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Enecarbamate 13
A
Schlenk tube was charged with a solution of pyrrolidine 5 (1.07 g, 2.5 mmol) in dry THF (6 mL)
under a nitrogen atmosphere. The solution was cooled at -78 ˚C
and TMEDA (0.75 mL, 5.0 mmol) and a cyclohexane solution of s-BuLi (1.4 M, 3.6 mL, 5.0 mmol) were
added. The mixture was stirred at -78 ˚C
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6.67 (d, J = 3.6
Hz, 1 H), 5.03 (m, 2 H), 3.80-3.46 (m, 2 H), 1.48 (s, 9
H), 0.91 and 0.89 (s, 9 H), 0.09 and 0.08 (s, 6 H). ¹³C
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(s), 132.4 (d), 109.8 (d), 80.4 (s), 73.6 (d), 72.5 (d), 54.6 (t),
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Enecarbamate
14
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(6 mL), extracted with Et2O (3 ¥ 10
mL), and the collected organic phases were dried over Na2SO4.
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chromatography (PE-EtOAc-concd NH3,
4:0.9:1) to afford compound 14 (0.372 g,
62%, 1:1 mixture of two rotamers in CDCl3). [α]D
²5 -167.7
(c 1.9, CHCl3). ¹H
NMR (200 MHz, CDCl3): δ = 6.78 and
6.66 (s, 1 H), 5.14 (br s, 1 H), 4.84 (ddd, J = 7.8,
3.0, 2.8 Hz, 1 H), 3.75-3.53 (m, 2 H), 2.75 (br s, 1 H),
1.43 (s, 9 H). ¹³C NMR (50 MHz, CDCl3): δ = 151.6
(s), 151.0 (s), 133.0 (d), 109.7 (d), 80.7 (s), 72.7 (d), 71.7 (d),
54.5 (t), 54.0 (t), 28.2 (q).
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For related reactions on α-alkoxy
amides, see, for example:
<A NAME="RG32210ST-30A">30a</A>
Huang PQ.
Wang SL.
Ye JL.
Ruan YP.
Huang YQ.
Zheng H.
Gao JX.
Tetrahedron
1998,
54:
12547
<A NAME="RG32210ST-30B">30b</A>
Zhou X.
Liu W.-J.
Ye J.-L.
Huang P.-Q.
Tetrahedron
2007,
63:
6346
<A NAME="RG32210ST-30C">30c</A>
Yoda H.
Shirakawa K.
Takabe K.
Chem.
Lett.
1991,
489
<A NAME="RG32210ST-30D">30d</A>
Sengoku T.
Suzuki T.
Kakimoto T.
Takahashi M.
Yoda H.
Tetrahedron
2009,
65:
2415
<A NAME="RG32210ST-31">31</A>
For cyanation of a related substrate,
see ref. 25e.
<A NAME="RG32210ST-32">32</A>
Synthesis of Pyrrolidines
22-24 - General Procedure
A Schlenk
tube was charged with a solution of pyrrolidine 21 (80
mg, 0.17 mmol) in dry CH2Cl2 (6 mL) under
a nitrogen atmosphere. The solution was cooled at -78 ˚C
and the appropriate silylated reagent (trimethylsilylcyanide (0.045
mL, 0.34 mmol), trimethylsilylazide (0.043 mL, 0.34 mmol), or allyltrimethylsilane
(0.054 mL, 0.34 mmol) and BF3˙OEt2 (0.030
mL, 0.24 mmol) were added. The mixture was left at -78 ˚C
under stirring for 1.5-2 h. The solution was quenched with
sat. Na2CO3 (1 mL) and left to warm to r.t.,
then was extracted with CH2Cl2 (3 × 3
mL), and the collected organic phases were dried over Na2SO4.
After filtration and concentration, the crude material was purified by
column chromatography (PE-Et2O, 15:1).
Compound 22: 52% yield, R
f
= 0.11,
white solid, mp 97-99 ˚C. ¹H
NMR (400 MHz, CDCl3, 2:1 mixture of two rotamers): δ = 4.55
and 4.38 (d, J = 6.8
Hz, 1 H), 4.16-4.11 (m, 2 H), 3.44 (d, J = 12.0
Hz, 1 H), 3.36 (dd, J = 11.6,
3.6 Hz, 1 H), 1.51 and 1.47 (s, 9 H), 0.95-0.92 (m, 18
H), 0.16-0.09 (m, 12 H). ¹³C
NMR (100 MHz, CDCl3): δ = 153.6 (s), 153.3
(s), 116.0 (s), 81.8 (s), 81.1 (s), 73.5 (d), 73.0 (d), 72.4 (d),
71.4 (d), 52.6 (d), 51.7 (d), 50.2 (t), 49.7 (t), 28.3 (q), 25.7
(q), 25.6 (q), 18.1 (s), -4.4 (q), -4.6 (q), -4.8
(q).
Compound 23: 56% yield, R
f
= 0.47,
colorless oil. ¹H NMR (400 MHz, CDCl3,
2:1 mixture of two rotamers): δ = 5.18 and 5.05
(d, J = 2.0
Hz, 1 H), 4.20-4.16 (m, 1 H), 3.81 (dd, J = 3.4,
2.0 Hz, 1 H), 3.50 and 3.44 (dd, J = 9.9,
6.3 Hz, 1 H), 3.36 and 3.28 (dd, J = 9.9,
7.5 Hz, 1 H), 1.52 and 1.50 (s, 9 H), 0.90 and 0.89 (s, 18 H), 0.09
(s, 12 H). ¹³C NMR (100 MHz, CDCl3): δ = 154.2
(s), 81.3 (s), 80.6 (s), 78.9 (d), 78.7 (d), 77.4 (d), 76.6 (d),
70.7 (d), 70.2 (d), 49.9 (t), 49.4 (t), 28.2 (q), 25.8 (q), 25.6
(q), 18.1 (s), 18.0 (s), -4.5 (q), -4.7 (q), -4.9
(q), -5.1 (q).
Compound 24:
77% yield, R
f
= 0.26,
colorless oil. ¹H NMR (400 MHz, CDCl3,
2:1 mixture of two rotamers): δ = 6.10-5.79
(m, 1 H), 4.98 (d, J = 16.2
Hz, 1 H), 4.92 (d, J = 9.2
Hz, 1 H), 4.08-4.04 (m, 1 H), 4.02-3.98 (m. 1
H), 3.83 and 3.68 (q, J = 5.8
Hz, 1 H), 3.52 (dd, J = 12.0,
4.8 Hz, 1 H), 3.27 and 3.20 (d, J = 12.0
Hz, 1 H), 2.74-2.35 (m, 2 H), 1.45 (s, 9 H), 0.91-0.89
(s, 18 H), 0.08-0.05 (s, 12 H). ¹³C
NMR (100 MHz, CDCl3): δ = 155.0 (s),
138.0 (d), 137.7 (d), 115.1 (t), 79.6 (s), 73.8 (d), 73.5 (d), 71.8
(d), 59.5 (d), 59.2 (d), 52.5 (t), 35.0 (t), 28.4 (q), 26.0 (q),
25.8 (q), 18.3 (s), 18.0 (s), -4.6 (q), -4.8 (q).
<A NAME="RG32210ST-33">33</A>
Ungureanu I.
Bologa C.
Chayer S.
Mann A.
Tetrahedron Lett.
1999,
40:
5315
