Synthesis and Structure of 7-Methyl-2-(4′-methyl-2′,3′-dihydro-1′H-inden-1′- yl)-1H-indene

Article abstract of DOI:10.1039/a708862k

We report research to find better conditions for the dehydration of 4-methylindan-1-ol to render 4-methylindene and 7-methyl-2-(4′-methyl-2′,3′-dihydro-1′H-inden-1′- yl)-1H-indene.

Full text of DOI:10.1039/a708862k

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6
06 J. CHEM. RESEARCH (S), 1998
J. Chem. Research (S),
Synthesis and Structure of 7-Methyl-2-(4'-methyl-
',3'-dihydro-1'H-inden-1'-yl)-1H-indene$
Albertina G. Moglioni, Dora G. Tombari and
1998, 606±607$
2
Graciela Y. Moltrasio Iglesias*
Departamento de QuõÂ
Universidad de Buenos Aires, Junõ
mica Orga
Â
nica, Facultad de Farmacia y Bioqu õÂ mica,
n 956, (1113), Buenos Aires, Argentina
Â
We report research to find better conditions for the dehydration of 4-methylindan-1-ol to render 4-methylindene and
-methyl-2-(4'-methyl-2',3'-dihydro-1'H-inden-1'-yl)-1H-indene.
7
A suitable starting material for the preparation of several
1
pterosines is the 4-methylindene 1. We have previously
reported the synthesis of 5,6-dimethoxyindene from 5,6-
dimethoxyindan-1-ol with thionyl chloride in benzene at
2
0
8C, so the same reaction was performed with 4-methyl-
indan-1-ol 2, but the reactions products were a complex
mixture from which a compound of molecular weight 260
was isolated. Bearing in mind that a dimeric compound had
been obtained when 5,6-dimethoxyindan-1-ol was treated
2
with toluene-p-sulfonic chloride or mesityl chloride,
and comparing MS and NMR spectra, the structure of
7
3
-methyl-2-(4'-methyl-2',3'-dihydro-1'H-inden-1'-yl)-1H-indene
w
was assigned tentatively to the compound of M 260.
Fig. 1 *Interchangeable
The formation of such a product was rationalized within
the framework of the previously proposed mechanism for
similar compounds (see Scheme 1).
But, taking into account that the benzylic carbocations
involved in the reaction could be transposed, several other
isomers are possible (e.g. 4±7).
respectively. With these techniques were elucidated the
connectivity of the carbon atoms to which the protons
were attached. The HH NOESY experiment showed the
proximity of the two methyl-H atoms (at d 2.31 and 2.33)
to the benzylic methylene protons. This con®rmed the
substitution system of 3. The position of the double
bond was also evaluated with an HH NOESY experiment.
The lack of spatial connectivity between the ole®nic
proton and the benzylic methylene H-atom let us rule out
isomer 7.
3
Structure 3 was con®rmed by employing 2D NMR
1
1
1
13
techniques (Fig. 1). The H± H and H± C correlation
spectra were measured using COSY and HSQC procedures
Smooth conditions have been described for the dehy-
5
4
dration of indan-1-ols. In 1963, Elvidge and Foster,
suggested the preparation of indenes from the reaction of
indan-1-ols with a few crystals of toluene-p-sulfonic acid
(
PTSA). However, when we repeated the procedure only the
6
dimeric product 3 was obtained. In 1977, Woodward et al.
quanti®ed the amount of PTSA for several tetrasubstituted
indan-1-ols, but when we employed their conditions with the
4-methylindan-1-ol 2, the alcohol was recovered without
modi®cation.
Scheme 1
*To receive any correspondence.
$This is a Short Paper as de®ned in the Instructions for Authors,
Section 5.0 [see J. Chem. Research (S), 1998, Issue 1]; there is there-
fore no corresponding material in J. Chem. Research (M).

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J. CHEM. RESEARCH (S), 1998 607
Table 1
a
Experiment
M (PTSA)/mg
Benzene/ml
Reflux time
Products (%)
1
2
3
4
5
6
7
30
20
4
4
4
75
75
10 min
10 min
10 min
100 min
150 min
180 min
24 h
Polymers
3 (35), 2 (25), 1 (14)
2 (100)
2 (40), 3 (40)
1 (60)
1 (80)
100
100
200
100
100
10
100
3 (90)
a
For each reaction 1 g of 4-methylindan-1-ol was used.
We now report research to ®nd better conditions under
which the yields of the dimeric compound and the indene
could be maximized and Table 1 summarizes our results.
We express our sincere gratitude to Dr Teodor Parella
from Universitat Autonoma de Barcelona, Spain, for the
NMR spectra. This work is part of a Research Project sup-
ported by the CONICET and SECYT (UBA).
Experimental
Melting points are uncorrected, and were determined on
a
Received, 9th December 1997; Accepted, 1st June 1998
Paper E/7/08862K
1
13
Thomas Hoover apparatus. H NMR and C NMR were recorded
on a Bruker AC400 spectrometer. The mass spectrum was recorded
on a Varian CH7A. Satisfactory microanalysis was obtained for
compound 3.
References
4-Methylindene 1.Ð4-methylindan-1-ol (1 g), PTSA (10 mg) and
benzene (100 ml) were heated at re¯ux for 180 min. Benzene was
1 (a) D. G. Tombari, A. G. Moglioni and G. Y. Moltrasio Iglesias,
Org. Prep. Proc. Int., 1995, 27, 679; (b) A. G. Moglioni and G. Y.
Moltrasio Iglesias, An. Asoc. Quim. Argent., 1997, 85, 77.
2 (a) W. Huckel, M. Sachs, J. Yantschulewitsch and F. Nerdel,
Liebigs. Ann. Chem., 1935, 518, 155. (b) Z. Gorin, M. J. Heeg
and S. Mobashery, J. Org. Chem., 1991, 56, 7186. (c) D. G.
Tombari, A. G. Moglioni and G. Y. Moltrasio Iglesias, An.
Quim. de la Real Sociedad EspanÄula de QuimõÂca., 1992, 88, 722.
3 (a) W. E. Noland, L. L. Landucci and J. C. Darling, J. Org.
Chem., 1979, 44, 1358; (b) B. R. Davies, S. J. Johnson and P. D.
Woodgate, J. Chem. Soc., Perkin Trans. 1, 1985, 2545.
4 (a) M. Braun and C. Bernard, Liebigs. Ann. Chem., 1985, 435;
(b) F. McCapra, P. D. Leeson, V. Donovan and G. Perry,
Tetrahedron, 1986, 42, 3223.
then distilled o€ (30 8C, 30 mmHg) and the residual product was
5
isolated by distillation in vacuo (64±66 8C, 2 mmHg, lit., 88 8C,
1
3 mmHg).
(CDCl
br d, J1,2 5.60, HC-2); 7.00±7.60 (4 H, m, HC-1 and ArH). d
CDCl ) 18.4; 37.7; 118.5; 125.6; 126.4; 132.6; 133.4; 142.1; 144.3.
-Methyl-2-(4'-methyl-2',3'-dihydro-1'H-inden-1'-yl)-1H-indene 3.Ð
To a solution of 4-methylindan-1-ol (1 g, 6.75 mmol) in benzene
100 ml), PTSA (100 mg) was added. The solution was stirred at
re¯ux for 24 h, then washed with 5% aqueous NaHCO
(2Â 30 ml)
SO ) and evaporated to dryness.
d
H
3 3
) 2.50 (3 H, s, CH ); 3.40 (2 H, br s, HC-3); 6.65 (1 H,
C
(
3
7
(
3
and water (2Â30 ml), dried (Na
2
4
The residue was puri®ed by ¯ash chromatography (hexane:ethyl
acetate, 4:1) to give 790 mg (yield 90%). Mp (ethanol) 98±99 8C.
5 (a) J. A. Elvidge and R. G. Foster, J. Chem. Soc., 1963, 590;
(b) 1964, 981.
6 R. B. Woodward and T. R. Hoye, J. Am. Chem. Soc., 1977, 99,
8007.
�
1
‡
ꢀ
/cm (neat): 2900, 1580 and 1450. MS, EI 261 (M ‡1, 11.4); 260
‡
(M , 50.5); 259 (2.0), 131 (100) (Found: C, 92.40; H, 7.91. C20
requires C, 92.26; H, 7.74%).
H
20