The use of benzamide derivatives of secondary amines for stereochemical studies by circular dichroism

Article abstract of DOI:10.1080/10242430212196

The benzamide chromophore is widely used as a Cottonogenic derivative of primary amines for stereochemical studies by circular dichroism. The assignments based on the exciton chirality method are reliable since the benzamide group has well-defined geometry and conformation. A recent report U.D. Chisholm, J. Golik, B. Krishnan, J.A. Matson, D.L. Van Vranken, J. Am. Chem. Soc. 1999, 121: 3801-3802) claimed a caveat in the application of the exciton chirality method to benzamides derived from secondary amines. By the use of benzoyl derivatives of amino alcohols (1-4) and diamines (5, 6) of known absolute configuration we demonstrate that the 250-210 nm range exciton Cotton effects due to secondary and tertiary benzamides are generally of opposite sign. The origin of such disparity is traced to different conformational equilibria of the amide C-N bond in secondary and tertiary benzamides, as shown by semiempirical molecular modelling and NMR data. This feature can be useful in the determination of absolute configuration by analysis of the CD spectra due to exciton coupling of tertiary benzamides.

Full text of DOI:10.1080/10242430212196

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The Use of Benzamide Derivatives of Secondary Amines
for Stereochemical Studies by Circular Dichroism
Jacek Gawroński a , Halina Kołbon a & Marcin Kwit a
a Department of Chemistry , Adam Mickiewicz University , Poznań, Poland
Published online: 17 Sep 2010.
To cite this article: Jacek Gawroński , Halina Kołbon & Marcin Kwit (2002) The Use of Benzamide Derivatives of Secondary
Amines for Stereochemical Studies by Circular Dichroism, Enantiomer: A Journal of Sterochemistry, 7:2-3, 85-92, DOI:
10.1080/10242430212196
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Enantiomer, Vol. 7, pp.85–92
c
Copyright 2002 Taylor & Francis
1024-2430/02 $12.00 + .00
DOI: 10.1080/10242430290015629
Full Paper
The Use of Benzamide Derivatives of
Secondary Amines for Stereochemical
Studies by Circular Dichroism
Jacek Gawron´ ski,
Halina Kolbon, and
Marcin Kwit
Department of Chemistry,
Adam Mickiewicz University,
Poznan´ , Poland
ABSTRACT The benzamide chromophore is widely used as a Cottono-
genic derivative of primary amines for stereochemical studies by circular
dichroism. The assignments based on the exciton chirality method are
reliable since the benzamide group has well-defined geometry and con-
formation. A recent report (J.D. Chisholm, J. Golik, B. Krishnan, J.A.
Matson, D.L. Van Vranken, J. Am. Chem. Soc. 1999, 121: 3801–3802)
claimed a caveat in the application of the exciton chirality method to
benzamides derived from secondary amines. By the use of benzoyl deriva-
tives of amino alcohols (1–4) and diamines (5, 6) of known absolute
configuration we demonstrate that the 250–210 nm range exciton Cot-
ton effects due to secondary and tertiary benzamides are generally of
opposite sign. The origin of such disparity is traced to different confor-
mational equilibria of the amide C N bond in secondary and tertiary
benzamides, as shown by semiempirical molecular modelling and NMR
data. This feature can be useful in the determination of absolute config-
uration by analysis of the CD spectra due to exciton coupling of tertiary
benzamides.
KEYWORDS absolute configuration, conformation, circular dichroism,
benzamides, exciton Cotton effects, amino alcohols, diamines
INTRODUCTION
Exciton coupling between the electric dipole-allowed transitions of
two or more chromophores has been successfully applied as a method
of stereochemical analysis, particularly for absolute configuration deter-
mination of a wide variety of organic synthetic and natural compounds
[1,2]. Chiral non-chromophoric diols and polyols have been studied
as the corresponding benzoates [3], whereas in the case of the primary
amino group in amino alcohols and diamines the benzamide [1,4] as well
as the phthalimide [5–8] chromophoric derivatives have been applied.
The success of the exciton chirality method, when applied to benzoates,
secondary benzamides and phthalimides, rests on the well-established
Received December 12, 2001;
accepted January 24, 2002.
Address correspondence to Jacek
Gawronski, Adam Mickiewicz
University, Department of Chemistry,
Laboratory of Organic
Stereochemistry, Grunwaldzka 6, 60
780 Poznan, Poland. E-mail:
gawronsk@amu.edu.pl
85

structure, electronic properties and conformational
preferences of the chromophore. Whereas secondary
amides (I, R = H) strongly prefer a conformation I
with Z planar amide group and the amide carbonyl
syn to the C H bond of the chiral center, tertiary
amides (I, R = alkyl) are conformationally more la-
bile. In particular two conformers, E and Z, of the
amide bond are of importance [9] since exciton cou-
pling due to each of the two conformers could lead
to opposite-sign Cotton effects, making the assign-
ment of the absolute configuration ambiguous. In
fact, configurational predictions based on the cir-
cular dichroism of tertiary amides are considered
difficult [10], and recently a caveat in the applica-
tion of the exciton chirality method to N,N-dialkyl
amides has been reported [11]. Moreover, unlike
N-phthaloyl derivatives, mixed imide derivatives of
amines (I, R = Ac) also present difficulty in interpret-
ing the CD spectra due to contributions of several
conformers [12].
configuration, all bearing another chromophore:
benzoate, benzamide or phthalimide. These model
compounds were obtained in two series: one with
secondary benzamide group (1a-6a) and the other
with tertiary benzamide group (N-benzyl derivatives
1b-6b,c). N-Benzyl benzamides 1b-6b,c were ob-
tained by Schiff base formation of the amine with
benzaldehyde, followed by NaBH4 reduction to the
corresponding N-benzylamine prior to benzoylation
with benzoyl chloride (see Experimental section).
The CD and UV spectra of six pairs of benzamide
derivatives 1a,b-6a,b,c are shown in Figures 1 and 2.
Inspection of the data in Figure 1 indicates that
the Cotton effects in the range 250–210 nm are of
opposite sign for the pairs of compounds of the
a and b series (the difference is less significant in
the case of 1a and 1b). In the case of secondary
benzamides (a series), the dominant if not exclu-
sive conformation of the amide bond is Z. Also,
the sign of the exciton Cotton effect reflects the
sign of the N C C O(or N) torsion angle in the
dominant conformer, since the directions of the elec-
tric dipole transition moments in the benzamide or
benzoate group are approximately parallel to the di-
rections of the C O or C N bond, while that of
the phthalimide chromophore is exactly in the di-
rection of the C N bond [5,6]. The Cotton effects
of 2a, 4a and 6a are similar to those reported in
methanol solution [13]. The dominant conformers
in the a series are g+ for 2a and g for 1a, 4a,
5a and 6a (g+ and g refer to gauche conforma-
tion of the N C C O or N C C N bonds). The
Chiral N-benzylamines are important products of
asymmetric synthesis. They can be obtained by ei-
ther asymmetric nucleophilic addition to or by re-
duction of N-benzyl imines. Therefore, it is com-
pelling to investigate more thoroughly the applica-
tion of the exciton chirality method to dibenzoyl
derivatives of N-benzyl amino alcohols and diamines
IIb, in comparison to the CD data of dibenzoyl
derivatives of primary amino alcohols and diamines
IIa. As a result of the study we expect to be able
to answer the following question: Can the N,O- or
N,N-dibenzoyl exciton chirality method be reliably
used to determine the absolute configuration of sec-
ondary amines, despite the contributions from sev-
eral conformers and the presence of an additional
benzyl chromophore?
RESULTS AND DISCUSSION
We set out to compare the CD spectra of benza-
mide derivatives of four chiral amino alcohols
(1–4) and one diamine (5, 6) of known absolute
´
J. GAWRONSKI ET AL.
86

FIGURE 1 CD spectra of 1a–6c in acetonitrile solution.
case of 3a is more complex. From the magnitude
of J1,2 coupling constant (3.6 Hz) it appears that in
addition to the trans conformer, a typical one for
the erythro (anti ) configuration [14], there is a con-
tribution of hydrogen-bonded conformers g+ and
g ; the positive exciton Cotton effect results mainly
from the contribution of the phenyl (1La transition)–
benzamide coupling in the trans conformer and from
the contribution due to the Ph-C-OBz unit, as in
structure 7. The reversal of the exciton Cotton ef-
fects in the b series compared to a can be traced to
the change of conformer population in tertiary ben-
zamides, as shown in Scheme 1.
The dominant E conformer of the tertiary ben-
zamide group produces positive exciton Cotton ef-
fect, whereas a negative exciton Cotton effect is due
to the Z conformer. Indeed, examination of the 1H
NMR spectra of two tertiary benzamides, 2b (acyclic)
and 5b (cyclic), reveals that at ambient tempera-
ture the resonance signals are broadened due to a
1
slow rate of exchange (see the H NMR data on
esters of N-benzoyl-N-benzyl- -amino acids [15]).
At lower temperatures, separate signals are observed
due to the presence of two (E, Z) conformers
(Figure 3).
For example, the methyl group resonance dou-
blets of 2b are seen in the ratio E:Z = 2.5:1 (at
20 C), whereas in the case of 5b the resonance
signals of the benzyl CH2 group (doublets of
doublets) are in the ratio E:Z = 3.5:1 (at 40 C).
These findings are supported by the results of com-
putational studies of conformational equilibria of 2b
and 5b. Semiempirical computations (AM1) indicate
that in both cases E conformer is of lower energy
(Scheme 2).
SCHEME 1
CD OF BENZAMIDE DERIVATIVES
87

It is noteworthy that other conformers, with the
N Bn bond eclipsing the vicinal C H bond, ac-
cording to computations are of significantly higher
energy and are not further considered as significant
contributors to the CD spectra.
The computed steric energy differences between
E and Z conformers correspond to E:Z conformer
ratio of 1.9:1 in the case of 2b and 3.2:1 in the case of
5b. The exciton Cotton effect due to the dominant E
conformer is negative in the case of 2b and positive
in the case of 5b. This is found experimentally for
both compounds (Figure 1).
The computed structures of 2b and 5b indicate
rather high degrees of non-planarity of the benzoyl
group in tertiary benzamides. Non-planarity of ter-
tiary benzamides is well documented [16,17]. It is
of interest to note that non-planarity brings about a
blue shift of the benzamide
-
absorption band
(ca 20 nm in ethanol solution) [16]. We observe
that such a blue shift results in negative electronic
absorption between 220 and 240 nm in the differ-
ential UV spectra 1b-1a, 2b-2a, 3b-3a, 6b-6a and
SCHEME 2
FIGURE 2 UV spectra of 1a-6c and the differential UV spectra, in acetonitrile solution.
´
J. GAWRONSKI ET AL.
88

FIGURE 3 Portions of the 1H NMR spectra of benzamides 2b and 5b in CDCl3 solution.
6b-6c shown in Figure 2. This negative absorption
corresponds to the position of the benzamide
band at ca. 225 nm. Non-planarity of the benzamide
group can contribute to the CD spectrum, if it is bi-
ased toward one of the two enantiomeric conformers
in the chiral molecule.
Finally, we briefly examined the effect of the
N-benzyl chromophore on the CD spectra of ben-
zamides of the b series. Direct comparison of the
CD spectrum of 6b with the reported CD of its
-
N,N 0-dimethyl analogue [10] reveals that the Cot-
ton effects in the 240–210 nm region are of the same
sign, although they differ in magnitude. Similarly,
the Cotton effects of N-benzyl derivative 4b are of
the same sign but are of higher amplitude compared
with those of the N-methyl analogue 4c (Figure 1).
In addition, we measured the CD spectra of deriva-
tives 8–10 (Figure 4).
Bichromophoric interaction of the benzyl chro-
mophores in 8 results in very weak Cotton effects,
probably due to conformational averaging. The in-
teraction of the benzyl and benzoyl chromophores
attached to the same nitrogen atom, as in 9, gives
a weak, bisignate Cotton effect. Only slightly larger
Cotton effects are obtained in the case of monoben-
zoyl derivative 10 of N,N 0-dibenzyl diamine 8.
Thus, chromophoric contribution of the N-benzyl
group to the CD spectra of N-benzyl benzamides
can be neglected for the purpose of qualitative stere-
ochemical analysis.
CONCLUDING REMARKS
The leading conclusion from the present work
is that exciton coupling can be used for stereo-
chemical assignments involving tertiary benzamides
FIGURE 4 CD spectra of N-benzyl derivatives 8–10 (in
acetonitrile).
CD OF BENZAMIDE DERIVATIVES
89

N,N0-Dibenzoyl-N,N0-dibenzyl Diamines
and N,O-dibenzoyl-N-benzyl Amino
Alcohols, Representative Procedure for 4b
if augmented by suitable analysis of the E,Z amide
conformer population, for example, by NMR spec-
troscopy or semiempirical computations.
The practical conclusion drawn from inspecting
the CD data is that in the cases studied the sign of the
Cotton effects due to the interactions of the benza-
A mixture of (1R,2R)-trans-2-aminocyclohexanol
(115 mg, 1 mmol) and benzaldehyde (106 mg,
1 mmol) in 10 mL of toluene (with a drop of DMF)
was refluxed for 5 h with a Dean-Stark adapter. After
cooling, the solvent was evaporated to dryness and
the crude (1R,2R)-trans-N-benzylidene-2-amino-
cyclohexanol was dissolved in MeOH (5 mL). Then,
sodium borohydride (76 mg, 2 mmol) was added in
one portion at 0 C. The mixture was allowed to warm
to room temperature and was stirred overnight. After
evaporation to dryness, CH2Cl2 (10 mL) and water
(10 mL) were added and the mixture was stirred for
1 h. The aqueous phase was separated and extracted
twice with CH2Cl2. The combined organic extracts
were washed with brine, dried and concentrated in
vacuum to give crude (1R,2R)-trans-N-benzyl-2-
aminocyclohexanol which was used directly for the
benzoylation reaction according to the procedure
described above.
mide/benzoate
-
transitions are opposite, when
comparing the data for R-NH-Bz and R-N(Bn)-Bz
derivatives. The sign of the exciton Cotton effect
due to the vicinal benzoate/benzamide or benza-
mide/benzamide interactions is of the same sign as
the sign of the N C C O(N) torsion angle in the
case of -NHBz amides, but of opposite sign in the
case of -NBnBz amides.
EXPERIMENTAL SECTION
Materials and Methods
NMR spectra were obtained using a Varian
Gemini 300 spectrometer, in CDCl3 solutions, with
tetramethylsilane (TMS) as an internal standard. Op-
tical rotations were determined on a Perkin-Elmer
243B polarimeter at 20 C in CHCl3 solutions. Cir-
cular dichroism and UV spectra were measured us-
ing a Jasco J-810 spectropolarimeter. Melting points
(R)-N,O-Dibenzoyl-1-amino-2-propanol (1a), color-
less crystals, mp. 70–72 C (benzene-hexane); [ ]D =
1
65.4 (c = 1); H NMR : 1.5 (d, J = 6.3 Hz,
3H), 3.7–3.8 (m, 2H), 5.3–5.4 (m, 1H), 6.7 (br s, 1H),
7.4–7.5 (m, 10H), 7.7 (d, J = 11.8 Hz, 2H), 8.0 (d,
J = 11.8 Hz, 2H).
¨
were measured using a Buchi B-545 apparatus and
are uncorrected. All reagents were purchased from
Sigma-Aldrich Chemical Co. and used without fur-
ther purification.
Semiempirical computations were performed us-
ing MOPAC97.
(R)-N,O-Dibenzoyl-N-benzyl-1-amino-2-propanol
1
(1b), oil, [ ]D
=
37.0 (c = 0.5); H NMR (1:3.5
mixture of Z and E conformers) : 1.1 and 1.4 (br
siglets, 3H), 3.3–3.9 (m, 2H), 4.6–5.1 (m, 2H), 5.4
and 5.6 (br singlets, 1H), 7.1–7.6 (m, 13H), 8.0 (br s,
1H), 8.1 (br s, 1H).
N,N 0-Dibenzoyl Diamines
and N,O-Dibenzoyl Amino Alcohols,
Representative Procedure for 6a
(S)-N,O-Dibenzoyl-2-amino-1-propanol (2a), color-
less crystals, mp. 104–107 C (benzene-hexane);
1
[ ]D
=
28.7 (c = 1); H NMR : 1.4 (d, J =
To a CH2Cl2 solution of (1R,2R)-trans-diamino-
cyclohexane (114 mg, 1 mmol) was added triethy-
lamine (0.4 mL, 2.87 mmol) and benzoyl chloride
(0.4 mL, 3.44 mmol) at 0 C and the mixture was
stirred overnight at room temperature. The reaction
was quenched by adding water (5 mL). The aqueous
layer was separated and extracted with Et2O. The
combined organic layers were washed with aqueous
sodium bicarbonate and brine, dried and evaporated.
The crude product was crystallized from benzene-
hexane to give (1R,2R)-trans-N,N 0-dibenzoyl-
(1R,2R)-trans-diaminocyclohexane 6a.
6.9 Hz, 3H), 4.4–4.5 (m, 2H), 4.6–4.7 (m, 1H), 6.5
(d, J = 6.6 Hz, 1H), 7.4–7.6 (m, 6H), 7.7 (d, J =
9.6 Hz, 2H), 8.0 (d, J = 9.6 Hz, 2H).
(S)-N,O-Dibenzoyl-N-benzyl-2-amino-1-propanol
(2b), colorless crystals, mp. 67–70 C (benzene-
hexane); [ ]D = +15.8 (c = 1); 1H NMR : 1.2 (br
s, 3H), 4.1–4.9 (br m, 5H), 7.2–7.5 (m, 12H), 7.6–7.7
(m, 1H), 7.9 (br s, 1H), 8.1–8.2 (m, 1H).
(1R,2RS)-N,O-Dibenzoyl-2-amino-1-phenyl-1-pro-
panol (3a), colorless crystals, mp.165–167 C; [ ]D =
+5.3 (c = 1); 1H NMR : 1.3 (d, J = 6.9 Hz, 3H), 4.8
(m, 1H), 6.2 (d, J = 3.6 Hz, 1H), 6.4 (d, J = 8.5 Hz,
´
J. GAWRONSKI ET AL.
90

(1R,2R)-trans-N-Benzoyl-N0-phtaloyldiaminocyclo-
hexane (5a), colorless crystals, mp. 260–261 C
(benzene-dioxane); [ ]D = 104.7 (c = 1); 1H NMR
: 1.3–1.4 (m, 2H), 1.5–1.6 (m, 1H), 1.8–2.0 (m, 3H),
2.2 (d, J = 10.4 Hz, 1H), 2.6–2.7 (m, 1H), 4.0–4.1
(m, 1H), 4.7–4.8 (m, 1H), 5.9 (d, J = 8.0 Hz, 1H),
7.3–7.4 (m, 4H), 7.5 (d, J = 8.2 Hz, 1H), 7.6–7.7 (m,
2H), 7.8 (m, 2H).
1H), 7.3–7.5 (m, 10H), 7.6 (m, 1H), 7.7 (d, J = 9.6 Hz,
2H), 8.1 (d, J = 9.6 Hz, 2H).
(1 R,2 S)-N,O-Dibenzoyl-N-benzyl-2-amino-1-phenyl-
1-propanol (3b), colorless crystals, mp. 157–159 C
1
(benzene); [ ]D = +2.2 (c = 1); H NMR : 1.4
(d, J = 7.1 Hz, 3H), 3.4 (d, J = 6.3 Hz, 1H), 4.3 (d,
J = 15.7 Hz, 1H), 4.6 (d, J = 15.7 Hz, 1H), 5.0 (s,
1H), 7.0 (d, J = 6.3 Hz, 2H), 7.2–7.3 (m, 8H), 7.4–
7.5 (m, 10H).
(1R,2R)-trans-N-Benzoyl-N-benzyl-N0-phtaloyldia-
minocyclohexane (5b), colorless crystals, mp.
(1 R,2 R)-trans-N,O-Dibenzoyl-2-aminocyclohexanol
(4a), colorless crystals, mp. 146–152 C (benzene-
1
157–159 C (benzene); [ ]D
=
25.8 (c = 0.5); H
NMR : 1.3 (br s, 2H), 1.5 (br d, J = 12.1 Hz, 1H),
1.7 (br s, 2H), 2.0 (br d, J = 12.1 Hz, 1H), 2.2 (br
s, 1H), 4.2 (d, J = 16.2 Hz, 1H), 4.3–4.4 (m, 1H),
4.5–4.6 (m, 2H), 5.2 (d, J = 15.7 Hz, 1H), 7.2–7.5
(m, 10H), 7.7 (br s, 2H), 7.9 (s, 2H).
hexane), (lit.[18] 153–155 C); [ ]D
0.5); H NMR data in agreement with previously
reported [18].
=
72.3 (c =
1
(1R,2R)-trans-N,O-Dibenzoyl-N-benzyl-2-amino-
cyclohexanol (4b), colorless crystals, mp. 114–117 C
(benzene-hexane); [ ]D = +17.4 (c = 0.5); 1H NMR
: 1.1–1.9 (m, 8H), 3.9–4.0 (m, 1H), 4.4 (d, J =
15.4 Hz, 1H), 5.0 (d, J = 15.4 Hz, 1H), 5.1 (br s,
1H), 7.1–7.6 (m, 13H), 7.9–8.1 (m, 2H).
(1 R,2 R)-trans-N,N0-Dibenzoyldiaminocyclohexane
(6a), colorless crystals, mp. 257–259 C (benzene-
dioxane) (lit.[19] > 300 C); 1H NMR data in agree-
ment with previously reported [19].
(1R,2R)-trans-N,N0-Dibenzoyl-N-benzyldiaminocy-
(1R,2R)-trans-N,O-Dibenzoyl-N-methyl-2-amino-
cyclohexanol (4c) was obtained as follows. To a pyri-
dine solution of (1R,2R)-trans-2-aminocyclohexanol
(115 mg, 1 mmol) was added a solution of ethyl chlo-
roformate (0.19 mL, 2 mmol) in CH2Cl2 (2 mL) at
0 C and the mixture was stirred overnight at room
temperature. The reaction was quenched by adding
water (5 mL). The aqueous layer was separated and
extracted with Et2O. The combined organic layers
were washed with aqueous sodium bicarbonate and
brine, dried and evaporated to dryness. The crude
(1R,2R)-trans-N,O-di(ethoxycarbonyl)-2-aminocycl-
ohexanol was dissolved in anhydrous THF, then
lithium aluminum hydride (76 mg, 2 mmol) was
added in one portion at 0 C. The mixture was al-
lowed to warm to room temperature and stirred over-
night. After addition of ethyl acetate (1 mL), the
mixture was stirred for an additional hour and the
water (5 mL) was added. The aqueous phase was sep-
arated and extracted twice with Et2O. The combined
organic extracts were washed with brine, dried and
concentrated in vacuum to give crude (1R,2R)-trans-
N-methyl-2-aminocyclohexanol which was used di-
rectly for the benzoylation reaction according to the
procedure described for 4b. Product 4c was obtained
clohexane (6b), solidified oil, mp. 69–70 C; [ ]D
=
+11.2 (c = 0.5); 1H NMR 1.3–1.4 (m, 4H), 1.7–1.8
(m, 2H), 1.9 (s, 1H), 2.3 (d, J = 12.4 Hz, 1H), 4.1 (d,
J = 12.4 Hz, 1H), 4.6 (s, 2H), 4.9 (br s, 1H), 7.1–7.2
(m, 10H), 7.4–7.5 (m, 4H), 7.9 (d, J = 8.0 Hz, 1H).
(1 R,2 R-trans-N,N0-Dibenzoyl-N,N 0-dibenzyldiam-
inocyclohexane (6c), colorless crystals, mp. 162–164 C
(benzene-hexane); [ ]D = +139.3 (c = 1); 1H NMR
(1:1 mixture of conformers) : 0.8–1.1 (m, 4H), 1.2–
1.3 (m, 4H), 1.5–1.6 (m, 3H), 1.8–2.0 (m, 4H), 2.1 (d,
J = 12.6 Hz, 1H), 3.2 (d, J = 15.7 Hz, 1H), 3.6 (d,
J = 17.0 Hz, 1H), 4.0–4.1 (m, 1H), 4.2 (d, J = 15.9
Hz, 1H), 4.5–4.6 (m, 2H), 4.8 (d, J = 15.1 Hz, 1H),
5.0 (d, J = 18.1 Hz, 2H), 5.2–5.3 (m, 2H), 5.5 (d,
J = 15.9 Hz, 1H), 6.8 (m, 2H), 7.0–7.6 (m, 38H).
(1R,2R)-trans-N,N0-Dibenzyldiaminocyclohexane(8),
obtained according to a reported procedure [20].
(1R,2R)-trans-N-Benzoyl-N-benzyl-2-aminocyclohe-
xanol (9), obtained according to general procedure
using one equivalent benzoyl chloride, with no tri-
ethylamine; oil; [ ]D = 19.7 (c = 1); 1H NMR :
1.1–1.3 (m, 3H), 1.5–1.7 (m, 3H), 1.8–1.9 (m, 1H),
2.1 (br s, 1H), 3.5 (br s, 2H), 4.5 (d, J = 15.6 Hz, 1H),
4.6 (br s, 1H), 5.0 (br d, J = 15.4 Hz, 1H), 7.3–7.6 9
(m, 10H).
1
as an oil; [ ]D = +18.8 (c = 0.6); H NMR (1:1.8
(1R,2R)-trans-N-Benzoyl-N,N0-dibenzyldiaminocy-
clohexane (10), obtained from 8 according to general
procedure using one equivalent benzoyl chloride,
with no triethylamine; oil; [ ]D = +2.4 (c = 1);
mixture of conformers) 1.1–2.0 (m, 7H), 2.1–2.3 (m,
1H); 2.8 and 3.0 (two singlets, 1H); 3.3 and 3.6 (two
broad singlets, 3H), 5.0–5.1 and 5.1–5.2 (two multi-
plets, 1H), 7.1–7.6 (m, 9H), 8.0–8.1 (m, 1H).
CD OF BENZAMIDE DERIVATIVES
91

1H NMR : 0.8–1.7 (m, 8H), 2.1 (d, J = 11.3 Hz,
1H), 2.5–2.6 (m, 1H), 3.3 (d, J = 12.9 Hz, 1H),
3.6–3.7 (m, 1H), 3.7 (d, J = 13.2 Hz, 1H), 4.3 (d,
J = 15.4 Hz, 1H), 4.8 (d, J = 15.4 Hz, 1H), 6.9–7.6
(m, 15 H).
[6] J. Gawron´ ski, F. Kaz´mierczak, K. Gawron´ ska, U.
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ACKNOWLEDGEMENT
[9] T. Heinz, D. M. Rudkevich, and J. Rebek, Jr., Angew.
Chem. Int. Ed. 1999, 38, 1136–1139.
Financial support by the Committee for Scientific
Research, grant no. PBZ 6.06, is gratefully
acknowledged.
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3802.
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