Indane dimerization products obtained by treatment of N-acylindan-1-amines with ethyl polyphosphate (EPP)

Article abstract of DOI:10.1039/a804707c

This report describes the diverse dimeric products obtained by treatment of N-acylindan-1-amines with ethyl polyphosphate in chloroform-diethyl ether solution at 80°C for 8 h. Possible mechanisms for such reactions are discussed.

Full text of DOI:10.1039/a804707c

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Indane dimerization products obtained by treatment of
N-acylindan-1-amines with ethyl polyphosphate (EPP)
Albertina G. Moglioni, Dora G. Tombari and Graciela Y. Moltrasio Iglesias*
Department of Organic Chemistry, Faculty of Pharmacy and Biochemistry,
University of Buenos Aires, Buenos Aires, Argentina
Received (in Cambridge) 22nd June 1998, Accepted 20th August 1998
This report describes the diverse dimeric products obtained by treatment of N-acylindan-1-amines with ethyl
polyphosphate in chloroform–diethyl ether solution at 80 ЊC for 8 h. Possible mechanisms for such reactions
are discussed.
Given the difficulties previously encountered on attempting to
synthesize 5,6-dimethoxyindane-1-carbonitrile 11 and bearing
in mind that several diarylacetonitriles were successfully pre-
pared from N-formyl(diaryl)methylamines 2 and ethyl poly-
phosphate (EPP),2 the same reagent and identical conditions
were employed with N-formyl-5,6-dimethoxyindan-1-amine 3a,
intermediate in the Bischler–Napieralski synthesis and retro-
Ritter amide degradation reaction.4
MW = 232
R
R
H3CO
H3CO
4b
4a
CN
NHCHO
1
2
which was prepared from 5,6-dimethoxyindan-1-one. The reac-
tion product isolated on treating the amide 3a with EPP for 8 h
at 80 ЊC had a molecular weight (MW) of 354 and its spectro-
scopic features showed that the indane structure had apparently
undergone dimerization (Scheme 1). The structure of the
4c
4d
MW = 234
R1
R1
6
5
NHCOR
R
3
3a R1 = OCH3, R = H
3b R1 = OCH3, R = Ph
MW = 354
R
MW = 354 and
benzonitrile
MW = 232 and
benzonitrile
3c R1 = H, R = Ph
7a R = H
7b R = OCH3
R
R
Scheme 1
The above dimers could be structurally similar to the estro-
genic, artificial hormones hexestrol and diethylstilbestrol,5
hence the importance of knowing with certainty the structures
of these dimers. Such dimers have been known for several
years and in the literature there are numerous relevant articles;6
however, there are serious discrepancies when attempting to
product of MW 354 was tentatively assigned to 5,5Ј,6,6Ј-
tetramethoxy-2,2Ј,3,3Ј-tetrahydro-1,2Ј-bi-1H-indenyl 7b.
This result prompted us to determine how the nitrogen group
had been eliminated. For this purpose amide 3b was prepared
and treated with EPP under identical conditions to render, in
addition to the 354 MW compound, benzonitrile. In an attempt
to explain whether the observed behaviour of amides 3
depended on the presence of methoxy groups in the aromatic
ring, the EPP reaction was tested on amide 3c, obtained by
direct benzoylation of indan-1-amine. When 3c was treated
with EPP according to the general method, a 232 MW oil and
benzonitrile were obtained. The product of MW 232 was tenta-
tively assigned structure 4a by comparison with data found in
the literature3 of similar compounds, as well as by its NMR
1
correlate their structures with H NMR spectroscopic data;7
furthermore, there are practically no 13C NMR data available.
For the 232 MW compound, with a single olefinic hydrogen
there are four possible isomers (4a, b, c and d). On hydrogen-
ation of the double bond the number decreases to three (5, 6 as
meso and/or racemic forms, and 7a). Through which carbon
atoms indane units are linked and what position is occupied by
the double bond are problems which must be solved to deter-
mine the structure of these dimers. Our first efforts were dir-
ected to determine which carbon atoms were involved in the
linkage of the indane units. For this purpose, the 232 MW
compound was catalytically hydrogenated, to render the 234
MW compound. The 13C NMR spectrum showed six aliphatic
carbons, which allowed the possibility of the C-2–C-2Ј isomer 5
1
spectroscopy data. The H NMR spectrum showed a single
vinylic proton, methine triplet and six methylene protons.
The presence of benzonitrile would support the conclusion that
the production of 4a and 7b dimers would take place via a
“nitrilium” ion. Such ions are the most commonly invoked
J. Chem. Soc., Perkin Trans. 1, 1998, 3459–3462
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Table 1 13C NMR Chemical shifts for compounds 4a, 6, 7a, 7b and 10
C-1
47.5
49.4
C-2
26.6
29.6
C-3
31.5
31.2
C-1Ј or C-3Ј
C-2Ј
C-3Ј or C-1Ј
OCH3
Aromatic carbons
6
123.8 124.3 125.8
126.2 144.5 145.7
124.2 124.4 125.8
126.0 126.3 143.1
143.4 144.3 146.3
107.7 134.7 134.9
136.0 138.0 147.7
147.8 148.0
7a
36.8
36.6
43.7
44.2
37.8
37.7
—
7b
49.4
29.8
31.1
55.9
C-1
C-1Ј
C-2Ј
C-3Ј
OCH3
Aromatic and alkenic carbons
4a
38.5
47.2
31.6
33.6
120.0 123.4 123.8
124.4 124.5 126.2
126.5 127.1 143.2
143.7 145.0 145.6
152.2
10
38.3
47.1
31.4
34.1
55.8
56.1
104.0 107.5 107.6
108.2 126.4 135.2
135.4 137.3 137.7
146.4 147.9 148.1
151.4
to be ruled out at once. Therefore, the syntheses of the other
two possible dimerization products, namely 2,2Ј,3,3Ј-
tetrahydro-1,1Ј-bi-1H-indenyl 6 and 2,2Ј,3,3Ј-tetrahydro-1,2Ј-
bi-1H-indenyl 7a, were carried out according to Scheme 2.
H+
EPP
H
–PhCN
+
HN COPh
H
TiCl3
O
AlCl3
Li
heat
+
H+
R
R
4a
Scheme 3
O
E
Z or E
9a R = H
molecule would generate an indanyl carbocation (Scheme 3),
which would then lose a proton to yield the indene.3 In turn,
this indene would attack through C-2 position another
molecule of carbocation to yield the more stabilized carbo-
cation intermediate. According to the proposed mechanism and
taking into account the stability of the probable carbocation,
the production of compound 4a is reasonable. As a further
confirmation of the structure, the methylene hydrogen atoms of
the indene unit in isomer 4a are diastereotopic. The fact that
9b R = OCH3
R
R
8
Zn-Hg
HCl
H2, Pd-C 5%
R
R
1
these hydrogen atoms are present in H NMR as two doublets
racemic
with J 19 Hz and the presence of four aliphatic atoms in the 13
NMR seems to confirm the structure of 4a.
C
R
R
6
7a R = H
7b R = OCH3
racemic (1RS,1′RS)
The demonstration of the structure of the dimer 7b was
made through the synthesis of this compound (Scheme 2).
Clemmensen reduction of 9b yielded two products, one of 354
MW and another of 352 MW. By spectroscopic comparison of
the latter with 4a, it was assigned structure 10. In addition on
catalytic hydrogenation of 10, compound 7b was obtained.
Finally the spectroscopic data of 7b are coincident with those
of the compound obtained by treatment of 3a and 3b with EPP.
The mechanism outlined in Scheme 3 strongly supports
the presence of compound 4a, and eventually 10, but fails to
Scheme 2
The racemic (1RS,1ЈRS) dimer 6 was successfully prepared
8
by treating indan-1-one with Li–TiCl3 to obtain 8 as the E
isomer;6 catalytic reduction of 8 rendered 6 in 85% yield as a
racemic mixture. The 13C NMR spectrum of 6 failed to coincide
with that of the 234 MW compound. It was then decided not to
synthesize the meso (1R,1ЈS) isomer but to start by synthesizing
compound 7a. This compound was prepared by treatment of
indan-1-one with AlCl3 to afford 9a.9,10 Clemmensen reduction
of 9a rendered 7a in 40% yield. The H and 13C NMR spectra
1
OCH3
(Table 1) of compound 7a allowed the 1,2Ј-biindanyl structure
to be assigned to the product of MW 234.
To assign the position of the double bond, both mechanistic
considerations and spectroscopic observations were taken into
account. As already mentioned, “nitrilium” ions seem to be
invariable intermediates in these reactions.4c The loss of a nitrile
OCH3
10
H3CO
OCH3
3460
J. Chem. Soc., Perkin Trans. 1, 1998, 3459–3462

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explain how the structure 7b was obtained, because production
of this compound would involve a reductive process.
stirred for 1 h. The resulting amine was extracted with chloro-
form. Evaporation of the solvent afforded the crude amine
which was converted into the appropriate N-acyl-derivative
without purification.
The reduction potentials of dimers 10 and 4a were analysed
by cyclic voltammetry (potentials from 0 to Ϫ2000 mV) to
find, as expected, that it proved easier to reduce the non-
methoxylated than the methoxylated compound.11 Similar
results were recorded in the cyclic voltammetry of N-benzoyl-
5,6-dimethoxyindan-1-amine 3b and N-benzoylindan-1-amine
3c. It could thus be concluded that if dimerization of N-formyl-
3a or N-benzoyl-5,6-dimethoxyindan-1-amine 3b takes place
by a mechanism similar to that of N-benzoylindan-1-amine
3c, then subsequent reduction should not occur as a redox
reaction.
N-Formyl-5,6-dimethoxyindan-1-amine (3a)
To a cold solution of acetic formic anhydride (obtained from
acetic anhydride (20 ml) and formic acid (10 ml) heated for 2 h)
was added, dropwise and with stirring, 5,6-dimethoxyindan-1-
amine (900 mg, 4.66 mmol) at such a rate that the temperature
never rose above 40 ЊC. After stirring for 30 min, ether was
added and the solution was stirred at room temperature
overnight. The reaction mixture was diluted with ether, washed
with water, saturated aqueous NaCO3H, aqueous HCl (5%),
and finally with water. The organic layer was dried (MgSO4),
filtered, and concentrated in vacuo to give 3a (630 mg, 2.85
mmol, 55% from 5,6-dimethoxyindan-1-one) as a solid. Mp:
106–108 ЊC (from ethanol–water) (Found: C, 65.28; H, 6.67;
N, 6.30. C12H15NO3 requires C, 65.14; H, 6.83; N, 6.33%);
νmax (neat)/cmϪ1: 3285 (NH), 2900 and 2820 (formyl group),
1640 (CO); δH: 1.60–1.90 (1H, m), 2.30–2.50 (1H, m), 2.60–2.90
(2H, m), 3.80 (6H, s, OCH3), 5.40 (1H, m), 6.25 (1H, br s, NH),
6.70 (2H, s, Ar), 8.20 (1H, br s, CHO).
A search of the literature showed that one non-catalytic
method for the reduction of alkenes, carbonyls, imines, alcohols
and halogen derivatives to alkanes is the so-called “ionic hydro-
genation” method.12 Such hydrogenation involves the form-
ation of a carbocation by protonation of a double bond or by
heterolysis of a C–X bond that reacts with a hydride donor to
form the hydrogenated product. Reagent pairs of trifluoroacetic
acid and an organosilane have proven to be the best though not
the only ones available. Thus, “ionic hydrogenation” may also
be carried out with phosphoric acid, polyphosphoric acid
and alkyl- and aryl-sulfonic acids, as well as other acids, as
proton donors, while cycloheptatriene, xanthene, adamantene,
aliphatic and aromatic hydrocarbons, alcohols and other com-
pounds have been employed as hydride donors. Considering the
controversial structure of EPP and taking into account the fact
that in these cases the reagent is generated in situ starting from
phosphorus pentoxide and diethyl ether–chloroform as solvent,
it could be that the more stable carbocation (MW 353, Scheme
2) favours the action of some of these components as hydride
donors, which could explain the observed result. It is not pos-
sible to eliminate the same substrate–product system as hydride
donor. Experimentally, it has been observed that the “ionic
hydrogenation” acts selectively on the double bond of several
2-benzylidene-1,3-dioxoindanes.11 However, even though we
have demonstrated that N-acyl-5,6-dimethoxyindan-1-amines
3a and b are deamidated, the formation of indene and the
corresponding carbocation fails to explain why the reduced
compound 7b is obtained. In other words, the formation
mechanism of this compound of MW 354 remains unclear.
N-Benzoyl-5,6-dimethoxyindan-1-amine (3b)
The corresponding amine (900 mg, 4.66 mmol) was treated with
benzoyl chloride (0.9 ml, 7.7 mmol) in dry benzene (1.5 ml) and
pyridine (2.5 ml) to give 3b (926 mg, 3.12 mmol, 60% from 5,6-
dimethoxyindan-1-one) as a solid. Mp: 142–143 ЊC (from
ethanol) (Found: C, 72.46; H, 6.62; N, 4.73. C19H20NO3 requires
C, 72.71; H, 6.44; N, 4.71%); νmax (neat)/cmϪ1: 3285 (NH), 1620
(CO); δH: 1.70–2.10 (1H, m), 2.30–2.80 (3H, m), 3.70 (3H, s,
OCH3), 3.80 (3H, s, OCH3), 5.50 (1H, m), 6.45 (1H, br s, NH),
6.60 (1H, s, ArH), 6.80 (1H, s, ArH), 7.20–7.40 (3H, m, ArH),
7.60–7.80 (2H, m, ArH).
N-Benzoylindan-1-amine (3c)
Indan-1-amine (620 mg, 4.66 mmol) was treated following the
above mentioned procedure for 3b to render the N-benzoyl
derivative 3c (860 mg, 3.66 mmol, 70% from indan-1-one) as a
solid. Mp: 135–136 ЊC (ethanol) (lit.,14 140–141 ЊC); νmax (neat)/
cmϪ1: 3250 (NH), 1620 (CO); δH: 1.80–2.10 (1H, m), 2.50–3.10
(3H, m), 5.60 (1H, m), 6.20 (1H, br s, NH), 7.10–7.50 (3H, m,
ArH), 7.60–7.80 (2H, m, ArH).
Experimental
General
Infrared spectra were recorded on a Jasco A200 spectrometer as
mulls or neat. The 1H NMR spectra were recorded on a Bruker
AC 200 or Bruker MSL 300 spectrometer using deuteriochloro-
form. Chemical shifts are reported in ppm units, and coupling
constants (J) are in Hz. The mass spectra were obtained on VG-
ZAB spectrometer. Melting points (uncorrected) were obtained
on a Thomas Hoover apparatus. The cyclovoltammetry experi-
ments were performed on a TEQ-V1.00 apparatus using
glassy carbon and platinum wire as working electrodes, and
calomel as reference electrode; support electrolyte: lithium
perchlorate 0.1 M; solvent: acetonitrile. Merck silica gel 60
PF254 was used for preparative thin-layer chromatography
(PTLC). Ethyl polyphosphate (EPP) was prepared by the
method of Pollman and Schramm.13 Solvents and reagents were
purified using standard procedures.
Treatment of amides (3a, b and c) with EPP
The amide (1 mmol) was heated with a solution of EPP in
CHCl3–ether (2.64 g EPP, concentration: 0.547 g mlϪ1) at 80 ЊC
for 8 h. The solvent was evaporated and the residue was treated
with ice–water and then extracted with CH2Cl2 (3 × 30 ml), the
extract was washed with 5% aqueous NaCO3H (2 × 40 ml) and
water, dried over MgSO4, filtered, concentrated in vacuo and
separated by PTLC.
5,5Ј,6,6Ј-Tetramethoxy-2,2Ј,3,3Ј-tetrahydro-1,2Ј-bi-1H-
indenyl (7b). The title compound was obtained from 3a with
EPP, and was separated by PTLC (eluted with benzene). The
upper band afforded 7b (35 mg, 20%) as an oil. In the case of
3b, the residue was chromatographed on a column of silica gel
60 (35–70 mesh, ASTM), elution with benzene gave the benzo-
nitrile, and elution with CH2CI2 gave 7b (50 mg, 30%) as an
oil (Found: C, 74.36; H, 7.29. C22H26O4 requires C, 74.55; H,
7.39%); δH: 1.85 (1H, m, H-2), 2.25 (1H, m, H-2), 2.60–3.00
(6H, m, Ar-CH2), 3.10 (1H, m, H-2Ј), 3.30 (1H, m, H-1), 3.85,
3.90, 3.95 (12H, s, OCH3), 6.70, 6.75, 6.77, 6.80 (4H, s, ArH);
δC: see Table 1; m/z 354 (Mϩ, 25.3%), 178 (17.9), 177 (100.0),
176 (6.9).
1-Aminoindanes
A solution of the appropriate indan-1-one (5.2 mmol), and
hydroxylamine hydrochloride (1 g, 14.5 mmol) in 30% aqueous
sodium hydroxide (10 ml), and ethanol (20 ml) was boiled
under reflux for 20 min, cooled, and diluted with water (10 ml).
Raney nickel (1.5 g) was added in ethanol (20 ml) and aqueous
sodium hydroxide (20 ml; 2 M). The mixture was magnetically
Compound 7b was obtained in a yield of 80% by catalytic
J. Chem. Soc., Perkin Trans. 1, 1998, 3459–3462
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reduction of 10 (100 mg) with Pd–C 10% (250 mg) at 55 psi, for
24 h. This compound was also obtained by the Clemmensen
reduction (see below).
tion of 9a and was isolated from the upper band of the PTLC
as a colourless oil (140 mg, 40%) (Found: C, 92.40; H, 7.80.
C18H18 requires C, 92.26; H, 7.74%); δH: 1.90 (1H, m, H-2), 2.20
(1H, m, H-2), 2.70–3.10 (6H, m, Ar-CH2), 3.15 (1H, m, H-2Ј),
3.35 (1H, m, H-1), 7.10–7.40 (8H, m, ArH); δC: see Table 1; m/z
234 (Mϩ, 21.7%), 118 (34. 4), 117 (100.0), 116 (36.1).
2-(2Ј,3Ј-Dihydro-1ЈH-inden-1Ј-yl)-1H-indene (4a). The title
compound was obtained from 3c and EPP, and was separated
by PTLC and eluted with hexane to give 4a3 (87 mg, 75%) as an
oil; δH: 2.10 (1H, m, H-2Ј), 2.50 (1H, m, H-2Ј), 3.05 (2H, m,
H-3Ј), 3.28 (1H, d, J 19, H-1); 3.38 (1H, d, J 19, H-1), 4.34 (1H,
t, J 7.89, H-1Ј), 6.70 (1H, br s, H-3), 7.10–7.40 (8H, m, ArH);
δC: see Table 1; m/z 232 (Mϩ, 34.2%), 217 (13.0), 215 (14.2), 118
(11.2), 117 (100.0), 116 (11.8).
Compound 7a was also obtained by catalytic reduction of 4a
using Pd/C (10%), during 24 h at 55 psi (80% yield).
5,5Ј,6,6Ј-Tetramethoxy-2,2Ј,3,3Ј-tetrahydro-1,2Ј-bi-1H-
indenyl (7b). The title compound was obtained by the Clem-
mensen reduction of 9b and was isolated from the upper band
of the PLTC as an oil (210 mg, 40%) and compound 10 was
isolated from the lower band as crystals (100 mg, 18%). Data
for compound 10: mp: 113–114 ЊC (ethanol) (lit.,16 113–114 ЊC);
δH 2.05 (1H, m, H-2Ј), 2.80–3.05 (1H, m, H-2Ј), 2.90 (2H, m, H-
3Ј), 3.20 (1H, d, J 19, H-1), 3.30 (1H, d, J 19, H-1), 4.25 (1H, t,
J 7.9, H-1Ј), 3.75, 3.80, 3.90, 3.95 (12H, s, OCH3), 6.53 (1H, br
s), 6.65 (1H, s), 6.80 (1H, s), 6.90 (1H, s), 7.00 (1H, s); δC: see
Table 1, m/z 352 (Mϩ, 100%), 321 (22.7), 178 (14.1), 177 (96.7),
176 (16.2).
(E)-2,2Ј,3,3Ј-Tetrahydro-1,1Ј-bi-1H-indenylidene (8)6
Lithium wire (0.5 g, 72.46 mmol) and TiCl3 (3.7 g, 24 mmol)
were slurried in 40 ml of dry 1,2-dimethoxyethane (DME)
under a nitrogen atmosphere, then the mixture was refluxed for
1 h and after cooling, a solution of indan-1-one (0.7 g, 5.3
mmol) in DME (3 ml) was added. After an additional 16 h at
reflux, the reaction mixture was cooled to room temperature,
diluted with petroleum ether, and filtered through a small pad
of Florisil on a sintered glass filter. The filtrate was concen-
trated in vacuo to yield the crude product 8 (406 mg, 66%) as a
solid. Mp: 138–139 ЊC (methanol) (lit.,6 140–141 ЊC); δH: 3.20
(8H, s), 7.10–7.40 (6H, m, ArH), 7.50–7.70 (2H, m, ArH).
The catalytic reduction of 10 using Pd/C (10%), for 24 h at
55 psi gave 7b (90% yield).
Acknowledgements
rac-2,2Ј,3,3Ј-Tetrahydro-1,1Ј-bi-1H-indenyl (6)
We are grateful to the CONICET and SECYT (UBA) for
financial support of this study. The authors wish to thank
Dr Irene Rezzano and the Biochemistry Viviana Campo for the
cyclic voltammetry experiments.
A mixture of 8 (140 mg, 0.6 mmol), heptane (40 ml), and Pd–C
5% (220 mg) was stirred with hydrogen under 57 psi at room
temperature for 24 h. The filtered solution was evaporated in
vacuo to yield 6 (120 mg, 85%) as an oil.6 δH: 1.60–2.20 (4H, m,
H-2), 3.00 (4H, br t, J 8, H-3), 3.80–4.10 (2H, m, H-1), 7.20
(8H, br s, ArH); δC: see Table 1, m/z 234 (Mϩ, 3.1%), 149 (27.1),
133 (36.6), 132 (39.4), 118 (20.3), 117 (100.0), 116 (46.4), 115
(49.3).
References
1 (a) D. G. Tombari, A. G. Moglioni, F. P Dominici and G. Y.
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General procedure for condensation of indan-1-ones
A few crystals of AlCl3 were added to melted indan-1-one
or 5,6-dimethoxyindan-1-one (500 mg), and the mixture was
heated for 15 min at a temperature 30 ЊC above the melting
temperature of the indanone. Then the residue was triturated
with cold water (20 ml) and the emulsion extracted with
CH2C12. The organic extract was washed with water and dried
over Na2SO4, and evaporated in vacuo to give 9a10 from indan-
1-one and 9b15 from 5,6-dimethoxyindan-1-one.
Compound 9a (290 mg, 65%) was obtained as yellow crystals.
Mp: 142–143 ЊC (from ethanol–ethyl acetate) (lit.,10 142–
143 ЊC); δH: 3.00–3.20 (2H, m), 3.50–3.70 (2H, m), 4.1 (2H, s),
7.30–7.60 (6H, m, ArH), 7.85 (2H, m, ArH).
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Compound 9b (300 mg, 65%) was obtained as orange
crystals. Mp: 142–143 ЊC (from benzene) (lit.,15 142–143 ЊC);
δH: 3.00 (2H, m), 3.50 (2H, m), 3.75 (2H, m), 3.80, 3.90, 4.00
(12H, s, OCH3), 6.60, 6.70, 7.20, 7.30 (4H, s, ArH).
7 (a) K. Suga, S. Watanabe and T. Fujita, Aust. J. Chem., 1972, 25,
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Clemmensen reduction of 9a and 9b
A mixture of zinc (8.3 g), HgCl2 (1.4 g), concentrated HCl
(0.6 ml), and water (14 ml) was stirred for 15 min at room
temperature. The aqueous solution was decanted, and the
amalgamated zinc was covered with ethanol (8.7 ml; 95%), and
concentrated HC1 (3.5 ml). The compound 9a or 9b (1.5 mmol)
was added, and the mixture was heated under reflux for 3 h, and
then water (15 ml) was added. The liquid phase was extracted
with CHCl3 (2 × 20 ml) and the combined organic extracts were
washed with water, dried over Na2SO4, filtered and concen-
trated in vacuo to give a residue which was chromatographed by
PTLC, and eluted with hexane–benzene (95:5).
2,2Ј,3,3Ј-Tetrahydro-1,2Ј-bi-1H-indenyl (7a)
The title compound was obtained by the Clemmensen reduc-
Paper 8/04707C
3462
J. Chem. Soc., Perkin Trans. 1, 1998, 3459–3462