Amine–Polyoxometalate Acid Hybrids as Iminium-Based Catalysts
59.5, 126.1, 128.4, 129.3, 139.6 ppm. HRMS: calcd. for C19H33N3
[M]+ 303.2674; found 303.2672.
3.0 Hz, 1 H, CH), 7.46 (m, 2 H, 2 CHAr), 7.60 (m, 1 H, 1 CHAr),
8.08 (m, 2 H, 2 CHAr), 9.53 (s, 1 H, CHO) ppm. 13C NMR
(75 MHz, CDCl3, 25 °C): δ = 36.9, 40.9, 47.7, 49.1, 89.9, 127.2,
128.2, 128.5, 129.0, 132.2, 140.6, 165.0, 196.8 ppm. The enantio-
meric excess was determined by HPLC (OD-H column, 254 nm, 2-
propanol/n-hexane = 1:99 as eluent, 0.5 mL/min): tR = 17.07
(major exo product), tR = 19.43 (minor exo product), 23.01 (major
endo product), 25.62 (major endo product); 83% ee for the exo iso-
mer. The absolute configuration was (–)-(1S,2S,4S) determined by
comparison of the HPLC chromatogram with the results obtained
with Ishihara’s catalyst. All the Diels–Alder adducts are known
compounds.[14d,14e,15]
(1R,2R)-N1-[(S)-2-Amino-3-phenylpropyl]-N2-ethylcyclohexane-1,2-
diamine (CPA-7): [α]2D0 = –69.1 (c = 1.0, MeOH). 1H NMR
(300 MHz, CDCl3, 25 °C): δ = 1.09 (m, 2 H, CH2), 1.18 (t, J =
5.6 Hz, 3 H, CH3), 1.25 (m, 5 H), 1.70 (m, 4 H), 2.11 (m, 4 H),
2.48 (m, 1 H), 2.56 (m, 2 H), 2.84 (m, 3 H), 3.04 (m, 1 H), 7.18–
7.32 (m, 5 H, 5 CHAr) ppm. 13C NMR (75 MHz, CDCl3): δ = 15.8,
25.0, 25.2, 31.7, 32.1, 41.3, 42.5, 53.3, 53.4, 61.9, 62.0, 126.1, 128.4,
129.1, 139.4 ppm. HRMS: calcd. for C17H29N3 [M]+ 275.2361;
found 275.2362.
(1R,2R)-N1,N2-Bis[(S)-2-amino-3-phenylpropyl]-N1,N2-dimethylcy-
clohexane-1,2-diamine (CPA-8): [α]2D0 = +22.5 (c = 1.0, MeOH). 1H
NMR (300 MHz, CDCl3, 25 °C): δ = 1.10–1.26 (m, 6 H, CH2),
1.71–1.75 (m, 8 H, CH2), 2.16 (s, 6 H, CH3), 2.29 (m, 3 H), 2.42
(m, 5 H), 2.64 (m, 4 H), 3.11 (m, 2 H, CH), 7.17–7.30 (m, 10 H,
10 CHAr) ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 25.6, 25.7,
34.9, 42.3, 50.1, 50.4, 62.8, 65.5, 126.1, 128.4, 129.2, 139.8 ppm.
HRMS: calcd. for C16H20N2 [M]+ 408.3253; found 408.3254.
(1S,2S)-N1,N2-Bis[(S)-2-amino-3-phenylpropyl]cyclohexane-1,2-di-
amine (CPA-9): [α]2D0 = +20.7 (c = 1.0, MeOH). 1H NMR
(300 MHz, CDCl3, 25 °C): δ = 1.00 (m, 2 H), 1.22 (m, 8 H, CH2),
1.68 (m, 2 H), 2.26 (m, 4 H, NH2), 2.32 (m, 2 H), 2.52 (m, 2 H),
2.82 (m, 4 H), 3.06 (m, 2 H, CH), 7.17–7.30 (m, 10 H, 10
CHAr) ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 25.1, 32.1,
42.8, 53.4, 53.5, 62.4, 126.2, 128.4, 129.3, 139.4 ppm. HRMS:
calcd. for C24H36N4 [M]+ 380.2940; found 380.2941.
2-Formylbicyclo[2.2.1]hept-5-en-2-yl 4-Methoxybenzoate (12b):
1
Yield 63 mg, 93%; colorless oil. exo: H NMR (300 MHz, CDCl3,
25 °C): δ = 1.24 (dd, J = 13, 3.7 Hz, 1 H, CH2), 1.42 (m, 1 H,
CH2), 1.68 (dd, J = 9.2, 3.2 Hz, 1 H, CH2), 2.52 (dd, J = 13, 3.7 Hz,
1 H, CH2), 3.18 (d, J = 1.2 Hz, 1 H, CH), 3.40 (s, 1 H, CH), 3.78
(s, 3 H, OCH3), 6.14 (dd, J = 5.5, 3.0 Hz, 1 H, CH), 6.39 (dd, J =
5.5, 3.0 Hz, 1 H, CH), 6.84 (m, 2 H, 2 CHAr), 7.84 (d, J = 6.9 Hz,
2 H, 2 CHAr), 9.66 (s, 1 H, CHO) ppm. 13C NMR (75 MHz,
CDCl3, 25 °C): δ = 38.0, 42.3, 45.7, 48.7, 55.5, 91.6, 113.8, 121.5,
131.9, 132.4, 140.9, 163.9, 166.3, 198.8 ppm. HRMS: calcd. for
C15H14O3 [M]+ 272.1049; found 272.1048. endo: 1H NMR
(300 MHz, CDCl3, 25 °C): δ = 1.76 (m, 1 H, CH2), 1.96 (m, 2 H,
CH2), 2.23 (dd, J = 13.3, 3.8 Hz, 1 H, CH2), 3.03 (s, 1 H, CH),
3.28 (d, J = 1.3 Hz, 1 H, CH), 3.87 (s, 3 H, OCH3), 5.95 (dd, J =
5.6, 3.0 Hz, 1 H, CH), 6.45 (dd, J = 5.6, 3.0 Hz, 1 H, CH), 6.94
(d, J = 5.3 Hz, 2 H, 2 CHAr), 8.03 (d, J = 6.9 Hz, 2 H, 2 CHAr),
9.53 (s, 1 H, CHO) ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ =
38.3, 42.2, 49.1, 50.3, 55.5, 90.8, 113.8, 121.8, 130.3, 131.9, 141.9,
163.8, 166.1, 198.4 ppm. HRMS: calcd. for C15H14O3 [M]+
272.1049; found 272.1047.
Representative Procedure for the Synthesis of CPA–POM Hybrid
Catalyst 10: H3PW12O40 (7.68 g, 2.67 mmol) was slowly added to
a solution of CPA-10 (760 mg, 2 mmol) in THF (60 mL) and the
resulting mixture was stirred for another 1 h. After removing the
solvent under vacuum, the solid obtained was dried under vacuum
at 50 °C overnight to give catalyst 10 (8.4 g, yield Ͼ99%) as a
2-Benzylbicyclo[2.2.1]hept-5-ene-2-carbaldehyde (12c): Yield 51 mg,
1
96%; colorless oil. H NMR (300 MHz, CDCl3, 25 °C): δ = 0.99
pale-yellow powder. IR (KBr): ν = 3469, 3138, 2559, 2872, 1616,
˜
1495, 1454, 1261, 1078, 980, 956, 809, 702, 518 cm–1.
C72H120O160N12P4W48 (12665.7): calcd. C 6.83, H 0.96, N 1.33;
found C 6.90, H 0.93, N 1.24.
(dd, J = 12.1, 2.7 Hz, 1 H, CH2), 1.27 (d, J = 8.8 Hz, 1 H, CH2),
1.39 (dd, J = 6.1, 2.8 Hz, 1 H, CH2), 2.20 (dd, J = 12.1, 2.7 Hz, 1
H, CH2), 2.70 (m, 1 H, CH), 2.95 (m, 3 H, CH and PhCH2), 6.25
(m, 1 H, CH), 6.39 (m, 1 H, CH), 7.06 (m, 2 H, 2 CHAr), 7.24 (m,
3 H, 3 CHAr), 9.75 (s, 1 H, CHO) ppm. 13C NMR (75 MHz,
CDCl3): δ = 28.0, 33.1, 41.6, 42.6, 47.3, 47.5, 59.9, 126.4, 128.4,
129.4, 133.3, 137.9, 140.1, 206.1 ppm. HRMS: calcd. for C15H16O
[M]+ 212.1201; found 212.1202.
General Procedure for the Diels–Alder Reaction: CPA–POM hybrid
catalyst 10 (53 mg, 0.0125 mmol amine) was added to THF/H2O
(0.2 mL, 1:1, v/v). After stirring for 10 min, 1-formylvinyl benzoate
(44 mg, 0.25 mmol) and 1,3-cyclopentadiene (0.06 mL, 0.75 mmol)
were added. The mixture was stirred for 12 h at 4 °C. Diethyl ether
(4 mL) was then added to precipitate the catalyst. The catalyst was
washed three times with diethyl ether (4 mL) and used directly in
next run after removing the residual solvent under vacuum at
50 °C. The combined organics were concentrated and purified by
flash chromatography to afford 12a as a colorless oil (56 mg, 92%
[2-(4-Methylbenzyl)bicyclo[2.2.1]hept-5-en-2-yl]methanol: The prod-
uct was obtained as a white solid by reduction of 12d with NaBH4.
1
Yield 52 mg, 92%. H NMR (300 MHz, CDCl3, 25 °C): δ = 1.00
(dd, J = 12, 2.5 Hz, 1 H, CH2), 1.41 (m, 2 H, CH2), 1.57 (m, 1 H,
CH2), 2.32 (s, 3 H, CH3), 2.56–2.67 (m, 3 H, CH and ArCH2), 2.82
(br., 1 H, OH), 3.52 (m, 2 H, CH2), 6.30 (m, 2 H, CH), 7.07–7.24
(m, 4 H, 4 CHAr) ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ =
21.0, 35.4, 40.9, 42.6, 47.0, 47.2, 68.0, 129.0, 129.8, 135.7,
137.5 ppm. HRMS: calcd. for C16H20O [M]+ 228.1514; found
228.1516.
1
yield). The exo/endo ratio was determined by H NMR (300 MHz,
CDCl3, 25 °C): δ = 9.74 (exo), 9.53 (endo) ppm. For the exo prod-
uct: 1H NMR (300 MHz, CDCl3, 25 °C): δ = 1.34 (dd, J = 13,
3.8 Hz, 1 H, CH2), 1.47 (dd, J = 9, 2.9 Hz, 1 H, CH2), 1.74 (d, J
= 9.2 Hz, 1 H, CH2), 2.62 (dd, J = 13, 3.6 Hz, 1 H, CH), 3.00 (s,
1 H, CH2), 3.28 (d, J = 1 Hz, 1 H, CH), 6.23 (dd, J = 5.5, 1.4 Hz,
1 H, CH), 6.47 (dd, J = 5.5, 1.4 Hz, 1 H, CH), 7.43 (m, 2 H, 2
(2-Methylbicyclo[2.2.1]hept-5-en-2-yl)methanol: The product was
CHAr), 7.57 (m, 1 H, 1 CHAr), 7.97 (m, 2 H, 2 CHAr), 9.74 (s, 1 obtained as a white solid by reduction of 12e with NaBH4. Yield
H, CHO) ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 38.1, 42.3,
45.7, 48.7, 92.0, 128.5, 129.3, 129.8, 132.4, 133.5, 140.9, 166.9,
198.5 ppm. HRMS: calcd. for C15H14O3 [M]+ 242.0943; found
242.0941. For the endo product: 1H NMR (300 MHz, CDCl3,
25 °C): δ = 1.74 (m, 1 H, CH2), 1.94 (m, 2 H, CH2), 2.23 (dd, J =
13.4, 3.2 Hz, 1 H, CH), 3.05 (s, 1 H, CH2), 3.31 (d, J = 1.1 Hz, 1
H, CH), 5.95 (dd, J = 5.6, 3.0 Hz 1 H, CH), 6.46 (dd, J = 5.6,
28 mg, 80%. H NMR (300 MHz, CDCl3, 26 °C): δ = 0.78 (dd, J
= 11.7, 2.7 Hz, 1 H, CH2), 0.94 (s, 3 H, CH3), 1.36 (dd, J = 7.2,
2.4 Hz, 1 H, CH2), 1.44 (dd, J = 5.8, 2.7 Hz, 1 H, CH), 1.56 (m, 2
H, CH2), 2.57 (br., 1 H, OH), 2.79 (s, 1 H, CH), 3.59 (m, 2 H,
CH2), 6.12 (m, 2 H, CH) ppm. 13C NMR (75 MHz, CDCl3, 25 °C):
δ = 22.8, 37.3, 43.1, 47.6, 47.8, 72.3, 135.4, 136.8 ppm. HRMS:
calcd. for C9H14O [M]+ 138.1045; found 138.1044.
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Eur. J. Org. Chem. 2009, 4486–4493
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
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