Stereoselective alkyne semihydrogenations with an air-stable copper(i) catalyst

Article abstract of DOI:10.1039/c6ob02271e

An air-stable and preactivated copper(i) hydroxide/N-heteroyclic carbene (NHC) complex for alkyne semihydrogenations is reported. Next to an enhanced practicability of the process, the resulting alkenes are obtained with high Z-selectivities and no overreduction to the corresponding alkanes.

Full text of DOI:10.1039/c6ob02271e

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DOI: 10.1039/C6OB02271E
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ARTICLE
Stereoselective alkyne semihydrogenations with an air-stable
copper(I) catalyst
mReceived 00th January 20xx,
Accepted 00th January 20xx
Niklas O. Thiel and Johannes F. Teichert*
An air-stable and preactivated copper(I) hydroxide/N-heteroyclic carbene (NHC) complex for alkyne semihydrogenations is
reported. Next to an enhanced practicability of the process, the resulting alkenes are obtained with high Z-selectivities and
no overreduction to the corresponding alkanes.
DOI: 10.1039/x0xx00000x
www.rsc.org/
Z-alkenes (Scheme 1a).6 This catalyst has to be activated with
an alkoxide at elevated temperatures (100 °C) and is limited to
mainly unfunctionalised substrates.15
Introduction
Catalytic stereoselective alkyne semihydrogenations are
powerful and atom-economic synthetic alternatives to
olefination reactions.1,2 The resulting alkenes are valuable
building blocks especially for diastereoselective follow-up
reactions.3 For Z-selective alkyne semihydrogenations, the
Lindlar catalyst4 has become first choice, however, it suffers
from E/Z-isomerisation processes and overreduction to the
corresponding alkanes.2 While the latter leads to loss of the
desired functionality, the former can be problematic with
foresight to tedious separations and consecutive
diastereoselective transformations.
Hydrogenations catalysed by readily available first row
transition metals are desirable from an economic point of
view.5 Among them, homogeneous catalysts based on
copper(I) have recently emerged as viable alternatives for Z-
selective alkyne semihydrogenations.6–10 Key reactivity for
these catalytic processes is the reported stereoselective
insertion of alkynes into copper(I) hydride bonds.11–13 While
most of the reported catalysts allow for good to excellent Z-
stereoselectivity in alkyne semihydrogenations, all studied
copper(I) complexes need to be prepared in situ as the active
catalysts are unstable. This feat can be ascribed to the
formation of a Cu–O-bond, which allows for H2 activation14 but
at the same time renders the corresponding complexes
Scheme 1: Approaches to Cu-catalysed alkyne semihydrogenations.
sensitive to air and moisture. The need for preactivation We have introduced
a
highly stereoselective alkyne
hampers the practicability of the overall processes, as can be semihydrogenation based upon copper(I)/N-heterocylic
seen
from
the
studied
catalysts
so
far:
A
carbene (NHC) complexes bearing an alkoxide tether (Scheme
triphenylphosphine/copper(I) complex can be used under an 1b).7 This system requires high H2 pressure (100 bar) and the
H2 amosphere (5 bar) at elevated temperatures in combination catalyst needs to be generated in situ from sensitive
with iso-propanol to transform alkynes into the corresponding mesitylcopper(I). More recently, an NHC/copper(I) complex
has
been
reported
which
allows
for
alkyne
semihydrogenations at 1 bar H2. The catalyst has to be
generated in situ from a copper(I) chloride/NHC precursor with
sodium tert-butanolate and shows somewhat reduced Z/E-
selectivity (Scheme 1c).8
Institut für Chemie, Technische Universität Berlin, Strasse des 17. Juni 115, 10623
Berlin, Germany. Email: johannes.teichert@chem.tu-berlin.de; Fax: +49 (0)30 314
28829; Tel: +49 (0)30 314 22791.
Electronic Supplementary Information (ESI) available: Preparation and
characterisation data as well as 1H and 13C NMR spectra of all compounds.
See DOI: 10.1039/x0xx00000x
Herein, we report on the identification of a preactivated and
air-stable NHC/copper(I) hydroxide complex, [IPrCuOH],16 for
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highly Z-selective alkyne semihydrogenations. The stability of Substrate Scope
View Article Online
DOI: 10.1039/C6OB02271E
the precatalyst allows for a more practical effectuation of the
With optimised reaction conditions in hand, we set out to
investigate the substrate scope of the Z-selective alkyne
semihydrogenation with [IPrCuOH] and found generally broad
applicability, while Z-stereoselectivity remained high (Scheme
2). A variety of electron-rich and electron-poor aryl/alkyl-
semihydrogenation
without
jeopardizing
the
stereoselectivity.17
Results and discussion
substituted alkynes 3a
-
3e based upon the pentynol-framework
4e in high yields. Unlike
Optimisation of the alkyne semihydrogenation
The alkyne semihydrogenation has been optimised using
pentynol-derived internal alkyne (Table 1): Generally, E/Z-
isomerisation processes and/or overreduction remained
negligible. Under previously optimised reaction conditions (40
°C, 100 bar H2)7 as well as with slightly reduced H2 pressure of
80 bar, [IPrCuOH] shows complete conversion of the internal
gave the corresponding Z-alkenes 4a
-
our previously reported copper(I)/NHC complex (Scheme 1b),7
[IPrCuOH] does not fully tolerate ketone functional groups,
which is showcased by partial overreduction of 4f to the
benzylic alcohol (ratio ketone/benzylic alcohol = 88:12). We
hypothesise that the presence of an intermediate alcohol(ate)
disturbs the overall chemoselectivity, as in this case
overreduction to the alkane was substantial (15%). This effect
of additional alcohol(ate)s mirrors those of our previous
study.7 In contrast, the tolerance of heterocycles differs from
our earlier results: Thiophene 4g, which was unreactive with
the tethered catalyst,7 can now be obtained in good yield
1
alkyne to the corresponding Z-styrene derivative
entries 1 and 2). Alkene could be isolated with 93% yield.
Lowering the pressure to 50 bar H2 led to incomplete
conversion of in THF (Table 1, entry 3). At these limiting
2 (Table 1,
2
1
conditions (40 °C, 50 bar H2), the alkyne semihydrogenation in
DMF or toluene gave little turnover (25% and 26%
respectively, Table 1, entries 4 and 5). During the investigation
of the substrate scope (see below), we found that generally
higher turnovers were obtained at higher H2 pressure.
Additionally, for some compounds, more forcing conditions
(100 bar H2, 60 °C) were required for full conversion (as in
Table 1, entry 6). When lowering the H2 pressure to 1 bar
(balloon) an alkyne semihydrogenation could not be observed
(Table 1, entry 7). The sterically more demanding copper(I)
hydroxide complex [IPr*CuOH]17b displayed lower activity
under forcing conditions (Table 1, entry 8).18
(94%): Pyridine isomers 3h-3j, viable substrates with our
earlier catalyst,7 give varying results in terms of overreduction
and/or E/Z isomerisation. This displays a vulnerability of the
copper(I) catalyst to strongly coordinating substrates. The
present protocol is applicable to diaryl- and dialkylalkynes
alike: Tolane (3k) and its derivatives prove to be suitable
precursors for Z-stilbenes 4k-4m under the semihydrogenation
conditions. Notably, methoxy-substituted tolane 3l required a
somewhat higher H2 pressure (100 bar). In a similar vein,
dialkylalkynes 3n and 3o require slightly more forcing
conditions (100 bar H2, 60 °C) to allow full conversion to the
desired Z-alkenes 4n and 4o. The protected allylic alcohol 4p is
available from the corresponding propargylic silyl ether in high
yields and excellent stereoselectivity using elevated
temperature and H2 pressure. This example marks one of the
strong points of our catalytic process, as Z-allylic alcohols are
important building blocks for diastereoselective follow-up
reactions (See below for a synthetic elaboration of 4p). Finally,
methyl-2-nonynoate (3q) shows excellent selectivity towards
the corresponding Z-acrylate in our semihydrogenation
protocol, albeit with low conversion (20%). Further
investigations are needed to identify superior catalysts for this
challenging, yet synthetically valuable semihydrogenation of
propiolates.
Table 1: Optimisation of alkyne semihydrogenation with IPrCuOHa,b
Entry
Conditions
Conversionc
1
2
3
4
5
6
7
THF, 40 °C, 100 bar H2
THF, 40 °C, 80 bar H2
THF, 40 °C, 50 bar H2
DMF, 40 °C, 50 bar H2
toluene, 40 °C, 50 bar H2
THF, 60 °C, 100 bar H2
THF, 60 °C, 1 bar H2
full
full (93%d)
87%
When investigating diyne 5, selectively only the E,E-diene 6
was isolated with high yield (87%) with our catalyst. This is of
note, as this class of compounds has been reported to get
25%
26%
full
n.d.
reduced to
a Z-monoalkene by an earlier copper(I)
hydrogenation catalyst6 in alkyne semihydrogenation. To
[IPr*CuOH] instead of [IPrCuOH],
60 °C, 100 bar H2
8
67%
investigate the possible origin of this unexpected E-selectivity,
we prepared E-enyne
stepwise diyne semihydrogenation from
this experiment, we isolated 96% of the E,Z-diene
7
, a potential reaction intermediate in a
aReactions were carried out on 0.13 mmol scale. bIn all cases, the E/Z/alkane ratio
was >99 : 1 : 1. cDetermined by 1H NMR and GC analysis. dIsolated yield,
0.26 mmol scale.
5
towards . From
6
8
,
representing only minor loss of stereochemical integrity of the
primarily installed E-alkene. With this result, it seems
reasonable to conclude that diynes such as
5 do not react step-
wise as isolated triple bonds. A potential alkenylcopper(I)
2 | J. Name., 2012, 00, 1-3
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intermediate could equilibrate to
ARTICLE
a
butatrienylcopper(I) Follow-up chemistry of (Z)-allylic alcohols
View Article Online
intermediate19 (not shown), which accounts for the formation
DOI: 10.1039/C6OB02271E
Finally, to demonstrate the usefulness of the present highly Z-
selective alkyne semihydrogenation, we further elaborated
silyl ether 4p (Scheme 4): After silyl ether deprotection with
of the thermodynamically more preferred E,E-diene
diyne 5.
6 from
TBAF to the allylic alcohol
9 (83%), subsequent oxidation with
the Dess-Martin periodinane20 gave Z-acrolein-derivative 10
(88%). Subsequent Horner-Wadsworth-Emmons reaction was
carried out to yield E,Z-sorbic acid derivative 11 in 86% yield.
This approach underlines that
a stereoselective alkyne
semihydrogenation with [IPrCuOH] can serve as key step to
generate alkene geometries with high selectivity.
Scheme 4: Derivatisation of allyl silyl ether 4p. Reaction conditions: i) 1.1 equiv.
TBAF, THF, rt, 3h, 83%; ii) 1.4 equiv. DMP, CH2Cl2, rt, 3h, 88%; iii) 1.5 equiv.
triethyl phosphonoacetate, 1.5 equiv. NaH, THF, 0 °C to rt, 22h, 86%,
Z,E/Z,Z = >20:1.
Conclusions
In summary, we have developed a highly Z-stereoselective
alkyne semihydrogenation protocol, relying on an air-stable
and preactivated NHC/copper(I) hydroxide complex,
[IPrCuOH]. The practicability of this catalyst circumvents
previous shortcomings of other copper(I) complexes as it does
not require preactivation. A variety of products is accessible
via this protocol in high yields and excellent Z-selectivities. The
findings presented here could make a contribution towards
widely applicable catalysis with easily accessible first-row
transition metals.
Scheme 2: Cu-catalyzed alkyne semihydrogenation with [IPrCuOH], substrate scope. If
not noted otherwise, the ratio Z/E/alkane is >99:1:1. aContains 5% alkane.
bKetone/benzylic alcohol ratio 88:12, contains 15% alkane. Reaction was run for 48 h.
c100 bar H2 employed. dReaction at 60 °C.
Experimental
All reactions were carried out in flame-dried glassware under a
nitrogen atmosphere using standard Schlenk techniques. NMR
spectra were recorded on AvanceII 400 MHz or AvanceIII 500
MHz or 700 MHz instruments (Bruker). Chemical shifts are
reported in parts per million (ppm) and are referenced to the
residual solvent resonance as the internal standard according
to literature values.[21] Data are reported as follows: chemical
shift, multiplicity (br s = broad singlet, s = singlet, d = doublet, t
= triplet, q = quartet, sept = septet, m = multiplet, mc
=
centrosymmetric multiplet), coupling constants (Hz),
integration. All hydrogenation reactions were carried out in
glass vials (50 x 14 mm, Schütt), equipped with a magnetic stir
bar, a rubber septum pinched with a needle (0.90 x 50 mm,
Scheme 3: Cu-catalysed semihydrogenation of a diyne and an enyne.
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Braun) in autoclaves Berghof BR-100 or BR-300 equipped with Prepared from 3b (72 mg, 0.26 mmol, 1.0VeieqwuAirvti.c)le Oanlninde
DOI: 10.1039/C6OB02271E
heating blocks. For preparation and characterisation of the [IPrCuOH] (6.0 mg, 13 µmol, 5 mol%) according to the general
starting materials, see the Supplementary Information.
procedure. The reaction mixture was stirred under H2
atmosphere (80 bar) at 40 °C for 19 h. Purification by flash
column chromatography on silica gel using cyclohexane/tert-
butyl methyl ether 50:1 as eluent afforded 4b (62 mg,
0.22 mmol, 86%) as a colorless oil. Rf = 0.41 (cyclohexane/tert-
General procedure alkyne semihydrogenation
The reaction vessel was placed in a N2-purged autoclave under
a counterflow of N2. The autoclave was purged with N2 (3 x 10
bar) and H2 (3 x 20 bar) before the appropriate H2 pressure
was applied (pressure is given as initial pressure before
heating). The heating block was pre-heated before the
autoclave was placed inside. After the reported reaction time
the autoclave was allowed to cool to rt and H2 was released.
The autoclave was purged with N2 (3 x 10 bar) before the
reaction vessel was taken out. The reaction mixture was
filtered through a small plug of silica (1 mL tert-butyl methyl
ether as eluent), and all volatiles were removed under reduced
pressure. Reactions were subsequently analysed either by GC
1
butyl methyl ether 10:1); H NMR (500 MHz, CDCl3): δ = 1.79
(mc, 2H), 2.45 (mc, 2H), 3.52 (t, J = 6.4 Hz, 2H), 3.81 (s, 3H), 4.49
(s, 2H), 5.58 (dt, J = 11.7 Hz, J = 7.3 Hz, 1H), 6.38 (mc, 1H), 6.86
(mc, 2H), 7.24 (mc, 2H), 7.27-7.36 (m, 5H) ppm; 13C NMR
(126 MHz, CDCl3): δ = 25.4, 30.2, 55.4, 69.9, 73.0, 113.7, 127.6,
127.7, 128.5, 128.9, 130.1, 130.5, 130.8, 138.8, 158.4 ppm;
+
HRMS (EI) calcd for C19H22O2 [(M)+]: 282.1614, found:
282.1610. The data is in accordance with literature.[7]
(Z)-1-(5-(Benzyloxy)pent-1-en-1-yl)-4-chlorobenzene (4c)
and/or NMR. The crude mixture was then subjected to Prepared from 3c (71 mg, 0.25 mmol, 1.0 equiv.) and
purification as indicated with the appropriate substrates.
[IPrCuOH] (6.0 mg, 13 µmol, 5 mol%) according to the general
procedure. The reaction mixture was stirred under H2
atmosphere (80 bar) at 40 °C for 19 h. Purification by flash
column chromatography on silica gel using cyclohexane/tert-
butyl methyl ether 50:1 as eluent afforded 4c (66 mg,
0.23 mmol, 92%) as a colorless oil. Rf = 0.59 (cyclohexane/tert-
(Z)-(5-(Benzyloxy)pent-1-en-1-yl)benzene (2)
Prepared from
1 (64 mg, 0.26 mmol, 1.0 equiv.) and [IPrCuOH]
(6.0 mg, 13 µmol, 5.0 mol%) according to the general
procedure. The reaction mixture was stirred under H2
atmosphere (80 bar) at 40 °C for 19 h. Purification by flash
column chromatography on silica gel using cyclohexane/tert-
1
butyl methyl ether 10:1). H NMR (500 MHz, CDCl3): δ = 1.78
(mc, 2H), 2.42 (mc, 2H), 3.51 (t, J = 6.4 Hz, 2H), 4.48 (s, 2H), 5.69
(dt, J = 11.7 Hz, J = 7.4 Hz, 1H), 6.39 (d, J = 11.7 Hz, 1H), 7.22
(m, 2H), 7.27-7.30 (m, 5H), 7.33-7.36 (m, 2H) ppm; 13C NMR
(126 MHz, CDCl3): δ = 25.4, 30.0, 69.7, 73.1, 127.6, 127.7,
128.3, 128.4, 128.5, 130.2, 132.4, 133.1, 136.2, 138.6 ppm;
HRMS (EI) calcd for C18H19ClO+ [(M)+]: 286.1119, found:
286.1133; IR (ATR) ν = 2854 (m), 1490 (s), 1453 (m), 1362 (m),
1091 (s), 1013 (m), 840 (s), 734 (s), 696 (s) cm-1.
butyl methyl ether 50:1 as eluent afforded
2 (60 mg, 0.24
mmol, 93%) as a colorless oil. Rf = 0.65 (cyclohexane/tert-butyl
1
methyl ether 10:1). H NMR (500 MHz, CDCl3): δ = 1.76-1.84
(m, 2H), 2.48 (mc, 2H), 3.53 (t, J = 6.5 Hz, 2H), 4.50 (s, 2H), 5.69
(dt, J = 11.7 Hz, J = 7.4 Hz, 1H), 6.46 (mc, 1H), 7.22-7.26 (m,
1H), 7.28-7.36 (m, 9H) ppm; 13C NMR (126 MHz, CDCl3): δ =
25.4, 30.1, 69.9, 73.0, 126.6, 127.6, 127.7, 128.3, 128.5, 128.9,
129.5, 132.4, 137.8, 138.7 ppm; HRMS (APCI) calcd for
C18H21O+ [(M+H)+]: Calculated 253.1587, found: 253.1582. The
data is in accordance with literature.[7]
(Z)-1-(5-(Benzyloxy)pent-1-en-1-yl)-4-bromobenzene (4d)
Prepared from 3d (83 mg, 0.25 mmol, 1.0 equiv.) and
[IPrCuOH] (6.0 mg, 13 µmol, 5 mol%) according to the general
procedure. The reaction mixture was stirred under H2
atmosphere (80 bar) at 40 °C for 19 h. Purification by flash
column chromatography on silica gel using cyclohexane/tert-
butyl methyl ether 50:1 as eluent afforded 4d (77 mg,
0.23 mmol, 91%) as a colorless oil. Rf = 0.69 (cyclohexane/tert-
Methyl (Z)-4-(5-(benzyloxy)pent-1-en-1-yl)benzoate (4a)
Prepared from 3a (79 mg, 0.26 mmol, 1.0 equiv.) and
[IPrCuOH] (6.0 mg, 13 µmol, 5 mol%) according to the general
procedure. The reaction mixture was stirred under H2
atmosphere (100 bar) at 40 °C for 24 h. Purification by flash
column chromatography on silica gel using cyclohexane/tert-
butyl methyl ether 25:1 as eluent afforded 4a (67 mg,
0.22 mmol, 85%) as a colorless oil. Rf = 0.33 (cyclohexane/tert-
butyl methyl ether 9:1); 1H NMR (500 MHz, CDCl3): δ = 1.79
(mc, 2H), 2.46 (mc, 2H), 3.51 (t, J = 6.4 Hz, 2H), 3.92 (s, 3H), 4.48
(s, 2H), 5.78 (dt, J = 11.7 Hz, J = 7.4 Hz, 1H), 6.46 (d, J = 11.7
Hz, 1H), 7.26-7.36 (m, 7H), 7.99 (mc, 2H) ppm; 13C NMR
(126 MHz, CDCl3): δ = 25.6, 30.0, 52.1, 69.7, 73.1, 127.6, 127.7,
128.2, 128.5, 128.7, 128.8, 129.6, 134.6, 138.6, 142.4, 167.1
1
butyl methyl ether 10:1); H NMR (500 MHz, CDCl3): δ = 1.77
(mc, 2H), 2.41 (mc, 2H), 3.50 (t, J = 6.4 Hz, 2H), 4.47 (s, 2H), 5.69
(dt, J = 11.7 Hz, J = 7.4 Hz, 1H), 6.36 (mc, 1H), 7.15 (mc, 2H),
7.27-7.30 (m, 3H), 7.33-7.36 (m, 2H), 7.43 (mc, 2H) ppm; 13C
NMR (126 MHz, CDCl3): δ = 25.4, 30.0, 69.7, 73.1, 120.5, 127.6,
127.7, 128.4, 128.5, 130.5, 131.4, 133.2, 136.6, 138.6 ppm;
HRMS (APCI) calcd for C18H20BrO+ [(M+H)+]: 331.0692, found:
331.0689; IR (ATR) ν = 2930 (m), 2856 (m), 1486 (s), 1453 (m),
1102 (s), 1071 (s), 1028 (m), 1009 (s), 837 (s), 734 (s), 696 (s)
cm-1.
+
ppm; HRMS (APCI) for C20H23O3 [(M+H)+]: Calculated
311.1642, found 311.1642. The data is in accordance with
literature.[7]
(Z)-1-(5-(Benzyloxy)pent-1-en-1-yl)-4-(trifluoromethyl)benzene
(4e)
(Z)-1-(5-(Benzyloxy)pent-1-en-1-yl)-4-methoxybenzene (4b)
4 | J. Name., 2012, 00, 1-3
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Prepared from 3e (82 mg, 0.26 mmol, 1.0 equiv.) and (Z)-1,2-Diphenylethene (4k)
View Article Online
DOI: 10.1039/C6OB02271E
[IPrCuOH] (3.0 mg, 6.4 µmol, 2.5 mol%) according to the
Prepared from 3k (46 mg, 0.26 mmol, 1.0 equiv.) and
[IPrCuOH] (6.0 mg, 13 µmol, 5 mol%) according to the general
procedure. The reaction mixture was stirred under H2
atmosphere (80 bar) at 40 °C for 19 h. Purification by flash
column chromatography on silica gel using cyclohexane as
eluent afforded 4k (38 mg, 0.21 mmol, 83%) as a colorless oil.
Rf = 0.58 (cyclohexane); 1H NMR (500 MHz, CD2Cl2): δ = 6.63 (s,
2H), 7.18-7.27 (m, 10H) ppm; 13C NMR (126 MHz, CD2Cl2): δ =
127.5, 128.6, 129.2, 130.6, 137.8 ppm; HRMS (EI) calcd for
general procedure. The reaction mixture was stirred under H2
atmosphere (80 bar) at 40 °C for 19 h. Purification by flash
column chromatography on silica gel using cyclohexane/tert-
butyl methyl ether 50:1 as eluent afforded 4e (87 mg,
0.26 mmol, 99%) as a colorless oil, containing 5% of the
corresponding alkane. Rf = 0.32 (cyclohexane/tert-butyl methyl
1
ether 30:1); H NMR (500 MHz, CDCl3): δ = 1.79 (mc, 2H), 2.44
(mc, 2H), 3.51 (t, J = 6.3 Hz, 2H), 4.48 (s, 2H), 5.79 (dt,
J = 11.7 Hz, J = 7.4 Hz, 1H), 6.46 (d, J = 11.7 Hz, 1H), 7.27-7.35
(m, 5H), 7.38 (mc, 2H), 7.56 (mc, 2H) ppm; 13C NMR (126 MHz,
CDCl3): δ = 25.5, 30.0, 69.7, 73.1, 124.4 (q, J = 272 Hz), 125.2
(q, J = 3.7 Hz), 127.7, 127.8, 128.3, 128.5, 129.1, 134.6, 138.6,
141.3 ppm; 19F NMR (470 MHz, CDCl3): δ = -62.4 ppm; HRMS
(EI) calcd for C12H12F3O+ [(M-Bn)+]: 229.0835, found: 229.0839;
IR (ATR) ν = 2861 (w), 1616 (m), 1454 (m), 1323 (s), 1162 (s),
1112 (s), 1066 (s), 1016 (s), 852 (m), 744 (m), 697 (m) cm-1.
+
C14H12 [(M)+]: 180.0934, found: 180.0933. The data is in
accordance with literature.[7]
(Z)-1-Methoxy-4-styrylbenzene (4l)
Prepared from 3l (53 mg, 0.26 mmol, 1.0 equiv.) and [IPrCuOH]
(6.0 mg, 13 µmol, 5 mol%) according to the general procedure.
The reaction mixture was stirred under H2 atmosphere
(100 bar) at 40 °C for 24 h. Purification by flash column
chromatography on silica gel using cyclohexane/tert-butyl
methyl ether 100:1 as eluent afforded 4l (48 mg, 0.23 mmol,
90%) as a colorless oil. Rf = 0.64 (cyclohexane/tert-butyl methyl
(Z)-1-(4-(5-(Benzyloxy)pent-1-en-1-yl)phenyl)ethan-1-one (4f)
Prepared from 3f (74 mg, 0.26 mmol, 1.0 equiv.) and [IPrCuOH]
(6.0 mg, 13 µmol, 5 mol%) according to the general procedure.
The reaction mixture was stirred under H2 atmosphere
(100 bar) at 60 °C for 48 h. Purification by flash column
chromatography on silica gel using cyclohexane/tert-butyl
methyl ether 30:1 as eluent afforded 4f (59 mg, 0.20 mmol,
80%) as a colorless oil, containing 15% of the corresponding
1
ether 10:1); H NMR (500 MHz, CD2Cl2): δ = 3.77 (s, 3H), 6.54
(mc, 2H), 6.75 (mc, 2H), 7.17-7.27 (m, 7H) ppm; 13C NMR
(126 MHz, CD2Cl2): δ = 55.5, 113.9, 127.3, 128.6, 129.1, 129.2,
130.1, 130.2, 130.5, 138.1, 159.2 ppm; HRMS (APCI) calcd for
C15H15O+ [(M+H)+]: 211.1117, found: 211.1124. The data is in
accordance with literature.[22]
1
alkane. Rf = 0.39 (cyclohexane/tert-butyl methyl ether 4:1); H
NMR (500 MHz, CDCl3): δ = 1.79 (mc, 2H), 2.46 (mc, 2H), 2.58 (s,
3H), 3.51 (t, J = 6.3 Hz, 2H), 4.47 (s, 2H), 5.79 (dt, J = 11.7 Hz, J
= 7.4 Hz, 1H), 6.46 (d, J = 11.7 Hz, 1H), 7.25-7.38 (m, 5H), 7.37
(mc, 2H), 7.90 (mc, 2H) ppm; 13C NMR (126 MHz, CDCl3): δ =
25.6, 26.7, 30.0, 69.7, 73.1, 127.6, 127.7, 128.4, 128.5, 128.7,
129.0, 134.8, 135.3, 138.6, 142.6, 197.8 ppm; HRMS (EI) calcd
(Z)-1-Chloro-4-styrylbenzene (4m)
Prepared from 3m (54 mg, 0.26 mmol, 1.0 equiv.) and
[IPrCuOH] (6.0 mg, 13 µmol, 5 mol%) according to the general
procedure. The reaction mixture was stirred under H2
atmosphere (80 bar) at 40 °C for 24 h. Purification by flash
column chromatography on silica gel using pentane as eluent
afforded 4m (48 mg, 0.22 mmol, 88%) as a colorless oil. Rf =
+
for C20H22O2 [(M)+]: 294.1614, found: 294.1621. The data is in
accordance with literature.[7]
1
0.67 (pentane); H NMR (500 MHz, CDCl3): δ = 6.54 (d, J = 12.2
(Z)-2-(5-(Benzyloxy)pent-1-en-1-yl)thiophene (4g)
Hz, 1H), 6.64 (d, J = 12.2 Hz, 1H), 7.17-7.20 (mc, 4H), 7.22-7.27
(m, 5H) ppm; 13C NMR (126 MHz, CDCl3): δ = 127.5, 128.5,
128.6, 128.9, 129.1, 130.4, 131.1, 132.9, 135.8, 137.0 ppm;
Prepared from 3g (69 mg, 0.27 mmol, 1.0 equiv.) and
[IPrCuOH] (6.0 mg, 13 µmol, 5 mol%) according to the general
procedure. The reaction mixture was stirred under H2
atmosphere (100 bar) at 40 °C for 19 h. Purification by flash
column chromatography on silica gel using cyclohexane/tert-
butyl methyl ether 60:1 as eluent afforded 4g (63 mg,
0.24 mmol, 94%) as a colorless oil. Rf = 0.68 (cyclohexane/tert-
+
HRMS (APCI) calcd for C14H11 [(M-Cl-)+]: 179.0855, found:
179.0857. The data is in accordance with literature.[22]
(Z)-((Hept-4-en-1-yloxy)methyl)benzene (4n)
1
Prepared from 3n (52 mg, 0.26 mmol, 1.0 equiv.) and
[IPrCuOH] (6.0 mg, 13 µmol, 5.0 mol%) according to the
general procedure. The reaction mixture was stirred under H2
atmosphere (100 bar) at 60 °C for 24 h. Purification via flash
column chromatography on silica using cyclohexane/tert-butyl
methyl ether 100:1 as eluent afforded 4n (47 mg, 0.23 mmol,
90%) as a colorless oil. Rf = 0.79 (cyclohexane/tert-butyl methyl
butyl methyl ether 10:1); H NMR (500 MHz, CDCl3): δ = 1.85
(mc, 2H), 2.53 (mc, 2H), 3.56 (t, J = 6.5 Hz, 2H), 4.52 (s, 2H), 5.59
(dt, J = 11.5 Hz, J = 7.3 Hz, 1H), 6.55 (mc, 1H), 6.99-7.02 (m,
2H), 7.25 (m, 1H), 7.27 (mc, 1H), 7.34 (mc, 4H) ppm; 13C NMR
(126 MHz, CDCl3): δ = 26.1, 29.7, 70.0, 73.1, 122.3, 125.1,
126.9, 127.3, 127.6, 127.8, 128.5, 130.5, 138.8, 140.8 ppm;
HRMS (APCI) calcd for C16H19OS+ [(M+H)+]: 259.1151, found:
259.1146; IR (ATR) ν = 2854 (w), 1452 (m), 1362 (m), 1102 (s),
1048 (m), 1027 (m), 851 (m), 826 (m), 734 (s), 693 (s) cm-1.
1
ether 10:1); H NMR (700 MHz, CDCl3): δ = 0.96 (t, J = 7.5 Hz,
3H), 1.68 (mc, 2H), 2.05 (mc, 2H), 2.14 (mc, 2H), 3.49 (t, J =
6.5 Hz, 2H), 4.51 (s, 2H), 5.33 (dtt, J = 10.8 Hz, J = 7.2 Hz, J = 1.3
Hz, 1H), 5.39 (dtt, J = 10.8 Hz, J = 7.2 Hz, J = 1.3 Hz, 1H), 7.27-
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
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Organic & Biomolecular Chemistry
Page 6 of 7
ARTICLE
7.31 (m, 1H), 7.33-7.36 (m, 4H) ppm; 13C NMR (175 MHz, Prepared from
Journal Name
(52 mg, 0.26 mmol, 1.0 equiv.) aVniedw[AIPrtircCleuOOnlHine]
7
CDCl3): δ = 14.5, 20.6, 23.9, 29.9, 70.0, 73.1, 127.6, 127.8, (6.0 mg, 13 µmol, 5.0 mol%) accordiDnOgI: 1t0o.103t9h/eC6OgBe0n22e7r1aEl
128.5, 128.5, 132.4, 138.8 ppm; HRMS (APCI) for C14H21O+ procedure. The reaction mixture was stirred under H2
[(M+H)+]: Calculated 205.1587, found 205.1585. The data is in atmosphere (80 bar) at 40 °C for 19 h. Purification by filtration
accordance with literature.[7]
through a plug of silica (3 cm) using cyclohexane as eluent
afforded (51 mg, 0.25 mmol, 96%) as a colorless oil. E,Z/Z,Z =
8
1
1
(Z)-Dodec-6-ene (4o)
96:4 as judged by H NMR. Rf = 0.41 (cyclohexane); H NMR
(500 MHz, CD2Cl2): δ = 6.45 (m, 1H), 6.55 (d, J = 11.5 Hz, 1H),
6.75 (d, J = 15.6 Hz, 1H), 7.23-7.43 (m, 11H) ppm. Spectrum
contains <5% alkane-containing products, which were not
further characterised; 13C NMR (126 MHz, CD2Cl2): δ = 125.6,
127.0, 127.5, 128.1, 128.8, 129.0, 129.5, 130.6, 130.7, 135.3,
137.8, 138.1 ppm; HRMS (EI) calcd for C16H14+ [(M)+]: 206.1090,
found: 206.1091. The data is in accordance with literature.[22]
Prepared from 3o (52 mg, 0.26 mmol, 1.0 equiv.) and
[IPrCuOH] (6.0 mg, 13 µmol, 5 mol%) according to the general
procedure. The reaction mixture was stirred under H2
atmosphere (100 bar) at 60 °C for 24 h. Purification by flash
column chromatography on silica gel using cyclohexane as
eluent afforded 4o (48 mg, 0.24 mmol, 92%) as a colorless oil.
1H NMR (500 MHz, CDCl3): δ = 0.89 (t, J = 7.0 Hz, 6H), 1.28-1.36
(m, 12H), 1.99-2.04 (m, 4H), 5.36 (mc, 2H) ppm; 13C NMR
(126 MHz, CDCl3): δ = 14.2, 22.7, 27.3, 29.6, 31.7, 130.1 ppm;
(Z)-6-(Benzyloxy)hex-2-en-1-ol (9)
HRMS (EI) calcd for [(M)+]: 168.1873, found: 168.1874. The In a flame-dried Schlenk tube (15 mL) equipped with a
data is in accordance with literature.[7]
magnetic stirring bar 4p (0.70 g, 1.9 mmol, 1.0 equiv.) was
dissolved in THF (4 mL). To this mixture, TBAF (1.0 in THF, 2.1
M
(Z)-((6-(Benzyloxy)hex-2-en-1-yl)oxy)triisopropylsilane (4p)
mL, 2.1 mmol, 1.1 equiv.) was added dropwise. After 3 h the
reaction was quenched by addition of H2O (10 mL). The
aqueous phase was extracted with tert-butyl methyl ether (2 x
10 mL) and the combined organic layers were dried over
Na2SO4. All volatiles were removed under reduced pressure to
give the crude product. Purification via flash column
chromatography on silica using cyclohexane/tert-butyl methyl
Prepared from 3p (92 mg, 0.26 mmol, 1.0 equiv.) and
[IPrCuOH] (6.0 mg, 13 µmol, 5 mol%) according to the general
procedure. The reaction mixture was stirred under H2
atmosphere (100 bar) at 60 °C for 24 h. Purification by flash
column chromatography on silica gel using cyclohexane/
tert-butyl methyl ether 50:1 as eluent afforded 4p (80 mg,
0.22 mmol, 86%) as a colorless oil. Rf = 0.68 (cyclohexane/tert-
ether 3:1 as eluent afforded
9 (0.33 g, 1.6 mmol, 83%) as a
1
colorless oil. Rf = 0.35 (cyclohexane/tert-butyl methyl ether
butyl methyl ether 10:1); H NMR (500 MHz, CDCl3): δ = 1.04-
1
1:1); H NMR (500 MHz, CDCl3): δ = 1.64 (br s, 1H), 1.70 (mc,
1.14 (m, 21H), 1.69 (mc, 2H), 2.15 (mc, 2H), 3.48 (t, J = 6.5 Hz,
2H), 4.31 (d, J = 6.0 Hz, 2H), 4.50 (s, 2H), 5.42 (dtt, J = 11.0 Hz, J
= 7.4 Hz, J = 1.6 Hz, 1H), 5.58 (dtt, J = 11.0 Hz, J = 5.9 Hz, J = 1.5
Hz, 1H), 7.26-7.31 (m, 1H), 7.33-7.36 (m, 4H) ppm; 13C NMR
(126 MHz, CDCl3): δ = 12.2, 18.2, 24.4, 29.7, 59.8, 69.8, 73.0,
127.6, 127.7, 128.5, 129.7, 130.7, 138.8 ppm; 29Si DEPT (99
MHz, J = 20 Hz, CDCl3): δ = 13.8 ppm; HRMS (EI) calcd for
C19H31O2Si+ [(M-C3H7)+]: 319.2088, found: 319.2095; IR (ATR) ν
= 2941 (m), 2864 (s), 1454 (m), 1362 (m), 1091 (s), 1068 (s),
881 (s), 804 (m), 732 (s), 676 (s), 657 (s) cm-1.
2H), 2.21 (mc, 2H), 3.49 (t, J = 6.3 Hz, 2H), 4.17 (d, J = 6.9 Hz,
2H), 4.50 (s, 2H), 5.50-5.56 (m, 1H), 5.63-5.68 (m, 1H), 7.27-
7.31 (m, 1H), 7.32-7.37 (m, 4H) ppm; 13C NMR (126 MHz,
CDCl3): δ = 24.0, 29.4, 58.5, 69.3, 73.0, 127.6, 127.7, 128.5,
+
129.4, 132.3, 138.5 ppm; HRMS (ESI) calcd for C13H19O2
[(M+H)+]: 207.1380, found: 207.1383; IR (ATR) ν = 3354 (m),
2859 (m), 1453 (m), 1363 (m), 1098 (s), 1028 (s), 734 (s), 696
(s), 612 (m) cm-1.
(Z)-6-(Benzyloxy)hex-2-enal (10)
(1E,3E)-1,4-Diphenylbuta-1,3-diene (6)
In a flame dried Schlenk tube (15 mL) equipped with a
magnetic stirring bar
dissolved in CH2Cl2 (0.15
mmol, 1.4 equiv.) was added. The mixture was stirred at rt for
3 h. The reaction mixture was filtered and concentrated under
9
(0.10 g, 0.49 mmol, 1.0 equiv.) was
, 3.2 mL) and DMP (0.29 g, 0.68
Prepared from
5 (53 mg, 0.26 mmol, 1.0 equiv.) and [IPrCuOH]
M
(6.0 mg, 13 µmol, 5 mol%) according to the general procedure.
The reaction mixture was stirred under H2 atmosphere (80 bar)
at 40 °C for 19 h. Purification by flash column chromatography
on silica gel using cyclohexane as eluent afforded
0.22 mmol, 87%) as a white crystalline solid. Rf = 0.35
reduced
pressure.
Purification
via
flash
column
6 (46 mg,
chromatography on silica using cyclohexane/tert-butyl methyl
ether 4:1 as eluent afforded 10 (87 mg, 0.43 mmol, 88%) as a
colorless oil. Rf = 0.41 (cyclohexane/tert-butyl methyl ether
1
(cyclohexane); H NMR (500 MHz, CD2Cl2): δ = 6.71 (mc, 2H),
7.00 (mc, 2H), 7.23-7.26 (m, 2H), 7.35 (mc, 4H), 7.46-7.47 (m,
1
4H) ppm; 13C NMR (126 MHz, CD2Cl2): δ = 126.8, 128.0, 129.1,
3:1); H NMR (500 MHz, CDCl3): δ = 1.82 (mc, 2H), 2.73 (mc,
129.6, 133.2, 137.8 ppm; HRMS (EI) calcd for C16H14 [(M)+]:
+
2H), 3.52 (t, J = 6.1 Hz, 2H), 4.49 (s, 2H), 5.97 (ddt, J = 11.2 Hz, J
= 8.1 Hz, J = 1.5 Hz, 1H), 6.62 (dt, J = 11.2 Hz, J = 8.2 Hz, 1H),
7.27-7.37 (m, 5H), 10.08 (d, J = 8.1 Hz, 1H) ppm; 13C NMR
(126 MHz, CDCl3): δ = 24.9, 29.3, 68.9, 73.2, 127.8, 128.6,
206.1090, found: 206.1093. The data is in accordance with
literature.[22]
+
130.7, 138.3, 152.5, 191.1 ppm; HRMS (EI) calcd for C13H16O2
(1Z,3E)-1,4-Diphenylbuta-1,3-diene (8)
6 | J. Name., 2012, 00, 1-3
[(M)+]: 204.1145, found: 204.1144; IR (ATR) ν = 2858 (m), 1676
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Organic & Biomolecular Chemistry
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Journal Name
ARTICLE
McGettigan and J. M. Stryker, Tetrahedron LeVttie.w, A1r9tic9le0O, n3lin1e
,
(s), 1452 (m), 1363 (m), 1099 (s), 1027 (m), 736 (s), 697 (s), 608
(m) cm-1.
2397–2400.
10 For catalytic alkyne semireductions usDinOgI: s1i0la.1n0e39s/,Cs6eOeB:0(2a2)71AE.
M. Whittaker and G. Lalic, Org. Lett., 2013, 15, 1112–1115;
(b) K. Semba, T. Fujihara, T. Xu, J. Terao and Y. Tsuji, Adv.
Synth. Catal., 2012, 354, 1542–1550.
11 N. P. Mankad, D. S. Laitar and J. P. Sadighi, Organometallics,
2004, 23, 3369–3371.
Ethyl (2E,4Z)-8-(benzyloxy)octa-2,4-dienoate (11)
To a cooled (0 °C) suspension of NaH (60 wt% in mineral oil, 44
mg, 1.1 mmol, 1.5 equiv.) in THF (0.15M, 5 mL) was added
triethyl phosphonoacetate (0.24 g, 1.1 mmol, 1.5 equiv.)
dropwise. The resulting mixture is stirred at 0 °C for 30 min.
Compound 10 (0.15 mg, 0.72 mmol, 1.0 equiv.) was added to
this mixture. After completion of the addition the resulting
mixture was warmed to rt and stirred for 22 h. The reaction
was quenched by addition of sat. aq. NH4Cl (4 mL). The
aqueous phase was extracted with tert-butyl methyl ether (2 x
5 mL) and the combined organic layers were washed with
brine (15 mL) and dried over Na2SO4. All volatiles were
removed under reduced pressure. Purification via flash column
chromatography on silica using cyclohexane/tert-butyl methyl
ether 20:1 as eluent afforded 11 (0.17 g, 0.62 mmol, 86%) as a
colorless oil. Rf = 0.56 (cyclohexane/tert-butyl methyl ether
4:1); 1H NMR (500 MHz, CDCl3): δ = 1.29 (t, J = 7.1 Hz, 3H), 1.74
(mc, 2H), 2.42 (mc, 2H), 3.49 (t, J = 6.4 Hz, 2H), 4.21 (q, J = 7.1
Hz, 2H), 4.50 (s, 2H), 5.85 (dt, J = 11.2 Hz, J = 7.9 Hz, 1H), 5.88
(d, J = 15.3 Hz, 1H), 6.14 (mc, 1H), 7.27-7.30 (m, 1H), 7.33-7.36
(m, 4H), 7.62 (ddd, J = 15.2 Hz, J = 11.2 Hz, 1H) ppm; 13C NMR
(126 MHz, CDCl3): δ = 14.4, 25.1, 29.5, 60.4, 69.5, 73.2, 121.7,
127.1, 127.7, 127.8, 128.5, 138.6, 139.4, 140.7, 167.3 ppm;
12 See also: A. J. Jordan, C. M. Wyss, J. Bacsa and J. P. Sadighi,
Organometallics, 2016, 35, 613–616.
13 (a) A. J. Jordan, G. Lalic and J. P. Sadighi, Chem. Rev., 2016,
116, 8318–8372; (b) C. Deutsch, N. Krause and B. H. Lipshutz,
Chem. Rev., 2008, 108, 2916–2927; (c) S. Rendler and M.
Oestreich, Angew. Chem. Int. Ed., 2007, 46, 498–504.
14 G. V. Goeden and K. G. Caulton, J. Am. Chem. Soc., 1981, 103
7354–7355.
,
15 It should be noted that this procedure represents a formal
hydrogenation, as the proton equivalent stems from the
iPrOH additive.
16 G. C. Fortman, A. M. Z. Slawin and S. P. Nolan,
Organometallics, 2010, 29, 3966–3972.
17 For the use of [IPrCuOH] as catalyst in related carboxylation
reactions, see: (a) I. I. F. Boogaerts, G. C. Fortman, M. R. L.
Furst, C. S. J. Cazin and S. P. Nolan, Angew. Chem. Int. Ed.,
2010, 49, 8674–8677; (b) O. Santoro, F. Lazreg, Y. Minenkov,
L. Cavallo and C. S. J. Cazin, Dalton Trans., 2015, 44, 18138–
18144.
18 It should be noted that other copper(I) hydroxide complexes
bearing NHC ligands are elusive at the moment, which
hampers further investigation of catalysts.
19 For
propargylcopper(I) complexes, see: (a) J. Canisius, T. A.
Mobley, S. Berger and N. Krause, Chem. Eur. J., 2001,
2671–2675; (b) N. Yoshikai, T. Yamashita and E. Nakamura,
Chem. Asian J., 2006, , 322–330.
the
equilibration
of
related
(sp3)-based
+
HRMS (EI) calcd for C17H22O3 [(M)+]: 274.1564, found:
7
,
274.1571; IR (ATR) ν = 2856 (m), 1709 (s), 1634 (s), 1605 (m),
1304 (m), 1266 (s), 1166 (s), 1098 (s), 961 (s), 995 (m), 872 (m),
735 (s), 696 (s) cm-1.
1
20 D. B. Dess and J. C. Martin, J. Org. Chem., 1983, 48, 4155–
4156.
21 (a) G. R. Fulmer, A. J. M. Miller, N. H. Sherden, H. E. Gottlieb,
A. Nudelman, B. M. Stoltz, J. E. Bercaw and K. I. Goldberg,
Organometallics 2010, 29, 2176–2179; (b) H. E. Gottlieb, V.
Kotlyar and A. Nudelman, J. Org. Chem. 1997, 62, 7512–
7515.
22 D.-J. Dong, H.-H. Li and S.-K. Tian, J. Am. Chem. Soc. 2010,
132, 5018–5020.
Acknowledgements
This research was supported by the Fonds der chemischen
Industrie (Liebig-Stipendium for J.F.T.) and the Daimler-und-
Benz-Foundation (Postdoctoral Scholarship for J.F.T.). We
kindly thank Prof. Dr. Martin Oestreich (TU Berlin) for
generous support.
Notes and references
1
(a) M. Crespo-Quesada, F. Cárdenas-Lizana, A.-L. Dessimoz
and L. Kiwi-Minsker, ACS Catal., 2012, , 1773–1786; (b) A.
2
Molnar, A. Sarkany and M. Varga, J. Mol. Catal. A: Chem.,
2001, 173, 185–221.
C. Oger, L. Balas, T. Durand and J.-M. Galano, Chem. Rev.,
2013, 113, 1313–1350.
W.-Y. Siau, Y. Zhang and Y. Zhao, Top. Curr. Chem., 2012,
327, 33–58.
2
3
4
5
6
H. Lindlar, Helv. Chim. Acta, 1952, 35, 446–450.
R. M. Bullock, Science, 2013, 342, 1054–1055.
K. Semba, R. Kameyama and Y. Nakao, Synlett, 2015, 26
,
,
318–322.
7
8
9
F. Pape, N. O. Thiel and J. F. Teichert, Chem. Eur. J., 2015, 21
15934–15938.
T. Wakamatsu, K. Nagao, H. Ohmiya and M. Sawamura,
Organometallics, 2016, 35, 1354–1357.
For alkyne semihydrogenation with stoichiometric use of
copper(I) hydride complexes, see: J. F. Daeuble, C.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
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