Molecules 2011, 16
3427
Dibenzyl (R)-1-(1-phenyl-2-hydroxyethyl)hydrazine-1,2-dicarboxylate (7d). Obtained as a white solid
(0.29 g, 70%). m.p. 140–141 °C; νmax(neat) 3273 br, 2946 s and 1711 cm-1 s; [α]D20 -38.0 (c = 0.4,
CHCl3); δH 3.2–3.5 (2H, m, CH2OH), 4.0–4.5 (2H, m, CH and OH), 4.8–5.1 (4H, m, 2 × CH2Ph)
7.0–7.4 (15H, m, ArH); δC(75 MHz) 56.7 (CH), 63.5 (CH2OH), 65.5 (CH2Ph), 70.2 (CH2Ph), 127.8
(ArCH), 127.9 (ArCH), 128.2 (ArCH), 128.6 (ArCH), 129.0 (ArCH), 135.7 (ArC), 136.2 (ArC), 156.3
(NCO2), 159.3 (NCO2); HPLC (Chiralpak AD-H using hexane: iPrOH (90:10) as solvent at a flow rate
of 0.5 mL/min) retention times 46.2 (minor) and 48.7 (major) minutes.
Dibenzyl (R)-1-(1-benzyl-2-hydroxyethyl)hydrazine-1,2-dicarboxylate (7e) [54]. Obtained as a white
solid (0.33 g, 76%). m.p. 105–106 °C (lit [68]. 110–116 °C); νmax(neat) 3272 br, 2963 s and 1716 cm−1
s; [α]D20 +11.1 (c = 0.9, CHCl3) (lit [68] [α]D25 +11.4 (c = 1.8, CHCl3)); δH 2.4–2.7 (2H, m, CH2Ph),
3.3–3.6 (2H, m, CH2OH) 4.4–4.6 (2H, m, CH and OH), 4.9–5.2 (4H, m, 2 × OCH2Ph), 6.8–7.4 (15H,
m, ArH); δC(75 MHz) 34.5 (CH2), 60.2 (CH), 61.8 (CH2OH), 68.0 (OCH2Ph), 68.3 (OCH2Ph), 128.2
(ArCH), 128.5 (ArCH), 128.7 (ArCH), 128.8 (ArCH), 128.9 (ArCH), 129.0 (ArCH), 129.1 (ArCH),
129.2 (ArCH), 129.4 (ArCH), 135.1 (ArC), 135.7 (ArC), 137.3 (ArC), 156.7 (NCO2), 158.8 (NCO2);
m/z(ES+) 443 (M+Na+, 50), 863 (2M+Na+), 1283 (3M+Na+); Found (ES+) 443.1550, C24H24N2O5Na,
(M+Na+) requires 443.1583; HPLC (Chiralpak AS-H using hexane: iPrOH (85:15) as solvent at a flow
rate of 1.0 mL/min) retention times 13.4 (major) and 31.5 (minor) minutes.
Dibenzyl (R)-1-(1-(1-methyl)ethyl-2-hydroxyethyl)hydrazine-1,2-dicarboxylate (7f) [54] Obtained as a
yellow oil (0.34 g, 87%). νmax(neat) 3272 br, 2963 s and 1716 cm−1 s; [α]D20 -21.0 (c = 0.4, CHCl3); δH
0.6–1.0 (6H, m, 2 × CH3), 1.4–1.7 (1H, m, CHMe2) 3.3–4.4 (4H, m, NCHCH2OH) 4.9–5.2 (4H, m, 2 ×
CH2Ph) 6.7–6.9 (1H, br s, NH) 7.1–7.4 (10H, m, ArH); δC (75 MHz) 19.3 (CH3), 20.0 (CH3), 27.5
(CH), 60.4 (CH), 67.2 (CH2OH), 68.4 (2 × OCH2Ph), 127.7 (ArCH), 128.0 (ArCH), 128.1 (ArCH),
128.2 (ArCH), 128.4 (ArCH), 128.6 (ArCH), 135.2 (ArC), 135.9 (ArC), 156.4 (NCO2), 157.4 (NCO2);
i
HPLC (Chiralpak OD-H using hexane: PrOH (90:10) as solvent at a flow rate of 1.0 mL/min)
retention times 14.4 (major) and 17.7 (minor) minutes.
3.4. General procedure for the synthesis of ketones 10a-d
To a stirred solution of dibenzyl azodicarboxylate (5a, 0.3 g, 1.0 mmol) and a ketone (1.5 mmol) in
propylene carbonate (3, 1 mL), was added (S)-proline (1, 5.9 mg, 0.05 mmol). The reaction was stirred
at 0 °C for 24 hours, then quenched by the addition of H2O (5 mL), extracted with Et2O (10 mL),
washed with H2O (4 × 10 mL) and dried (Na2SO4). Volatiles were removed by evaporation in vacuo
and the residue was purified by silica gel chromatography eluting with hexane:EtOAc (70:30) and
recrystallized with cold isopropanol to give ketones 10-d.
Dibenzyl (R)-1-(2-oxocyclohexyl)hydrazine-1,2-dicarboxylate (10a) [66]. Obtained as a colourless oil
(0.28 g, 71%). νmax(neat) 3271 br, 2965 s, 1797 s, 1743 s and 1679 cm−1 m; [α]D20 -21.0 (c = 0.1,
20
CH2Cl2) (lit [66]. [α]D -24.1 (c=0.1, CH2Cl2)); δH 1.6–2.5 (8H, m, (CH2)4), 5.1-5.2 (5H, m,
2 × CH2Ph and NCH), 6.88 (1H, br, NH), 7.3–7.5 (10H, m, ArH); δC (75 MHz) 24.4 (CH2), 26.7
(CH2), 30.8 (CH2), 41.2 (CH2), 66.5 (2 × OCH2Ph), 67.9 (NCH), 127.7 (ArCH), 128.0 (ArCH), 128.1