A highly Z-selective isomerization (double-bond migration) procedure for Allyl acetals and Allyl ethers mediated by Nickel complexes

Article abstract of DOI:10.1055/s-1998-2028

A novel procedure for a highly Z-selective isomerization (double-bond migration) of acyclic allyl acetals and allyl ethers based on NiCl₂dppb catalysis by activation with SuperHydride (lithium triethylborohydride) is described. The stereochemical outcome is compared with the results obtained with Ru and Rh catalysts. The applicability of the new process is demonstrated in the stereoselective synthesis of Claisen substrates (allyl vinyl ethers) from diallyl ethers.

Full text of DOI:10.1055/s-1998-2028

March 1998
SYNTHESIS
305
A Highly Z-Selective Isomerization (Double-Bond Migration) Procedure
for Allyl Acetals and Allyl Ethers Mediated by Nickel Complexes
Andrea Wille, Sabine Tomm, Herbert Frauenrath*
Universität Gh Kassel, Fachbereich 19 – Biologie/Chemie, Heinrich-Plett-Str. 40, D-34109 Kassel, Germany
Fax +49(561)8044649; E-mail: frauenra@hrz.uni-kassel.de
Received 11 July 1997; revised 13 October 1997
Abstract: A novel procedure for a highly Z-selective isomeriza-
tals. Activation of this complex with lithium tri-
ethylborohydride (Super-Hydride) probably affords a hy-
dridonickel species as an intermediate,16 which then ini-
tiates the catalytic cycle.17
tion (double-bond migration) of acyclic allyl acetals and allyl
ethers based on NiCl2dppb catalysis by activation with Super-
Hydride (lithium triethylborohydride) is described. The stereo-
chemical outcome is compared with the results obtained with Ru
and Rh catalysts. The applicability of the new process is demon-
strated in the stereoselective synthesis of Claisen substrates (allyl
vinyl ethers) from diallyl ethers.
As optical active ligands such as diop are not essential for
the isomerization of acyclic substrates (Table), we ex-
plored the isomerization of allylic substrates with nickel
complexes comprising achiral diphenylphosphino lig-
ands. Though a few nickel-based catalysts have been re-
ported for allylic rearrangements,18,19 to our knowledge
the isomerization of acyclic allyl ethers or acetals by nick-
el complexes and activation with lithium triethylborohy-
dride has not yet been described.
Key words: isomerization, stereoselectivity, nickel complexes,
allyl acetals, allyl ethers
The well-known double-bond migration (isomerization)
of allyl ethers and allyl acetals to vinyl ethers (prop-1-enyl
ethers) or vinyl acetals, respectively, has found many ap-
plications in organic chemistry.1 For example, the allyl
and the but-3-en-2-yl moieties have been introduced as
stable protecting groups for carbohydrates, which are eas-
ily removed via isomerization and hydrolysis of the re-
spective vinyl ether.2,3 Vinyl glycosides were used as
substrates in the Lewis-acid mediated oligosaccharide
synthesis.4
The activity of nickel catalysts proved to be very sensitive
to the chelate ring size and the bite angle of the bis(diphe-
nylphosphino) ligand to the metal.20,21 Thus, the iso-
merization with NiCl2dppe [dppe = 1,2-bis(diphenyl-
phosphino)ethane] as the catalyst precursor22 completely
failed and led to quantitative recovery of the starting ma-
terial, whereas NiCl2dppb [dppb = 1,4-bis(diphenylphos-
phino)butane] activated with Super-Hydride readily
isomerizes allylic substrates with high yields and with
high Z-selectivities.23 As a typical example, treatment of
a mixture of acetamide 1a with NiCl2dppb (4 mol%) and
LiBHEt3 (4 mol%) in THF at room temperature afforded
virtually pure (Z)-2a (> 99:1) in 83% isolated yield
(Scheme 1, Table).
The double-bond geometry resulting from the isomeriza-
tion process is without interest as far as the allyl moiety is
used only as a protecting group. However, the Z/E-selec-
tivity of this process plays an important role especially
when the vinylic products are used for stereoselective re-
actions. Thus, vinyl acetals are used for the diastereose-
lective construction of aldol ethers and b-(N-acyl-
amino)aldehydes (Mannich products) by Lewis acid-in-
duced rearrangement,5,6 and allyl vinyl ethers prepared by
transition metal catalyzed rearrangement of diallyl ethers
are of interest in the stereoselective synthesis of aliphatic
Claisen products.7–10
Several catalysts have been reported in the literature for
the isomerization of allyl ethers and acetals, e.g., potassi-
um tert-butoxide in DMSO11 and Rh, Ru, Ir, and Fe com-
plexes, or palladium on active charcoal.12 Among them,
only the potassium tert-butoxide/DMSO method leads to
high Z-selectivities. However, this method is hampered by
the strong basic conditions, the tedious workup and only
moderate yields. On the other hand, excellent yields are
obtained with transition metal catalysts, but these proce-
dures usually afford Z/E-mixtures,12–14 and they are often
complicated by the formation of reduced by-products
(propyl ethers and acetals) due to the activation procedure
of the catalyst precursor.4,5
Scheme 1
In comparison, the isomerization of 1a with RuCl2(PPh3)3
(4 mol%) activated with NaBH4 (16 mol%) in EtOH at
room temperature gave an 85:15 Z/E-mixture of 2a to-
gether with 30% of the corresponding propyl derivative.24
However, the formation of hydrogenated by-products is
completely suppressed, when the activation of the Ru pre-
catalyst is performed with lithium triethylborohydride.
Thus, treatment of 1a at room temperature with
RuCl2(PPh3)3 (4 mol%) activated with LiBHEt3 (4 mol%)
resulted in an 81:19 mixture of (Z)- and (E)-2a as the only
reaction products. Wilkinson’s catalyst activated with Su-
per-Hydride or butyllithium25 failed to catalyze the
isomerization at room temperature.
During the course of our investigations on the asymmetric
isomerization of cyclic allyl acetals using NiCl2diop/
LiBHEt3 [diop = 2,3-O-isopropylidene-2,3-dihydroxy-
1,4-bis(diphenylphosphino)butane] as a catalyst15 we
found, that NiCl2diop is also an effective catalyst precur-
sor for the isomerization of acyclic allyl ethers and ace-
We also found, that the Z/E-selectivity strongly depends
on the reaction temperature. The NiCl2dppb/LiBHEt3 cat-
alyzed isomerization of 1a in refluxing THF for 4 hours

306
Papers
SYNTHESIS
Table. NiCl2dppb/LiBHEt3 Catalyzed Isomerization of Acyclic Allyl Acetals and Allyl Ethers
Product
X
R
R1
R2
Reaction
Yieldb
(%)
bp
(°C)/Torr
Z/Ec
Conditionsa
2a
2b
2c
2d
2e
2f
N(Me)Ac
N(Me)Ac
N(Me)Ac
N(Me)Ac
OMe
t-Bu
Ph
t-Bu
t-Bu
Bn
H
H
H
Me
H
H
H
Me
H
H
r.t., 18 h
r.t., 18 h
r.t., 18 h
reflux, 48 h
reflux, 48 h
r.t., 1 h
83
91
83
84
83
87
81
37/0.01
87/0.01
60/0.01
40/0.01
115/20
>99:1
99:1
96:4
75:25
96:4
95:5
95:5
Ph
H
H
H
H
H
H
86/760
110/760
2g
MeCH=CH
reflux, 2 h
a THF was used as a solvent.
b Values refer to isolated yields after distillation (quantitative conversion according to NMR spectroscopy).
c Determined by1H NMR spectroscopy.
relative configuration of the Claisen-rearrangement prod-
uct 3..9,10 Treatment of 1g with NiCl2dppb and LiBHEt3 in
refluxing THF for 2 hours gave rearranged product 2g in a
95:5 Z/E-ratio (Scheme 3). In contrast, the reaction of 1g
usingRuCl2(PPh3)3/LiBHEt3 asacatalystinrefluxingTHF
for 2 hours produces a 53:47 Z/E-mixture of 2g.
gave a 95:5 Z/E-mixture of 2a, whereas the Ru catalyst in
refluxing THF for 4 hours and Wilkinson’s catalyst in re-
fluxing THF for 18 hours upon activation with LiBHEt3
produced Z/E-mixtures in 75:25 and 62:38 ratios, respec-
tively. A stereoisomeric mixture, in which the E-isomer
outweighs the Z-isomer (75:25), was obtained when 1a
was refluxed with RuCl2(PPh3)3 and NaBH4 in EtOH for
14 hours. We assume that the decrease in the selectivity is
due to a metal induced Z/E-equilibration, which obviously
occurs faster with the Ru and the Rh than with the Ni cat-
alyst. This assumption also emerges from an equilibration
experiment with 2c. Thus, when a 96:4 Z/E-mixture of 2c
was refluxed in a high boiling solvent, e.g. methyl glycol,
with NiCl2dppb activated with LiBHEt3 for 4 hours, the
selectivity remained unchanged. However, refluxing the
same mixture of 2c with RuCl2(PPh3)3 activated with
LiBHEt3 in methyl glycol for 4 hours led quantitatively to
a 57:43 Z/E-mixture (Scheme 2).
Scheme 3
The latter example also demonstrates the remarkable regio-
selectivity exhibited by the NiCl2dppb/LiBHEt3 catalyst.
Only the terminally unsubstituted double-bond is rear-
ranged, whereas the crotyl moiety remaines unchanged.
This result is in agreement with the high regioselectivity
already observed with other transition metal cata-
lysts7,12,26
In conclusion, NiCl2dppb upon activation with LiBHEt3
proves to be a readily available catalyst for the isomer-
ization (double-bond migration) of a wide range of allyl-
ic substrates. This nickel-based catalyst is superior to
other metal catalysts with respect to selectivity and
price. It may be used in stereoselective organic synthesis
as a substitute for potassium tert-butoxide/DMSO as a Z-
selective catalyst for the isomerization of allylic sub-
strates. Limitations with respect to the stereochemistry
arise in the rearrangement of 1-substituted prop-2-enyl
derivatives.
Scheme 2
As demonstrated for the synthesis of 2c, the NiCl2dppb/
LiBHEt3 isomerization procedure is not only applicable to
unsubstituted N-acylated N,O-acetals (1a, 1b), but also to
substituted allylic substrates (1c, 1d) as well as O,O-ace-
tals (1e) and allyl ethers (1f, 1g). The but-3-en-2-yl deriv-
ative 1d, which usually rearranges slower than sterically
less hindered allyl derivatives,7,26 and the acetal 1e re-
quired higher temperatures and prolonged reaction times,
whereas complete conversion for the allyl ether 1f was
achieved within 1 hour at room temperature.
All reactions were carried out under a dry nitrogen atmosphere. The
reagents used were of commercial grade from freshly opened contain-
ers, or were distilled prior to use. Organic solvents were purified by
standard procedures. Allyl benzyl ether (1f), Super-Hydride
(LiBHEt3, 1 M solution in THF), and dppb were purchased from Sig-
The usefulness of the new process is il]ustrated in the syn-
thesis of the Claisen substrate 2g, for which control of the
ma-Aldrich Chemie GmbH Deutschland. Boiling points are uncor-
1
vinyl double bond geometry is important with respect to the rected. H NMR (500 MHz) and 13C NMR (125 MHz) spectra were

March 1998
SYNTHESIS
307
1
13C NMR: d = 9.19 (CH3, Z), 9.28 (CH3, E), 22.37 (H3CCO, E), 22.40
(H3CCO, Z), 26.11 [C(CH3)3, Z], 26.49 [C(CH3)3, E], 30.65 (NCH3,
E), 30.72 (NCH3, Z), 36.80 [C(CH3)3, Z], 37.50 [C(CH3)3, E], 88.63
(NCHO, Z), 93.81 (NCHO, E), 103.00 (=CHCH3, Z), 104.81
(=CHCH3, E), 141.80 (OCH=, E), 143.42 (OCH=, Z), 170. 86 (CO,
E), 172.21 (CO, Z).
recorded on a Varian Unity INOVA 500 spectrometer in CDCl3. H
chemical shifts are reported in ppm by using TMS as an internal stan-
dard. (J)-Values are given in Hz. 13C chemical shifts are reported in
ppm and referenced to the solvent signal. 1R spectra were recorded on
a Bio-Rad FTS-40A spectrometer. Elemental analyses were deter-
mined on an Elementar Vario EL apparatus. Allyl acetals and ethers
1 (except 1e and 1f) were synthesized according to Ref. 6 or standard
literature procedures. Selectivities, boiling points and yields of the re-
arrangement products 2 are given in the Table. For the new com-
pounds satisfactory microanalyses were obtained: C ± 0.28, H ± 0.29,
N ± 0.18
(Z)-N-[Phenyl(prop-1-en-1-yloxy)methyl]-N-methylacetamide (2b):
Amide rotamer ratio: E{Z = 22:78.
IR: n = 3039, 2941, 1662, 1450, 1394, 1321, 1250, 1967, 1008 cm–1.
1H NMR: d = 1.70 (dd, 3H, J = 6.8, 1.7, CH3, Z), 1.71 (dd, 3H, J =
6.7, 1.7, CH3, E), 2.18 (s, 3H, H3CCO, Z), 2.32 (s, 3H, H3CCO, E),
2.66 (s, 3H, NCH3, E), 2.68 (s, 3H, NCH3, Z), 4.59 (dq, 1H, J = 6.1,
6,8, =CHCH3, Z), 4,71 (dq, 1H, J = 6.1, 6.1, =CHCH3, E), 6.10 (dq,
1H, J = 6.1, 1.7, OCH=, E), 6.18 (dq, 1H, J = 6.1, 1.7, OCH=, Z), 6.26
(s, 1H, NCHO, E), 7.19 (s, 1H, NCHO, Z), 7.32 (m, 1Harom,Hp, E/Z),
7.17 (m, 2Harom, Hm, E/Z), 7.42 (m, 2Harom, Ho, E/Z).
[2-Methoxy-2-(prop-2-en-1-yloxy)ethyl]benzene (1e):
Allyl alcohol (16.4 mL, 0.24 mol) was added dropwise to a mixture
of phenylacetaldehyde dimethyl acetal (40 g, 0.24 mol) and p-TsOH
(50 mg) at r.t. Then the mixture was heated to 75 °C and stirred for
20 h. After cooling to r.t. the mixture was poured into aq sat. K2CO3
solution (30 ml) and extracted with Et2O (3 ´ 10 mL), The combined
organic layers were dried (K2CO3), concentrated in vacuo and puri-
fied by distillation (Fischer column) to give 1e (23.04 g, 50 %) as a
colorless liquid; bp 116–118°C/20 Torr.
13C NMR: d = 9.33 (CH3, Z), 9.45 (CH3, E), 21.93 (H3CCO, E), 22.18
(H3CCO, Z), 27.72 (NCH3, E), 29.22 (NCH3, Z), 82.23 (NCHO, Z),
88.04 (NCHO, E), 104.00 (=CHCH3, Z), 106.09 (=CHCH3, E),
125.96 (arom Cm, E), 126.14 (arom Cm, Z), 128.18 (arom Co, E),
128.36 (arom Co, Z), 128.67 (arom Cp, E/Z), 136.66 (arom Cq, E),
137.22 (arom Cq, Z), 170.52 (CO, E), 172.14 (CO, Z).
IR: n = 3087, 2930, 2832, 1497, 1434, 1347, 1123, 1061, 748,
700 cm–1.
1H NMR: d = 2.94 (d, 2H, J = 5.6, CH2), 3.34 (s, 3H, OCH3), 3.98
(dddd, 1H, J = 12.7, 5.6, 1.5, 1.5, OCHH), 4.12 (dddd, 1H, J = 12.7,
5.4, 1.5, 1.5, OCHH), 4.65 (t, 1H, J = 5.6, OCHO), 5.13 (dddd, 1H, J
= 1.7, 10.4, 1.5, 1.5, =CHH), 5.23 (dddd, 1H, J = 1.7, 17.1, 1.5, 1.5,
=CHH), 5.86 (dddd, 1H, J = 17.1, 10.4, 5.6, 5.4, CH=), 7.26 (m,
5Harom).
(Z)-N-[1-(But-1-en-1-yloxy)-2,2-dimethylpropyl]-N-methylacetamide
(2c):
Amide rotamer ratio: E/Z = 24:76.
IR: n = 3037, 2966, 2876, 1662, 1645, 1481, 1368, 1245, 1203, 1142,
1077, 1008 cm–1.
1H NMR: d = 0.97 (dd, 3H, J = 6.4, 6.4, =CHCH2CH3, E), 0.98 (dd,
3H, J = 7.6, 7.6, =CHCH2CH3, Z), 0.98 [s, 9H, C(CH3)3, Z], 1.04 [s,
9H, C(CH3)3, E], 2.12 (s, 3H, H3CCO, Z), 2.13 (m, 2H, =CHCH2CH3,
Z), 2.15 (m, 2H, =CHCH2CH3, E), 2.17 (s, 3H, H3CCO, E), 2.81 (s,
3H, NCH3, E), 2.88 (s, 3H, NCH3, Z), 4.43 (ddd, 1H, J = 6.2, 7.2, 7.2,
=CHCH2CH3, Z), 4.53 (ddd, 1H, J = 6.1, 7.3, 7.3, =CHCH2CH3, E),
5.38 (s, 1H, NCHO, E), 5.65 (s, 1H, NCHO, Z), 5.82 (ddd, 1H, J =
6.1, 1.5, 1.5, OCH=, E), 5.84 (ddd, 1H, J = 6.2, 1.5, 1.5, OCH=, Z).
13C NMR: d = 14.26 (=CHCH2CH3, E), 14.38 (=CHCH2CH3, Z),
17.36 (=CHCH2CH3, Z), 17.42 (=CHCH2CH3, E), 22.27 (H3CCO, Z),
22.27 (H3CCO, E), 26.00 [C(CH3)3, Z], 26.39 [C(CH3)3, E], 30.57
(NCH3, E), 30.58 (NCH3, Z), 36.7 [C(CH3)3, Z], 37.41 [C(CH3)3, E],
87.38 (NCHO, E), 88.62 (NCHO, Z), 110.52 (=CHCH2CH3, Z),
112.21 (=CHCH2CH3, E), 140.54 (OCH=, E), 142.14 (OCH=, Z),
172.09 (CO, Z), 180.37 (CO, E).
13C NMR: d = 40.09 (CH2), 53.09 (OCH3), 67.16 (OCH2), 104.03
(OCHO), 116.69 (=CH2), 126.36 (arom Cp), 128.27 (arom Co),
129.49 (arom Cm), 134.48 (CH=), 136.98 (arom Cq).
NiCl2dppb:
A solution of dppb (2.13 g, 5 mmol) in anhyd CH2Cl2 (15 mL) was
added slowly to a solution of NiCl2. 6H2O (1.19 g, 5 mmol) in anhyd
EtOH (10 mL). After addition of anhyd Et2O (10 mL), the resulting
mixture was stirred for 10 min. Then, the precipitate was filtered un-
der a dry nitrogen atmosphere and washed with Et2O (2 ´ 5 mL) to
afford NiCl2dppb (2.7 g, 96 %).
Transition Metal-Catalyzed Isomerization of Allyl Derivatives 1
by Activation with LiBHEt3; Geueral Procedure:
The catalyst precursor [NiCl2dppb, RuCl2(PPh3)3, RhCl(PPh3)3]
(4 mol%, 0.8 mmol) was added to a solution of the respective allyl ac-
etal or allyl ether (20 mmol) in anhyd THF (10 mL) at 0°C. After
dropwise addition of LiBHEt3 (4 mol%, 800 mL, 0.8 mmol) the mix-
ture was allowed to warm up to r.t. or heated and stirred for the re-
quired time (Table). After evaporation of the solvent, the crude
product was purified by distillation.
N-[1-(But-2-en-2-yloxy)-2,2-dimethylpropyl]-N-methylacetamide (2d):
Geometric isomers of the amide moiety are assigned with Z, E; geo-
metric isomers of the vinyl double-bond are assigned with Z¢, E¢.
Amide rotamer ratios: (Z¢)E/Z = 20:80; (E¢)E/Z = 20:80.
IR: n = 2964, 2874, 1661, 1646, 1480, 1400, 1376, 1327, 1233, 1199,
1142, 1071, 1006 cm–1.
1H NMR: d = 0.90 [s, 9H, C(CH3)3, E, Z¢), 0.95 (s, 9H, C(CH3)3, Z,
E¢), 1.01 (s, 9H, C(CH3)3, Z, Z¢], 1.06 [s, 9H, C(CH3)3, E, E¢], 1.51
(dq, 3H, J = 6.7, 1.0, =CHCH3, Z, E¢), 1.54 (dq, 3H, J = 6.8, 1.1,
=CHCH3, E, E¢), 1.59 (dq, 3H, J = 6.5, 1.5, =CHCH3, E, Z¢), 1.60 (dq,
3H, J = 6.7, 1.6, =CHCH3, Z, Z,), 1.74 (m, 3H, OCCH3, E/Z, Z¢), 1.77
(m, 3H, OCCH3, E/Z, E¢), 2.08 (s, 3H, H3CCO, Z, E¢), 2.09 (s, 3H,
H3CCO, Z, Z¢), 2.12 (s, 3H, H3CCO, E, Z¢), 2.16 (s, 3H, H3CCO, E,
E¢), 2.81 (s, 3H, NCH3, Z, E¢), 2.82 (s, 3H, NCH3, E, E¢), 2.90 (s, 3H,
NCH3, E, Z¢), 2.91 (s, 3H, NCH3, Z, Z¢), 4.41 (m, 1H, =CHCH3, E, Z¢),
4.43 (qq, 1H, J = 6.7, 1.1, =CHCH3, Z, Z¢), 4.54 (s, 1H, NCHO, E, Z¢),
4.57 (m, 1H, =CHCH3, E, E¢), 4.59 (qq, 1H, J = 6.7, 1.1, =CHCH3, Z,
E¢), 5.01 (s, 1H, NCHO, E, E¢), 5.73 (s, 1H, NCHO, Z, E¢), 5.88 (s,
1H, NCHO, Z, Z¢).
RuCl2(PPh3)3/NaBH4Catalyzed Isomerization of Allyl Deriva-
tives 1; General Procedure:
RuCl2(PPh3)3 (4 mol%, 0.77 g, 0.8 mmol) was added to a solution of
the respective allyl acetal (20 mmol) in anhyd THF or EtOH (10 mL).
After addition of NaBH4 (16 mol%, 0.12 g, 3.2 mmol) the mixture
was stirred at r.t. or heated for the required time. After evaporation of
the solvent, the crude product was purified by distillation.
(Z)-N-[2,2-Dimethyl-1-(prop-1-en-1-yloxy)propyl]-N-methylacetamide
(2a):
Amide rotamer ratio: E/Z = 20:80.
IR: n = 3047, 2965, 2875, 1661, 1645, 1481, 1368, 1329, 1253, 1203,
1075, 1009 cm–1.
13C NMR: d = 10.48 (–CHCH3, Z, Z¢), 10.73 (=CHCH3, E, E¢), 12.51
(=CHCH3, E, Z¢), 15.46 (=CHCH3, Z, E¢), 17.95 (OCCH3, Z, Z¢),
18.64 (OCCH3, E, Z¢), 20.44 (OCCH3, E, E¢), 21.56 (OCCH3, Z, E¢),
22.57 (H3CCO, E, E¢), 22.79 (H3CCO, Z, E¢), 22.91 (H3CCO, Z, Z¢),
22.99 (H3CCO, E, Z¢), 26.35 [C(CH3)3, Z, E¢], 26.63 [C(CH3)3, Z, Z¢),
26.93 (C(CH3)3, E, Z¢], 27.08 [C(CH3)3, E, E¢], 28.65 (NCH3, E, E¢),
31.01 (NCH3, Z, E¢), 31.20 (NCH3, E, Z¢), 31.55 (NCH3, Z, Z¢), 37.05
1H NMR: d = 0.95 [s, 9H, C(CH3)3, Z], 1.00 [s, 9H, C(CH3)3, E], 1.58
(dd, 3H, J = 6.8, 1.7, CH3, Z), 1.59 (dd, 3H, J = 6.7, 1.6, CH3, E), 2.07
(s, 3H, H3CCO, Z), 2.13 (s, 3H, H3CCO, E), 2.78 (s, 3H, NCH3, E),
2.84 (s, 3H, NCH3, Z), 4.42 (dq, 1H, J = 6.2, 6.8, =CHCH3, Z), 4.53
(dq, 1H, J = 6.2, 6.7, =CHCH3, E), 4.73 (s, 1H, NCHO, E), 5.62 (s,
1H, NCHO, Z), 5.81 (dq, 1H, J = 6.2, 1.6, OCH=, E), 5.84 (dq, 1H, J
= 6.2, 1.7, OCH=, Z).

308
Papers
SYNTHESIS
(9) Hansen, H.-J.; Schmid, H. Tetrahedron 1974, 30, 1959.
Vittorelli, P.; Winkler, T.; Hansen, H.-J.; Schmid, H. Helv.
Chim. Acta 1968, 51, 1457.
(10) For a review on the stereoselective Claisen rearrangement, see:
Frauenrath, H. In Houben-Weyl, Vol. E21d; Helmchen, G.;
Hoffmann, R. W.; Mulzer, J.; Schaumann, E.; Eds.; Thieme:
Stuttgart, 1995; p 3301.
(11) Price, C. C.; Snyder, W. H. J. Am. Chem. Soc. 1961, 83, 1773.
(12) Davies, S. G. Organotransition Metal Chemistry: Applications
To Organic Synthesis; Pergamon: Oxford, 1982.
(13) Pertici, P.; Malanga, C.; Giuntoli, A.; Vitulli, G.; Martra, G.
Gazz. Chim. It. 1996, 126, 587.
(14) A few exceptions, however, have been reported:
For the synthesis of (Z)-propenyl ethers by using
(Ph3P)2PtH(ClO4) as a catalyst, see:
[C(CH3)3, Z, E¢], 37.42 [C(CH3)3, E, Z¢], 37.55 [C(CH3)3, Z, Z¢], 37.64
[C(CH3)3, E, E¢], 84.14 (NCHO, Z, E¢), 84,28 (NCHO, Z, Z¢), 85.43
(NCHO, E, Z¢), 86.71 (NCHO, E, E¢), 103.21 (=CHCH3, Z, Z¢),
114.41 (=CHCH3, E, E¢), 117.95 (=CHCH3, E, Z¢), 118.03 (=CHCH3,
Z, E¢), 139.36 (OCCH3, E, Z¢), 140.35 (OCCH3, Z, E¢), 149.16
(OCCH3, Z, Z¢), 150.23 (OCCH3, E, E¢), 171.94 (CO, Z, Z¢), 172.21
(CO, Z, E¢), 172.41 (CO, E, Z¢), 173.21 (CO, E, E¢).
(Z)-[2-Methoxy-2-(prop-1-en-1-yloxy)ethyl]benzene (2e):
IR: n = 3063, 3032, 2957, 2843, 1670, 1497, 1453, 1370, 1244,
1134 cm–1.
1H NMR: d = 1.59 (dd, 3H, J = 6.7, 1.7, =CHCH3), 2.97 (d, 2H, J =
5.7, CH2), 3.37 (s, 3H, OCH3), 4.49 (dq, 1H, J = 6.7, 6.5, =CHCH3),
4.78 (t, 1H, J = 5.7, OCHO), 6.18 (dq, 1H, J = 6.5, 1.7, OCH=), 7.24
(m, 5Harom).
13C NMR: d = 9.41 (CH3), 40.74 (CH2), 54.66 (OCH3), 102.78
(OCHO), 105.33 (=CHCH3), 126.52 (arom Cp), 128.29 (arom Co),
129.62 (arom Cm), 136.38 (arom Cq), 140.73 (OCH=).
Clark, H. C.; Kurosawa, H. Inorg. Chem. 1973, 12, 357.
Clark, H. C.; Kurosawa, H. Inorg. Chem. 1973, 12, 1566.
For the synthesis of (E)-propenyl ethers by using
[(Ph2MeP)2Ir(1,5-COD)]+PF6– as a catalyst, see:
Baudry, D.; Ephritikhine, M.; Felkin, H. J. Chem. Soc., Chem.
Commun. 1978, 694.
(Z)-Benzyl Prop-1-en-1-yl Ether (2f):
1H NMR: d = 1.67 (dd, 3H, J = 6.8, 1.7, CH3), 4.43 (dq, 1H, J = 6.2,
6.8, =CHCH3), 4.77 (s, 2H, CH2O), 6.01 (dq, J = 6.2, 1.7, OCH=),
7.33 (m, 5Harom).
(15) The isomerization of 2-tert-butyl-5-methylene-1,3-dioxane
with NiCl2diop activated with diisopropylmagnesium bromide
in THF at 0°C afforded 2-tert-butyl-5-methyl-4H-1,3-dioxin
with 73% ee. The same reaction by using NiBr2diop as the cata-
lyst precursor upon activation with LiBHEt3 in Et2O at –63°C
gave 90% ee; Frauenrath, H.; Reim, S.; Wiesner, A. to be
published.
(16) Fischer, K.; Jonas, K.; Misbach, P.; Stabba, R.; Wilke, G. An-
gew. Chem. 1973, 23, 1002; Angew. Chem., Int. Ed. Engl. 1973,
12, 943.
13C NMR: d = 9.28 (CH3), 73.42 (CH2O), 101.76 (= CHCH3), 127.20
(arom Cp), 127.70 (arom Cm), 128. 38 (arom Co), 137.78 (arom Cq),
145.14 (OCH=).
(Z)-Crotyl Prop-1-en-1-yl Ether (2g):
IR: n = 2869, 1730, 1669, 1456, 1259, 1130, 1001 cm–1.
1H NMR: d = 1.59 (dd, 3H, J = 6.8, 1.7, OCH=CHCH3), 1.72 (ddt,
3H, J = 6.4, 1.7, 1.2, CH3), 4.18 (ddq, 2H, J = 6.1, 1.2, 1.2, OCH2),
4.39 (dq, 1H, J = 6.4, 6.8, OCH=CHCH3), 5.60 (m, 1H, =CHCH3),
5.74 (m, 1H, CH=), 5.96 (dq, 1H, J = 6.4, 1.7, OCH=CHCH3).
13C NMR: d = 9.71 (OCH=CHCH3), 18.20 (CH3), 72.85 (OCH2),
101.36 (OCH=CHCH3), 127.47 (=CHCH3), 130.27 (CH=), 145.41
(OCH=CHCH3).
(17) For mechanistic aspects of the isomerization of allylic sub-
strates, see:
Noyori, R. Asymmetric Catalysis In Organic Synthesis; Wiley:
New York, 1994.
Cornils, B.; Herrmann, W. A. Applied Homogeneous Catalysis
with Organometallic Compounds; Vol. 2; Verlag Chemie:
Weinheim, 1996.
This work was supported by Fonds der Chemischen Industrie. A
genereous gift of chemicals by Bayer AG, Leverkusen, is gratefully
acknowledged.
(18) Lochow, C. F.; Miller, R. G. J. Org. Chem. 1976, 41, 3020.
(19) Malanga, C.; Urso, A.; Lardicci, L. Tetrahedron Lett. 1995, 36,
1133.
(20) Trost, B. M.; Murphy, D. J. Organometallics 1985, 4, 1143.
(21) Casey, C. P.; Whiteker, G. T. Isr. J. Chem. 1990, 30, 299.
(22) Menicagli, R.; Malanga, C.; Finato, B.; Lardicci, L. Gazz. Chim.
It. 1989, 119, 69 (cf. also Ref. 18).
(23) The activation of the Ni precursor can also be performed with
diisopropylmagnesium bromide. However, the Grignard re-
agent often causes side reactions by reaction with the substrate
or product, respectively.
(1) For a review on the reactions of vinyl acetals, see:
Frauenrath, H. In Houben-Weyl, Vol. E15/1; Kropf, H.; Schau-
mann, E.; Eds.; Thieme: Stuttgart, 1993; p 1.
(2) Greene, T. W.; Wuts, P. G. M. Protective Groups in Organic
Synthesis; 2nd ed.; Wiley: New York, 1991.
(3) Boons, G.-J.; Burton, A.; Isles, S. J. Chem. Soc., Chem. Com-
mun. 1996, 141.
(24) Use of less amounts of NaBH4 results in an incomplete conver-
sion.
(4) Boons, G.-J.; Isles, S. J. Org. Chem. 1996, 61, 4262.
(5) Frauenrath, H.; Runsink, J. J. Org. Chem. 1988, 53, 1860.
(6) Frauenrath, H.; Arenz; T.; Raabe, G.; Zorn, M. Angew. Chem.
1993, 105, 74; Angew. Chem., Int. Ed. Engl. 1993, 32, 83.
Arenz, N. T.; Frauenrath, H.; Raabe, G.; Zorn, M. Liebigs Ann.
Chem. 1994, 931.
(7) Reuter, J. M.; Salomon, R. G. J. Org. Chem. 1977, 42, 3360.
(8) Tsuji, J.; Kobayashi, Y.; Shimizu, I. Tetrahedron Lett. 1979, 20,
39.
(25) A solution of 1a (10 mmol) and RhCl(PPh3)3 (4 mol%) in anhyd
THF at 0°C was treated with BuLi (4 mol%, 1.6 M solution in
hexane) stirred for 18 h at r.t., and purified by usual workup. For
other reaction conditions for the activation of Wilkinson’s cata-
lyst with BuLi, see Ref. 4.
(26) Gent, P. A.; Gigg, R. J. Chem. Soc., Chem. Commun. 1974, 277.
Gigg, R. J. Chem. Soc., Perkin Trans 1 1980, 738.