Synthesis and hydrolysis of [alkenyl(alkoxy)carbene]manganese complexes: Evidence for a transient allylic intermediate on the way to α,β-unsaturated aldehydes

Article abstract of DOI:10.1002/(SICI)1099-0682(199905)1999:5<739::AID-EJIC739>3.0.CO;2-I

A variety of alkenylcarbene complexes [Cp'(CO)2Mn= C(OEt)CH=CHR] (3) (Cp' = TiS-MeCsH4) was obtained in a straightforward manner upon aldol condensation of [Cp'(CO)₂Mn=C(OEt)CH₃] (1) with aromatic and α,β- unsaturated aldehydes RC(H)O (2). The reaction is totally stereoselective, giving (E)- or (all-E)-alkenylcarbenes only. The protonation of 3 at low temperature followed by reaction with water affords the α,β-unsaturated aldehyde complexes [Cp'(CO)₂Mn(n²-RCH=CHCHO] (5), from which the aldehydes RC(H)=C(H)C(H)O (6) were displaced by acetonitrile. The intermediate aldehyde complexes are shown to result from the hydrolysis of a transient cationic π- allyl species [Cp'(CO)₂Mn(n³-RCHCHC(OEt)H]⁺ ([4]⁺) formed upon protonation of 3.

Full text of DOI:10.1002/(SICI)1099-0682(199905)1999:5<739::AID-EJIC739>3.0.CO;2-I

SHORT COMMUNICATION
Synthesis and Hydrolysis of [Alkenyl(alkoxy)carbene]manganese Complexes:
Evidence for a Transient Allylic Intermediate on the Way to
␣,β-Unsaturated Aldehydes
[a]
[a]
[a]
[a]
´
¨
Carole Mongin, Yannick Ortin, Noel Lugan,* and Rene Mathieu
Keywords: Manganese / Carbenes / Hydrolyses / Aldehydes / Vinylogation
A
variety of alkenylcarbene complexes [CpЈ(CO)2Mn=
with water affords the α,β-unsaturated aldehyde complexes
[CpЈ(CO)2Mn(η2-RCH=CHCHO] (5), from which the
aldehydes RC(H)=C(H)C(H)O (6) were displaced by
acetonitrile. The intermediate aldehyde complexes are
shown to result from the hydrolysis of a transient cationic π-
C(OEt)CH=CHR] (3) (CpЈ = η5-MeC5H4) was obtained in a
straightforward manner upon aldol condensation of
[CpЈ(CO)2Mn=C(OEt)CH3] (1) with aromatic and α,β-
unsaturated aldehydes RC(H)O (2). The reaction is totally
stereoselective, giving (E)- or (all-E)-alkenylcarbenes only. allyl species [CpЈ(CO)2Mn(η3-RCHCHC(OEt)H]+ ([4]+)
The protonation of 3 at low temperature followed by reaction
formed upon protonation of 3.
of our investigation and provides insight into the mecha-
nism of the hydrolysis of alkenyl-substituted Fischer car-
Introduction
Alkenyl-alkoxy-substituted Fischer carbene complexes bene complexes under acidic conditions.[10]
have been shown in some cases to release α,β-unsaturated
aldehydes upon hydrolysis, with optimum efficiency at high
pH values.[1,2] Though mechanistically clear under such
Results and Discussion
conditions,[2b] the reaction has received little attention as a
synthetic procedure. Yet, if we keep in mind that alkenyl-
alkoxy-substituted Fischer carbenes can be obtained upon
aldol condensation of alkyl(alkoxy)carbene complexes with
aldehydes,[3,4] their hydrolysis can be regarded as part of a
potential process for the homologation of aldehydes into
α,β-unsaturated aldehydes (Scheme 1).
The carbenemanganese anion [CpЈ(CO)2MnϭC(OEt)-
CH2]Ϫ ([1]Ϫ), generated in situ by addition of nBuLi to a
THF solution of [CpЈ(CO)2MnϭC(OEt)CH3] (1) cooled at
Ϫ60°C,[11] was treated at low temperature with one molar
equivalent of various aromatic and α,β-unsaturated alde-
hydes RCHO (2aϪh, Table 1). An aldol/elimination reac-
tion subsequently occurred upon return to room tempera-
ture, giving the corresponding alkenyl(alkoxy)carbenes
[CpЈ(CO)2MnϭC(OEt)CHϭCHR] (3aϪh) in valuable
yields (Scheme 2, Table 1, entries 1Ϫ8).
Scheme 1
The vinylogation of aldehydes is of special interest for the
synthesis of molecular materials[5] and natural products.[6]
Though several procedures derived from general olefination
reactions have been devised,[7] the search for easy-to-
handle, selective, and versatile reagents is still of current
interest.[7e,8] As part of an ongoing effort to develop syn-
thetically useful reactions employing cheap and readily
available group-7 Fischer carbene complexes obtained from
[CpЈMn(CO)3] (CpЈ ϭ η5-MeC5H4),[9] we were challenged
to examine the scope of [CpЈ(CO)2MnϭC(OEt)CH3] (1) for
the above reaction. The present paper deals with the results
Scheme 2. Aldol condensation of 1 with aldehydes 2aϪh
This sequence was reproduced with a dialdehyde, namely
1,1Ј-bis(formyl)ferrocene. Depending on the stoichiometry,
the reaction could be directed toward either [{η5-
(CpЈ(CO)2MnϭC(OEt)CHϭCHC5H4)}Fe{η5-C5H4CHO}]
(3i1), or [{η5-(CpЈ(CO)2MnϭC(OEt)CHϭCHC5H4}2Fe]
(3i2) (Scheme 3, Table 1, entries 9Ϫ10).
Complexes 3aϪi were characterized by 1H-, 13C-, and
1
(when necessary) HMQC H-13C NMR analysis.[12] Their
formation is totally stereoselective, giving (E) (for 3aϪb, f,
i) or (all-E) (for 3cϪe, gϪh) isomers only, as indicated by
3JHH coupling constants of ca. 15 Hz for the protons adja-
cent to the carbonϪcarbon double bonds.
In a first attempt to release α,β-unsaturated aldehydes
from the above alkenyl(alkoxy)carbenes upon hydrolysis in
[a]
Laboratoire de Chimie de Coordination du CNRS (UPR 8241),
205, route de Narbonne, F-31077 Toulouse Cedex 4, France
Fax: (internat.) ϩ 33-5/61553003
E-mail: lugan@lcc-toulouse.fr
Supporting Information for this article is available on the
WWW under http://www.wiley-vch.de/home/eurjic or from the
author.
Eur. J. Inorg. Chem. 1999, 739Ϫ742
WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999
1434Ϫ1948/99/0505Ϫ0739 $ 17.50ϩ.50/0
739

C. Mongin, Y. Ortin, N. Lugan, R. Mathieu
SHORT COMMUNICATION
1
Table 1. Aldol condensation of 1 with aldehydes 2, hydrolysis of 3, the H dimension, and they correlate with the signals ob-
served at δ ϭ 138.1, 77.3, and 62.2 in the 13C dimension.
and demetalation of the α,β-unsaturated aldehydes 6 (see Sche-
mes 2Ϫ5)
The proton H1 clearly originates from TfOH, since the
NMR spectrum of [D-4c]ϩ, generated from 3c upon treat-
ment with TfOD, does not show any resonance in the area
around δ ϭ 6.12. Within the 13C{1H}-NMR sensitivity and
resolution limits, the formation of [4aϪc]ϩ is quantitative
and stereoselective. However, due to the systematic forma-
tion of paramagnetic impurities, their stereochemistry could
Product Yield (%)[f]
Entry Aldehyde RCHO (2)[a]
series 3[g] 5[j] 6[k]
1
2
3
4
5
6
7
8
9
10
PhCHO
a
b
c
59 87 95
87 83 96
65 88 92
64 73 75
66 72 97
85 72 97
77 72 97
54 92 98
86[h] 89 93
71[i] 80 98
FcCHO
(E)-PhCHϭCHCHO
(E)-MeCHϭCHCHO
(E)-PhCHϭC(Me)CHO
1,4-Me2NC6H4CHO
(E)-FcCHϭCHCHO[b]
(E,E)-PhCHϭCHCHϭCHCHO[c]
1,1Ј-diformylferrocene[d]
1,1Ј-diformylferrocene[e]
d
e
1
not be determined by H NMR.
f
When an excess of water was added to CH2Cl2 solutions
of [4a؊i]ϩ, IR monitoring showed the gradual disappear-
ance of the bands due to [4a؊i]ϩ whereas three new bands
grew at ca. 1965, 1905, and 1670 cmϪ1 indicative of the
formation of the α,β-unsaturated aldehyde complexes
[CpЈ(CO)2Mn(η2-RCHϭCHCHO)] (5a؊i) (Scheme 3,
Table 1).[16] The NMR data of 5a؊i clearly indicate that
the α,β-unsaturated aldehyde ligand is coordinated in an η2
fashion through the carbonϪcarbon double bond adjacent
to the aldehyde function, and that the (E) or (all-E) ar-
rangement of the alkenyl moieties in 3a؊i is maintained
through their conversion into 5aϪi.[12] Finally, when [D-
4c]ϩ was treated with water, the deuterium label on C1 was
totally retained in the aldehyde function of
[CpЈ(CO)2Mn(η2-PhCHϭCHCHϭCDO)] [D-5c].[17]
The overall transformation of the alkenyl(alkoxy)carbene
complexes 3 into the α,β-unsaturated aldehyde complexes 5
is depicted in Scheme 4.
g
h
i1
i2
1 equiv. of 2 vs. [1]Ϫ was used, unless otherwise noted. Ϫ
[a]
[b]
[c]
Prepared from 2b using 1 as a vinylogation reagent. Ϫ Prepa-
[d]
red from 2c using 1 as a vinylogation reagent. Ϫ 1.5 equiv. of 2i
vs. [1]Ϫ was used. Ϫ
0.33 equiv. of 2i vs. [1]Ϫ was used. Ϫ
[e]
[f]
Yields of isolated products. Ϫ [g] See Scheme 2. Ϫ [h] Based on [1]Ϫ.
[i]
[j]
[k]
Ϫ
Based on 2i. Ϫ See Scheme 4. Ϫ
See Scheme 5; except
hitherto unkown 6i1, which has been fully characterized,[12] the al-
dehydes were identified by comparison of their NMR spectra with
literature data, or data recorded directly from authentic samples.
Scheme 3. Aldol condensation of 1 with 1,1Ј-diformylferrocene (2i)
basic conditions, 3c was treated with urotropine in the pres-
ence of water according to a procedure Aumann et al. de-
scribed for group-6 analogs.[1] No reaction was observed
after 24 hours. This may be attributed to the insufficient
electrophilic character of the carbene carbon atom that dis-
favors the required nucleophilic attack of hydroxide
ions.[1,2b]
Scheme 4. Proposed mechanism for the formation of 5
Though no intermediate hydride species could be ob-
served, the context of chemistry and the results of previous
Keeping in mind that Fischer carbene complexes can be studies on protonation reactions of electron-rich carbene
protolytically cleaved to form the corresponding alde- complexes suggest that [4]ϩ is likely to result from a pro-
hydes,[10] we next treated complexes 3 with one equivalent tonation of 3 at the metal center followed by hydride mi-
of TfOH at Ϫ80 °C in CH2Cl2 (but two equivalents in the gration to the carbene carbon atom,[18,19] and concomitant
case of 3f[13] and in the case of the dialkenylcarbene 3i2). An stabilization of the resulting 16eϪ species by coordination
instantaneous reaction occurred, leading to a fairly stable of the pendant alkenyl moiety.[20] Upon addition of water,
species, whose IR spectra displayed two bands at ca. 2015 hydrolysis of the highly electrophilic π-allyl ligand in
and 1970 cmϪ1 characteristic of [CpЈ(CO)2MnLX]ϩ-type [4]ϩ[15c] would then take place through initial nucleophilic
complexes.[14,15] These were indeed identified as the π-allyl addition of water (or hydroxide ions) at the carbon atom
species [CpЈ(CO)2Mn(η3-RCHCHC(OEt)H]ϩ ([4]ϩ) on the bearing the ethoxy group to give the final aldehyde com-
1
1
basis of H-, 13C-, and HMQC H-13C NMR spectroscopy plexes 5.
for [4aϪc]ϩ.[12] In particular, the signals of the protons H1,
Finally, the α,β-unsaturated aldehydes RCHϭCHCHO
H2, and H3 within the π-allyl moiety (see Scheme 4) in [4c]ϩ (6, Table 1) could be released in nearly quantitative yields
were observed at δ ϭ 6.12, 5.55, and 3.41, respectively, in by displacement by triphenylphosphane in THF, or by
740
Eur. J. Inorg. Chem. 1999, 739Ϫ742

[Alkenyl(alkoxy)carbene]manganese Complexes
SHORT COMMUNICATION
1. Typical Procedure for the Synthesis of the Alkenyl(alkoxy)carbene
Complexes [CpЈ(CO)2Mn؍C(OEt)CH؍CHR] (3) as Illustrated for
3c [R ؍ (E)-PhCH؍CH]: The carbene anion [1]Ϫ was generated in
situ by addition of nBuLi (0.630 mL of a 1.6  solution in hexanes,
1.1 mmol) to a solution of [CpЈ(CO)2MnϭC(OEt)CH3] (1, 0.260 g,
1.0 mmol) in THF (15 mL) at Ϫ60°C. After stirring for 20 min,
the solution was cooled to Ϫ80°C and (E)-cinnamaldehyde (2c,
0.125 mL, 1.0 mmol) was added. The cooling bath was removed to
allow the reaction medium to reach room temperature gradually.
After stirring for an additional 1 h, the solvents were removed un-
der vacuum. The brown oily residue was extracted with pentane
(ca. 20 mL), and applied on top of an alumina column. Elution
with pentane afforded a yellow band which was discarded. Elution
with a diethyl ether/pentane (1:10) mixture gave a brown band con-
taining [CpЈ(CO)2MnϭC(OEt)CHϭCHCHϭCHPh] (3c), which
was isolated as a brown solid after removal of the solvents under
acetonitrile in neat acetonitrile, under refluxing conditions
(Scheme 5).
Scheme 5. Demetalation of the α,β-unsaturated aldehydes 6
Considering the satisfactory yields of the individual steps,
as well as the efficient demetalation of the newly formed
α,β-unsaturated aldehydes from the final complex, we logi-
cally became interested in a possible application of the
above sequence to the vinylogation of aldehydes. A one-
vessel procedure was thus developed (Scheme 6) giving the
α,β-unsaturated aldehydes 6 in synthetically useful yields.
vacuum (0.245 mg, 0.65 mmol, 65% yield).
Ϫ C21H21MnO3
(376.33): calcd. C 67.02, H 5.58; found C 67.13, H 5.65. Ϫ Mp
1
94Ϫ96°C. Ϫ IR (νCO, THF): ν˜ ϭ 1940, 1876 cmϪ1. Ϫ NMR H
(C6D6, 250 MHz, 298 K): δ ϭ 7.27Ϫ7.09 (Ph), 7.00 (m, 1 H, H2,
JH2H3 ϭ 15 Hz), 6.73 (m, 1 H, H3, JH3H4 ϭ 11 Hz), 6.63 (m, 2 H,
H4 and H5, JH3H4 ϭ 11 Hz, JH5H4 ϭ 15 Hz), 4.82 (q, 2 H,
OCH2CH3, JHH ϭ 7 Hz), 4.55Ϫ4.35 (m, 4 H, MeCp), 1.71 (s, 3 H,
MeCp), 1.29 (t, 3 H, OCH2CH3). Ϫ NMR 13C{1H} (C6D6,
63 MHz, 298 K): δ ϭ 316.1 (C1), 233.9 (MnCO), 143.4 (C2), 139.4
(C5), 137.2Ϫ126.8 (Ph), 128.6 (C3), 123.4 (C4), 104.1, 87.7, 86.5
(MeCp), 71.6 (OCH2CH3), 14.8 (OCH2CH3), 13.4 (MeCp). Ϫ MS
(EI); m/z: 376 [Mϩ].
2. In Situ Formation of the π-Allyl Complexes CpЈ(CO)2Mn(η3-
RCHC)C(OEt)H]؉ ([4][TfO]) as Illustrated for [4c][TfO] [R ؍
(E)-PhCH؍CH]: TfOH (0.018 mL, 0.2 mmol) was added to a solu-
tion of [CpЈ(CO)2MnϭC(OEt)CHϭCHCHϭCHPh] (3c, 0.080 mg,
0.2 mmol) in CD2Cl2 (1 mL) at Ϫ80°C. The brown solution instan-
taneously turned red. The reaction mixture was allowed to reach
room temperature, and the solution was filtered through a plug of
celite directly into an NMR tube for analysis. Complex [D-4c][TfO]
Scheme 6. Reagents and reaction conditions: i) [1]Ϫ, Ϫ78°C Ǟ
20°C, THF; ii) HCl (aq.), MeCN; iii) reflux
The best performances were recorded with formylferro-
cene (2b) and 4-(dimethylamino)benzaldehyde (2f) giving
the corresponding vinylogated aldehydes 6b and 6f in 75%,
and 68% yield, respectively. A practical limitation of the
procedure is still the need of chromatographic workup to
separate the newly formed aldehyde 6 from its precursor 2.
In conclusion, whereas a recurrent problem with or-
ganometallic synthons is the difficulty to establish the
mechanism of their participation in organic reactions, the
carbenemanganese system disclosed here appears to be
both synthetically useful and amenable to mechanistic stud-
ies due to the relative stability of the intermediates. In par-
ticular, we suggest that the mechanism established here for
the hydrolysis of the (alkenylcarbene)manganese complexes
under acidic conditions may serve as a model for parallel
transformations occurring in related systems.[2b,10d]
was generated in a similar manner from 3c and TfOD. Ϫ IR (νCO
,
1
CH2Cl2): ν˜ ϭ 2010, 1970 cmϪ1. Ϫ H NMR (CD2Cl2, 300 MHz,
223 K): δ ϭ 7.7Ϫ7.3 (m, 5 H, Ph), 7.2Ϫ6.7 (m, 2 H, H4 and H5),
6.12 [s (br.), 1 H, H1], 5.55 [s (br.), 1 H, H2], 5.3Ϫ4.9 (m, 4 H,
MeCp), 4.30 [s (br.), 2 H, OCH2CH3], 3.41 [s (br.), 1 H, H3], 1.73
(s, 3 H, MeCp), 1.29 [s (br.), 3 H, OCH2CH3]. Ϫ 13C{1H} NMR
(CD2Cl2, 75 MHz, 223 K): δ ϭ 227.5, 226.4 (MnCO), 138.1 (C5),
132.2 (C1), 134.8, 128.8, 128.4, 126.9 (Ph), 125.4 (C4), 105.9, 90.9,
90.8, 89.5, 89.2 (MeCp), 77.3 (C2), 72.6 (OCH2CH3), 62.2 (C3),
14.1 (OCH2CH3), 12.2 (MeCp).
Experimental Section
General Remarks: All synthetic manipulations were carried out
using standard Schlenk techniques under dry N2. THF used for the
synthesis was distilled under N2 from Na/benzophenone ketyl just
before use. Other solvents were purified according to standard pro-
cedures, and stored under N2. A liquid N2/2-propanol slush bath
was used to maintain samples at the desired low temperature. Ϫ
Chromatographic separations were performed on alumina. Ϫ
[CpЈ(CO)2MnϭC(OEt)CH3] (1) was prepared by modifications of
literature procedures for related complexes.[21] 1,1Ј-Diformylferro-
3. Typical Procedure for the Synthesis of the Aldehyde Complexes
[CpЈ(CO)2Mn(η2-RCH؍CHCHO)] (5) as Illustrated for 5c [R ؍
(E)-PhCH؍CH]: TfOH (0.180 mL, 2.0 mmol) was added to a solu-
tion of [CpЈ(CO)2MnϭC(OEt)CHϭCHCHϭCHPh] (3c, 0.750 g,
2.0 mmol) in dichloromethane (15 mL) at Ϫ80°C. The cooling bath
was removed to allow the reaction medium to reach room tempera-
ture. An excess of water (5 mL) was added. After stirring for
30 min, the organic phase was separated and the volatiles were re-
cene (2i) was synthesized according to a published procedure.[22] moved under vacuum. The brownish oily residue was purified by
Ϫ Solution-IR spectra were recorded with PerkinϪElmer 225 or
PerkinϪElmer 983 spectrophotometers with 0.1-mm cells equipped
column chromatography on alumina. Elution with a diethyl ether/
pentane (1:1) mixture gave a brown band, which was discarded.
Elution with pure dichloromethane released [CpЈ(CO)2Mn(η2-
PhCHϭCHCHϭCHCHO) (5c), isolated as an orange solid after
evaporation of the solvent (0.610 mg, 1.76 mmol, 88% yield). Ϫ
C19H17MnO3 (348.28): calcd. C 65.51, H 4.88; found C 65.68, H
4.81. Ϫ Mp 136°C (dec.). Ϫ IR (νCO, CH2Cl2): ν˜ ϭ 1965, 1904,
1
with CaF2 windows. Ϫ H- and 13C-NMR spectra were obtained
with Bruker AC200, WM250, DPX300, or AMX400 spectrometers
and were referenced to the residual signals of the solvents. Ϫ Mass
spectra were recorded with a Nermag R10Ϫ10 mass spectrometer.
Ϫ Microanalyses were performed with a PerkinϪElmer 2400
CHN analyzer.
1
1675 cmϪ1. Ϫ H NMR (C6D6, 250 MHz, 298 K): δ ϭ 8.32 (d, 1
Eur. J. Inorg. Chem. 1999, 739Ϫ742
741

C. Mongin, Y. Ortin, N. Lugan, R. Mathieu
SHORT COMMUNICATION
H, H1, JH1H2 ϭ 7 Hz), 7.26Ϫ7.05 (Ph), 6.67 (d, 1 H, H5, JH5H4
ϭ
Chem. Soc. 1993, 115, 3806.
[5]
[5a]
´
C. Andraud, T. Brotin, C. Garcia, F. Pelle,
See for example:
16 Hz), 5.55 (dd, 1 H, H4, JH4H3 ϭ 10 Hz), 3.83, 3.79, 3.75, 3.60
P. Goldner, B. Bigot, A. Collet, J. Am. Chem. Soc. 1994, 116,
(m, 4 H, MeCp), 4.05 [AB(X) pattern, 2 H, H2 and H3, JH2H3
ϭ
[5b]
´ `
T.-T. Nguyen, Y. Gouriou, M. Salle, P. Frere, M.
2094. Ϫ
11 Hz], 1.47 (s, 3 H, MeCp). Ϫ 13C{1H} NMR (C6D6, 63 MHz,
298 K): δ ϭ 233.0, 229.8 (MnCO), 192.2 (C1), 131.9 (C5),
131.8Ϫ125.0 (Ph), 129.9 (C4), 103.2, 86.2, 85.8, 85.5, 84.3 (MeCp),
67.8 (C3), 60.5 (C2), 12.8 (MeCp). Ϫ MS (EI); m/z: 348 [Mϩ].
Jubault, A. Gorgues, L. Toupet, A. Riou, Bull. Chem. Soc. Fr.
1996, 133, 301.
See for example: [6a] A. P. Kozikowski, P. J. Stein, J. Org. Chem.
[6]
[7]
[6b]
1984, 49, 2301. Ϫ
1984, 3421. Ϫ
P. DeShong, J. M. Leginus, J. Org. Chem.
H. Hopf, N. Krause, Tetrahedron Lett. 1986,
[6c]
27, 6177.
4. Typical Procedure for the Demetallation of α,β-Unsaturated Alde-
hydes RCH؍CHCHO (6) as Illustrated for (E,E)-PhCH؍CHCH؍
CHCHO [6c (ϵ 2h)]: Complex [CpЈ(CO)2Mn(η2-PhCHϭCHCHϭ
CHCHO)] (5c, 0.610 g, 1.76 mmol) was dissolved in degassed
acetonitrile (15 mL) and then heated under reflux for 1 h. After
cooling, acetonitrile was removed under vacuum. The oily yellow
residue was chromatographed on an alumina column. Elution with
a pentane/diethyl ether (1:1) mixture afforded a yellow band con-
taining [CpЈ(CO)2Mn(NCMe)]. A second elution with pure diethyl
ether afforded (E,E)-5-phenyl-2,4-pentadienal [6c (ϵ 2h)], which
was isolated as a yellow solid (0.255 g, 1.62 mmol, 95% yield).
These include aldol condensation,[7a] Wittig-,[7b] HornerϪWads-
worthϪEmmons-,[7c] or Peterson-type[7d,7e] reactions, see for in-
[7a]
stance:
G. Wittig, H. Reiff, Angew. Chem., Int. Ed. Engl.
[7b]
1968, 7, 7. Ϫ
B. Maryanoff, A. B. Reitz, Chem. Rev. 1989,
89, 863. Ϫ [7c] J. Boutagy, R. Thomas, Chem. Rev. 1974, 74, 87.
[7d]
Ϫ
L. Duhamel, J. Gralak, B. Ngono, J. Organomet. Chem.
[7e]
1989, 363, C4. Ϫ
1993, 58, 2517.
M. Bellassoued, A. Majidi, J. Org. Chem.
[8]
[9]
J. A. Cabezas, A. C. Oehlschlager, Tetrahedron Lett. 1995, 36,
5127.
C. Mongin, N. Lugan, R. Mathieu, Organometallics 1997, 16,
3873.
[10] [10a]
E. O. Fischer, S. Walz, G. Kreis, F. R. Kreissl, Chem. Ber.
1977, 110, 1651. Ϫ [10b] W. D. Wulff, D. C. Yang, J. Am. Chem.
[10c]
5. One-Vessel Vinylogation of Aldehydes as Illustrated for Formyl-
ferrocene (2b) To Give (3-Oxo-1-propenyl)ferrocene [6b (ϵ 2g)]: The
carbene anion [CpЈ(CO)2MnϭC(OEt)CH2]Ϫ [1]Ϫ was generated in
situ by addition of nBuLi (1.25 mL of a 1.6  solution in hexanes,
2.0 mmol) to a solution of [CpЈ(CO)2MnϭC(OEt)CH3] (1, 525 mg,
2.0 mmol) in THF (15 mL) at Ϫ60 °C in a two-necked flask fitted
with a reflux condenser. After stirring for 20 min, the solution was
cooled to Ϫ80°C and formylferrocene was added as a powder
(430 mg, 2.0 mmol). The cooling bath was removed to allow the
reaction medium to reach room temperature gradually, and the
solution was stirred for an additional 1 h. THF was evaporated
under vacuum and replaced by degassed acetonitrile (30 mL). Hy-
drochloric acid (0.330 mL of a 10  solution in water) was added
dropwise, and the mixture was heated under reflux for 1 h. After
cooling, the volatiles were removed under vacuum. The oily residue
was purified by column chromatography on alumina. Elution with
a pentane/diethyl ether (1:1) mixture afforded a yellow band
containing traces of [CpЈ(CO)3Mn], traces of 1, and
[CpЈ(CO)2Mn(NCMe)], which was discarded. A second elution
with pure diethyl ether gave a purple band followed by an orange
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2g)], isolated as
a microcrystalline purple material (360 mg,
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