Synthesis of chiral sulfonamide/Schiff base ligands

Article abstract of DOI:10.1016/S0957-4166(98)00431-5

We report a facile two step synthesis of chiral ligands for bonding to transition metals. The ligands are easily prepared from trans, 1,2- diaminocyclohexane by reaction with sulfonyl chlorides to give amino- sulfonamide compounds. These intermediates are

Full text of DOI:10.1016/S0957-4166(98)00431-5

TETRAHEDRON:
ASYMMETRY
Pergamon
Tetrahedron: Asymmetry 9 (1998) 4135–4142
Synthesis of chiral sulfonamide/Schiff base ligands
Jaume Balsells,a Lupe Mejorado,a Mimi Phillips,a Fernando Ortega,b Gerardo Aguirre,b
Ratnasamy Somanathan b and Patrick J. Walsh a,b,∗
aDepartment of Chemistry, San Diego State University, San Diego, CA 92182-1030, USA
bCentro de Graduados e Investigación, Instituto Tecnológico de Tijuana, Apartado Postal 1166, 22000 Tijuana, B.C. Mexico
Received 8 September 1998; accepted 19 October 1998
Abstract
We report a facile two step synthesis of chiral ligands for bonding to transition metals. The ligands are easily
prepared from trans-1,2-diaminocyclohexane by reaction with sulfonyl chlorides to give amino-sulfonamide com-
pounds. These intermediates are then condensed with salicylaldehyde derivatives to provide sulfonamide/Schiff
base compounds which represent a new class of chiral ligands. © 1998 Elsevier Science Ltd. All rights reserved.
The preparation of new ligands is perhaps the most important step in the development of metal
complexes which exhibit unique properties and novel reactivity. Changes in the electronic, steric, and
geometric properties of the ligand alter the orbitals at the metal center and thus affect its properties.
In catalytic asymmetric systems, small changes in the donating ability of the ligand or the size of its
substituents can have a dramatic effect on the catalyst efficiency and enantioselectivity.1–6 The work of
Jacobsen et al. in the asymmetric epoxidation of olefins stands as an excellent example of the optimization
of these parameters to achieve high enantioselectivities.7 The salen ligands used in the Jacobsen
epoxidation have proven to be exceptional in several asymmetric processes including aziridination8,9
and cyclopropanation of olefins,10 epoxide opening11–14 and kinetic resolution of epoxides,12,15–17 the
Diels–Alder cycloaddition,16,18 and the trimethylsilylcyanation of aldehydes.19 Another class of ligands
that is also prepared from chiral diamines is the bis(sulfonamide) complexes. These ligands have been
used in the asymmetric Diels–Alder reaction,20,21 alkylation of aldehydes,22–29 the cyclopropanation of
allylic alcohols,29–34 and the amination of N-acyloxazolidones.35
The salen and bis(sulfonamide) ligands are electronically very different. The tetradentate salen ligand
is a strong electron donor.36,37 In contrast, in the deprotonated bis(sulfonamide) ligand, the electron
density is delocalized into the sulfonyl group and the ligand is a poor electron donor. The resulting
bis(sulfonamido) complexes exhibit enhanced Lewis acidity. Although the bis(sulfonamide) ligands bind
well to early transition metals28,38–40 and main group elements,20 they have not been shown to coordinate
to late transition metals. Because the salen and bis(sulfonamide) ligands impart different properties on the
∗
Corresponding author. E-mail: pwalsh@sundown.sdsu.edu
0957-4166/98/$ - see front matter © 1998 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(98)00431-5

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J. Balsells et al. / Tetrahedron: Asymmetry 9 (1998) 4135–4142
metal, we decided to prepare hybrids of these ligands and explore their use in transition metal chemistry
and asymmetric catalysis. The imine and phenol groups of the salen will assure strong binding to the
metal as found in tetradentate salen complexes while the deprotonated sulfonamide will increase the
Lewis acidity of the metal center. Since a large number of inexpensive salicylaldehyde derivatives and
sulfonyl chlorides are commercially available, a wide range of ligands are synthetically accessible in two
easy steps.
The synthesis of the ligands is outlined in Eq. 1. The first step involves derivatization of trans-1,2-
diaminocyclohexane with the sulfonyl chloride to give the amino-sulfonamide. Using a 1:1 ratio of
diamine to sulfonyl chloride is problematic because the amino-sulfonamide initially formed competes
effectively with the diamine for the remaining sulfonyl chloride. As a result, substantial amounts of the
bis(sulfonamide) product can be formed. Surprisingly, even with the bulky 2,4,6-triisopropylbenzene
sulfonyl chloride, a 1.2:1 ratio of amino-sulfonamide to bis(sulfonamide) was obtained. As reported by
Xu and coworkers, the addition of one equivalent of ethyl trifluoroacetate, a highly selective reagent for
the differentiating of amino groups,41 and trans-1,2-diaminocyclohexane, caused the ratio of the mono-
amide to the bis(amide) to increase to 1.8:1. This is in sharp contrast with cis-1,2-diaminocyclohexane
which gives the monoamide and bis(amide) in a ratio of 68:1.41 To circumvent the need for separation
of the amino-sulfonamide from the bis(sulfonamide), Neumann and coworkers employed a three fold
excess of the diamine relative to the sulfonyl chloride.42 In our synthesis, we started with the tartrate
salt of the diamine, which is the product obtained in the resolution of the diamine. The tartrate salt was
added to 2 M NaOH to generate the free diamine, then dichloromethane was added and the solution
cooled in an ice bath. Next, the sulfonyl chloride was added slowly as a solution in dichloromethane. The
isolated amino-sulfonamide products were very clean and no bis(sulfonamide) product was detected for
1–3 (500 MHz NMR). However, in the case of 4, the product was chromatographed to remove traces of
the bis(sulfonamide). We have made a sterically diverse group of amino-sulfonamides and anticipate that
this methodology should be applicable using a range of sulfonyl chlorides.
(1)
We were able to crystallize 4 and performed an X-ray diffraction study. Two molecules were found in
the unit cell which differed in their conformations. The structure of one of these is illustrated in Fig. 1.
In the second step, the amino-sulfonamide was allowed to react with the salicylaldehyde derivatives in
dichloromethane at room temperature. The product sulfonamide-Schiff bases were isolated by removing
the solvent and drying under high vacuum. The reactions were very clean and proceeded readily, even in
the case of the bulky amino-sulfonamide 1 reacting with the di-tert-butyl substituted aldehyde c (Eq. 1
and Table 1). We were able to grow X-ray quality crystals of 5b. The results of the X-ray structure
determination are shown in Fig. 1.
In related work, Bu and coworkers reported complementary methodology which may be suitable

J. Balsells et al. / Tetrahedron: Asymmetry 9 (1998) 4135–4142
4137
Figure 1. X-Ray crystal structures of 4 (left) and 5b (right)
Table 1
Chiral sulfonamide/Schiff base ligands
for the synthesis of sulfonamide-Schiff base ligands.43 They derivatized trans-1,2-diaminocyclohexane
with one equivalent of salicylaldehyde to provide the unsymmetrical amino-Schiff base. Apparently this
reaction proceeds without formation of the tetradentate salen ligand (although mention is made of use of
up to 1.5 equivalents of diamine). Reaction of this intermediate with different salicylaldehyde derivatives
gave the unsymmetrical tetradentate salen ligands. It is likely that the unsymmetrical amino-Schiff base
compound would react with sulfonyl chlorides to provide the sulfonamide-Schiff base ligands.
Although both our method and that of Bu et al. are simple, they each have minor shortcomings. In
our methodology, an excess of the chiral diamine must be used. However, based on the results of Xu
et al., excess diamine is not likely to be necessary in the synthesis of amino-sulfonamides with other
diamines.41 In the procedure of Bu et al., it is necessary to use the diamine as starting material because
of the anhydrous conditions needed for imine formation. Liberation of the diamine from the tartrate salt
is a two step procedure which must be done carefully because of the water solubility and air sensitivity
of the diamine.44
In conclusion, we have developed an efficient method to synthesize modular sulfonamide-Schiff
base ligands. Compounds containing the Schiff base moiety have an extensive and well documented
coordination chemistry while the transition metal chemistry of sulfonamides is just beginning to be
addressed. We are currently exploring the structure of complexes derived from these hybrid ligands and
will evaluate their use in asymmetric catalysis in due course.

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J. Balsells et al. / Tetrahedron: Asymmetry 9 (1998) 4135–4142
1. Experimental
1.1. Synthesis and characterization of 1–4
The procedures for the preparation of compounds 1–4 were identical, and details are given for the
synthesis of 1.
To a stirred solution of the L-tartrate salt of (R,R)-1,2-diaminocyclohexane (1.98 g, 7.5 mmol) in 8 ml
of a 2 N NaOH solution, were added 20 ml of dichloromethane. The mixture was cooled to 0°C and a
solution of 2,4,6-triisopropylbenzene sulfonyl chloride (757 mg, 2.5 mmol) in 20 ml of dichloromethane
was added dropwise over 20 min. After the addition was complete, the mixture was allowed to warm to
room temperature and stirred overnight. The resulting solution was washed with water (3×50 ml) and the
solvent removed at reduced pressure. In this manner, 1 was isolated in 99% yield (950 mg, 2.49 mmol).
Data for 1: m.p. 199°C; [α]D −26.2 (c 0.50, CHCl3); 1H NMR (CDCl3, 500 MHz) δ 1.0–1.23 (m, 3H),
1.25 (d, J=7.0 Hz, 6H), 1.27 (d, J=7.0 Hz, 6H), 1.28 (d, J=7.0 Hz, 6H), 1.3–1.6 (m, 3H), 1.6–1.7 (m, 2H),
1.9–2.0 (m, 2H), 2.33 (td, J1=3.0 Hz, J2=10.0 Hz, 1H), 2.84 (td, J1=3.5 Hz, J2=10.5 Hz, 1H), 2.89 (hept,
J=7.0 Hz, 1H), 4.16 (hept, J=7.0 Hz, 2H), 4.90 (b, 1H), 7.15 (s, 2H) ppm; 13C{1H} NMR (CDCl3, 125
MHz) δ 23.55 (CH3), 23.56 (CH3), 24.8 (2CH3), 24.95 (CH2+CH2), 24.97 (2CH3), 29.8 (2CH), 33.0
(CH2), 34.1 (CH), 36.1 (CH2), 55.0 (CH), 60.1 (CH), 123.8 (2CH), 133.9 (C), 149.9 (2C), 152.6 (C)
ppm; IR (KBr) 3348, 3287, 2957, 2863, 1604, 1568, 1461, 1425, 1364, 1313, 1154, 1118, 1082, 1037,
944, 914, 878, 847 cm−1; ME (EI, 70 eV) m/z: 381 (M+, 5%), 113 (95%), 96 (100%).
Data for 2: The yield was 100%. M.p. 63°C; [α]D −32.3 (c 0.51, CHCl3); 1H NMR (CDCl3, 500 MHz)
δ 0.8–1.2 (m, 3H), 1.2–1.4 (m, 1H), 1.45–1.52 (m, 1H), 1.52–1.6 (m, 1H), 1.6–1.7 (m, 1H), 1.8–1.9 (m,
1H), 2.33 (td, J1=4.0 Hz, J2=10.0 Hz, 1H), 2.60 (td, J1=4.0 Hz, J2=10.5 Hz, 2H), 7.54 (dd, J1=7.5 Hz,
J2=8.0 Hz, 1H), 7.59 (m, 1H), 7.67 (m, 1H), 7.94 (d, J=8.0 Hz, 1H), 8.06 (d, J=8.5 Hz, 1H), 8.31 (dd,
J1=1.0 Hz, J2=7.0 Hz, 1H), 8.68 (dd, J1=0.5 Hz, J2=8.5 Hz, 1H) ppm; 13C{1H} NMR (CDCl3, 125 MHz)
δ 24.7 (CH2), 24.8 (CH2), 32.5 (CH2), 35.3 (CH2), 54.7 (CH), 60.7 (CH), 124.1 (CH), 124.5 (CH), 126.8
(CH), 128.1 (C), 128.2 (CH), 129.1 (CH), 129.6 (CH), 134.1 (CH), 135.4 (C), 145.7 (C) ppm; IR (KBr)
3288, 3057, 2934, 2857, 1555, 1499, 1448, 1320, 1161, 1134, 1069, 986, 913, 805, 771, 676, 598 cm−1
ME (EI, 70 eV) m/z: 304 (M+, 4%), 113 (70%), 96 (100%).
;
Data for 3: The reaction mixture was extracted with a 2 N HCl solution (3×50 ml). The organic layer
was rejected and the aqueous phase was basified with 2 N NaOH, and extracted with CH2Cl2 (3×50
ml). Removal of the solvent at reduced pressure yielded 634 mg (2.36 mmol, 94%) of compound 3 as a
white solid. M.p. 104°C; [α]D −42.7 (c 0.52, CHCl3); 1H NMR (CDCl3, 500 MHz) δ 1.0–1.3 (m, 4H),
1.45–1.95 (m, 4H), 2.34 (m, 1H), 2.42 (s, 3H), 2.77 (m, 1H), 7.30 (d, J=8.0 Hz, 2H), 7.78 (d, J=8.0 Hz,
2H) ppm; 13C{1H} NMR (CDCl3, 125 MHz) δ 21.5 (CH3), 24.2 (CH2), 24.8 (CH2), 32.6 (CH2), 35.5
(CH2), 54.8 (CH), 60.5 (CH), 127.0 (2CH), 129.6 (2CH), 137.9 (C), 143.2 (C) ppm; IR (KBr) 3338,
3281, 3055, 2920, 1594, 1491, 1448, 1327, 1160, 1091, 949, 812, 709, 662 cm−1; ME (EI, 70 eV) m/z:
269 (M+, 12%), 113 (72%), 96 (100%).
Data for 4: The white solid obtained from the reaction was purified by column chromatography
using SiO2. Traces of bis-sulfonamide were eluted using ethyl acetate, while pure 4 was eluted using
CH2Cl2:CHCl3 (10% v/v). The yield was 85% (627 mg, 2.11 mmol). M.p. 127°C; [α]D −44.8 (c 0.50,
CHCl3); 1H NMR (CDCl3, 500 MHz) δ 1.0–1.25 (m, 4H), 1.6–1.7 (m, 2H), 1.85–1.95 (m, 2H), 2.29 (s,
3H), 2.34 (m, 1H), 2.58 (m, 1H), 2.66 (s, 6H), 6.94 (s, 2H) ppm; 13C{1H} NMR (CDCl3, 125 MHz) δ
21.8 (CH3), 23.0 (2CH3), 24.8 (CH2), 24.9 (CH2), 32.5 (CH2), 35.8 (CH2), 54.7 (CH), 60.2 (CH), 131.9
(2CH), 134.6 (C), 138.7 (2C), 141.9 (C) ppm; IR (KBr) 3360, 3300, 2922, 1606, 1583, 1458, 1405, 1315,

J. Balsells et al. / Tetrahedron: Asymmetry 9 (1998) 4135–4142
4139
1145, 1112, 1076, 963, 934, 847, 653, 578, 539 cm−1; ME (EI, 70 eV) m/z: 297 (M+, 3%), 113 (68%),
96 (100%).
1.2. Synthesis and characterization of 5a–8c
The procedures for the preparation of compounds 5a–8c were identical, and details are given for the
synthesis of 5a.
To a stirred solution of 5a (190 mg, 0.5 mmol) in 6 ml of CH2Cl2 were added at room temperature
61 mg (0.5 mmol) of salicylaldehyde in 4 ml of CH2Cl2. The mixture was stirred at room temperature
overnight. Anhydrous sodium sulfate was added, the solution filtered and the solvent removed at reduced
pressure to obtain 244 mg (0.5 mmol, 100%) of 5a as a yellow solid. M.p. 150°C; [α]D −59.2 (c 0.50,
CHCl3); 1H NMR (CDCl3, 500 MHz) δ 1.0–1.4 (m, 4H), 1.20 (d, J=7.0 Hz, 6H), 1.22 (d, J=7.0 Hz, 6H),
1.23 (d, J=7.0 Hz, 6H), 1.6–1.7 (m, 2H), 1.7–1.8 (m, 1H), 1.8–1.9 (m, 1H), 2.0–2.1 (m, 1H), 2.9 (hept,
J=7.0 Hz, 1H), 3.1–3.2 (m, 1H), 3.4–3.5 (m, 1H), 4.1 (hept, J=7.0 Hz, 2H), 4.35–4.45 (m, 1H), 6.84 (t,
J=7.5 Hz, 1H), 6.91 (d, J=8.0 Hz, 1H), 7.10 (s, 2H), 7.20 (dd, J1=7.5 Hz, J2=2.0 Hz, 1H), 7.28 (td, J1=8.0
Hz, J2=2.0 Hz, 1H), 8.33 (s, 1H), 12.9 (b, 1H) ppm; 13C{1H} NMR (CDCl3, 125 MHz) δ 23.2 (CH2),
23.4 (CH3), 23.5 (CH3), 23.8 (CH2), 24.7 (2CH3), 24.8 (2CH3), 29.7 (2CH), 31.2 (CH2), 33.0 (CH2),
34.0 (CH), 56.7 (CH), 71.3 (CH), 117.0 (CH), 118.5 (CH), 123.7 (2CH), 131.4 (CH), 132.3 (CH), 133.9
(C), 149.7 (2C), 152.6 (C), 161.0 (C), 165.2 (CH) ppm; IR (KBr) 3216, 2931, 2861, 1636, 1565, 1458,
1284, 1156, 1040, 943, 884, 766, 679, 569, 517 cm−1; ME (EI, 70 eV) m/z: 484 (M+, 48%), 217 (100%),
122 (62%), 96 (67%).
Data for 5b: The yield was 100% (258 mg, 0.50 mmol). M.p. 139°C; [α]D −54.9 (c 0.51, CHCl3); 1H
NMR (CDCl3, 500 MHz) δ 1.20–1.25 (m, 18H), 1.2–1.44 (M, 3H), 1.54–1.64 (m, 2H), 1.68–1.76 (m,
1H), 1.8–1.9 (m, 1H), 1.95–2.20 (m, 1H), 2.86 (hept, J=7.0 Hz, 1H), 3.26–3.33 (m, 1H), 3.38–3.45 (m,
1H), 3.88 (s, 3H), 4.12 (hept, J=7.0 Hz, 2H), 4.55–4.65 (m, 1H), 6.79 (t, J=8.0 Hz, 1H), 6.82 (dd, J1=8.0
Hz, J2=1.5 Hz, 1H), 6.91 (dd, J1=8.0 Hz, J2=1.5 Hz, 1H), 7.10 (s, 2H), 8.33 (s, 1H), 13.55 (b, 1H) ppm;
13C{1H} NMR (CDCl3, 125 MHz) δ 22.6 (CH2), 23.2 (CH2), 23.40 (CH3), 23.41 (CH3), 24.7 (2CH3),
24.8 (2CH3), 29.6 (2CH), 30.2 (CH2), 32.0 (CH2), 33.9 (CH), 56.0 (CH3), 56.1 (CH), 70.3 (CH), 114.3
(CH), 117.8 (CH), 118.5 (C), 123.1 (CH), 123.7 (2CH), 133.7 (C), 148.4 (C), 149.7 (2C), 151.7 (C),
152.5 (C), 165.1 (CH) ppm; IR (KBr) 3240, 2932, 2863, 1636, 1601, 1465, 1255, 1163, 1087, 1031, 973,
942, 884, 789, 731, 680, 571 cm−1; ME (EI, 70 eV) m/z: 514 (M+, 100%), 247 (63%), 152 (75%), 96
(40%).
Data for 5c: The yield was 100% (300 mg, 0.50 mmol). M.p. 118°C; [α]D −43.0 (c 0.53, CHCl3); 1H
NMR (CDCl3, 500 MHz) δ 1.20 (d, J=7.0 Hz, 6H), 1.23 (d, J=7.0 Hz, 6H), 1.25 (d, J=7.0 Hz, 6H), 1.30
(s, 9H), 1.0–1.4 (m, 4H), 1.44 (s, 9H), 1.6–1.7 (m, 2H), 1.7–1.8 (m, 1H), 1.78–1.87 (m, 1H), 2.1–2.2 (m,
1H), 2.86 (hept, J=7.0 Hz, 1H), 3.1–3.2 (m, 1H), 3.4–3.5 (m, 1H), 3.7–3.8 (m, 1H), 4.12 (hept, J=7.0
Hz, 2H), 4.38–4.42 (m, 1H), 7.06 (d, J=2.5 Hz, 1H), 7.12 (s, 2H), 7.37 (d, J=2.5 Hz, 1H), 8.36 (s, 1H),
13.2 (b, 1H) ppm; 13C{1H} NMR (CDCl3, 125 MHz) δ 23.3 (CH2), 23.5 (CH3+CH3), 23.7 (CH2), 24.7
(2CH3), 24.8 (2CH3), 29.4 (3CH3), 29.7 (2CH), 30.7 (CH2), 31.5 (3CH3), 33.0 (CH2), 34.0 (CH), 34.1
(C), 35.0 (C), 56.9 (CH), 71.5 (CH), 117.7 (C), 123.7 (2CH), 126.1 (CH), 127.2 (CH), 133.7 (C), 136.6
(C), 140.1 (C), 149.7 (2C), 152.6 (C), 157.9 (C), 166.6 (CH) ppm; IR (KBr) 3281, 2958, 2865, 1628,
1600, 1458, 1437, 1362, 1314, 1275, 1253, 1152, 1060, 941, 881, 827, 773, 660, 575 cm−1; ME (EI, 70
eV) m/z: 596 (M+, 100%), 581 (24%).
Data for 6a: The yield was 100% (203 mg, 0.50 mmol). M.p. 179°C; [α]D −127.6 (c 0.50, CHCl3); 1H
NMR (CDCl3, 500 MHz) δ 1.2–1.8 (m, 7H), 2.2–2.3 (m, 1H), 2.8–2.9 (m, 1H), 3.25–3.35 (m, 1H), 5.33
(d, J=8.0 Hz, 1H), 6.58 (td, J1=7.5 Hz, J2=1.5 Hz, 1H), 6.60–6–64 (m, 2H), 7.16 (td, J1=7.7 Hz, J2=2.0

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J. Balsells et al. / Tetrahedron: Asymmetry 9 (1998) 4135–4142
Hz, 1H), 7.19 (td, J1=8.0 Hz, J2=1.0 Hz, 1H), 7.26 (td, J1=7.0 Hz, J2=1.5 Hz, 1H), 7.40 (t, J=8.0 Hz,
1H), 7.56 (d, J=8.5 Hz, 1H), 7.80 (s, 1H), 8.22 (dd, J1=7.0 Hz, J2=1.0 Hz, 1H), 8.41 (d, J=8.5 Hz, 1H),
12.2 (b, 1H) ppm; 13C{1H} NMR (CDCl3, 125 MHz) δ 23.6 (CH2), 24.6 (CH2), 33.7 (CH2), 33.8 (CH2),
57.7 (CH), 72.4 (CH), 116.6 (CH), 118.0 (C), 118.1 (CH), 123.8 (CH), 1, 127.7 (CH), 128.9 (CH), 129.0
(CH), 131.3 (CH), 131.7 (CH), 134.0 (C), 134.1 (CH), 135.1 (C), 160.5 (C), 164.4 (CH) ppm; IR (KBr)
3277, 3052, 2934, 2858, 1629, 1577, 1496, 1458, 1419, 1320, 1279, 1199, 1158, 1132, 1093, 1067, 984,
949, 914, 841, 811, 773, 754, 675, 599, 516 cm−1; ME (EI, 70 eV) m/z: 408 (M+, 75%), 217 (77%), 127
(53%), 96 (100%).
Data for 6b: The yield was 100% (219 mg, 0.50 mmol). M.p. 88°C; [α]D −106.4 (c 0.50, CHCl3); 1H
NMR (CDCl3, 500 MHz) δ 1.2–1.8 (m, 7H), 2.2–2.3 (m, 1H), 2.8–2.9 (m, 1H), 3.25–3.35 (m, 1H), 3.88
(s, 3H), 5.36 (d, J=8.5 Hz, 1H), 6.22 (dd, J1=8.0 Hz, J2=1.0 Hz, 1H), 6.56 (t, J=8.0 Hz, 1H), 6.78 (dd,
J1=8.0 Hz, J2=1.5 Hz, 1H), 7.17 (td, J1=7.0 Hz, J2=1.0 Hz, 1H), 7.27 (td, J1=7.7 Hz, J2=1.5 Hz, 1H),
7.42 (t, J=7.7 Hz, 1H), 7.53 (d, J=8.0 Hz, 1H), 7.78 (s, 1H), 7.80 (d, J=8.5 Hz, 1H), 8.21 (dd, J1=7.5 Hz,
J2=1.5 Hz, 1H), 8.40 (d, J=8.5 Hz, 1H), 12.6 (b, 1H) ppm; 13C{1H} NMR (CDCl3, 125 MHz) δ 23.4
(CH2), 24.4 (CH2), 33.4 (CH2), 33.5 (CH2), 56.0 (CH3), 57.6 (CH), 72.0 (CH), 113.6 (CH), 117.4 (CH),
117.8 (C), 123.0 (CH), 123.7 (CH), 123.8 (CH), 126.0 (CH), 127.5 (C), 127.6 (CH), 128.7 (CH), 129.0
(CH), 134.0 (CH+C), 135.0 (C), 148.0 (C), 151.0 (C), 164.3 (CH) ppm; IR (KBr) 3299, 3058, 2928,
2857, 1628, 1464, 1320, 1254, 1161, 1131, 1080, 974, 900, 839, 800, 769, 736, 677, 595, 517 cm−1; ME
(EI, 70 eV) m/z: 438 (M+, 100%), 247 (30%), 152 (70%), 127 (72%), 96 (63%).
Data for 6c: The yield was 100% (260 mg, 0.50 mmol). M.p. 159°C; [α]D −56.3 (c 0.54, CHCl3); 1H
NMR (CDCl3, 500 MHz) δ 1.2–1.8 (m, 7H), 1.26 (s, 9H), 1.39 (s, 9H), 2.24–2.34 (m, 1H), 2.8–2.9 (m,
1H), 3.3–3.4 (m, 1H), 5.32 (d, J=8.0 Hz, 1H), 6.57 (d, J=2.5 Hz, 1H), 7.24 (t, J=7.5 Hz, 1H), 7.28 (d,
J=2.5 Hz, 1H), 7.36 (t, J=8.5 Hz, 2H), 7.58 (d, J=8.5 Hz, 1H), 7.78 (t, J=8.5 Hz, 1H), 7.87 (s, 1H), 8.23
(dd, J1=7.0 Hz, J2=1.0 Hz, 1H), 8.50 (d, J=8.5 Hz, 1H), 12.8 (b, 1H) ppm; 13C{1H} NMR (CDCl3, 125
MHz) δ 23.5 (CH2), 24.4 (CH2), 29.5 (3CH3), 31.4 (3CH3), 33.1 (CH2), 33.7 (CH2), 33.9 (C), 34.9 (C),
57.6 (CH), 72.3 (CH), 117.2 (C), 123.9 (CH), 124.1 (CH), 126.0 (CH), 126.2 (CH), 126.8 (CH), 127.7
(C), 127.8 (CH), 128.7 (CH), 129.0 (CH), 133.8 (C), 133.9 (CH), 135.3 (C), 136.0 (C), 139.4 (C), 157.6
(C), 165.7 (CH) ppm; IR (KBr) 3257, 3057, 2953, 2860, 1629, 1595, 1440, 1361, 1320, 1274, 1242,
1201, 1160, 1133, 1092, 1067, 984, 900, 856, 827, 799, 769, 677, 633, 596, 518 cm−1; ME (EI, 70 eV)
m/z: 520 (M+, 100%), 505 (55%), 477 (24%), 127 (43%).
Data for 7a: The yield was 100% (184 mg, 0.50 mmol). M.p. 137°C; [α]D −16.4 (c 0.50, CHCl3); 1H
NMR (CDCl3, 500 MHz) δ 1.2–1.8 (m, 7H), 2.2–2.3 (m, 1H), 2.25 (s, 3H), 2.88–2.98 (m, 1H), 3.18–3.26
(m, 1H), 5.2 (b, 1H), 6.76 (td, J1=7.5 Hz, J2=1.0 Hz, 1H), 6.83 (d, J=8.5 Hz, 1H), 6.93 (d, J=8.5 Hz, 2H),
7.01 (dd, J1=7.5 Hz, J2=1.5 Hz, 1H), 7.2–7.3 (m, 1H), 7.53 (d, J=8.5 Hz, 2H), 8.14 (s, 1H), 12.5 (b, 1H)
ppm; 13C{1H} NMR (CDCl3, 125 MHz) δ 21.5 (CH3), 23.6 (CH2), 24.5 (CH2), 33.5 (CH2), 33.6 (CH2),
57.2 (CH), 72.0 (CH), 116.6 (CH), 118.3 (C), 118.5 (C), 126.5 (2CH), 129.3 (2CH), 131.4 (CH), 132.0
(CH), 137.5 (C), 142.9 (C), 160.9 (C), 165.1 (CH) ppm; IR (KBr) 3260, 2946, 2861, 1631, 1577, 1495,
1456, 1406, 1315, 1280, 1211, 1150, 1089, 953, 904, 812, 765, 666, 566, 546 cm−1; ME (EI, 70 eV)
m/z: 372 (M+, 62%), 217 (57%), 134 (30%), 122 (38%), 96 (100%).
Data for 7b: The yield was 100% (202 mg, 0.50 mmol). M.p. 159°C; [α]D −44.4 (c 0.50, CHCl3); 1H
NMR (CDCl3, 500 MHz) δ 1.2–1.8 (m, 7H), 2.2–2.3 (m, 1H), 2.23 (s, 3H), 2.9–3.0 (m, 1H), 3.18–3.26
(m, 1H), 3.89 (s, 3H), 5.2 (b, 1H), 6.64–6.76 (m, 2H), 6.88 (d, J=7.5 Hz, 1H), 6.94 (d, J=7.5 Hz, 2H),
7.53 (d, J=7.5 Hz, 2H), 8.13 (s, 1H), 13.1 (b, 1H) ppm; 13C{1H} NMR (CDCl3, 125 MHz) δ 21.3 (CH3),
23.4 (CH2), 24.3 (CH2), 33.2 (CH2+CH2), 55.9 (CH3), 57.1 (CH), 71.5 (CH), 113.9 (CH), 117.6 (C),
118.3 (C), 123.1 (CH), 126.5 (2CH), 129.3 (2CH), 137.5 (C), 142.9 (C), 148.2 (C), 151.5 (C), 165.0

J. Balsells et al. / Tetrahedron: Asymmetry 9 (1998) 4135–4142
4141
(CH) ppm; IR (KBr) 3299, 2938, 2861, 1636, 1565, 1465, 1437, 1325, 1253, 1157, 1080, 969, 901, 810,
741, 665, 570, 548 cm−1; ME (EI, 70 eV) m/z: 402 (M+, 100%), 247 (28%), 152 (72%), 96 (59%).
1
Data for 7c: The yield was 100% (243 mg, 0.50 mmol). M.p. 91°C; [α]D −4.7 (c 0.51, CHCl3); H
NMR (CDCl3, 500 MHz) δ 1.2–1.8 (m, 7H), 1.28 (s, 9H), 1.45 (s, 9H), 2.3–2.4 (m, 1H), 2.23 (s, 3H),
2.96–3.04 (m, 1H), 3.20–3.27 (m, 1H), 4.9 (b, 1H), 6.95 (d, J=2 Hz, 1H), 7.05 (d, J=8.0 Hz, 2H), 7.36 (d,
J=2.0 Hz, 1H), 7.61 (d, J=8.0 Hz, 2H), 8.24 (s, 1H), 13.0 (b, 1H) ppm; 13C{1H} NMR (CDCl3, 125 MHz)
δ 21.4 (CH3), 23.7 (CH2), 24.2 (CH2), 29.5 (3CH3), 31.4 (3CH3), 32.8 (CH2), 33.6 (CH2), 34.0 (C), 35.0
(C), 57.5 (CH), 71.7 (CH), 117.6 (C), 126.1 (CH), 126.7 (2CH), 127.0 (CH), 129.5 (2CH), 136.3 (C),
137.4 (C), 140.0 (C), 142.8 (C), 157.7 (C), 166.6 (CH) ppm; IR (KBr) 3277, 2948, 2862, 1629, 1598,
1440, 1362, 1322, 1274, 1157, 1092, 1066, 899, 811, 772, 713, 665, 573, 549 cm−1; ME (EI, 70 eV)
m/z: 484 (M+, 100%), 469 (65%), 441 (28%).
Data for 8a: The yield was 100% (200 mg, 0.50 mmol). M.p. 133°C; [α]D −49.8 (c 0.49, CHCl3); 1H
NMR (CDCl3, 500 MHz) δ 1.2–1.8 (m, 7H), 2.12 (s, 3H), 2.3–2.4 (m, 1H), 2.25 (s, 6H), 2.88–2.98 (m,
1H), 3.18–3.26 (m, 1H), 5.17 (d, J=8.5 Hz, 1H), 6.59 (s, 2H), 6.78–6.86 (m, 2H), 7.07 (d, J=7.5 Hz, 1H),
7.24–7.30 (m, 1H), 8.12 (s, 1H), 12.4 (b, 1H) ppm; 13C{1H} NMR (CDCl3, 125 MHz) δ 20.9 (CH3),
23.0 (2CH3), 23.6 (CH2), 24.7 (CH2), 33.6 (CH2), 33.7 (CH2), 57.5 (CH), 72.5 (CH), 116.6 (CH), 118.2
(CH), 118.4 (C), 131.2 (CH), 131.7 (2CH), 131.9 (CH), 134.2 (C), 138.0 (2C), 141.7 (C), 161.0 (C),
164.4 (CH) ppm; IR (KBr) 3292, 2936, 2858, 1628, 1577, 1496, 1457, 1324, 1279, 1152, 1093, 1060,
953, 911, 853, 765, 659, 585, 538, 425 cm−1; ME (EI, 70 eV) m/z: 400 (M+, 29%), 217 (100%), 96
(77%).
Data for 8b: The yield was 100% (215 mg, 0.50 mmol). M.p. 114°C; [α]D −67.0 (c 0.51, CHCl3); 1H
NMR (CDCl3, 500 MHz) δ 1.3–1.8 (m, 7H), 2.09 (s, 3H), 2.25–2.35 (m, 1H), 2.48 (s, 6H), 2.9–3.0 (m,
1H), 3.15–3.25 (m, 1H), 3.88 (s, 3H), 4.97 (d, J=8.5 Hz, 1H), 6.58 (s, 2H), 6.71 (dd, J1=7.5 Hz, J2=1.5 Hz
1H), 6.76 (t, J=7.5 Hz, 1H), 6.88 (dd, J1=7.5 Hz, J2=1.5 Hz, 1H), 8.11 (s, 1H), 12.9 (b, 1H) ppm; 13C{1H}
NMR (CDCl3, 125 MHz) δ 20.7 (CH3), 23.0 (2CH3), 23.4 (CH2), 24.6 (CH2), 33.4 (CH2+CH2), 55.9
(CH3), 57.4 (CH), 72.1 (CH), 113.7 (CH), 117.5 (CH), 118.3 (C), 123.0 (CH), 131.7 (2CH), 134.2 (C),
138.0 (2C), 141.7 (C), 148.1 (C), 151.5 (C), 164.4 (CH) ppm; IR (KBr) 3290, 2934, 2858, 1630, 1604,
1559, 1462, 1322, 1255, 1154, 1085, 974, 901, 852, 782, 729, 662, 584, 537, 448 cm−1; ME (EI, 70 eV)
m/z: 430 (M+, 97%), 247 (100%), 152 (93%), 96 (71%).
Data for 8c: The yield was 100% (255 mg, 0.50 mmol). M.p. 111°C; [α]D −2.0 (c 0.53, CHCl3); 1H
NMR (CDCl3, 500 MHz) δ 1.2–1.8 (m, 7H), 1.30 (s, 9H), 1.43 (s, 9H), 2.09 (s, 3H), 2.3–2.4 (m, 1H),
2.52 (s, 6H), 2.94–3.02 (m, 1H), 3.14–3.22 (m, 1H), 4.8 (b, 1H), 6.73 (s, 2H), 6.94 (d, J=2.5 Hz, 1H),
7.34 (d, J=2.5 Hz, 1H), 8.20 (s, 1H), 12.9 (b, 1H) ppm; 13C{1H} NMR (CDCl3, 125 MHz) δ 20.8 (CH3),
23.0 (2CH3), 23.7 (CH2), 24.4 (CH2), 29.4 (3CH3), 31.5 (3CH3), 32.8 (CH2), 33.7 (CH2), 34.0 (C), 34.9
(C), 57.5 (CH), 72.3 (CH), 117.5 (C), 126.0 (CH), 127.0 (CH), 131.9 (2CH), 134.1 (C), 136.1 (C), 138.4
(2C), 139.8 (C), 141.5 (C), 157.8 (C), 166.3 (CH) ppm; IR (KBr) 3281, 2952, 2860, 1628, 1603, 1473,
1437, 1320, 1274, 1153, 1063, 896, 848, 772, 713, 659, 583, 539 cm−1; ME (EI, 70 eV) m/z: 512 (M+,
100%), 497 (49%), 469 (21%), 119 (37%).
Acknowledgements
This work was supported by the National Science Foundation in the form of a Career Award to PJW
(CHE-9733274), the National Institute of Health (GM58101), and DuPont Aid to Education. We would
like to thank the National Science Foundation for funding of a 500 MHz NMR spectrometer (CHE-

4142
J. Balsells et al. / Tetrahedron: Asymmetry 9 (1998) 4135–4142
9413802), and SDSU and CONACYT Proyecto Infraestructura (F264-E9207) for funding of an X-ray
diffractometer for Instituto Tecnológico de Tijuana.
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