K. Yu. Koltunov et al. / Tetrahedron Letters 46 (2005) 8391–8394
8393
O
on solid as in liquid acid, involves monocations 3a as the
O
PhCH3,
key reactive intermediates. In contrast, reaction 1b!2b,
which is not catalytic, probably involves the intermedi-
acy of 5b. That is also in accord with found competition
of this reaction with intermolecular alkylation of benz-
ene, when used as solvent to give mostly 1,3,3-triphen-
yl-1-propanone.16 Even the use of o-dichlorobenzene,
normally inert toward monocationic C-electrophiles,17
but often reactive with dicationic species,3,4,5c,8 offers
about 5% of impurity of 6,18 thus supporting the idea
of generation of highly activated dicationic19 species
5b upon the reaction conditions. The strong dependence
of reactivity of 1b and, in less extent of 1a, on the ratio
of acidic sites/enone can be related to the influence of
adsorption on the acidity of catalyst.15,20 This influence,
of course, will play a critical role when the second
protonation (or protonation of enone!LA complex)
is required to initiate cyclization.
HUSY, 130 ˚C
COOH
70 h
7
H3C
H3C
8
79%
Scheme 2.
none in 66% yield.16 These results can be rationalized
as it was done for 1b,d,e, by involvement of key dicat-
ionic intermediacy in the cyclization step. On the con-
trary, the catalytic reaction of 7 with sufficiently
activated xylenes should involve monocationic
intermediates.
In summary, the successful cyclization of phenyl vinyl
ketones into indanones using HUSY and other available
solid acids seems promising for practical applications.
We think that the necessity of the excess of acidic sites
to accomplish cyclization of 1b,d,e into 2b,d,e as well
as the conversion of 7 into 8 is not occasional and, in
accord with our previous results,4 can be interpreted in
terms of key dicationic intermediates. We also suggest
to take into account this argument, which may clarify
the involvement of mono- or dicationic intermediates
in mechanistic considerations.
Ph
O
Ph
Cl
6
Cl
Unfortunately, intermediates 5 cannot be observed on
the solid spectroscopically due to both their short life-
time and low concentration. The analogous dications,
as was mentioned above, have been generated as long-
living species by only using extremely acidic
HF(HSO3F)–SbF5–SOClF systems at ꢀ80 to ꢀ40 °C.
An alternate possibility could be the Nazarov electro-
cyclization suggested by Shudo.5a However, deuterium
labeling of the acid catalyst would not enable us to dis-
tinguish between Nazarov and Friedel–Crafts mecha-
nisms as H/D exchange between catalyst and substrate
is known to be very fast under our conditions on the
aromatic ring21 as well as on the a-carbon due to the
keto-enolic tautomerization of 3.22
Acknowledgements
Financial support of the work by the Loker Hydrocar-
bon Institute, U.S.C., Los-Angeles, and the ÔCNRSÕ is
gratefully acknowledged.
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.
The difference found in reactivity of 1a and 1b as model
substrates motivated us to investigate the reaction of
analogous ketones 1c–e (Table 1). As expected, 1-phen-
yl-2-methyl-2-propenone (1c) reacts in the same way as
1a, in the presence of moderate amounts of acid. In con-
trast, enones 1d–e due to electrodonating nature of sub-
stituents R00(R0) react similar to 1b, generally requiring
5–10 molar excess of acidic sites. These results could
be also interpreted in terms of mono- and dicationic
activation, respectively. In the series of experiments,
we have used CCl4 as solvent due to its low boiling point
facilitating separation from products. However, when
using this solvent we should be aware that it is not
totally inert toward zeolites.23
2. Berkessel, A.; Thauer, R. K. Angew. Chem., Int. Ed. Engl.
1995, 34, 2247–2250.
3. (a) Vukics, K.; Fodor, T.; Fischer, J.; Fellegvary, I.; Levai,
S. Org. Process Res. Dev. 2002, 6, 82; (b) Repinskaya, I.
B.; Koltunov, K. Yu.; Shakirov, M. M.; Shchegoleva, L.
N.; Koptyug, V. A. Russ. J. Org. Chem. 1993, 29, 803–812;
(c) Repinskaya, I. B.; Koltunov, K. Yu. Sib. Khim. Zh.
1993, 3, 73–76.
4. (a) Koltunov, K. Yu.; Walspurger, S.; Sommer, J. Chem.
Commun. 2004, 15, 1754–1755(b) Koltunov, K. Yu.;
Walspurger, S.; Sommer, J. J. Mol. Catal. A, accepted
for publication.
5. For general synthetic routs to 1-indanones and their
practical applications see, for example: (a) Suzuki, T.;
Ohwada, T.; Shudo, K. J. Am. Chem. Soc. 1997, 119,
6774–6780; (b) Prakash, G. K. S.; Yan, P.; Torok, B.;
Olah, G. A. Catal. Lett. 2003, 87, 109–112; (c) Rendy, R.;
Zhang, Y.; McElrea, A.; Gomez, A.; Klumpp, D. A. J.
Org. Chem. 2004, 69, 2340–2347; (d) Gagnier, S. V.;
Larock, R. C. J. Am. Chem. Soc. 2003, 125, 4804–4807; (e)
Cui, D.-M.; Zhang, C.; Kawamura, M.; Shimada, S.
Tetrahedron Lett. 2004, 45, 1741–1745, and references
cited therein.
In addition, we reinvestigated the related reaction of
crotonic acid (7) with toluene, previously carried out
in the presence of catalytic amount of heteropolyacids
and large-pore zeolites to obtain indanones 8 in negligi-
ble yield, whereas similar reaction with isomeric xylenes
gave better results.24 As expected, the use of HUSY (Si/
Al 2.5), providing ꢁ10 molar excess of acidic sites, gave
8 in good yield (Scheme 2). Moreover, 7 also reacts with
benzene in similar conditions to give 3-methyl-1-inda-