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General Procedure
for the Synthesis of 4-Piperidones 5
Methyltrichlorosilane
(1.5 mmol) was added dropwise to a mixture of β-keto ester 4 (1 mmol) and bisaminol ether 3 (1.2 mmol) in dry MeCN (3 mL) then stirred
at r.t. for 20 h. The reaction was then quenched with aq sat. NaHCO3 until
basic, extracted with EtOAc (3 × 3 mL),
dried (MgSO4), and concentrated in vacuo to give the
crude product, which was purified by flash chromatography to afford
the 4-piperidones 5 in 51-90% yields.
General Procedure for the Synthesis of 4-Piperidols
6
A solution of piperidone 5 (1
mmol) in THF (4 mL) was added to a solution of NaBH4 (0.5
mmol) in THF (4 mL) and deionized H2O (4 mL). The mixture
was stirred for 30 min at 0 ˚C, then stirred for 3 h at
r.t. The reaction was quenched with 2 M NaOH and extracted with
Et2O (3 × 10 mL). The combined
organic extracts were washed with brine, dried (MgSO4),
and concentrated in vacuo to give the crude product, which was purified
by flash chromatography to afford the 4-piperidol 6.
Spectral Data for Selected ProductsEthyl
(3
R
*,5
R
*)-1-Butyl-3,5-dimethyl-4-oxopiperidine-3-carboxylate
(5e)
¹H NMR (300 MHz, CDCl3): δ = 0.90
(3 H, t, J = 7.2
Hz, NCH2CH2CH2CH
3),
1.00 (3 H, d, J = 6.5
Hz, 5-CH3), 1.20 (3 H, s, 3-CH3), 1.23 (3
H, t, J = 6.0
Hz, OCH2CH
3), 1.28-1.39
(2 H, m, NCH2CH2CH
2CH3),
1.41-1.51 (2 H, m, NCH2CH
2CH2CH3),
1.95 (1 H, d, J = 11.5
Hz, 2A-H), 1.97 (1 H, dd, J = 10.9,
10.9 Hz, 6A-H), 2.26-2.47 (2 H, m, NCH
2CH2CH2CH3),
2.89-3.01 (1 H, m, 5-H), 3.03-3.10 (1 H, m, 6B-H),
3.54 (1 H, dd, J = 11.5,
3.1 Hz, 2B-H), 4.17 (2 H, q, J = 7.11
Hz, OCH
2CH3). ¹³C
NMR (75 MHz, CDCl3): δ = 11.6 (CH3,
5-CH3), 13.9 [CH3, N(CH2)3
CH3], 14.0 (CH3, OCH2
CH3), 17.9 (CH3,
3-CH3), 20.4 (CH2, NCH2CH2
CH2CH3), 29.2 (CH2,
NCH2
CH2CH2CH3),
43.2 (CH, C-5), 56.8 (CH2, NCH2CH2CH2CH3),
56.8 (q, C-3), 61.2 (CH2, OCH2CH3),
62.2 (CH2, C-6), 63.2 (CH2, C-2), 173.1 (q,
COO), 208.1 (q, C-4).
Ethyl (3
R
*,5
R
*)-1-Butyl-5-ethyl-3-methyl-4-oxopiperi-dine-3-carboxylate
(5f)
¹H NMR (400 MHz, CDCl3): δ = 0.88-0.95
(6 H, m,
5-CH2CH
3,
NCH2CH2CH2CH
3),
1.12-1.19 (1 H, m, 1 ×
5-CH2CH
3), 1.21
(3 H, s, 3-CH3), 1.24-1.29 (3 H, m, OCH2CH
3), 1.31-1.38 (2
H, m, NCH2CH2CH
2CH3),
1.45-1.53 (2 H, m, NCH2CH
2CH2CH3),
1.86 (1 H, p, J = 5.4
Hz, 1 × 5-CH
2CH3),
1.95 (1 H, dd, J = 8.6,
1.0 Hz, 2A-H), 1.98 (1 H, dd, J = 11.0,
8.5 Hz, 6A-H), 2.29-2.50 (2 H, m, NCH
2CH2CH2CH3),
2.73-2.81 (1 H, m, 5-H), 3.10-3.15 (1 H, m, 6B-H),
3.57 (1 H, dd, J = 8.6,
2.2 Hz, 2B-H), 4.15-4.25 (2 H, m, OCH
2CH3). ¹³C
NMR (100 MHz, CDCl3): δ = 11.6 (CH3,
5-CH2
CH3), 13.9
(2 × CH3, OCH2
CH3, NCH2CH2CH2
CH3), 17.8 (CH3,
3-CH3), 19.7 (CH2,
5-CH2CH3), 20.4 (CH2,
NCH2CH2
CH2CH3),
29.2 (CH2, NCH2
CH2CH2CH3),
50.1 (CH, C-5), 56.8 (q, C-3), 56.9 (CH2, NCH2CH2CH2CH3),
60.4 (CH2, C-6), 61.1 (OCH2CH3),
63.0 (CH2, C-2), 173.0 (q, COO), 207.62
(q,
C-4).
Ethyl 1-Butyl-3,5,5-trimethyl-4-oxopiperidine-3-carboxylate
(5h)
¹H NMR (300 MHz, CDCl3): δ = 0.85
(3 H, t, J = 7.2
Hz, NCH2CH2CH2CH
3),
1.03 and 1.05 [2 × 3 H, d, J = 6.7 Hz,
5-(CH3)2],
1.24 (3 H, t, J = 7.1
Hz, OCH2CH
3), 1.22-1.40
(4 H, m, NCH2CH
2CH2CH3,
NCH2CH2CH
2CH3),
1.38 (3 H, s, 3-CH3), 2.53 (2 H, t, J = 6.9
Hz, NCH
2CH2CH2CH3),
2.86 (2 H, d, J = 6.7
Hz, 6-H), 2.91 (2 H, d, J = 1.5
Hz, 2-H), 4.16 (2 H, q, J = 10.7
Hz, OCH
2CH3). ¹³C
NMR (75 MHz, CDCl3): δ = 13.9 (CH3,
NCH2CH2CH2
CH3),
14.0 (CH3, OCH2
CH3), 18.4
(CH3, 3-CH3), 19.9 [CH3,
1 × 5-(CH3)2],
20.1 (q, C-3), 20.2 (CH2, NCH2CH2
CH2CH3), 20.3 [CH3,
1 × 5-(CH3)2], 32.0
(CH2, NCH2
CH2CH2CH3),
37.0 (CH2, C-6), 50.2 (CH2, NCH2CH2CH2CH3),
54.2 (q, C-5), 54.2 (CH2, C-2), 61.1 (CH2,
OCH2CH3), 172.7
(q, COO), 212.9 (q, C-4).
Ethyl (3
R
*,4
S
*,5
R
*)-1-Butyl-3,5-dimethyl-4-hydroxy-piperidine-3-carboxylate
(6b)
¹H NMR (300 MHz, CDCl3): δ = 0.86
(3 H, t, J = 7.1
Hz, NCH2CH2CH2CH
3),
0.97 (3 H, d, J = 6.5
Hz, 5-CH3), 1.22-1.28 (8H, m, 3-CH3,
OCH2CH
3, NCH2CH2CH
2CH3), 1.30-1.44
(2 H, m, NCH2CH
2CH2CH3),
1.61 (1 H, d, J = 11.5
Hz, 2A-H), 1.64 (1 H, t, J = 11.1,
6A-H), 1.90-2.01 (1 H, m, 5-H), 2.08-2.31
(2 H, m, NCH
2CH2CH2CH3),
2.69 (1 H, t, J = 11.2
Hz, 4-H), 2.73-2.79 (1 H, m, 6B-H), 3.26 (1
H, dd, J = 11.5,
5.2 Hz, 2B-H), 3.36 (1 H, d, J = 11.8
Hz, OH), 4.14 (2 H, q, J = 7.1
Hz, OCH
2CH3). ¹³C
NMR (75 MHz, CDCl3): δ = 13.9 (CH3,
NCH2CH2CH2
CH3),
14.0 (CH3, OCH2
CH3), 20.4
(CH2, NCH2CH2
CH2CH3),
21.3 (CH3, 3-CH3), 29.2 (CH2, NCH2
CH2CH2CH3),
36.3 (CH, C-5), 47.9 (q, C-3), 57.4 (CH2, NCH2CH2CH2CH3),
60.4 (CH2, OCH2CH3),
61.7 (CH2, C-6), 62.1 (CH2, C-2), 81.9 (CH,
C-4), 177.4 (q, COO).
Ethyl (3
R
*,4
S
*,5
R
*)-1-Butyl-4-hydroxy-5-isopropyl-3-methylpiperidine-3-carboxylate
(6d)
¹H NMR (300 MHz, CDCl3): δ = 0.83 [3
H, d, J = 7.1
Hz, 1 × CH(CH
3)2],
0.87 (3 H, t, J = 7.2
Hz, NCH2CH2CH2CH
3), 0.88-0.97
(2 H, m, NCH2CH2CH
2CH3),
0.93 [3 H, d, J = 7.2 Hz,
1 × CH(CH
3)2],
1.25 (3 H, t, J = 7.1
Hz, OCH2CH
3), 1.26
(3 H, s, 3-CH3), 1.32-1.45 (2 H, m, NCH2CH
2CH2CH3),
1.54 (1 H, d, J = 11.5
Hz, 2A-H), 1.70 (1 H, d, J = 11.3
Hz, 6A-H), 1.79-1.88 (1 H, m, 5-H), 2.03-2.34 [3H,
m, CH(CH3)2, NCH
2CH2CH2CH3],
2.70-2.75 (1 H, m, 6B-H), 3.00 (1 H, d, J = 10.5 Hz,
4-H), 3.26 (1 H, dd, J = 12.3,
3.3 Hz, 2B-H), 3.72-3.74 (1 H, m, OH), 4.14
(2 H, qd, J = 7.1,
1.7 Hz, OCH
2CH3). ¹³C
NMR (100 MHz, CDCl3): δ = 14.0 (2 × CH3,
OCH2
CH3, NCH2CH2CH2
CH3), 16.8 [CH3,
1 × CH(CH3)2],
20.5 (CH2, NCH2CH2
CH2CH3), 20.9
(CH3, 3-CH3), 21.5 [CH3,
1 × CH(CH3)2],
25.6 [CH, CH(CH3)2],
29.2 (CH2, NCH2
CH2CH2CH3),
45.6 (CH, C-5), 47.8 (q, C-3), 54.4 (CH2, C-6), 57.8
(CH2, NCH2CH2CH2CH3),
60.4 (CH2, OCH2CH3),
61.7 (CH2,
C-2), 77.6 (CH, C-4), 177.5 (q,
COO).
Ethyl (3
R
*,4
S
*)-1-Butyl-4-hydroxy-3,5,5-trimethyl-piperidine-3-carboxylate
and Ethyl (3
R
*,4
R
*)-1-Butyl-4-hydroxy-3,5,5-trimethylpiperidine-3-carboxylate
(6e)
¹H NMR (300 MHz, CDCl3): δ (* denotes
signals from the second diastereomer) = 0.82-0.96 [18
H, m, 2 × C(CH
3)2, 2 × C(CH
3)2*,
NCH2CH2CH2CH
3,
NCH2CH2CH2CH
3*], 1.08
(3 H, s, 3-CH3*), 1.20 (3 H, s, 3-CH3),
1.23 (3 H, t, J = 7.13
Hz, OCH2CH
3), 1.24
(3 H, t, J = 6.3
Hz, OCH2CH
3*),
1.28-1.34 (2 × 2H, m, NCH2CH2CH
2CH3, NCH2CH2CH
2CH3*),
1.35-1.43 (4 H, m, NCH2CH
2CH2CH3,
NCH2CH
2CH2CH3*),
2.58-2.48 (4 H, m, NCH
2CH2CH2CH3,
NCH
2CH2CH2CH3*),
2.64 (1 H, d, J = 10.5
Hz, 6-H*), 2.78 (1 H, d, J = 12.4
Hz, 6-H), 2.97
(2 H, d, J = 9.8
Hz, 2-H*), 3.01 (2 H, d, J = 8.13
Hz, 2-H), 3.49 (1 H, d, J = 4.0
Hz, 4-H*), 3.81 (1 H, d, J = 5.5
Hz,
4-H), 4.06-4.16 (6 H, m, OCH
2CH3,
OCH
2CH3*,
OH, OH*). ¹³C NMR (75 MHz,
CDCl3): δ (* denotes signals from the
second diastereomer) = 13.8-14.1 (4 × CH3, OCH2
CH3, OCH2
CH3*, NCH2CH2CH2
CH3, NCH2CH2CH2
CH3*), 16.8 (CH3,
3-CH3*), 16.9 [CH3, 1 ×
5-(CH3)2*],
18.5 [CH3, 1 × 5-(CH3)2],
20.2 (CH3, NCH2CH2
CH2CH3*),
20.36 (CH3, 3-CH3), 21.32 [CH3, 1 × 5-(CH3)2*],
21.99 [CH3, 1 × 5-(CH3)2],
29.61 (q, C-3*), 30.91 (q, C-3), 31.78 (CH2,
NCH2
CH2CH2CH3*),
31.85 (CH2, NCH2
CH2CH2CH3),
48.74 (q, C-5*), 49.68 (CH2, NCH2CH2CH2CH3*),
49.98 (q, C-5), 50.07 (CH2, NCH2CH2CH2CH3),
56.30 (2 × CH2, C-2*,
C-6*), 56.66 (2 × CH2,
C-2, C-6), 60.46 (CH2, OCH2CH3*),
60.57 (CH2, OCH2CH3),
80.95 (CH, C-4*), 82.27 (CH, C-4), 175.91 (q, COO*),
176.32 (q, COO).
(3
S
*,4
S
*,5
R
*)-(1-Butyl-5-ethyl-4-hydroxy-3-methylpiperidin-3-yl)methanol
(7)
¹H NMR (300 MHz, CDCl3): δ = 0.84
(3 H, s, 3-CH3), 0.87 (3 H, t, J = 7.2
Hz, 5-CH2CH
3),
0.94 (3 H, d, J = 6.4
Hz, NCH2CH2CH2CH
3),
1.22-1.34 (4 H, m, 5-CH
2CH3, NCH2CH2CH
2CH3), 1.37-1.44
(2 H, m, NCH2CH
2CH2CH3),
1.57 (1 H, t, J = 11.4
Hz, 6A-H), 1.91
(1 H, dd, J = 11.9,
1.9 Hz, 2A-H), 2.20 (2 H, td, J = 14.4,
2.0 Hz, NCH
2CH2CH2CH3),
2.28-2.40 (1 H, m, 5-H), 2.53 (1 H, m, 4-H), 2.79-2.84
(2 H, m, 2B-H, 6B-H), 3.52 (1 H, br,
4-OH),
3.60 (1 H, d, J = 10.8
Hz, 1 × CH
AOH),
3.81 (1 H, dd, J = 10.8,
1.9 Hz, 1 × CH
BOH),
5.48 (1 H, s, CH2OH).
¹³C
NMR (75 MHz, CDCl3): δ = 13.9
(CH3, NCH2CH2CH2
CH3), 16.8 (CH3,
5-CH2
CH3), 20.5
(CH2, NCH2CH2
CH2CH3),
22.5 (CH3, 3-CH3), 29.1 (CH2, NCH2
CH2CH2CH3),
29.7 (CH2, 5-CH2CH3),
35.2 (CH, C-5), 39.7 (q, C-3), 57.5 (CH2, NCH2CH2CH2CH3),
60.7 (CH2, C-6), 64.7 (CH2, C-2), 68.9 (CH2,
CH2OH), 87.0 (CH, C-4).