The Journal of Organic Chemistry
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(R)-(+)-4-Methylphenyl prop-2′-ynyl Sulfoxide (6c, Table 2,
Entry 7).24 Crude product contained a mixture of sulfide and
sulfoxide (78:22). Purification by chromatography afforded the
product as a white solid (23 mg, 14%, 4% ee).
(1H, dd, J = 11.2 and 9.8 Hz), 3.82−4.10 (1H, brs), 3.96−4.06 (1H,
brm), 7.04 (1H, d, J = 2.5 Hz), 7.27 (1H, d, J = 2.4 Hz), 8.12 (1H, s);
13C NMR δC (75.5 MHz) 26.9, 32.9, 61.7, 78.5, 116.9, 120.2, 124.5,
129.6, 133.4, 162.3, 164.8; m/z (ESI) [(M + H)+] 290; HRMS (ESI)
exact mass calculated for C13H17Cl2NO2 [(M + H)+] 290.0715; found,
290.0723; IR νmax/cm−1 (KBr) 3322, 2971, 1645, 1502 1209, 1058
(found C, 54.07; H, 5.91; N, 4.64; C13H17Cl2NO2 requires C, 53.81;
H, 5.90; N, 4.64); [α]D20 = −23.6 (c 1.0, acetone).
(S)-2-(N-3,5-Diiodosalicylidene)-amino-3,3-dimethyl-1-buta-
nol (10, Table 4):.22,36 Yellow solid, 79%, mp 164−165 °C (lit. mp
163−164);22 1H NMR δH (300 MHz) 1.00 (9H, s), 2.53 (1H, brs),
3.08 (1H, dd, J = 9.5 and 2.5 Hz), 3.68 (1H, dd, J = 11.1 and 9.8 Hz),
3.93−4.07 (1H, brm), 7.51 (1H, d, J = 2.1 Hz), 8.01 (1H, d, J = 2.1
Hz), 8.10 (1H, s); IR νmax/cm−1 (KBr) 3320, 2965, 1638, 1479, 1217,
1060; [α]D20 = −18.5 (c 0.1, acetone), lit.22 [α]D20 = −16.6 (c 1.0 for S in
acetone).
(S)-2-(N-3′-tert-Butylsalicylidene)-amino-3,3-dimethyl-1-bu-
tanol (11, Table 4):.37 Yellow oil, 88%; 1H NMR δH (300 MHz) 0.99
(9H, s), 1.44 (9H, s), 2.93 (1H, dd, J = 9.4 and 2.7 Hz), 3.73 (1H, dd,
J = 11.0 and 9.7 Hz), 3.90 (1H, dd, J = 11.1 and 2.8 Hz), 6.84 (1H, t, J
= 7.5 Hz), 7.15 (1H, dd, J = 7.6 and 1.6 Hz), 7.35 (1H, dd, J = 7.6 and
1.6 Hz), 8.42 (1H, s); IR νmax/cm−1 (film) 3367, 2959, 1633, 1458,
1436; [α]D20 = −54.3 (c 0.3, acetone).
1H NMR δH (300 MHz) 2.33 (1H, t, J = 2.7 Hz), 2.44 (3H, s), 3.59
(1H, A of ABX system, JAB = 14.2 Hz, JAX = 2.6 Hz), 3.67 (1H, B of
ABX system, JAB = 14.4 Hz, JBX = 2.6 Hz) 7.35 (2H, d, J = 8.3 Hz),
7.61 (2H, d, J = 8.2 Hz); HPLC tR (R) = 14.6 min, tR (S) = 17.5 min
[Chiracel OD-H; flow rate = 1 mL min−1; hexane-2-PrOH (90:10); 20
°C]; [α]D20 = +5.2 (c 1.0, CHCl3).
(R)-(+)-2-Naphthylmethyl Phenyl Sulfoxide (6i, Table 2,
Entry 14). Crude product contained a mixture of sulfide and sulfoxide
(45:55). Purification by chromatography afforded the product as a
white solid (80 mg, 30%, 93% ee).
mp 85−87 °C; 1H NMR δH (400 MHz) 4.15 (1H, A of AB system,
J = 12.4 Hz), 4.26 (1H, B of AB system, J = 12.4 Hz), 7.08 (1H, dd, J =
8.6 Hz and J = 1.6 Hz), 7.31−7.53 (8H, m), 7.66−7.85 (3H, m); 13C
NMR δC (75 MHz) 64.0, 124.5, 126.3, 126.4, 126.7, 127.7, 127.75,
127.9, 128.1, 128.9, 129.8, 131.2, 132.9, 133.1, 142.9 (found C, 76.43;
H, 5.58; S, 12.10; C17H14OS requires C, 76.66; H, 5.30; S, 12.04);
HPLC tR (R) = 32.1 min, tR (S) = 40.6 min [Chiracel OD-H; flow rate
= 1 mL min−1; hexane-2-PrOH (90:10); 20 °C]; [α]D20 = +75.4 (c 1.0,
CHCl3).
(R)-(+)-Benzyl 4-Methoxyphenyl Sulfoxide (2d, Table 1,
Entry 4).19,35 Crude product contained a mixture of sulfide and
sulfoxide (54:46). Purification by chromatography afforded the
product as a white solid (81 mg, 33%, 54% ee).
(S)-2-(N-5′-tert-Butylsalicylidene)-amino-3,3-dimethyl-1-bu-
tanol (12, Table 4).38 Yellow solid, 82%, mp 119−120 °C; 1H NMR
δH (300 MHz) 0.96 (9H, s), 1.31 (9H, s), 1.62 (1H, brs), 2.93 (1H,
dd, J = 9.5 and 2.8 Hz), 3.75 (1H, dd, J = 11.0 and 9.6 Hz), 3.92 (1H,
dd, J = 11.1 and 2.8 Hz), 6.91 (1H, d, J = 8.6 Hz), 7.26−7.28 (1H, m),
7.36 (1H, dd, J = 8.6 and 2.5 Hz), 8.36 (1H, s); 13C NMR δC (75.5
MHz) 27.0, 31.4, 33.2, 34.0, 62.5, 81.3, 116.5, 117.8, 128.0, 129.8,
141.5, 158.9, 166.4 (HCN); IR νmax/cm−1 (KBr) 3422, 2958, 1633,
1493 (found C, 73.31; H, 9.89; N, 5.12; C17H27NO2 requires C, 73.61;
H, 9.81; N, 5.05); [α]D20 = −46.8 (c 0.3, acetone).
1H NMR δH (300 MHz) 3.84 (3H, s), 3.95 (1H, A of AB system, J
= 12.0 Hz), 4.11 (1H, B of AB system, J = 12.0 Hz), 6.89−7.02 (4H,
m), 7.20−7.33 (5H, m), δC (75.5 MHz) 55.5, 63.8, 114.4, 126.4, 128.2,
128.5, 129.3, 130.4, 133.6, 162.0; HPLC tR (R) = 15.5 min, tR (S) =
18.4 min [Chiracel OD-H; flow rate = 1 mL min−1; hexane-2-PrOH
(90:10); 40 °C]; [α]D20 = +48.2 (c 1.0, acetone), {ref 19, [α]D20 = +31.9
(c 0.28, acetone) for (R) = 44% ee}.
(R)-(+)-Cyclohexylmethyl Phenyl Sulfoxide (6e, Table 2,
Entry 5).31 Crude product contained a mixture of sulfide and
sulfoxide (71:29). Purification by chromatography afforded the
product as a clear oil that solidified to form a white solid (44 mg,
20%, 60% ee).
(S)-2-(N-3′,5′-Dibromosalicylidene)-amino-3-methyl-1-buta-
1
nol (13, Table 4). Yellow solid, 76%, mp 136−138 °C; H NMR δH
(300 MHz) 0.99 (3H, d, J = 6.7 Hz), 1.01 (3H, d, J = 6.7 Hz), 1.88−
2.07 (1H, m), 3.17−3.30 (1H, m), 3.65−3.80 (1H, m), 3.99 (1H, dd, J
= 11.4 and 2.6 Hz), 7.25 (1H, d, J = 2.5 Hz), 7.60 (1H, d, J = 2.5 Hz)
8.14 (1H, s); 13C NMR δC (75.5 MHz) 18.4, 19.8, 29.6, 64.0, 74.8,
1H NMR δH (300 MHz) 1.01−1.41 (5H, m), 1.60−1.83 (4H, m),
1.89−2.08 (1H, m), 2.09−2.17 (1H, m), 2.45−2.52 (1H, A of ABX
system, J = 12.9 and 9.0 Hz), 2.76−2.82 (1H, B of ABX system, J =
12.9 and 4.8 Hz), 7.42−7.72 (5H, m); IR (KBr) ν = 2920, 1443, 1034,
752 cm−1; HPLC tR (R) = 17.3 min, tR (S) = 20.3 min [Chiracel OD-
H; flow rate = 1 mL min−1; hexane-2-PrOH (90:10); 20 °C]; [α]D20=
+47.8 (c 1.0, CHCl3).
107.2, 114.8, 117.6, 133.5, 138.8, 163.0, 164.6; m/z IR (KBr) νmax
/
cm−1 3259, 2965, 1645, 1497, 1212, 1043, 857, 690 (found C, 39.73;
H, 4.14; N, 3.57; C12H15Br2NO2 requires C, 39.48; H, 4.14; N, 3.84);
[α]D20 = −9.1 (c 1.0, acetone).
(S)-2-(N-3′,5′-Difluorosalicylidene)-amino-3,3-dimethyl-1-
butanol (14, Table 4). Yellow solid, 57%, mp 161−163 °C; 1H NMR
δH (300 MHz) 0.99 (9H, s), 2.08 (1H, brs), 3.01 (1H, dd, J = 9.6 and
2.7 Hz), 3.70 (1H, dd, seen as t, J = 9.9 and 9.9 Hz), 3.99 (1H, brd, J =
9.8 Hz), 6.75−6.82 (1H, m), 6.86−6.96 (1H, m), 8.26 (1H, s); 13C
NMR δC (75.5 MHz) 26.9, 33.1, 62.0, 80.4, 107.4−108.0 (m), 111.2−
111.5 (m), 164.6; m/z (ESI) [(M + H)+] 258; HRMS (ESI) exact
mass calculated for C13H17F2NO2 [(M + H)+] 258.1328; found,
258.1317; IR (KBr) νmax/cm−1 3308, 2966, 1638, 1479, 1215, 1059,
857; [α]D20 = −35.6 (c 0.5, acetone).
(S)-2-(N-3′-Chloro-5′-fluorosalicylidene)-amino-3,3-dimeth-
yl-1-butanol (15, Table 4). Yellow solid, 75%, mp 103−105 °C; 1H
NMR δH (300 MHz) 1.00 (9H, s), 2.81 (1H, bs), 3.06 (1H, dd, J = 9.6
and 2.4 Hz), 3.70 (1H, overlapping dd, J = 11.1 and 9.6 Hz), 3.99 (1H,
dd, J = 11.4 and 2.7 Hz), 6.87 (1H, dd, J = 8.1 and 3.0 Hz), 7.14 (1H,
dd, J = 8.1 and 3.0 Hz), 8.22 (1H, s); 13C NMR δC (75.5 MHz) 26.9,
33.0, 61.9, 79.8, 115.2, 117.0 (d, 3JCF = 8 Hz), 121.0 (d, 2JCF = 26 Hz),
122.8 (d, 3JCF = 10 Hz), 153.4 (d, 1JCF = 239 Hz), 157.0, 164.6 (d, 4JCF
= 3 Hz, HCN); m/z (ESI) [(M + H)+] 274; HRMS (ESI) exact
mass calculated for C13H17FClNO2 [(M + H)+] 274.1010; found,
274.1006; IR (KBr) νmax/cm−1 3288, 2973, 1643, 1471, 1366, 1209,
1063, 803 (found C, 57.41; H, 6.30; N, 5.24; C13H17ClFNO2 requires
C, 57.04; H, 6.26; N, 5.12); [α]D20 = −27.4 (c 1.0, acetone).
EXPERIMENTAL PROCEDURE FOR SCHIFF BASE
LIGAND SYNTHESIS
■
Commercially available salicylaldehyde (1 mmol) and sodium sulfate
(0.5 g) were added to a solution of (S)-tert-leucinol (1 mmol) or L-
valinol (1 mmol) in ethanol (20 mL). The reaction mixture was stirred
under reflux for 16 h, filtered, and concentrated under reduced
pressure. The reaction mixture was then dissolved in dichloromethane
(10 mL) and washed with water (3 × 10 mL) and brine (15 mL). The
organic layer was dried and concentrated under reduced pressure to
leave the crude product, which was purified by column chromatog-
raphy on silica gel (8:2 hexane/ethyl acetate) to yield the pure ligand.
(S)-2-(N-3′,5′-Dibromosalicylidene)-amino-3,3-dimethyl-1-
butanol (3, Table 4):.36,37 Yellow solid, 73%, mp 160−162 °C; H
1
NMR δH (300 MHz) 1.01 (9H, s), 3.10 (1H, dd, J = 9.5 and 2.4 Hz),
3.11 (1H, brs), 3.70 (1H, dd, J = 11.2 and 9.8 Hz), 3.98−4.08 (1H,
brm), 7.35 (1H, d, J = 2.5 Hz), 7.58 (1H, d, J = 2.4 Hz), 8.12 (1H, s);
13C NMR δC (75.5 MHz) 27.3, 33.4, 62.2, 79.2, 107.9, 114.8, 118.2,
133.8, 139.1, 162.9, 164.9; m/z (ESI) [(M + H)+] 378; HRMS (ESI)
exact mass calculated for C13H1779Br2NO2 [(M + H)+] 377.9704;
found, 377.9710; [α]D20 = −16.1 (c 1.0, acetone).
(S)-2-(N-3′,5′-Dichlorosalicylidene)-amino-3,3-dimethyl-1-
butanol (4, Table 4): Yellow solid, 72%, mp 153−156 °C; 1H NMR
δH (300 MHz) 1.02 (9H, s), 3.11 (1H, dd, J = 9.5 and 2.4 Hz), 3.69
3294
dx.doi.org/10.1021/jo2026178 | J. Org. Chem. 2012, 77, 3288−3296