2004
K. AKASAKA et al.
of 1 are significantly shielded, while those of the C3–C7
alkyl chain are not (Fig. 2A). These results indicate that
the C1-methyl group exists in the deshielded region of
anisotropy by the anthracenedicarboximide group and
that the C3–C7 alkyl chain is not in the preferred
conformation of 1 in CD3OD. The preferred conforma-
tions of 1 and 2 can be attained by the conformation of
H10–C10–C=O as s-trans and of O=C–NH–C2–H2 as
1,3-syn, the most stable conformation of N-secondary-
alkylcyclohexanecaroxamide, as shown in Fig. 2.
C30H35N2O3 [ðM þ HÞþ], 471.2647; found, 471.2656.
N-(R)-2-Heptyl (1R,2R)-2-(2,3-anthracenedicarbox-
imido)cyclohexanecarboxamide (2). Yellow crystals
22
(40% from methanol), mp 223–224 ꢀC, ½ꢀꢁ ꢂ75:33ꢀ
1
(c 0.15, CHCl3); H-NMR ꢅ: 0.075 (d, J ¼ 6:8 Hz, 3H),
0.44 (m, 4H), 0.70 (m, 2H), 0.931 (d, J ¼ 6:3 Hz, 3H),
0.98 (m, 2H), 1.36–1.54 (m, 2H), 1.55–1.65 (m, 1H),
1.78–1.96 (m, 4H), 2.16–2.25 (m, 1H), 3.33 (dt, J ¼
3:4 Hz, 11.7 Hz, 3H), 3.60 (m, 1H), 4.47 (dt, J ¼ 3:9 Hz,
12.2 Hz, 1H), 7.62 (m, 2H), 8.11 (m, 2H), 8.50 (s, 2H),
8.75 (s, 2H); HRMS (FAB) m=z: calcd. for C30H35N2O3
[ðM þ HÞþ], 471.2647; found, 471.2651.
CH-ꢄ interaction is one of the important factors to
stabilize a conformation.6–8) If 1 had the same crystal
structure as the preferred conformation in the solution,
the C1 methyl group should be located over the aromatic
ring. However, the crystalline structure of 1 differed
from its preferred conformation in methanol. In this
crystal structure, the C3–C7 alkyl chain was laid
between two aromatic rings to stabilize the structure
by both intra- and inter-molecular CH-ꢄ interactions
(Fig. 1B). Although the three single bonds, C10–CO,
CO–NH and NH–C2, of the amide part of 1 could rotate
to provide the conformation for CH-ꢄ interaction, only
the C10–CO bond rotated in the crystalline structure.
These results suggest that the 1,3-syn conformation at
O=C–NH–C2(R,R0)–H2 was more stable than the s-
trans conformation at H10–C10–C=O. In the solution,
inter-molecular CH-ꢄ interaction between the C3–C7
alkyl chain and the anthracene ring of another molecule
may be too weak to form. This might be due to the
difference of molecular structure in the solid state and in
the solution for this system. The foregoing results
suggest that CH-ꢄ interaction is one of the important
factors causing structural differences in the two states.
In the solution, the stereochemistry of the amino
group on a chiral secondary carbon atom determines
which alkyl group on the chiral carbon atom is laid on
the aromatic ring, because they form s-trans at H10–
C10–C=O, 1,3-syn at O=C–NH–C2–H2, and 1,3-syn at
H20–C20–N–C=O conformations as most preferred
ones. This allows us to exploit 2-(2,3-anthracenedicar-
boximido)cyclohexanecarbonyl chloride as a chiral
conversion reagent to determine the absolute configu-
Acknowledgments
The authors express their thanks to Prof. Dr. Lindner
of Vienna University for useful discussions.
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22
(76.1% from methanol), mp 207–208 ꢀC, ½ꢀꢁ
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6:3 Hz, 3H), 0.743 (t, J ¼ 6:8 Hz, 3H), 1.13 (m, 6H),
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1.79–1.98 (m, 4H), 2.15–2.24 (m, 1H), 3.34 (dt,
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