Asymmetric allylation reactions of aromatic aldehydes with allyltrichlorosilane catalyzed by chiral bisformamide-type organocatalysts

Article abstract of DOI:10.1016/j.tetasy.2012.02.015

Asymmetric allylation reactions of aromatic aldehydes with allyltrichlorosilane were catalyzed by C₂-symmetrical chiral bisformamides in the presence of potassium carbonate and potassium phosphate, to afford the corresponding homoallylic alcoho

Full text of DOI:10.1016/j.tetasy.2012.02.015

Tetrahedron: Asymmetry 23 (2012) 345–349
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Tetrahedron: Asymmetry
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Asymmetric allylation reactions of aromatic aldehydes with
allyltrichlorosilane catalyzed by chiral bisformamide-type organocatalysts
Yuya Tanimura a, Kaori Ishimaru b,
⇑
a National Defence Academy of Japan, Japan
b Department of Chemistry, National Defence Academy, Hashirimizu 1-10-20, Yokosuka 239-8686, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 19 January 2012
Accepted 16 February 2012
Asymmetric allylation reactions of aromatic aldehydes with allyltrichlorosilane were catalyzed by C2-
symmetrical chiral bisformamides in the presence of potassium carbonate and potassium phosphate,
to afford the corresponding homoallylic alcohols in excellent yields with up to 83% ee.
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
72 h using bisformamide 1a in the presence of additives (Table 1).
Fortunately, the catalytic reaction proceeded in the presence of 1a
The asymmetric allylation reaction of aldehydes is one of the
most powerful and important synthetic approaches for the con-
struction of chiral organic compounds.1 The reactions utilizing Le-
wis base catalysts via the nucleophilic activation of allylsilanes
have now evolved into an attractive and environmentally benign
methodology.2 Although a great deal of effort has been devoted
toward the development of Lewis base catalysts, such as forma-
mides,3 phosphoramides,4 bisphosphoramides,5 sulfoxides,6
bis-sulfoxides,7 N-oxides,8 di-N-oxides,9 tri-N-oxides,10 and bis-
phosphine oxides,11 the catalytic reaction with chiral bisforma-
(40 mol %) and cesium carbonate to give the homoallylic alcohol in
Table 1
Asymmetric allylation reaction of benzaldehyde using Lewis base 1a in the presence
of additivesa
Bn
N
CHO
CHO
N
mides has not yet been reported. In the case of
a
Bn
monoformamide-type Lewis base, a recent publication has shown
that strong electron donors such as HMPA are necessary for the
catalytic reaction.3 We suspected that the bidentate coordination
of a bisformamide to a silicon atom would enhance the reactivity
of an allylsilane reagent. Recently we have reported the novel chi-
ral bisformamide-promoted allylation (5 equiv to aldehyde) with-
out strong electron donors to afford the corresponding
homoallylic alcohols (up to 66% ee).12 We next envisioned that
the catalytic reactions would proceed even with weak bases as
additives due to the bidentate coordination of the bisformamides.
Herein we report the first chiral bisformamide-catalyzed asym-
metric allylation reaction in the presence of additives.
OH
1a (0.4 equiv)
additive
SiCl3
Ph
+
PhCHO
CH2Cl2, -78 oC, 72 h
2a
(R)-
Entry
Additive (equiv to aldehyde)
Yieldb (%)
eec (%)
1d
2
3
4
5
6
7
8
9
—
80
82
49
58
50
48
34
60
49
1
54
55
70
0
Cs2CO3 (2)
Li2CO3 (8)
Na2CO3 (8)
K2CO3 (8)
KHCO3 (8)
KSbF6 (8)
KBPh4 (1.2)
KBr (8)
15
Quant
85
12
11
38
24
2. Results and discussion
10
11
12
K3PO4 (8)
HMPA (8)
K3PO4 (4) + K2CO3 (4)
Quant
68
67
The chiral bisformamide 1a was prepared in three steps from
commercially available (1R,2R)-1,2-cyclohexanediamine.11 In our
initial study, the allylation reaction of benzaldehyde with allyltri-
chlorosilane was carried out in dichloromethane at ꢀ78 °C for
a
All reactions were carried out with PhCHO (2 mmol) and allyltrichlorosilane
(6 equiv to the aldehyde) in CH2Cl2 (2 mL) using 1a (0.4 equiv to the aldehyde) in
the presence of an additive.
b
Isolated yields after column chromatography.
Determined by Daicel Chiralcel OD (n-hexane/i-PrOH = 19:1). The major enan-
c
⇑
Corresponding author. Tel.: +81 46 841 3810; fax: +81 46 844 5901.
E-mail address: kaoriisi@nda.ac.jp (K. Ishimaru).
tiomer was (R).
d
5 equiv of 1a were used.12
0957-4166/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2012.02.015

346
Y. Tanimura, K. Ishimaru / Tetrahedron: Asymmetry 23 (2012) 345–349
82% yield (50% ee, entry 2). In order to improve the yields and
enantioselectivities, various carbonates were utilized in the reac-
tion (entries 3–6). The use of potassium carbonate gave the prod-
Under the optimal reaction conditions, the bisformamide 1e
was used in the allylations of various aromatic aldehydes in the
presence of potassium carbonate and potassium phosphate (Ta-
ble 3). The reaction of benzaldehyde gave the corresponding homo-
allylic alcohol 2a in 80% yield and 77% ee (entry 1). The highest
enantioselectivity was observed with o-tolualdehyde (83% ee, en-
try 2). m- and p-tolualdehydes and 1-naphthaldehyde were also re-
acted to give the corresponding products 2c (61% ee), 2d (67% ee)
and 2e (76% ee), respectively (entries 3–5).
uct in
a
quantitative yield without decreasing the
enantioselectivity (entry 5) compared to a reaction with no addi-
tives (entry 1). Allylations with other potassium salts such as
potassium hexafluoroantimonate, potassium tetraphenylborate,
and potassium bromide were also explored, however, the yields
were low (entries 7–9). It was found that potassium phosphate
was effective for obtaining higher enantioselectivities but that
decomposition products were also detected (70% ee, entry 10). Un-
like in the case of monoformamide,3 HMPA dramatically decreased
the enantioselectivity (entry 11) presumably because of the strong
coordination of HMPA to the silicon atom. After some experiments,
the best result was obtained in the presence of potassium carbon-
ate and potassium phosphate (67% ee and 68% yield, entry 12). Car-
rying out the reaction at ꢀ40 °C gave 55% ee of the product in 40%
yield with decomposed products. The role of potassium carbonate
and potassium phosphate remains unclear, however the additives
might trap a small amount of H+ or return the bisformamide to
the catalytic cycle effectively.
We next examined reactions with various chiral cyclohexanedi-
amine derivatives. In our previous work, we have reported that the
chiral bisformamides with N,N0-benzyl groups were effective in
obtaining the product with good enantioselectivity.12 We thus pre-
pared bisformamides 1b–j and used them for the reaction in the
presence of potassium carbonate (Table 2). The bisformamide 1b
with a 3-methylbenzyl group gave 2a in quantitative yield with
56% ee (entry 1). The use of bisformamides 1c–d with 2,3- and
2,4,5-substituted benzyl groups gave products in low enantioselec-
tivities and yields (entries 2 and 3). However, the bisformamides
1e–g with bulky substituents at the ortho-position on the aromatic
ring gave higher enantioselectivities (entries 4–6). The best result
was obtained with bisformamide 1e (76% ee, entry 5). Attempts
to use the bisformamides 1h–j gave low yields of the products (en-
tries 7–9).
Table 3
Asymmetric allylation reaction of various aromatic aldehydesa
1e
(0.4 equiv)
OH
K2CO3 (4 equiv)
K3PO4 (4 equiv)
O
SiCl3
+
R
CH2Cl2, -60 oC, 72 h
R
H
(R)
Entry
R
Product
Yieldb (%)
eec (%)
1
2
3
4
5
Phenyl
o-Tolyl
m-Tolyl
p-Tolyl
1-Naphthyl
2a
2b
2c
2d
2e
80
64
57
69
60
77
83d
61
67
76
a
All reactions were carried out with the aldehyde (2 mmol) and allyltrichloros-
ilane (6 equiv to the aldehyde) in CH2Cl2 (2 mL) using 1e (0.4 equiv to the aldehyde)
in the presence of K2CO3 (4 equiv to aldehyde) and K3PO4 (4 equiv to the aldehyde).
b
Isolated yields after column chromatography.
Determined by Daicel Chiralcel OD. The major enantiomer was (R).
Determined by chiralpak AD-H.
c
d
In order to examine the effect of the two formyl groups on the
enantioselectivities, we prepared monoformamide 1k (Scheme 1)
and conducted the reaction under the same conditions as in Table 1,
entry 5. The enantioselectivity using 1k was lower (36% ee) than
that with bisformamide 1a (60% ee), suggesting that the two for-
myl groups play an important role in achieving higher
enantioselectivities.
Table 2
Bn
a
Asymmetric allylation reactions of benzaldehyde using various Lewis bases 1b–j
N
R
Me
CHO
N
N
CHO
CHO
N
Bn
OH
1k
(0.4 equiv.)
K2CO3 (8 equiv.)
R
SiCl3
OH
PhCHO
Ph
(R)-2a
yield 95%, 36% ee
+
1b-j
(0.4 equiv)
K2CO3 (8 equiv)
CH2Cl2, -78 oC, 72 h
SiCl3
Ph
(R)-
+
PhCHO
CH2Cl2, -78 oC, 72 h
2a
Scheme 1. Asymmetric allylation reaction using monoformamide 1k.
Entry
R (Lewis base)
Yieldb (%)
eec (%)
1
2
3
4
5
6
7
8
9
3-Methylbenzyl 1b
Quant
40
38
Quant
72
56
22
25
76
78
68
46
64
A plausible mechanism is shown in Scheme 2. We propose
chair-like six-membered ring transition states TS1 and TS2 in
which the two formyl groups of the Lewis base coordinate to the
silicon atom. Due to the steric repulsion between the aromatic ring
of the Lewis base and the phenyl group of benzaldehyde TS2, the
reaction would mainly proceed via TS1 to predominantly afford
the (R)-enantiomer. Two forms of the bisformamide might exist;
however the observed enantioselectivities indicate that the struc-
ture of TS1 mainly gives the (R)-isomer due to chirality transfer
from the stereogenic carbons of the cyclohexanediamine to the
nitrogen atoms. In the case of an alternative structure of TS1, the
chirality of the nitrogens might be lost, and the coordination of
the two formyl groups to the silicon atom might be difficult due
to the strained structure having two sp2 nitrogens.
2,3-Dimethylbenzyl 1c
2,4,5-Trimethylbenzyl 1d
2-Isopropylbenzyl 1e
2-sec-Butylbenzyl 1f
2-tert-Butylbenzyl 1g
2-(3,5-Dimethylphenyl)benzyl 1h
1-Naphthylmethyl 1i
89
60
32
10
9-Anthracenylmethyl 1j
ꢀ40d
a
All reactions were carried out with PhCHO (2 mmol) and allyltrichlorosilane
(6 equiv to the aldehyde) in CH2Cl2 (2 mL) using 1b–j (0.4 equiv to the aldehyde) in
the presence of K2CO3 (8 equiv to the aldehyde).
Isolated yields after column chromatography.
Determined by Daicel Chiralcel OD (n-hexane/i-PrOH = 19:1). The major enan-
tiomer was (R).
b
c
d
The major enantiomer was (S).

Y. Tanimura, K. Ishimaru / Tetrahedron: Asymmetry 23 (2012) 345–349
347
N
H
OH
N
O
Ph
Cl
2a
(R)-
H
H
H
H
Si
favored
O
O
Cl
PhCHO
1e
TS1
SiCl3
N
H
N
OH
O
Ph
Cl
H
H
H
Si
(S)-2a
O
O
unfavored
Cl
TS2
H
Scheme 2. Plausible mechanism.
idue was purified by flash column chromatography on SiO2 (n-hex-
ane/ethyl acetate = 4:1) to afford the product. Products 2a, 2b, 2c,
2d, and 2e were identified by comparison with the spectroscopic
data reported in the literature.7a,12 The enantiomeric ratios were
determined by HPLC analysis according to the literature, 2a,12
2b,12 2c,7a 2d,7a and 2e.12
3. Conclusion
In conclusion, we have found that the asymmetric allylation
reactions of various aromatic aldehydes can be smoothly catalyzed
by using the novel bisformamide 1e in the presence of potassium
carbonate and potassium phosphate. Further mechanistic studies
and applications are currently in progress.
4.3. General procedure for the synthesis of a chiral bisform-
amide
4. Experimental
4.1. General
Chiral bisformamides 1a–j were prepared as previously re-
ported.11 (1R,2R)-1,2-Cyclohexanediamine (10 mmol), aldehyde
(25 mmol), MS 4 Å (4 g) and amberlyst 15 (0.2 g) in toluene
(120 mL) were refluxed for 12 h, and the reaction mixture was
cooled to room temperature. After the mixture was filtered, the
solvent was concentrated and the residue was recrystallized from
hexane to afford the corresponding imine.
To a solution of the imine (5 mmol) in dry MeOH (30 mL) was
slowly added sodium borohydride (12 mmol) at 0 °C. After the
mixture was stirred for 20 h at room temperature, the reaction
mixture was quenched by adding 1 M hydrochloric acid (10 mL)
at 0 °C. The mixture was extracted with dichloromethane, and
the organic layers were dried over anhydrous magnesium sulfate,
filtered and concentrated. The crude product was purified by flash
column chromatography (ethyl acetate/dichloromethane = 3:1
then triethylamine) to afford the corresponding secondary
amine.
All reactions were performed in oven-dried glassware with
magnetic stirring under an argon atmosphere, unless otherwise
stated. Dichloromethane was freshly distilled from calcium hy-
dride before use. Solvents for chromatography and extraction were
purchased from commercial suppliers and used without further
purification. Flash column chromatography was performed using
silica gel 60 (230–400 mesh). 1H NMR spectra were recorded at
300 MHz (JEOL JNM-AL300 BK1) in CDCl3. Enantiomeric excess val-
ues of the homoallylic alcohols were determined by high perfor-
mance liquid chromatography (HPLC) with Daicel Chiralcel OD or
Chiralpak AD-H. Elemental analyses were performed on a Thermo
Finnigan EA 1112 Series Flash Elemental Analyzer. Optical rota-
tions were measured at the sodium D-line with a JASCO P-1020
polarimeter.
To a stirred solution of the amine (5 mmol) in dry dichloro-
methane was added acetic formic anhydride13 (12 mmol) at 0 °C.
After the mixture was stirred for 24 h at room temperature, the
solvent was evaporated and the mixture was concentrated in va-
cuo. The crude product was purified by flash column chromatogra-
phy (ethyl acetate/dichloromethane = 1:3) to afford the
corresponding Lewis base.
4.2. General procedure for the asymmetric allylation reaction
To a stirred suspension of Lewis base (1.0 mmol), potassium
carbonate (1.38 g, 10.0 mmol) and potassium phosphate (2.12 g,
10.0 mmol) in dry dichloromethane (2 mL) was added the alde-
hyde (2.5 mmol) at room temperature. The mixture was cooled
to –78 °C, and allyltrichlorosilane (2.17 mL, 15.0 mmol) was added
slowly. After the reaction mixture was stirred at –78 °C for 3 days,
the resulting mixture was filtered and quenched with 1 mL of
aqueous saturated NaHCO3. The mixture was extracted with
dichloromethane (10 mL ꢁ 3), and the organic layers were dried
over anhydrous sodium sulfate, filtered, and concentrated. The res-
4.3.1. (1R,2R)-N,N0-Bisformyl-N,N0-bis(3-methylbenzyl)-1,2-
cyclohexanediamine 1b
Colorless oil. ½a D15
ꢂ
¼ þ16:0 (c 1.0, CHCl3). 1H NMR (CDCl3, mix-
ture of rotamers)14: d 1.17–1.25 (m, 4H, –CH2–), 1.60–1.79 (m,

348
Y. Tanimura, K. Ishimaru / Tetrahedron: Asymmetry 23 (2012) 345–349
4H, –CH2–), 2.31–2.36 (m, 6H, –CH3), 3.72–3.93 (m, 1H,
–CHN(CHO)–), 4.10–4.24 (m, 2H, –N(CHO)CH2–), 4.35–4.41 (m,
2H, –N(CHO)CH2–), 4.63–4.66 (m, 1H, –CHN(CHO)–), 6.98–7.11
(m, 6H, Ph), 7.14–7.28 (m, 2H, Ph), 8.25 (s, 2H, –CHO) (8.21, s, rot-
amer) ppm. Anal. Calcd for C24H30N2O2: C, 76.16; H, 7.99; N, 7.40.
Found: C, 76.19; H, 8.07; N, 7.30.
4.3.7. (1R,2R)-N,N0-Bisformyl-N,N0-bis[2-(3,5-dimethylphenyl)-
benzyl]-1,2-cyclohexanediamine 1h
Colorless crystals. ½a D15
ꢂ
¼ þ22:9 (c 1.0, CHCl3). 1H NMR (CDCl3,
mixture of rotamers): d 0.61–0.92 (m, 4H, –CH2–), 1.11–1.25 (m,
1H, –CH2–), 1.37–1.47 (m, 3H, –CH2–), 2.33 (s, 3H, –CH3), 2.35 (s,
3H, –CH3), 2.38 (s, 3H, –CH3), 2.41 (s, 3H, –CH3), 3.80–3.85 (m,
1H, –CHN(CHO)–), 3.95–4.00 (m, 1H, –CHN(CHO)–), 4.36–4.46
(m, 2H, –N(CHO)CH2–) (4.26–4.28, m, rotamer), 4.75–4.80 (m,
2H, –N(CHO)CH2–), 6.73–7.07 (m, 7H, Ph), 7.01–7.38 (m, 7H, Ph),
8.12 (br s, 2H, –CHO) ppm. Anal. Calcd for C38H42N2O2: C, 81.68;
H, 7.58; N, 5.01. Found: C, 81.47; H, 7.59; N, 4.77.
4.3.2. (1R,2R)-N,N0-Bisformyl-N,N0-bis(2,3-dimethylbenzyl)-1,2-
cyclohexanediamine 1c
Colorless oil. ½a D15
ꢂ
¼ ꢀ63:9 (c 1.0, CHCl3). 1H NMR (CDCl3, mix-
ture of rotamers): d 0.99–1.23 (m, 4H, –CH2–), 1.65–1.90 (m, 4H,
–CH2–), 2.24–2.31 (m, 12H, –CH3), 3.93–4.15 (m, 1H,
–CHN(CHO)–), 4.25–4.38 (m, 2H, –N(CHO)CH2–) (4.03–4.06, m,
rotamer), 4.47–4.57 (m, 2H, –N(CHO)CH2–) (4.72–4.74, m, rot-
amer), 4.65–4.80 (m, 1H, –CHN(CHO)–), 6.92–7.11 (m, 6H, Ph),
8.09 (s, 1H, –CHO), 8.21 (s, 1H, –CHO) (8.21–8.31, m, rotamer)
ppm. Anal. Calcd for C26H34N2O2: C, 76.81; H, 8.43; N, 6.89. Found:
C, 76.66; H, 8.49; N, 6.90.
4.3.8. (1R,2R)-N,N0-Bisformyl-N,N0-bis(1-naphthylmethyl)-1,2-
cyclohexanediamine 1i
Colorless crystals. ½a D15
ꢂ
¼ ꢀ11:7 (c 1.0, CHCl3). 1H NMR (CDCl3,
mixture of rotamers): d 0.87–1.21 (m, 3H, –CH2–), 1.53–1.87 (m,
3H, –CH2–), 2.00–2.29 (m, 2H, –CH2–), 4.22–4.87 (m, 4H,
–N(CHO)CH2–
and
–CHN(CHO)–),
5.10–5.16
(m,
2H,
–N(CHO)CH2–), 7.04–8.24 (m, 14H, Ph), 8.28 (s, 2H, –CHO) (8.36,
br s, rotamer) (8.57, br s, rotamer) ppm. Anal. Calcd for
4.3.3. (1R,2R)-N,N0-Bisformyl-N,N0-bis(2,4,5-trimethylbenzyl)-
C30H30N2O2: C, 79.97; H, 6.71; N, 6.22. Found: C, 79.88; H, 6.94;
1,2-cyclohexanediamine 1d
N, 6.44.
Colorless oil. ½a D15
ꢂ
¼ ꢀ31:8 (c 1.0, CHCl3). 1H NMR (CDCl3, mix-
4.3.9. (1R,2R)-N,N0-Bis(9-anthracenylmethyl)-N,N0-bisformyl-
ture of rotamers): d 1.01–1.29 (m, 4H, –CH2–), 1.65–1.69 (m, 4H,
–CH2–), 2.17–2.28 (m, 18H, –CH3), 4.11–4.17 (m, 1H,
–CHN(CHO)–), 4.28 (d, 2H, J = 16.7 Hz, –N(CHO)CH2–), 4.39–4.48
(m, 2H, –N(CHO)CH2–), 4.69–4.72 (m, 1H, –CHN(CHO)–), 6.82–
6.98 (m, 4H, Ph), 8.12 (s, 1H, –CHO), 8.30 (s, 1H, –CHO) (8.13–
8.18, m, rotamer) ppm. Anal. Calcd for C28H38N2O2: C, 77.38; H,
8.81; N, 6.45. Found: C, 77.72; H, 8.67; N, 6.47.
1,2-cyclohexanediamine 1j
Colorless crystals. ½a D15
ꢂ
¼ ꢀ88:9 (c 1.0, CHCl3). 1H NMR (CDCl3,
mixture of rotamers): d 0.41–0.75 (m, 2H, –CH2–), 1.02–1.25 (m,
2H, –CH2–), 1.47–1.80 (m, 2H, –CH2–), 2.09–2.12 (m, 2H, –CH2–),
2.30–2.40 (m, 2H, –CHN(CHO)–), 5.23 (d, 2H, J = 13.8 Hz,
–N(CHO)CH2–), 5.31–5.35 (m, 2H, –N(CHO)CH2–), 7.24–7.65 (m,
10H, Ph), 7.94–8.05 (m, 7H, Ph), 8.17–8.20 (m, 1H, Ph), 8.48 (s,
2H, –CHO) (8.28, br s, rotamer) ppm. Anal. Calcd for C38H34N2O2:
C, 82.88; H, 6.22; N, 5.09. Found: C, 82.55; H, 6.23; N, 5.36.
4.3.4. (1R,2R)-N,N0-Bisformyl-N,N0-bis(2-isopropylbenzyl)-1,2-
cyclohexanediamine 1e
Colorless oil. ½a D15
ꢂ
¼ ꢀ63:0 (c 1.0, CHCl3). 1H NMR (CDCl3, mix-
4.3.10. (1R,2R)-N,N0-Dibenzyl-N-formyl-N0-methyl-1,2-cyclo-
hexanediamine 1k
ture of rotamers): d 0.87–1.25 (m, 16H, –CH2–, –CH(CH3)2), 1.57–
1.83 (m, 4H, –CH2–), 3.06–3.17 (m, 2H, –CH(CH3)2) (2.78–2.87, m,
rotamer) (2.94–3.03, m, rotamer), 4.10–4.14 (m, 1H, –CHN(CHO)–
), 4.34 (d, 2H, J = 16.5 Hz, –N(CHO)CH2–), 4.59 (d, 2H, J = 16.5 Hz,
–N(CHO)CH2–) (4.45, d, J = 15.8 Hz, rotamer), 4.67–4.69 (m, 1H, –
CHN(CHO)–), 7.03–7.26 (m, 8H, Ph), 8.05 (s, 1H, –CHO), 8.29 (s,
1H, –CHO) (8.21, s, rotamer) ppm. Anal. Calcd for C28H38N2O2: C,
77.38; H, 8.81; N, 6.45. Found: C, 77.61; H, 8.67; N, 6.42.
To a stirred solution of Lewis base 1a (10.51 g, 30.0 mmol) in
dry THF (200 mL) was slowly added lithium aluminum hydride
(0.86 g, 22.5 mmol) at 0 °C. The mixture was stirred for 6.5 h at
room temperature. Next, water (50 mL) and a solution of 10% aque-
ous sodium hydroxide (50 mL) were slowly added to the mixture,
after which additional water (150 mL) was added to the slurry.
After filtration through Celite, the mixture was extracted with
dichloromethane and the organic layers were dried over anhydrous
magnesium sulfate, filtered, and concentrated. The crude mixture
was purified by flash column chromatography to afford product
4.3.5. (1R,2R)-N,N0-Bisformyl-N,N0-bis(2-sec-butylbenzyl)-1,2-
cyclohexanediamine 1f
Colorless oil. ½a D15
ꢂ
¼ þ57:0 (c 1.0, CHCl3). 1H NMR (CDCl3, mix-
1l (0.91 g, 9%). Colorless oil. ½a D15
ꢂ
¼ ꢀ15:2 (c 1.0, CHCl3). 1H NMR
ture of rotamers): d 0.84–0.94 (m, 6H, -CH2CH3), 1.19–1.41 (m,
10H, -CH2CH3 and –CH2–), 1.60–1.71 (m, 6H, -CH(CH3) (C2H5)),
1.81–2.08 (m, 2H, –CH2–), 2.80–2.98 (m, 2H, –CH(CH3)(C2H5)–,
4.11–4.22 (m, 2H, –N(CHO)CH2–), 4.34–4.47 (m, 2H, –CHN(CHO)–
), 4.63–4.76 (m, 2H, –N(CHO)CH2–), 7.12–7.34 (m, 8H, Ph), 8.12
(s, 1H, –CHO), 8.38 (s, 1H, –CHO) (8.29, s, rotamer) (8.31, s, rot-
amer) ppm. Anal. Calcd for C30H42N2O2: C, 77.88; H, 9.15; N,
6.05. Found: C, 77.54; H, 9.10; N, 5.94.
(CDCl3, mixture of rotamers): d 1.07–1.33 (m, 4H, –CH2–), 1.52–
1.79 (m, 4H, –CH2–), 2.09 (s, 3H, –CH3) (2.17, s, rotamer), 2.60
(dt, 1H, J = 11.1, 3.5 Hz, –CHN(CHO)–), 3.34 (dt, 1H, J = 11.1,
3.8 Hz, –CHN(CHO)–), 3.47 (d, 1H, J = 13.2 Hz, –N(CH3)CH2–), 3.63
(d, 1H, J = 13.2 Hz, –N(CHO)CH2–) (3.71, d, J = 13.0 Hz, rotamer),
3.93 (d, 1H, J = 15.6 Hz, –N(CH3)CH2–) (4.13–4.24, m, rotamer)
(4.36–4.45, m, rotamer), 4.82 (d, 1H, J = 15.6 Hz, –N(CHO)CH2–),
7.12–7.36 (m, 10H, Ph), 8.23 (s, 1H, –CHO) (8.28, s, rotamer)
ppm. Anal. Calcd for C22H28N2O: C, 78.53; H, 8.39; N, 8.33. Found:
C, 78.55; H, 8.36; N, 8.34.
4.3.6. (1R,2R)-N,N0-Bisformyl-N,N0-bis(2-tert-butylbenzyl)-1,2-
cyclohexanediamine 1g
Colorless crystals. ½a D15
ꢂ
¼ ꢀ19:8 (c 1.0, CHCl3). 1H NMR (CDCl3,
References
mixture of rotamers): d 1.16–1.28 (m, 4H, –CH2–), 1.37–1.39 (m,
3H, –CH3), 1.42–1.44 (m, 6H, –CH3), 1.50 (s, 9H, –CH3), 1.64–1.72
(m, 4H, –CH2–), 4.51 (d, 2H, J = 16.7 Hz, –N(CHO)CH2–), 4.75–4.78
(m, 2H, –CHN(CHO)–), 4.98 (d, 2H, J = 16.7 Hz, –N(CHO)CH2–),
7.13–7.26 (m, 5H, Ph), 7.35–7.44 (m, 3H, Ph), 8.12 (s, 2H, –CHO)
ppm. Anal. Calcd for C30H42N2O2: C, 77.88; H, 9.15; N, 6.05. Found:
C, 77.83; H, 8.97; N, 6.19.
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