618
4.3. General procedure for the preparation of
N-(2-propenyl)-1-naphthylamines 2
767, 749, 674. Anal. Calcd for C13H13N: C, 85.20; H, 7.15;
N, 7.65. Found: C, 85.03; H, 7.18; N, 7.77.
1
4.4.3. 2-Methyl-1H-benz[g]indole14a (5a). Yield 3%. H
1-Naphthylamine 1 (12.88 g, 90 mmol) was dissolved in
ethanol (100 ml) and 3-chloropropene (2.29 g, 30 mmol) or
1-chloro-2-butene (2.71 g, 30 mmol) was added. The
reaction mixture was heated at reflux temperature for 5 h.
After cooling at room temperature, the solvent was removed
under reduced pressure, and aqueous NaOH 5% (200 ml)
was added to the solid residue. The resulting suspension was
stirred at room temperature for 5 min, and then extracted
with dichlorometane (2!75 ml). The combined organic
layer was washed with water (100 ml) and dried over
anhydrous MgSO4. The dichloromethane was removed
under reduced pressure and the resulting material was
purified by column chromatography [silica gel; hexanes/
diethyl ether 9:1 (v/v)].
NMR (CDCl3) dZ2.45 (d, 3H, JZ0.9 Hz), 6.32–6.34 (m,
1H), 7.36 (ddd, 1H, JZ8.1, 6.9, 1.3 Hz), 7.41–7.48 (m, 2H),
7.61 (dd, 1H, JZ8.6, 0.3 Hz), 7.80–7.83 (m, 1H), 7.86–7.89
(m, 1H), 8.45 (br s, 1H).
4.5. Thermal treatment of (E)-N-(2-butenyl)-1-
naphthylamine 2b
(E)-N-(2-Butenyl)-1-naphthylamine 2b (3.94 g, 20 mmol)
was heated in a sealed tube at 260–270 8C for 3 h. After
cooling at room temperature, the crude material was
dissolved in dichloromethane (20 ml) and transferred to a
round bottom flask. The solvent was removed under reduced
pressure and the resulting oil was chromatographed on a
silica gel column using dichloromethane/hexanes (4:1, v/v)
as eluent.
4.3.1. N-(2-Propenyl)-1-naphthylamine12a (2a). Yield
1
67%. H NMR (CDCl3) dZ3.92 (d, 2H, JZ5.2 Hz), 4.43
(br s, 1H), 5.18–5.24 (m, 1H), 5.29–5.40 (m, 1H), 5.96–6.16
(m, 1H), 6.65 (d, 1H, JZ7.4 Hz), 7.20–7.44 (m, 4H), 7.75–
7.81 (m, 2H).
In this reaction a 25% of the starting material was recovered.
4.5.1. 2-(1-Methyl-2-propenyl)-1-naphthylamine12c (3b)
1
4.3.2. (E)-N-(2-Butenyl)-1-naphthylamine12e (2b). Yield
Yield 54%. H NMR (CDCl3) dZ1.48 (d, 3H, JZ7.0 Hz),
1
3.64–3.72 (m, 1H), 4.24 (br s, 2H), 5.11 (dt, 1H, JZ6.2,
1.6 Hz), 5.14–5.15 (m, 1H), 5.99–6.07 (m, 1H), 7.28 (d, 1H,
JZ8.5 Hz), 7.32 (d, 1H, JZ8.5 Hz), 7.38–7.46 (m, 2H),
7.75–7.81 (m, 2H).
84%. H NMR (CDCl3) dZ1.78–1.83 (m, 3H), 3.88–3.90
(m, 2H), 4.38 (br s, 1H), 5.73–5.91 (m, 2H), 6.67 (dd, 1H,
JZ7.5, 0.9 Hz), 7.28–7.31 (m, 1H), 7.37–7.52 (m, 3H),
7.81–7.86 (m, 2H).
When (E)-N-(2-butenyl)-1-naphthylamine 2b was heated
at 260–270 8C for 6 h the reaction products were trans-
2,3-dimethyl-2,3-dihydro-1H-benz[g]indole 4b and 2,3-
dimethyl-1H-benz[g]indole 5b.
4.4. Thermal treatment of N-(2-propenyl)-1-naphthyl-
amine 2a
N-(2-Propenyl)-1-naphthylamine 2a (3.66 g, 20 mmol) was
heated in a sealed tube at 260–270 8C for 4 h. After cooling
at room temperature, the crude material was dissolved in
dichloromethane (20 ml) and transferred to a round bottom
flask. The solvent was removed under reduced pressure and
the resulting oil was chromatographed on a silica gel
column using hexanes/diethyl ether (4:1, v/v) as eluent. The
fractions containing the major component were combined
and the solvent removed under reduced pressure to give an
oily residue which was subjected to a second column
chromatography using dichloromethane/hexanes (9:1; v/v)
as eluent.
4.5.2. trans-2,3-Dimethyl-2,3-dihydro-1H-benz[g]indole
1
(4b). Yield 22%; dark oil. H NMR (CDCl3) dZ1.37 (d,
3H, JZ6.8 Hz), 1.41 (d, 3H, JZ6.2 Hz), 3.04 (dq, 1H, JZ
8.7, 6.8 Hz), 3.64 (dq, 1H, JZ8.7, 6.2 Hz), 3.74 (br s, 1H),
7.23–7.31 (m, 2H), 7.35–7.45 (m, 2H), 7.60–7.63 (m, 1H),
7.75–7.81 (m, 1H). 13C NMR (CDCl3) dZ18.3, 21.1, 45.2,
64.5, 118.9, 120.7 (s), 121.5, 122.2, 124.7, 125.1, 127.9 (s),
128.5, 133.6 (s), 145.6 (s). MS m/z (I%): 197 (MC, 27), 194
(100). IR (nujol) n cmK1: 3368, 1574, 1519, 1453, 1441,
1420, 1375, 1335, 1267, 1257, 1082, 976, 937, 805, 777,
747, 678. Anal. Calcd for C14H15N: C, 85.24; H, 7.66; N,
7.10. Found: C, 85.05; H, 7.78; N, 7.16.
4.4.1. 2-(2-Propenyl)-1-naphthylamine12b (3a). Yield
1
4.5.3. 2,3-Dimethyl-1H-benz[g]indole14d (5b). Yield 21%.
1H NMR (CDCl3) dZ2.28 (d, 3H, JZ0.5 Hz), 2.40 (s, 3H),
7.35 (ddd, 1H, JZ8.2, 6.9, 1.2 Hz), 7.45 (ddd, 1H, JZ8.2,
6.9, 1.2 Hz), 7.47 (d, 1H, JZ8.2 Hz), 7.59 (d, 1H, JZ
8.6 Hz), 7.87 (t, 2H, JZ8.9 Hz), 8.32 (br s, 1H).
38%. H NMR (CDCl3) dZ3.47 (dt, 2H, JZ6.2, 1.7 Hz),
4.16 (br s, 2H), 5.09 (dq, 1H, JZ8.2, 1.7 Hz), 5.14–5.56 (m,
1H), 5.90–6.10 (m, 1H), 7.20 (d, 1H, JZ8.4 Hz), 7.29 (d,
1H, JZ8.4 Hz), 7.36–7.48 (m, 2H), 7.73–7.83 (m, 2H).
4.4.2. 2-Methyl-2,3-dihydro-1H-benz[g]indole (4a). Yield
35%; mp 76–77 8C; colorless prisms (n-hexane). H NMR
1
4.6. General procedure for the preparation of
2-(2-propenyl)-1-(triphenylphosphoranylideneamino)
naphthalenes 6
(CDCl3) dZ1.34 (d, 3H, JZ6.3 Hz), 2.81 (dd, 1H, JZ15.3,
7.5 Hz), 3.32 (dd, 1H, JZ15.3, 9.0 Hz), 3.89 (br s, 1H),
4.10–4.18 (m, 1H), 7.26 (s, 2H), 7.31–7.38 (m, 2H), 7.55–
7.59 (m, 1H), 7.74–7.79 (m, 1H). 13C NMR (CDCl3) dZ
22.7, 38.6, 55.7, 118.7, 120.7 (s), 121.4, 122.5 (s), 123.6,
124.7, 125.0, 128.5, 133.5 (s), 146.3 (s). MS m/z (I%): 183
(MC, 63), 168 (100). IR (nujol) n cmK1: 3355, 1575, 1523,
1423, 1332, 1284, 1160, 1126, 1103, 1080, 880, 867, 803,
The corresponding 2-(2-propenyl)-1-naphthylamine 3
(10 mmol) and triphenylphosphane (5.24 g, 20 mmol)
were dissolved in a mixture of anhydrous acetonitrile
(25 ml) and triethylamine (15 ml). Then carbon tetrachlor-
ide was added (10 ml), and the reaction mixture was kept at

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M. Alajarın et al. / Tetrahedron 61 (2005) 7613–7621
7619
room temperature without stirring for 16 h. The precipitated
solid was filtered and washed with anhydrous acetonitrile
(2!2 ml). From the filtrate the solvent was removed under
reduced pressure, and the crude material was purified by
column chromatography using silica gel deactivated with
triethylamine as solid phase and hexanes/diethyl ether (3:2,
v/v) as eluent. After removing the solvent from the
combined fractions containing 6 the resulting white solid
was treated with diethyl ether (5 ml), filtered and dried.
pressure and the crude material was chromatographed on
a silica gel column using hexanes/diethyl ether (9:1, v/v) as
eluent.
4.7.1. 13-Phenyl-7,7a,8,14-tetrahydrodibenz[b,h]acri-
dine (8a). Yield 40%; mp 212–213 8C; yellow prisms
1
(diethyl ether). H NMR (CDCl3) dZ2.92–3.13 (m, 4H),
3.44–3.54 (m, 1H), 6.52 (dd, 1H, JZ7.6, 1.2 Hz), 6.79 (s,
1H), 6.91 (td, 1H, JZ7.2, 1.4 Hz), 6.95–6.99 (m, 1H), 7.07
(d, 2H, JZ8.3 Hz), 7.13 (d, 1H, JZ8.3 Hz), 7.21 (d, 1H,
JZ8.3 Hz), 7.26–7.34 (m, 2H), 7.40–7.42 (m, 2H), 7.46 (tt,
1H, JZ7.4, 1.4 Hz), 7.56–7.60 m, 2H), 7.68–7.71 (m, 1H).
13C NMR (CDCl3) dZ33.4, 34.9, 36.0, 110.1 (s), 116.4 (s),
118.3, 118.8, 121.5 (s), 122.9, 123.7, 125.2, 125.4, 126.7,
126.8, 126.9, 127.7, 128.8, 129.8, 131.2, 131.6 (s), 133.5 (s),
133.7 (s), 137.0 (s), 138.1 (s), 138.2 (s). MS m/z (I%): 359
(MC, 76), 354 (100). IR (nujol) n cmK1: 3428, 1622, 1594,
1563, 1334, 1314, 1293, 1277, 1182, 1156, 1098, 1011, 857,
803, 759, 737. Anal. Calcd for C27H21N: C, 90.21; H, 5.89;
N, 3.90. Found: C, 90.35; H, 5.78; N, 3.83.
4.6.1. 2-(2-Propenyl)-1-(triphenylphosphoranylidenea-
mino)naphthalene (6a). Yield 49%; mp 131–132 8C;
colorless prisms (diethyl ether/n-pentane). 1H NMR
(CDCl3) dZ3.32 (ddd, 2H, JZ6.5, 3.1, 1.5 Hz), 4.78–4.86
(m, 2H), 5.59–5.69 (m, 1H), 6.97 (ddd, 1H, JZ8.1, 6.8,
1.0 Hz), 7.17–7.22 (m, 2H), 7.25 (dd, 1H, JZ8.3, 2.5 Hz),
7.35–7.40 (m, 6H), 7.45–7.50 (m, 3H), 7.58–7.65 (m, 7H),
7.99 (d, 1H, JZ8.3 Hz). 13C NMR (CDCl3) dZ37.1 (d, JZ
1.3 Hz), 114.7, 118.9 (d, JZ3.6 Hz), 123.6, 124.2, 126.0,
127.5, 128.3 (d, JZ3.3 Hz), 128.5 (d, JZ12.2 Hz), 129.0
(d, JZ8.7 Hz) (s), 131.4 (d, JZ2.6 Hz), 132.2 (d, JZ
5.7 Hz) (s), 132.4 (d, JZ101.3 Hz) (s), 132.6 (d, JZ
9.6 Hz), 133.8 (d, JZ2.1 Hz) (s), 138.4 (d, JZ1.2 Hz),
143.9 (d, JZ1.6 Hz) (s). 31P NMR (CDCl3, 121 MHz,
H3PO4) dZK2.4. MS m/z (I%): 443 (MC, 5), 262 (100). IR
(nujol) n cmK1: 1637, 1557, 1407, 1153, 1131, 1116, 996,
843, 808, 755, 747, 725, 713, 696. Anal. Calcd for
C31H26NP: C, 83.95; H, 5.91; N, 3.16. Found: C, 83.79;
H, 5.78; N, 3.10.
4.7.2. 3,3-Diphenyl-4-vinyl-3,4-dihydrobenzo[h]quino-
line (9a). Yield 37%; mp 151–152 8C; colorless prisms
(diethyl ether/n-pentane). 1H NMR (CDCl3) dZ4.22 (d, 1H,
JZ8.4 Hz), 4.66 (ddd, 1H, JZ16.9, 1.5, 1.0 Hz), 4.78 (ddd,
1H, JZ10.1, 1.5, 0.6 Hz), 5.54 (ddd, 1H, JZ16.9, 10.1,
8.4 Hz), 7.08–7.16 (m, 3H), 7.19–7.33 (m, 7H), 7.36 (d, 1H,
JZ8.3 Hz), 7.40–7.53 (m, 2H), 7.77 (d, 2H, JZ8.3 Hz),
8.56–8.60 (m, 1H), 8.71 (d, 1H, JZ1.2 Hz). 13C NMR
(CDCl3) dZ49.9, 52.3 (s), 116.9, 123.6, 124.9 (s), 125.9,
126.0, 126.5, 126.9, 127.0, 127.7, 128.2, 128.3, 128.4,
128.6, 128.8, 130.3 (s), 133.5 (s), 136.1, 136.3 (s), 142.9 (s),
143.8 (s), 164.6. MS m/z (I%): 359 (MC, 93), 165 (100). IR
(nujol) n cmK1: 1617, 1596, 1497, 1185, 1149, 1128, 1037,
997, 971, 951, 925, 885, 823, 768, 752, 701. Anal. Calcd for
C27H21N: C, 90.21; H, 5.89; N, 3.90. Found: C, 90.32; H,
5.80; N, 3.79.
4.6.2. 2-(1-Methyl-2-propenyl)-1-(triphenylphosphora-
nylideneamino)naphthalene (6b). Yield 42%; mp 138–
139 8C; colorless prisms (diethyl ether/n-pentane). 1H NMR
(CDCl3) dZ0.98 (d, 3H, JZ7.0 Hz), 4.05–4.12 (m, 1H),
4.77 (dt, 1H, JZ17.3, 1.9 Hz), 4.83 (dt, 1H, JZ10.5,
1.9 Hz), 5.57 (ddd, 1H, JZ17.3, 10.5, 4.9 Hz), 6.97 (ddd,
1H, JZ8.2, 6.8, 1.1 Hz), 7.14 (dd, 1H, JZ8.5, 1.5 Hz), 7.20
(ddd, 1H, JZ8.0, 6.8, 1.1 Hz), 7.28 (dd, 1H, JZ8.5,
2.5 Hz), 7.36–7.41 (m, 6H), 7.47–7.51 (m, 3H), 7.57–7.65
(m, 7H), 8.00 (d, 1H, JZ8.5 Hz). 13C NMR (CDCl3) dZ
19.3, 37.0, 111.8, 119.2 (d, JZ3.8 Hz), 123.7, 124.3, 126.0
(d, JZ3.1 Hz), 126.3 (d, JZ1.3 Hz), 127.5, 128.5 (d, JZ
11.9 Hz), 131.4 (d, JZ2.8 Hz), 132.2 (d, JZ5.5 Hz) (s),
132.3 (d, JZ101.2 Hz) (s), 132.6 (d, JZ9.5 Hz), 133.6 (d,
JZ2.2 Hz) (s), 134.2 (d, JZ8.8 Hz) (s), 143.2 (d, JZ
2.8 Hz) (s), 143.8 (d, JZ1.1 Hz). 31P NMR (CDCl3,
121 MHz, H3PO4) dZK2.0. MS m/z (I%): 457 (MC, 17),
262 (100). IR (nujol) n cmK1: 1630, 1559, 1505, 1436,
1303, 1158, 1131, 1114, 1098, 1029, 997, 897, 749, 727,
713, 697. Anal. Calcd for C32H28NP: C, 84.00; H, 6.17; N,
3.06. Found: C, 84.19; H, 6.06; N, 3.10.
4.7.3. 3-Methyl-3-phenyl-4-vinyl-3,4-dihydrobenzo[h]
quinoline (9b). Yield 73%. Mixture of two diastereo-
isomers (1:1). 1H NMR (CDCl3) dZ1.49 (s, 3H), 1.59
(s, 3H), 3.57 (d, 1H, JZ8.9 Hz), 3.77 (d, 1H, JZ9.4 Hz),
4.88–5.12 (m, 4H), 5.36–5.45 (m, 1H), 5.81–5.90 (m, 1H),
7.16–7.32 (m, 12H), 7.44–7.82 (m, 8H), 8.07 (s, 1H), 8.21
(s, 1H), 8.70 (d, 1H, JZ8.4 Hz), 8.76 (d, 1H, JZ8.4 Hz).
13C NMR (CDCl3) dZ19.5, 23.2, 43.7 (s), 43.8 (s), 52.5,
52.6, 118.2, 118.7, 123.6, 123.7, 124.3 (s), 124.6 (s), 125.7,
125.8, 125.9, 126.0, 126.4, 126.5, 126.7, 126.8, 127.1,
127.5, 127.6, 127.7, 127.9, 128.4, 128.5, 130.1 (s), 130.2 (s),
133.2 (s), 133.5 (s), 133.6 (s), 135.0, 136.3, 136.7 (s), 140.0
(s), 144.0 (s), 167.8, 168.4. MS m/z (I%): 297 (MC, 66), 280
(100). IR (neat) n cmK1: 1620, 1600, 1582, 1562, 1494,
1444, 1376, 1264, 1212, 1144, 1074, 1028, 1000, 922, 818,
758. Anal. Calcd for C22H19N: C, 88.85; H, 6.44; N, 4.71.
Found: C, 88.55; H, 6.78; N, 4.66.
4.7. Reaction of 2-(2-propenyl)-1-(triphenylphosphora-
nylideneamino)naphthalene 6a with ketenes
To a solution of 2-(2-propenyl)-1-(triphenylphosphoranyli-
deneamino)naphthalene 6a (0.55 g, 1.25 mmol) in anhy-
drous toluene (20 ml) a solution of diphenylketene (0.34 g,
1.75 mmol) or methylphenylketene (0.23 g, 1.75 mmol) in
the same solvent (5 ml) was added. The reaction mixture
was stirred at room temperature for 10 min, and then heated
at reflux temperature for 1 h. After cooling at room
temperature, the solvent was removed under reduced
4.8. Reaction of 2-(1-methyl-2-propenyl)-1-(triphenyl-
phosphoranylideneamino)naphthalene 6b with
diphenylketene
To a solution of 2-(1-methyl-2-propenyl)-1-(triphenylphos-
phoranylideneamino)naphthalene 6b (0.69 g, 1.5 mmol) in
anhydrous toluene (20 ml) a solution of diphenylketene

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M. Alajarın et al. / Tetrahedron 61 (2005) 7613–7621
7620
(0.44 g, 2.25 mmol) in the same solvent (5 ml) was added.
The reaction mixture was stirred at room temperature for
10 min, and then heated at reflux temperature for 1 h. After
cooling at room temperature, the solvent was removed
under reduced pressure and the crude material was
chromatographed on a silica gel column, using hexanes/
diethyl ether (20:1, v/v) as eluent, upto the total elution of
8b, and then hexanes/diethyl ether (9:1, v/v).
dZ7.36–7.46 (m, 2H), 7.49 (d, 1H, JZ9.3 Hz), 7.52–7.72
(m, 9H), 8.01–8.05 (m, 2H), 8.56 (s, 1H), 8.67 (s, 1H), 8.89–
8.92 (m, 1H). 13C NMR (CDCl3) dZ124.7 (s), 125.4, 125.7,
125.8, 125.9, 126.6, 127.1, 127.3, 127.5, 127.6, 127.7,
127.8, 128.6, 129.3, 131.5 (s), 132.2 (s), 132.3 (s), 132.5,
134.0 (s), 134.9, 137.8 (s), 138.3 (s), 142.1 (s), 148.5 (s).
FAB(C) m/z (I%): 356 (MCC1, 100). IR (nujol) n cmK1
:
1631, 1594, 1329, 1308, 1157, 1140, 1123, 1073, 1009, 962,
922, 874, 845, 803, 755, 700, 692. Anal. Calcd for C27H17N:
C, 91.24; H, 4.82; N, 3.94. Found: C, 91.09; H, 4.89; N,
3.99.
We could not separate chromatographically compound 8b
from an unidentified impurity. Thus, after removing the
solvent from the fractions containing compound 8b the
residue was treated with diethyl ether (4 ml), from which
pure 8b crystallized.
4.9.2. 7-Methyl-13-phenyldibenz[b,h]acridine (14b).
Yield 82%; mp 213–214 8C; red prisms (diethyl ether). H
1
NMR (CDCl3) dZ3.20 (s, 3H), 7.41 (ddd, 1H, JZ7.8, 6.4,
1.3 Hz), 7.46–7.50 (m, 1H), 7.53–7.72 (m, 9H), 7.92 (d, 1H,
JZ9.5 Hz), 7.99–8.02 (m, 1H), 8.10–8.13 (m, 1H), 8.85 (s,
1H), 8.89–8.91 (m, 1H). 13C NMR (CDCl3) dZ14.1, 122.3,
122.7 (s), 123.4, 125.1 (s), 125.3, 126.0, 126.1, 127.0, 127.1,
127.3, 127.4, 127.5, 127.6, 129.0, 129.1, 131.3 (s), 131.9 (s),
132.6, 132.8 (s), 133.6 (s), 138.4 (s), 138.7 (s), 140.4 (s),
141.5 (s), 147.8 (s). FAB(C) m/z (I%): 370 (MCC1, 100).
IR (nujol) n cmK1: 1557, 1543, 1509, 1157, 1074, 1027,
958, 869, 835, 792, 754, 738, 698, 681. Anal. Calcd for
C28H19N: C, 91.02; H, 5.18; N, 3.80. Found: C, 90.81; H,
5.29; N, 3.88.
4.8.1. 7-Methyl-13-phenyl-7,7a,8,14-tetrahydrodi-
benz[b,h]acridine (8b). Yield 14%. Mixture of two
diastereoisomers (1:1). H NMR (CDCl3) dZ1.26 (d, 3H,
1
JZ7.0 Hz), 1.57 (d, 3H, JZ6.1 Hz), 2.76 (dd, 1H, JZ15.2,
6.6 Hz), 2.97–3.09 (m, 4H), 3.18–3.21 (m, 1H), 3.30 (t, 1H,
JZ15.2 Hz), 3.44–3.52 (m, 1H), 6.51 (dd, 1H, JZ7.6,
1.4 Hz), 6.56 (dd, 1H, JZ7.6, 1.2 Hz), 6.77 (s, 1H), 6.88 (s,
1H), 6.90–7.01 (m, 3H), 7.07–7.13 (m, 4H), 7.16–7.49 (M,
15H), 7.60 (t, 4H, JZ7.1 Hz), 7.70–7.72 (m, 2H). 13C NMR
(CDCl3) dZ15.6, 16.5, 31.5, 34.4, 35.0, 35.3, 37.9, 41.1,
110.2 (s), 111.4 (s), 118.5, 118.6, 118.8, 119.1, 120.6 (s),
121.3 (s), 121.7 (s), 122.7, 122.8, 123.4, 123.6, 123.7, 123.8
(s), 125.2, 125.3, 125.4, 126.5, 126.6, 126.8, 127.0, 127.1,
127.2, 127.7, 128.6, 128.8, 129.9, 131.4, 131.5 (s), 132.0 (s),
132.2 (s), 133.1 (s), 133.3 (s), 133.4 (s), 136.5 (s), 137.0 (s),
137.1 (s), 137.5 (s), 137.9 (s), 138.0 (s). MS m/z (I%): 373
(MC, 100). IR (nujol) n cmK1: 3436, 1620, 1594, 1564,
1296, 1275, 1210, 1191, 1109, 1041, 942, 926, 858, 804,
759, 743, 708. Anal. Calcd for C28H23N: C, 90.04; H, 6.21;
N, 3.75. Found: C, 89.85; H, 6.29; N, 3.86.
Acknowledgements
This work was supported by the MCYT and FEDER
´
(Project BQU2001-0010) and Fundacion Seneca-CARM
(Project 00458/PI/04). One of us (M.-M. O.) thanks
´
´
Fundacion Cajamurcia for a fellowship.
4.8.2. 4-Methyl-3-(2,2-diphenylethyl)benzo[h]quinoline
(13). Yield 17%; mp 197–198 8C; colorless prisms (diethyl
ether). 1H NMR (CDCl3) dZ2.46 (s, 3H), 3.61 (d, 2H, JZ
7.7 Hz), 4.27 (t, 1H, JZ7.7 Hz), 7.17–7.27 (m, 10H), 7.62–
7.72 (m, 2H), 7.79 (d, 1H, JZ9.1 Hz), 7.85–7.89 (m, 2H),
8.49 (s, 1H), 9.19–9.23 (m, 1H). 13C NMR (CDCl3) dZ
14.3, 37.6, 52.7, 121.6, 124.6, 125.5 (s), 126.6, 127.0, 127.3,
127.6, 127.8, 128.1, 128.6, 131.8 (s), 131.9 (s), 132.9 (s),
141.7 (s), 143.9 (s), 144.6 (s), 150.7. MS m/z (I%): 373
(MC, 16), 167 (100). IR (nujol) n cmK1: 1600, 1577, 1518,
1495, 1338, 827, 799, 753, 743, 727, 704. Anal. Calcd for
C28H23N: C, 90.04; H, 6.21; N, 3.75. Found: C, 89.84; H,
6.29; N, 3.85.
References and notes
1. (a) Carruthers, W. Cycloaddition Reactions in Organic
Synthesis; Pergamon: Oxford, 1990. (b) Fringuelli, F.;
Taticchi, A. Dienes in the Diels–Alder Reaction; Wiley-
Interscience: New York, 1990. (c) Oppolzer, W. In Trost,
B. M., Fleming, I., Eds.; Comprehensive Organic Synthesis;
Pergamon: Oxford, 1991; Vol. 5, pp 315–399. (d) Brocksom,
T. J.; Nakamura, J.; Ferreira, M. L.; Brocksom, U. J. Braz.
Chem. Soc. 2001, 12, 597–622.
2. (a) Evans, D. A.; Johnson, J. S. In Jacobsen, E. N., Pfaltz, A.,
Yamamoto, H., Eds.; Comprehensive Asymmetric Catalysis;
4.9. Preparation of 13-phenyldibenz[b,h]acridines 14
´
Springer: Berlın, 1999; Vol. 3, pp 1177–1235. (b) Oppolzer,
W. Angew. Chem., Int. Ed. Engl. 1984, 23, 876–889. (c) Corey,
E. J. Angew. Chem., Int. Ed. 2002, 41, 1650–1667.
To a solution of the corresponding 7,7a,8,14-tetrahydrodi-
benz[b,h]acridine 8 (150 mg) in ortho-xylene (5 ml) Pd/C
(75 mg) was added, and the reaction mixture was heated at
reflux temperature for 3 h. The hot solution was filtered over
a short path of Celite, which was further washed with
toluene (3!5 ml). The solvent was removed under reduced
pressure an the resulting red solid was purified by column
chromatography [silica gel; hexanes/diethyl ether (10:1, v/v)].
3. Nicolaou, K. C.; Snyder, S. A.; Montagnon, T.; Vassiliko-
ginnakis, G. Angew. Chem., Int. Ed. 2002, 41, 1668–1698.
4. (a) Boger, D. L.; Weinreb, S. M. Hetero Diels–Alder
Methodology in Organic Synthesis; Academic: San Diego,
1987. (b) Weinreb, S. M. In Trost, B. M., Fleming, I., Eds.;
Comprehensive Organic Synthesis; Pergamon: Oxford, 1991;
Vol. 5, pp 401–449. (c) Boger, D. L. In Trost, B. M., Fleming,
I., Eds.; Comprehensive Organic Synthesis; Pergamon:
Oxford, 1991; Vol. 5, pp 451–512. (d) Boger, D. L.
Tetrahedron 1983, 39, 2869–2939. (e) Sakamoto, M.;
4.9.1. 13-Phenyldibenz[b,h]acridine (14a). Yield 97%; mp
202–203 8C; red prisms (diethyl ether). H NMR (CDCl3)
1

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M. Alajarın et al. / Tetrahedron 61 (2005) 7613–7621
7621
Kawasaki, T.; Ishii, K.; Tamura, O. Yakugaku Zasshi 2003,
123, 717–759.
Hill, M. S. J. Am. Chem. Soc. 2005, 127, 2042–2043. For
examples of transition-metal complex-catalyzed cyclization of
aminoalquenes see: (c) Hegedus, L. S. In Trost, B. M.,
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