General route from simple methyl, alkyl, and cycloalkyl arenes to polycyclic cyclopentenyl aryl derivatives. The CpFe+ group as an activator and tag

Article abstract of DOI:10.1021/ol0172875

The CpFe⁺ group activates the perallylation of the benzylic groups of arenes using KOH and allylbromide under ambient conditions. This reaction can be followed by ruthenium-catalyzed RCM metathesis using Grubbs' catalyst at room temperature to give polycyclic aromatic derivatives in high yields, and these products are easily separated from the catalyst by extraction using ether. Alternatively, the RCM metathesis can be best carried out in ionic liquids at 80°C, and extraction using ether is then facile.

Full text of DOI:10.1021/ol0172875

ORGANIC
LETTERS
2
002
Vol. 4, No. 4
51-653
General Route from Simple Methyl,
Alkyl, and Cycloalkyl Arenes to
Polycyclic Cyclopentenyl Aryl
6
+
Derivatives. The CpFe Group as an
Activator and Tag
†
‡
,†
Victor Martinez, Jean-Claude Blais, and Didier Astruc*
Laboratoire de Chimie Organique et Organom e´ tallique, UMR CNRS 5802,
UniVersit e´ Bordeaux I 33405 Talence Cedex, France, and Laboratoire de Chimie
Structurale Organique et Biologique EP CNRS Nï. 103, UniVersit e´ Paris VI,
4
Place Jussieu, 75252 Paris, France
d.astruc@lcoo.u-bordeaux.fr
Received December 21, 2001
ABSTRACT
The CpFe+ group activates the perallylation of the benzylic groups of arenes using KOH and allylbromide under ambient conditions. This
reaction can be followed by ruthenium-catalyzed RCM metathesis using Grubbs’ catalyst at room temperature to give polycyclic aromatic
derivatives in high yields, and these products are easily separated from the catalyst by extraction using ether. Alternatively, the RCM metathesis
can be best carried out in ionic liquids at 80 °C, and extraction using ether is then facile.
Sequential, multistep, and tandem reactions mediated by
transition metals are becoming a major goal in synthetic
chemistry in order to minimize costs and waste. Arenes and
natural compounds. We now report a two-step, high-yield
route at room temperature from simple alkyl aromatics to
cyclopentenyl aryl derivatives in their sandwich complexes
1
olefins are obvious candidates for such a strategy because
they are abundant at low cost. The transition-metal-catalyzed
(
3) (a) Morken, J. P.; Didiuk, M. T.; Visser, M. S.; Hoveyda, A. H. J.
Am. Chem. Soc. 1994, 116, 3123-3124. (b) Grigg, R.; Sridharan, V.; York,
M. Tetrahedron Lett. 1998, 39, 4139-4142. (c) La, D. S.; Ford, G. J.;
Sattely, E. S.; Schrock, R. R.; Hoveyda, A. H. J. Am. Chem. Soc. 1999,
2
polymerization of olefins and tandem reactions including
3
olefin metathesis are remarkable examples along this line.
1
21, 11603-11604. (d) Weatherhead, G. S.; Ford, J. G.; Alexanian, E. J.;
4
Cyclopentene derivatives are easily functionalized and
Schrock, R. R.; Hoveyda, A. M. J. Am. Chem. Soc. 2000, 122, 1828-
5
heterobifunctionalized and are precursors of unnatural and
1829.
(4) Sharpless, K. B. Pure Appl. Chem. 1983, 55, 1823. (b) Herrmann,
W. A.; Fischer, R. W.; Marz, D. W. Angew. Chem., Int. Ed. Engl. 1991,
30, 1638-1640. (c) Yudin, A. K.; Sharpless, K. R. J. Am. Chem. Soc. 1997,
119, 11536-11537. (d) Wai, J. S. M.; Mark o´ , I.; Svendson, J. S.; Finn, M.
G.; Jacobsen, E. N.; Sharpless, K. B. J. Am. Chem. Soc. 1989, 111, 1123-
1125.
(5) Hamed, O.; Henry, P. M. Organometallics 1998, 17, 5184-5189.
(b) Sakurada, I.; Yamasaki, S.; G o¨ ttlich, R.; Ida, T.; Kanai, M.; Shibasaki,
M. J. Am. Chem. Soc. 2000, 122, 1245-1246. (c) Yamasaki, S.; Kanai,
M.; Shibasaki, M. J. Am. Chem. Soc. 2001, 123, 1256-1257.
†
Universit e´ Bordeaux I.
Universit e´ Paris VI (MALDI TOF mass spectrometry).
‡
(1) (a) Tietze, L. F.; Haunert, F. In Stimulating Concepts in Chemistry;
V o¨ gtle, F., Stoddart, J. F., Shibasaki, M., Eds.; Wiley-VCH: Weinheim,
Germany, 2000; p 39. (b) Trost, B. M. Science 1991, 254, 1471-1473. (c)
Hall, N. Science 1994, 266, 32-34.
(2) (a) Johnson, L. K.; Killian, C. M.; Brookhart, M. J. Am. Chem. Soc.
1
995, 117, 6414-6415.
1
0.1021/ol0172875 CCC: $22.00 © 2002 American Chemical Society
Published on Web 01/19/2002

6
+ 7
5
+
[
(
FeCp(η -arene)] (Cp ) η -C
5 5
H ), as exemplified in eq 1
The first step is the CpFe -induced perallylation 1af1b,
5
+
-
FE ) [η -CpFe] PF
6
).
etc. (Table 1) in the benzylic position of alkyl arenes, which
has been known for some time in the case of polymethyl-
arenes. We now find that this reaction can be carried out
8
under more simple conditions at ambient temperature using
KOH, allyl bromide, and THF, and that it can be extended
to the iron complexes 2a, 4a, 5a, 7a, and 9a. The first
example using a binuclear biaryl complex, 4a, leads to the
remarkable diiron dodecaallyl dendritic core 4b and its iron-
free dodecaallyl organic analogue. A perfect selectivity is
observed in all the cases, and high yields are obtained for
most compounds.
6
,7
Temporary π complexation of the arenes as well as their
7
b
+
decomplexation after the CpFe -induced transformation
also proceeds in high yields, so that new families of
sophisticated organo-iron complexes in Table 1 and the free
aromatic derivatives become available.
The second reaction is the ring-closing metathesis (RCM)
9,10
using Grubbs’ commercial catalyst [Ru(dCHPh)Cl
which readily proceeds at room temperature in NMR tubes
using CDCl as well as in CH Cl in Schlenk tubes yielding
c-9c (Table 1). This reaction can be carried out on the
2 3 2
(PCy ) ],
3
2
2
2 2
Table 1. Perallylation (in THF) and RCM (in CH Cl )
1
Productsa
metal complexes. Alternatively, the perallylated iron deriva-
tives can be decomplexed in MeCN by photolysis using
7
b
visible light in the presence of PPh
3
,
providing excellent
yields of the metal-free perallylated arenes 1d-7d. The role
+
of the CpFe group is also important for solubility and
selectivity reasons in the metathesis reactions, however.
Indeed, the RCM reaction can then be successfully applied
with a good selectivity to iron-free organic compounds for
the syntheses of 3e and 6e, but not 1e or 2e (vide supra and
Figure 1).
Figure 1.
In all the cases of RCM metathesis, it is much more
convenient to use the former method with the iron complex,
(6) The alkyl arene complexes are synthesized in high yields and large
scale by reaction between ferrocene and the arene in the presence of Al2Cl6
7
overnight around 100 °C or at reflux of the arene. Decomplexation of the
arene after activation is usually carried out by photolysis using visible light
in MeCN in the presence of PPh3, or in the case of arylamine complexes
I
9
(
b and 9c, by exergonic single-electron reduction using 1 equiv [Fe Cp-
6
7b
η -C6Me6)].
7) (a) Nesmeyanov, A. N.; Vol’kenau, N. A.; Bolesova, I. N. Tetra-
hedron Lett. 1963, 1765-1768. (b) Astruc, D. Top. Curr. Chem. 1991, 160,
7-95.
8) (a) Moulines, F.; Gloaguen, B.; Astruc, D. Angew. Chem., Int. Ed.
(
4
(
Engl. 1992, 28, 458-460. (b) Moulines, F.; Djakovitch, L.; Boese, R.;
Gloaguen, B.; Thiel, W.; Fillaut, J.-L.; Delville M.-H.; Astruc, D. Angew.
Chem., Int. Ed. Engl. 1993, 32, 1075-1077. (c) Buchholz, D.; Gloaguen,
B.; Fillaut, J.-L.; Cotrait, M.; Astruc, D. Chem. Eur. J. 1995, 1, 374-381.
(9) Schwab, P.; France, M. B.; Ziller, J. W.; Grubbs, R. H. Angew. Chem.
Int. Ed. Engl. 1995, 34, 2039-2041. (b) Trnka, T. M.; Grubbs, R. H. Acc.
Chem. Res. 2001, 34, 18-29;
(
10) For the most recent reviews on olefin metathesis, see: ref 9b and
(
a) F u¨ rstner, A. Angew. Chem. Int. Ed. Engl. 2000, 39, 3012. (b) Maier,
a
t (h) ) reaction times (rt); yield % ) yields of isolated and purified
M. E. Angew. Chem., Int. Ed. 2000, 39, 2073-2077. (c) Buchmeiser, M.
R. Chem. ReV. 2000, 100, 1565-1604. (d) Roy, R.; Das, S. K. Chem.
Commun. 2000, 519-529. For other reviews, see ref 9b.
products.
652
Org. Lett., Vol. 4, No. 4, 2002

however, because the ruthenium catalyst can be very easily
separated from the cationic iron complex after the metathesis
reaction. The catalyst is extracted using ether in which the
iron complexes are not soluble. The separation of the catalyst
has appeared as a non-trivial problem in the myriad of
decomplexation of 1c, whereas it is not available in pure
form by metathesis of the iron-free derivative 1d (Scheme
1). The same situation arises in the p-xylene series 2a-g.
1
0
+
publications dealing with the RCM of organic substrates
Scheme 1. Selectivity Effected by the CpFe Moiety in the
Metathesis Reactionsa
11
and has been the special subject of very recent papers. After
metathesis of the iron complexes, separation of the ruthenium
catalyst is followed by the easy observation of its methylene
1
signal at 19 ppm vs SiMe
4
in H NMR, as reported by Grubbs
2 2 3 2
for the less active complex [Ru(dCH )Cl (PCy ) ] in which
the benzylidene ligand has been replaced by the methylene
12
group coming from the terminal olefin. An excellent green
alternative is to carry out the RCM reaction of the neutral,
iron-free aromatic compound 3d in the ionic liquid 1-butyl-
6
3-imidazolium hexafluorophosphate ([bmin]PF ) at 80 °C,
which gives a 75% yield of 3e after extraction of the neutral
a
methathesis product using ether.13
(i) 5% [Ru(dCH )Cl (PCy ) ], CH Cl , rt, 1 h; (ii) hν (vis),
2
2
3 2
2
2
MeCN, 1 equiv PPh
3
; (iii) 10% [Ru(dCH
2
)Cl
2 3 2 2 4 2
(PCy ) ], C H Cl ,
The case of toluene, p-xylene, mesitylene, and tetra-
methylbiphenyl leading to triple allylation at each benzylic
carbon is distinct from the others for which only two allyl
groups are found in the benzylic position (Table 1). The
RCM reaction rapidly forms a cyclopentene ring in benzylic
position, and the third allyl group is left, which is not the
case when only two allyl groups are present. Thus, the third
allyl group can potentially give rise to cross metathesis (CM)
in the case of the mono- and polymethylaromatics except
8
0 °C, 3 days; (iv) 5% [Ru(dCH
2
)Cl (PCy )
2
3 2
], rt, 3 days.
+
Interestingly, the iron-free arene 3d resulting from CpFe -
8b
mediated nonallylation of mesitylene in 3a gives the RCM
reaction selectively since its CM reaction is slow, again
probably for steric reasons. Both the RCM and RCM + CM
products are of interest. The RCM products are hetero-
bifunctional. For instance, the RCM products provided from
3b and 4b are heterobifunctional dendritic cores. The RCM
+ CM products will have potential in materials chemistry
since linear polymers should be available from p-xylene by
ADMET and dendritic polymers should be accessible from
mesitylene. This aspect of the research line is under study.
In conclusion, we have provided, from very simple arenes,
a general and facile method of synthesis of a new class of
organometallic and organic polycyclic cyclopentenyl aryl
8a
8c
when methyl groups are adjacent (6af6b and 8af8b in
5
+
-
6
which Co ) η -CpCo , PF ). This possibility has been
scrutinized in the example of toluene. Its iron-free, triallylated
derivative 1d gives competitive RCM and CM reaction, and
no selectivity is observed. It is only possible to isolate the
organic bis-arene product 1g resulting from concomitant
RCM and CM of 1d. On the other hand, CM is considerably
1
4
+
slowed in the CpFe complex 1b, probably for steric reasons,
+
whereas RCM proceeds readily. Thus, the RCM product 1c
is selectively obtained with the iron complex 1b at 20 °C;
the corresponding free arene 1e can be obtained by photolytic
derivatives. The CpFe moiety not only provides a straight-
forward polyallylation method under routine conditions,
providing new, remarkable topologies, but also plays a key,
useful role in the metathesis process for the separation of
(
11) (a) Maynard, H. D.; Grubbs, R. H. Tetrahedron Lett. 1999, 40,
1
5
the products and the selectivity.
4
137-4140. (b) Paquette, L. A.; Schloss, J. D.; Efremoy, F.; Gallou, F.;
Mendez-Andino, J.; Yang, J. Org. Lett. 2000, 2, 1259-1261. (c) Ahn, Y.
M.; Yang, K.; Georg, G. I. Org. Lett. 2001, 3, 1411-1413.
Acknowledgment. We thank Dr. J. Ruiz for samples of
a and 8a and Drs. J. Juiz and S. Nlate (Bordeaux) for fruitful
(12) Schwab, P.; Grubbs, R. H.; Ziller, J. W. J. Am. Chem. Soc. 1996,
2
1
18, 100-110.
13) Buijsman, R. C.; Van Vuuren, E.; Sterrenburg J. G. Org. Lett. 2001,
, 3785-3787.
14) (a) Newkome, G. R.; Moorefield, C. N.; V o¨ gtle, F. Dendritic
Molecules: Concepts, Syntheses and PerspectiVes; VCH: New York, 1996.
b) Sunder, A.; Heinemann, J.; Frey, H. Chem. Eur. J. 2000, 6, 2499-
506.
15) All the new complexes have been suitably characterized by H and
(
discussions.
3
(
Supporting Information Available: Experimental pro-
1
13
cedures and spectroscopic data ( H and C NMR spectra
and MALDI TOF mass spectra) for all the new compounds.
This material is available free of charge via the Internet at
http://pubs.acs.org.
(
2
1
(
13
C NMR (including the distinct endo and exo positions of the new
8
c
complexes 6c and 8c in which the directionality is expected ) and by their
molecular peak in the MALDI TOF mass spectrum. Spectroscopic and
analytical data are provided in Supporting Information.
OL0172875
Org. Lett., Vol. 4, No. 4, 2002
653