Novel N,N-bidentate ligands for enantioselective copper(I)-catalyzed allylic oxidation of cyclic olefins

Article abstract of DOI:10.1002/adsc.200800457

New N,N-bidentate Schiff base ligands containing the 2-quinolyl moiety proved to be effective in conferring high reactivity and moderate to high enantioselectivity (up to 84% ee) to the copper(I)-catalyzed asymmetric allylic oxidation of various cylic ole

Full text of DOI:10.1002/adsc.200800457

FULL PAPERS
DOI: 10.1002/adsc.200800457
Novel N,N-Bidentate Ligands for Enantioselective Copper(I)-
Catalyzed Allylic Oxidation of Cyclic Olefins
Qitao Tana,b and Masahiko Hayashib,*
a
Department of Frontier Research and Technology, Headquarters for Innovative Cooperation and Development, Kobe
University, Nada, Kobe 657-8501, Japan
Department of Chemistry, Graduate School of Science, Kobe University, Kobe 657-8501, Japan
b
Fax : (+81)-78-803-5688; e-mail: mhayashi@kobe-u.ac.jp
Received: July 24, 2008; Published online: October 16, 2008
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/adsc.200800457.
Abstract: New N,N-bidentate Schiff base ligands nitrile)copper
hexafluorophosphate
[Cu-
containing the 2-quinolyl moiety proved to be effec- (CH3CN)4PF6]. Using the same N,N-bidentate Schiff
AHCTUNGTRENNUNG
tive in conferring high reactivity and moderate to base ligand, the former showed high reactivity and
high enantioselectivity (up to 84% ee) to the cop- the latter showed high enantioselectivity.
per(I)-catalyzed asymmetric allylic oxidation of vari-
ous cylic olefins with tert-butyl perbenzoate. As cop-
per(I) sources, we employed copper(II) triflate/phe- Keywords: allylic oxidation; bidentate ligands;
nylhydrazine [CuACHTNUTRGNEUNG(OTf)2/PhNHNH2] and tetra(aceto- copper; enantioselectivity
Introduction
type of chiral Schiff base ligand that contains a quino-
line moiety for asymmetric allylic oxidation. To the
In the late 1950s, Kharasch and Sosnovsky reported best of our knowledge, there is only one report of the
for the first time the allylic oxidation of olefins using use of a Schiff base for asymmetric allylic oxidation.
tert-butyl perbenzoate catalyzed by copper bromide.[1] However, in that system, the optical yield of the prod-
After that report, much effort has been made to im- uct was less than 10% ee, judging from the optical ro-
prove the copper-catalyzed allylic oxidation of olefins tation after derivatization to the corresponding olefin-
because of its potential utility in organic synthesis.[2] ic alcohol.[10]
Asymmetric versions of this reaction have been well
studied. Initially, the enantiomeric excess (ee) of the
product was low.[3] However, in the mid 1990s, moder- Results and Discussion
ate to high enantioselectivity was realized. Most of
the reactions used chiral oxazoline-based ligands.[4] We first examined the effect of the addition of our
Unfortunately, one problem remains to this day: low newly designed N,N-bidentate Schiff base ligand con-
reactivity. For example, in Katsukiꢀs system, the taining a quinoline moiety on the reaction of cyclo-
Cu
ACHTUNGTRENNUNG
the oxidation of cyclopentene (08C, 84% ee, 44% Table 1, the addition of phenylhydrazine to CuACHTUNGTRENNUNG
yield) and 670 h for that of cycloheptene (À208C, increased the reactivity (entry 3). Further addition of
69% ee, 10% yield).[4c] Singh et al. reported that the designed N,N-bidentate ligands 1 and 2 to the above
addition of phenylhydrazine greatly reduced the reac- system dramatically increased the reaction rate (en-
tion time without affecting enantioselectivity,[5] and tries 4 and 5).
this method has been used by other researchers.[6]
It should be mentioned that as for the nature of
Other non-oxazoline-type ligands, bis(imidazolines)[7] copper(I) precursor, (CuOTf)2 C6H6 showed a higher
.
and (iminophosphoranyl)ferrocenes,[8] especially the reactivity than Cu
latter, showed high enantioselectivity. Shul’pin et al. (CuOTf)2 C6H6 produced undesired products to give a
(CH3CN)4PF6, however, the use of
.
reported a mechanistic study in alkene hydroperoxi- lower yield (20%). In the case of CuACTHNUTRGNE(UNG CH3CN)4PF6,
dation with peroxides catalyzed by copper complexes the reactivity was lower, but a higher yield of the
in the racemic version.[9] We herein disclose a new product was obtained (40% yield).
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Table 1. Rate enhancement by the addition of bidentate ni-
Table 2. Enantioselective allylic oxidation of cyclohexene
trogen ligands in Cu
G
using CuACTHNGUTERNNUG
(OTf)2/PhNHNH2 system.[a]
[a]
Cyclohexene:PhCO3t-Bu=5:1. Six mol% of additive
and/or ligands were added.
Isolated yield.
46% ee (R). Determined by HPLC (CHIRALCEL OD-
H column).
[b]
[c]
[a]
Then, chiral Schiff base ligands 3–9 were prepared.
Cyclohexene:PhCO3t-Bu=5:1.
Isolated yield.
Determined by HPLC analysis (CHIRALCEL OD-H).
[b]
[c]
Aldimines were readily prepared by simple condensa-
tion of 2-pyridylaldehyde or 2-quinolylaldehyde with
chiral amines. For the synthesis of ketoimine ligands,
the reaction of 2-quinolyl nitrile with Grignard re-
agents gave the corresponding ketones, which were
reacted with chiral amines in the presence of TiCl4 used, the reaction was sluggish and yield and ee were
and Et3N to give the desired ketoimines (Scheme 1). low. However, when the 2-quinolyl moiety was intro-
Then, we carried out the asymmetric allylic oxida- duced instead of the 2-pyridyl moiety, the reaction
tion of cyclohexene with tert-butyl perbenzoate in the rate was enhanced dramatically: within 30 min, the re-
presence of 5 mol% CuACHTNUGTREN(UNG OTf)2, 6 mol% PhNHNH2, actions were completed to give the product in 70–
and 6 mol% chiral ligands 2–9 (Table 2) When Schiff 88% yield. As for ee, ketoimine-type N,N-bidentate li-
bases 3 and 4 containing the 2-pyridyl moiety were gands (R1 =Me, Et) gave higher ee than the corre-
sponding aldimine-type N,N-bidentate ligands (R1 =
H). For example, in the reaction using ketoimine-type
N,N-bidentate ligands 2 and 9, products with 46% ee
and 44% ee were obtained, respectively, whereas aldi-
mine-type N,N-bidentate ligand 8 gave a product
having only 19% ee. Among the N,N-bidentate li-
gands examined, ligand 2 gave the best result (88%
yield, 46% ee). As for the nature of copper precursor,
we examined this aspect as follows.
Based on the above results, we examined the asym-
metric allylic oxidation of various cyclic olefins using
the CuACTHNUTRGENNG(U OTf)2/PhNHNH2 or the CuHCATUNGTRNE(NNGU CH3CN)4PF6
system. The results when chiral N,N-bidentate ligand
2 was employed are summarized in Table 3. Among
the cyclic olefins, the reaction of cycloheptene with t-
butyl perbenzoate in the presence of the
Cu
oxidation product in 84% ee (08C, 48 h, 51% yield).
Generally, the Cu(CH3CN)4PF6 system (B) gave
ACHTNUGTNERN(UGN CH3CN)4PF6/ligand 2 catalyst system afforded the
Scheme 1. Preparation of ketoimine-type N,N-bidentate li-
gands.
ACHTUNGTRENNUNG
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Adv. Synth. Catal. 2008, 350, 2639 – 2644

Novel N,N-Bidentate Ligands for Enantioselective Copper(I)-Catalyzed Allylic Oxidation
FULL PAPERS
Table 3. Enantioselective allylic oxidation of various cyclic
Conclusions
olefins.[a]
In summary, the copper complex of ketoimine 2 pos-
sessing the 2-quinoline moiety was proven to catalyze
the asymmetric allylic oxidation of various cycloole-
fins and cyclooctadienes with high efficiency and in
moderate to high enantioselectivity (up to 84% ee).
In view of the high reactivity compared with those of
previously reported catalyst systems and the ready
modification of these ligands, we plan to conduct
more studies in this field.
Experimental Section
General Remarks
All reactions were performed under an argon atmosphere
using Schlenk tube techniques and freshly distilled solvents.
All melting points were measured on a Yanaco MP-500D
and were uncorrected. 1H and 13C NMR spectra (400 and
100.6 MHz, respectively) were recorded on a JEOL JNM-
LA 400 using Me4Si as the internal standard (0 ppm). The
following abbreviations are used: s=singlet, d=doublet, t=
triplet, q=quartet, m=multiplet. IR spectra were measured
with a Perkin–Elmer FT-IR spectrometer Spectrum 1000.
Elemental analyses were performed with a Yanaco CHN
Corder MT-5. Mass spectra were measured on a Thermo
Quest LCQ DECA plus. Optical rotations were measured
on a Horiba Sepa-300 Polarimeter for solutions in a 1 dm
cell. Preparative column chromatography was carried out on
Fuji Silysia BW-820MH or YMC*GEL silica (6 nm I-40–63
mm). Thin layer chromatography (TLC) was carried out on
Merck 25 TLC aluminum sheets of silica gel 60 F254. Chiral
HPLC was performed on a Hitachi l-2000 series instrument
equipped with an L-2455 diode array detector.
[a]
[b]
[c]
[d]
Cyclic olefins:PhCO3t-Bu=5:1.
A: Cu(OTf)2/PhNHNH2; B: Cu
Isolated yield.
The ee values were determined on a chiral HPLC
column (CHIRALCEL OD-H for entries 1–4, 7 and 8,
CHIRALPAK AD-H for entries 5 and 6).
G
ACHTNUGRTNE(NUGN CH3CN)4PF6
higher ee, although the reactivity was slightly lower
than that of the Cu(OTf)2/PhNHNH2 system (A).
Finally, we examined the asymmetric allylic oxida-
tion of 1,5-cyclooctadiene. As shown in Scheme 2,
AHCTUNGTRENNUNG
the Cu
ACHTUNGTRENNUNG(OTf)2/PhNHNH2/ligand 2 system and the
General Procedure for the Synthesis of Aldimine
Ligands (3–6 and 8)
Cu(CH3CN)4PF6/ligand 2 system afforded a product
ACHTUNGTRENNUNG
with 65% ee (208C, 3 h, 63% yield) and 74% ee (08C,
48 h, 62% yield), respectively. The second oxidation
did not take place under the present reaction condi-
tions.
A mixture of chiral amines (1.10 mmol) and corresponding
aldehydes (1.00 mmol) was dissolved in toluene (5 mL).
Na2SO4 (1.0 g) was added and the mixture was heated to
1108C for 12 h. After filtration, the solvent was evaporated
in vacuum to give the desired compounds. The sample for
analysis was obtained by silica gel (pre-neutralized with
Et3N) chromatography or recrystallization.
(S)-1-Phenyl-N-(pyridin-2-ylmethylene)ethylamine
(3):[11]Yield: 85%; light yellow oil; [a]D24: +38 (c 1.0, CHCl3);
IR (thin film): nmax =3060, 2971, 1645, 1586, 1493, 1467,
1436, 1371, 1080, 762, 700, 612 cmÀ1 1H NMR (400 MHz,
;
CDCl3): d=1.61 (d, J=6.8 Hz, 3H), 4.65 (q, J=6.8 Hz, 1H),
7.2–7.4 (m, 6H), 7.72 (dt, J=7.2 Hz, 1.6 Hz, 1H), 8.09 (d,
J=7.6 Hz, 1H), 8.46 (s, 1H), 8.63 (d, J=4.8 Hz, 1H);
13C NMR (100.6 MHz, CDCl3): d=24.5, 69.5, 121.4, 124.6,
126.6, 126.9, 128.5, 136.4, 144.5, 149.3, 154.8, 160.4.
(S)-N-[(6-Methylpyridin-2-yl)methylene]-1-phenylethyl-
AHCTUNGTRENNUNG
amine (4):[12] Yield: 83%; light yellow oil; [a]2D5: +5.6 (c 1.0,
CHCl3); IR (thin film): nmax =2971, 2862, 1646, 1591, 1456,
1
Scheme 2. Asymmetric allylic oxidation of 1,5-cycloocta-
1369, 1085, 792, 764, 699 cmÀ1; H NMR (400 MHz, CDCl3):
diene.
d=1.60 (d, J=6.8 Hz, 3H), 2.58 (s, 3H), 4.62 (q, J=6.8 Hz,
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FULL PAPERS
1H), 7.16 (d, J=7.2 Hz, 1H), 7.23 (d, J=6.8 Hz, 1H), 7.34
(t, J=7.2 Hz, 2H), 7.4–7.5 (m, 2H), 7.61 (t, J=7.8 Hz, 1H),
7.92 (d, J=7.8 Hz, 1H), 8.45 (s, 1H); 13C NMR (100.6 MHz,
CDCl3): d=24.3, 24.5, 69.5, 118.4, 124.3, 126.7, 126.9, 128.5,
136.7, 144.6, 154.3, 158.0, 160.8.
7.87 (d, J=8.0 Hz, 1H), 8.13 (d, J=8.8 Hz, 1H), 8.20 (d, J=
8.8 Hz, 1H), 8.27 (d, J=8.0 Hz, 1H); 13C NMR (100.6 MHz,
CDCl3): d=25.5, 117.9, 127.6, 128.5, 129.5, 130.0, 130.6,
136.8, 147.3, 153.3, 200.7.
(S)-1-Phenyl-N-(quinolin-2-ylmethylene)ethylamine (5):[13]
Yield: 82%; yellow solid (from CH3CN); mp 90–928C; [a]26:
À54 (c 1.0, CHCl3); IR (KBr): nmax =2966, 2860, 1633, 159D6,
Ethyl 2-Quinolyl Ketone
The preparation is the same as that of methyl 2-quinolyl
ketone except that EtMgBr (1.0M in THF) was used; yield:
62%; colorless solid; mp 56–578C (lit.[15] 59–608C); IR
(KBr): nmax =2977, 1692, 1560, 1460, 1399, 1358, 1115, 968,
1504, 1452, 1367, 1086, 835, 774, 759, 706 cmÀ1 1H NMR
;
(400 MHz, CDCl3): d=1.65 (d, J=7.2 Hz, 3H), 4.72 (q, J=
7.2 Hz, 1H), 7.2–7.3 (m, 1H), 7.3–7.4 (m, 2H), 7.48 (d, J=
7.2 Hz, 2H), 7.5–7.6 (m, 1H), 7.7–7.8 (m, 1H), 7.83 (d, J=
10.4 Hz, 1H), 8.13 (d, 8.4 Hz, 1H), 8.17 (d, J=8.4 Hz, 1H),
8.26 (d, J=8.4 Hz, 1H), 8.64 (s, 1H); 13C NMR (100.6 MHz,
CDCl3): d=24.6, 69.6, 118.6, 126.7, 127.0, 127.4, 127.7, 128.5,
128.8, 129.6, 129.7, 136.4, 144.5, 147.8, 155.1, 160.9.
935, 806, 789, 753, 621 cmÀ1 1H NMR (400 MHz, CDCl3):
;
d=1.28 (t, J=7.6 Hz, 3H), 3.43 (q, J=7.6 Hz, 2H), 7.64 (td,
J=8.0 Hz, 0.8 Hz, 1H), 7.78 (td, J=6.8 Hz, 1.2 Hz, 1H),
7.87 (d, J=8.4 Hz, 1H), 8.14 (d, J=8.4 Hz, 1H), 8.20 (d, J=
8.4 Hz, 1H), 8.26 (d, J=8.4 Hz, 1H); 13C NMR (100.6 MHz,
CDCl3): d=8.1, 30.9, 118.2, 127.7, 128.4, 129.6, 129.9, 130.5,
136.9, 147.2, 153.1, 203.2.
(S)-1-(Naphthalen-1-yl)-N-(quinolin-2-ylmethylene)ethyl-
amine (6):[14] Yield: 84%; yellow oil; [a]2D6: +152 (c 1.0,
CHCl3) [lit.[14] À130.6 (c 0.83, CHCl3) (R)]; IR (thin film):
nmax =2977, 2864, 1649, 1595, 1502, 1429, 1369, 1304, 1119, General Procedure for the Synthesis of Ketoimine
959, 837, 778, 753, 619 cmÀ1 1H NMR (400 MHz, CDCl3):
;
Ligands (1, 2, 7, and 9)
d=1.79 (d, J=6.8 Hz, 3H), 5.54 (q, J=6.8 Hz, 1H), 7.5–7.6
(m, 4H), 7.7–7.9 (m, 5H), 8.10 (d, J=8.4 Hz, 1H), 8.18 (d,
J=8.4 Hz, 1H), 8.27 (d, J=8.4 Hz, 1H), 8.31 (d, J=8.4 Hz,
1H), 8.68 (s, 1H); 13C NMR (100.6 MHz, CDCl3): d=24.1,
65.3, 118.6, 123.6, 124.1, 125.4, 125.6, 125.9, 127.3, 127.6,
127.7, 128.8, 128.9, 129.5, 129.7, 130.7, 134.0, 136.4, 140.3,
147.7, 155.1, 161.2.
To the corresponding ketone (2.0 mmol), chiral amine
(3.2 mmol), and Et3N (4.0 mmol) in toluene (20 mL) was
added dropwise TiCl4 (135 mL, 1.2 mmol) in toluene (3 mL).
After stirring for an additional hour at room temperature,
the mixture was heated to 908C for 24 h. The mixture was
then cooled to 08C, quenched with 1M NaOH (10 mL), and
extracted with EtOAc (3ꢂ20 mL). The combined organic
layer was washed with 1M NaOH (10 mL) and brine (3ꢂ
10 mL), and dried (Na2SO4). After removal of the solvent,
the solid sample for analysis was obtained by recrystalliza-
tion from solvent.
N-[1-(Quinolin-2-yl)ethylidene]pentan-3-amine (1): Yield:
95%; light yellow oil; IR (thin film): nma1x =2965, 1697, 1640,
1597, 1502, 1358, 1123, 837, 754 cmÀ1; H NMR (400 MHz,
CDCl3): d=0.87 (t, J=7.2 Hz, 6H), 1.6–1.7 (m, 4H), 2.52 (s,
3H), 3.5–3.6 (m, 1H), 7.52 (td, J=8.0 Hz, 1.2 Hz, 1H), 7.71
(td, J=8.8 Hz, 1.2 Hz, 1H), 7.80 (d, J=8.0 Hz, 1H), 8.1–9.1
(m, 2H), 8.28 (d, J=8.8 Hz, 1H); 13C NMR (100.6 MHz,
CDCl3): d=11.0, 14.0, 28.9, 64.2, 119.1, 126.7, 127.5, 128.3,
129.1, 129.8, 135.7, 147.2, 158.2, 164.7; MS (ESI): m/z=241.3
(M+H)+; anal. calcd. for C16H20N2: C 79.96, H 8.39, N
11.66; found: C 79.79, H 8.40, N 11.85.
(S)-3,3-Dimethyl-N-(quinolin-2-ylmethylene)butan-2-
amine (8): Yield: 81%; light yellow oil; [a]2D5: +73 (c 1.0,
CHCl3); IR (thin film): nmax =2958, 2866, 1646, 1595, 1502,
1458, 1393, 1364, 1204, 1121, 961, 834, 750, 620 cmÀ1
;
1H NMR (400 MHz, CDCl3): d=0.98 (s, 9H), 1.20 (d, J=
6.4 Hz, 3H), 3.15 (q, J=6.4 Hz, 1H), 7.5–7.6 (m, 1H), 7.7–
7.8 (m, 1H), 7.83 (d, J=8.4 Hz, 1H), 8.1–8.2 (m, 3H), 8.50
(s, 1H); 13C NMR (100.6 MHz, CDCl3): d=17.3, 26.6, 34.3,
75.3, 118.6, 127.2, 127.7, 128.7, 129.5, 129.6, 136.3, 147.8,
155.3, 160.0; MS (ESI): m/z=241.4 (M+H)+, 263.3 (M+
Na)+; anal. calcd. for C16H20N2: C 79.96, H 8.39, N 11.66;
found: C 79.89, H 8.33, N 11.40.
Synthesis of Methyl 2-Quinolyl Ketone
To a solution of 2-quinolinecarbonitrile (2.0 g, 13.0 mmol) in
anhydrous Et2O (50 mL) cooled to 08C was added dropwise
a solution of MeMgI in Et2O (30 mL) [prepared from Mg
(0.343 g, 14.3 mmol) and MeI (2.05 g, 14.3 mmol)]. After ad-
dition, the mixture was allowed to warm to room tempera-
ture and stirred overnight. After cooling to 08C, the mixture
was quenched by adding ice water and 2M H2SO4 (25.0 mL,
50.0 mmol) successively. The mixture was stirred at room
temperature for 5 h and washed with aqueous NaOH solu-
tion. The organic layer was separated and the aqueous layer
was extracted with Et2O (3ꢂ30 mL). The combined organic
phase was washed with brine twice and dried (Na2SO4).
After evaporation of the solvent, the residue was purified by
silica gel chromatography (hexane:EtOAc=20:1) to give
the desired compound as a colorless solid; yield: 1.25 g
(56%); mp 50–518C (lit.[15] 50–528C); IR (KBr): nmax =3012,
1691, 1592, 1504, 1355, 1306, 1287, 1123, 942, 838, 756,
(S)-3,3-Dimethyl-N-[1-(quinolin-2-yl)ethylidene]butan-2-
amine (2): Yield: 92% (from CH3CN); colorless needles;
mp 97–998C; [a]D27: +105 (c 1.0, CHCl3); IR (KBr): nmax
=
2970, 2867, 1633, 1596, 1558, 1499, 1366, 1127, 842, 763,
1
620 cmÀ1; H NMR (400 MHz, CDCl3): d=0.98 (s, 9H), 1.08
(d, J=6.4 Hz, 3H), 2.49 (s, 3H), 3.50 (q, J=6.4 Hz, 1H),
7.52 (td, J=8.4 Hz, 0.8 Hz, 1H), 7.68 (td, J=8.4 Hz, 0.8 Hz,
1H), 7.80 (d, J=8.4 Hz, 1H), 8.0–8.1 (m, 2H), 8.33 (d, J=
8.8 Hz, 1H); 13C NMR (100.6 MHz, CDCl3): d=12.9, 15.5,
26.5, 34.8, 65.0, 119.0, 126.7, 127.5, 128.3, 129.1, 129.8, 135.7,
147.2, 158.2, 163.4; MS (ESI): m/z=255.3 (M+H)+, 277.3
(M+Na)+; anal. calcd. for C17H22N2: C 80.27, H 8.72, N
11.01; found: C 79.97, H 8.89, N 11.01.
(S)-1-(Naphthalen-1-yl)-N-[1-(quinolin-2-yl)ethylidene]-
AHCTUNGTREGeNNNU thylamine (7): Yield: 80%; yellow needles (from MeOH);
mp 111–1128C; [a]2D6: +215.4 (c 1.0, CHCl3); IR (KBr):
nmax =2971, 1640, 1593, 1559, 1501, 1445, 1353, 1129, 837,
658 cmÀ1; H NMR (400 MHz, CDCl3): d=2.88 (s, 3H), 7.65
800, 781, 758, 736, 624 cmÀ1 1H NMR (400 MHz, CDCl3):
;
1
(td, J=8.0 Hz, 1.2 Hz, 1H), 7.79 (td, J=6.8 Hz, 1.2 Hz, 1H),
d=1.76 (d, J=6.4 Hz, 3H), 2.53 (s, 3H), 5.70 (q, J=6.4 Hz,
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Novel N,N-Bidentate Ligands for Enantioselective Copper(I)-Catalyzed Allylic Oxidation
FULL PAPERS
1H), 7.5–7.6 (m, 4H), 7.70 (qt, J=6.8 Hz, 1H), 7.75 (d, J=
8.0 Hz, 1H), 7.82 (d, J=8.0 Hz, 1H), 7.8–7.9 (m, 2H), 8.11
(d, J=8.4 Hz, 1H), 8.16 (d, J=8.8 Hz, 1H), 8.34 (d, J=
8.0 Hz, 1H), 8.49 (d, J=8.4 Hz, 1H); 13C NMR (100.6 MHz,
CDCl3): d=14.0, 24.3, 57.3, 119.1, 123.6, 124.1, 125.3, 125.8,
126.9, 127.2, 127.5, 128.5, 129.0, 129.2, 129.9, 134.1, 135.9,
142.0, 147.2, 165.9; MS (ESI): m/z=325.3 (M+H)+, 347.3
(M+Na)+; anal. calcd. for C23H20N2: C 85.15, H 6.21, N
8.63; found: C 84.87, H 6.23, N 8.77.
(R)-2-Cyclopentenyl 1-benzoate (Table 3, entry 2):[4l] The
ee was determined as 51% ee by HPLC on a CHIRALCEL
OD-H (DAICEL) column [hexane:2-propanol=99.9:0.1];
0.5 mLminÀ1; tR of S-isomer=24.6 min, tR of R-isomer=
29.5 min; [a]26: +101.2 (c 1.0, CHCl3) {lit.[4l] [a]2D5: À136.2 (c
0.9, CHCl3) fDor 70% ee (S)}.
(R)-2-Cyclohexenyl 1-benzoate (Table 3, entry 4):[4l] The
ee was determined as 51% ee by HPLC on a CHIRALCEL
OD-H (DAICEL) column [hexane:2-propanol=99.9:0.1];
0.5 mLminÀ1; tR of S-isomer=25.6 min, tR of R-isomer=
27.0 min; [a]D24: +96.6 (c 1.0, CHCl3) {lit.[4l] [a]2D5: À167.2 (c
4.4, CHCl3) for 93% ee (S)}.
(S)-3,3-Dimethyl-N-[1-(quinolin-2-yl)propylidene]butan-
2-amine (9): Yield: 89%; colorless needles (from CH3CN);
mp 63–648C; [a]D21: +108 (c 1.0, CHCl3); IR (KBr): nmax
=
2967, 2866, 1630, 1558, 1500, 1455, 1361, 1130, 835, 761,
(R)-2-Cycloheptenyl 1-benzoate (Table 3, entry 6):[5] The
ee was determined as 84% ee by HPLC on a CHIRALPAK
AD-H (DAICEL) column [hexane:2-propanol=99.7:0.3];
0.5 mLminÀ1; tR of R-isomer=18.4 min, tR of S-isomer=
19.8 min; [a]D24: +40.5 (c 1.0, CHCl3) {lit.[5] [a]2D5: À38.2 (c
4.4, CHCl3) for 82% ee (S)].
1
620 cmÀ1; H NMR (400 MHz, CDCl3): d=0.99 (s, 9H), 1.10
(d, J=6.8 Hz, 3H), 1.15 (t, J=7.2 Hz, 3H), 2.9–3.0 (m, 1H),
3.2–3.3 (m, 1H), 3.54 (q, J=6.8 Hz, 1H), 7.52 (td, J=
8.4 Hz, 0.8 Hz, 1H), 7.69 (td, J=6.8 Hz, 1.2 Hz, 1H), 7.80
(dd, J=8.4 Hz, 0.8 Hz, 1H), 8.10 (d, J=8.4 Hz, 2H), 8.28 (d,
J=8.4 Hz, 1H); 13C NMR (100.6 MHz, CDCl3): d=12.4,
16.5, 19.6, 26.5, 34.6, 64.2, 119.6, 126.6, 127.4, 128.3, 129.0,
129.9, 135.6, 147.3, 157.3, 168.2; MS (ESI): m/z=269.4 (M+
H)+, 291.3 (M+Na)+; anal. calcd. for C18H24N2: C 80.55, H
9.01, N 10.44; found: C 80.23, H 9.00, N 10.64.
(R)-2-Cyclooctenyl 1-benzoate (Table 3, entry 8):[4l] The
ee was determined as 70% ee by HPLC on a CHIRALCEL
OD-H (DAICEL) column [hexane:2-propanol=99.9:0.1];
0.5 mLminÀ1; tR of R-isomer=27.1 min, tR of S-isomer=
29.4 min; [a]D25: À58.0 (c 1.0, CHCl3) {lit.[4l] [a]2D5: +86.5 (c
1.2, CHCl3) for 94% ee (S)}.
(R)-2,6-Cyclooctadienyl 1-benzoate (Scheme 2): The ee
was determined as 74% ee by HPLC on a CHIRALCEL
OB (DAICEL) column [hexane:2-propanol=99.7:0.3];
0.75 mLminÀ1; tR of minor isomer=11.9 min, tR of major
isomer=16.1 min; [a]2D8: À33.3 (c 1.0, CHCl3).
General Procedure for Asymmetric Allylic Oxidation
of Cycloolefins in the Presence of Cu
PhNHNH2/Ligand Complexes
ACHTUNGERTN(NUNG OTf)2/
A solution of chiral Schiff base ligand (0.06 mmol) and
Cu(OTf)2 (0.05 mmol) in acetone (3 mL) was stirred at
ACHTUNGTRENNUNG
208C for 1 h. To this dark red solution was added phenylhy-
drazine (6.5 mg, 0.06 mmol), and the mixture was stirred for
30 min during which the solution became clear red. Then, an
olefin (5.0 mmol) was added, followed by dropwise addition
of tert-butyl perbenzoate (1.0 mmol) under an argon atmos-
phere. For the most reactive cycloolefins (cyclopentene and
cyclohexene), the reaction was completed immediately after
the addition of tert-butyl perbenzoate and the heat released
could be detected even by hand. For the relatively less reac-
tive cycloolefins, the color changed to green after several
minutes and the reaction was left to proceed at 208C until it
was completed (determined by the disappearance of pere-
ster from TLC or the change of color to red). The solvent
was then removed and the residue was purified by silica gel
chromatography using hexane:EtOAc (100:1) as eluent to
give the product as a light yellow liquid.
Acknowledgements
This work was supported by a Grant-in-Aid for Scientific Re-
search on Priority Areas “Advanced Molecular Transforma-
tions of Carbon Resources” and No. B17340020 from the
Ministry of Education, Culture, Sports, Science and Technol-
ogy, Japan.
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