Dichotomy within 1,4-addition of organolithium and Grignard reagents to α,β-unsaturated Fischer alkoxycarbenes: A new synthesis of Fischer carbenes

Article abstract of DOI:10.1016/j.tet.2019.02.038

The reaction of organolithium and Grignard reagents with pentacarbonyl[(ethoxy)(2-phenylethenyl)carbene]chromium(0) gave, after the quenching of the initially formed product of the 1,4-addition, different products depending on the organometallic and quenching reagents used. The addition of organolithiums, followed by a work-up with acid (AcOH or HCl), afforded the corresponding carbene complexes. In contrast, quenching the reaction mixture with ethanol led to the stereoselective formation of (Z)-enol ethers. The usage of Grignard reagents led to the formation of the carbene complexes regardless of which quenching reagent was used.

Full text of DOI:10.1016/j.tet.2019.02.038

Tetrahedron xxx (xxxx) xxx
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Dichotomy within 1,4-addition of organolithium and Grignard
reagents to
a,b-unsaturated Fischer alkoxycarbenes: A new synthesis
of Fischer carbenes
a
,
**
a
a
a, *
ꢀ b
ꢁꢀ
ꢁ
ꢀꢁ
Tomas Tobrman
ꢀ
ꢁꢀ
ꢁꢀ
, Peter Polak , Marek Cubinak , Hana Dvorakova , Dalimil Dvorak
a
ꢀ
Department of Organic Chemistry, University of Chemistry and Technology, Prague, Technicka 5, 166 28 Prague 6, Czech Republic
Laboratory of NMR Spectroscopy, University of Chemistry and Technology, Prague, Technicka 5, 166 28 Prague 6, Czech Republic
b
ꢀ
a r t i c l e i n f o
a b s t r a c t
Article history:
The reaction of organolithium and Grignard reagents with pentacarbonyl[(ethoxy)(2-phenylethenyl)
carbene]chromium(0) gave, after the quenching of the initially formed product of the 1,4-addition,
different products depending on the organometallic and quenching reagents used. The addition of
organolithiums, followed by a work-up with acid (AcOH or HCl), afforded the corresponding carbene
complexes. In contrast, quenching the reaction mixture with ethanol led to the stereoselective formation
of (Z)-enol ethers. The usage of Grignard reagents led to the formation of the carbene complexes
regardless of which quenching reagent was used.
Received 12 December 2018
Received in revised form
12 February 2019
Accepted 15 February 2019
Available online xxx
Keywords:
© 2019 Elsevier Ltd. All rights reserved.
Alkoxycarbene
Organolithium
Grignard reagent
1,4-addition
Enolether
1. Introduction
Iwasawa reported that alkylcerium reagents derived from primary
and secondary butyllithium gave almost quantitatively, with
unsaturated carbene complexes, products of a 1,4-addition [5]
(Scheme 1). Reactivity of -unsaturated carbene complexes still
reminds active area [6]. In connection with our previous experience
with metalated Fischer aminocarbene complexes [7], we turned
our attention to the reaction of vinylcarbene complexes with
organometallic reagents.
a,b-
The characteristic feature of the Fischer carbene complexes of
Group 6 elements, which are already known from 1964 [1], is the
strong electron-withdrawing character of the pentacarbonyl metal
group. Therefore, it is not surprising that the conjugate addition to
the double bond, which is in conjugation with the metal fragment
of these complexes, was already attempted in the early seventies.
Casey reported a reaction of these compounds with organolithium
compounds and lithium enolates. This reaction afforded, depend-
ing on the structure of the carbene complex and nucleophile,
products of the 1,2 and/or 1,4 addition in low yield (Scheme 1) [2].
Later, it was shown that not only alkenylcarbene complexes, but
also (alkoxy)(aryl)carbene complexes, react with organolithiums in
the 1,2-, 1,4- or 1,6-fashion, and considerable attention was paid to
the addition of lithium enolates [3]. It was shown that the addition
of organolithium reagents to optically active Fischer vinylcarbene
complexes proceeds with high diastereoselectivity [4]. Later,
a,b
2. Results and discussion
In contrast to Casey, who observed the formation of the carbene
complex 2a in low yield together with the enol ether 3, we
observed that the Fischer a,b-unsaturated alkoxycarbene 1b reac-
ted with n-butyllithium, affording the carbene complex 2b in 91%
NMR yield after quenching with dry HCl (Table 1, entry 1). This led
us to explore this addition reaction in detail. In contrast to the
above result, quenching the reaction of carbene complex 1b with n-
butyllithium in dry THF or cyclopentyl methyl ether with ethanol
led to the formation of the enol ether 4b in good yield as the sole
product (Table 1, entries 2,3). Casey had already observed the for-
mation of this type of enol ether 4a in very low yield using an
organocopper reagent. Both of our products, carbene 2b and enol
* Corresponding author.
** Corresponding author.
E-mail addresses: tomas.tobrman@vscht.cz (T. Tobrman), dalimil.dvorak@vscht.
ꢁꢀ
cz (D. Dvorak).
https://doi.org/10.1016/j.tet.2019.02.038
0040-4020/© 2019 Elsevier Ltd. All rights reserved.
Please cite this article as: T. Tobrman et al., Dichotomy within 1,4-addition of organolithium and Grignard reagents to
alkoxycarbenes: A new synthesis of Fischer carbenes, Tetrahedron, https://doi.org/10.1016/j.tet.2019.02.038
a,b-unsaturated Fischer

2
T. Tobrman et al. / Tetrahedron xxx (xxxx) xxx
Scheme 1. Reaction of a,b-unsaturated alkoxycarbene complexes with alkyllithium reagents.
Table 1
reagent to 1b is protonated. The stronger, and therefore harder,
Addition of organometallic reagents to the carbene 1b.
acids prefer protonation on the harder base, which, in this case, is
the carbon atom. This results in the formation of the carbene 2b. In
contrast, the softer, weak acids prefer to protonate on the soft metal
centre of the aduct, leading, after reductive elimination, to the enol
ether 4b. In the case of the Grignard reagent, the resonance
structure A prevails in the resonance hybrid because of the more
covalent MgeC bond, while the more electropositive Li atom pre-
fers the ionic resonance structure B. The protonation then accord-
ingly leads to the corresponding product 2b or 4b. The exclusive
formation of the (Z)-isomer of 4b is then a result of steric in-
teractions between bulky Cr(CO)5 and the RCHPh groups, which
leads to the (E)-configuration of the 1,4-adduct. Protonation on
metal and subsequent reductive elimination forms the (Z)-4b
(Scheme 2).
entry
M
solvent/acid
2b (%)a
4b (%)a
1
2
3
4
5
6
7
Li
Li
Li
Li
THF/HCl
THF/EtOH
CpOMe/EtOH
Et2O/EtOH
EtOH,THF/AcOH
THF/EtOH
91, 75b
e
e
73, 61b
e
75
59
e
e
We then began to explore the scope of the transformation of
carbene 1b to the enol ethers 4 (Table 2). Similar results to those
Li
91
90b
MgBr
Bu2CuLi
e
c
c
THF/EtOH
ꢀ
ꢀ
a
1H NMR yield, 1,3,5-trimethoxybenzene was used as the internal standard.
Isolated yield.
A complex mixture of products was formed.
b
c
ether 4b, are the result of a 1,4-addition, while the enol ether 3
observed by Casey results from a 1,2-addition to the -unsatu-
rated carbene [8]. The reduction of -unsaturated alkoxycarbene
a,b
a,b
complexes with NaBH4 is also reported to proceed via 1,2-addition
[9]. Running the reaction in diethyl ether dropped the yield of 4b to
59% (Table 1, entry 4). The work-up of the reaction mixture with
acetic acid afforded the same result as that with HCl (Table 1, entry
5). In contrast to n-butyllithium, the corresponding Grignard re-
agent afforded the carbene complex 2b in 90% isolated yield as the
only product when quenched with ethanol (Table 1, entry 6). The
Gilman cuprate was shown to be non-effective in this case,
affording a complex reaction mixture under the same conditions
(Table 1, entry 7). The enol ether 4b was in all cases obtained
exclusively as the (Z)-isomer, which follows from the 3JHH coupling
constant of the olefin protons (6.25 Hz). Such exclusive formation of
(Z)-enolether is well known not only as result of 1,2-addition [9,10],
but recently also from 1,4-addition [6c,d].
The observed dichotomy of this reaction can be explained by the
way in which the initially formed 1,4-adduct of an organometallic
Scheme 2. Formation of 2b and 4b by the protonation of the 1,4-adduct of n-butyl-
lithium to the a,b-unsaturated carbene 1b.
Please cite this article as: T. Tobrman et al., Dichotomy within 1,4-addition of organolithium and Grignard reagents to
alkoxycarbenes: A new synthesis of Fischer carbenes, Tetrahedron, https://doi.org/10.1016/j.tet.2019.02.038
a,b-unsaturated Fischer

T. Tobrman et al. / Tetrahedron xxx (xxxx) xxx
3
Table 2
Table 3
Preparation of enol ethers 4 via 1,4-addition of alkyllithium reagents.
Preparation of carbene complexes 2 by the addition of Grignard reagents to the
carbene complex 1b.
entry
R
M
4, yield (%)a
entry
Grignard reagent
2, yield (%)a
1
2
3
4
5
6
7
8
9
nBu
Cr
Cr
Cr
Cr
Cr
Cr
Cr
W
W
4b, 61
4c, 56
4d, 34
4e, 77
4f, 72
4g, 44
1
2
3
4
5
6
BuMgBr
2b, 90
2c, 97
2d, 97
PhCH2CH2
tBu
CpMgCl
tBuMgCl
TMSCH2Li
cycloheptenyl
Ph
CH2¼CHCH2MgCl
2e, 47
PhMgCl
2f, 36, 50b
2g, ꢀ, 90c
b
TMSCH2MgBr
TMSC≡C
ꢀ
nBu
4b, 54
4e, 75
a
Isolated yield.
TMSCH2Li
b
c
PhLi was used, and the reaction mixture was quenched with AcOH/EtOH.
TMSCH2Li was used, and the reaction mixture was quenched with AcOH/EtOH.
a
Isolated yield.
A complex mixture of products was formed.
b
observed instead (Table 3, entry 6). However, using trimethylsi-
lylmethyllithium, followed by quenching with a solution of acetic
acid in ethanol, afforded the desired carbene complex 2g in 90%
yield (Table 3, entry 6). Other tested Grignard reagents, including 2-
thienylmagnesium bromide, phenethyl magnesium iodide and
vinylmagnesium chloride, failed to give the expected alkox-
ycarbenes, and the formation of a complex reaction mixture was
instead observed.
In addition, the analogous reaction of Fischer carbene 6, con-
taining a conjugated triple bond with organolithiums, was briefly
tested. The carbene complex 6 was treated with n-butyllithium
at ꢀ78 ꢁC, and acetic acid was subsequently added. In this case, the
crude reaction mixture was more complicated compared to the
reactions with the previously studied alkenylcarbenes. Despite
that, we were able to isolate the expected unsaturated carbene 7a
in 31% yield by chromatography (Scheme 3). The reaction with
phenethyllithium proceeded with even lower yield (16%) and was
not stereoselective, giving an approximately 1:1 mixture of E/Z
isomers (Scheme 3). The loss of stereoselectivity can be attributed
to the low rotational barrier around the CeC bond in the resonance
hybrid A4B (Scheme 3) and the similar steric interactions of the
ethoxycarbene moiety with the butyl and the R groups in the pri-
mary product of the addition.
with n-butyllithium were obtained with phenethyllithium (Table 2,
entry 2), while bulkier tert-butyllithium afforded the desired enol
ether 4d in low yield (Table 2, entry 3). Trimethylsilylmethyllithium
and cycloheptenyllithium reacted smoothly, forming the enol
ethers 4e and 4f in good yield (Table 2, entries 4,5). The use of
phenyllithium, prepared by the reaction of bromobenzene with
tert-butyllithium, furnished the expected product 4g in 44% iso-
lated yield (Table 2, entry 6). In contrast, the trimethylsilylethy-
nyllithium failed to react in a reasonably good yield, and a complex
reaction mixture was formed in this case (Table 2, entry 7). It is
worthwhile to mention that the corresponding tungsten carbene
complex 1c reacted with n-butyllithium and trimethylsilylme-
thyllithium in the same fashion and in similar yields to the chro-
mium carbene 1b (Table 2, entries 8,9). In all cases, (Z)-isomers of
the enol ethers 4 were exclusively formed.
The obtained enol ethers can be easily hydrolysed to the cor-
responding b-substituted aldehydes. This was demonstrated on the
enol ethers 4b, e and f. Their treatment with 1M aqueous hydro-
chloric acid in acetone afforded the desired aldehydes 5b, e and 5f
in high yield.
The reaction of alkoxycarbene 1b with Grignard reagents was
explored next. This reaction, which was accomplished under the
same conditions as the reaction with organolithiums, was more
sluggish, requiring about 30 min to finish. This was easily followed
by the colour change from deep red to yellow. Butylmagnesium
bromide gave the carbene 2b in almost quantitative yield (Table 3,
entry 1), just as did the cyclopentyl and tert-butylmagnesium
chlorides (Table 3, entries 2,3). A moderate yield of the corre-
sponding carbene 2e was observed in the reaction of 1b with
allylmagnesium chloride (Table 3, entry 4). Similar results were also
obtained with phenylmagnesium chloride, but in this case, the
addition reaction had to be carried out at 0 ꢁC to achieve the
complete conversion of the starting 1b. Here, the better yield of the
carbene 2f was obtained when phenyllithium was used instead of
the Grignard reagent and the reaction mixture was quenched with
acetic acid in ethanol (Table 3, entry 5). Trimethylsilylmethyl
magnesium bromide failed to give the corresponding carbene
complex 2g, and the formation of a complex reaction mixture was
Scheme 3. Addition of alkyllithiums to alkynylcarbene complex 6.
Please cite this article as: T. Tobrman et al., Dichotomy within 1,4-addition of organolithium and Grignard reagents to
alkoxycarbenes: A new synthesis of Fischer carbenes, Tetrahedron, https://doi.org/10.1016/j.tet.2019.02.038
a,b-unsaturated Fischer

4
T. Tobrman et al. / Tetrahedron xxx (xxxx) xxx
4.1.1. Cycloheptenyllithium
t-BuLi (1.18 mL, 2.0 mmol) was added to a solution of 1-
bromocyclohept-1-ene in dry ether (3 mL) cooled to ꢀ78 ꢁC. The
resultant mixture was stirred for 30 min at ꢀ78 ꢁC, then the
mixture was warmed to ambient temperature and the cyclo-
heptenyllithium was used as prepared.
4.1.2. Pentacarbonyl[ethoxy(phenylethenyl)carbene]tungsten(0)
(1c) was prepared by modified literature procedure [9]. Trie-
thylamine (13.35 mL, 96 mmol), trimethylsilyl chloride (11.0 mL,
87 mmol) and benzaldehyde (2.52 g, 24.0 mmol) were added to the
solution of pentacarbonyl[ethoxy(methyl)carbene]tungsten(0)
(6.230 g, 15.73 mmol) in dry ether (30 mL). The resultant mixture
was stirred for 48 h at ambient temperature. Then 10 g of alumina
was added, solvents were removed under reduce pressure, and
column chromatography (hexane, Rf ¼ 0.30) afforded the title
compound 2.55 g (33%) as black solid. 1H NMR (300 MHz, CDCl3):
Scheme 4. One-pot conversion of alkynylcarbene 6 to 3-butylhept-2-enal 8.
As with alkenylcarbene 1b, when the reaction of the alky-
d
1.68 (t, J ¼ 7.2 Hz, 3H), 4.95 (q, J ¼ 7.2 Hz, 2H), 7.20 (d, J ¼ 15.6 Hz,
nylcarbene 6 with organolithium was quenched with ethanol, the
corresponding allenyl enol ethers were formed. These enol ethers
were not isolated. Evidence of their formation comes from the
hydrolysis of the crude reaction mixture of 1b with BuLi, which
afforded 3-butylhept-2-enal 8 in low yield (Scheme 4).
1H), 7.41e7.43 (m, 3H), 7.61e7.63 (m, 2H), 7.88 (d, J ¼ 15.6 Hz, 1H).
13C NMR (126 MHz, CDCl3):
d 15.0, 78.9, 129.2, 129.3, 130.9, 134.1,
134.6, 143.6, 197.6 (1JW-C ¼ 127 Hz), 203.9 (1JW-C ¼ 116 Hz), 305.2
(1JW-C ¼ 104 Hz). HRMS (ESI) calcd for C16H11O6W [M-H]-:
483.0070. Found: 483.0076.
3. Conclusions
The 1,4-addition of organometallic reagents to the a,b-unsatu-
4.2. General procedure for the reaction of alkoxycarbene 1b with
rated alkoxycarbene complexes of chromium gives different prod-
ucts depending on the organometallic reagent and/or the method
of quenching used. The addition of organolithium reagents fol-
lowed by acidic (HCl or AcOH) work-up gives carbene complexes,
products of conjugated addition. This reaction represents new
synthetic approach to certain alkoxycarbene complexes. In
contrast, quenching the reaction mixture with ethanol leads to the
loss of the metal and to the formation of enol ethers as the only
products. These enol ethers are formed exclusively as (Z)-isomers.
In contrast to the lithium reagents, the Grignard reagents afford
carbenes in high yield regardless of whether HCl or ethanol is used
for the quenching.
Grignard reagents e formation of carbene complexes
A solution of Grignard reagent (1.5 equiv) was added to the
solution of the carbene 1b (1.0 equiv) in dry THF (9 mL/mmol)
cooled to ꢀ78 ꢁC. The resulting mixture was stirred for
30 min at ꢀ78 ꢁC followed by the addition of EtOH (6 mL/mmol).
The mixture was then stirred for 15 min at ꢀ78 ꢁC, warmed to
ambient temperature and concentrated under reduce pressure.
Column chromatography on silica gel afforded the target
compound.
4.2.1. Pentacarbonyl[ethoxy(2-phenylhexyl)methylene]
chromium(0) (2b)
4. Experimental
The general procedure starting from the carbene 1b (0.212 g,
0.60 mmol), butylmagnesium bromide (0.42 mL, 0.90 mmol), dry
THF (6 mL), and EtOH (4 mL) afforded after column chromatog-
raphy (hexane Rf ¼ 0.55, PMA detection) the title compound
0.222 g (90%) as a yellow oil. Alternatively, the title compound was
prepared from the carbene 1b (0.053 g, 0.15 mmol), butyllithium
(0.09 mL, 0.023 mmol), dry THF (3 mL) and HCl (0.5 mL, 1.5 mmol of
3M solution in CpOMe). Column chromatography afforded the title
compound 0.092 g (75%) as a yellow oil. 1H NMR (600 MHz, CDCl3):
4.1. General information
All reactions were performed under an argon atmosphere. The
NMR spectra were measured on a Varian Gemini 300 (1H,
300.07 MHz, 13C, 75.46 MHz), a Bruker DRX 500 Avance (1H,
500.13 MHz, 13C, 125.78 MHz) and a Bruker 600 Avance III (1H,
600.13 MHz, 13C, 150.92 MHz) spectrometer at 298 K. The mass
spectra were measured on a ZAB-SEQ (VG Analytical). The dry and
degassed solvents were prepared with PureSolv MD7 silica gel
d
0.86 (t, J ¼ 7.2 Hz, 3H, CH3Hex), 1.11e1.16 (m, 2H, CH2 Hex), 1.24e1.34
(Merck, Silica Gel 60, 40e63 mm), and aluminium oxide 90 stan-
(m, 2H, CH2 Hex),1.44 (t, J ¼ 7.0 Hz, 3H, CH3EtO), 1.57e1.64 (m, 2H, CH2
dardized (Merck, 0.063e0.200 mm) was used for the column
chromatography. BuLi (2.5 M solution in hexane) and other com-
pounds were purchased. Phenethyllithium [11], pentacarbonyl
[ethoxy(phenylethenyl)carbene]chromium(0) (1b) [12] and pen-
tacarbonyl[ethoxy(hept-1-ynyl)carbene]chromium(0) (6) [13]
were prepared according to the procedure in the literature; other
compounds were purchased. A concentration of n-BuLi, t-BuLi, was
determined by titration using menthol and 1,10-phenanthroline
before use. The concentration of Grignard reagents was deter-
mined by titration using iodine.
Hex), 3.14 (m, 1H, CHPh), 3.63 (dd, J ¼ 8.8, 15.1 Hz, 1H, CH2C(OEt)
Cr(CO)5), 3.72 (dd, J ¼ 5.7, 15.1 Hz, 1H, CH2C(OEt)Cr(CO)5),
4.94e4.95 (m, 2H, CHE2tO), 7.13e718 (m, 2H, CHPh), 7.20e7.21 (m, 1H,
CHPh), 7.28e7.30 (m, 2H, CHPh). 13C NMR (151 MHz, CDCl3):
d 13.9
(CH3Hex), 14.7 (CHE3tO), 22.5 (CHH2 ex), 29.6 (CH2Hex), 36.1 (CHH2 ex), 43.5
(CHPh), 70.0 (CH2C(OEt)Cr(CO)5), 77.9 (CHE2tO), 126.3 (CHPh), 127.5
(CHPh), 128.3 (CHPh), 144.1 (CPqh), 216.4 (CO), 223.1 (CO), 359.1 (C]
Cr). HRMS (ESI) calcd for C20H21CrO6 [M-H]-: 409.0749. Found:
409.0775.
Please cite this article as: T. Tobrman et al., Dichotomy within 1,4-addition of organolithium and Grignard reagents to
alkoxycarbenes: A new synthesis of Fischer carbenes, Tetrahedron, https://doi.org/10.1016/j.tet.2019.02.038
a,b-unsaturated Fischer

T. Tobrman et al. / Tetrahedron xxx (xxxx) xxx
5
4.2.2. Pentacarbonyl[ethoxy(2-phenyl-2-cyclopentylethyl)
4.2.6. Pentacarbonyl{ethoxy[2-phenyl-3-(trimethylsilylmethyl)
methylene]chromium(0) (2c)
propyl]methylene}chromium(0) (2g)
This compound was prepared according to the general proced-
ure starting from the carbene 1b (0.212 g, 0.60 mmol), cyclopentyl
magnesium bromide (0.45 mL, 0.90 mmol), dry THF (6 mL), and
EtOH (4 mL). Column chromatography (hexane Rf ¼ 0.60, PMA
detection) afforded the title compound 0.246 g (97%) as a yellow oil.
The general procedure starting from the carbene 1b (0.212 g,
0.60 mmol), trimethylsilylmethyllithium (3.0 mL, 1.0 mmol), dry
THF (6 mL) was followed. The reaction mixture was stirred for
15 min at ꢀ78 ꢁC, quenched by addition of a solution of acetic acid
(0.240 g, 4.0 mmol) in EtOH (4 mL). After 15 min at ꢀ78 ꢁC the re-
action mixture was warmed to ambient temperature, concentrated
under reduce pressure, and column chromatography (hexane
Rf ¼ 0.55, PMA detection) afforded the title compound 0.238 g
1H NMR (300 MHz, CDCl3):
d 0.92e1.03 (m, 1H), 1.19e1.69 (m, 9H),
1.90e2.04 (m, 2H), 2.88 (dt, J ¼ 4.5, 10.5 Hz, 1H), 3.66e3.86 (m, 2H),
4.79e4.85 (m, 2H), 7.06e7.23 (m, 5H). 13C NMR (76 MHz, CDCl3):
d
14.5, 24.7, 25.2, 31.4, 31.5, 46.4, 49.2, 68.9, 77.8, 126.1, 127.7, 128.1,
(90%) as a red oil. 1H NMR (500 MHz, CDCl3):
d
ꢀ0.24 (s, 9H), 0.83
144.0, 216.3, 223.0, 358.9. HRMS (ESI) calcd for C21H21CrO6[M-H]-:
421.0749. Found: 421.0768.
(dd, J ¼ 4.8 Hz, 1H), 1.04 (dd, J ¼ 11.1, 14.1 Hz, 1H), 1.40 (t, J ¼ 6.9 Hz,
3H), 3.27e3.33 (m, 1H), 3.59 (dd, J ¼ 9.0, 14.7 Hz, 1H), 3.70 (dd,
J ¼ 6.0, 14.7 Hz, 1H), 4.90 (q, J ¼ 6.9 Hz, 2H), 7.11e7.18 (m, 3H),
7.22e7.26 (m, 2H). 13C NMR (126 MHz, CDCl3):
d
ꢀ1.3, 14.6, 25.0,
4.2.3. Pentacarbonyl[ethoxy(2-phenyl-2-tert-butylethyl)methylene]
chromium(0) (2d)
40.0, 73.5, 77.8, 126.4, 127.4, 128.3, 145.1, 216.4, 223.1, 359.1. HRMS
(ESI) calcd for C20H23CrO6Si [M-H]-: 439.0675. Found: 439.0699.
The general procedure starting from the carbene 1b (0.196 g,
0.56 mmol), tert-butylmagnesium chloride (0.45 mL, 0.90 mmol),
dry THF (6 mL), and EtOH (4 mL) afforded after column chroma-
tography (hexane Rf ¼ 0.60, PMA detection) the title compound
4.3. General procedure for the reaction of alkoxycarbenes 1b and 1c
with alkyllithium reagents e formation of enolethers
0.223 g (97%) as a red oil. 1H NMR (300 MHz, CDCl3):
d 0.90 (s, 9H),
A solution of alkyllithium (1.5 equiv) was added to a solution of
carbene 1b or 1c (1.0 equiv) in dry THF (9 mL/mmol) cooled
to ꢀ78 ꢁC. The resulting mixture was stirred for 15 min at ꢀ78 ꢁC
followed by the addition of EtOH (6 mL/mmol). The mixture was
stirred for 15 min at ꢀ78 ꢁC, warmed to ambient temperature and
concentrated under reduce pressure. Column chromatography
(silica gel) afforded the target compound.
1.24 (t, J ¼ 6.9 Hz), 2.95 (dd, J ¼ 3.6, 11.4 Hz, 1H), 3.66 (dd, J ¼ 3.9,
16.2 Hz, 1H), 4.13 (dd, J ¼ 11.1, 16.2 Hz, 1H), 4.75e4.82 (m, 2H),
7.07e7.09 (m, 2H), 7.15e7.25 (m, 3H). 13C NMR (76 MHz, CDCl3):
d
14.4, 28.0, 33.8, 52.5, 64.1, 78.1, 126.1, 127.5, 129.2, 141.7, 216.4,
222.9, 358.4. HRMS (ESI) calcd for C20H21CrO6 [M-H]-: 409.0749.
Found: 409.0769.
4.3.1. (Z)-1-Ethoxy-3-phenylhept-1-ene (4b)
4.2.4. Pentacarbonyl[ethoxy(2-phenylpent-4-enyl)methylene]
chromium(0) (2e)
This compound was prepared according to the general proced-
ure starting from the carbene 1b (0.212 g, 0.60 mmol), BuLi
(0.38 mL, 0.9 mmol), dry THF (6 mL), and EtOH (4 mL). Column
chromatography (hexane/DCM 1/9, Rf ¼ 0.35, PMA detection)
afforded the title compound 0.080 g (61%) as a colorless oil. The title
compound was also prepared from the tungsten carbene complex
1c (0.290 g, 0.60 mmol) according to the general procedure. Col-
umn chromatography (hexane/DCM 1/9, Rf ¼ 0.35, PMA detection)
afforded the title compound 0.070 g (54%) as a colourless oil. 1H
The general procedure starting from the carbene 1b (0.212 g,
0.60 mmol), allylmagnesium chloride (0.50 mL, 0.90 mmol), dry
THF (6 mL), and EtOH (4 mL) afforded after column chromatog-
raphy (hexane/DCM 9/1 Rf ¼ 0.25, PMA detection) the title com-
pound 0.110 g (47%) as a yellow oil. 1H NMR (300 MHz, CDCl3):
d
1.42 (t, J ¼ 7.2 Hz, 3H), 2.24e2.40 (m, 2H), 3.16e3.24 (m, 1H),
3.67e3.70 (m, 2H), 4.89e5.04 (m, 4H), 5.56e5.67 (m, 1H), 7.10e7.30
(m, 5H). 13C NMR (76 MHz, CDCl3):
14.6, 40.8, 43.1, 68.8, 77.9,
d
NMR (500 MHz, CDCl3):
d
0.92 (t, J ¼ 7.1 Hz, 3H, CHH3 ept), 1.28 (t,
116.9, 126.4, 127.4, 128.4, 136.0, 143.5, 216.3, 223.0, 358.5. HRMS
J ¼ 7.1 Hz, 3H, CHE3tO), 1.35e1.38 (m, 4H, CHH2 ept), 1.62e1.77 (m, 2H,
(ESI) calcd for C19H17CrO6 [M-H]-: 393.0436. Found: 393.0458.
CHH2 ept), 3.80e3.85 (m, 3H, 2H CHE2tO þ 1H CHPh), 4.56 (dd, J ¼ 6.2,
9.6 Hz, 1H, ¼CHe), 6.02 (d, J ¼ 6.2 Hz, 1H, ¼CHeO), 7.19e7.22 (m,
1H, CHPh), 7.28e7.32 (m, 4H, CHPh). 13C NMR (126 MHz, CDCl3):
4.2.5. Pentacarbonyl[ethoxy(2,2-diphenylethyl)methylene]
chromium(0) (2f)
d
14.1 (CHH3 ept), 15.3 (CH3EtO), 22.7 (CHH2 ept), 29.8 (CHH2 ept), 36.6
(CHH2 ept), 40.3 (CHPh), 67.6 (CH2EtO), 111.3 (¼CHe), 125.6 (CHPh), 127.3
(CHPh), 128.3 (CHPh), 144.3 (¼CHeO), 146.5 (CPqh). HRMS (ESI) calcd
for C15H23O [MþH]þ: 219.1743. Found: 219.1742.
Prepared according to the general procedure starting from the
carbene 1b (0.106 g, 0.30 mmol), phenylmagnesium chloride
(0.45 mL, 0.24 mmol), dry THF (3 mL). The reaction mixture was
stirred for 30 min at 0 ꢁC before EtOH (4 mL) was added. Column
chromatography (hexane, Rf ¼ 0.40, PMA detection) afforded the
title compound 0.046 g (36%). Analogously, the starting compound
was prepared from the carbene 1b (0.212 g, 0.60 mmol), phenyl-
lithium (3.0 mL, 1.0 mmol), dry THF (6 mL). The reaction mixture
was stirred for 15 min at ꢀ78 ꢁC, quenched by addition of a solution
of acetic acid (0.240 g, 4.0 mmol) in EtOH (4 mL). After
15 min at ꢀ78 ꢁC the reaction mixture was warmed to ambient
temperature, concentrated under reduce pressure, and column
chromatography (hexane/DMC 9/1, Rf ¼ 0.15, PMA detection)
afforded the title compound 0.130 g (50%) as a yellow solid. 1H NMR
4.3.2. (Z)-1-Ethoxy-3,5-diphenylpent-1-ene (4c)
The general procedure starting from the carbene 1b (0.212 g,
0.60 mmol), phenethyllithium (3.1 mL, 1.0 mmol), dry THF (6 mL),
and EtOH (4 mL) afforded after column chromatography (hexane/
DCM 4/1, Rf ¼ 0.30, PMA detection) the title compound 0.090 g
(56%) as a yellow oil. 1H NMR (500 MHz, CDCl3):
d
1.32 (t, J ¼ 7.1 H,
3H), 2.00e2.08 (m, 2H), 2.60e2.65 (m, 1H), 2.70e2.75 (m, 1H),
3.84e3.93 (m, 3H), 4.62 (dd, J ¼ 6.2, 9.60 Hz, 1H), 6.09 (d, J ¼ 6.2 Hz,
1H), 7.21e7.25 (m, 4H), 7.31e7.36 (m, 6H). 13C NMR (126 MHz,
CDCl3):
d 15.4, 34.0, 38.7, 40.2, 67.7, 110.7, 125.6, 125.8, 127.3, 128.2,
128.4, 128.5, 142.6, 144.7, 146.0. HRMS (EI) [M]þ calcd for C19H22O:
266.1665. Found: 266.1645.
(500 MHz, CDCl3):
4.58 (t, J ¼ 7.7 Hz), 4.98 (q, J ¼ 7.0 Hz, 2H), 7.23e7.25 (m, 6H),
7.30e7.34 (m, 4H). 13C NMR (126 MHz, CDCl3):
14.5, 48.1, 68.4,
d
1.35 (t, J ¼ 7.0 Hz, 3H), 4.21 (d, J ¼ 7.7 Hz, 2H),
d
78.2, 126.5, 127.7, 128.6, 143.3, 216.3, 222.9, 356.5. HRMS (ESI) calcd
4.3.3. (Z)-1-Ethoxy-3-phenyl-4,4-dimethylpent-1-ene (4d)
for C22H17CrO6 [M-H]-: 429.0436. Found: 429.0461.
The compound was prepared according to the general
Please cite this article as: T. Tobrman et al., Dichotomy within 1,4-addition of organolithium and Grignard reagents to
alkoxycarbenes: A new synthesis of Fischer carbenes, Tetrahedron, https://doi.org/10.1016/j.tet.2019.02.038
a,b-unsaturated Fischer

6
T. Tobrman et al. / Tetrahedron xxx (xxxx) xxx
procedure starting from carbene 1b (0.212 g, 0.60 mmol), tert-
butyllithium (0.53 mL, 0.90 mmol), dry THF (6 mL), and EtOH
(4 mL). Column chromatography (hexane/DCM 9/1, Rf ¼ 0.35, PMA
detection) afforded the title compound 0.045 g (34%) as a red oil. 1H
title compound 0.060 g (31%) as a red oil. 1H NMR (300 MHz,
CDCl3):
d
0.89e0.95 (m, 6H), 1.32e1.51 (m, 8H), 1.65 (t, J ¼ 6.9 Hz,
3H), 2.08e2.18 (m, 4H), 5.06 (q, J ¼ 6.9 Hz, 2H), 7.20 (s, 1H). 13C NMR
(126 MHz, CDCl3): d 13.9, 14.0, 15.2, 22.6, 23.3, 30.3, 31.2, 33.8, 38.5,
NMR (500 MHz, CDCl3):
d
0.93 (s, 9H),1.22 (t, J ¼ 7.1 Hz, 3H), 3.68 (d,
76.8, 140.9, 147.3, 216.9, 224.1, 337.0. HRMS (ESI) calcd for
C
J ¼ 10.7 Hz,1H), 3.78 (q, J ¼ 7.1 Hz, 2H), 4.89 (dd, J ¼ 6.4,10.7 Hz,1H),
18H23CrO6 [M-H]-: 387.09052. Found: 387.09045.
6.06 (d, J ¼ 6.4 Hz, 1H), 7.20e7.30 (m, 5H). 13C NMR (126 MHz,
CDCl3):
d 15.3, 27.8, 34.3, 50.5, 67.5, 107.5, 125.6, 127.5, 129.4, 143.5,
4.3.8. (E) and (Z)-Pentacarbonyl[ethoxy(2-phenethyl-hex-1-enyl)
methylene]chromium(0) (7b)
144.8. HRMS (EI) [M]þ calcd for C14H19O: 203.1430. Found:
203.1419.
The carbene was prepared according to the general procedure
starting from the carbene
5 (0.195 g, 0.591 mmol), phene-
4.3.4. (Z)-Trimethyl(4-ethoxy-2-phenylbut-3-enyl)silane (4e)
thyllithium (3.0 mL, 1.0 mmol), dry THF (6 mL). The reaction
mixture was stirred for 15 min at ꢀ78 ꢁC, quenched by addition of a
solution of acetic acid (0.240 g, 4.0 mmol) in EtOH (4 mL). After
15 min at ꢀ78 ꢁC the reaction mixture was warmed to ambient
temperature, concentrated under reduce pressure, and column
chromatography (hexane Rf ¼ 0.35, PMA detection) afforded the
title compound 0.040 g (16%) as a 1/1 mixture of E/Z isomers in
The general procedure starting from the carbene 1b (0.212 g,
0.60 mmol), trimethylsilylmethyllithium (0.90 mL, 0.90 mmol), dry
THF (6 mL), and EtOH (4 mL) afforded after column chromatog-
raphy (hexane/DCM 9/1, Rf ¼ 0.40, PMA detection) the title com-
pound 0.115 g (77%) as a yellow oil. The title compound was also
prepared from the tungsten carbene complex 1c (0.290 g,
0.60 mmol) by the same procedure. Column chromatography
(hexane/DCM 1/9, Rf ¼ 0.40, PMA detection) afforded the title
compound 0.111 g (75%) as a colourless oil. 1H NMR (500 MHz,
form of a red oil. 1H NMR (300 MHz, CDCl3):
d 0.92e0.98 (m, 6H),
1.35e1.45 (m, 6H), 1.51e1.56 (m, 2H), 1.63 (t, J ¼ 7.1 Hz, 3H), 1.67 (t,
J ¼ 7.1 Hz, 3H), 2.14 (t, J ¼ 7.8 Hz, 2H, CHZ2), 2.21 (t, J ¼ 8.2 Hz, 2H,
CHE2), 2.47 (t, J ¼ 7.9 Hz, 2H CHE2), 2.55 (t, J ¼ 7.7 Hz, 2H, CHZ2), 2.74 (t,
J ¼ 8.6 Hz, 2H, CHZ2), 2.85 (t, J ¼ 8.3 Hz, 2H, CHE2), 5.04e5.08 (m, 4H,
CDCl3):
d
0.02 (s, 9H), 1.07 (d, J ¼ 7.8 Hz, 2H), 1.30 (t, J ¼ 7.0 Hz, 3H),
3.83 (q, J ¼ 7.0 Hz, 2H), 4.03 (m, 1H), 4.56 (dd, J ¼ 6.2, 9.7 Hz, 1H),
5.92 (d, J ¼ 6.2 Hz, 1H), 7.18e7.20 (m, 1H), 7.30e7.34 (m, 4H). 13C
CH2), 7.18e7.34 (m, 12H). 13C NMR (126 MHz, CDCl3):
d 13.9, 14.0,
NMR (126 MHz, CDCl3):
d 15.4, 25.3, 36.2, 67.6, 113.6, 125.6, 126.9,
15.2, 15.4, 22.5, 23.2, 30.3, 31.1, 33.7, 34.6, 34.9, 35.2, 38.4, 40.1, 76.8,
76.9, 126.19, 126.23, 128.1, 128.3, 128.52, 128.53, 140.9, 141.0, 141.2,
141.3, 216.81, 216.82, 224.0, 337.4, 338.4. HRMS (ESI) calcd for
128.3, 143.0, 148.7. HRMS (EI) [M]þ calcd for C15H24OSi: 248.1591.
Found: 248.1586.
C
22H23CrO6 [M-H]-: 435.09052. Found: 435.09057.
4.3.5. (Z)-1-(3-ethoxy-1-phenylallyl)cyclohept-1-ene (4f)
The general procedure starting from the carbene 1b (0.212 g,
0.60 mmol), cycloheptenyllithium (3.0 mL, 1.0 mmol), dry THF
(6 mL), and EtOH (4 mL) afforded after column chromatography
(hexane/DCM 9/1, Rf ¼ 0.40, PMA detection) the title compound
4.4. General procedure for hydrolysis of enolethers
Hydrochloric acid (1 M solution in water, 4.5 mL/mmol) was
added to a solution of enolether 4 in acetone (15 mL/mmol). The
resultant mixture was stirred for 2 h at ambient temperature. Then
acetone was removed under reduce pressure, water layer was
diluted with ether, water layer was removed, and organic layer was
washed with K2CO3 (aq), and brine. Organic phase was then dried
over MgSO4, concentrated under reduce pressure and column
chromatography afforded the expected product.
0.110 g (72%) as a yellow oil. 1H NMR (500 MHz, CDCl3):
d 1.28 (t,
J ¼ 7.1 Hz, 3H), 1.37e1.42 (m, 2H), 1.51e1.55 (m, 2H), 1.71e1.75 (m,
2H), 2.04e2.07 (m, 2H), 2.18e2.22 (m, 2H), 3.81e3.87 (m, 2H), 4.55
(d, J ¼ 9.8 Hz, 1H), 4.70 (dd, J ¼ 6.2, 9.8 Hz, 1H), 5.80 (t, J ¼ 6.4 Hz,
1H), 6.09 (d, J ¼ 6.2 Hz, 1H), 7.20e7.22 (m, 1H), 7.30e7.31 (m, 4H).
13C NMR (126 MHz, CDCl3):
d 15.4, 27.2, 27.3, 28.5, 31.8, 32.7, 48.7,
67.7, 108.2, 125.8, 127.0, 128.06, 128.10, 144.0, 144.3, 146.2. HRMS
(ESI) calcd for C18H25O [MþH]þ: 257.1900. Found: 257.1899.
4.4.1. 3-Phenylheptanal (5b)
The general procedure starting from enol ether 4b (0.077 g,
0.35 mmol), HCl (1.5 mL, 1M aq solution) and acetone (5 mL)
afforded after column chromatography (hexane/DCM 4/1, Rf ¼ 0.15,
PMA detection) the title compound 0.060 g (89%) as a colourless oil.
4.3.6. (Z)-1-Ethoxy-3,3-diphenylprop-1-ene (4g)
This compound was prepared according to the general proced-
ure starting from the carbene 1b (0.212 g, 0.60 mmol), phenyl-
lithium (3.0 mL, 1.0 mmol), dry THF (6 mL), and EtOH (4 mL).
Column chromatography (hexane / hexane/DCM 9/1, Rf ¼ 0.35,
PMA detection) afforded the title compound 0.063 g (44%) as a
1H NMR (300 MHz, CDCl3):
d
0.83 (t, J ¼ 6.9 Hz, 3H, CHH3 ept),
1.10e1.32 (m, 4H, CH2Hept), 1.59e1.68 (m, 2H, CHH2 ept), 2.69e2.72 (m,
2H, CH2CHO), 3.16 (p, J ¼ 7.8 Hz, 1H, CHPh), 7.17e7.33 (m, 5H, CHPh),
yellow oil. 1H NMR (500 MHz, CDCl3):
d
1.29 (t, J ¼ 7.0 Hz, 3H), 3.87
9.66 (t, J ¼ 2.4 Hz, 1H, CHO). 13C NMR (126 MHz, CDCl3):
d 14.0
(q, J ¼ 7.0 Hz, 2H), 4.95 (dd, J ¼ 6.3, 9.9 Hz, 1H), 5.31 (d, J ¼ 9.9 Hz,
1H), 6.18 (d, J ¼ 6.3 Hz, 1H), 7.21e7.24 (m, 2H), 7.27e7.28 (m, 4H),
(CHH3 ept), 22.6 (CHH2 ept), 29.5 (CHH2 ept), 36.4 (CHH2 ept), 40.1 (CH2Hept),
50.7 (CHPh), 126.5 (CHPh), 127.5 (CHPh), 128.6 (CHPh), 144.0 (CPqh),
202.1 (CHO). HRMS (EI) [M]þ calcd for C13H18O: 190.1352. Found:
190.1350.
7.30e7.34 (m, 4H). 13C NMR (126 MHz, CDCl3):
d 15.4, 45.3, 67.8,
109.3, 126.0, 128.2, 128.3, 144.7, 145.1. HRMS (EI) [M]þ calcd for
17H18O: 238.1352. Found: 238.1347.
C
4.3.7. Pentacarbonyl[ethoxy(2-butyl-hex-1-enyl)methylene]
chromium(0) (7a)
4.4.2. 3-Phenyl-4-(trimethylsilyl)butanal (5e)
The general procedure starting from the enol ether 4e (0.092 g,
0.37 mmol), HCl (1.5 mL, 1M aq solution) and acetone (5 mL)
afforded after column chromatography (hexane/DCM 4/1, Rf ¼ 0.20,
PMA detection) the title compound 0.080 g (98%) as a colourless oil.
This compound was prepared according to the general proced-
ure starting from the carbene 5 (0.165 g, 0.50 mmol), n-butyl-
lithium (0.31 mL, 0.75 mmol) in dry THF (5 mL). The reaction
mixture was stirred for 15 min at ꢀ78 ꢁC, quenched by addition of a
solution of acetic acid (0.240 g, 4.0 mmol) in EtOH (4 mL). After
15 min at ꢀ78 ꢁC the reaction mixture was warmed to ambient
temperature, concentrated under reduce pressure, and column
chromatography (hexane Rf ¼ 0.50, PMA detection) afforded the
1H NMR (300 MHz, CDCl3):
d
ꢀ0.15 (s, 9H), 0.98e1.10 (m, 2H),
2.70e2.82 (m, 2H), 3.33e3.39 (m, 1H), 7.22e7.34 (m, 5H), 9.67 (t,
J ¼ 2.1 Hz, 1H). 13C NMR (126 MHz, CDCl3):
d
ꢀ1.2, 25.1, 36.8, 54.4,
126.7, 127.4, 128.6, 145.3, 202.2. HRMS (ESI) calcd for C13H20ONaSi
[MþNa]þ: 243.11756. Found: 243.11757.
Please cite this article as: T. Tobrman et al., Dichotomy within 1,4-addition of organolithium and Grignard reagents to
alkoxycarbenes: A new synthesis of Fischer carbenes, Tetrahedron, https://doi.org/10.1016/j.tet.2019.02.038
a,b-unsaturated Fischer

T. Tobrman et al. / Tetrahedron xxx (xxxx) xxx
7
4.4.3. 3-Phenyl-3-(cyclohepten-1-yl)propanal (5f)
acknowledged.
The general procedure starting from the enol ether 4f (0.099 g,
0.39 mmol), HCl (1.5 mL, 1M aq solution) in acetone (5 mL) afforded
after column chromatography (hexane/DCM 4/1, Rf ¼ 0.20, PMA
detection) the title compound 0.083 g (94%) as a colourless oil. 1H
Appendix A. Supplementary data
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.tet.2019.02.038.
NMR (300 MHz, CDCl3):
d 1.20e1.30 (m, 2H), 1.42e1.48 (m, 2H),
1.62e1.70 (m, 2H), 1.95e1.99 (m, 2H), 2.12e2.17 (m, 2H), 2.69e2.88
(m, 2H), 3.86 (t, J ¼ 7.5 Hz, 1H), 5.77 (t, J ¼ 6. Hz, 1H), 7.18e7.32 (m,
References
5H), 9.69 (t, J ¼ 2.2 Hz, 1H). 13C NMR (126 MHz, CDCl3):
d 26.7, 27.0,
28.3, 31.8, 32.6, 47.0, 48.4, 126.6, 127.7, 127.9, 128.4, 141.9, 145.0,
202.2. HRMS (ESI) calcd for C16H20NaO [MþNa]þ: 251.14064.
Found: 251.14058.
€
[1] E.O. Fischer, A. Maasbol, Angew. Chem., Int. Ed. Engl. 3 (1964) 580e581.
[2] C.P. Casey, W.R. Brunsvold, J. Organomet. Chem. 77 (1974) 345e352.
ꢀ
~
ꢀ
[3] For review see: J. Barluenga, J. Florez, F.J. Fananas J. Organomet. Chem. 624
(2001) 5e17.
ꢀ
[4] J. Barluenga, J.M. Montserrat, J. Florez, S. Garcia-Garda, E. Martin, Angew.
4.4.4. 3-Butylhept-3-enal (8)
Chem. Int. Ed. Engl. 33 (1994) 1392e1394.
[5] K. Fuchibe, N. Iwasawa, Tetrahedron 56 (2000) 4907e4915.
[6] For recent examples see: a) E.A. Giner, A. Santiago, M. Gomez-Gallego, C.R. de
A solution of n-butyllithium (0.86 mL, 2.07 mmol) was added to
the solution of carbene 5 (0.456 g, 1.38 mmol) in dry THF (13 mL)
cooled to ꢀ78 ꢁC. The resulting mixture was stirred for
15 min at ꢀ78 ꢁC followed by the addition of EtOH (10 mL). The
mixture was then stirred for 15 min at ꢀ78 ꢁC, warmed to ambient
temperature and concentrated under reduce pressure. The isolated
crude product was dissolved in acetone (10 mL) and 1M aqueous
HCl (6 mL) was added. The resultant mixture was stirred for 2 h at
ambient temperature. Then acetone was removed under reduce
pressure, water layer was diluted with ether, water layer was
removed, and organic layer was washed with K2CO3 (aq), and brine.
Organic phase was then dried over MgSO4, concentrated under
reduce pressure and column chromatography (hexane/EtOAc 20/1,
Rf ¼ 0.40) afforded the title compound 0.071 g (31%) as a yellow oil.
ꢀ
Arellano, R.C. Poulten, M.K. Whittlesey, M.A. Sierra, Inorg. Chem. 54 (2015)
5450e5461;
ꢀ
ꢀ
ꢀ
b) L. Alvarez-Rodríguez, J.A. Cabeza, P. García-Alvarez, M. Gomez-Gallego,
A.D. Merinero, M.A. Sierra, Chem. Eur. J. 23 (2017) 4287e4291;
ꢀ
c) M.A. Sierra, A.D. Merinero, E.A. Giner, M. Gomez, C.R. de Arellano, Chem.
Eur. J. 22 (2016) 13521e13531;
ꢀ
d) A. Collado, M. Gomez-Gallego, A. Santiago, M.A. Sierra, Eur. J. Org. Chem.
(2019) 369e377.
ꢀꢁ
ꢀ
ꢀ
ꢁꢀ
[7] a) H. Vanova, T. Tobrman, I. Hoskovcova, D. Dvorak, Organometallics 35 (2016)
2999e3006;
ꢀ
ꢀ
ꢀ
ꢀ
ꢁꢀ
ꢀꢁ
b) T. Tobrman, I. Juraskova, D. Dvorak, Organometallics 33 (2014) 6593e6603;
c) T. Tobrman, I. Juraskova, H. Vanova, D. Dvorak, Organometallics 33 (2014)
2990e2996.
ꢀ
ꢁꢀ
[8] This difference between Casey and our findings is not clear. It might be result
of somewhat different reaction conditionseusage of THF instead of ether,
solution of HCl in CpOMe. Also the fact, that Casey obtained inseparable
mixture of carbene and enolether and therefore had to hydrolyze enolether to
the corresponding aldehyde undoubtedly contributed to low yield of carbene
product in his case.
1H NMR (300 MHz, CDCl3):
d 0.90e0.96 (m, 6H), 1.26e1.56 (m, 8H),
2.22 (t, J ¼ 8.4 Hz, 2H), 2.55 (t, J ¼ 7.5 Hz, 2H), 5.85 (d, J ¼ 8.1 Hz, 1H),
ꢀ
~
~
[9] M. Gomez, M.J. Mancheno, P. Ramírez, C. Pinar, M.A. Sierra, Tetrahedron 56
9.99 (d, J ¼ 8.1 Hz, 1H), in accordance with reference [14].
(2000) 4893e4905.
~
ꢀ
[10] M.J. Mancheno, M.A. Sierra, M. Gomez-Gallego, P. Ramírez, Organometallics
18 (1999) 3252e3254.
Acknowledgments
[11] W.F. Bailey, E.R. Punzalan, J. Org. Chem. 55 (1990) 5404e5406.
[12] R. Aumann, H. Heinen, Chem. Ber. 120 (1987) 537e540.
[13] R. Aumann, P. Hinterding, Chem. Ber. 126 (1993) 421e427.
[14] A.R. Katritzky, H. Wu, L. Xie, S. Rachwal, B. Rachwal, J. Jiang, G. Zhang, H. Lang,
Synthesis (1995) 1315e1323.
Financial support from specific university research (MSMT No
21-SVV/2018), and the Ministry of Education, Youth and Sports of
the Czech Republic (grant no. 17-21770S) is gratefully
Please cite this article as: T. Tobrman et al., Dichotomy within 1,4-addition of organolithium and Grignard reagents to
alkoxycarbenes: A new synthesis of Fischer carbenes, Tetrahedron, https://doi.org/10.1016/j.tet.2019.02.038
a,b-unsaturated Fischer