A catalytic system for the activation of diorganozinc reagents

Article abstract of DOI:10.1002/ejoc.201402138

We report a novel catalytic system for the activation of diorganozinc reagents. We assumed that the nucleophilic activation of diethylzinc should be efficiently performed by simple alkali metal salts. Indeed, the combination of sodium salts and 15-crown-5 significantly accelerates the rate of diethylzinc addition to benzaldehyde under mild conditions. The activity of the catalytic system strongly depends on the nature of the anion, decreasing in the order I^->Br^->Cl^->F^-. Under the optimized reaction conditions, various aryl, hetero aryl, and aliphatic aldehydes were converted with diethylzinc and the corresponding product was obtained in excellent yields. The first X-ray absorption spectroscopy measurements on such type of reactions provide initial insights that support the proposed catalytic cycle and suggest the formation of a zincate complex.

Full text of DOI:10.1002/ejoc.201402138

Job/Unit: O42138
/KAP1
Date: 18-06-14 17:58:41
Pages: 9
FULL PAPER
DOI: 10.1002/ejoc.201402138
A Catalytic System for the Activation of Diorganozinc Reagents
Thomas Werner,*[a] Matthias Bauer,*[b] Abdol Majid Riahi,[a] and Heiko Schramm[a]
Keywords: Homogeneous catalysis / C–C coupling / Zinc / Chelates / Crown compounds / Aldehydes
We report a novel catalytic system for the activation of dior-
Under the optimized reaction conditions, various aryl, hetero
ganozinc reagents. We assumed that the nucleophilic acti- aryl, and aliphatic aldehydes were converted with dieth-
vation of diethylzinc should be efficiently performed by sim-
ple alkali metal salts. Indeed, the combination of sodium salts
and 15-crown-5 significantly accelerates the rate of dieth-
ylzinc addition to benzaldehyde under mild conditions. The
activity of the catalytic system strongly depends on the na-
ture of the anion, decreasing in the order I– ϾBr– ϾCl– ϾF–.
ylzinc and the corresponding product was obtained in excel-
lent yields. The first X-ray absorption spectroscopy measure-
ments on such type of reactions provide initial insights that
support the proposed catalytic cycle and suggest the forma-
tion of a zincate complex.
cleophilic activation has been proposed and might be ex-
pected for σ-donor ligands, for example iodide.[3a,3b,5a,5b,8]
Moreover organozincates[9] are valuable reagents, and
anions of the type shown in Scheme 1 have been reported
by Richey Jr. and co-workers.[9k] We chose the addition of
diethylzinc to benzaldehyde 1a as a model reaction to inves-
tigate the envisioned nucleophilic activation by the halogen
anion of these salts.
Introduction
Among organic reactions, those that form new carbon–
carbon bonds are of major interest for synthetic chemists.
The nucleophilic addition of different organometallic rea-
gents to carbonyl compounds has long been known and
offers a very elegant opportunity to form a broad variety
of different products.[1] Along with organolithium and
Grignard compounds, zinc organyls are among the most
important reagents for such transformations. Although
known for a long time, their application in organic synthesis
has only developed significantly over the last few decades.[2]
In contrast to other organometallic reagents,[2d] zinc or-
ganyls constitute a unique class of compounds because they
tolerate a large number of functional groups[3] and often
react stereo- and chemoselectively in the presence of a suit-
able catalyst.[4] Positive effects of halides as additives in
transition-metal-catalyzed processes have been reported fre-
quently.[5] In our efforts to employ phosphonium salts as
Lewis acidic catalysts, we reported their application in the
conversion of diethylzinc with aldehydes.[6] Notably, we ob-
served that the catalytic activity of the phosphonium salts
strongly depends on the nature of the anion.[6a] Recently,
Song et al. reported synergistic effects of quaternary ammo-
nium salts on the asymmetric addition of diethylzinc to al-
dehydes as well as their utilization as catalysts in the ad-
dition of Grignard reagents to ketones.[7] In this context,
we were interested in the nucleophilic activation of dieth-
ylzinc by simple alkali metal salts (Scheme 1). Similar nu-
Scheme 1. Proposed catalytic cycle for the addition of Et2Zn to
benzaldehyde (1a). Product 2a is obtained after aqueous work up.
Results and Discussion
Initial experiments showed that simple phosphonium
salts efficiently catalyzed the addition of diethylzinc to
benzaldehyde (1a).[6b] The activity of those catalysts mainly
depended on the nature of the anion (Table 1). In the ab-
sence of a catalyst the reaction proceeded sluggishly and the
desired product was obtained in only low yields up to 11%
(entry 1). The addition of crown ethers had no influence on
the outcome of the reaction (entries 2–4). In the presence
of sodium fluoride, chloride, bromide, or iodide the yield
was slightly improved to 33% (entries 5–8). The utilization
[a] Leibniz-Institut für Katalyse e. V. an der Universität Rostock,
Albert-Einstein-Straße 29a, 18059 Rostock, Germany
E-mail: thomas.werner@catalysis.de
http://www.catalysis.de
[b] University Paderborn, Department Chemie,
Warburger Str. 100, 33098 Paderborn, Germany
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201402138.
Eur. J. Org. Chem. 0000, 0–0
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T. Werner, M. Bauer, A. M. Riahi, H. Schramm
FULL PAPER
of the corresponding lithium and potassium salts had no Table 2. Conversion of aryl aldehydes 1 with Et2Zn.
significant influence (entries 9 and 10). Finally, crown
ethers were employed as co-catalysts to improve the activity
of the anions further. Crown ethers are known to generate
activated “naked anions” in aprotic organic solvents in situ
by forming a chelate complex with the cation.[10] The utili-
zation of sodium salts in a 1:1 molar ratio with 15-crown-5
led to significantly increased conversions and yields (en-
tries 11–14). The best result was obtained for NaI in combi-
nation with the crown ether, giving the desired product 2a
in 98% yield (entry 10). Reducing the reaction time to 6 h
led to 94% yield (entry 15), however, significantly lower
yield was obtained when the reaction time was reduced fur-
ther to 3 h (entry 16). The utilization of LiCl and KCl in
combination with 12-crown-4 and 18-crown-6, respectively
(entries 17 and 18), had no significant influence on the out-
come of the reaction compared with that using the NaCl/
15-crown-5 system (entry 12).
Table 1. Catalyst screening for the conversion of 1a with dieth-
ylzinc.[a]
Entry Catalyst
t [h] Conv. 1a [%][b] Yield 2a [%][b]
1
2
3
4
5
6
7
8
–
24
24
24
24
24
24
24
24
24
24
24
24
24
24
6
14
10
18
15
23
33
31
36
35
31
46
91
Ͼ99
Ͼ99
94
85
88
11
8
11
10
21
30
29
33
33
31
35
86
12-crown-4
15-crown-5
18-crown-6
NaF
NaCl
NaBr
NaI
LiCl
KCl
NaF/15-crown-5
NaCl/15-crown-5
NaBr/15-crown-5
NaI/15-crown-5
NaI/15-crown-5
NaI/15-crown-5
LiCl/12-crown-4
KCl/18-crown-6
9
10
11
12
13
14
15
16
17
18
94
98, 97[c]
94, 75[d], 40[e]
3
24
24
80
87
90
93
[a] Reaction conditions: NaX/15-crown-5 (1:1, 7 mol-%), benzalde-
hyde (1a; 1.0 equiv.), Et2Zn (2.0 equiv.), anhydrous toluene, 23 °C.
[b] Determined by GC analysis with hexadecane as internal stan-
dard. [c] In THF. [d] Et2Zn (1.0 equiv.). [e] Et2Zn (0.5 equiv.).
Encouraged by the initial results, we next evaluated the
effectiveness of the system in the conversion of diethylzinc
with aryl aldehydes 1 into the corresponding alcohols 2
(Table 2). Conversion of the model substrate 1a gave the
desired product 2a after 24 h reaction time in 99% isolated
yield. In general, shorter reaction times were possible and
2a could be obtained in 80% yield after 3 h (entry 1). When
[Bu4P]Cl was employed as the catalyst the yield of 2a was
only 72% after 6 h. This result shows the increased reactiv-
ity of the new catalytic system. The conversion of other
substrates was monitored by GC analysis and the reaction
was stopped when full conversion was reached. para-Methyl
and para-phenyl-substituted aldehydes 1b and 1c could be
quantitatively converted into the corresponding alcohols 2b
and 2c, respectively, in 12 h (entries 2 and 3). The corre-
sponding methoxy-substituted derivative 2d was isolated in
[a] Product 2 was obtained after aqueous work up. Isolated yields
are given. [b] Determined by GC analysis with hexadecane as in-
ternal standard.
2
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Activation of Diorganozinc Reagents
good yield (74%; entry 4). In contrast, para-halogen-func- yield of 75% (entry 2). The reaction of thiophene-2-carb-
tionalized products 2e–g were obtained in excellent yields aldehyde (3ac) with diethylzinc gave 4ac in 79% yield after
(Ͼ90%) after 6 h (entries 5–7). The yield was independent 48 h (entry 3). Similar results were obtained in the conver-
of the substitution pattern, for example ortho- (2h), meta- sion of aliphatic aldehydes 3b. The conversion of n-hexanal
(2i), and para-chlorobenzaldehyde (2f) were obtained in 88– (3ba) was complete after 24 h, giving 76% yield of 4ba,
96% yield (entries 6, 8, and 9), although longer reaction whereas 3-phenylpropanal (3bb) and citronellal (3bc) gave
time was necessary for full conversion of 1i (entry 9). No- the desired products 4ba and 4bc in 71 and 63% yield,
tably, the conversion of base-sensitive phenol derivative 1j respectively (entries 4–6).
gave the desired product 2j in excellent yield of 99%. More-
Finally, the utilization of other readily available dior-
over, naphthalene-1-carbaldehyde (1k) and dimethoxybenz- ganozinc reagents (R2Zn, R = Me, nBu, iPr, Ph) in the con-
aldehyde (1l) were converted into the corresponding alcohol version of 1a under the same reaction conditions was inves-
in 99 and 94% yield, respectively (entries 11 and 12).
tigated (Table 4). Although other R2Zn compounds could
The chemoselectivity of the reaction was tested in the be converted, the yields of the corresponding products 5
conversion of cinnamaldehyde (1m) and 4-acetylbenzalde- were only moderate or even low. The best result was ob-
hyde (1n) with diethylzinc for 24 h at room temperature in tained with dimethylzinc (R = Me), which gave 5a in 71%
the presence of 7 mol-% NaI/15-crown-5. In both cases, ex- yield (entry 1). The conversion of 1a with dibutyl- and di-
clusive 1,2-addition to the aldehyde functionality was ob- isopropylzinc gave 1-phenyl-1-pentanol (5b) and 2-methyl-
served. The corresponding products 2m and 2n were ob- 1-phenylpropanol (5c) in only 48 and 31% yield, respec-
tained in 37 and 50% yield, respectively. The formation of tively (entries 2 and 3). In contrast, diphenylmethanol (5d)
byproducts was not observed. Furthermore, we were inter- could be observed in moderate yield of 60% (entry 4).
ested in examining the scope and limitations of the reaction.
To this end, we investigated the conversion of hetero aryl
Table 4. Conversion of benzaldehyde 1a with various R2Zn com-
and aliphatic aldehydes under the same reaction conditions pounds; product 5 was obtained after aqueous workup.
(Table 3). The obtained yields were still good but they were
considerably lower than in the conversion of aryl aldehydes
1 shown in Table 2. The conversion of pyridine-2-carb-
aldehyde (3aa) only led to 62% yield of the desired product
4aa even after 90 h reaction time (Table 3, entry 1). The
same reaction time was needed for full conversion of furan-
2-carbaldehyde (3ab) and product 4ab was obtained in good
Table 3. Conversion of hetero aryl 3a and aliphatic aldehydes 3b
with Et2Zn; product 4 was obtained after aqueous workup.
1
[a] Determined by H NMR spectroscopic analysis with 1,3,5-tri-
methylbenzol as internal standard.
To gain initial insights into the mechanism of the de-
scribed reaction, X-ray absorption spectroscopy (XAS)
techniques were applied. This method is able to provide in-
formation about the oxidation state and coordination
geometry by XANES (X-ray absorption near edge struc-
ture) of a metal atom in an element-sensitive manner.[11]
Additionally, EXAFS (extended X-ray absorption fine
structure) delivers the number, type, and distance of coordi-
nating atoms around a metal atom. As model systems to
study the mechanism of this reaction, a solution of Et2Zn
in toluene (a) and with stoichiometric amounts of NaI and
15-crown-5 (b), as well as this mixture with a stoichiometric
amount of 1a (c) were studied by XAS. Figure 1 shows the
XANES spectra of the solutions, and Figure 2 shows the
Fourier-transformed EXAFS spectra. The structural pa-
rameters obtained by fitting the experimental spectra with
[a] Isolated yield.
theoretical models are summarized in Table 5.
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T. Werner, M. Bauer, A. M. Riahi, H. Schramm
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Two carbon shells are found at distances of 1.97 and
3.40 Å, with the according coordination numbers. No Zn–
Zn contributions that would be characteristic for higher ag-
gregates were detected. Addition of NaI and 15-crown-5
leaves the intensity of A almost unchanged, indicating that
no significant change in the orbital structure behind the
1s-4p transition occurs. In the linear structure of Et2Zn, the
final p states are the degenerate px,y states and pz with a
slightly higher energy. In case of a trigonal planar structure
there are still two degenerate final states, but now the py,z,
have a higher energy than the single px.[13] With the resolu-
tion of our experiments, these cases are difficult to distin-
guish from the XANES spectra, therefore the linear and
trigonal planar structure are both plausible after the ad-
dition of NaI and 15-crown-5.
Figure 1. XANES spectra of Et2Zn in toluene, with 15-crown-5 and
NaI, and with additional 1a. The resonances discussed in the text
are indicated with A and B.
Unfortunately, the EXAFS results are also not equivocal;
2.6 carbon neighbors could be fitted, which is in agreement
with an unchanged Zn–C coordination. Clearly, this
number is too small for coordinating 15-crown-5, therefore,
complexation of Zn by 15-crown-5 can be excluded. The
coordination of I– to Zn2+ is assumed because the halide
ion has significant influence on the catalytic activity. The
inclusion of a direct Zn–I pair in the EXAFS fit is feasible,
and the fitting results given in Table 5 are reproducible.
However, the Zn–I is not of statistical significance, that is,
it does not increase the quality of fit in comparison to a
single shell fit with only Zn–C. Moreover, the Zn–I shell
suffers from large thermal disorder, which could explain the
lack of significance. Additionally, destructive interference
effects are well-known in X-ray absorption spectroscopy,[14]
which lead to the annihilation of two backscattering signals,
and it cannot be excluded that such effects contribute to
the weak Zn–I signal. Nonetheless, the Zn–I pair is given
in parentheses in Table 5. Still, together with the slightly
changed XANES signature and the first Zn–C shell, which
is identical to pure Et2Zn, we interpret these results as indi-
cating the formation of a zincate complex as given in
Scheme 1.
Support for this conclusion is provided by the results ob-
tained after addition of 1a. It is assumed that 1a substitutes
the I– of the zincate complex. Since in this sample the Zn–
C shell is visible again, the hypothesis of destructive inter-
ference caused by iodine is supported. Moreover, a second
light atom nearest neighbor (denoted as Zn–O) and a sec-
ond Zn–C shell can be detected at 2.11 and 2.94 Å, respec-
tively, which is characteristic of coordinating 1a. The four-
fold coordination of the Zn center is also reflected in the
XANES spectrum, in which the position of A shifts to
higher energies, and the ratio between the first (A) and sec-
ond resonance (B) is also altered, which is characteristic of
a tetrahedral coordination geometry.[12a] Finally, a dimeric
Figure 2. Fourier transformed EXAFS spectra of Et2Zn in toluene,
with 15-crown-5 and NaI, and with additional 1a. The signals are
discussed in the text.
Table 5. Structural parameters obtained by fitting the experimental
EXAFS data with theoretical models.
Sample
Abs-Bs[a]
N(Bs)[b]
R(Abs-Bs) /Å[c]
Et2Zn in toluene (a)
Zn-C
Zn-C
2.6Ϯ0.3
3.1Ϯ0.6
1.97Ϯ0.02
3.40Ϯ0.03
Et2Zn in toluene + 15-crown-5/NaI (b)
Zn-C
2.6Ϯ0.3
0.8Ϯ0.2
1.96Ϯ0.02
3.21Ϯ0.03
(Zn-I)
2.3Ϯ0.2
2.00Ϯ0.02
2.11Ϯ0.02
3.07Ϯ0.03
2.94Ϯ0.03
3.51Ϯ0.04
[a] Abs = X-ray absorbing atom, Bs = backscattering neighbor.
[b] Number of backscattering neighbor atoms. [c] Distance between
absorber and backscatterer.
The XANES spectrum of Et2Zn is in accordance with structure is formed by coordination of 1a, because a Zn–
previous reports.[12] The sharp resonance A found at ap- Zn shell significantly increased the quality of fit.
proximately 9660 eV in Figure 1 is due to a 1s-4p transition.
According to the linear coordination in Et2Zn in toluene,
the intensity of this resonance is rather large. This is also
Conclusions
reflected in the structural parameters obtained by fitting the
EXAFS data with theoretical models (Table 5).
We have established a new method for the activation of
diorganozinc reagents with catalytic amounts of sodium
4
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Activation of Diorganozinc Reagents
1.72–1.97 (m, 3 H), 4.66 (dt, J = 3.0, 6.4 Hz, 1 H), 7.32–7.38 (m,
1 H), 7.31–7.50 (m, 4 H), 7.56–7.77 (m, 4 H) ppm. 13C NMR
(CDCl3, 75 MHz): δ = 10.16 (CH3), 31.85 (CH2), 75.74 (CH),
126.39 (2CH), 127.04 (2CH), 127.13 (2CH), 127.22 (CH), 128.73
(2CH), 140.40 (C), 140.84 (C), 143.59 (C) ppm. MS (EI, 70 eV):
m/z (%) = 212 (15) [M]+, 194 (22), 184 (14), 183 (100), 178 (10),
155 (44), 154 (10), 153 (16), 152 (20), 77 (12).
iodide in the presence of 15-crown-5. Although other dior-
ganozinc reagents could be employed, the procedure proved
to be most efficient in the acceleration of diethylzinc ad-
dition to a variety of aromatic, heteroaromatic, and ali-
phatic aldehydes under mild conditions. The corresponding
alcohols were usually obtained in good to excellent yields.
XAS experiments support the formation of a zincate com-
plex as the active species, although further experiments are
required to resolve this issue. This simple system might be
useful to enhance reactivity and selectivity in organozinc
addition reactions or halogen–zinc exchange reactions,
respectively.
1-(4-Methoxyphenyl)propan-1-ol (2d):[16] Compound 1d (204 mg,
1.50 mmol) was converted for 12 h according to the general pro-
cedure. After chromatography (SiO2; cyclohexane/EtOAc, 20:1; Rf
= 0.66), 2d was obtained as a colorless oil (185 mg, 1.11 mmol,
1
74%). H NMR (400 MHz, CDCl3): δ = 0.95 (t, J = 7.6 Hz, 3 H),
1.71–1.92 (m, 2 H), 1.97–2.00 (m, 1 H), 3.85 (s, 3 H), 4.58 (dt, J =
2.3, 7.3 Hz, 1 H), 6.91–6.95 (m, 2 H), 7.28–7.33 (m, 2 H) ppm. 13
C
NMR (CDCl3, 75 MHz): δ = 10.16 (CH3), 31.72 (CH2), 55.22
(CH3), 75.59 (CH), 113.72 (2CH), 127.16 (2CH), 136.74 (C), 158.94
(C) ppm. MS (EI, 70 eV): m/z (%) = 166 (10) [M]+, 148 (28), 147
(16), 137 (100), 109 (22), 94 (17), 77 (22).
Experimental Section
All reactions were carried out under an argon atmosphere using
Schlenk techniques. Toluene was dried with sodium and freshly dis-
tilled before use. All starting materials were commercially available
and used without further purification. TLC was performed on Ma-
cherey–Nagel silica gel plates 60 (UV254). Preparative column
chromatography was carried out using Macherey–Nagel M60 silica
gel (0.04–0.063 mm) with cyclohexane and ethyl acetate (EtOAc)
as eluents for flash column chromatography.
1-(4-Fluorophenyl)propan-1-ol (2e):[16] Compound 1e (186 mg,
1.50 mmol) was converted for 6 h according to the general pro-
cedure. After chromatography (SiO2; cyclohexane/EtOAc, 20:1; Rf
= 0.47), 2e was obtained as a colorless oil (215 mg, 1.39 mmol,
1
93%). H NMR (300 MHz, CDCl3): δ = 0.81 (t, J = 7.4 Hz, 3 H),
1.57–1.76 (m, 2 H), 2.00 (br. s, 1 H), 4.48 (t, J = 6.6 Hz, 1 H),
6.91–6.98 (m, 2 H), 7.18–7.24 (m, 2 H) ppm. 13C NMR (CDCl3,
75 MHz): δ = 10.17 (CH3), 31.09 (CH2), 75.45 (CH), 115.28 (d,
2JC,F = 21.3 Hz, 2CH), 127.70 (d, 3JC,F = 7.9 Hz, 2CH), 140.39 (d,
4JC,F = 3.0 Hz, C), 163.75 (d, 1JC,F = 245.2 Hz, C) ppm. 19F NMR
(282 MHz, CDCl3): δ = –115.0 ppm. MS (EI, 70 eV): m/z (%) =
154 (6) [M]+, 125 (100), 97 (46), 95 (14), 77 (14).
General Procedure for the Addition of Et2Zn: The aldehyde
(1.0 equiv.) was added to a mixture of 15-crown-5 (7 mol-%) and
sodium iodide (7 mol-%) in toluene [c(aldehyde) = 2.5 molL–1].
Subsequently, Et2Zn in toluene (c = 1.1 molL–1, 2.0 equiv.) was
added dropwise at 0 °C. The solution was warmed to 23 °C and
stirring was continued for 3–90 h. The mixture was diluted with
HCl (1 n, 3.3 mL per mmol of aldehyde). The aqueous layer was
extracted with CH2Cl2 (3ϫ 6.5 mL·per mmol of aldehyde) and the
combined organic layers were dried (Na2SO4). All volatiles were
removed in vacuo and the residue was purified by chromatography
(SiO2; cyclohexane/EtOAc).
1-(4-Chlorophenyl)propan-1-ol (2f):[16] Compound 1f (210 mg,
1.49 mmol) was converted for 6 h according to the general pro-
cedure. After chromatography (SiO2; cyclohexane/EtOAc, 20:1; Rf
= 0.66), 2f was obtained as a colorless oil (245 mg, 1.44 mmol,
1
96%). H NMR (300 MHz, CDCl3): δ = 0.85 (t, J = 7.4 Hz, 3 H),
1.54–1.81 (m, 2 H), 1.84–1.88 (m, 1 H), 1.86 (br. s, 1 H), 4.50 (dt,
J = 3.3, 6.4 Hz, 1 H), 7.17–7.21 (m, 2 H), 7.22–7.27 (m, 2 H) ppm.
13C NMR (CDCl3, 75 MHz): δ = 9.90 (CH3), 31.86 (CH2), 75.20
(CH), 127.26 (2CH), 128.43 (2CH), 132.99 (C), 142.91 (C) ppm.
MS (EI, 70 eV): m/z (%) = 170 (10) [M]+, 143 (34), 142 (10), 141
(100), 139 (12), 117 (15), 115 (17), 113 (16), 77 (56), 51 (10), 32
(43) ppm.
1-Phenylpropan-1-ol (2a):[15] Compound 1a (159 mg, 1.50 mmol)
was converted for 24 h according to the general procedure. After
chromatography (SiO2; cyclohexane/EtOAc, 10:1; Rf = 0.68), 2a
was obtained as a colorless oil (201 mg, 1.48 mmol, 99%). 1H
NMR (300 MHz, CDCl3): δ = 0.83 (t, J = 7.3 Hz, 3 H), 1.59–1.79
(m, 2 H), 1.94 (br. s, 1 H), 4.50 (t, J = 6.9 Hz, 1 H), 7.16–7.29 (m,
5 H) ppm. 13C NMR (CDCl3, 75 MHz): δ = 10.09 (CH3), 31.82
(CH2), 75.96 (CH), 125.93 (2CH), 127.44 (CH), 128.34 (2CH),
144.54 (C) ppm. MS (EI, 70 eV): m/z (%) = 136 (12) [M]+, 107
(100), 79 (70), 77 (39), 51 (26).
1-(4-Bromophenyl)propan-1-ol (2g):[17] Compound 1g (277 mg,
1.50 mmol) was converted for 6 h according to the general pro-
cedure. After chromatography (SiO2; cyclohexane/EtOAc, 20:1; Rf
= 0.77), 2g was obtained as a colorless oil (296 mg, 1.38 mmol,
1-(4-Methylphenyl)propan-1-ol (2b):[16] Compound 1b (180 mg,
1.50 mmol) was converted for 12 h according to the general pro-
cedure. After chromatography (SiO2; cyclohexane/EtOAc, 20:1; Rf
= 0.83), 2b was obtained as a colorless oil (224 mg, 1.49 mmol,
1
92%). H NMR (300 MHz, CDCl3): δ = 0.89 (t, J = 7.4 Hz, 3 H),
1.62–1.87 (m, 2 H), 1.98 (br. s, 1 H), 4.56 (t, J = 6.6 Hz, 1 H),
7.18–7.23 (m, 2 H), 7.43–7.49 (m, 2 H) ppm. 13C NMR (CDCl3,
75 MHz): δ = 9.94 (CH3), 31.87 (CH2), 75.26 (CH), 121.13 (C),
127.67 (CH), 131.41 (CH), 143.47 (C) ppm. MS (EI, 70 eV): m/z
(%) = 216 (11) [MH]+, 214 (10), 187 (94), 185 (100), 159 (15), 157
(20), 78 (29), 77 (58), 51 (10).
1
99%). H NMR (300 MHz, CDCl3): δ = 0.91 (t, J = 7.4 Hz, 3 H),
1.66–1.90 (m, 2 H), 1.92 (d, J = 3.0 Hz, 1 H), 2.35 (s, 3 H), 4.55
(dt, J = 2.6, 6.8 Hz, 1 H), 7.14–7.19 (m, 2 H), 7.21–7.27 (m, 2
H) ppm. 13C NMR (CDCl3, 75 MHz): δ = 10.16 (CH3), 21.07
(CH3), 31.75 (CH2), 75.84 (CH), 125.89 (2CH), 129.03 (2CH),
137.09 (C), 141.60 (C) ppm. MS (EI, 70 eV): m/z (%) = 150 (9)
[M]+, 121 (100), 93 (47), 91 (43), 77 (25), 65 (10).
1-(2-Chlorophenyl)propan-1-ol (2h):[16] Compound 1h (210 mg,
1.49 mmol) was converted for 6 h according to the general pro-
cedure. After chromatography (SiO2; cyclohexane/EtOAc, 20:1; Rf
= 0.55), 2h was obtained as a colorless oil (223 mg, 1.31 mmol,
1
1-(Biphenyl-4-yl)propan-1-ol (2c):[16] Compound 1c (273 mg,
1.50 mmol) was converted for 12 h according to the general pro-
cedure. After chromatography (SiO2; cyclohexane/EtOAc, 10:1; Rf
= 0.69), 2c was obtained as a colorless solid (308 mg, 1.47 mmol,
88%). H NMR (300 MHz, CDCl3): δ = 0.91 (t, J = 7.4 Hz, 3 H),
1.55–1.83 (m, 2 H), 2.02 (br. s, 1 H), 4.95–5.05 (m, 1 H), 7.08–7.14
(m, 1 H), 7.18–7.33 (m, 2 H), 7.43–7.54 (m, 1 H) ppm. 13C NMR
(CDCl3, 75 MHz): δ = 9.99 (CH3), 30.40 (CH2), 71.89 (CH), 126.95
(CH), 127.08 (CH), 128.28 (CH), 129.29 (CH), 131.90 (C), 141.92
1
98%). H NMR (300 MHz, CDCl3): δ = 0.97 (t, J = 7.4 Hz, 3 H),
Eur. J. Org. Chem. 0000, 0–0
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T. Werner, M. Bauer, A. M. Riahi, H. Schramm
FULL PAPER
(C) ppm. MS (EI, 70 eV): m/z (%) = 170 (7) [M]+, 143 (34), 142
70 eV): m/z (%) = 137 (12) [M]+, 120 (14), 109 (77), 108 (100), 106
(9), 141 (100), 113 (15), 77 (52), 51 (9).
(12), 80 (21), 79 (20), 78 (36), 53 (12), 52 (14), 51 (11).
1-(Furan-2-yl)propan-1-ol (4ab):[16] Compound 3ab (144 mg,
1.50 mmol) was converted for 90 h according to the general pro-
cedure. After chromatography (SiO2; cyclohexane/EtOAc, 20:1; Rf
= 0.68), 3ab was obtained as a pale-yellow oil (141 mg, 1.12 mmol,
1-(3-Chlorophenyl)propan-1-ol (2i):[16] Compound 1i (210 mg,
1.49 mmol) was converted for 12 h according to the general pro-
cedure. After chromatography (SiO2; cyclohexane/EtOAc, 20:1; Rf
= 0.48), 2i was obtained as a yellow oil (231 mg, 1.35 mmol, 91%).
1H NMR (300 MHz, CDCl3): δ = 0.92 (t, J = 7.4 Hz, 3 H), 1.65–
1.88 (m, 2 H), 2.01 (br. s, 1 H), 4.58 (t, J = 6.5 Hz, 1 H), 7.18–7.31
(m, 3 H), 7.33–7.36 (m, 1 H) ppm. 13C NMR (CDCl3, 75 MHz): δ
= 9.92 (CH3), 31.86 (CH2), 75.26 (CH), 124.07 (CH), 126.09 (CH),
127.51 (CH), 129.61 (CH), 134.23 (C), 146.59 (C) ppm. MS (EI,
70 eV): m/z (%) = 170 (12) [M]+, 143 (33), 142 (8), 141 (100), 115
(15), 113 (14), 77 (66), 51 (8).
1
75%). H NMR (300 MHz, CDCl3): δ = 0.94 (t, J = 7.5 Hz, 3 H),
1.76–1.96 (m, 2 H), 2.04 (br. s, 1 H), 4.59 (t, J = 6.6 Hz, 1 H),
6.21–6.24 (m, 1 H), 6.31–6.34 (m, 1 H), 7.35–7.38 (m, 1 H) ppm.
13C NMR (CDCl3, 75 MHz): δ = 9.89 (CH3), 28.55 (CH2), 69.15
(CH), 105.85 (CH), 110.04 (CH), 141.84 (CH), 156.61 (C) ppm.
MS (EI, 70 eV): m/z (%) = 126 (15) [M]+, 97 (100), 69 (12), 41 (18),
39 (12) ppm.
1-(Thien-2-yl)propan-1-ol (2ac):[19] Compound 4ac (168 mg,
2.50 mmol) was converted for 48 h according to the general pro-
cedure. After chromatography (SiO2; cyclohexane/EtOAc, 20:1; Rf
= 0.68), 4ac was obtained as a colorless oil (168 mg, 1.18 mmol,
2,4-Di-tert-butyl-6-(1-hydroxypropyl)phenol (2j):[18] Compound 1j
(351 mg, 1.50 mmol) was converted for 48 h according to the gene-
ral procedure (note: 10 mol-% NaI/15-crown-5 was employed) Af-
ter chromatography (SiO2; cyclohexane/EtOAc, 25:1; Rf = 0.86), 2j
was obtained as a colorless oil (396 mg, 1.50 mmol, 99%). 1H
NMR (300 MHz, CDCl3): δ = 1.00 (t, J = 7.3 Hz, 3 H), 1.30 (s, 9
H), 1.44 (s, 9 H), 1.80–2.04 (m, 2 H), 2.44 (d, J = 2.3 Hz, 1 H),
4.69–4.74 (m, 1 H), 6.81 (d, J = 2.4 Hz, 1 H), 7.25 (d, J = 2.4 Hz,
1 H), 8.19 (s, 1 H) ppm. 13C NMR (CDCl3, 75 MHz): δ = 10.54
(CH3), 29.69 (CH2), 29.70 (3CH3), 31.62 (3CH3), 34.16 (CH), 35.06
(C), 79.08 (CH), 122.11 (CH), 123.27 (CH), 126.30 (C), 136.74 (C),
140.94 (C), 152.46 (C) ppm. MS (EI, 70 eV): m/z (%) = 246 (21)
[M – H2O]+, 232 (18), 231 (100).
1
79%). H NMR (300 MHz, CDCl3): δ = 0.88 (t, J = 7.5 Hz, 3 H),
1.68–1.90 (m, 2 H), 2.12 (br. s, 1 H), 4.74 (t, J = 6.6 Hz, 1 H),
6.86–6.91 (m, 2 H), 7.14–7.18 (m, 1 H) ppm. 13C NMR (CDCl3,
75 MHz): δ = 10.09 (CH3), 32.14 (CH2), 71.66 (CH), 123.71 (CH),
124.40 (CH), 126.50 (CH), 148.55 (C) ppm. MS (EI, 70 eV): m/z
(%) = 142 (16) [M]+, 113 (100), 85 (50), 45 (11).
Nonan-3-ol (4ba):[19] Compound 3ba (171 mg, 1.50 mmol) was con-
verted for 24 h according to the general procedure. After
chromatography (SiO2; cyclohexane/EtOAc, 25:1; Rf = 0.86), 4ba
was obtained as a colorless oil (164 mg, 1.14 mmol, 76%). 1H
NMR (300 MHz, CDCl3): δ = 0.87 (t, J = 7.3 Hz, 3 H), 0.92 (t, J
= 7.5 Hz, 3 H), 1.22–1.34 (m, 8 H), 1.34–1.56 (m, 4 H), 3.47–3.54
(m, 1 H) ppm. 13C NMR (CDCl3, 75 MHz): δ = 9.82 (CH3), 14.02
(CH3), 22.58 (CH2), 25.59 (CH2), 29.35 (CH2), 30.09 (CH2), 31.81
(CH2), 36.93 (CH2), 73.26 (CH) ppm. MS (EI, 70 eV): m/z (%) =
144 (10) [M]+, 115 (30), 97 (72), 69 (18), 59 (100), 58 (11), 57 (16),
55 (73), 43 (22), 41 (30), 31 (14), 29 (16).
1-Phenyl-3-pentanol (4bb):[16] Compound 3bb (134 mg, 1.00 mmol)
was converted for 48 h according to the general procedure After
chromatography (SiO2; cyclohexane/EtOAc, 2:1; Rf = 0.41), 4bb
was obtained as a colorless oil (116 mg, 0.71 mmol, 71%). 1H
NMR (400 MHz, CDCl3): δ = 1.00–1.07 (m, 3 H), 1.47–1.71 (m, 2
H), 1.75–1.91 (m, 3 H), 2.69–2.81 (m, 1 H), 2.83–2.95 (m, 1 H),
3.57–3.70 (m, 1 H), 7.23–7.43 (m, 5 H) ppm. 13C NMR (CDCl3,
75 MHz): δ = 9.78 (CH3), 30.16 (CH2), 31.98 (CH2), 38.48 (CH2),
72.50 (CH), 125.68 (CH), 128.29 (2CH), 128.33 (2CH) ppm. MS
(EI, 70 eV): m/z (%) = 164 (4) [M]+, 146 (43), 117 (65), 104 (33),
91 (100), 78 (15), 65 (13), 59 (12), 51 (6).
1-(Naphthalen-1-yl)propan-1-ol (2k):[16] Compound 1k (234 mg,
1.50 mmol) was converted for 12 h according to the general pro-
cedure. After chromatography (SiO2; cyclohexane/EtOAc, 25:1; Rf
= 0.71), 2k was obtained as a yellow oil (275 mg, 1.48 mmol, 99%).
1H NMR (300 MHz, CDCl3): δ = 1.04 (t, J = 7.4 Hz, 3 H), 1.85–
2.11 (m, 3 H), 5.39 (dd, J = 5.1, 7.5 Hz, 1 H), 7.44–7.57 (m, 3 H),
7.61–7.68 (m, 1 H), 7.77–7.84 (m, 1 H), 7.86–7.93 (m, 1 H), 8.09–
8.18 (m, 1 H) ppm. 13C NMR (CDCl3, 75 MHz): δ = 10.47 (CH3),
31.02 (CH2), 72.52 (CH), 122.84 (CH), 123.18 (CH), 125.34 (CH),
125.42 (CH), 125.85 (CH), 127.81 (CH), 128.82 (CH), 130.44 (C),
133.75 (C), 140.16 (C) ppm. MS (EI, 70 eV): m/z (%) = 186 (29)
[M]+, 168 (12), 158 (12), 157 (100), 153 (24), 152 (12), 130 (11), 129
(99), 128 (55), 127 (32).
1-(2,4-Dimethoxyphenyl)propan-1-ol (2l):[19] Compound 1l (249 mg,
1.50 mmol) was converted for 24 h according to the general pro-
cedure. After chromatography (SiO2; cyclohexane/EtOAc, 10:1; Rf
= 0.38), 2l was obtained as a colorless oil (277 mg, 1.41 mmol,
1
94%). H NMR (300 MHz, CDCl3): δ = 0.93 (t, J = 7.4 Hz, 3 H),
2,6-Dimethyldec-2-ene-8-ol (4bc):[21] Compound 3bc (154 mg,
1.00 mmol) was converted for 48 h according to the general pro-
cedure. After chromatography (SiO2; cyclohexane/EtOAc, 10:1; Rf
= 0.55), 4bc was obtained as a colorless oil (117 mg, 0.63 mmol,
63%, 1:1 mixture of diastereoisomers). 1H NMR (400 MHz,
CDCl3): δ = 0.91 (dd, J = 5.9, 6.5 Hz, 3 H), 0.93 (t, J = 7.5 Hz, 3
H), 1.06–1.55 (m, 7 H), 1.60 (s, 3 H), 1.67 (s, 3 H), 1.90–2.07 (m,
2 H), 3.57–3.66 (m, 1 H), 5.12–5.06 (m, 1 H) ppm. 13C NMR
(CDCl3, 75 MHz): δ = 9.74 (CH3), 9.91 (CH3), 17.60 (CH3), 19.10
(CH3), 20.29 (CH3), 25.31 (CH2), 25.45 (CH2), 25.67 (CH3), 28.85
(CH), 28.23 (CH), 30.33 (CH2), 30.99 (CH2), 36.61 (CH2), 37.94
(CH2), 44.39 (CH2), 44.59 (CH2), 70.88 (CH), 71.20 (CH), 124.75
(CH), 131.12 (C), 131.17 (C) ppm. MS (EI, 70 eV): m/z (%) = 184
(2), 155 (15), 137 (9), 123 (20), 109 (58), 99 (70), 95 (62), 82 (100),
69 (71), 67 (47), 59 (29), 55 (47).
1.74–1.87 (m, 2 H), 2.44–2.50 (m, 1 H), 3.80 (s, 3 H), 3.82 (s, 3 H),
4.72 (q, J = 6.0 Hz, 1 H), 6.44–6.47 (m, 1 H), 6.47–6.49 (m, 1 H),
7.17–7.21 (m, 1 H) ppm. 13C NMR (CDCl3, 75 MHz): δ = 10.53
(CH3), 30.11 (CH2), 55.25 (CH3), 55.33 (CH3), 72.02 (CH), 98.64
(CH), 103.95 (CH), 124.91 (C), 127.63 (CH), 157.73 (C), 159.95
(C) ppm. MS (EI, 70 eV): m/z (%) = 196 (5) [M]+, 178 (11), 168
(10), 167 (100), 151 (14), 137 (18).
1-(Pyridin-2-yl)propan-1-ol (4aa):[20] Compound 3aa (160 mg,
1.49 mmol) was converted for 90 h according to the general pro-
cedure. After chromatography (SiO2; cyclohexane/EtOAc, 20:1; Rf
= 0.68), 4aa was obtained as a pale-yellow oil (126 mg, 0.92 mmol,
1
62%). H NMR (300 MHz, CDCl3): δ = 0.87 (t, J = 7.5 Hz, 3 H),
1.56–1.72 (m, 1 H), 1.74–1.89 (m, 1 H), 4.23 (br. s, 1 H), 4.62 (dd,
J = 6.9, 4.8 Hz, 1 H), 7.08–7.15 (m, 1 H), 7.16–7.21 (m, 1 H),
7.56–7.65 (m, 1 H), 8.44–8.49 (m, 1 H) ppm. 13C NMR (CDCl3,
75 MHz): δ = 9.36 (CH3), 31.28 (CH2), 73.72 (CH), 120.34 (CH),
122.16 (CH), 136.54 (CH), 148.09 (CH), 161.96 (C) ppm. MS (EI,
X-ray Absorption Measurements: XAS measurements were per-
formed at beamline X1 at the Hamburger Synchrotron Strahlungs-
6
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Activation of Diorganozinc Reagents
labor (HASYLAB) under ambient conditions at 293 K. A Si(111)
double crystal monochromator was used for measurements at the
Zn K-edge (9.659 keV). The second monochromator crystal was
tilted for optimal harmonic rejection. The spectra were recorded in
transmission mode with ionization chambers filled with nitrogen.
The individual pressures were adjusted to optimize the signal-to-
noise ratio. Energy calibration was performed with a zinc metal
foil, which was measured simultaneously with the samples between
the second and third ionization chamber. To avoid errors in the
XANES region due to small changes in the energy calibration be-
tween two measurements, all spectra were calibrated to the edge
position of the zinc foil. The liquid samples were measured in a
specially designed transmission sample cell for air- and moisture-
sensitive samples, which was equipped with tabs to be connected
to a Schlenk line. The cell could be evacuated under elevated tem-
perature and flushed with argon prior to the measurements. Air-
sensitive samples could be added by using a syringe under inert
conditions. Operando studies were carried out with a set-up de-
scribed previously.[22]
from Prof. Beller. M. B. thanks HASYLAB (Hamburg) for provi-
sion of beamtime.
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Data evaluation started with background absorption removal from
the experimental absorption spectrum by subtracting a Victoreen-
type polynomial. Due to several inflection points in the absorption
edge, the threshold energy E0 was determined consistently by tak-
ing the energy at half the edge jump;[23] for copper metal, this pro-
cedure causes a shift of the energy scale in comparison with the
most published data by around 5 eV. All spectra were corrected in
a consistent way so this shift does not lead to misinterpretations.
To determine the smooth part of the spectrum, corrected for pre-
edge absorption, a piecewise polynomial was used; it was adjusted
in such a way that the low-R components of the resulting Fourier
transform were minimal. After division of the background-sub-
tracted spectrum by its smooth part, the photon energy was con-
verted into photoelectron wave numbers k. The resulting χ(k)-func-
tion was weighted with k3 and Fourier transformed using a Han-
ning window function. Data analysis was performed in k-space
with Fourier filtered data. The filtered range was chosen according
to the range of significant data and is given in Table 5 together with
the results of the fitting procedure. Adjustment of the common
theoretical EXAFS expression
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(1)
(Nj: one type of neighbor atoms j in a shell, rj: distance of atoms j
from the X-ray absorbing atom, S0 : amplitude reduction factor, Fj:
2
backscattering amplitude, σ2: Debye-Waller like factor, δj : overall
phaseshift) according to the curved wave formalism of the EX-
CURV98 program with XALPHA phase and amplitude func-
tions.[24] The mean free path of the scattered electrons was calcu-
lated from the imaginary part of the potential (VPI set to –4.00 eV).
An inner potential correction Ef was introduced when fitting exper-
imental data with theoretical models that accounts for an overall
phase shift between the experimental and calculated spectra.
Supporting Information (see footnote on the first page of this arti-
cle): Copies of H and 13C NMR spectra.
1
Acknowledgments
T. W. gratefully acknowledges financial support from the Deutsche
Forschungsgemeinschaft (DFG) (WE 3605/3-1) and the Leibniz-
Institute for Catalysis (LIKAT) as well as the support and advice
Eur. J. Org. Chem. 0000, 0–0
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T. Werner, M. Bauer, A. M. Riahi, H. Schramm
FULL PAPER
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Eur. J. Org. Chem. 0000, 0–0

Job/Unit: O42138
/KAP1
Date: 18-06-14 17:58:41
Pages: 9
Activation of Diorganozinc Reagents
Synthetic Methods
T. Werner,* M. Bauer,* A. M. Riahi,
H. Schramm ...................................... 1–9
A Catalytic System for the Activation of
Diorganozinc Reagents
Keywords: Homogeneous catalysis / C–C
coupling / Zinc / Chelates / Crown com-
pounds / Aldehydes
Sodium salts in combination with crown
ethers efficiently activate diorganozinc.
Catalytic amounts of sodium iodide and
15-crown-5 promote the conversion of vari-
ous aldehydes. Efforts to apply EXAFS
techniques to verify the mode of activation
are described.
Eur. J. Org. Chem. 0000, 0–0
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