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Typical Experimental
Procedure for α-Hydroxy-amination Reaction of β-Carbonyl
Esters Using Squaramide Catalyst at Room Temperature: To a solution
of squaramide catalyst 3 (5 mol%)
in Et2O (1.0 mL) were added nitrosobenzene 2 (0.125 mmol, 1.2 equiv) and β-carbonyl
esters 1 (1.0 equiv). The mixture was stirred
at r.t. until TLC analysis showed that 1 was
completely consumed. The reaction was directly purified by silica
gel chroma-tography to afford the desired product 4.
Enantiomeric excess was determined by HPLC analysis using AD-H or OJ-H,
AS-H column. Benzyl 1-[hydroxy(phenyl)amino]-2-oxocyclopentane-carboxylate
(4b): purification by column chromatography
on silica gel (PE-EtOAc, 15:1 → 8:1); enantiomeric
excess was determined by HPLC; [α]D
²0
-43.44˚ (c = 1.0, CHCl3).
IR: 3386, 2961, 2918, 2849, 1759, 1724, 1597, 1491, 1263, 1115,
759, 694 cm-¹. ¹H
NMR (400 MHz, CDCl3): δ = 1.26 (t, J = 7.0 Hz, 3 H), 1.89-1.95
(m, 2 H), 2.31-2.42 (m, 3 H), 2.51-2.58 (m, 1
H), 4.25 (q, J = 7.0 Hz, 2 H),
7.01 (t, J = 7.2 Hz, 1 H), 7.07
(d, J = 8.0, 3 H), 7.18 (t, J = 8.0 Hz, 2 H). ¹³C
NMR (100 MHz, CDCl3): δ = 14.0, 18.6,
29.2, 37.4, 62.3, 80.7, 120.2, 124.1, 128.3, 148.8, 168.6, 209.9.
HRMS (ESI): m/z [M + Na]+ calcd
for C14H17NO4Na: 286.1055; found:
286.1064. HPLC analysis (Daicel Chiralcel AD-H, 0.46 cm × 25
cm), hexane-i-PrOH (93:7), flow
rate: 0.5 mL/min, t
R
(
minor) = 35.1
min, t
R
(
major) = 25.9
min, 98% ee.
12 To a solution of hydroxyamination
adduct 4b (0.125 mmol) in CH2Cl2 (1.0
mL) were added AcOH (0.6 mL) and Zn dust (60 mg) at 0 ˚C.
The mixture was stirred vigorously at 30 ˚C. When the reaction
was completed, the reaction mixture was treated with sat. aq NaHCO3,
and extracted with CH2Cl2. The combined organic
layer was washed with brine, dried over anhyd Na2SO4,
and concentrated in vacuo. The crude residue was purified by flash
column chromatography (15% EtOAc-PE) to afford
product 5b. Enantiomeric excess was determined
by HPLC; [α]D
²0 34.26˚ (c = 1.0, CHCl3).
IR: 3375, 2978, 2919, 1757, 1724, 1603, 1504, 1261, 1221, 1178,
1025, 751, 693 cm-¹. ¹H
NMR (400 MHz, CDCl3) :
δ = 1.07
(t, J = 7.6 Hz, 3 H), 2.06-2.27
(m, 3 H), 2.38-2.49 (m, 1 H), 2.55-2.16 (m, 1
H), 3.04-3.15 (m, 1 H), 4.02-4.18 (m, 2 H), 4.76
(s, 1 H), 6.64 (d, J = 8.0 Hz,
2 H), 6.79 (t, J = 7.8 Hz, 1
H), 7.17 (t, J = 7.8 Hz, 2 H). ¹³C
NMR (100 MHz, CDCl3): δ = 13.8, 18.3,
34.5, 35.3, 62.0, 70.8, 115.1, 119.0, 129.1, 1445.1, 169.3, 211.2.
HRMS (ESI): m/z [M + H]+ calcd
for C14H18NO3: 248.1287; found:
248.1286. HPLC analysis (Daicel Chiralcel AD-H, 0.46 cm × 25
cm), hexane-i-PrOH (93:7), flow
rate: 0.5 mL/min, t
R
(
minor) = 14.9
min, t
R
(
major) = 13.1
min, 98% ee.