Synthesis of chiral ligands containing the N-(S)-α-phenylethyl group and their evaluation as activators in the enantioselective addition of Et2Zn to benzaldehyde

Article abstract of DOI:10.1016/j.tetasy.2006.06.005

The synthesis of chiral ligands 4-18 derived from N-[(S)-α-phenylethyl]-trans-β-aminocyclohexanols (S,S,S)-1a and (R,R,S)-2 is described. Addition of diethylzinc to benzaldehyde catalyzed by ligands 4-18 (6 mol %) proceeds in fair to good yield (45-86%),

Full text of DOI:10.1016/j.tetasy.2006.06.005

Tetrahedron: Asymmetry 17 (2006) 1663–1670
Synthesis of chiral ligands containing the N-(S)-a-phenylethyl
group and their evaluation as activators in the
enantioselective addition of Et2Zn to benzaldehyde
Virginia M. Mastranzo,a,b Ericka Santacruz,a,b Gabriela Huelgas,a,b Evelyn Paz,b
b
b
c,
b,
*
*
`
Martha V. Sosa-Rivadeneyra, Sylvain Bernes, Eusebio Juaristi, Leticia Quintero and
Cecilia Anaya de Parrodia,*
aUniversidad de las Ame´ricas Puebla, Departamento de Ciencias Quı´mico-Biolo´gicas, Santa Catarina Ma´rtir s/n, Cholula,
Puebla 72820, Mexico
bCentro de Investigacio´n de la Facultad de Ciencias Quı´micas, Universidad Auto´noma de Puebla, 72570 Puebla, Mexico
cCentro de Investigacio´n y de Estudios Avanzados del Instituto Polite´cnico Nacional, Departamento de Quı´mica, Me´xico, DF 07000, Mexico
Received 20 April 2006; accepted 5 June 2006
Abstract—The synthesis of chiral ligands 4–18 derived from N-[(S)-a-phenylethyl]-trans-b-aminocyclohexanols (S,S,S)-1a and (R,R,S)-2
is described. Addition of diethylzinc to benzaldehyde catalyzed by ligands 4–18 (6 mol %) proceeds in fair to good yield (45–86%), and
low to good enantioselectivities (1–76% ee). Highest enantioselectivities were induced by ligands (S,S,S)-4 and (S,S,S,S,R,R)-18 (76%
and 68% ee, respectively). The configuration of the major enantiomer of carbinol 3 is (R) in both cases.
ꢀ 2006 Elsevier Ltd. All rights reserved.
1. Introduction
to give (R)-3 in 81–90% isolated yield and 57–76% ee. By
contrast the diastereomeric (R,R,S)-2 ligand gave (S)-3 in
50% ee (Scheme 1).11
The asymmetric addition of dialkylzinc to aldehydes has
become a standard test in the design of new ligands for cat-
alytic enantioselective synthesis.1–7 Indeed, the chiral alco-
hols that are produced in this reaction are ubiquitous in
Nature and in many drugs. Furthermore, they are impor-
tant precursors to many other organic molecules of rele-
vance. The application of the (S)-a-phenylethyl group as
chiral auxiliary has proven quite effective in asymmetric
synthesis.8,9 Recently, ligands containing trans-b-aminocy-
clohexanol10,11 and trans-1,2-diaminocyclohexane12 cores
have been reported as effective constituents of catalysts in
the enantioselective addition of diethylzinc to aldehydes.
There are also some examples in the literature of the use
of chiral oxazolidines13 and imidazolidines,14 derived from
b-aminoalcohols and 1,2-diamines as catalysts.
OH
NR
OH
NH
OH
Et
PhCHO
(1 equiv)
toluene-
hexanes
or
+
Et2Zn
Ph
*
Ph
Ph
(S,S,S)-1a-f
0.06 equiv
(R,R,S)-2
0.06 equiv
(R)- or (S)-3
% eea
2.03 equiv
R
β-Aminoalcohol
(S,S,S)-1a
(S,S,S)-1b
(S,S,S)-1c
(S,S,S)-1d
(S,S,S)-1e
(S,S,S)-1f
(R,R,S)-2
H
Me
Et
Pr
Bu
57 (R)
65 (R)
73 (R)
76 (R)
75 (R)
68 (R)
50 (S)
Our group has reported the asymmetric addition of dieth-
ylzinc to benzaldehyde in the presence of N-(alkylated)-
N-[(S)-a-phenylethyl]-b-aminocyclohexanols (S,S,S)-1a–f
Pent
H
aConfiguration of major product.
*
Scheme 1.
Corresponding authors. E-mail: cecilia.anaya@udlap.mx
0957-4166/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2006.06.005

1664
V. M. Mastranzo et al. / Tetrahedron: Asymmetry 17 (2006) 1663–1670
Herein, we report the synthesis of related ligands 4–18 con-
taining multiple stereogenic centers. These ligands were
prepared from trans-N-[(S)-a-phenylethyl]-b-aminocyclo-
hexanols (S,S,S)-1a and (R,R,S)-2 (Chart 1). We also eval-
uated the potential of these chiral ligands as catalysts in the
enantioselective addition of diethylzinc to benzaldehyde.
OH
NH
O
N
i.
96%
Ph
Ph
(S,S,S)-4
(S,S,S)-1a
OH
O
i.
93%
N
O
N
O
NH
O
N
O
N
Ph
Ph
(R,R,S)-2
(R,R,S)-5
Ph
Ph
Ph
Scheme 2. Reagents and conditions: (i) excess (CH2O)n, toluene, reflux,
(S,S,S)-6
(S,S,S)-4
(R,R,S)-5
1.5 h.
O
O
O
N
O
O
O
N
N
Ph
Ph
Ph
O
N
(R,R,S)-9
(S,S,S)-8
(R,R,S)-7
Ph
Ph
Ph
Ph
NH
NH
NH
NH
(S,S,S)-4
NH
Ph
NH2
Figure 1. Computer-generated structure of (3aS,7aS)-3-[(S)-a-phenyl-
ethyl]-octahydrobenzo[d]oxazole 4 based upon the X-ray diffraction data.
t-BuO
O
(S,S,S,S)-10
(S,S,S)-11
(S,S,S)-12
Ph
Ph
N
Ph
puter-generated X-ray diffraction structure of oxazole
(S,S,S)-4, which shows like relative configurations between
stereocenters at C(3a) and C(7a) and the known (S)-config-
ured a-phenylethylamino group.
N
O
N
N
N
N
Ph
Ph
O
t-BuO
(S,S,S)-14
Ph
The 4-oxazin-2-ones (S,S,S)-6 and (R,R,S)-7 were prepared
separately from (S,S,S)-1a and (R,R,S)-2 (1 equiv) in the
presence of glyoxal (40% aqueous solution v/v), following
the procedure described in the literature (Scheme 3).15
(S,S,S,S)-13
(S,S,S,S)-15
Ph
Ph
O
Ph
Ph
N
N
N
N
N
N
OMe
OMe
OH
OH
OH
OH
O
N
O
OH
NH
i.
O
Ph
(S,S,S,S)-16
Ph
(S,S,S,S)-17
Ph
80%
(S,S,S,S,R,R)-18
Ph
Ph
Chart 1.
(S,S,S)-1a
(S,S,S)-6
O
O
OH
i.
2. Results and discussion
85%
N
NH
2.1. Synthesis of N-[(S)-a-phenylethyl]-trans-b-aminocyclo-
hexanols derivatives 4–9
Ph
Ph
(R,R,S)-2
(R,R,S)-7
N-[(S)-a-Phenylethyl]-b-aminocyclohexanols
(S,S,S)-1a
Scheme 3. Reagents and conditions: (i) OHCCHO 40% aq/THF/rt, 2 h.
and (R,R,S)-2 were prepared from cyclohexene oxide and
(S)-a-phenylethylamine as described in the literature.10,11
Both aminoalcohols (S,S,S)-1a and (R,R,S)-2 (1 equiv)
were treated separately with paraformaldehyde (6 equiv)
in toluene and heated to reflux for 1.5 h, to afford
(3aS,7aS)- and (3aR,7aR)-3-[(S)-a-phenylethyl]-octahydro-
benzo[d]oxazoles (S,S,S)-4 and (R,R,S)-5 (96% and 93%
yield, respectively, Scheme 2). Figure 1 shows the com-
The oxazolidin-2-ones (S,S,S)-8 and (R,R,S)-9 were pre-
pared following the procedure described in the literature,16
with (S,S,S)-1a and (R,R,S)-2 in the presence of methyl
chloroformate and NaH in THF by heating to reflux for
2.5 h (Scheme 4). The intermediate (S,S,S)- and (R,R,S)-
carbamates were separated by column chromatography

V. M. Mastranzo et al. / Tetrahedron: Asymmetry 17 (2006) 1663–1670
1665
OH
OH
NH
OH
NH
O
N
ii.
i.
O
N
+
95%
43%
47%
Ph
NCO2CH3
80%
OH
NH
OH
+
NH
Ph
(S,S,S)
Ph
(S,S,S)-8
i.
Ph
(S,S,S)-1a
Ph
(R,R,S)-2
(S)-19
O
OH
iii.
Ph
Ph
(S,S,S)-1a (R,R,S)-2
Ph
O
94%
N
NH
NH
NCO2CH3
ii.
N
53%
Ph
(R,R,S)-9
Ph
Ph
Ph
(R,R,S)
(S)-19
Ph
Scheme 4. Reagents and conditions: (i) (1) ClCO2Me, NaH, THF, reflux,
2.5 h; (2) column chromatography; (ii) NaH, THF, reflux, 6 h; (iii) NaH,
THF, reflux, 4.5 h.
(S,S,S,S)-10
Ph
Ph
NH
NH
iii.
iv.
96%
N
on silica gel [hexanes–EtOAc (5:1)], in 43% and 47%,
respectively. Next, the (S,S,S)- and (R,R,S)-carbamates
were cyclized under basic conditions by treatment with
NaH in THF under reflux, for 4.5 and 6 h, respectively,
to give the desired oxazolidinones (S,S,S)-8 and (R,R,S)-
9 (95% and 94% yield).
59%
N3
NH2
(S,S,S)-11
(S)-19
(S,S,S)-20
Scheme 5. Reagents and conditions: (i) MsCl, Et3N, THF, rt, 48 h; (ii)
(S)-H2NCHCH3Ph, LiClO4, CH3CN, reflux; column chromatography;
(iii) NaN3, CH3CN–H2O (9:1), CeCl3Æ7H2O, 3 h; (iv) (1) H2/Pd(OH)2/C
10%; (2) column chromatography.
2.2. Synthesis of N,N0-di[(S)-a-phenylethyl]- and N-[(S)-a-
phenylethyl]-trans-1,2-cyclohexanediamine derivatives 10–18
As part of an ongoing project involving chiral diamines
containing the trans-1,2-diaminocyclohexane core,17 we
decided to prepare several ligands derived from b-amino-
alcohol (S,S,S)-1a (Chart 1).
Boc protected amine (S,S,S)-12 (Scheme 6). The reaction
of diamine (S,S,S,S)-10 with formaldehyde (37% aqueous
solution v/v) took place in 2 h, in the presence of K2CO3
(2.5 equiv) and MgSO4 (3.0 equiv), using CHCl3 as solvent
affording the imidazolidine (S,S,S)-13. By the same token,
(S,S,S)-11 leads to the N-Boc protected imidazolidine
(S,S,S)-14 (Scheme 6).
N-(S)-(a-Phenylethyl)cyclohexene aziridine (S)-19 was used
as the starting material for the synthesis of trans-1,2-
cyclohexanediamines (S,S,S,S)-10 and (S,S,S)-11. Azir-
idine (S)-19 was prepared from the diastereoisomeric mix-
ture of b-aminoalcohols (S,S,S)-1a and (R,R,S)-2 by
mesylation of the hydroxyl group followed by spontaneous
intramolecular nucleophilic substitution (SN2). The reac-
tion was performed following the procedure described in
the literature (Scheme 5).17
Ph
NH
Ph
N
N
i.
98%
NH
Diamine (S,S,S,S)-10 was prepared by aminolysis of (S)-19
in the presence of (S)-a-phenylethylamine, 1 equiv of lith-
ium perchlorate as activator and acetonitrile as solvent at
reflux, as previously reported (Scheme 5).17 Diastereomer
(S,S,S,S)-10 was the major product (ca. 67% ds) and was
separated by column chromatography on deactivated silica
gel [Et3N/SiO2 = 2.5% v/v, hexanes–EtOAc (30:1)] in 53%
yield. The ring opening of aziridine (S)-19 by ring opening
with sodium azide catalyzed by CeCl3Æ7H2O (0.5 equiv)
in CH3CN–H2O (9:1) was also stereoselective affording
amines (S,S,S)-20 and (R,R,S)-20 in ca. 2:1 ratio.18 The
major product trans-(S,S,S)-2-azido amine was purified
by column chromatography on deactivated silica gel
[Et3N/SiO2 = 2.5% v/v, hexanes–EtOAc (30:1)] in 59%
yield. Reduction of the major diastereomer (S,S,S)-20
under a hydrogen atmosphere in the presence of 10%
palladium hydroxide on carbon as catalyst afforded
diamine (S,S,S)-11 in 96% yield (Scheme 5).
Ph
Ph
(S,S,S,S)-13
(S,S,S,S)-10
Ph
NH
ii.
98%
Ph
NH
Boc
NH
(S,S,S)-12
NH2
Ph
(S,S,S)-11
N
iii.
98%
N
Boc
(S,S,S)-14
Scheme 6. Reagents and conditions: (i) K2CO3/MgSO4/CHCl3, CH2O–
H2O (37% v/v); (ii) (Boc)2O; (iii) (1) K2CO3/MgSO4/CHCl3, CH2O–H2O
(37% v/v); (2) (Boc)2O.
The addition of di-tert-butyl dicarbonate to diamine
(S,S,S)-11, followed by stirring for 24 h, afforded the N-

1666
V. M. Mastranzo et al. / Tetrahedron: Asymmetry 17 (2006) 1663–1670
Ligand (S,S,S,S)-15 was prepared from diamine (S,S,S,S)-
10 and glyoxal according to the same procedure as de-
scribed for the synthesis of 4-oxazin-2-ones (S,S,S)-6 and
(R,R,S)-7 (Scheme 7).15
2.3. Enantioselective addition of diethylzinc to benzaldehyde
The asymmetric addition reaction of diethylzinc
(2.03 equiv) to benzaldehyde (1.0 equiv) using 6 mol % of
chiral ligands 4–18 containing the trans-b-aminocyclohexa-
nol moiety (Table 1, entries 1–6), and trans-1,2-diaminocy-
clohexane core (Table 1, entries 7–15) afforded carbinol 3
with satisfactory yields (45–86%), and low to good enantio-
selectivities (1–76% ee; Table 1).
Ph
Ph
NH
N
N
O
i.
85%
NH
Table 1. Enantioselective ethylation of benzaldehyde
Ph
(S,S,S,S)-15
Ph
(S,S,S,S)-10
OH
Ligand*
PhCHO
+
Et2Zn
Ph
Et
*
Scheme 7. Reagents and conditions: (i) OHCCHO 40% aq, CH2Cl2, rt,
2 h.
1.0 equiv
2.03 equiv 0.06 equiv
3
Entry
Liganda
% ee (yield, %)b
Predominant
configurationc
The C2-symmetric 1,2-diamine (S,S,S,S)-10 was also used
as the starting material for the synthesis of tetradentated
ligands. In particular, dialkylation of diamine (S,S,S,S)-10
in the presence of 2 equiv of methyl bromoacetate afforded
compound (S,S,S,S)-16 (98% yield). Reduction of (S,S,
S,S)-16 with LiAlH4 in THF at room temperature gave diol
(S,S,S,S)-17 in an excellent 98% yield (Scheme 8).
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
(S,S,S)-4
(R,R,S)-5
(S,S,S)-6
(R,R,S)-7
(S,S,S)-8
(R,R,S)-9
(S,S,S,S)-10
(S,S,S)-11
(S,S,S)-12
(S,S,S)-13
(S,S,S)-14
(S,S,S,S)-15
(S,S,S,S)-16
(S,S,S,S)-17
76 (79)
25 (80)
18 (75)
57 (86)
2 (78)
7 (75)
3 (75)
5 (50)
44 (60)
9 (55)
4 (46)
1 (45)
7 (54)
10 (65)
(R)
(S)
(S)
(R)
(R)
(S)
(S)
(S)
(R)
(R)
(S)
(R)
(S)
(R)
(R)
(R)
Ph
Ph
Ph
O
N
N
NH
NH
N
N
i.
98%
OMe
OMe
ii.
98%
OH
OH
O
Ph
Ph
(S,S,S,S)-10
Ph
(S,S,S,S)-17
(S,S,S,S)-16
(S,S,S,S,R,R)-18
(S,S,R,R)-22
68 (70)
37 (65)
Scheme 8. Reagents and conditions: (i) BrCH2COOMe/K2CO3/CH3CN;
(ii) LiAlH4, THF, rt, 2 h.
a All reactions were performed using 6 mol % of the chiral ligand.
b The analyses for determining enantiomeric excess were performed after
purification by column chromatography on deactivated silica gel (Et3N/
SiO2 = 2.5% v/v, hexanes–EtOAc, 94:6) by HPLC using a Chiralcel OD
column under conditions reported previously.
c Optical rotations were measured and compared with those reported in
the literature.11
b-Aminoalcohol (S,S,S,S,R,R)-18 and its open chain ana-
logue (S,S,R,R)-22 were prepared from the corresponding
diamines (S,S,S,S)-10 and 1,2-bis-[(S)-a-phenylethyl]-ethyl-
enediamine (S,S)-21,19 by aminolysis of (R)-styrene oxide
(2 equiv), in the presence of LiClO4 (2 equiv) in acetonitrile
at reflux. Both reactions proceeded in 70% yield (Scheme 9).
Most reports on the catalyzed addition of dialkylzinc to
aldehydes use b-aminoalcohols as ligands.3–7 The three no-
vel b-aminoalcohols prepared in this work [(S,S,S,S)-17,
(S,S,S,S,R,R)-18, and (S,S,R,R)-22] do activate diethylzinc
for efficient addition to benzaldehyde (65–70% yield). On
the other hand, some examples of activation with diamine
ligands have been reported.12,20 Disappointingly, the diam-
ines examined in this work (10–16, entries 7–13 in Table 1)
did promote the addition of diethylzinc to benzaldehyde
but with quite low enantioinduction (1–44% ee).
Ph
Ph
NH
Ph
Ph
N
N
i.
OH
OH
70%
(a)
(b)
NH
Ph
Ph
(S,S,S,S,R,R)-18
(S,S,S,S)-10
The highest enantioselectivities were observed with b-
aminoalcohol (S,S,S,S,R,R)-18 (68% ee) and with oxazoli-
dine (S,S,S)-4 (76% ee). Interestingly, (R,R,S)-5, which is
diastereomer of (S,S,S)-4 appears to present a mismatched
combination of stereogenic centers21 since carbinol (S)-3 is
produced in a poor 25% ee. Several groups have reported
the effectiveness of chiral oxazolidines as catalysts in the
enantioselective addition of diethylzinc to aromatic and ali-
phatic aldehydes.13 In the present study, partial hydrolysis
(10–15%) of oxazolidines (S,S,S)-4 and (R,R,S)-5 was ob-
Ph
Ph
Ph
N
NH
i.
OH
OH
70%
N
NH
Ph
Ph
Ph
(S,S)-21
(S,S,R,R)-22
Scheme 9. Reagents and conditions: (i) (R)-styrene oxide (2.0 equiv)/
LiClO4 (2.0 equiv)/CH3CN.

V. M. Mastranzo et al. / Tetrahedron: Asymmetry 17 (2006) 1663–1670
1667
served under the reaction conditions; nevertheless, the ob-
served enantiomeric ratios of (R)- and (S)-3 (Table 1) seem
to originate from oxazolidine rather than b-aminoalcohol
catalysis (compare with ee values reported in Scheme 1).
Thus, it seems that for oxazolidines (S,S,S)-4 and
(R,R,S)-5 the a-phenylethyl substituent does not play an
important role on the stereochemical outcome—apparently
the stereocenter at C(3a) plays this role.
matography on deactivated silica gel [Et3N/SiO2 = 2.5%
v/v, hexanes–EtOAc (95:5)].
4.4. (3aS,7aS)-3-N-[(S)-a-Phenylethyl]-octahydrobenzo-
[d]oxazole, (S,S,S)-4
0.50 g (96% yield) as white solid, mp = 80–82 ꢁC;
1
[a]D = +39.8 (c 1, CHCl3); H NMR (200 MHz, CDCl3)
d 0.79–0.84 (m, 2H), 0.90–1.31 (m, 3H), 1.34 (d, 3H,
J = 6.6 Hz), 1.43 (dd, 1H, J = 3.0 Hz, J0 = 11.4 Hz),
1.63–1.72 (m, 1H), 1.91–2.08 (m, 2H), 3.32–3.39 (m, 1H),
3.48 (q, 1H, J = 6.6 Hz), 4.26 (d, 1H, J = 2.6 Hz), 4.80
(d, 1H, J = 2.6 Hz), 7.22–7.36 (m, 5H). 13C NMR
(50 MHz, CDCl3) d 23.1, 24.4, 25.1, 30.7, 30.9, 63.7, 68.8,
83.4, 85.8, 127.0, 127.3, 127.9, 144.5; Colorless plate,
3. Conclusions
Chiral ligands 4–18 were prepared from cyclohexene oxide
in good yields. These chiral ligands were examined as cat-
alysts in the enantioselective addition of Et2Zn to benzalde-
hyde. Best results (highest enantioinduction) were found
with (S,S,S)-4 and (S,S,S,S,R,R)-18. On the other hand,
1,2-diamines (S,S,S,S)-10 and (S,S,S,S)-11 showed very
poor enantioselection compared with the analogous b-
aminoalcohol (S,S,S)-1a. By contrast, it was observed that
oxazolidine (S,S,S)-4 afforded higher enantioselectivities
than the corresponding imidazolidines (S,S,S,S)-12 and
(S,S,S,S)-14. The same behavior was observed with the 4-
oxazin-2-ones (S,S,S)-6 and (R,R,S)-7, compared with
oxazolidin-2-ones (S,S,S)-8, (R,R,S)-9, and piperazin-2-
one (S,S,S)-15. Furthermore, the introduction of addi-
tional coordinating sites in the ligand, and the presence
of multiple stereogenic centers as in the case of diamino
diol (S,S,S,S,R,R)-18 led to improved enantioselectivity.
Finally, comparing ligand (S,S,S,S,R,R)-18 with
(S,S,R,R)-22 we observed that the presence of the cyclo-
hexane core gave better enantioselection, presumably
owing to a more rigid transition state for the addition
reaction in the former ligand.
0.7 · 0.7 · 0.3 mm3, C15H21NO. Monoclinic, P21, a =
˚
5.5837(5),
b = 11.6568(13),
c = 10.3392(8) A,
b =
97.912(5)ꢁ, Z = 2, qcalc = 1.153 g cmꢀ3. A set of 7043
reflections was collected at T = 296(1) K using Mo-Ka
˚
radiation (k = 0.71073 A, Bruker P4 diffractometer), corre-
sponding to 2hmax = 60ꢁ. 2034 independent reflections
(Rint = 0.0359) were used for the refinement of 156 para-
meters, without neither restraints nor constraints (SHELXTL
5.10 package).22 All H atoms were placed in idealized
positions and refined using a standard riding model. The
absolute configuration was assigned as (S,S,S) assuming
the same configuration as for the starting material
(S,S,S)-1a. Final R indices: R1 = 0.0371 for 1858 reflec-
tions with I > 2r(I) and wR2 = 0.1123 for all data. CCDC
deposition number: 601707. Structure factors and raw files
are available on request to authors. HRMS-FAB m/z
found 232.1699 [(M+H)+ calcd 232.1701 for C15H22ON].
4.5. (3aR,7aR)-3-N-[(S)-a-Phenylethyl]-octahydrobenzo-
[d]oxazole, (R,R,S)-5
4. Experimental
0.49 g (93% yield) as white solid, mp 96–97 ꢁC;
1
[a]D = +23.8 (c 1, CHCl3); H NMR (400 MHz, CDCl3)
4.1. General methods
d 0.88–0.97 (m, 1H), 1.21–1.29 (m, 2H), 1.37 (d, 3H,
J = 6.6 Hz), 1.48–1.52 (m, 1H), 1.68–1.78 (m, 2H), 2.06–
2.18 (m, 3H), 3.34–3.38 (m, 1H), 3.73 (q, 1H,
J = 6.6 Hz), 4.12 (d, 1H, J = 3.6 Hz), 4.40 (d, 1H,
J = 3.6), 7.17–7.28 (m, 5H); 13C NMR (100 MHz, CDCl3)
d 23.8, 24.5, 25.2, 30.7, 32.0, 63.6, 67.7, 83.2, 85.7, 126.6,
126.8, 127.9, 144.0; HRMS-FAB m/z found 232.1710
[(M+H)+ calcd 232.1701 for C15H22ON].
All manipulations involving diethylzinc were carried out
under an argon atmosphere. Benzaldehyde was distilled
prior to use. NMR spectra were obtained on 200, 300,
1
and 400 MHz Fourier transform spectrometers. H NMR
spectra were referenced to tetramethylsilane; 13C{1H}
NMR spectra were referenced to residual CHCl3.
4.2. (1S,2S)- and (1R,2R)-1-N-[(S)-a-Phenylethyl]-b-amino-
cyclohexanol, (S,S,S)-1a and (R,R,S)-2
4.6. (4aS,8aS)- and (4aR,8aR)-4-N-[(S)-a-Phenylethyl]-
octahydrobenzo[1,4]oxazin-2-one, (S,S,S)-6 and (R,R,S)-7
These b-aminoalcohols were prepared from cyclohexene
oxide and (S)-a-phenylethylamine according to the litera-
ture procedure.10,11
These 4-oxazin-2-ones were prepared from glyoxal (40%
aqueous solution v/v) and b-aminoalcohols (S,S,S)-1a or
(R,R,S)-2, according to the literature procedure.15
4.3. General procedure for the preparation of
octahydrobenzo[d]oxazoles
4.7. (3aS,7aS)- and (3aR,7aR)-3-N-[(S)-a-Phenylethyl]-
hexahydrobenzoxazolidin-2-ones, (S,S,S)-8 and (R,R,S)-9
A solution of b-aminoalcohol (S,S,S)-1a or (R,R,S)-2
(0.50 g, 2.3 mmol), under argon atmosphere, in toluene
(20 mL) and paraformaldehyde (0.41 g, 14 mmol) was
heated to reflux for 1.5 h, cooled to rt, and concentrated
under vacuum. The product was purified by column chro-
These oxazolidin-2-ones were prepared from methyl chlo-
roformate and b-aminoalcohols (S,S,S)-1a or (R,R,S)-2,
according to the literature procedure.16

1668
V. M. Mastranzo et al. / Tetrahedron: Asymmetry 17 (2006) 1663–1670
4.8. (1S,2S)-N,N0-Di-[(S)-a-phenylethyl]cyclohexane-1,2-
diamine, (S,S,S,S)-10
less liquid (1.8 g, 98% yield); [a]D = +15.8 (c 1, CHCl3);
1H NMR (400 MHz, CDCl3) d 0.87–1.00 (m, 8H), 1.36
(d, 6H, J = 6.6 Hz), 2.25–2.34 (m, 2H), 3.60 (q, 2H,
J = 6.6 Hz), 3.77 (s, 2H), 7.28–7.42 (m, 10H); 13C NMR
(100 MHz, CDCl3) d 19.6, 24.5, 31.0, 61.6, 68.7, 71.2,
126.9, 127.7, 128.1, 145.2; HRMS-FAB m/z found
335.2477 [(M+H)+ calcd 335.2487 for C23H31N2].
This (S,S,S,S)-1,2-diamine was prepared from the N-[(S)-
a-phenylethyl]cyclohexene aziridine and (S)-a-phenylethyl-
amine as described in the literature.17
4.9. (1S,2S)-N-[(S)-a-Phenylethyl]-cyclohexane-1,2-diamine
(S,S,S)-11
4.12. (3aS,7aS)-tert-Butyl-3-N-[(S)-a-phenylethyl]-octa-
hydrobenzo[d]imidazole-1-carboxylate, (S,S,S)-14
To
a solution of 2-azido-amine (S,S,S)-20 (0.29 g,
1.2 mmol) in methanol (10 mL) was added Pd(OH)2/C
10% mol (0.11 g). The mixture was stirred for 24 h at rt un-
der H2 atmosphere (1 atm). The crude product was filtered
over Celite and washed with EtOAc (30 mL). The com-
bined organic extract was evaporated and purified by col-
umn chromatography on silica gel [hexanes–EtOAc (1:2)].
The product was recovered as a colorless oil (0.25 g, 96%
yield); [a]D = +28.5 (c 1, CHCl3); 1H NMR (400 MHz,
CDCl3) d 0.78–0.90 (m, 1H), 1.13–1.24 (m, 3H), 1.33 (d,
3H, J = 6.4 Hz), 1.58–1.65 (m, 2H), 1.88–1.93 (m, 2H),
2.16–2.21 (m, 1H), 2.31–2.36 (m, 1H), 2.6 (br, 3H), 3.88
(q, 1H, J = 6.4 Hz), 7.18–7.35 (m, 5H); 13C NMR
(100 MHz, CDCl3) d 23.6, 25.0, 25.5, 32.4, 34.6, 55.7,
55.8, 61.3, 126.3, 126.6, 128.1, 146.8; HRMS-FAB m/z
found 219.1867 (M+H)+ calcd 219.1861 for C14H23N2.
The diamine (S,S,S)-11 (1.8 g, 8.3 mmol), was added to
formaldehyde (37% aqueous solution) (0.45 mL, 17 mmol),
K2CO3 (2.9 g, 21 mmol), and MgSO4 (3.0 g, 25 mmol) in
CH2Cl2 (25 mL) under inert atmosphere and stirred at rt
for 4 h. Di-tert-butyl carbonate, (Boc)2O (2.1 mL,
9.1 mmol) was then added and the resulting solution was
stirred for a further 24 h. The reaction mixture was ex-
tracted with CH2Cl2 (3 · 20 mL). The combined organic
layer was dried with Na2SO4, filtered, and evaporated un-
der reduced pressure. The crude product was purified by
column chromatography on silica gel [hexane–EtOAc
(4:1)]. The product was isolated as white crystals, mp 75–
76 ꢁC (2.7 g, 98% yield); [a]D = +96.1 (c 1, CHCl3); 1H
NMR (200 MHz, CDCl3) d 0.78–0.94 (m, 1H), 1.06–1.26
(m, 4H), 1.33 (d, 3H, J = 6.6 Hz), 10.45 (s, 9H), 1.52–1.66
(m, 2H), 2.09 (dt, 1H, J = 2.8 Hz, J = 10.6 Hz), 2.48 (br,
1H), 3.02–3.12 (m, 1H), 3.46 (q, 1H, J = 6.6 Hz), 3.66 (d,
1H, J = 6.0 Hz), 4.55 (br, 1H), 7.19–7.35 (m, 5H); 13C
NMR (50 MHz, CDCl3) d 22.0, 24.9, 25.3, 29.2, 30.7,
31.0, 61.9, 63.5, 67.9, 71.1, 79.7, 126.7, 126.8, 127.9,
144.8, 154.2; HRMS-FAB m/z found 331.2381 [(M+H)+
calcd 331.2386 for C20H31O2N2].
4.10. tert-Butyl (1S,2S)-2-N-[(S)-a-phenylethylamino]cyclo-
hexylcarbamate, (S,S,S)-12
A solution of diamine (S,S,S)-11 (0.20 g, 0.91 mmol), di-
tert-butyl dicarbonate (0.22 mL, 1.0 mmol), and K2CO3
(0.12 g, 0.91 mmol) in CHCl3 (25 mL) was stirred for
24 h. The mixture was extracted with CH2Cl2
(3 · 15 mL). The combined organic layer was dried with
Na2SO4, filtered, and evaporated under reduced pressure.
The crude product was purified by column chromatogra-
phy on silica gel [hexane–EtOAc (4:1)]. The product was
recovered as a white solid (0.28 g, 98% yield); mp 79–
80 ꢁC; [a]D = ꢀ17.5 (c 1, CHCl3); 1H NMR (CDCl3/
TMS) d 1.05–1.24 (m, 4H), 1.28 (d, 3H, J = 6.6 Hz), 1.47
(s, 9H), 1.54–1.61 (m, 3H), 1.74–1.80 (m, 1H), 2.00–2.05
(m, 1H), 2.15–2.25 (m, 1H), 3.22–3.27 (m, 1H), 3.90 (q,
1H, J = 6.6 Hz), 4.53 (d, 1H, J = 7.0 Hz), 7.15–7.35 (m,
5H); 13C NMR (CDCl3/TMS) d 25.5, 29.2, 33.6, 34.2,
55.9, 57.3, 60.5, 79.4, 126.4, 128.0, 146.5, 155.6; HRMS-
FAB m/z found 319.2378 [(M+H)+ calcd 319.2386 for
C19H31N2O2].
4.13. (4aS,8aS)-1,4-N,N0-Bis[(S)-a-phenylethyl]-octahydro-
quinoxalin-2(1H)-one, (S,S,S,S)-15
Diamine (S,S,S,S)-10 (0.50 g, 1.5 mmol), in CH2Cl2
(10 mL), was added to glyoxal (1.5 mmol, 2.5 mL, 40%
aqueous solution v/v) at rt and the solution was stirred
for 24 h. The mixture was extracted with CH2Cl2
(3 · 20 mL) and the combined organic layer was dried with
K2CO3, filtered, and evaporated under reduced pressure.
The crude product was purified by column chromatogra-
phy on silica gel [hexane–EtOAc (6:1)]. The product was
a yellow liquid (0.53 g, 98% yield); [a]D = +5.0 (c 1,
CHCl3); 1H NMR (200 MHz, CDCl3) d 0.82–0.94 (m,
1H), 1.10–1.17 (m, 3H), 1.24 (d, 3H, J = 6.6 Hz), 1.51–
1.58 (m, 2H), 1.64 (d, 3H, J = 7.3 Hz), 1.90–1.97 (m,
1H), 2.12–2.17 (m, 1H), 2.40–2.48 (m, 1H), 2.97–3.07 (m,
1H), 3.13 (s, 2H), 4.27 (q, 1H, J = 7.0 Hz), 5.48 (q, 1H,
J = 7.0 Hz), 7.15–7.41 (m, 10H); 13C RMN (50 MHz,
CDCl3) d 9.7, 19.4, 24.9, 25.4, 29.1, 31.3, 50.9, 52.8, 53.3,
62.4, 62.7, 126.2, 126.3, 126.8, 127.4, 127.7, 139.5, 142.1,
168.4; HRMS-FAB m/z found 363.2444 [(M+H)+ calcd
363.2436 for C24H31O1N2].
4.11. (3aS,7aS)-1,3-N,N0-Bis-[(S)-a-phenylethyl]-octahydro-
1H-benzo-[d]-imidazole (S,S,S,S)-13
Diamine (S,S,S,S)-10 (1.8 g, 5.6 mmol) was added to a
mixture of 37% aqueous solution of formaldehyde
(0.30 mL, 11 mmol), K2CO3 (2.0 g, 15 mmol), and MgSO4
(2.0 g, 17 mmol) in CHCl3 (25 mL) under argon atmo-
sphere. The reaction mixture was stirred at rt for 24 h.
The mixture was extracted with CH2Cl2 (3 · 15 mL). The
combined organic layer was dried with Na2SO4, filtered
and evaporated under reduced pressure. The crude product
was purified by column chromatography on silica gel [hex-
ane–EtOAc (10:1)]. The product was obtained as a color-
4.14. (1S,2S)-N,N0-Bis-[(S)-a-phenylethyl]-N,N0-bis-
(methylacetate)-1,2-cyclohexanediamine, (S,S,S,S)-16
A solution of 1,2-diamine (S,S,S,S)-10 (3.5 g, 11 mmol), in
acetonitrile (50 mL) and dry Na2CO3 (2.8 g, 26 mmol) was

V. M. Mastranzo et al. / Tetrahedron: Asymmetry 17 (2006) 1663–1670
1669
treated under argon atmosphere with ethyl bromoacetate
(4.1 g, 26 mmol). The resulting mixture was heated to re-
flux for 15 h, and cooled to rt. The organic solution was
washed with 25 mL of H2O, extracted with 3 · 25 mL of
CH2Cl2, and the combined organic phase was dried over
MgSO4. The solvent was then removed under reduced pres-
sure and the product was purified by column chromatogra-
phy on silica gel [hexanes–EtOAc (10:1)]. The product was
recovered as a colorless oil (4.0 g, 78% yield); [a]D = +20.5
(c 1, CHCl3); 1H NMR (200 MHz, CDCl3) d 1.09–1.12 (m,
4H), 1.30 (d, 6H, J = 7.0 Hz), 1.61–1.70 (m, 2H), 2.09 (br,
2H), 2.93–2.97 (m, 2H), 3.18 (d, 2H, J = 17.6 Hz), 3.59 (s,
6H), 3.63 (d, 2H, J = 16.6 Hz), 4.55 (q, 2H, J = 7.0 Hz),
7.17–7.31 (m, 10H); 13C NMR (50 MHz, CDCl3) d 21.6,
26.8, 30.1, 47.7, 51.6, 57.5, 59.1, 126.3, 127.3, 127.9,
145.6, 173.7; HRMS-FAB m/z found 467.2905 [(M+H)+
467.2910 for C28H39N2O4].
J0 = 12.0 Hz), 3.83 (q, 1H, J = 6.6 Hz), 4.01 (q, 1H,
J = 7.2 Hz,), 4.46 (br, 1H), 7.18–7.37 (m, 20H); 13C
NMR (75 MHz, CDCl3) d 17.3, 23.7, 23.9, 25.0, 26.1,
29.0, 32.6, 32.7, 55.7, 56.1, 56.2, 59.2, 60.3, 75.5, 125.9,
126.6, 126.7, 126.8, 127.0, 127.5, 128.2, 128.3, 143.3,
145.2, 147.5, 147.6; HRMS-FAB+ m/z found 563.3636
[(M+H)+ calcd 563.3638 for C38H47N2O2].
4.17. N-[(S)-a-Phenylethyl]cyclohexene aziridine, (S)-19
The aziridine was prepared from the diastereoisomeric mix-
ture of b-aminoalcohols (S,S,S)-1a and (R,R,S)-2, accord-
ing to the literature procedure.16
4.18. (1S,2S)-2-Azido-N-[(S)-a-phenylethyl]cyclohexan-
amine, (S,S,S)-20
In a dry two-necked flask fitted with condenser and mag-
netic stirrer were placed aziridine (S)-19 (6.0 g, 30 mmol)
4.15. (1S,2S)-N,N0-Bis[(S)-a-phenylethyl]-bis(2-hydroxy-
ethyl)-1,2-cyclohexanediamine, (S,S,S,S)-17
and CeCl3Æ7H2O (5.5 g, 15 mmol) in
a mixture of
CH3CN–H2O (9:1, 30 mL). To the stirred solution was
added NaN3 (2.1 g, 33 mmol) at rt and the reaction mixture
was heated to reflux for 8 h. The organic phase was ex-
tracted with CH2Cl2 (3 · 25 mL) and H2O (25 mL). The
combined organic layer was dried with Na2SO4, and evap-
orated under reduced pressure. The separation of the major
diastereomeric trans-2-azido amine was performed by col-
umn chromatography on deactivated silica gel [Et3N/
SiO2 = 2.5% v/v, hexanes–EtOAc (30:1)], (S,S,S)-20 was
A suspension of (S,S,S,S)-16 (0.12 g, 0.26 mmol) and
LiAlH4 (0.051 g, 1.4 mmol) in THF (50 mL) was stirred
under argon atmosphere for 24 h at rt. An aqueous satu-
rated solution of NH4Cl (10 mL) was added to quench
the reaction. The organic solution was extracted with
3 · 25 mL of CH2Cl2 and the combined organic phase
was dried over MgSO4. The solvent was then removed un-
der reduced pressure and the product was purified by col-
umn chromatography on silica gel [hexanes–EtOAc
(10:1)]. The product was recovered as colorless crystals,
mp = 183–184 ꢁC (0.085 g, 80% yield), [a]D = +47.0 (c 1,
CHCl3). 1H NMR (200 MHz, CDCl3) d 1.12–1.21 (m,
4H), 1.39 (d, 6H, J = 7 Hz), 1.75–1.82 (m, 2H), 1.96–2.02
(m, 2H), 2.51–2.69 (m, 2H), 2.88–3.08 (m, 8H), 3.82 (br,
2H), 5.11 (br, 2H), 7.09–7.37 (m, 10H); 13C NMR
(50 MHz, CDCl3) d 21.5, 25.4, 26.6, 50.2, 60.7, 62.3,
126.9, 127.8, 128.1, 144.6; HRMS-FAB+ m/z found
411.3003 [(M+H)+ calcd 411.3012 for C26H39N2O2].
recovered as
a colorless liquid (4.2 g, 58% yield);
1
[a]D = +23.5 (c 1, CHCl3); H NMR (200 MHz, CDCl3)
d 1.10–1.27 (m, 4H), 1.33 (d, 3H, J = 6.6 Hz), 1.44 (s,
1H), 1.49–1.60 (m, 1H), 1.64–1.75 (m, 2H), 1.92–2.11 (m,
1H), 2.29–2.40 (m, 1H), 3.04–3.21 (m, 1H), 3.89 (q, 1H,
J = 6.6 Hz), 7.16–7.39 (m, 5H); 13C NMR (50 MHz,
CDCl3) d 24.3, 24.4, 30.6, 32.5, 56.6, 59.4, 66.3, 126.5,
126.7, 128.3, 147.2; HRMS-FAB+ m/z found 245.1756
[(M+H)+ calcd 245.1766 for C14H21N4].
4.19. N,N0-Bis[(S)-a-phenylethyl]-1,2-ethylenediamine,
(S,S)-21
4.16. (1S,2S)-N,N0-Bis[(S)-a-phenylethyl]-bis[(R)-2-
hydroxyphenethyl]-1,2-cyclohexanediamine, (S,S,S,S,R,R)-
18
The diamine was prepared from 1,2-dichloroethane and
(S)-a-phenylethylamine, according to the literature
procedure.19
A solution of 1,2-diamine (S,S,S,S)-10 (1.9 g, 5.8 mmol), in
acetonitrile (20 mL) and lithium perchlorate (1.2 g,
12 mmol) was stirred under argon atmosphere until com-
plete dissolution before the addition of (R)-styrene oxide
(1.3 mL, 12 mmol). The resulting mixture was refluxed
for 32 h, and cooled to rt. The organic solution was washed
with 25 mL of H2O, extracted with 3 · 25 mL of CH2Cl2,
and the combined organic phase was dried over MgSO4.
The solvent was then removed under reduced pressure
and the product was purified by column chromatography
on silica gel [hexane–EtOAc (10:1)]. The product was
4.20. N,N0-Bis[(S)-a-phenylethyl]-bis[(R)-hydroxyphen-
ethyl]-1,2-ethylenediamine, (S,S,R,R)-22
A solution of 1,2-diamine (S,S)-21 (2.7 g, 10 mmol) in ace-
tonitrile (20 mL) and lithium perchlorate (2.1 g, 20 mmol)
was stirred under argon atmosphere until complete dissolu-
tion. (R)-Styrene oxide (2.4 g, 20 mmol) was added to the
reaction mixture and the resulting mixture was heated to
reflux for 36 h, and cooled to rt. The organic solution
was washed with 25 mL of H2O, extracted with 3 ·
25 mL of CH2Cl2, and the combined organic phase was
dried over MgSO4. The solvent was then removed under re-
duced pressure and the product was purified by column
chromatography on silica gel [hexanes–EtOAc (8:1)]
affording a colorless liquid (3.5 g, 70% yield); [a]D =
ꢀ47.2 (c 1.10, CHCl3); 1H NMR (300 MHz, CDCl3) d
recovered as
a
yellowish oil (2.4 g, 75% yield);
1
[a]D = ꢀ0.70 (c 1, CHCl3); H NMR (300 MHz, CDCl3)
d 0.58–0.72 (m, 1H), 0.84–0.95 (m, 1H), 1.04–1.17 (m,
2H), 1.22 (d, 3H, J = 6.6 Hz), 1.31–1.34 (m, 1H), 1.37 (d,
3H, J = 6.9 Hz), 1.47–1.57 (m, 2H), 1.71–1.80 (m, 4H),
2.25–2.28 (m, 1H), 2.66–2.78 (m, 3H), 3.18 (dd, 1H,
J = 3.0 Hz, J = 14.4 Hz), 3.73 (dd, 1H, J = 6.6 Hz,

1670
V. M. Mastranzo et al. / Tetrahedron: Asymmetry 17 (2006) 1663–1670
´
8. Juaristi, E.; Escalante, J.; Leon-Romo, J. L.; Reyes, A.
1.49 (d, 6H, J = 6.6 Hz), 2.38–2.70 (m, 6H), 2.84–2.89 (m,
2H), 3.98 (q, 2H, J = 6.6 Hz), 4.58–4.63 (m, 2H), 4.80 (br,
2H), 7.21–7.28 (m, 20H); 13C NMR (75 MHz, CDCl3) d
18.4, 49.5, 59,7, 60.1, 70.7, 125.8, 127.3, 127.4, 128.2,
128.3, 140.9, 142.3. The diamine dihydrochloride was pre-
pared adding HCl 10% ethereal solution (10 mL), affording
white crystals, mp 165–166 ꢁC. Elemental analysis: found C
68.34%, H 7.75% [calcd for C34H40N2O2Æ2HClÆH2O: C
68.09%, H 7.39%].
Tetrahedron: Asymmetry 1998, 9, 715–740.
9. Juaristi, E.; Leon-Romo, J. L.; Reyes, A. Tetrahedron:
Asymmetry 1999, 10, 2441–2495.
10. (a) Anaya de Parrodi, C.; Juaristi, E.; Quintero-Cortes, L. An.
´
´
Quı´m., Int. Ed. 1996, 92, 400–404; (b) Anaya de Parrodi, C.;
Juaristi, E.; Quintero-Cortes, L.; Amador, P. Tetrahedron:
´
Asymmetry 1996, 7, 1915–1918.
11. Sosa-Rivadeneyra, M.; Munoz-Muniz, O.; Anaya de Parrodi,
˜
˜
C.; Quintero, L.; Juaristi, E. J. Org. Chem. 2003, 68, 2369–
2375.
12. (a) Cobb, A. J. A.; Marson, C. M. Tetrahedron 2005, 61,
1269–1279; (b) Trost, B. M.; Crawley, M. L. Chem. Rev.
2003, 103, 2921–2943.
13. (a) Prasad, K. R. K.; Joshi, N. N. J. Org. Chem. 1997, 62,
3770–3771; (b) Braga, A. L.; Appelt, H. R.; Schneider, P. H.;
Silveira, C. C.; Wessjohann, L. A. Tetrahedron: Asymmetry
1999, 10, 1733–1738; (c) Abato, P.; Seto, C. T. J. Am. Chem.
Soc. 2001, 123, 9206–9207.
4.21. Diethylzinc addition to benzaldehyde
The ligands 4–18 and 22 (6 mol %) were weighed into the
reaction vessel and diethylzinc (1.0 M toluene, 2.03 equiv,
0.94 mL) was added at rt. After 10 min, benzaldehyde
(1.0 equiv, 0.47 mmol) was added neat. The homogeneous
reaction mixture was stirred at rt. After 20 h the reaction
was quenched with water (5 mL), diluted with EtOAc,
filtered through Celite, and the layers separated. The aque-
ous layer was extracted with EtOAc (2 · 40 mL) and the
combined organic layers washed with brine, dried over
MgSO4, and concentrated in vacuo. The residue was puri-
fied by column chromatography on deactivated silica gel
[Et3N/SiO2 = 2.5% v/v, hexanes–EtOAc (97:3)] to afford
1-phenyl-1-propanol 3.11
14. Okaniwa, M.; Yanada, R.; Ibuka, T. Tetrahedron Lett. 2000,
41, 1047–1050.
´
15. Sosa-Rivadeneyra, M.; Quintero-Cortes, L.; Anaya de Par-
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rodi, C.; Bernes, S.; Castellanos, E.; Juaristi, E. Arkivoc 2003,
Part (xi), 61–71.
16. Anaya de Parrodi, C.; Juaristi, E.; Quintero, L.; Clara-Sosa,
A. Tetrahedron: Asymmetry 1997, 8, 1075–1082.
17. (a) Anaya de Parrodi, C.; Moreno, G. E.; Quintero, L.;
Juaristi, E. Tetrahedron: Asymmetry 1998, 9, 2093–2099; (b)
´
Anaya de Parrodi, C.; Vazquez, V.; Quintero, L.; Juaristi, J.
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This work was supported by CONACYT, Consejo Nac-
´
ional de Ciencia y Tecnologıa (Project V39500-Q and
Scholarships No. 144893, 144937, and 145001).
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