δ Ϫ2.0, Ϫ1.7, 12.6, 12.8, 14.8, 17.3, 17.5,17.9, 18.3, 19.6, 19.9,
28.0, 28.2, 28.2, 28.5, 40.3, 40.5, 40.9, 41.4, 46.9, 58.9, 60.5,
79.4, 127.5, 127.6, 128.5, 128.6, 131.5, 131.8, 132.7, 133.7,
133.9, 139.1, 156.3, 168.7; MS (ESϩ) 483 (MNaϩ); HRMS
C26H44N2O3SiNa: calcd. 483.3018, found 482.9908.
2952, 1740, 1691, 1368, 1306, 1151 cmϪ1; 1H NMR (d6-DMSO,
95ЊC) δ 0.42rot, 0.45 (6H, d, J = 2.5), 1.24rot, 1.34 (3H, d, J = 7.0),
1.40rot, 1.41 (9H, s), 1.79rot, 1.67 (3H, d, J = 7.0), 3.62, 3.64rot
(3H, s), 3.91, 4.08rot (1H, d, J = 16.1), 4.05, 4.17rot (1H, d,
J = 16.1), 4.10 (1H, q. J = 7.0), 6.19, 6.31rot (1H, q, J = 7.0),
7.37–7.39 (3H, m), 7.52–7.57 (2H, m); 13C NMR δ Ϫ2.9, Ϫ1.5,
14.9, 15.2, 18.2, 18.9, 28.0, 28.3, 29.8, 44.4, 49.8, 51.8, 53.6,
54.0, 80.3, 127.8, 128.9, 129.0, 133.7, 134.0, 136.2, 138.4,
139.1, 142.0, 154.8, 173.1; MS (ESϩ) 392 (MHϩ); HRMS
C21H34NO4Si: calcd. 392.2257, found 392.2291. Anal Calcd. for
C21H33NO4Si: C, 64.41; H, 8.49; N, 3.58. Found C, 64.22; H,
8.69; N, 3.59%.
(Z )-N,N-Diethyl-{Nꢀ-tert-butoxycarbonyl-Nꢀ-[2-(phenyl-
dimethylsilyl)but-2-enyl]}phenylalanine amide (8)
Prepared from 12 (R = Bn, 250 mg, 0.61 mmol) in an analogous
fashion to 7. Purified by flash-column chromatography (2 × 15
cm, eluting with 10% EtOAc–hexane) to afford 8 (230 mg, 74%)
as a pale yellow oil; IR νmax 2972, 1683, 1647, 1453, 1252, 1168
1
cmϪ1; H NMR δ 0.44 (6H, br s), 0.88–1.12 (6H, br m), 1.36
(Z )-N-tert-Butoxycarbonyl-Nꢀ-[2-(phenyldimethylsilyl)but-2-
enyl]valine methyl ester (16)
(9H, br s), 1.55 (3H, br d, J = 6.9), 2.87–2.91 (1H, br m), 3.01
(2H, dq, J = 14.2, 7.1), 3.13–3.18 (1H, br m), 3.40–3.49 (1H,
br m), 3.62 (1H, dq, J = 14.4, 7.2), 4.03 (2H, br s), 4.96–5.01 and
5.26–5.32 (1H, br m, due to rotamers), 5.82–5.87 (1H, br m),
7.17–7.25 (5H, br m), 7.34–7.36 (3H, br m), 7.53–7.61 (2H, br
m); 13C NMR δ Ϫ0.4, Ϫ0.3, 14.1, 15.8, 18.8, 29.5, 29.7, 38.3,
41.8, 43.0, 56.1, 81.0, 127.7, 129.1, 129.6, 130.2, 131.1, 133.7,
138, 135.2, 140.4, 155.6, 169.6; MS (ESϩ) 509 (MHϩ); HRMS
C30H45N2O3Si: calcd. 509.3199, found 509.3220. Anal Calcd.
for C30H44N2O3Si: C, 70.82; H, 8.72; N, 5.51. Found C, 70.81;
H, 8.82; N, 5.22%.
Alkylation of N-Boc-valine methyl ester, (250 mg, 1.08 mmol)
with 5 was performed according to general procedure A. The
crude mixture (450 mg) was purified by flash-column chroma-
tography (2 × 15 cm, eluting with 5% EtOAc–hexane) to furnish
16 (349 mg, 77%) as a colourless oil; IR νmax 2964, 2931, 1737,
1
1682, 1455, 1367, 1109 cmϪ1; H NMR δ 0.40 (3H, br s), 0.41
(3H, br m), 0.88 (3H, d, J = 6.8), 0.94 (3H, br d, J = 5.3), 1.42–
4.48 (9H, br m), 1.60–1.67 (3H, br m), 2.18–2.28 (1H, br m),
3.49–3.62 (3H, br m), 3.70–4.45 (3H, br m), 5.87–6.23 (1H, br
m), 7.34–7.35 (3H, m), 7.53–7.55 (2H, m); 13C NMR δ Ϫ2.9,
Ϫ1.5, 14.9, 15.2, 18.2, 18.9, 28.0, 28.3, 29.8, 44.4, 49.8, 51.8,
53.6, 54.0, 80.3, 127.8, 128.9, 129.0, 133.7, 134.0, 136.2, 138.4,
139.1, 142.0, 154.8, 173.1; MS (FAB) 420 (MHϩ); HRMS
C23H38NO4Si: calcd. 420.2570, found 420.2560. Anal Calcd. for
C23H37NO4Si: C, 65.83; H, 8.89; N, 3.34. Found C, 66.19; H,
8.75; N, 3.04%.
(Z )-N,N-Diethyl-{Nꢀ-tert-butoxycarbonyl-Nꢀ-[2-(phenyl-
dimethylsilyl)but-2-enyl]}phenylglycine amide (9)
Prepared from 12 (R = Ph, 300 mg, 0.76 mmol) in an analogous
fashion to 7. Purified by flash-column chromatography (2 ×
15 cm, eluting with 15% EtOAc–hexane) to afford 9 (279 mg,
74%) as a pale yellow oil; IR νmax (thin film) 2974, 1685,
1
1654, 1452, 1167 cmϪ1; H NMR δ 0.09 (3H, s), 0.19 (3H, s),
(Z )-N-tert-Butoxycarbonyl-Nꢀ-[2-(phenyldimethylsilyl)but-2-
enyl]phenylalanine methyl ester (17)
1.05 (3H, br t, J = 6.5), 1.13 (3H, br t, J = 6.7), 1.34 (3H, br d,
J = 5.3), 1.44 (9H br s), 3.12–3.39 (3H, m), 3.47–3.61 (1H,
m), 3.78 (1H, br d, J = 17.7), 4.27 (1H, br d, J = 17.9), 5.82,
(1H, br m), 5.97rot, 6.22 (1H, br s), 7.15–7.32 (10H, m);
13C NMR δ Ϫ1.7, 12.8, 13.8, 14.18, 17.2, 28.3, 28.4, 40.4, 41.7,
49.8, 59.7, 60.4, 79.5, 127.5, 128.2, 128.5, 130.1, 131.3, 133.6,
135.0, 139.1, 155.8, 169.8; MS (ESϩ) 495 (MHϩ); HRMS
C29H43N2O3Si: calcd. 495.3042, found 495.3074. Anal Calcd.
for C29H42N2O3Si: C, 70.40; H, 8.56; N, 5.66. Found C, 70.02;
H, 8.31; N, 5.34%.
Alkylation of N-Boc-phenylalanine methyl ester (505 mg, 1.81
mmol) with 5 was performed according to general procedure A.
The crude mixture (936 mg) was purified by flash-column
chromatography (2 × 15 cm, eluting with 10% EtOAc–hexane)
to give 17 (720 mg, 85%) as a colourless oil; IR νmax (thin film)
3065, 2975, 1744, 1699, 1426, 1165 cmϪ1; 1H NMR δ 0.38 (3H,
br s), 0.37 (3H, s), 1.47 (9H, br s), 1.59 (3H, br d, J = 6.9), 2.77–
3.12 (2H, br m), 3.28 (1H, br m), 3.61–6.66 (3H, br m), 3.97–
4.10 (1H, br m), 4.25–4.40 (1H, br s), 5.95–6.07 (1H, br m),
7.17–7.23 (3H, br m), 7.28–7.33 (5H, br m), 7.45–7.48 (2H, br
m); 13C NMR δ Ϫ1.9, Ϫ1.6, 18.1, 28.3, 28.6, 36.5, 51.6, 53.9,
53.9, 59.3, 80.4, 80.5, 126.5, 127.7, 128.4, 128.7, 128.8, 129.4,
129.6, 133.6, 133.9, 138.3, 139.1, 142.7, 155.1, 171.7; MS (EIϩ)
395 (MHϩ); HRMS C27H37NO4SiNa: calcd. 490.2389, found
490.2354.
(2S*,3R*)-N,N-Diethyl-2-(Nꢀ–tert-butoxycarbonylamino)-2,3-
dimethyl-4-dimethylphenylsilylpent-4-enamide (14)
Rearrangement precursor 6 (200 mg, 0.47 mmol) was subjected
to the reaction conditions of general procedure B. The crude
reaction mixture (211 mg) was purified by flash-column
chromatography (12 × 2 cm, eluting with 20% EtOAc–hexane)
to give 14 (154 mg, 77%) as a pale yellow oil in an inseparable
>20 : 1 mixture of diastereoisomers which crystallised on stand-
ing at rt; IR νmax 3421, 2977, 2952, 1737, 1711, 1454, 1368, 1112
cmϪ1; 1H NMR δ 0.44 (3H, s), 0.48 (3H, s), 0.93–0.977 (3H, br
m), 0.98 (3H, br d, J = 7.0), 0.99–1.08 (3H, br m), 1.34 (9H, s),
1.44 (3H, s), 2.75 (1H, br q, J = 7.0), 3.06–3.54 (4H, m), 4.47
(1H, br s), 5.91 (1H, s), 6.09 (1H, s), 7.37–7.41 (3H, m), 7.52–
7.55 (2H, m); 13C NMR δ Ϫ2.4, 12.4, 13.8, 17.6, 19.4, 28.3, 41.0,
41.4, 63.7, 79.2, 128.4, 129.6, 132.7, 134.1, 136.9, 150.7, 153.8,
170.8; MS (ESϩ) 433 (MHϩ); HRMS C24H41N2O3Si: calcd.
433.2886, found 433.2886.
(Z )-N-tert-Butoxycarbonyl-Nꢀ-[2-(phenyldimethylsilyl)but-2-
enyl]phenylglycine methyl ester (18)
Alkylation of N-Boc-phenylglycine methyl ester, (500 mg, 1.89
mmol) with 5 was performed according to general procedure A.
The crude reaction mixture (962 mg) was purified by flash-
column chromatography (2 × 15 cm, eluting with 5% EtOAc–
hexane) to give 18 (609 mg, 71%) as a colourless crystalline
solid, mp 116–119 ЊC; IR νmax 2978, 2933, 1737, 1714, 1455,
1
1367, 1108 cmϪ1; H NMR 0.31 (3H, br s), 0.38 (3H, br s),
1.10rot, 1.40 (9H, br m), 1.59 (3H, d, J = 7.1), 3.27–3.51 (2H, br
m), 3.56 (3H, br s), 5.04rot, 6.01 (1H, br s), 6.16–6.23 (1H, br m),
7.09–7.40 (8H, m), 7.48–7.53 (2H, m); 13C NMR δ Ϫ1.5, Ϫ0.9,
Ϫ0.3, 0.0, 15.9, 20.1, 29.0, 35.6, 40.2, 53.2, 53.4, 66.5, 66.7, 79.2,
126.6, 128.1, 128.3, 128.4, 128.9, 129.0, 129.3, 129.4, 132.9,
134.4, 134.8, 134.9, 140.6, 145.1, 145.2, 155.0, 173.9; MS (ESϩ)
476 (MNaϩ); HRMS C26H35NO4SiNa: calcd. 476.2233, found
476.2203. Anal Calcd. for C26H35NO4Si: C, 68.84; H, 7.78; N,
3.09. Found C, 68.86; H, 7.78; N, 3.07 %.
(Z )-N-tert-Butoxycarbonyl-Nꢀ-[2-(phenyldimethylsilyl)but-2-
enyl]glycine methyl ester (15)
Alkylation of N-Boc-alanine methyl ester, (0.78 g, 3.84 mmol)
with 5 was performed according to general procedure A. The
crude reaction mixture (1.60 g) was purified by flash-column
chromatography (2 × 15 cm, eluting with 7% EtOAc–hexane) to
give 15 (1.34 g, 89%) as a colourless oil; IR νmax 2978, 2933,
J. Chem. Soc., Perkin Trans. 1, 2002, 2871–2879
2877