A Grignard-type phase-vanishing method: Generation of organomagnesium reagent and its subsequent addition to carbonyl compounds

Article abstract of DOI:10.1055/s-0034-1380381

Abstract A quadraphasic phase-vanishing system comprised of diethyl ether, magnesium, perfluoropolyether, and iodoalkane efficiently generated the corresponding Grignard reagents, which subsequently added to carbonyl compounds in the ether layer to afford alkylated alcohols in good yields.

Full text of DOI:10.1055/s-0034-1380381

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© Georg Thieme Verlag Stuttgart · New York
2015, 26, A–E
letter
A
H. Matsubara et al.
Letter
Synlett
A Grignard-Type Phase-Vanishing Method: Generation of Organo-
magnesium Reagent and Its Subsequent Addition to Carbonyl
Compounds
O
Hiroshi Matsubara*
Yuki Niwa
R
OH
R2
RI, Mg
(R = Me, Et)
R1
R2
R1
Et2O, Galden
"PV method"
Ryosuke Matake
Department of Chemistry, Graduate School of Science,
Osaka Prefecture University, Sakai, Osaka 599-8531, Japan
matsu@c.s.osakafu-u.ac.jp
carbonyl compound
Mg
alkylation
product
Et2O
Galden
MeI, EtI
25 °C, 2 d
Received: 19.01.2015
Accepted after revision: 16.02.2015
Published online: 30.03.2015
O
R
OH
RI, Mg
R1
R2
R1 R2
2 (R = Me)
3 (R = Et)
Et2O, Galden
"PV method"
DOI: 10.1055/s-0034-1380381; Art ID: st-2015-u0037-l
1
Abstract A quadraphasic phase-vanishing system comprised of diethyl
ether, magnesium, perfluoropolyether, and iodoalkane efficiently gen-
erated the corresponding Grignard reagents, which subsequently add-
ed to carbonyl compounds in the ether layer to afford alkylated alcohols
in good yields.
carbonyl compound
Mg (d = 1.74)
alkylation
product
Et2O
Key words fluorous solvent, phase-vanishing, Grignard reaction,
Galden
(1.74 < d <
1.95)
MeI (d = 2.28)
EtI (d = 1.95)
Barbier reaction, magnesium, perfluoropolyether
Perfluorinated compounds are generally immiscible
with most organic solvents and are denser than typical or-
ganic molecules.1 By utilizing these characteristics, in con-
junction with the Curran group, we developed a triphasic
reaction system, termed the ‘phase-vanishing (PV) method’,
in which fluorous media act as liquid membranes to trans-
port reagents into the organic layer, which contains the
substrates.2 Since the first demonstration of the viability of
the PV method,3 which was used for the bromination of
alkenes with molecular bromine, various reactions have
been carried out using the PV method by us4 as well as by
others.5 For example, in a photoirradiative PV method,4e hy-
drogen bromide was efficiently generated from a PV system
comprised of an alkane, perfluorohexanes, and molecular
bromine under irradiation; it subsequently reacted with 1-
alkanes to afford terminal bromides in high yields. Perfluo-
rohexanes (FC-72, d = 1.69) are usually employed as the fluo-
rous phase, and perfluoropolyethers such as Galden have
also been used.6 Typical reagents utilized in PV systems are
denser than fluorous media (d > 1.7) and include Br2, BBr3,
SnCl4, and CH2I2. The PV method is suitable for controlling
heat evolution in exothermic reactions, and the fluorous
phase regulates the transport of reagents by passive diffu-
sion.
Scheme 1 Concept of Grignard-type phase-vanishing alkylation of car-
bonyl compounds
The Grignard reaction is one of the most important re-
actions in organic synthesis.7 Although some Grignard re-
agents are commercially available, researchers often pre-
pare Grignard reagents from organic halides and magne-
sium in ethereal solvents. The slow addition of halides to
magnesium is usually required to safely prepare Grignard
reagents in good yields. Thus, we utilized the PV method to
prepare Grignard reagents. The concept behind the ‘Gri-
gnard-type PV reaction’ is shown in Scheme 1. Iodometh-
ane (d = 2.28) and iodoethane (d = 1.95) were used as the
reagent phase (bottom layer), because these iodides were
denser than the fluorous media. Diethyl ether was em-
ployed as the organic phase (top layer) and carbonyl com-
pounds were added to the top layer. Tetrahydrofuran (THF)
did not dissolve the methylmagnesium reagent, and FC-72
was miscible with diethyl ether; therefore, these solvents
were not suitable in this system. As such, perfluoropoly-
ethers (Galden) were employed as the fluorous phase. Tun-
ing of the fluorous phase was necessary because magne-
sium (d = 1.74) was required to be between the fluorous
© Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, A–E

B
H. Matsubara et al.
Letter
Synlett
Table 1 Grignard-Type Phase-Vanishing Reaction with Carbonyl Com-
magnesium in the appropriate position and also because it
facilitated the transport of iodoalkanes to the magnesium
phase through diffusion, as shown in Figure 1.
poundsa
Entry RI
Substrate
Product
Isolated
yield (%)
With the optimized fluorous solvent in hand, we exam-
ined the generation of Grignard reagents from iodomethane
and the subsequent addition of the Grignard reagent to 2-
decanone as a model (Figure 1). In a test tube (13 mm φ),
iodomethane (4 mmol) was covered with Galden
HT135/200 (2 mL), which, in turn, was covered with an
ether solution (4 mL) containing 2-decanone (1a; 2 mmol).
Magnesium powder (4 mmol) was floated between the fluo-
rous layer and organic solution to form a quadraphasic sys-
tem. The bottom layer was gently stirred at 25 °C, with care
not to mix the four layers. After 2 d, the bottom layer van-
ished. The ether layer and magnesium salt were taken and
quenched with dilute hydrochloric acid. The organic phase
was collected, dried over Na2SO4 and concentrated. After
column chromatography on silica gel, 2-methyl-2-decanol
(2a) was obtained in 93% yield.
The generality of the Grignard-type PV reaction is
demonstrated in Table 1.8 Acyclic (entries 1–5) and cyclic
(entry 6) ketones underwent addition of the methylmagne-
sium reagent to afford the corresponding carbinols in high
yields. On the other hand, an aldehyde gave the correspond-
ing carbinol in low yield because the dominant process was
the reduction of the substrate with magnesium to afford
the corresponding primary alcohol (entry 7). The reactivity
of iodoethane was slightly lower than that of iodomethane
(entries 3 and 9). With an excess of the generated Grignard
reagents, esters (entries 8–9) and a diester (entry 10) af-
forded the corresponding alcohols and diol in good yields,
respectively.
The reactivity of the Grignard-type PV method was
compared to that of the Barbier reaction.9 Methylation of
carbonyl compounds under Barbier conditions was carried
out as follows: a mixture of iodomethane (4 mmol), magne-
sium (4 mmol), and carbonyl compounds (2 mmol) in di-
ethyl ether (10 mL) was stirred for two days at 25 °C, fol-
lowed by the same workup as used in the PV method. As
shown in Table 2, the Grignard-type PV method gave the
corresponding carbinols in higher or similar yields with ke-
tones (entries 1 and 2) or an ester (entry 4) respectively,
while the Barbier conditions suppressed the reduction of
the substrate with magnesium better than the PV method,
and thereby afforded the addition product in a higher yield
when an aldehyde was used (entry 3).
We also examined the generation of alkynylmagnesium
reagents10 using the Grignard-type PV method. 1-Octyne
was added to the ether solution in the Grignard-type PV
method, in which methylmagnesium iodide was reacted
with 1-octyne to afford the 1-octynylmagnesium reagent in
situ. After two days, carbonyl compounds were added to the
ether solution and the mixture was gently stirred for one
day at 25 °C. As shown in Table 311,12 ketones gave the cor-
responding alcohols 4 with an octynyl moiety in good
O
OH
C8H17
1
MeI
93
C8H17
2a
1a
R
OH
C5H11
O
2
3
MeI
EtI
87
80
H11C5
2b (R = Me)
3b (R = Et)
H11C5
C5H11
1b
O
OH
4
5
MeI
MeI
79
75
2c
1c
O
O
OH
OH
Ph
2d
Ph
1d
6
7
MeI
MeI
91
2e
2f
1e
O
OH
R
30b
H
1f
C11H23
C11H23
C11H23
R
O
8c
9c
MeI
EtI
81
77
HO
2g (R = Me)
3g (R = Et)
EtO
1g
C11H23
O
O
OH
OH
10d
MeI
71
EtO
OEt
4
4
2h
1h
a Reaction conditions: substrate (2.0 mmol), Mg (2.0 equiv), RI (2.0 equiv),
Et2O (4 mL), Galden HT135/200 = 1:1 (2 mL), 25 °C, 2 d.
b 1-Dodecanol (47%) was also obtained.
c Mg (4.0 equiv), RI (4.0 equiv).
d Mg (6.0 equiv), RI (6.0 equiv).
and organic phases. The use of Galden HT135 (d = 1.72) as
the fluorous phase was attempted. However, this solvent
was not sufficiently dense to float the magnesium on it.
Therefore, Galden HT200 (d = 1.79) was subsequently em-
ployed as the fluorous phase. This solvent kept the magne-
sium between the two phases; however, Galden HT200 pre-
vented the diffusion of the iodoalkanes, because the kinetic
viscosity of Galden HT200 is 2.4 times larger than that of
Galden HT135.6 As such, we mixed Galden HT135 and
Galden HT200 in a 1:1 (v/v) ratio. The mixed fluorous sol-
vent (d = 1.75) worked well, in that it could be used to float
© Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, A–E

C
H. Matsubara et al.
Letter
Synlett
Figure 1 Grignard-type phase-vanishing methylation of 2-decanone
Table 2 Comparison of the Grignard-Type PV Methoda and the Barbier
Table 3 Alkynylation of Carbonyl Compounds by the Grignard-Type PV
Reactionb
Methoda
O
R1
Entry
Substrate
Product
Isolated yield (%)
OH
R2
1
R1
R2
MeI, Mg
PV
Barbier
H13C6
Et2O, Galden
"PV method"
O
H13C6
OH
4
1
93
63
C8H17
C8H17
2a
1a
1e
Entry
Substrate
Product
Isolated
yield (%)
O
OH
OH
C8H17
O
2
91
67
1
2
3
72
83
93
C8H17
H13C6
4a
2e
2f
1a
O
OH
H11C5
OH
O
3
30c
81
62d
89
H
1f
C11H23
C11H23
C5H11
H11C5
1b
C5H11
H13C6
4b
O
C11H23
Et
OH
Ph
4e
O
HO
2g
EtO
1g
C11H23
Ph
1d
H13C6
4d
a Reaction conditions: substrate (2.0 mmol), Mg (2.0 equiv), MeI (2.0
equiv), Et2O (4 mL), Galden HT135/200 = 1:1 (2 mL), 25 °C, 2 d.
b Reaction conditions: (2.0 mmol), Mg (2.0 equiv), MeI (2.0 equiv), Et2O
(10 mL), 25 °C, 2 d.
OH
O
c 1-Dodecanol (47%) was also obtained.
4
5
21
C11H23
d 1-Dodecanol (27%) was also obtained.
H
C11H23
e Mg (4.0 equiv), MeI (4.0 equiv).
H13C6
4f
1f
OH
yields (entries 1–3), whereas aldehydes resulted in complex
mixtures and lower yields of the desired products (entries 4
and 5).
O
12b
Ph
Ph
H
1i
H13C6
4i
In summary, by using mixed perfluoropolyethers as the
fluorous phase, we have demonstrated the generation of
Grignard reagents from iodomethane or iodoethane by
floating magnesium between the organic and fluorous lay-
ers. Whereas aldehydes did not undergo alkylation satisfac-
torily, ketones and esters gave the desired products in high
yields. The Grignard-type PV method afforded superior or
similar results to those obtained with the Barbier reaction
for the alkylation of ketones or esters, respectively. Genera-
a Reaction conditions: 1-octyne (2.0 mmol), Mg (2.5 mmol), MeI (2.7
mmol), Et2O (4 mL), Galden HT 135/200 = 1:1 (2 mL), 25 °C, 2 d; then sub-
strate (2.0 mmol), 25 °C, 1 d.
b Determined by 1H NMR spectroscopic analysis.
tion of alkynylmagnesium reagents by using this method
was also carried out successfully. It should be noted that by
© Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, A–E

D
H. Matsubara et al.
Letter
Synlett
using the PV method, Grignard-type reactions can be car-
ried out in a simple apparatus, namely just a test tube.
Named Reactions in Organic Synthesis; Elsevier Academic Press:
Burlington, 2005, 188; and references therein. (d) Raston, C. L.;
Salem, G. The Chemistry of the Carbon–Metal Bond; Vol. 4;
Hartley, F. R.; Patai, S., Eds.; Wiley: New York, 1987, 159.
(e) Wakefield, B. J. Organomagnesium Method in Organic Synthe-
sis; Academic Press: San Diego, 1996, 21.
Acknowledgment
We thank the Japan Society for the Promotion of Science (JSPS) for fi-
nancial support of this work. We also thank Prof. Ilhyong Ryu for help-
ful discussions.
(8) Grignard-Type Phase-Vanishing Alkylation of Carbonyl Com-
pounds; Typical Procedure (Table 1, entry 1): Galden
HT135/200
= 1:1 (2 mL) was placed in a test tube
(13 mm Φ × 105 mm), to which MeI (571 mg, 4.0 mmol) was
added slowly using a glass pipette under argon. Anhydrous Et2O
(1 mL) was added slowly, whereupon three layers formed. Mg
powder (98 mg, 4.0 mmol) was then added slowly, and floated
between the Galden and ether layers, whereupon four layers
formed. Subsequently, a solution of 2-decanone (1a, 313 mg, 2.0
mmol) in anhydrous Et2O (3 mL) was added to the ether layer.
The bottom layer was stirred slowly at 25 °C for 2 d, taking care
not to mix the four layers. The ether solution and Mg salt were
taken into a flask, to which hydrochloric acid (2 M) was added
to quench the reaction, while cooling in an ice bath. The organic
layer was separated, and the aqueous layer was extracted with
Et2O. The organic layer was collected, dried over Na2SO4, and
concentrated. The residue was purified by column chromatog-
raphy on silica gel (hexane–Et2O, 3:1) to give 2-methyl-2-
decanol (2a)13 (320 mg, 93%) as a colorless oil; 1H NMR (500
MHz, CDCl3): δ = 1.47–1.43 (m, 2 H, C-CH2), 1.34–1.28 (m, 12 H,
alkyl), 1.21 (s, 6 H, 2 × C-CH3), 0.88 (t, J = 7.1 Hz, 3 H, CH2-CH3);
13C NMR (126 MHz, CDCl3): δ = 70.97, 43.95, 31.81, 30.12, 29.53,
29.20, 29.13, 24.28, 22.58, 14.01.
Supporting Information
Supporting information for this article is available online at
http://dx.doi.org/10.1055/s-0034-1380381.
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References and Notes
(1) For a general review on fluorous chemistry, see: Handbook of
Fluorous Chemistry; Gladysz, J. A.; Curran, D. P.; Horváth, I. T.,
Eds.; Wiley-VCH: Weinheim, 2004.
(2) For reviews on the ‘Phase-vanishing’ method, see: (a) Ryu, I.;
Matsubara, H.; Nakamura, H.; Curran, D. P. Chem. Rec. 2008, 8,
351. (b) Iskra, J. Lett. Org. Chem. 2006, 3, 170. (c) Van Zee, N. J.;
Dragojlovic, V. Chem. Eur. J. 2010, 16, 7950.
(3) Ryu, I.; Matsubara, H.; Yasuda, S.; Nakamura, H.; Curran, D. P. J.
Am. Chem. Soc. 2002, 124, 12946.
(4) (a) Nakamura, H.; Usui, T.; Kuroda, H.; Ryu, I.; Matsubara, H.;
Yasuda, S.; Curran, D. P. Org. Lett. 2003, 5, 1167. (b) Matsubara,
H.; Yasuda, S.; Ryu, I. Synlett 2003, 247. (c) Rahman, Md. T.;
Kamata, N.; Matsubara, H.; Ryu, I. Synlett 2005, 2664.
(d) Matsubara, H.; Tsukida, M.; Yasuda, S.; Ryu, I. J. Fluorine
Chem. 2008, 129, 951. (e) Matsubara, H.; Tsukida, M.; Ishihara,
D.; Kuniyoshi, K.; Ryu, I. Synlett 2010, 2014.
(5) (a) Jana, N. K.; Verkade, J. G. Org. Lett. 2003, 5, 3787. (b) Iskra, J.;
Stavber, S.; Zupan, M. Chem. Commun. 2003, 2496. (c) Curran, D.
P.; Werner, S. Org. Lett. 2004, 6, 1021. (d) Podgoršek, A.; Stavber,
S.; Zupan, M.; Iskra, J. Eur. J. Org. Chem. 2006, 483. (e) Windmon,
N.; Dragojlovic, V. Tetrahedron Lett. 2008, 49, 6543.
(f) Windmon, N.; Dragojlovic, V. Beilstein J. Org. Chem. 2008, 4,
29. (g) Ma, K.; Li, S.; Weiss, R. G. Org. Lett. 2008, 10, 4155. (h) Van
Zee, N. J.; Dragojlovic, V. Org. Lett. 2009, 11, 3190. (i) Pels, K.;
Dragojlovic, V. Beilstein J. Org. Chem. 2009, 5, 75. (j) Tojino, M.;
Hirose, Y.; Mizuno, M. Tetrahedron Lett. 2013, 54, 7124.
(6) Galden HT135 and HT 200 are polyether-type perfluorinated
solvents, which is commercially available from Solvay Solexis
Inc. The general structure of the solvents is shown in Figure 2.
Kinetic viscosity of Galden HT135 and HT200 at 25 °C are 1.0
and 2.4 cSt, respectively.
(9) For example, see: Kürti, L.; Czakó, B. Strategic Applications of
Named Reactions in Organic Synthesis; Elsevier Academic Press:
Burlington, 2005, 38.
(10) For example, see: Blagoev, B.; Ivanov, D. Synthesis 1970, 615.
(11) Alkynylation of Carbonyl Compounds by the Grignard-Type
Phase-Vanishing Method; Typical Procedure (Table 3, entry
2): Galden HT135/200 = 1:1 (2 mL) was placed in a test tube
(13 mm φ × 105 mm), to which MeI (391 mg, 2.7 mmol) was
added slowly using a glass pipette under argon. Anhydrous Et2O
(1 mL) was added slowly, whereupon three layers formed. Mg
powder (61 mg, 2.5 mmol) was then added slowly, which
floated between the Galden and ether layers, whereupon four
layers formed. Subsequently, a solution of 1-octyne (221 mg, 2.0
mmol) in anhydrous Et2O (3 mL) was added to the ether layer.
The bottom layer was stirred slowly at 25 °C for 2 d, taking care
not to mix the four layers. After confirming that the MeI layer
vanished and Mg was consumed, a solution of dipentyl ketone
(1b, 341 mg, 2 mmol) anhydrous Et2O (1 mL) was slowly added
to the organic layer. The mixture was then stirred at 25 °C for 1
d. The ether solution and Mg salt were taken into a flask, to
which hydrochloric acid (2 M) was added to quench the reac-
tion, while cooling in an ice bath. The organic layer was sepa-
rated, and the aqueous layer was extracted with ether. The
organic layer was collected, dried over Na2SO4, and concen-
trated. The residue was purified by column chromatography on
silica gel (hexane–Et2O, 9:1) to give 6-(1-octynyl)undecan-6-ol
(4b; 466 mg, 83%) as a colorless oil. 1H NMR (500 MHz, CDCl3):
δ = 2.19 (t, J = 7.1 Hz, 2 H, -CH2C≡), 1.82 (s, 1 H, OH), 1.61–1.57
(m, 6 H, 2 × -CH2CO + -CH2CH2C≡), 1.51–1.46 (m, 6 H, alkyl),
1.38–1.26 (m, 12 H, alkyl), 0.91–0.86 (m, 9 H, 3 × CH3); 13C NMR
(126 MHz, CDCl3): δ = 84.62, 83.19, 71.31, 42.24, 32.00, 31.50,
31.24, 28.66, 28.38, 23.93, 22.53, 18.54, 13.94; MS (EI, 70 eV):
m/z (%) = 280 (0.07), 262 (3), 209 (100), 195 (1), 177 (3), 163 (1),
F
F
F F
F
O
F3C
O
OCF3
m
n
CF3
Figure 2 General structure of the solvents used herein
(7) For example, see: (a) Eicher, T. The Chemistry of Carbonyl Group;
Patai, S., Ed.; Wiley: New York, 1966, Part 1 621. (b) Fieser, L. F.;
Fieser, M. Reagents for Organic Synthesis, Coll. Vol. 1; Wiley: New
York, 1967, 415. (c) Kürti, L.; Czakó, B. Strategic Applications of
© Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, A–E

E
H. Matsubara et al.
Letter
Synlett
135 (5); HRMS (EI, 70 eV): m/z calcd for C19H36O: 280.2766;
4 H, alkyl), 0.95–0.89 (m, 6 H, 2 × CH3); 13C NMR (126 MHz,
CDCl3): δ = 145.08, 127.95, 127.39, 125.56, 86.86, 82.38, 73.96,
38.49, 31.28, 28.66, 28.54, 22.53, 18.73, 14.01, 9.13; MS (EI,
70 eV): m/z (%) = 244 (0.5), 227 (29), 215 (100), 185 (2), 167 (3),
157 (6), 144 (13); HRMS: m/z calcd for C17H24O: 244.1827;
found: 244.1820; IR (neat): 3424, 3060, 3028, 2932, 2243, 1666,
found: 280.2764; IR (neat): 3424, 2932, 2238, 1378, 1342, 1140,
1025 cm–1
.
(12) Spectroscopic data for new compounds: Compound 4a:
1H NMR (500 MHz, CDCl3): δ = 2.18 (t, J = 6.9 Hz, 2 H, CH2C≡),
1.86 (s, 1 H, OH), 1.63–1.59 (m, 2 H, CH2CO), 1.50–1.40 (m, 5 H,
CH2CH2C≡ + CH3C), 1.38–1.24 (m, 18 H, alkyl), 0.90–0.86 (m,
6 H, 2 × CH3CH2); 13C NMR (126 MHz, CDCl3): δ = 84.10, 83.75,
68.36, 44.01, 31.88, 31.31, 30.13, 29.75, 29.55, 29.25, 28.68,
28.47, 24.79, 22.66, 22.54, 18.59, 14.10; MS (EI, 70 eV): m/z (%) =
266 (0.3), 251 (35), 181 (2), 165 (3), 157 (5), 153 (100), 137 (6);
HRMS (EI, 70 eV): m/z [M – H]+ calcd for C18H33O: 265.2531;
found: 265.2532; IR (neat): 3364, 2928, 2240, 1630, 1466, 1370,
1600, 1448, 1329, 1213, 1051, 973, 758, 700 cm–1
.
Compound 4f: 1H NMR (500 MHz, CDCl3): δ = 4.34 (t, J = 5.6 Hz,
1 H, CHO), 2.19 (m, 2 H, CH2C≡), 1.67–1.64 (m, 2 H, CH2CHO),
1.50–1.25 (m, 26 H, alkyl), 0.90–0.86 (m, 6 H, 2 × CH3); 13C NMR
(126 MHz, CDCl3): δ = 85.52, 81.33, 62.79, 38.22, 31.91, 31.32,
29.63, 29.56, 29.34, 28.63, 28.50, 25.20, 22.68, 22.54, 18.67,
14.10, 14.03; MS (EI, 70 eV): m/z (%) = 294 (2), 237 (9), 209 (47),
181 (5), 167 (7), 153 (25), 139 (100); HRMS (EI, 70 eV): m/z (%)
calcd for C20H38O: 294.2923; found: 294.2917; IR (neat): 3357,
1131, 930 cm–1
.
Compound 4d: 1H NMR (500 MHz, CDCl3): δ = 7.63 (d, J =
7.3 Hz, 2 H, PhH), 7.35 (t, J = 7.6 Hz, 2 H, PhH), 7.27 (t, J = 7.3 Hz,
1 H, PhH), 2.30 (t, J = 7.1 Hz, 2 H, CH2C≡), 2.17 (s, 1 H, OH), 1.98–
1.85 (m, 2 H, CH2CO), 1.54–1.42 (m, 4 H, alkyl), 1.34–1.27 (m,
2925, 2234, 1701, 1465, 1033 cm–1
(13) Dragovich, P. S.; Prins, T. J.; Zhou, R. J. Org. Chem. 1995, 60, 4922.
.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, A–E