Menthane-Based Chloride-Bridged η3-Bis-π-Allylpalladium Chloride Dimers: Catalytic Asymmetric Allylation of Imines

Article abstract of DOI:10.1002/ejoc.201900177

Menthane-based η³-bis-π-allylpalladium chloride dimer complexes have been prepared for the first time. They exist as dimeric η³-bis-π-allylpalladium with four chloride bridges. The complexes catalyze the asymmetric allylation of vari

Full text of DOI:10.1002/ejoc.201900177

DOI: 10.1002/ejoc.201900177
Full Paper
Bridged Dimers
Menthane-Based Chloride-Bridged η3-Bis-π-Allylpalladium
Chloride Dimers: Catalytic Asymmetric Allylation of Imines
Amit K. Jha[a] and Rodney A. Fernandes*[a]
Abstract: Menthane-based η3-bis-π-allylpalladium chloride water to give chiral homoallylamines in yields of 60–77 % and
dimer complexes have been prepared for the first time. They enantioselectivity up to er = 93:7. The stereochemical informa-
exist as dimeric η3-bis-π-allylpalladium with four chloride tion from the menthane framework was translated successfully
bridges. The complexes catalyze the asymmetric allylation of through the η3-bis-π-allylpalladium catalysts in asymmetric all-
various imines with allyltributylstannane and one equivalent of ylation of imines.
Introduction
iary.[13] The menthane-based chiral catalyst effected asymmetric
allylation of imines up to 89:11 er.[12b] Various monomeric
π-allylpalladium complexes have been reported till date,[5,7,8]
but there is no report on η3-bis-π-allylpalladium chloride com-
plexes to the best of our knowledge. Knowing that monomer
complexes exist as dimers through chloride bridges, the pro-
posed synthesis of bis complexes intrigued us to study their
formation and dimerization similar to the monomeric com-
plexes. The intriguing question at this juncture was whether
the complexes would dimerize intramolecular or intermolecular.
Therefore, in continuation to our ongoing research,[12] we have
synthesized various menthane-based η3-bis-π-allylpalladium
chloride complexes 2 and noted that dimerization of these
complexes occurs intermolecular through four chloride bridges
as can be seen in the X-ray structure. The complexes were then
employed in the asymmetric allylation of imines 1 (Scheme 1).
η3-Allylpalladium chloride dimers were first prepared by Hüt-
tel[1] and Hafner[2] independently in 1959. These were later em-
ployed as allylating agents by Tsuji and co-workers.[3] Trost et
al.[4] combined both Hüttel's method of preparation and Tsuji's
allylation and disclosed the synthetic potential of these species.
This chemistry today is widely referred to as “Tsuji-Trost” reac-
tion and the species involved as “π-allylpalladium”. Various π-
allylpalladium complexes have been prepared by Trost and co-
workers[5] involving both aliphatic and cyclic olefins. Moving
away from stoichiometry to catalytic version of their use was a
remarkable achievement.[6] Today most reactions involving π-
allylpalladium are catalytic in nature with respect to palladium.
Yamamoto and co-workers[7] reported the first catalytic
enantioselective synthesis of homoallylamines by the use of
various chiral π-allylpalladium catalysts prepared from different
chiral moieties. Although the simple π-allylpalladium com-
plexes derived from allyl acetate or halide act as electrophiles,[8]
the bis-π-allylpalladium formed in situ exhibit nucleophilic char-
acter in delivering the allyl unit to the prochiral imine.[9] It has
been demonstrated that the bis-π-allylpalladium complex un-
der catalytic conditions, can undergo an initial electrophilic at-
tack on one of the allyl moieties followed by a nucleophilic
attack on the other, thereby, displaying amphiphilic charac-
ter.[9,10] Considering the limited chiral frameworks examined by
Yamamoto and co-workers and low overall yield in catalyst
preparation,[7,9,11] in 2012 we reported the improved synthesis
of π-allylpalladium chloride complexes based on pinene skele-
ton and also achieved higher enantioselectivity up to 99:1
er.[12a] In the same year, we also developed the first menthane-
based chiral π-allylpalladium catalysts;[12b] since before the
menthane moiety had been used extensively as a chiral auxil-
Scheme 1. Menthane-based dimeric η3-bis-π-allylpalladium chloride com-
plexes and asymmetric allylation of imines.
Results and Discussion
Our initial efforts focused on the preparation of several dimeric
olefins 6a-f starting from (–)-menthone 5 [prepared by PCC
oxidation of (–)-menthol 4][14] with various dimeric phosphon-
ium salts[15] (Scheme 2). Treatment of these Wittig salts with
t-BuOK generated the ylides and further reaction with
(–)-menthone 5 provided the olefins 6a-f in 30–50 % yields
(Scheme 2) as single diastereomers (E-olefins). The single peak
[a] Department of Chemistry, Indian Institute of Technology Bombay,
Powai Mumbai 400076 Maharashtra, India
E-mail: rfernand@chem.iitb.ac.in
http://www.chem.iitb.ac.in/~rfernand/default.htm
Supporting information and ORCID(s) from the author(s) for this article are
available on the WWW under https://doi.org/10.1002/ejoc.201900177.
1
in the olefinic region in the H NMR spectrum clearly indicated
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the formation of single diastereomer (see Supporting Informa- note that these complexes get associated intermolecular as di-
1
tion). The E-geometry of olefins was confirmed by H-1H COSY, mers with four chloride bridges involving two molecules of the
1H-1H NOESY correlations and also with the help of NOE similar η3-bis-π-allylpalladium chloride. We did not observe the forma-
to our earlier report for monomeric olefins.[12b] We could not tion of an intramolecular dimer with two chloride bridges, such
prepare the dimeric olefin with a three carbon spacer between as 2′ (Scheme 2).
the menthyl moieties. The Wittig reaction failed in this case.
The reaction of these dimeric olefins with Pd(OCOCF3)2 and
nBu4NCl in acetone furnished the desired η3-bis-π-allylpalla-
dium chloride complexes 2a-f as single regioisomers. The com-
plexes 2a-d have long un-substituted carbon chains separating
the two menthyl moieties. The complex 2e has a quaternary
carbon mid-way with gem-dimethyl group. An aryl spacer is
present in complex 2f. The structure of these complexes was
The allylation of aldimines and derivatives has been estab-
lished as one of the important C–C bond forming reactions.
Due to the strong coordinating ability of nitrogen in compari-
son to oxygen, the enantioselective allylation of aldimines
shows incredible selectivity toward the synthesis of chiral ho-
moallylamines.[7,11,12,17–19] The latter are found to be conse-
quential intermediates for a wide range of pharmaceuticals,
agrochemicals, and N-heterocyclic compounds.[20] Thus, the de-
velopment of a general and efficient method for the synthesis
of this type of chiral amines has been of great interest. We
screened the prepared complexes 2a-f for the asymmetric allyl-
ation of model imine 1a (Scheme 3). We employed similar reac-
tion conditions as reported by us earlier using water (1.0 equiv.)
and allyltributylstannane (1.25 equiv.) in THF solvent at 0 °C.[12]
Among the catalysts 2a-d with un-substituted long chain sepa-
rating the two menthyl moieties, 2a delivered the homoallyl-
amine 3a in 68 % yield and 90:10 er, indicating that the longer
chains were not as effective. We could not prepare the dimer
catalyst with a three-carbon spacer as the corresponding olefin
was not accessible. However, we believe an optimum chain
length would be required for the Pd complexes to be formed
considering over-crowding between the menthyl moieties. A
gem-dimethyl group containing catalyst 2e offered 3a in 58 %
yield and 85:15 er. We also attempted the preparation of the
1
determined by H-1H COSY, NOE, HSQC, and with the help of
HRMS (see Supporting Information). The complex 2e gave crys-
tals for X-ray analysis indicating the dimeric nature with four
chloride bridges[16] (Scheme 2). From the HRMS data of all com-
plexes 2a-e and crystal structure of 2e, it was remarkable to
Scheme 2. Synthesis of menthane-based dimeric η3-bis-π-allylpalladium
chloride complexes 2a-f and crystal structure of 2e.
Scheme 3. Asymmetric allylation of model imine 1a with allyltributylstannane
using catalysts 2a-f. Note: mol-% of 2 is with respect to two Pd.
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olefin with two methylene groups less as in 2e and having the well with those prepared by us using the pinene-based cata-
gem-dimethyl group, but this was not successful. The catalyst lyst[12a] indicating them to have the (R) configuration. This is
with an aryl spacer 2f provided 3a in 55 % yield and 82:18 er. also opposite to our work reported earlier[12b] [using (+)-
Considering 2a to be better, we further reduced the catalyst menthol] as here, we used (–)-menthol 4. The addition of the
loading to observe that 1–2 mol-% was not as effective and allyl group to the Si face of the imine is disfavored in having
gave lower er for 3a. An increase in catalyst loading to 5– the R group of the imine in a sterically hindered position with
10 mol-% of 2a gave no beneficial results. Thus, we chose 2a respect to the isopropyl group (Figure 1, model A). However,
under 2.5 mol-% as optimum requirement for asymmetric allyl- attack on the Re face of the imine is favored as the R group of
ation of imines.
the imine is placed away from the menthyl moiety resulting in
the formation of (R)-homoallylamines (model B). It is remarka-
ble to note that the dimeric complexes also catalyzed the asym-
metric allylation of imines similar to monomeric complexes and
transferred the chiral information from the menthane skeleton
to the product.
We next investigated the scope of complex 2a for asymmet-
ric allylation of various imines using allyltributylstannane
(1.25 equiv.) and water (1.0 equiv.) at 0 °C (Scheme 4). The imine
1b delivered the homoallylamine 3b in good yield of 71 % and
er = 82:18. Imines with electron donating groups like 1c, 1d
and 1e worked well with increased er of 3c (88:12), 3d (93:7)
and 3e (86:14), respectively. The imine 1f with p-Ph group pro-
vided the corresponding amine 3f in 74 % yield and er = 75:25.
The p-Cl-aryl imine 1g worked well giving 3g in 61 % yield and
er = 80:20. The piperonyl imine 1a gave 3a in good yield (68 %)
and er = 90:10. The similar imine with PMB group on N for 1h
lowered the er of 3h to 86:14. The naphthyl based imines 1i
and 1j provided the corresponding homoallylamines 3i (er =
77:23) and 3j (er = 76:24). The 2-thienyl imine 1k reacted well
to furnish the homoallylamine 3k with er = 72:28. Change of
Bn to allyl group on N, i.e. imine 1l also worked well providing
the homoallylamine 3l in 70 % yield and er = 78:22.
Figure 1. Probable transition state models.
Conclusions
We have synthesized various menthane-based dimeric chiral η3-
bis-π-allylpalladium chloride complexes for the first time. It was
remarkable to note that the complexes exist as intermolecular
dimers with four chloride bridges. They catalyze the asymmetric
allylation of various imines to afford chiral homoallylamines in
good yields and enantioselectivities. The homoallylamines have
the same configuration as those obtained by us previously us-
ing a pinene-based catalyst.[12a] Currently, we are investigating
the nature of the dimerization to find out whether it can occur
within the bis complex (intramolecular) while having an opti-
mum chain and substituents to fold as 2′ with two chloride
bridges (Scheme 2).
Experimental Section
General remarks: The solvents were dried by standard procedures.
Thin layer chromatography was performed on EM 250 Kieselgel 60
F254 silica gel plates. The spots were visualized by staining with
KMnO4 or by using a UV lamp. (–)-Menthol, palladium(II) trifluoro-
acetate, allyltributylstannane and nBu4NCl were purchased from
Scheme 4. Catalytic asymmetric allylation of imines 1 with allyltributyl-
stannane using catalyst 2a. Allyltributylstannane (1.25 equiv.), H2O
(1.0 equiv.), catalyst 2a (2.5 mol-%), THF, 0 °C. er determined by HPLC. Note:
2.5 mol-% of 2a is with respect to two Pd.
1
Sigma Aldrich Chemical Co. H and 13C NMR were recorded at 400
or 500 MHz and 100 or 125 MHz respectively as CDCl3 solutions
and the chemical shifts are based on the TMS peak at δ = 0.00 pm
for the 1H NMR and the CDCl3 peak at δ = 77.00 ppm (t) for the
The reaction would follow similar mechanistic path (Figure 1)
as described by us earlier using the monomeric catalyst.[12b]
The sign of optical rotation of the homoallylamines matched 13C NMR spectra. IR spectra were recorded with a Perkin–Elmer
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Spectrum One FTIR spectrometer. Optical rotations were measured
(1E,10E)-1,10-bis[(2S,5R)-2-Isopropyl-5-methylcyclohexylidene]
with a Jasco P-2000 polarimeter. The HRMS data were recorded decane (6d): The title compound was prepared from (–)-5 (1.313 g,
with a Micromass: Q-Tof micro (YA-105) spectrometer. HPLC was
performed with a JASCO-(PU-2089PLUS) quaternary gradient pump
equipped with a MD-2010PLUS multi-wavelength detector. Imines
were prepared as previously reported under microwave condi-
tions.[21] For the π-allylpalladium chloride complexes although are
solids, we did not determine melting points as they decomposed
upon slight heating.
8.51 mmol) and Br–Ph3P+CH2(CH2)8CH2Ph3P+Br– (3.34 g, 4.05 mmol)
by a similar procedure to that described for 6a to produce 6d
(504 mg, 30 %, reaction time = 72 h) as a colorless oil; [α]D25 –25.3
(c 1.0, CHCl3); IR (CHCl3) νmax 2953, 2923, 2861, 1457, 1376, 907,
˜
1
734, 678 cm–1; H NMR (400 MHz, CDCl3) δ 0.86 (d, J = 6.7 Hz, 6H),
0.89 (d, J = 6.5 Hz, 6H), 0.92 (d, J = 6.1 Hz, 6H), 1.09–1.18 (m, 2H),
1.22–1.38 (m, 16H), 1.55–1.63 (m, 2H), 1.63–1.75 (m, 4H), 1.75–1.83
(m, 2H), 1.86–2.08 (m, 6H), 2.27–2.39 (m, 2H), 5.10 (t, J = 7.3 Hz, 2H)
ppm; 13C NMR (125 MHz, CDCl3) δ 19.8, 20.6, 22.1, 26.4, 26.8, 27.2,
29.3, 29.6, 30.3, 31.9, 32.3, 35.0, 51.2, 121.9, 139.5 ppm; HRMS (ESI-
TOF): m/z [M + H]+ calcd. for C30H55 415.4298, found 415.4296.
General procedure for synthesis of olefins (6a-f): The following
preparation of 6a is representative.
(1E,4E)-1,4-bis[(2S,5R)-2-Isopropyl-5-methylcyclohexylidene]-
butane (6a): To a stirred slurry of Br–Ph3P+CH2(CH2)2CH2Ph3P+Br–
(3.0 g, 4.05 mmol) in dry THF (30 mL) was added t-BuOK (1.363 g,
12.15 mmol, 3.0 equiv.) in portions at room temperature under an
argon atmosphere. After stirring for 30 min, a solution of (–)-5
(1.313 g, 8.51 mmol) in dry THF (5 mL) was added dropwise to the
orange colored ylide solution and the mixture was stirred from
room temperature to reflux for 72 h. It was then cooled to room
temperature and quenched with a saturated aqueous solution of
NH4Cl (5 mL), and the resulting mixture was extracted with EtOAc
(2 × 50 mL). The combined organic layers were washed with brine,
dried (Na2SO4) and concentrated. The crude residue was purified
by silica gel column chromatography using petroleum ether as the
eluent to afford 6a (602.5 mg, 45 %) as a colorless oil. [α]D25 –48.8
(1E,7E)-1,7-bis[(2S,5R)-2-Isopropyl-5-methylcyclohexylidene]-
4,4-dimethylheptane (6e): The title compound was prepared from
(–)-5 (1.313 g, 8.51 mmol) and I–Ph3P+CH2(CH2)2C(CH3)2(CH2)2-
CH2Ph3P+I– (3.664 g, 4.05 mmol) by a similar procedure to that de-
scribed for 6a to afford 6e (633 mg, 39 %, reaction time = 70 h) as
a colorless oil; [α]D25 –34.6 (c 0.5, CHCl3); IR (CHCl3) νmax 2952, 2868,
˜
1660, 1455, 1383, 1364, 1326, 1163, 1089, 1063, 1017, 866, 810, 610,
545 cm–1; 1H NMR (400 MHz, CDCl3) δ 0.85 (d, J = 6.6 Hz, 6H), 0.87–
0.90 (m, 12H), 0.92 (d, J = 6.4 Hz, 6H), 1.07–1.17 (m, 2H), 1.18–1.24
(m, 4H), 1.25–1.33 (m, 4H), 1.53–1.62 (m, 2H), 1.64–1.74 (m, 4H),
1.74–1.81 (m, 2H), 1.85–2.0 (m, 6H), 2.27–2.37 (m, 2H), 5.10 (t, J =
7.1 Hz, 2H) ppm; 13C NMR (125 MHz, CDCl3) δ 19.8, 20.6, 22.0, 22.1,
26.5, 26.7, 27.3, 31.9, 32.3, 32.9, 34.9, 42.4, 51.2, 122.4, 139.1 ppm;
HRMS (ESI-TOF): m/z [M + K]+ calcd. for C29H52K 439.3701, found
437.3704.
(c 0.50, CHCl ); IR (CHCl ) νmax 2954, 2869, 1661, 1457, 1380, 1267,
˜
3
3
1163, 1062, 865, 739, 613, 545 cm–1; 1H NMR (500 MHz, CDCl3) δ
0.85 (d, J = 6.7 Hz, 6H), 0.87 (d, J = 6.6 Hz, 6H), 0.91 (d, J = 6.4 Hz,
6H), 1.07–1.15 (m, 2H), 1.23–1.31 (m, 2H), 1.53–1.60 (m, 2H), 1.62–
1.70 (m, 4H), 1.70–1.81 (m, 4H), 1.87–1.97 (m, 2H), 2.03–2.08 (m, 4H),
2.30–2.37 (m, 2H), 5.12 (t, J = 6.3 Hz, 2H) ppm; 13C NMR (125 MHz,
CDCl3) δ 19.7, 20.6, 22.1, 26.5, 26.8, 28.0, 32.1, 32.4, 35.2, 51.2, 121.5,
1,4-Bis[(E)-3-((2S,5R)-2-Isopropyl-5-methylcyclohexylidene)-
propyl] benzene (6f): The title compound was prepared from (–)-5
(1.313 g, 8.51 mmol) and I–Ph3P+CH2(CH2)2-pC6H4-(CH2)2CH2Ph3P+I–
(3.801 g, 4.05 mmol) by a similar procedure to that described for
6a to give 6f (880 mg, 50 %, reaction time = 72 h) as a colorless
139.8 ppm; HRMS (ESI-TOF): m/z [M + K]+ calcd. for C24H42
K
oil; [α]D25 –36.0 (c 1.0, CHCl3); IR (CHCl3) νmax 3013, 2952, 2927, 2867,
˜
369.2918, found 369.2917.
1661, 1513, 1454, 1381, 1365, 1163, 1021, 862, 805, 670 cm–1
;
1H
NMR (400 MHz, CDCl3) δ 0.85–0.94 (m, 18H), 1.09–1.18 (m, 2H),
1.24–1.36 (m, 2H), 1.53–1.83 (m, 10H), 1.86–2.0 (m, 2H), 2.26–2.43
(m, 6H), 2.54–2.71 (m, 4H), 5.19 (t, J = 6.8 Hz, 2H), 7.13 (d, J = 1.8 Hz,
4H) ppm; 13C NMR (100 MHz, CDCl3) δ 19.7, 20.6, 22.1, 26.5, 26.8,
29.5, 31.9, 32.3, 35.1, 36.3, 51.2, 120.8, 128.25, 128.3, 139.7,
140.4 ppm; HRMS (ESI-TOF): m/z [M + Na]+ calcd. for C32H50Na
457.3805, found 457.3803.
(1E,6E)-1,6-bis[(2S,5R)-2-Isopropyl-5-methylcyclohexylidene]-
hexane (6b): The title compound was prepared from (–)-5 (1.313 g,
8.51 mmol) and Br–Ph3P+CH2(CH2)4CH2Ph3P+Br– (3.113 g,
4.05 mmol) by a similar procedure to that described for 6a to de-
liver 6b (552 mg, 38 %, reaction time = 70 h) as a colorless oil;
[α]D25 –31.0 (c 0.50, CHCl3); IR (CHCl3) νmax 2955, 2926, 2854, 1658,
˜
1463, 1115, 1021, 858 cm–1; 1H NMR (400 MHz, CDCl3) δ 0.85 (d, J =
6.7 Hz, 6H), 0.87 (d, J = 6.6 Hz, 6H), 0.91 (d, J = 6.3 Hz, 6H), 1.06–
1.16 (m, 2H), 1.23–1.30 (m, 2H), 1.30–1.39 (m, 4H), 1.53–1.61 (m, 2H),
1.62–1.81 (m, 8H), 1.86–2.06 (m, 6H), 2.27–2.38 (m, 2H), 5.09 (t, J =
7.1 Hz, 2H) ppm; 13C NMR (100 MHz, CDCl3) δ 19.8, 20.6, 22.1, 26.4,
26.8, 27.1, 29.9, 32.0, 32.3, 35.1, 51.2, 121.8, 139.6 ppm; HRMS (ESI-
TOF): m/z [M + H]+ calcd. for C26H47 359.3672, found 359.3669.
General procedure for the synthesis of π-allylpalladium chlor-
ide complexes (2a–f): To a solution of Pd(OCOCF3)2 (0.2 g,
0.6 mmol, 3.0 equiv.) in dry acetone (10 mL) at room temperature
and under an argon atmosphere was added olefin 6 (0.2 mmol,
1.0 equiv.). The mixture was stirred for 8 h (monitored by TLC).
nBu4NCl (0.23 g, 0.8 mmol, 4.0 equiv.) in dry acetone (2 mL) was
added and the reaction mixture stirred for additional 1 h. The clear
brown colored solution was then filtered through a plug of celite
to remove suspended Pd-black and washed with acetone (2 ×
10 mL). The filtrate was concentrated, and the residue was purified
by silica gel column chromatography using petroleum ether/EtOAc
(5:1) as the eluent to give complex 2a-f.
(1E,8E)-1,8-bis[(2S,5R)-2-Isopropyl-5-methylcyclohexylidene]-
octane (6c): The title compound was prepared from (–)-5 (1.313 g,
8.51 mmol) and Br–Ph3P+CH2(CH2)6CH2Ph3P+Br– (3.226 g,
4.05 mmol) by a similar procedure to that described for 6a to give
25
6c (563.8 mg, 36 %, reaction time = 72 h) as a colorless oil; [α]D
–
34.2 (c 0.50, CHCl3); IR (CHCl3) νmax 2927, 2854, 1662, 1455, 1381,
˜
1168, 1095, 1022, 868 cm–1; 1H NMR (500 MHz, CDCl3) δ 0.86 (d, J =
6.7 Hz, 6H), 0.89 (d, J = 6.6 Hz, 6H), 0.92 (d, J = 6.4 Hz, 6H), 1.09–
π-Allylpalladium chloride complex (2a): Isolated yield (55.1 mg,
25
45 %); yellow powder; [α]D +24.0 (c 1.0, CHCl3); IR (CHCl3) νmax
˜
1.17 (m, 2H), 1.25–1.34 (m, 12H), 1.55–1.61 (m, 2H), 1.64–1.73 (m, 2956, 2921, 2868, 1742, 1644, 1463, 1363, 1378, 1260, 1183, 1081,
1
4H), 1.75–1.82 (m, 2H), 1.90–1.98 (m, 2H), 1.98–2.08 (m, 4H), 2.30–
806, 722, 604 cm–1; H NMR (400 MHz, CDCl3) δ 0.88 (d, J = 6.8 Hz,
2.35 (m, 2H), 5.10 (t, J = 7.2 Hz, 2H) ppm; 13C NMR (100 MHz, CDCl3) 6H), 1.0 (d, J = 6.2 Hz, 6H), 1.22 (d, J = 6.8 Hz, 6H), 1.29–1.39 (m,
δ 19.7, 20.6, 22.1, 26.4, 26.8, 27.2, 29.2, 30.3, 31.9, 32.3, 35.0, 51.2, 2H), 1.41–1.69 (m, 8H) 1.81–1.95 (m, 4H), 2.11–2.27 (m, 2H), 2.34–
121.9, 139.5 ppm; HRMS (ESI-TOF): m/z [M + K]+ calcd. for C28H50
K
2.52 (m, 4H), 3.84 (t, J = 5.4 Hz, 2H) ppm; 13C NMR (125 MHz, CDCl3)
δ 20.1, 21.8, 24.1, 27.6, 29.1, 29.2, 30.0, 32.2, 36.3, 75.5, 99.4,
425.3544, found 425.3540.
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117.0 ppm; HRMS (ESI-TOF): m/z [M – Cl]+ calcd. for C48H80Pd4Cl3
1189.1482, found 1189.1480.
turbid reaction mixture was quenched with HCl (1 N solution,
2.0 mL). CH3CN (1.0 mL) was added, and the reaction mixture was
stirred at room temperature for 10 min. The two-layered solution
was extracted with hexane (2 × 3 mL), and the hexane layer was
discarded. The aqueous layer was basified with NaOH (10 % aque-
ous solution, 1.0 mL), and the resulting solution was stirred for
5 min. The solution was extracted with EtOAc (2 × 5 mL), and the
combined organic layers were dried (Na2SO4) and concentrated. Pu-
rification of the residue by silica gel column chromatography using
petroleum ether/EtOAc (5:1) offered the corresponding homoallyl-
amines 3 as colorless oils. The characterization data for most of the
homoallylamines is same as reported by us earlier.[12] The enantio-
meric excess was determined by HPLC of the trifluoroacetylamide
forms of all of the homoallylamines with UV detection at 254 nm.
π -Allylpalladium chloride complex (2b): Isolated yield (44.8 mg,
25
35 %); yellow powder; [α]D +34.2 (c 2.2, CHCl3); IR (CHCl3) νmax
˜
2955, 2925, 2868, 1734, 1661, 1456, 1382, 1361, 1322, 1261, 1034,
666 cm–1; H NMR (400 MHz, CDCl3) δ 0.88 (d, J = 6.8 Hz, 6H), 1.01
1
(d, J = 6.1 Hz, 6H), 1.24 (d, J = 6.8 Hz, 6H), 1.44–1.69 (m, 12H), 1.73–
1.83 (m, 4H), 1.83–1.96 (m, 4H), 2.33–2.54 (m, 4H), 3.80 (t, J = 5.6 Hz,
2H) ppm; 13C NMR (125 MHz, CDCl3) δ 20.1, 21.9, 24.0, 27.3, 28.9,
29.1, 29.2, 29.9, 32.3, 36.1, 74.9, 99.9, 117.1 ppm; HRMS (ESI-TOF):
m/z [M – Cl]+ calcd. for C52H88Pd4Cl3 1245.2110, found 1245.2125.
π-Allylpalladium chloride complex (2c): Isolated yield (40.1 mg,
30 %); yellow powder; [α]D25 +23.9 (c 0.70, CHCl3); IR (CHCl3) νmax
˜
2945, 2925, 2867, 1742, 1666, 1456, 1044, 909, 765, 699, 616 cm–1
;
(R)-N-Benzyl-1-phenyl-3-butenylamine (3b):[12a] Isolated yield
(56.3 mg, 71 %), colorless oil; [α]D25 +39.1 (c 0.60, CHCl3); 1H NMR
(500 MHz, CDCl3) δ 2.01 (br s, 1H), 2.43–2.52 (m, 2H), 3.55–3.61 (m,
1H), 3.69–3.79 (m, 2H), 5.05–5.16 (m, 2H), 5.69–5.81 (m, 1H), 7.25–
7.45 (m, 10H) ppm; 13C NMR (125 MHz, CDCl3) δ 43.0, 51.3, 61.5,
117.5, 126.8, 127.0, 127.3, 128.1, 128.3, 128.4, 135.4, 140.4,
143.6 ppm; HPLC analysis: er = 82:18, Chiralpak OD-H column, n-
hexane/iPrOH = 99.8:0.2, flow rate 0.5 mL/min, (tmajor = 12.64 min,
tminor = 15.63 min).
1H NMR (500 MHz, CDCl3) δ 0.87 (d, J = 6.6 Hz, 6H), 1.01 (d, J =
5.8 Hz, 6H), 1.23 (d, J = 6.6 Hz, 6H), 1.33–1.53 (m, 12H), 1.59–1.73
(m, 8H), 1.77–1.85 (m, 2H), 1.86–1.95 (m, 2H), 2.35–2.50 (m, 4H), 3.8
(t, J = 5.6 Hz, 2H) ppm; 13C NMR (125 MHz, CDCl3) δ 20.0, 21.8, 24.1,
27.3, 29.08, 29.1, 29.4, 29.9, 30.1, 32.2, 36.1, 75.3, 99.7, 117.1 ppm;
HRMS (ESI-TOF): m/z [M + H – Cl]+ calcd. for C56H97Pd4Cl3 1301.2814,
found 1301.2819.
π-Allylpalladium chloride complex (2d): Isolated yield (58.5 mg,
25
42 %); yellow powder; [α]D +44.6 (c 0.5, CHCl3); IR (CHCl3) νmax
˜
(R)-N-Benzyl-1-(4-methylphenyl)-3-butenylamine (3c):[12a] Iso-
lated yield (63.8 mg, 76 %), colorless oil; [α]D25 +33.1 (c 0.25, CHCl3);
1H NMR (500 MHz, CDCl3) δ 1.86 (br s, 1H), 2.40 (s, 3H), 2.42–2.48
(m, 2H), 3.56 (d, J = 13.3 Hz, 1H), 3.66–3.75 (m, 2H), 5.04–5.16 (m,
2H), 5.70–5.81 (m, 1H), 7.21 (d, J = 7.7 Hz, 2H), 7.26–7.32 (m, 5H),
7.32–7.37 (m, 2H) ppm; 13C NMR (125 MHz, CDCl3) δ 21.1, 43.1,
51.3, 61.2, 117.4, 126.7, 127.2, 128.1, 128.3, 129.1, 135.5, 136.5, 140.6,
140.7 ppm; HPLC analysis: er = 88:12, Chiralpak OD-H column, n-
hexane/iPrOH = 99.5:0.5, flow rate 0.7 mL/min, (tmajor = 8.25 min,
tminor = 9.38 min).
2955, 2924, 2852, 1645, 1463, 1044, 909 cm–1
;
1H NMR (500 MHz,
CDCl3) δ 0.88 (d, J = 6.8 Hz, 6H), 1.0 (d, J = 6.1 Hz, 6H), 1.23 (d, J =
6.6 Hz, 6H), 1.30–1.37 (m, 8H), 1.41–1.55 (m, 8H), 1.56–1.73 (m, 8H),
1.76–1.86 (m, 2H), 1.86–1.98 (m, 2H), 2.37–2.53 (m, 4H), 3.82 (t, J =
6.15 Hz, 2H) ppm; 13C NMR (125 MHz, CDCl3) δ 20.0, 21.9, 24.1, 27.3,
28.7, 29.1, 29.4, 29.8, 29.9, 32.3, 36.1, 75.2, 99.9, 117.1 ppm; HRMS
(ESI-TOF): m/z [M – Cl]+ calcd. for C60H104Pd4Cl3 1357.3365, found
1357.3365.
π-Allylpalladium chloride complex (2e): Isolated yield (43.7 mg,
32 %); yellow powder; [α]D25 +38.20 (c 0.50, CHCl3); IR (CHCl3) νmax
˜
2955, 2927, 2868, 1643, 1459, 1378, 1363, 1272, 912, 806, 734 cm–1
;
(R)-N-Benzyl-1-(4-tert-butylphenyl)-3-butenylamine (3d): Iso-
lated yield (75.5 mg, 77 %), colorless oil; [α]D25 +34.2 (c 0.75, CHCl3);
1H NMR (500 MHz, CDCl3) δ 0.85–0.91 (m, 12H), 1.03 (d, J = 6.6 Hz,
6H), 1.24 (m, 8H), 1.46–1.53 (m, 4H), 1.55–1.68 (m, 8H), 1.79–1.88
(m, 4H), 1.88–1.95 (m, 2H), 2.36–2.51 (m, 4H), 3.71 (t, J = 5.4 Hz, 2H)
ppm; 13C NMR (125 MHz, CDCl3) δ 20.1, 21.9, 24.05, 24.1, 26.7, 27.2,
29.2, 29.7, 29.9, 31.9, 32.2, 33.0, 36.1, 41.4, 75.2, 99.9, 116.7 ppm;
HRMS (ESI-TOF): m/z [M – Cl]+ calcd. for C58H100Pd4Cl3 1329.3051,
found 1329.3051.
IR (CHCl3) νmax 3369, 2959, 2927, 2855, 1682, 1510, 1463, 1364,
˜
1265, 1203, 1110, 1028, 919, 835, 745, 703 cm–1; 1H NMR (500 MHz,
CDCl3) δ 1.36 (s, 9H), 1.79 (br s, 1H), 2.37–2.50 (m, 2H), 3.54 (d, J =
13.3 Hz, 1H), 3.65–3.73 (m, 2H), 5.02–5.15 (m, 2H), 5.67–5.78 (m, 1H),
7.21–7.34 (m, 7H), 7.35–7.39 (m, 2H) ppm; 13C NMR (125 MHz,
CDCl3) δ 31.4, 34.4, 43.0, 51.4, 61.2, 117.4, 125.2, 126.8, 126.9, 128.1,
128.3, 135.7, 140.6, 149.8 ppm; HRMS (ESI-TOF): m/z [M + H]+ calcd.
for C21H28N 294.2216, found 294.2211; HPLC analysis: er = 93:7,
Chiralpak OD-H column, n-hexane/iPrOH = 99.5:0.5, flow rate
0.7 mL/min, (tmajor = 7.69 min, tminor = 8.28 min).
π-Allylpalladium chloride complex (2f): Isolated yield (43 mg,
30 %); yellow powder; [α]D25 –9.0 (c 1.0, CHCl3); IR (CHCl3) νmax 2956,
˜
2921, 2851, 1742, 1642, 1463, 1378, 1260, 1022, 804, 722, 612 cm1;
1H NMR (400 MHz, CDCl3) δ 0.90 (d, J = 6.7 Hz, 6H), 1.0 (d, J =
5.9 Hz, 6H) 1.20–1.28 (m, 8H), 1.46–1.75 (m, 10H), 1.80–1.95 (m, 6H),
2.42–2.49 (m, 2H), 2.75–2.90 (m, 2H), 3.09–3.23 (m, 2H), 3.82–3.91
(m, 2H), 7.21 (s, 4H) ppm; 13C NMR (100 MHz, CDCl3) δ 20.0, 21.8,
24.1, 27.4, 29.1, 29.9, 31.9, 32.3, 34.7, 36.3, 74.6, 99.9, 117.3, 128.4,
139.7 ppm; HRMS (ESI-TOF): m/z [M – Cl]+ calcd. for C64H96Pd4Cl3
1397.2740, found 1397.2740.
(R)-N-Benzyl-1-(4-methoxyphenyl)-3-butenylamine (3e):[12a] Iso-
lated yield (67.9 mg, 76 %), colorless oil; [α]D25 +31.8 (c 0.30, CHCl3);
1H NMR (500 MHz, CDCl3) δ 1.74 (br s, 1H), 2.38–2.43 (m, 2H), 3.53
(d, J = 13.3 Hz, 1H), 3.62–3.72 (m, 2H), 3.83 (s, 3H), 5.01–5.12 (m, 2
H), 5.65–5.78 (m, 1H), 6.90 (d, J = 8.6 Hz, 2H), 7.22–7.36 (m, 7H)
ppm; 13C NMR (125 MHz, CDCl3) δ 43.1, 51.3, 55.2, 60.9, 113.7, 117.4,
126.8, 128.1, 128.3, 128.3, 135.6, 135.7, 140.6, 158.6 ppm; HPLC anal-
ysis: er = 86:14 Chiralpak OD-H column, n-hexane/iPrOH = 99.5:0.5,
flow rate 1.0 mL/min, (tmajor = 16.47 min, tminor = 18.10 min).
General procedure for asymmetric allylation of imines 1 using
catalyst 2a: The imine 1 (0.334 mmol) was placed in a Wheaton
micro reactor (5 mL capacity), and under an argon atmosphere, dry
THF (1.0 mL), degassed water (6 μL, 0.334 mmol, 1.0 equiv.), and (R)-N-Benzyl-1-(biphenyl-4-yl)-3-butenylamine (3f): Isolated
25
allyltributylstannane (130 μL, 0.420 mmol, 1.25 equiv.) were added
sequentially. The mixture was cooled to 0 °C, and the chiral palla-
dium chloride complex 2a (5.2 mg, 0.0042 mmol, 2.5 mol-% with
respect to two Pd) was added under argon. The reaction mixture
was flushed with argon and stirred at 0 °C for the specified time.
yield (77.5 mg, 74 %), colorless oil; [α]D +8.5 (c 0.24, CHCl3); IR
(CHCl3) νmax 3420, 3061, 3027, 2837, 1640, 1605, 1579, 1566, 1485,
˜
1452, 1374, 1305, 1169, 112, 1080, 912, 836, 734, 695 cm–1; 1H NMR
(500 MHz, CDCl3) δ 1.78 (br s, 1H), 2.41–2.53 (m, 2H), 3.58 (d, J =
13.3 Hz, 1H), 3.70–3.79 (m, 2H), 5.06–5.16 (m, 2H), 5.70–5.81 (m, 1H),
The reaction progress was monitored by TLC. After completion, the 7.25–7.38 (m, 6H), 7.43–7.48 (m, 4H), 7.58–7.67 (m, 4H) ppm; 13C
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NMR (125 MHz, CDCl3) δ 43.0, 51.4, 61.3, 117.7, 126.8, 127.0, 127.1, 5.17 (m, 2H), 5.69–5.81 (m, 1H), 6.91–6.95 (m, 1H), 6.96–6.99 (m, 1H),
127.7, 128.1, 128.3, 128.7, 135.4, 139.9, 140.5, 141.0 142.9 ppm;
7.23–7.28 (m, 2H), 7.28–7.37 (m, 4H) ppm; 13C NMR (125 MHz, CDCl3)
δ 43.5, 51.2, 57.0, 118.0, 124.0, 124.2, 126.3, 126.9, 128.2, 128.4,
HRMS (ESI-TOF): m/z [M + Na]+ calcd. for C23H23NNa 336.1723, found
336.1725; HPLC analysis: er = 75:25, Chiralpak OD-H column, n-hex- 134.8, 140.2, 148.9 ppm; HPLC analysis: er = 72:28, Chiralpak OD-H
ane/iPrOH = 99:1, flow rate 0.7 mL/min, (tminor = 13.63 min, tmajor
17.43 min).
=
column, n-hexane/iPrOH = 99.5:0.5, flow rate 0.7 mL/min, (tmajor
9.83 min, tminor = 11.99 min).
=
(R)-N-Benzyl-1-(4-chlorophenyl)-3-butenylamine (3g):[12b] Iso-
lated yield (55.4 mg, 61 %), colorless oil; [α]D +28.1 (c 0.5, CHCl3);
(R)-N-Allyl-1-phenyl-3-butenylamine (3l):[12b] Isolated yield
25
(43.8 mg, 70 %), Colorless oil; [α]D 18.8 (c 1.250, CHCl3); 1H NMR
25
1H NMR (500 MHz, CDCl3) δ 1.79 (br s, 1H), 2.35–2.37 (m, 2H), 3.49
(d, J = 13.3 Hz, 1H), 3.62 (d, J = 13.2 Hz, 1H), 3.62–3.68 (m, 1H),
5.03–5.08 (m, 2H), 5.61–5.72 (m, 1H), 7.2–7.4 (m, 9H) ppm; 13C NMR
(125 MHz, CDCl3) δ 43.0, 51.4, 60.9, 117.9, 126.9, 128.1, 128.4, 128.5,
128.7, 132.6, 134.9, 140.3, 142.3 ppm; HPLC analysis: er = 80:20,
Chiralpak IA column, n-hexane/iPrOH = 99:1, flow rate 0.5 mL/min,
(tmajor = 10.45 min, tminor = 11.68 min).
(400 MHz, CDCl3) δ 2.05 (br s, 1H), 2.41–2.48 (m, 2H), 2.99–3.06 (m,
1H), 3.10–3.17 (m, 1H), 3.70 (dd, J = 6.3, 1.2 Hz, 1H), 5.04–5.16 (m,
4H), 5.64– 5.78 (m, 1H), 5.81–5.93 (m, 1H), 7.22–7.34 (m, 5H) ppm;
13C NMR (100 MHz, CDCl3) δ 42.7, 49.9, 61.7, 116.0, 117.6, 127.1,
127.4, 128.3, 135.2, 136.5, 143.3 ppm; HPLC analysis: er = 78:22,
Chiralpak OD-H column, n-hexane/iPrOH = 98:2, flow rate 0.6 mL/
min, (tmajor = 8.13 min tminor = 8.98 min).
(R)-N-Benzyl-1-piperonyl-3-butenylamine (3a):[12a] Isolated yield
Conflict of interest
(63.9 mg, 68 %), Colorless oil; [α]D +31.7 (c 0.4, CHCl3); 1H NMR
25
The authors declare no conflict of interest
(500 MHz, CDCl3) δ 1.91 (br s, 1H), 2.35–2.42 (m, 2H), 3.53 (d, J =
13.3 Hz, 1H), 3.62 (t, J = 7.1 Hz, 1H), 3.69 (d, J = 13.3 Hz, 1H), 5.01–
5.11 (m, 2H), 5.64–5.75 (m, 1H), 5.96 (s, 2H), 6.79 (s, 2H), 6.93 (s, 1H),
7.21–7.35 (m, 5H) ppm; 13C NMR (100 MHz, CDCl3) δ 43.1, 51.2, 61.3,
100.8, 107.3, 107.9, 117.5, 120.6, 126.8, 128.1, 128.3, 135.3, 137.7,
140.4, 146.5, 147.8 ppm; HPLC analysis: er = 90:10, Chiralpak OD-H
Acknowledgments
We thank CSIR New Delhi [Grant No. 02(0158)/13/EMR-II] for
financial support for this work and a senior research fellowship
to A. K. J.
column, n-hexane/iPrOH = 98:2, flow rate 0.5 mL/min, (tmajor
14.45 min, tminor = 15.69 min).
=
(R)-N-(4-Methoxybenzyl)-1-piperonyl-3-butenylamine (3h):[12a]
Isolated yield (72.8 mg, 70 %), Colorless oil; [α]D25 +33.4 (c 1.0,
CHCl3); 1H NMR (500 MHz, CDCl3) δ 1.81 (br s, 1H), 2.37–2.45 (m,
2H), 3.45 (d, J = 13.3 Hz, 1 H), 3.57–3.64 (m, 2H), 3.79 (s, 3H), 5.00–
5.09 (m, 2H), 5.62–5.73 (m, 1H), 5.95 (s, 2H), 6.77 (s, 2H), 6.85 (d, J =
8.5 Hz, 2H), 6.91 (s, 1H), 7.17 (d, J = 8.6 Hz, 2H) ppm; 13C NMR
(125 MHz, CDCl3) δ 43.1, 50.6, 55.2, 61.2, 100.8, 107.3, 107.9, 113.7,
117.5, 120.6, 129.3, 132.5, 135.4, 137.8, 146.5, 147.8, 158.5 ppm;
HPLC analysis: er = 86:14, Chiralpak OD-H column, n-hexane/iPrOH =
99:1, flow rate 1 mL/min, (tmajor = 15.01 min, tminor = 22.55 min).
Keywords: Asymmetric catalysis · Homogeneous catalysis ·
C–C coupling · Allylation · Palladium · Enantioselectivity
[1] a) R. Hüttel, J. Kratzer, Angew. Chem. 1959, 71, 456; b) R. Hüttel, M. Bech-
ter, Angew. Chem. 1959, 71, 456; c) R. Hüttel, J. Kratzer, M. Bechter, Chem.
Ber. 1961, 94, 766; d) R. Hüttel, H. Christ, Chem. Ber. 1963, 96, 3101.
[2] J. Smidt, W. Hafner, Angew. Chem. 1959, 71, 284.
[3] J. Tsuji, H. Takahashi, M. Morikawa, Tetrahedron Lett. 1965, 6, 4387.
[4] a) B. M. Trost, T. J. Fullerton, J. Am. Chem. Soc. 1973, 95, 292; b) B. M.
Trost, L. Weber, J. Am. Chem. Soc. 1975, 97, 1611.
(R)-N-Benzyl-1-(2-naphthyl)-3-butenylamine (3i):[12a] Isolated
[5] B. M. Trost, P. E. Strege, L. Weber, T. J. Fullerton, T. J. Dietsche, J. Am.
Chem. Soc. 1978, 100, 3407.
yield (65.3 mg, 68 %), colorless oil; [α]D +46.5 (c 1.0, CHCl3); 1H
25
NMR (500 MHz, CDCl3) δ 1.87 (br s, 1H), 2.48–2.57 (m, 2H), 3.58 (d,
J = 13.3 Hz, 1H), 3.72 (d, J = 13.4 Hz, 1H), 3.89 (t, J = 6.8 Hz, 1H),
5.03–5.15 (m, 2H), 5.69–5.80 (m, 1H), 7.23–7.36 (m, 5H), 7.45–7.52
(m, 2H), 7.54–7.58 (m, 1H), 7.80 (s, 1H), 7.83–7.90 (m, 3H) ppm; 13C
NMR (125 MHz, CDCl3) δ 42.9, 51.4, 61.7, 117.7, 125.3, 125.5, 125.9,
126.2, 126.9, 127.7, 127.8, 128.1, 128.2, 128.4, 133.0, 133.4, 135.3,
140.4, 141.1 ppm; HPLC analysis: er = 77:23, Chiralpak OD-H column,
n-hexane/iPrOH = 98:2, flow rate 0.5 mL/min, (tmajor = 15.34 min,
tminor = 19.38 min).
[6] a) W. E. Walker, R. M. Manyik, K. E. Atkins, M. L. Farmer, Tetrahedron Lett.
1970, 43, 3817; b) K. E. Atkins, W. E. Walker, R. M. Manyik, Tetrahedron
Lett. 1970, 43, 3821; c) G. Hata, K. Takahashi, A. Miyake, J. Chem. Soc. D
1970, 1392; d) T. S. Shryne, E. J. Smutny, D. P. Stevenson, US Patent,
1970, 3493617; e) S. Uemura, S.-I. Fukuzawa, A. Toshimitsu, M. Okano,
Tetrahedron Lett. 1982, 23, 87; f) S. Winstein, C. B. Anderson, J. Org. Chem.
1963, 28, 605.
[7] H. Nakamura, K. Nakamura, Y. Yamamoto, J. Am. Chem. Soc. 1998, 120,
4242.
[8] B. M. Trost, Acc. Chem. Res. 1980, 13, 385.
(R)-N-Benzyl-1-(1-naphthyl)-3-butenylamine (3j):[12a] Isolated
yield (62.4 mg, 65 %), Colorless oil; [α]D25 +26.5 (c 0.55, CHCl3); 1H
NMR (500 MHz, CDCl3) δ 1.90 (br s, 1H), 2.47–2.55 (m, 1H), 2.65–
2.73 (m, 1H), 3.61 (d, J = 13.2 Hz, 1H), 3.78 (d, J = 13.2 Hz, 1H), 4.62
(dd, J = 8.2, 4.7 Hz, 1H), 5.07–5.18 (m, 2H), 5.78–5.88 (m, 1H), 7.24–
7.36 (m, 5H), 7.48–7.57 (m, 3H), 7.78–7.85 (m, 2H), 7.89–7.93 (m, 1H),
8.20 (d, J = 7.1 Hz, 1H) ppm; 13C NMR (125 MHz, CDCl3) δ 42.1,
51.6, 57.0, 117.7, 123.0, 123.9, 125.3, 125.6, 125.7, 126.8, 127.4, 128.2,
128.3, 129.0, 131.6, 134.0, 135.5, 139.0, 140.6 ppm; HPLC analysis:
er = 76:24, Chiralpak OD-H column, n-hexane/iPrOH = 99:1, flow
rate 0.8 mL/min, (tmajor = 9.13 min, tminor = 10.79 min).
[9] H. Nakamura, J.-G. Shim, Y. Yamamoto, J. Am. Chem. Soc. 1997, 119, 8113.
[10] a) K. Ohno, T. Mitsuyasu, J. Tsuji, Tetrahedron 1972, 28, 3705; b) K. J.
Zabó, Chem. Eur. J. 2000, 6, 4413.
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b) R. A. Fernandes, A. Stimac, Y. Yamamoto, J. Am. Chem. Soc. 2003, 125,
14133; c) R. A. Fernandes, Y. Yamamoto, J. Org. Chem. 2004, 69, 735.
[12] a) R. A. Fernandes, J. L. Nallasivam, Org. Biomol. Chem. 2012, 10, 7789;
b) R. A. Fernandes, D. A. Chaudhari, Eur. J. Org. Chem. 2012, 1945.
[13] For selected references, see: a) C. Spino, Chem. Commun. 2011, 47, 4872;
b) C. Spino, C. Godbout, C. Beaulieu, M. Harter, T. M. Mwene-Mbeja, L.
Boisvert, J. Am. Chem. Soc. 2004, 126, 13312; c) J. K. Whitesell, Chem. Rev.
1992, 92, 953; d) B. L. Feringa, B. de Lange, J. F. G. A. Jansen, J. C. de Jong,
M. Lubben, W. Faber, E. P. Schudde, Pure Appl. Chem. 1992, 64, 1865.
[14] (+)-Menthone was prepared from commercially available (+)-menthol, as
the latter is available in higher enantiomeric purity. For this oxidation,
we followed a procedure similar to the literature, see: F. A. Luzzio, R. W.
Fitch, W. J. Moore, K. J. Mudd, J. Chem. Educ. 1999, 76, 974.
(R)-N-Benzyl-1-(2-thiophenyl)-3-butenylamine (3k):[12a] Isolated
yield (48.8 mg, 60 %), Colorless oil; [α]D25 12.7 (c 1.0, CHCl3); 1H NMR
(400 MHz, CDCl3) δ 2.0 (br s, 1H), 2.48–2.57 (m, 2H), 3.64 (d, J =
13.3 Hz, 1H), 3.82 (d, J = 13.3 Hz, 1H), 4.03 (t, J = 6.8 Hz, 1H), 5.04–
Eur. J. Org. Chem. 2019, 2857–2863
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[15]
[16]
M. Kanai, M. A. Shibasaki, J. Am. Chem. Soc. 2002, 124, 6536; b) H. Sakurai,
Synlett 1989, 1.
Dimeric phosphonium salts were prepared following literature proce-
dure, see: K. M. Redies, T. Fallon, M. Oestreich, Organometallics 2014, 33,
3235.
CCDC 1878829 (for 2e) contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre.
[19] For asymmetric allylation of N-acylhydrazones see: a) R. Berger, P. M. A.
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Received: February 3, 2019
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