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Russ.Chem.Bull., Int.Ed., Vol. 50, No. 11, November, 2001
Doyle et al.
gel (eluent AcOEthexanes, 1 : 1, Rf 0.24) to yield 0.377 g
Methyl 3-benzyloxycarbonyl-1-(l-menthoxyacetoxyacetyl)-
2-oxoimidazolidine-4(S)-carboxylate (13). A clear solution of
(+)-menthoxyacetic acid (11) (0.27 g, 1.25 mmol) and DBU
(0.2 mL, 1.4 mmol) was prepared in benzene. After addition of
bromide 10 (0.5 g, 1.25 mmol), the mixture was heated at
reflux for 1 h. Upon cooling, DBU salts precipitated and the
benzene solution was decanted. The solvent was removed
under reduced pressure yielding the title compound 13 as a
white solid (100% yield). 1H NMR (CDCl3), δ: 0.700.95
(m, 13 H); 1.201.34 (m, 1 H); 1.541.64 (m, 2 H); 2.04
(d, 1 H); 2.24 (dq, 1 H); 3.16 (dt, 1 H); 3.70 (s, 3 H); 3.84.0
(dd, 2 H); 4.19 (d, 2 H); 4.68 (dd, 1 H); 5.22 (s, 2 H);
5.125.39 (dd, 2 H); 7.237.39 (m, 5 H). 13C NMR (CDCl3),
δ: 20.8, 22.1, 23.0, 25.2, 31.3, 34.2, 39.6, 44.0, 47.8, 47.9,
50.6, 53.1, 63.2, 65.2, 68.8, 80.0, 128.0, 128.1, 128.2, 128.4,
128.5, 128.6, 134.4, 149.2, 150.4, 167.1, 168.6, 170.1.
Methyl 1-(l-menthoxyacetoxyacetyl)-2-oxoimidazolidine-
4(S)-carboxylate (7c). A solution of methyl carboxylate 13
(1.25 g, 2.4 mmol) in AcOEt containing a small scoop of 10%
Pd/C was shaken in a Parr hydrogenator under H2 (2.38 atm)
until TLC indicated 100% conversion. The Pd/C catalyst was
removed by filtration through a Celite plug, washed with
CH2Cl2, and the filtrate was concentrated under reduced
pressure and purified by silica gel column chromatography
(eluent AcOEthexanes, 3 : 1) yielding the ligand 7c (0.56 g,
60%). 1H NMR (CDCl3), δ: 0.791.02 (m, 13 H); 1.201.38
(m, 2 H); 1.601.70 (m, 2 H); 2.11 (d, 1 H); 2.32 (dq, 1 H);
3.21 (dt, 1 H); 3.53 (dd, 1 H); 3.80 (s, 3 H); 3.803.91
(m, 1 H); 4.24 (d, 2 H); 4.85 (dd, 1 H); 5.185.47 (dd, 2 H);
6.08 (s, 1 H). 13Ñ (CDCl3), δ: 16.2, 20.9, 22.2, 23.2, 25.3,
31.4, 34.3, 39.8, 41.3, 48.1, 53.1, 54.3, 63.1, 65.4, 80.1, 155.5,
166.9, 169.4, 170.4.
(95%) of product 7b as a white powder with m.p. 7677 °C,
23.5
[α]D
+92.3 (c 0.64, CH2Cl2). 1H NMR (CDCl3), δ: 0.79
(d, 3 H, J = 6.8 Hz); 0.93 (m, 9 H); 1.29 (m, 2 H); 1.64
(m, 2 H); 2.08 (m, 1 H); 2.29 (m, 1 H); 3.20 (dt, 1 H,
J = 10.5 Hz, J = 3.9 Hz); 3.81 (s, 3 H); 4.08, 4.14 (AB, 2 H,
J = 11.7 Hz); 4.39 (m, 1 H); 4.61, 4.73 (AB, 2 H, J = 17.8 Hz);
6.86 (s, 1 H). 13C NMR (CDCl3), δ: 15.9, 20.6, 21.9, 22.9,
25.1, 31.1, 34.0, 39.6, 44.2, 47.6, 50.1, 52.6, 67.8, 79.7, 155.2,
170.0, 170.4. MS (FAB+, in mixture matrix), m/z (Irel (%)):
341 [M + H]+ (25); 681 [2 M + H]+ (2).
Dirhodium(II) tetrakis[methyl 1-(d-menthoxyacetyl)-2-
oxoimidazolidine-4(S)-carboxylate], Rh2(4S-MDMIM)4 (16).
Rhodium(II) acetate (0.301 g, 0.68 mmol), methyl carboxylate
7d (1.64 g, 4.83 mmol), and 20 mL of anhydrous PhCl were
mixed in a round bottom flask fitted with a Soxhlet extraction
apparatus into which was placed a thimble containing an oven
dried mixture of two parts Na2CO3 and one part sand. The
resulting blue-green solution was heated at reflux under nitro-
gen for about 48 h. The progress of ligand displacement
was followed by HPLC (µ-Bondapak-CN column, eluent
MeOHMeCN, 99 : 1, flow 1.5 mL min1). The initial
Rh2(OAc)4 band disappeared and was replaced by several
bands with longer retention times. After 48 h one principal
band (tr
= 5.9 min), in addition to that for the ligand
(tr = 1.6 min) was observed. The resulting blue solution was
cooled to ∼20 °C, and the solvent was evaporated under
reduced pressure. The residue was dissolved in minimal vol-
ume of MeOH and gray decomposition products were removed
by filtration. The filtrate was chromatographed on a column
with Bakerbond Cyano 40 µm prep LC packing eluting with
MeOH. The first slightly brown band containing excess of
ligand was removed. The following purple band was collected
and concentrated under reduced pressure. The residue (0.97 g)
contained the title compound and a considerable amount of
ligand. A second purification on a column with Bakerbond
Cyano 40 µm prep LC packing eluting with MeOH gave 0.68 g
(60%) of the desired complex 16. 1H NMR (CDCl3), δ: 0.80
(d, 12 H, J = 6.6 Hz); 0.92 (m, 36 H); 1.32 (m, 8 H); 1.65
(m, 8 H); 2.14 (m, 4 H); 2.29 (m, 4 H); 3.19 (m, 4 H); 3.61
(s, 6 H); 3.78 (s, 6 H); 3.914.15 (m, 12 H); 4.53 (m, 8 H).
13C NMR (CDCl3), δ: 16.3, 21.1, 22.4, 23.1, 25.4, 31.6, 34.4,
40.3, 46.3, 46.6, 48.4, 52.0, 59.5, 60.2, 67.9, 79.9, 164.8,
168.6, 172.4, 172.9.
Dirhodium(II) tetrakis[methyl 1-l-(menthoxyacetoxyacetyl)-
2-oxoimidazolidine-4(S)-carboxylate], Rh2(S,S-MAOIM)4
(17). The title compound was prepared by a standard proce-
dure using Rh2(OAc)4 (0.105 g, 0.24 mmol) and ligand 7c
(0.538 g, 1.44 mmol) in PhCl. After purification on a column
with Bakerbond Cyano 40 µm prep LC packing eluting with
MeOH, complex 17 (95 mg, 22%) was isolated as a purple
solid. 13C (CDCl3), δ: 16.1, 20.9, 22.2, 23.1, 25.4, 31.4, 34.3,
39.8, 48.0, 60.3, 65.5, 75.1, 75.7, 80.5, 80.8, 106.0, 108.5,
109.3, 170.4. MS (FAB+), m/z: 1796 [M + H]+.
Methyl 3-benzyloxycarbonyl-1-[(1-benzyl-5-oxopyrrolidine-
2(S)-carbonyloxy)acetyl]-2-oxoimidazolidine-4(S)-carboxylate
(14). A clear solution of 1-benzyl-5-oxopyrrolidine-2(S)-car-
boxylic acid (12) (2.29 g, 10.4 mmol) and DBU (1.58 g,
10.4 mmol) was prepared in benzene. After addition of 10
(3.50 g, 8.7 mmol), the mixture was stirred at reflux for 1 h.
Upon cooling, DBU salts precipitated and the benzene solu-
tion was decanted. The solvent was removed under reduced
pressure and the product purified by silica gel column chroma-
tography (eluent AcOEthexanes, 1 : 1, Rf 0.20) to give the
Methyl 3-benzyloxycarbonyl-1-bromoacetyl-2-oxoimid-
azolidine-4(S)-carboxylate (10). To a mixture of methyl car-
boxylate 6 (4.95 g, 17.8 mmol) and anhydrous THF (75 mL)
under inert atmosphere was added NaH (0.427 g, 17.8 mmol).
After effervescence ceased, the solution was cooled to 78 °C
and bromoacetyl bromide (7.19 g, 35.6 mmol) was added.
After stirring for 30 min at 78 °C, the reaction was allowed to
warm to ∼20 °C during ∼15 h. Solvent was removed under
reduced pressure and the residue dissolved in CH2Cl2 (200 mL).
The pale white solution was washed with H2O (100 mL), brine
(100 mL) and concentrated under reduced pressure. Purification
by silica gel column chromatography (eluent AcOEthexanes,
1 : 1, Rf 0.25) gave the title compound 10 (6.24 g) as a white
19
title compound 14 (2.42 g, 51%) as a white solid, [α]D 36
(c 1.0, CHCl3). 1H NMR (CDCl3), δ: 2.27 (m, 2 H); 2.54 (m,
2 H); 3.80 (s, 3 H); 4.09 (m, 4 H); 4.77 (dd, 1 H, J = 10.2 Hz,
J = 3.3 Hz); 5.12 (d, 1 H, J = 15 Hz); 5.15 (d, 1 H,
J = 17.1 Hz); 5.31 (s, 2 H); 5.40 (d, 1 H, J = 17.4 Hz); 7.38
(m, 10 H). 13C NMR (CDCl3), δ: 22.7 (t), 29.5 (t), 44.1 (t),
45.3 (t), 50.6 (q), 53.3 (d), 58.3 (d), 63.7 (t), 69.1 (t),
127.7 (d), 128.3 (d), 128.5 (d), 128.6 (d), 128.8 (d), 134.3 (s),
135.6 (s), 149.2 (s), 150.4 (s), 166.8 (s), 168.5 (s), 171.2 (s),
175.3 (s). MS (FAB+), m/z: 538 [M + H]+.
19
solid in 87% yield with m.p. 110112 °C, [α]D 20.9 (c 1.2,
CHCl3). 1H NMR (CDCl3), δ: 3.80 (s, 3 H); 3.89 (dd, 1 H,
J = 11.1 Hz, J = 3.3 Hz); 4.09 (dd, 1 H, J = 11.1 Hz,
J = 10.2 Hz); 4.57 (dd, 2 H, J = 4.8 Hz, J = 12.9 Hz); 7.41
(m, 5 H); 4.78 (dd, 1 H, J = 10.5 Hz, J = 3.6 Hz); 5.31
(s, 2 H). 13C NMR (CDCl3), δ: 28.3 (t), 43.3 (t), 51.3 (q),
53.2 (d), 68.7 (t), 128.3 (d), 128.6 (d), 128.7 (d), 134.4 (s),
149.9 (s), 150.0 (s), 166.1 (s), 168.6 (s).
Methyl 1-[(1-benzyl-5-oxopyrrolidine-2(S)-carbonyl-
oxy)acetyl]-2-oxoimidazolidine-4(S)-carboxylate (7d). A so-
lution of methyl carboxylate 14 (1.47 g, 2.7 mmol) in AcOEt