K. Yu. Koltunov / Tetrahedron Letters 48 (2007) 5631–5634
5633
When activated in 15 M excess triflic acid, 1 smoothly
3. Typical procedure
3.1. 3,3-Diphenyl-1-indanone (4)
reacts with cyclohexane at room temperature to give 1-
indanone (7) in ꢂ90% yield in 40 h (Scheme 2). While
1 is inert towards cyclohexane in the heterogeneous
AlCl3–CH2Cl2 system, it reacted with cyclohexane in
the homogenous AlBr3–CH2Br2 system to give 7 in
84% yield (fourfold molar excess of AlBr3, 25 °C,
30 h). Also, 1 reacted with cyclohexane in the presence
of aluminum chloride at 80 °C without solvent to give
7 in ꢂ70% yield in 2 h.
To a solution of 1 (0.1 g, 0.7 mmol) in CF3SO3H (4 g,
26 mmol) was added benzene (1 mL). The resulting mix-
ture was stirred at 25 °C for 4 h followed by quenching
with several grams of ice and subsequent extraction with
CHCl3.17 The organic phase was washed with aqueous
NaHCO3 and then dried over anhydrous MgSO4. Con-
centration in vacuo provided pure (according to NMR
data) compound 4 (0.187 g, 96%), mp 128–130 °C (benz-
ene), lit.18 mp 128–130 °C. 1H NMR (CDCl3): d 3.51 (s,
2H), 7.15–7.35 (m, 10H), 7.37 (d, J = 7.7 Hz, 1H), 7.42
(td, J = 7.7, 1.3 Hz, 1H), 7.6 (t, J = 7.7 Hz, 1H), 7.82
(d, J = 7.7 Hz, 1H).18 13C NMR (CDCl3): d = 56.2,
56.3, 123.8, 126.7, 128.1, 128.2, 128.6, 134.9, 135.9,
146.9, 160.1, 205.1.18 GC–MS (M+): 284.
The probable mechanism of these reactions includes
involvement of dicationic species 3 (Table 1, Scheme
2), which is more electrophilic than isoelectronic dica-
tion 8, since phthalimide reacted more slowly with benz-
ene and cyclohexane.3 This however, may be related to
a lower stability (concentration in the reaction media) of
8, generated earlier in the extremely acidic HF(HSO3F)–
SbF5–SO2ClF systems at ꢁ80 °C.9 The enhanced reac-
tivity of 3 and 8 is in sharp contrast with the poor reac-
Analytical data of indanones 2, 5 and 7, isolated by sil-
ica gel column chromatography with benzene-acetone,
were analogous with those previously reported.5,7
tivity of closely-related dication
9 (derived from
diprotonation of 1,4-naphthalenediol), which is totally
inert towards benzene and cyclohexane.10 On the other
hand, compound 1 (like phthalimide)3 does not react
with o-dichlorobenzene, even when using a 100 M ex-
cess of triflic acid (25 °C) or a 10-fold molar excess of
AlBr3 (120 °C). This indicates the relatively moderate
reactivity of 3 in comparison with other dicationic spe-
cies, which are often reactive towards o-dichlorobenz-
ene.11
In summary, superacidic as well as HUSY-zeolite acti-
vation of 1 leads to superelectrophilic (dicationic) reac-
tivity towards weak nucleophiles, such as benzene and
cyclohexane.19 The reaction procedures using readily
available acids are simple and reproducible. When
HUSY is used, the necessity for excess of acidic sites is
required and, in accord with previous results,4 can be
interpreted in terms of key dicationic intermediates on
the solid.
+
+
OH
OH
NH
Acknowledgements
OH
+
OH
+
9
8
Students of Novosibirsk State University: I. Skobelev,
Z. Danzanov and K. Akhmetova are gratefully
acknowledged for their contribution in the experimental
work.
Furthermore, the analogous reactions of 1 with benzene
and cyclohexane have been carried out using HUSY
zeolite.12 In accordance with our previous observations,4
dicationic activation on this solid requires a large molar
excess of acidic sites.13 Thus, 1 reacted with benzene at
130 °C (pressure tube) to give a mixture of 4, 5 and bin-
done 2 in a 1:6:2 molar ratio after 6 h, providing ꢂ20 M
excess of acidic sites. When less HUSY was used, com-
pound 2 formed predominantly. 1,3-Indandione 1 reacts
more selectively with cyclohexane and HUSY. Indeed,
under similar conditions (20 M excess of acidic sites,
130 °C, 10 h) 1 underwent ionic reduction to give inda-
none 7 in 78% yield, while the mass balance was the
starting material 1 and traces of 2.
References and notes
1. (a) Olah, G. A. Angew. Chem., Int. Ed. Engl. 1993, 32,
767–788; (b) Nenajdenko, V. G.; Shevchenko, N. E.;
Balenkova, E. S.; Alabugin, I. V. Chem. Rev. 2003, 103,
229–282; (c) Olah, G. A.; Klumpp, D. A. Acc. Chem. Res.
2004, 37, 211–220.
2. Klumpp, D. A.; Fredrick, S.; Lau, S.; Jin, K. K.; Bau, R.;
Prakash, G. K. S.; Olah, G. A. J. Org. Chem. 1999, 64,
5152–5155, and references cited therein.
3. Koltunov, K. Yu.; Prakash, G. K. S.; Rasul, G.; Olah, G.
A. Eur. J. Org. Chem. 2006, 21, 4861–4866.
It seems that the HUSY framework provides sufficient
proximity of Lewis acidic sites (LAS) and/or proton acid
4. (a) Koltunov, K. Yu.; Walspurger, S.; Sommer, J. Chem.
Commun. 2004, 15, 1754–1755; (b) Koltunov, K. Yu.;
Walspurger, S.; Sommer, J. Tetrahedron Lett. 2005, 46,
8391–8394; (c) Koltunov, K. Yu.; Walspurger, S.; Som-
mer, J. J. Mol. Catal. A 2006, 245, 231–234.
5. The indanone motif can be found in natural products and
in synthetic compounds. Indanones have also been used as
starting materials towards biologically active molecules.
For general synthetic routes to 1-indanones and their
practical applications see, for example: (a) Suzuki, T.;
sites for the formation of dicationic species
3
(X = LASꢁ or H), and the lack of acid strength is com-
pensated by a confinement effect14 and nucleophilic
assistance of lattice oxygens in the transition state15 dur-
ing the second protonation (complexation). Obviously,
intermediates 3 on the solid can not be observed by spec-
troscopy due to both their short life time and low
concentration.16