Enantioselective olefin epoxidation using novel biphenyl and binaphthyl azepines and azepinium salts

Article abstract of DOI:10.1016/j.tetasy.2006.08.018

Homologous biphenyl and (diastereomeric) binaphthyl tertiary azepines and quaternary iminium salts were prepared from (S)- and (R)-3,3-dimethylbutan-2-amine. Both the amines and iminium ions behave as effective catalysts for the enantioselective epoxidati

Full text of DOI:10.1016/j.tetasy.2006.08.018

Tetrahedron: Asymmetry 17 (2006) 2334–2338
Enantioselective olefin epoxidation using novel biphenyl and
binaphthyl azepines and azepinium salts
a
a
b
a,
*
´ ˆ
´
´ ˆ
Jerome Vachon, Cedric Lauper, Klaus Ditrich and Jerome Lacour
a
`
`
De´partement de Chimie Organique, Universite´ de Geneve, quai Ernest Ansermet 30, CH-1211 Geneve-4, Switzerland
bBASF Aktiengesellschaft, Forschung Feinchemikalien and Biokatalyse, 67056 Ludwigshafen, Germany
Received 20 July 2006; accepted 21 August 2006
Available online 26 September 2006
Abstract—Homologous biphenyl and (diastereomeric) binaphthyl tertiary azepines and quaternary iminium salts were prepared
from (S)- and (R)-3,3-dimethylbutan-2-amine. Both the amines and iminium ions behave as effective catalysts for the enantioselective
epoxidation of unfunctionalized olefins (ee up to 87%).
ꢀ 2006 Elsevier Ltd. All rights reserved.
1. Introduction
renders the development of catalytic processes possible.5
Several successful enantioselective variants of the reaction
have already been reported,6–9 among which are studies
using biphenyl 1i and 2i,10–12 and binaphthyl 3i and 4i
iminium salts (Fig. 1);13 compounds [3i][X] and [4i][X]
being some of the most effective iminium salt catalysts to
date (ee up to 95%).14
Chiral nonracemic epoxides are useful precursors in syn-
thetic chemistry, and frequent structures in natural prod-
ucts, often related to their biological activities (Eq. 1).1 A
few efficient catalytic methods currently exist for their
preparation from olefins and many of them are based on
transition metals such as the Katsuki–Sharpless or Kat-
suki–Jacobsen protocols.2 In recent years, much effort
has been devoted to the development of organocatalyzed
epoxidation conditions that afford metal-free procedures;
the catalysts being perhydrate, dioxirane, oxaziridine, or
oxoammonium moieties as well as ammonium or oxazirid-
inium salts.3
TT
X
Me
O
O
N
N
Ph
(L)-[2i][X]
(
S
)-[1i][TT]
catalyst
NaHCO3, oxone
CH2Cl2 / Water 3:2
R1
R2
H
ð1Þ
O
18-C-6, 0oC
R1
R2
H
R3
X
X
O
O
R3
N
N
O
O
Ph
Ph
Sa,L)-[4i][X]
Oxaziridinium ions are attractive alternatives to the com-
monly used dioxiranes.4 These organic salts are effective
oxygen transfer reagents towards nucleophilic substrates
and electron-rich unfunctionalized olefins in particular.
Moreover, the propensity of iminium ions to react with
an Oxoneꢁ triple salt to generate the oxaziridinium species
(
(
Ra,L)-[3i][X]
Figure 1. Selected nonracemic iminium salts and their absolute conꢀfigu-
ration, Xꢀ symbolizes a lipophilic noncoordinating anion (BPh4 or
TRISPHAT—abbreviated TT).
In compounds 1i and 2i, the stereocontrol over the reaction
is provided by the exocyclic chiral appendages derived
from enantiopure 3,3-dimethylbutan-2-amine 5 [(S)- or
*
Corresponding author. Fax: +41 22 379 3215; e-mail: jerome.lacour@
chiorg.unige.ch
0957-4166/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2006.08.018

J. Vachon et al. / Tetrahedron: Asymmetry 17 (2006) 2334–2338
2335
(R)-enantiomers] and L-acetonamine 6, respectively
(Fig. 2).15 Significantly, with 1i and 2i, similar levels of
reactivity and enantioselectivity were obtained indicating
that amines 5 and 6 display similar stereochemical effi-
ciency (ee up to 80% and 79%, respectively).12
Br
Br
i)
ii)
Me
Me
O
O
H2N
H2N
H2N
Ph
Me
Me
N
N
5
)-
5
(R)-
L
-
6
(S
Figure 2. Nonracemic amines used as chiral auxiliaries.
(
Ra,R)-8a
(
Ra,S)-7a
Compounds 3i and 4i are diastereomers that incorporate
both a configurationally rigid binaphthyl core and L-ace-
tonamine as stereogenic elements. In this case, the atropos
binaphthyl core has a predominant stereochemical influ-
ence. The enantioselectivity of the epoxidation reaction is
controlled by the configuration of the biaryl moiety rather
than the exocyclic appendage.13 Essentially identical ee val-
ues are obtained in the reactions of prochiral olefins in the
presence of diastereomeric 3i and 4i in favor of epoxides of
opposite configurations.
iii), iv)
iii), iv)
[7i][TRISPHAT]
[8i][TRISPHAT]
Scheme 1. Reagents and conditions: (i) (S)-5 (1.2 equiv), K2CO3 (4.0
equiv), CH3CN, reflux, 72%; (ii) (R)-5 (1.2 equiv), K2CO3 (4.0 equiv),
CH3CN, reflux; 76%; (iii) NBS (1.1 equiv), CHCl3, 20 ꢂC; (iv) [Et2NH2]-
[TRISPHAT] (1.2 equiv), chromatography (basic Al2O3, CH2Cl2) (two
steps), 86–88%.
To the best of our knowledge, for these dinaphthylazepi-
nium systems, with the exception of (ꢀ)-isopinocamphenyl-
amine which leads to less selective catalysts than those
derived from L-(+)-acetonamine,13 no other chiral exocy-
clic appendages have been reported to date. In view of
our results with 1i and 2i, it was debatable whether binaph-
thyl iminium ions 7i and 8i derived from 3,3-dimethyl-
butan-2-amine 5 (Fig. 3) would display similar or better
levels of selectivity to that of salts 3i and 4i and whether
the biaryl core would still predominate in the stereocontrol.
Herein, we report that tertiary amines 1a, 7a, and 8a, and
iminium cations 7i and 8i behave as efficient catalysts for
the enantioselective epoxidation of unfunctionalized alk-
enes (ee up to 87%).
2. Results and discussion
The preparation of azepine 1a and its derived iminium salt
[1i][TRISPHAT] has been previously reported.12
For the synthesis of the novel binaphthyl derivatives 7a, 8a,
7i, and 8i, a short three steps protocol was developed using
the known (Ra)-2,20-bis(bromomethyl)-1,10-binaphthyl as
the starting material and standard reactions (Scheme 1):16
(i) an alkylation with (S)-5 or (R)-5 to afford diastereo-
meric amines 7a and 8a (72% and 76% respectively); (ii)
subsequent eliminations with N-bromosuccinimide to form
the iminium salts; and (iii) ion pair metatheses with an
ammonium TRISPHAT salt to afford the final products
[7i][TRISPHAT] and [8i][TRISPHAT] (86% and 88%
respectively, two steps).17
TT
TT
Me
Me
N
N
(
Ra,R)-[8i][TT]
(
Ra,S)-[7i][TT]
Figure 3. Binaphthyl iminium salts [7i][TT] and [8i][TT] derived from (S)-5
and (R)-5, respectively, TT = TRISPHAT.
Furthermore and maybe more importantly, as we have re-
cently demonstrated that azepine precursors to iminium
ions 2i, 3i, and 4i are essentially as effective catalysts for
the enantioselective epoxidation of prochiral olefins as their
unsaturated derivatives,16 we wondered whether azepines
1a (Fig. 4), 7a and 8a (Scheme 1) would behave similarly
and also display effective enantioselective oxidation
abilities.
One set of epoxidation conditions (CH2Cl2/NaHCO3/
18-crown-6/H2O) and five different prochiral di- and
tri-substituted unfunctionalized alkenes 9–13 (Fig. 5) were
selected for the study. The results are reported in Tables 1
and 2 for biphenyl 1a and 1i and binaphthyls 7a, 8a, 7i and
8i catalysts, respectively.
Significantly, amine 1a behaves as an effective catalyst
essentially performing as well as iminium 1i in terms of
conversions; enantiomeric excesses were however globally
lower with the azepine moiety. Ee values up to 70% and
80% were nevertheless obtained with olefin 10 as substrate
and catalysts 1a and [1i][TRISPHAT], respectively. With
the exception of alkene 13, nonracemic epoxides of
Me
N
(S)-1a
Figure 4. Azepine precursor 1a to azepinium catalyst 1i.

2336
J. Vachon et al. / Tetrahedron: Asymmetry 17 (2006) 2334–2338
This general lack of ‘matched’/‘mismatched’ distinction, as
far as enantiomeric excesses are concerned, does not apply
to conversions. Catalyst 7i performed better than 8i. Amine
7a also catalyzed the reaction better than 8a (e.g., olefin 10,
7a: 100% vs 8a: 44%). As such, the ‘matched’ catalysts in
terms of selectivity (ee values) are ‘mismatched’ in terms
of conversions.
Me
9
12
13
10
11
Comparing the selectivity of the homologous amine and
iminium salts—that is, 7a with 7i, and 8a with 8i—it can
be seen that the amines and iminium salts induce the same
sense of stereoselective induction into the nonracemic
epoxides; the iminium cations leading to (slightly) better
enantiomeric excesses, in particular in the case of olefin
13 (e.g., ee: 7i: 30% vs 7a: 3%).
Figure 5. Prochiral di- and tri-substituted alkenes.
analogous absolute configurations were isolated from the
reactions with 1a and [1i][TRISPHAT]; the result with
trans-stilbene that sees an inversion in the sense of induc-
tion is, at the moment, unexplained.
As mentioned, olefins 9–13 were also treated with substoi-
chiometric amounts (5 mol %) of 7a, 8a, [7i][TRISPHAT]
and [8i][TRISPHAT]. The results are reported in Table 2;
all four derivatives behaved as catalysts. Careful analysis
of the data reveals a number of subtleties but some general
trends can be found.
3. Conclusion
Commercially available (S)- and (R)-3,3-dimethylbutan-2-
amine 5 lead, in only two or three steps, to effective amine
and iminium catalysts for the enantioselective epoxidation
of prochiral unfunctionalized olefins. Although the exocy-
clic auxiliary is not the predominant force for stereocontrol
of the reaction in the diastereomeric series, it has, unlike
(ꢀ)-isopinocamphenylamine,13 no detrimental influence
on the enantioselectivity. It promotes, under biphasic
CH2Cl2/water conditions, even better ee values than L-ace-
tonamine derived catalysts (e.g., olefin 10, ee: 8a: 86% vs
3a: 78% and 8i: 87% vs 3i: 69%).16
If one compares the selectivity of the diastereomeric cata-
lysts together—that is, 7a with 8a, and 7i with 8i—one
generally observes analogous levels of stereoinduction in
the (Ra,S) and (Ra,R) series with, to the exception of ole-
fin 11, slightly better ee with the (Ra,R)-configurated cat-
alysts 8a and 8i. An identical sense of induction was
obtained for the nonracemic epoxides in all examples.
This indicates that the binaphthyl framework is
(again13,16) a more effective chiral auxiliary than 3,3-
dimethylbutan-2-amine, since the configuration of the
epoxides does not change with opposite absolute configu-
ration of the chiral appendage.
It is also noteworthy that the amines and iminium ions lead
to such similar enantiomeric excess values. It is, therefore,
reasonable to consider a single mechanistic pathway for the
two processes.18 Investigations are currently underway to
Table 1. Enantioselective epoxidation of olefins 9–13 using azepine 1a and iminium salt [1i][TRISPHAT] as catalystsa,b
Alkene
Amine 1a
Iminium salt [1i][TRISPHAT]
Conv. (%)
ee (%)
Conf.
Conv. (%)
ee (%)
Conf.
9
58
100
60
74
61
39
70
15
22
22
(ꢀ)-(S,S)
(+)-(1R,2S)
(+)-(S)
68
100
61
75
64
66
80
31
46
17
(ꢀ)-(S,S)
(+)-(1R,2S)
(+)-(S)
10
11
12
13
(ꢀ)-(S,S)
(ꢀ)-(S,S)
(+)-(R,R)
(ꢀ)-(S,S)
a 5 mol % of catalyst, 2.5 mol % 18-C-6, 1.1 equiv Oxoneꢁ, 4.0 equiv NaHCO3, CH2Cl2/H2O (3:2), 2 h, 0 ꢂC. Average of at least two runs.
b The enantiomeric excesses were determined by CSP-GC (9, Chiraldex Hydrodex b-3P) or CSP-HPLC (10–13, CHIRALPAKꢁ-IB, 0.5 ml minꢀ1, hexane–
i-PrOH 95:5, k 230 nm); the conversions using an internal standard (naphthalene).
Table 2. Enantioselective epoxidation of olefins 9–13 using azepines 7a and 8a and iminium salts [7i][TRISPHAT] and [8i][TRISPHAT] as catalystsa,b
Alkene
Amines
Iminium salts
7a
8a
Conv. (%) ee (%) Conf.
[7i][TRISPHAT]
[8i][TRISPHAT]
Conv. (%) ee (%) Conf.
Conv. (%) ee (%) Conf.
Conv. (%) ee (%) Conf.
9
70
100
56
70
87
74
81
37
49
3
(ꢀ)-(S,S)
43
86
86
26
59
14
(ꢀ)-(S,S)
67
84
86
38
61
30
(ꢀ)-(S,S)
48
86
87
29
61
30
(ꢀ)-(S,S)
(+)-(1R,2S)
(+)-(S)
10
11
12
13
(+)-(1R,2S) 44
(+)-(1R,2S) 85
(+)-(1R,2S) 61
(+)-(S)
50
23
28
(+)-(S)
82
75
98
(+)-(S)
62
54
75
(ꢀ)-(S,S)
(ꢀ)-(S,S)
(ꢀ)-(S,S)
(ꢀ)-(S,S)
(ꢀ)-(S,S)
(ꢀ)-(S,S)
(ꢀ)-(S,S)
(ꢀ)-(S,S)
a 5 mol % of catalyst, 2.5 mol % 18-C-6, 1.1 equiv Oxoneꢁ, 4.0 equiv NaHCO3, CH2Cl2/H2O (3:2), 2 h, 0 ꢂC. Average of at least two runs.
b The enantiomeric excesses were determined by CSP-GC (9, Chiraldex Hydrodex b-3P) or CSP-HPLC (10–13, CHIRALPAKꢁ-IB, 0.5 ml minꢀ1, hexane–
i-PrOH 95:5, k 230 nm); the conversions using an internal standard (naphthalene).

J. Vachon et al. / Tetrahedron: Asymmetry 17 (2006) 2334–2338
2337
help understand the mechanism of the catalytic process
with these particular tertiary azepines and azepinium salts.
tography (SiO2, CH2Cl2) to yield the desired compound as
a yellow solid (185 mg, 72%).
20
Mp 174 ꢂC; ½aꢁD ¼ ꢀ272:4 (c 0.10, MeOH); IR (neat) 3054,
4. Experimental
2968, 2858, 2795, 1689, 1595, 1507, 1459, 1268, 1143,
1
1114 cmꢀ1; H NMR (400 MHz, CDCl3): d 7.94 (2d, 4H,
NMR spectra were recorded on Bruker AMX-400 at room
temperature, unless otherwise stated. H NMR: chemical
J = 8.1 Hz), 7.58 (d, 2H, J = 8.3 Hz), 7.46–7.41 (m, 4H),
7.26–7.22 (m, 2H), 3.73 (d, 2H, J = 12.4 Hz), 3.53 (d, 2H,
J = 12.4 Hz), 2.51 (q, 1H, J = 7.1 Hz), 1.13 (d, 3H,
J = 7.1 Hz), 0.97 (s, 9H); 13C NMR (100 MHz, CDCl3):
d 135.3 (CIV), 134.9 (CIV), 133.0 (CIV), 131.5 (CIV), 128.7
(CH), 128.6 (CH), 128.4 (CH), 127.8 (CH), 125.7 (CH),
125.4 (CH), 68.1 (CH), 54.3 (CH2), 36.9 (CIV), 27.3
(CH3), 12.3 (CH3); MS-ES (+) m/z (rel intensity) 479.5
(50), 412.5 (60), 396.3 (80), 379.3 (100, M), 294.1 (95,
MꢀC6H13), 279.1 (100), 266.1 (97), 252.3 (75); HRMS
(ESI) calcd for C28H30N [M+H]+ 380.2372, found
380.2367.
1
shifts are given in ppm relative to Me4Si with the solvent
resonance used as the internal standard. 31P NMR
(162 MHz): chemical shifts are reported in ppm relative
to H3PO4. 13C NMR (100 MHz): chemical shifts are given
in ppm relative to Me4Si, with the solvent resonance used
as the internal standard (CDCl3 d 77.0 ppm, DMSO-d6 d
39.5 ppm, CD2Cl2 d 53.8). IR spectra were recorded with
a Perkin–Elmer 1650 FT-IR spectrometer using a diamond
ATR Golden Gate sampling. Melting points (Mp) were
measured in open capillary tubes on a Stuart Scientific
SMP3 melting point apparatus and are uncorrected. Elec-
trospray mass spectra (ES-MS) were obtained on a Finni-
gan SSQ 7000 at the Department of Mass Spectroscopy
of the University of Geneva. Optical rotations were mea-
sured on a JASCO P-1030 polarimeter in a thermostated
4.3. (ꢀ)-(Ra)-4,5-Dihydro-3H-4-[(R)-3,3-dimethylbutan-2-
yl]dinaphth[2,1-c;10,20-e]azepine (Ra,R)-8a
Prepared in an analogous fashion to 7a with (R)-5
(20 ꢂC) 10.0 cm long microcell with high pressure lamps
(82.2 mg) to afford 8a as a yellow solid (195 mg, 76%).
20
20
of sodium or mercury and are reported as follows: ½aꢁk (c
Mp 193 ꢂC; ½aꢁD ¼ ꢀ255:8 (c 0.10, MeOH); IR (neat)
1
(g/100 ml), solvent). Chiral stationary phase (CSP) HPLC
analyses were performed on an Agilent 1100 apparatus
(binary pump, autosampler, column thermostat and diode
array detector) and a DAICEL CHIRALPAKꢁ-IB column
(25 · 4.6 cm). CSP GC analysis was performed on a Hew-
lett–Packard 6890 GC chromatograph using a Hydrodex-b
column (25 m · 0.25 mm, H2, 40 psi). Retention times (tR)
are given in minutes (min).
3052, 2957, 2866, 1592, 1457, 1377, 1357, 1109 cmꢀ1; H
NMR (400 MHz, CDCl3): d 7.94 (d, 4H, J = 8.1 Hz),
7.55 (d, 2H, J = 8.4 Hz), 7.49 (d, 2H, J = 8.6 Hz), 7.45
(d, 2H, J = 7.0 Hz), 7.26 (m, 2H), 3.58 (d, 2H,
J = 12.1 Hz), 3.52 (d, 2H, J = 12.4 Hz), 2.81 (q, 1H,
J = 7.1 Hz), 0.97 (s, 9H), 0.84 (d, 3H, J = 7.1 Hz); 13C
NMR (100 MHz, CDCl3): d 136.0 (CIV), 134.6 (CIV),
133.0 (CIV), 131.3 (CIV), 128.6 (CH), 128.3 (CH), 127.6
(CH), 127.5 (CH), 125.6 (CH), 125.2 (CH), 69.7 (CH),
53.4 (CH2), 37.1 (CIV), 27.3 (CH3), 11.7 (CH3); MS-ES
(+) m/z (rel intensity) 394.3 (75), 379.3 (97, M), 294.3
(100, MꢀC6H13), 267.3 (95), 252.3 (20); HRMS (ESI) calcd
for C28H30N [M+H]+ 380.2372, found 380.2337.
4.1. Biphasic enantioselective epoxidation procedure
In a 10 ml flask equipped with a magnetic stirring bar,
NaHCO3 (67.0 mg, 0.80 mmol, 4.0 equiv) was added to
800 ll of water. Oxoneꢁ (132.0 mg, 0.21 mmol, 1.0 equiv)
was then added and the solution stirred for 2 min until
effervescence subsided. A solution (500 ll) of a 0.4 mol/l
of the alkene (0.20 mmol, 1.0 equiv) and naphthalene
(0.20 mmol, 1.0 equiv, internal reference) in CH2Cl2 was
added and the resulting biphasic mixture cooled to 0 ꢂC
with a cryostatic bath. The catalyst (10.0 lmol, 5 mol %)
in CH2Cl2 (500 ll) was added, followed by a solution of
18-crown-6 (1.0 mg, 5.0 lmol, 2.5 mol %) in CH2Cl2
(200 ll). The reaction mixture was then stirred at room
temperature for 2 h.
4.4. (ꢀ)-(Ra)-[(S)-3,3-Dimethylbutan-2-yl]-3H-4-azapinium-
cyclohepta[2,1-a;3,4-a0]dinaphthalene (rac)-tris(tetrachloro-
benzenediolato)phosphate(V) [(Ra,S)-7i][rac-TRISPHAT]
To a solution of (Ra,S)-7a (115 mg, 0.303 mmol) in CHCl3
(2.0 ml) was added NBS (59.3 mg, 0.333 mmol) as a solid.
After 20 min of stirring at 20 ꢂC (till complete consumption
of the starting material as monitored by TLC, SiO2, and
CH2Cl2), was added a solution of [Et2NH2][rac-TRIS-
PHAT] (296.0 mg, 0.364 mmol) in acetone (2.0 ml). After
2 min stirring, the mixture was evaporated to dryness.
The desired salt was isolated after column chromatography
(SiO2, CH2Cl2) as an intense yellow solid (300 mg, 86%).
4.2. (ꢀ)-(Ra)-4,5-Dihydro-3H-4-[(S)-3,3-dimethylbutan-2-
yl]dinaphth[2,1-c;10,20-e]azepine or (Ra,S)-7a
20
In a 25 ml round bottomed flask containing a solution of
(S)-3,3-dimethylbutan-2-amine (82.2 mg, 0.812 mmol) in
acetonitrile (10 ml) was added (Ra)-2-(bromomethyl)-1-(2-
Rf = 0.70 (CH2Cl2/EtOAc 9:1). Mp 251 ꢂC; ½aꢁD ¼ ꢀ207:4
(c 0.10, MeOH); IR (neat) 2959, 1611, 1590, 1548, 1445,
1388, 1302, 1235, 970, 818 cmꢀ1 1H NMR (400 MHz,
;
(bromomethyl)naphthalen-1-yl)naphthalene
(298.0 mg,
CDCl3): d 8.98 (s, 1H), 8.13 (d, 1H, J = 8.3 Hz), 8.01 (d,
1H, J = 8.3 Hz), 7.95 (m, 3H), 7.74 (t, 1H, J = 8.1 Hz),
7.59 (d, 1H, J = 8.3 Hz), 7.56 (t, 1H, J = 7.8 Hz), 7.50
(d, 1H, J = 8.6 Hz), 7.40 (t, 1H, J = 8.3 Hz), 7.29 (d,
1H, J = 8.6 Hz), 7.07 (d, 1H, J = 8.8 Hz), 5.02 (d, 1H,
J = 13.1 Hz), 4.56 (d, 1H, J = 12.6 Hz), 4.15 (q, 1H,
0.677 mmol) and potassium carbonate (374.3 mg, 2.708
mmol). The mixture was heated at reflux (80 ꢂC) for circa
3 h (till the complete consumption of the starting material
as monitored by TLC, SiO2, and CH2Cl2) and concen-
trated in vacuo. The solid was directly purified by chroma-

2338
J. Vachon et al. / Tetrahedron: Asymmetry 17 (2006) 2334–2338
J = 6.8 Hz), 1.71 (d, 3H, J = 6.6 Hz), 1.09 (s, 9H); 13C
NMR (100 MHz, CDCl3): d 168.8 (N@CH), 142.7 (CIV),
142.2 (CIV, TT, J = 6.4 Hz), 142.1 (CIV, TT, J = 5.5 Hz),
135.9 (CIV), 134.2 (CIV), 134.1 (CIV), 132.3 (CH), 132.1
(CIV), 132.0 (CIV), 131.7 (CIV), 130.1 (CH), 129.7 (CH),
129.0 (CH), 128.9 (CH), 128.4 (CH), 128.1 (CH), 127.9
(CH), 127.5 (CH), 126.0 (CH), 125.6 (CIV), 125.3 (CH),
122.9 (CIV, TT), 122.8 (CIV, TT), 114.2 (CIV, TT,
J = 7.4 Hz), 114.0 (CIV, TT, J = 7.4 Hz), 79.7 (CH), 36.4
(CIV), 29.9 (CH2), 27.3 (CH3), 14.2 (CH3); 31P NMR
(162 MHz, CDCl3): d ꢀ80.70, ꢀ80.75; MS-ES (+) m/z
(rel intensity) 378.3 (100, M+), 294.3 (70, MꢀC6H13),
267.5 (80). MS-ES (ꢀ) m/z (rel intensity) 768.3 (100, TRIS-
PHAT); HRMS (ESI-positive) calcd for C28H28N [M]+
378.2216, found 380.2227 and (ESI-negative) calcd for
C18Cl12O6P [M]ꢀ 764.5666, found 764.5758.
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Lusinchi, X.; Hanquet, G. Tetrahedron 1997, 53, 13727–
13738.
6. Bohe, L.; Hanquet, G.; Lusinchi, M.; Lusinchi, X. Tetra-
hedron Lett. 1993, 34, 7271–7274.
7. For cyclic iminium catalysts, see: Aggarwal, V. K.; Wang, M.
F. Chem. Commun. 1996, 191–192; Page, P. C. B.; Rassias, G.
A.; Bethell, D.; Schilling, M. B. J. Org. Chem. 1998, 63, 2774–
2777; Page, P. C. B.; Rassias, G. A.; Barros, D.; Bethell, D.;
Schilling, M. B. J. Chem. Soc., Perkin Trans. 1 2000, 3325–
3334; Page, P. C. B.; Rassias, G. A.; Barros, D.; Ardakani,
A.; Buckley, B.; Bethell, D.; Smith, T. A. D.; Slawin, A. M. Z.
J. Org. Chem. 2001, 66, 6926–6931; Page, P. C. B.; Barros, D.;
Buckley, B. R.; Ardakani, A.; Marples, B. A. J. Org. Chem.
2004, 69, 3595–3597; Page, P. C. B.; Buckley, B. R.; Heaney,
H.; Blacker, A. J. Org. Lett. 2005, 7, 375–377; Page, P. C. B.;
Buckley, B. R.; Rassias, G. A.; Blacker, A. J. Eur. J. Org.
Chem. 2006, 803–813; Page, P. C. B.; Buckley, B. R.; Barros,
D.; Blacker, A. J.; Heaney, H.; Marples, B. A. Tetrahedron
2006, 62, 6607–6613.
8. For acyclic iminium catalysts, see: Armstrong, A.; Ahmed,
G.; Garnett, I.; Goacolou, K.; Wailes, J. S. Tetrahedron 1999,
55, 2341–2352; Minakata, S.; Takemiya, A.; Nakamura, K.;
Ryu, I.; Komatsu, M. Synlett 2000, 1810–1812; Wong, M.-K.;
Ho, L.-M.; Zheng, Y.-S.; Ho, C.-Y.; Yang, D. Org. Lett.
2001, 3, 2587–2590.
9. For mechanistic studies, see: Washington, I.; Houk, K. N. J.
Am. Chem. Soc. 2000, 122, 2948–2949; Page, P. C. B.; Barros,
D.; Buckley, B. R.; Marples, B. A. Tetrahedron: Asymmetry
2005, 16, 3488–3491.
4.5. (ꢀ)-(Ra)-[(R)-3,3-Dimethylbutan-2-yl]-3H-4-azapinium-
cyclohepta[2,1-a;3,4-a0]dinaphthalene (rac)-tris(tetrachloro-
benzenediolato)phosphate(V) [(Ra,R)-8i][rac-TRISPHAT]
Prepared in an analogous fashion to [7i][TRISPHAT] with
(Ra,R)-8a (103 mg) to afford [8i][TRISPHAT] as an intense
yellow solid (275 mg, 88%). Rf = 0.76 (CH2Cl2). Mp
20
220 ꢂC; ½aꢁD ¼ ꢀ264:3 (c 0.10, MeOH); IR (neat) 3052,
1
2957, 2866, 1592, 1457, 1377, 1357, 1109 cmꢀ1; H NMR
(400 MHz, CDCl3):
d 9.35 (s, 1H), 8.14 (d, 1H,
J = 8.3 Hz), 8.00 (d, 1H, J = 8.1 Hz), 7.75–7.64 (m, 4H),
7.57 (t, 1H, J = 7.1 Hz), 7.44–7.36 (m, 2H), 7.31 (d, 1H,
J = 8.6 Hz), 7.10 (d, 1H, J = 8.8 Hz), 4.97 (d, 1H, J =
13.6 Hz), 4.66 (d, 1H, J = 13.4 Hz), 4.36 (q, 1H,
J = 6.6 Hz), 1.65 (d, 3H, J = 6.3 Hz), 1.08 (s, 9H); 13C
NMR (100 MHz, CDCl3): d 168.6 (N@CH), 142.6 (CIV),
142.1 (CIV, TT, J = 6.4 Hz), 135.8 (CIV), 134.1 (CIV),
134.0 (CIV), 132.2 (CIV), 132.0 (CH), 131.7 (CIV), 131.3
(CH), 129.6 (CH), 129.3 (CH), 129.0 (CH), 128.8 (CH),
128.2 (CH), 127.9 (CH), 127.8 (CH), 126.1 (CIV), 125.7
(CH), 123.1 (CIV, TT), 123.0 (CIV, TT), 114.2 (CIV, TT,
J = 7.4 Hz), 114.0 (CIV, TT, J = 7.4 Hz), 77.3 (CH), 36.4
(CIV), 29.9 (CH2), 27.2 (CH3), 14.4 (CH3); 31P NMR
(162 MHz, CDCl3): d ꢀ80.77, ꢀ80.81; MS-ES (+) m/z
(rel intensity) 393.3 (33), 378.1 (100, M+), 294.3 (90,
MꢀC6H13), 267.3 (85), 252.3 (20). MS-ES (ꢀ) m/z (rel
intensity) 768.3 (100, TRISPHAT); HRMS (ESI-positive)
calcd for C28H28N [M]+ 378.2216, found 380.2245 and
(ESI-negative) calcd for C18Cl12O6P [M]ꢀ 764.5666, found
764.5563.
10. Page, P. C. B.; Rassias, G. A.; Barros, D.; Ardakani, A.;
Bethell, D.; Merifield, E. Synlett 2002, 580–582.
11. Lacour, J.; Monchaud, D.; Marsol, C. Tetrahedron Lett.
2002, 43, 8257–8260.
´
12. Vachon, J.; Perollier, C.; Monchaud, D.; Marsol, C.; Ditrich,
K.; Lacour, J. J. Org. Chem. 2005, 70, 5903–5911.
13. Page, P. C. B.; Buckley Benjamin, R.; Blacker, A. J. Org.
Lett. 2004, 6, 1543–1546.
14. X isꢀ a lipophilic noncoordinating anion, for example,
BPh4 or TRISPHAT (tris(tetrachlorobenzenediolato)phos-
phate(V): Favarger, F.; Goujon-Ginglinger, C.; Monchaud,
D.; Lacour, J. J. Org. Chem. 2004, 69, 8521–8524). No major
differences are observed between the two ion pairing systems.
15. (+)-L-Acetonamine is (+)-5-amino-2,2-dimethyl-4-phenyl-
1,3-dioxane.
Acknowledgements
16. Gonc¸alves, M.-H.; Martinez, A.; Grass, S.; Page, P. C. B.;
Lacour, J. Tetrahedron Lett. 2006, 47, 5297–5301.
17. TRISPHAT is chiral. However, it was shown (see Ref. 11)
that its configuration plays no role in the enantioselective
epoxidation reaction. Racemic [Et2NH2][rac-TRISPHAT]
was used as a source of hexacoordinated phosphate anion.
18. It is, in that sense, very different from the recent studies of
Aggarwal and Yang on the epoxidation of olefins mediated
by catalytic aliphatic secondary ammonium salts: Adamo, M.
F. A.; Aggarwal, V. K.; Sage, M. A. J. Am. Chem. Soc. 2002,
124, 11223; Aggarwal, V. K.; Lopin, C.; Sandrinelli, F. J. Am.
Chem. Soc. 2003, 125, 7596–7601; Armstrong, A. Angew.
Chem., Int. Ed. 2004, 43, 1460–1462; Aggarwal, V. K.; Fang,
G. Y. Chem. Commun. 2005, 3448–3450; Ho, C. Y.; Chen, Y.
C.; Wong, M. K.; Yang, D. J. Org. Chem. 2005, 70, 898–906.
We are grateful for financial support of this work by the
University of Geneva, the Swiss National Science Founda-
tion and the State Secretariat for Research and Science.
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