T. J. Southwood et al. / Tetrahedron 62 (2006) 236–242
241
4.2.2. 2-((E)-2-Phenylethenyl)-1,3,2-dioxaborolane (7b).
Colourless liquid which solidified on standing, 93%; mp
50.2, 48.4, 19.6; IR nmax (cmK1) 2922, 1699; MS m/z (ESI)
284 [MCH]C(100%); HRMS m/z (ESI) found 284.1650,
C18H22NO2 requires 284.1651.
1
47–48 8C; H NMR (200 MHz, CDCl3) d 7.53–7.48 (3H,
m), 7.39–7.32 (3H, m), 6.20 (1H, d, JZ18.4 Hz), 4.29 (4H,
s); 13C NMR (50 MHz, CDCl3) d 150.2, 129.1, 128.7, 127.2
65.7 (carbon bearing boron substituent not observed); MS
m/z (EI) 173.9 [MC%] (100%); HRMS m/z (EI) found
174.0857, C10H11BO2 requires 174.0852.
4.3.5. N-Benzyl-a-(E)-phenylethenylglycine (8a). Method
A. Off white solid, 79%; 1H NMR (200 MHz, D2OC
K2CO3) d 7.35–7.11 (10H, m), 6.47 (1H, d, JZ15.9 Hz),
6.12 (1H, dd, JZ8.2, 15.9 Hz), 3.70 (1H, d, JZ8.1 Hz),
3.56 (2H, m); 13C NMR (50 MHz, D2OCK2CO3) d 171.2,
136.1, 133.3, 129.0, 128.6, 128.5, 128.4, 128.2, 128.0,
127.7, 126.9, 63.5, 49.2; data in accordance with literature
values.1
4.2.3. 4,4,5,5-Tetramethyl-2-((E)-2-phenylethenyl)-1,3,2-
dioxaborolane (7c). Colourless liquid, 93%; 1H NMR
(200 MHz, CDCl3) d 7.50–7.26 (6H, m), 6.17 (1H, d, JZ
18.4 Hz), 1.30 (12H, s); 13C NMR (50 MHz, CDCl3) d
149.6, 137.5, 128.9, 128.6, 127.1, 83.4, 24.8 (carbon bearing
boron substituent not observed); MS m/z (EI) 230 [MC%
]
4.3.6. N,N-Dibenzyl-a-(E)-phenylethenylglycine (8b).
Method B. Colourless oil, 64%; 1H NMR (200 MHz,
CDCl3) d 8.26 (1H, br s), 7.45–7.24 (15H, m), 6.70 (1H,
d, JZ16.0 Hz), 6.38 (1H, dd, JZ8.4, 16.0 Hz), 4.23 (1H, d,
JZ8.4 Hz), 4.06 (2H, d, JZ13.5 Hz), 3.78 (2H, d, JZ
13.5 Hz); 13C NMR (50 MHz, CDCl3) d 172.9, 138.1,
136.1, 136.0, 129.3, 128.9, 128.7, 128.5, 128.2, 126.9,
120.7, 65.5, 55.1; IR nmax (cmK1) 3021, 2849, 1711, 1628;
HRMS m/z (ESI) found 358.1813, C24H24NO2 requires
358.1807.
(20%), 129 (100), 144 (66); spectral data in accordance with
literature values.21
4.3. Petasis reactions
Method A. To a suspension of glyoxylic acid monohydrate 2
(1 mmol) in dichloromethane (5 mL) was added the amine 1
(1 mmol) and organoboron reagent (1 mmol) and the
reaction was stirred under N2 for 48 h. The resulting
precipitate was isolated by filtration and washed with
dichloromethane to yield the product.
4.3.7. N,N-Diisopropyl-a-(E)-phenylethenylglycine (8c).
Method A. White solid, 84%; mp 111–112 8C; H NMR
1
Method B. To a suspension of glyoxylic acid monohydrate 2
(1 mmol) in dichloromethane (5 mL) was added the amine
(1 mmol) and organoboron reagent (1 mmol) and the
reaction was stirred under N2 for 48 h. The solvent was
removed in vacuo and the crude product purified by
chromatography on silica to yield the product.
(300 MHz, D2O) d 7.61–7.41 (5H, m), 7.03 (1H, d, JZ
15.7 Hz), 6.36 (1H, dd, JZ9.8, 15.7 Hz), 4.69 (1H, d, JZ
9.8 Hz), 3.90 (2H, br m), 1.48–1.37 (12H, m); 13C NMR
(75 MHz, D2O) d 173.3, 141.3, 136.0, 129.8, 129.6, 119.7,
65.7, 54.7, 20.1; IR nmax (cmK1) 3011, 2973, 1628, 1616;
MS m/z (EIC) 284.1 [MCNa]C(100%); HRMS m/z (ESI)
found 262.1810, C16H24NO2 requires 262.1807.
4.3.1. N-Benzylphenylglycine (6a). Method A. White solid,
10%; mp 219–220 8C (lit.22 220–221 8C); 1H NMR
(200 MHz, D2OCK2CO3) d 7.45–7.34 (10H, m), 4.16
(1H, s), 3.70 (2H, m); data in accordance with literature
values.22
4.3.8. N-Benzyl-N-isopropyl-a-(E)-phenylethenylglycine
(8d). Method A. White solid, 90%; mp 116–117 8C; H
1
NMR (300 MHz, D2O/DMSOCK2CO3) d 7.17–6.85 (10H,
m), 6.41 (1H, d, JZ16.1 Hz), 6.04 (1H, dd, JZ8.7,
16.1 Hz), 3.93 (1H, d, JZ8.7 Hz), 3.57 (1H, d, JZ
15.0 Hz), 3.46 (1H, d, JZ15.0 Hz), 3.04 (1H, septet, JZ
6.2 Hz), 0.92 (6H, m); 13C NMR (75 MHz, D2O/DMSOC
K2CO3) d 179.4, 141.5, 137.3, 132.7, 129.5, 129.3, 129.0,
128.6, 128.0, 127.0, 126.9, 71.4, 51.5, 51.1, 20.9; IR nmax
(cmK1) 3029, 2983, 1621, 1616; MS m/z (ESI) 332.1
[MCNa]C(100%); HRMS m/z (ESI) found 310.1810,
C20H24NO2 requires 310.1807.
4.3.2. N,N-Dibenzyl-a-phenylglycine (6b). Method B.
Clear colourless oil, 64%; H NMR (200 MHz, CDCl3) d
1
9.61 (1H, br s), 7.53–7.25 (15H, m), 4.83 (1H, s), 4.02 (2H,
d, JZ13.7 Hz), 3.78 (2H, d, JZ13.7 Hz); 13C NMR
(50 MHz, CDCl3) d 174.2, 137.0, 134.0, 130.2, 129.8,
129.2, 128.7, 128.6, 127.8, 67.1, 54.7; data in accordance
with literature values.23
4.3.3. N,N-Diisopropyl-a-phenylglycine (6c). Method A.
White solid, 94%; mp 135–136 8C; H NMR (300 MHz,
1
4.3.9. N-((S)-1-Phenylethyl)-(R)-a-(E)-phenylethenylgly-
cine (8e). Method A. White solid, 97%; 1H NMR (200 MHz,
D2OCK2CO3) major isomer d 7.55–7.35 (10H, m), 6.48
(1H, d, JZ15.9 Hz), 6.22 (1H, dd, JZ8.4, 15.9 Hz), 3.91
(1H, q, JZ6.6 Hz), 3.70 (1H, d, JZ8.4 Hz), 1.42 (3H, d,
JZ6.6 Hz); minor isomer d 7.55–7.35 (10H, m), 6.53 (1H,
d, JZ16.0 Hz), 6.17 (1H, dd, JZ8.0, 16.0 Hz), 3.89 (1H, q,
JZ6.6 Hz), 3.61 (1H, d, JZ8.0 Hz), 1.44 (3H, d, JZ
6.6 Hz); 13C NMR (75 MHz, D2O/DMSOCK2CO3) major
isomer d 178.9, 144.3, 137.1, 134.2, 129.2, 129.1, 128.5,
128.2, 127.7, 127.3, 126.9, 64.2, 54.7, 24.0; minor isomer d
179.5, 145.2, 137.1, 132.8, 129.2, 129.1, 128.5, 128.1,
127.5, 127.3, 126.9, 65.1, 55.9, 22.7; data in accordance
with literature values.1
D2O) d 7.82–7.32 (5H, m), 5.08 (1H, s), 3.51 (2H, septet,
JZ6.5 Hz), 1.31 (12H, d, JZ6.5 Hz); 13C NMR (75 MHz,
D2O) d 176.9, 134.3, 131.9, 131.8, 128.8, 63.2, 47.9, 18.9;
IR nmax (cmK1) 3015, 2873, 1696, 1622; MS m/z (ESI)
236.1 [MCH]C(100%); HRMS m/z (EI) found 235.1566,
C14H22NO2 requires 235.1572.
4.3.4. N-Benzyl-N-isopropyl-a-phenylglycine (6d).
Method A. White solid, 99%; mp 101–102 8C; H NMR
1
(200 MHz, D2OCK2CO3) d 7.60–7.20 (10H, m), 5.09 (1H,
br s), 3.82 (2H, br s), 2.94 (1H, septet, JZ6.5 Hz), 1.05 (6H,
d, JZ6.5 Hz); 13C NMR (75 MHz, d6-DMSO) d 177.5,
134.9, 133.5, 132.7, 130.6, 129.6, 129.5, 128.2, 126.9, 92.1,