Methylenepyran unsaturated Fischer carbene complexes from γ-methylpyrylium salts and alkynylcarbenes. Evolution to spiro-pyran-cyclopentenone compounds

Article abstract of DOI:10.1016/j.tetlet.2009.11.072

Push-pull methylenepyran compounds 3 containing ferrocenyl or aryl groups are synthesized from reaction of condensation between γ-methyl-pyrylium salts 1 as precursors of γ-methylenepyrans and alkynylcarbene complexes 2 as Michae?l-type acceptors. The new

Full text of DOI:10.1016/j.tetlet.2009.11.072

Tetrahedron Letters 51 (2010) 605–608
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Methylenepyran unsaturated Fischer carbene complexes from
c-methylpyrylium salts and alkynylcarbenes. Evolution to
spiro-pyran-cyclopentenone compounds
*
Fatou Ba, Pascal Le Poul, Françoise Robin-Le Guen, Nolwenn Cabon, Bertrand Caro
Sciences Chimiques de Rennes UMR CNRS 6226, I.U.T. Lannion, rue Edouard Branly BP 30219, Lannion Cedex, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Push–pull methylenepyran compounds 3 containing ferrocenyl or aryl groups are synthesized from reac-
tion of condensation between -methyl-pyrylium salts 1 as precursors of -methylenepyrans and alky-
nylcarbene complexes 2 as Michaël-type acceptors. The new carbenes 3 evolve in CH2Cl2 solution at room
temperature to provide spiro-fused-pyran-cyclopentenenone 4 and polysubstituted cyclopentenones 5.
Ó 2009 Elsevier Ltd. All rights reserved.
Received 16 September 2009
Revised 13 November 2009
Accepted 16 November 2009
Available online 20 November 2009
c
c
Keywords:
Push–pull molecules
Methylenepyrans
Fischer alkynylcarbenes complexes
Spiro-fused-pyran-cyclopentenenone
Due to their exceptional reactivity towards a great variety of
nucleophiles, pyrylium salts and their chalcogeno congeners
(Scheme 1) are versatile reagents for the synthesis of carbocyclic
and heterocyclic compounds.1 Taking advantage of these proper-
ties, we have recently shown that organometallic pyrylium salts
which display nucleophilic properties1,7 (Scheme 1B for
lenepyran R3 = H or -alkylidenepyran R3 = CH3, C2H5 group).
While our main aim was to explore redox properties of metall-
ocenyl extended bispyrans, a new class of metallocenyl electron-
rich molecules potentially precursor of molecular materials, we
suspected that reaction of ferrocenyl alkynyl Fischer-type carbene
c-methy-
c
act as convenient markers for proteins (Scheme 1A; R3 = g5
-
C5H4Re(CO)3, cymentrenyl, benchrotrenyl, ferrocenyl and ruthen-
complexes, acting as Michael acceptors, with
c-methylpyrylium
ocenyl groups).2
salts in basic media could provide -methylenepyran alkenyl car-
c
On the other hand, we have recently reported on an efficient
access to push–pull methylenepyran Fischer-type carbene com-
plexes. This was achieved by the action of stabilized carbanions of
CH3–C(Y)@M(CO)5 carbenes (Y = OCH3, SPh) towards 2,6-substi-
tuted pyrylium salts, free of substituent or bearing a methoxy leav-
bene complexes containing metallocenyl group. Subsequent Sierra
self-dimerization should allow a convenient access to the expected
extended electron-rich bispyran molecules.6
Indeed, the role of group 6 metal alkynylcarbene complexes as
Michael-type acceptor is well documented.8 They react easily with
ing group on the 4 (c
) position (Scheme 1A; R3 = H or OCH3).3,4
Methylenechalcogenopyran carboxaldehydes and vinylogues
(Scheme 1B; R3 = –CHO, R3 = –CH@CH–CHO) provided efficient
NLO phores in which the methylenechalcogenopyran groups act
as proaromatic donors (Scheme 1B; R3 = –(CH@CH)n–C(Y)M(CO)5).5
Moreover, Pd0 catalytic self-dimerization of these carbenes al-
lowed the formation of extended bischalcogenopyrans, a class of
molecules having interesting redox electrochemical dynamic prop-
R3
H
R3
X
R2
R1
R2
X
R1
erties mainly due to the presence of electron-rich
Another interest of pyrylium salt lies in the acidity of hydrogen
atoms of the methyl or alkyl groups in or position (Scheme 1A).
Deprotonation gives - and -methylene or alkylidenepyrans
p
spacers.6
Z
1B
1A
Pyrylium salts (X = O)
chalcogenopyrylium salts (X = S, Se, Te)
R1 = R2 = aryl, tBu, thienyl.
a
c
Alkylidene pyrans (X = O)
a
c
Chalcogenoalkylidene pyrans (X = S, Se, Te)
R1 = R2 = aryl, tBu, thienyl.
R3 (see text)
R
3 (see text)
* Corresponding author. Fax: +33 2 9648 1320.
E-mail address: Bertrand.caro@univ-rennes1.fr (B. Caro).
Scheme 1. Pyrylium salts and methylene pyran compounds.
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.11.072

606
F. Ba et al. / Tetrahedron Letters 51 (2010) 605–608
O, N, P and C nucleophiles including electron-rich C@C double
tute the first example of methylenepyran addition to electron-defi-
cient alkynes.
bonds.9 In particular, it has been reported by Aumann group that
a- and
c-methylene dihydroquinoleine and
c
-methylidenedihy-
The reaction of trimethylpyrylium salt 1c and the ferrocenyl
dropyridine undergo a 1,4-addition to phenylethynyl carbene com-
plexes to give unstable heterocyclic metallahexatrienes which
evolve, by cyclization, to spiro-fused cyclopentadienes.9c On the
carbene 2a gives only one product resulting from c-condensation.
This agrees with the regioselectivity of other condensation reac-
tions involving this salt, which is closely linked with the higher
other hand less sterically
c
-methylene dihydropyridines gave a
acidity of the hydrogen atoms borne by the
to undergo deuteration about 10 times faster than the
hydrogens.1 This is also in line with theoretical calculations which
indicate lower energies for the symmetrical
-methylenepyrans.11
c
-methyl group, known
1,2-addition, leading to a zwitterionic pyridinium carbonyl metal-
a-methyl
lates after a 1,2-migration of the W(CO)5 moiety.9c Therefore, it
was of interest to test the reactivity of
alkynylcarbenes.
The following describes, in contrast with the results obtained in
dihydropyridine series, the formation of -methylenepyran ferr-
ocenyl or aryl substituted alkenyl carbene complexes. Their con-
version to spiro-fused pyran-cyclopentenones is also reported.
Such evolution was not previously observed by us for analogous
carbene complexes of similar length, but free of ferrocenyl or aryl
substituent in the alkene spacer.5
c-methylenepyrans towards
c
It can be noted that we have not detected the formation of zwit-
terionic metal compounds corresponding to a 1–2 addition of
methylenepyrans to alkynyl carbene, as observed for analogous
c
c
-methylene dihydropyridine.9c
Moreover, cross-conjugated carbenes coming from a metathesis
of the C–C exocyclic double bond of methylenepyrans were not ob-
served. Similar behaviour was noted for methylene dihydroquino-
line series.9c
First, we chose to study the reaction between 2,6-diphenyl-4-
methylpyrylium tetrafluoroborate 1a and ferrocenylalkynylcar-
bene complex 2a (Scheme 2). When a mixture of 1a and 2a in
THF, cooled to 0 °C, is treated with 3 equiv. of triethylamine, a col-
our change immediately occurs (red to blue). After five minutes, a
careful control of the reaction mixture by TLC analysis (silica plate)
reveals a complete transformation (observation of a single blue
spot). After hydrolysis on ice, extraction with diethylether, drying
on anhydrous MgSO4 and evaporation of the solvent at 20–30 °C,
a dark solid is isolated. At this stage, a TLC monitoring shows below
and above the initial spot, uncoloured and coloured spots suggest-
ing partial evolution of the initially formed blue compound. A flash
chromatography on silica gel and distillation of the solvent in the
cold furnished a pure solid for which NMR spectra, recorded at
low temperature (ꢀ40 °C) are consistent with the formation of
the heterocyclic carbene 3a (Scheme 2, Table 1, carbene 3a10).
The reaction has been extended, without any modification to 2,6-
ditertiobutyl-4-methyl 1b or 2,4,6-trimethylpyrylium salt 1c and
ferrocenyl or aryl alkynyl carbenes complexes 2a–c (Scheme 2,
Table 1).
Therefore the given results are well rationalized by Michael-
type addition of the pyran electron-rich carbon–carbon exocyclic
double bond, stemming from deprotonation of the pyrylium salt,
to the alkynyl carbene leading to the zwitterionic intermediate A
(Scheme 3).
Successive protonation, deprotonation steps gave the expected
unsaturated carbene 3. Intermediates of type A were commonly
evoked in conjugated nucleophilic addition to alkynyl carbenes,12
and in some instance were characterized by NMR experiments at
low temperature13 and by X-ray analysis.14 As exemplified by the
1H and 13C NMR spectra of 3a–f it seems that protonation of the
central carbon of the allenic moiety is stereospecific (one isomer
detected) (Table 1).
One of main features of 3a–c 1H NMR recordings (CDCl3 solu-
tion) is the progressive disappearance of the carbene signals and
the concomitant appearance of new signals when raising the tem-
perature from ꢀ40 °C to room temperature. This suggests a conver-
sion of carbenes 3a–c to other products in CDCl3 solution. Thus,
solution of ferrocenyl carbenes 3a–c in CH2Cl2 was left at room
temperature for 24 h under N2 atmosphere. Successive TLC analy-
sis showed the slow formation of red compounds and W(CO)6,
respectively. After complete reaction, the solutions were chro-
matographed on silica gel to give red solid for which IRFT, 1H
and 13C NMR and mass spectrography analyses are consistent with
The push–pull
c-methylenepyran alkenyl carbene complexes
3b–f were obtained in fair yields. Carbenes 3a–f are moderately
stable solids at room temperature but can be stocked for weeks
in the cold (ꢀ20 °C). As far as we are aware these reactions consti-
R
O
R
R'
BF4-
W(CO)5
OCH3
NEt3
THF
+
R'
OCH3
(OC)5W
R
O
R
1
2
3
Scheme 2. Formation of aryl and ferrocenyl methylenepyran carbene complexes.
Table 1
Yield of isolated carbene complexes
Pyrylium salts
Alkynyl carbenes
Alkenyl carbenes
Yield%
ꢀ
1
2
3
4
5
6
1a: R = Ph, Zꢀ = BF4
2a: R0 = Fc
3a: R = Ph, R0 = Fc
63
46
64
30
54
40
1b: R = tBu, Zꢀ = BF4 ꢀ
2a: R0 = Fc
3b: R = tBu, R0 = Fc
3c: R = CH3, R0 = Fc
3d: R = Ph, R0 = Ph
ꢀ
1c: R = CH3, Zꢀ = PF6
2a: R0 = Fc
1d: R = Ph, Zꢀ = BF4
2b: R0 = Ph
ꢀ
1b: R = tBu, Zꢀ = BF4ꢀ
2b: R0 = Ph
3e: R = tBu, R0 = Ph
3f: R = tBu, R0 = p-OMeC6H4
ꢀ
1b: R = tBu, Zꢀ = BF4
2c: R0 = p-OMeC6H4

F. Ba et al. / Tetrahedron Letters 51 (2010) 605–608
607
+
NHEt3
R'
R
O
R
R
W(CO)5
OCH3
R
O
R
W(CO)5
R'
C
C
C
OCH3
O
NEt3
NHEt3+ X-
CH3
+
A
R
Z
Z
1) +H+
2) -HX
3
Scheme 3. Formation of zwitterionic intermediate.
R
O
R
R'
2
3
1
R'
OCH3
R'
4
(OC)5W
3
O
O
H3CO
+
R
R'
W(CO)5
1
R
2
3
O
R
O
R
O
R
O
R
4
4
5
R' = H
Scheme 4. Cyclopentenone formation.
Table 2
Yield of cyclopentenone formation
Entry
Spiro-pyran cyclopentenone 4
Yield%
Substituted cyclopentenones 5
Yield%
1
2
3
4
5
6
4a: R = Ph, R0 = Fc
83
85
85
27
29
No
5a: R = Ph, R0 = Fc
No
No
No
No
16
89
4b: R = tBu, R0 = Fc
4c: R = CH3, R0 = Fc
4d: R = Ph, R0 = Ph
4e: R = tBu, R0 = Ph
4f: R = tBu, R0 = p-OMeC6H4
5b: R = tBu, R0 = Fc
5c: R = CH3, R0 = Fc
5d: R = Ph, R0 = Ph
5e: R = tBu, R0 = Ph
5f: R = tBu, R0 = p-OMeC6H4
the spiro-pyran-cyclopentenone skeleton 4a–c as exemplified in
Scheme 4 (Table 2).15
In summary we have described a simple procedure for the
synthesis of push–pull methylenepyran ferrocenyl and aryl substi-
tuted alkenyl carbene complexes using pyrylium salts as precur-
Aryl carbenes 3d–f evolve similarly. Nevertheless a pyran ring
opening occurred, leading to the formation of tricetones 5 as the
sole and minor compounds from 3f and 3e conversion, respec-
tively. For 3d ester formation resulting from W(CO)5 substitution
by O was also observed (18% yield).
The reaction reported here is a new example of cyclization of
metallahexatrienes to cyclopentenones, a conversion which rarely
provided spiranic structures.8
sors of c-methylenepyrans and alkynyl carbenes as Michael-type
acceptors. The obtained heterocyclic metallahexatrienes evolve in
solution at room temperature to spiro-pyran-cyclopentenone
compounds or/and to polysubstituted cyclopentenones substituted
by two CH2COR groups. The reported process constitutes a new
approach to cyclopentenone framework18 and to ferrocenyl cyclo-
pentenone19 which could have possible medicinal applications.20
Thus, further developments aimed at the formation of polycyclic
skeletons taking advantage of the presence of three ketones func-
tions in 5. However, the low stability of carbenes 3 makes tricky
the formation of extended diferrocenyl bispyrans using the Sierra
Pd0 catalytic self-dimerization methodology.21
It is noteworthy, that the presence of a pyran ring in 4, which
can act as 1–5 pentadione equivalent16 could offer further syn-
thetic opportunities in cyclopentenone chemistry.
Finally, given that methylenepyran carbene complexes (Scheme 4)
of similar unsaturated chain length, free of ferrocenyl or aryl
groups, which display a trans (E) configuration for the C2–C3 dou-
ble bond are stable compounds,5,6 we propose that the conversion
of carbene 3 to cyclopentenones is favoured by a E configuration.
Such a stereochemistry allows the proximity between the exocy-
clic double bond and the carbene carbon atom, a necessary condi-
tion to observe the ring closure9,17 (Scheme 4).
Acknowledgements
This work is supported by the CNRS and the University of Re-
nnes1. We are grateful to N. Kervarec, S. Cerantola and G. Simon
for recording NMR spectra. Sincere gratitude towards N. Kervarec

608
F. Ba et al. / Tetrahedron Letters 51 (2010) 605–608
68.8 (OCH3), 71.0 (C5H5), 71.2 (C5H4), 71.9 (C5H4), 88.8 (CqFc), 107.6 (Cpyran),
109.5 (Cpyran), 116.9 (C4), 128.8 (CPh(meta)), 129.0 (CPh(para)), 131.9 (CPh(ortho)),
from Service Commun de Recherche de RMN et de RPE, Université
de Bretagne Occidentale for NOESY/ROESY experiments.
139.7 (C2), 139.9 (Cpyran), 154.8 (Cpyran), 155.4 (Cpyran), 286.1 (C1). IR (KBr):
m
2050, 1921, 1900, 1643, 1535, 1429, 1104, 940, 797 cmꢀ1
.
11. Zvezdina, E. A.; Zhadanova, M. P.; Bren, A.; Dorofeenko, G. N. Khim. Geterotsikl.
Soeden. 1976, 1494.
Supplementary data
12. See for example (a) Stein, F.; Duetsch, M.; Pohl, E.; Herbst-Irmer, R.; De Mejeire,
A. Organometallics 1993, 12, 2556–2564; (b) Pipoh, R.; Van Heldick, R.; Henkel,
G. Organometallics 1993, 12, 2236–2242; (c) Dötz, K. H.; Christoffers, C.;
Knochel, P. J. Organomet. Chem. 1995, 489, C84; (d) Aumann, R.; Yu, Z.; Fröhlich,
R. J. Organomet. 1997, 459, 311–318; (e) Aumann, R.; Roths, K.; Fröhlich, R.
Organometallics 1997, 16, 5893–5899; (f) Aumann, R.; Roths, K. B.; Köbmerer,
M.; Fröhlich, R. J. Organomet. Chem. 1998, 556, 119–127; (g) Aumann, R.;
Hildmann, B.; Fröhlich, R. Organometallics 1998, 17, 1197–1201; (h) Aumann,
R.; Kömeier, M.; Mück-Lichtenfeld, C.; Zippel, F. Eur. J. Org. Chem. 2000, 37–49;
(i) Gu, K.; Yang, G.; Zhang, W.; Liu, X.; Yu, Z.; Han, X.; Bao, X. J. Organomet.
Chem. 2006, 691, 1984–1992; (j) Barluenga, J.; Garcia-Garcia, P.; De Saa, D.;
Fernandez-Rodrighez, M. A.; De La Rua, R. B.; Ballesteros, A.; Aguilar, E.; Tomas,
M. Angew. Chem., Int. Ed. 2007, 46, 2610–2612.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tetlet.2009.11.072.
References and notes
1. Balaban, A. T.; Dinculescu, A.; Dorofeenko, G. N.; Mezheritskii, V. V.; Koblik, A.
V.; Fischer, G. W. In Pyrylium Salt: Synthesis, Reactions and Physical Properties.
Advances in Heterocyclic Chemistry, Katrizky, A. R., Ed.; Academic New York,
1982.
2. (a) Salmain, M.; Lamisza, K. L.; Jaouen, G.; Senechal-Tocquer, M.-C.; Senechal,
D.; Caro, B. Bioconjugate Chem. 1994, 5, 655–659; (b) Maliska, K. L.; Top, S.;
Vaisserman, J.; Caro, B.; Senechal-Tocquer, M.-C.; Senechal, D.; Saillard, J.-Y.;
Triki, S.; Kahlal, S.; Britten, J. F.; McGlinchey, M.; Jaouen, G. Organometallics
1995, 14, 5273–5280; (c) Caro, B.; Robin-Le Guen, F.; Salmain, M.; Jaouen, G.
Tetrahedron 2000, 56, 257–263; (d) Egan, D.; Salmain, M.; Mc Ardle, P.; Jaouen,
G.; Caro, B. Spectrochim. Acta 2002, 58, 941–951; (e) Salmain, M.; Caro, B.;
Robin-Le Guen, F.; Blais, J.-C.; Jaouen, G. Chem. Biochem. 2004, 5, 99–109.
3. Caro, B.; Le Poul, P.; Robin-Le Guen, F.; Saillard, J.-Y.; Kahlal, S.; Moinet, C.; Le
Poul, N.; Vaissermann, J. Tetrahedron 2002, 58, 7519–7530.
4. Le Bihan, J.-Y.; Faux, N.; Caro, B.; Robin-Le Guen, F.; Le Poul, P. J. Organomet.
Chem. 2007, 692, 5517–5522.
5. (a) Faux, N.; Caro, B.; Robin-Le Guen, F.; Le Poul, P.; Nakatani, K.; Ishow, E. J.
Organomet. Chem. 2005, 690, 4982–4988; (b) Faux, N.; Robin-Le Guen, F.; Le
Poul, P.; Caro, B.; Nakatani, K.; Ishow, E.; Golhen, S. Eur. J. Inorg. Chem. 2006, 17,
3489–3497.
6. Faux, N.; Robin-Le Guen, F.; Le Poul, P.; Caro, B.; Le Poul, N.; Le Mest, Y.; Green,
S. J.; Le Roux, S.; Kahlal, S.; Saillard, J.-Y. Tetrahedron 2007, 63, 7142–7153.
7. Mezheritskii, V. V.; Vaisserman, A. L.; Dorofeenko, G. N. Heterocycles 1979, 12, 51.
8. (a) Herndon, J. W. Coord. Chem. Rev. 2009, 253, 1517–1595; (b) Herndon, J. W.
Coord. Chem. Rev. 2006, 250, 1889–1964; (c) Barluenga, J.; Fernandez-
Rodriguez, M. A.; Aguilar, E. J. Organomet. Chem. 2005, 690, 539–587; (d)
Barluenga, J.; Santamaria, J.; Tomas, M. Chem. Rev. 2004, 104, 2259–2284; (e)
Herndon, J. W. Tetrahedron 2000, 56, 1257–1280; (f) Aumann, R. Eur. J. Org.
Chem. 2000, 17–31; (g) De Maijere, A.; Schirmer, H.; Duetsch, M. Angew. Chem.,
Int. Ed. 2000, 39, 3964–4002; (h) Sierra, M. Chem. Rev. 2000, 100, 3591–3638; (i)
Lian, Y.; Wulff, W. D. J. Am. Chem. Soc. 2005, 127, 17162–17163.
13. Barluenga, J.; Tomas, M.; Lopez-Pelegrin, J. A.; Rubio, E. Tetrahedron Lett. 1997,
38, 3981–3984.
14. (a) Aumann, R.; Jasper, B.; Läge, M.; Krebs, D. Chem. Ber. 1994, 127, 2475–2482;
(b) Ortin, Y.; Lugan, N.; Mathieu, R. Dalton Trans. 2005, 1620–1636.
15. General procedure:
A CH2Cl2 solution of carbenes
3 was left at room
temperature under N2 for 24 h. The blue solution progressively turned red
(for 3a–c) and colourless (for 3d–f). The solution was chromatographed (silica
gel diethylether–petroleum ether 30/70) to give the expected cyclopentenone
4 or (and) 5. For 3d an ester coming from W(CO)5 substitution by O was also
isolated in low yield.
Selected spectroscopic data: 4c (Scheme 4, Table 2) 1H NMR (500 MHz, CDCl3) d
0
1.14 (18H, s, C(CH3)3), 2.81 (2H, s, H1), 4.14 (5H, s, C5H5), 4.37 (2H, s, H3 and
H5 ), 4,52 (2H, s, C5H4), 4.60 (2H, s, C5H4), 6.07 (1H, s, H2),. 13CNMR (125 MHz,
0
0
CDCl3) d 29.1 (CH3), 35.0 (CqtBu), 47.5 (C4 ), 51.0 (C4), 68.1 (C5H4), 70.1 (C5H5),
0
0
0
0
71.7 (C5H4), 78.0 (CqFc), 94.9 (C3 and C5 ), 121.1(C2), 159.6 (C2 and C6 ), 174.7
(C3), 209.9 (CO). IR (KBr):
m 2973, 1690, 1593, 1359, 1256, 1168, 1090,
823 cmꢀ1. HRMS (EI): C27H32O2Fe M+ requires 444.1751, found 444.1735.
Compound 5f (Scheme 4, Table 2): 1H NMR (500 MHz, CDCl3) d 1.11 (18H, s,
C(CH3)3), 2.64 (2H, d, 2J = 18.5 Hz, H3 and H5 ), 3.04 (2H, s, H1), 3.15 (2H, d,
0
0
2J = 18.5 Hz, H3 and H5 ), 3.85 (3H, s, OCH3), 6.51 (1H, s, H2), 6.93 (2H, d,
0
0
3J = 7.0 Hz, HPh(para)), 7.62 (2H, d, 3J = 7.0 Hz, HPh(meta)). 13CNMR (125 MHz,
0
0
0
0
CDCl3) d 26.6 (C(CH3)3), 42.7 (C3 and C5 ), 43,1 (C3 and C5 ), 43.7 (C(CH3)3), 44.0
0
(C4 ), 55.6 (OCH3), 113.0 (CPh(ortho)), 122.7 (C2), 126.3 (Cipso), 129.4 CPh(meta)),
0
0
162.0 (CPh(para)), 170.0 (C3), 210.0 (C1), 214.0 (C2 and C6 ). IR (KBr):
m 1706,
1681, 1594, 1513, 1336, 1260, 1182, 831 cmꢀ1. HRMS (EI): C24H32O4 [M+Na+]
requires 407.2198, found 407.2198. NOESY experiment, performed on 4a,
showed the through space proximity of the methylene hydrogens and the b
pyran hydrogens. This is in favour of the proposed structure.
9. (a) Aumann, R.; Meyer, A. G.; Fröhlich, R. Organometallics 1996, 15, 5018–5027;
(b) Göttker-Schnetmann, I.; Aumann, R.; Berganger, K. Organometallics 2001,
20, 3574–3581; (c) Göttker-Schnetmann, I.; Aumann, R.; Kataeva, O.; Holst, C.;
Frölich, R. Organometallics 2001, 20, 2889–2904.
16. Balaban, T. S.; Balaban, A. T. Tetrahedron Lett. 1997, 28, 1341–1344.
17. ROESY experiment performed on carbene 3c (ꢀ40 °C, CDCl3), showed ROE
between the hydrogen atom borne by the carbon 2 (Scheme 4, d = 7.70 ppm) and
the hydrogen atom of the ferrocenyl group and consequently confirmed the
proposed stereochemistry for the C–C double bond bearing the ferrocenyl and
carbene groups. This result is in accordance with the stereochemistry proposed
by Aumann3e for analogous heterocyclic carbenes formed by the reaction
between phenyl alkynylcarbene and methylene dihydrocyanoquinoléines.
18. Rezgui, F.; Amri, H.; Moncef El Gaied, M. Tetrahedron 2003, 59, 1369–1380.
19. Li, J.; Ma, J. P.; Liu, F.; Wu, X.-W.; Dong, Y.-B.; Huang, R. Q. Organometallics 2008,
27, 5446–5452.
10. Formation of 3a (Scheme 2, Table 1): A THF solution of pyrylium salt 1a
(0.290 g, 8.68.10ꢀ4 mol) was cooled to 0 °C. NEt3and carbene 2a (0.500 g,
8.68.10ꢀ4 mol) were then added. The solution turned blue. After 10 min, the
THF solution was poured on ice. Extraction with diethylether, drying on
MgSO4, and distillation under vacuum led to a blue residue. The solid was
dissolved in cold CH2Cl2 (ꢀ10 °C) and a flash chromatography was performed
(silica gel, mixture of cold petroleum ether/diethylether 90/10). Distillation of
the solvent under vacuum provides a blue solid (447 mg). TLC analysis shows
only a blue spot.
1H NMR (500 MHz, CDCl3, ꢀ40 °C) d 4.24 (5H, s, C5H5), 4.52 (2H, s, C5H4), 4.53
(3H, s, OCH3), 4.67 (2H, s, C5H4), 6.27 (1H, s, Hpyran), 6.35 (1H, s, Hexocyclic), 6.68
(1H, s, Hpyran), 7.40 (2H, m, HPh(para)), 7.57 (4H, m, HPh(meta)), 7.80 (4H, m,
HPh(ortho)), 7.88 (1H, s, HC@C(Fc)). 13C NMR (HMQC, HMBC, CDCl3, ꢀ40 °C) d
20. Zora, M.; Ash Tumay, T.; Büyükgüngör, O. Tetrahedron 2007, 63, 4018–4026.
21. Gomez-Callego, M.; Mancheno, M. J.; Sierra, M. Acc. Chem. Res. 2005, 38,
44–53.