Synthesis of atropoisomeric pyridines via cobalt-catalyzed cocyclotrimerization of diynes with benzonitrile

Article abstract of DOI:10.1016/j.tet.2005.10.034

Arylpyridines (precursors for potential organocatalysts) are easily accesible by cobalt-catalyzed cocyclotrimerization of ortho-substituted 1-aryl-1,7-octadiynes with benzonitrile. The scope of the reaction with respect to the ortho substituents (OMe, Me,

Full text of DOI:10.1016/j.tet.2005.10.034

Tetrahedron 62 (2006) 968–976
Synthesis of atropoisomeric pyridines via cobalt-catalyzed
cocyclotrimerization of diynes with benzonitrile
a
Radim Hrdina, Irena G. Stara, Lenka Dufkova, Scott Mitchel,
b
a
a
´
Ivana Cısarova and Martin Kotora
´
a,b,
´ ˇ ´c
*
aDepartment of Organic and Nuclear Chemistry, Faculty of Science, Charles University, Hlavova 8, 128 43 Prague 2, Czech Republic
b
´
ˇ ´
Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo namestı 2, 166 10 Prague 6, Czech Republic
cDepartment of Inorganic Chemistry, Faculty of Science, Charles University, Hlavova 8, 128 43 Prague 2, Czech Republic
Received 11 July 2005; revised 29 September 2005; accepted 13 October 2005
Available online 10 November 2005
Abstract—Arylpyridines (precursors for potential organocatalysts) are easily accesible by cobalt-catalyzed cocyclotrimerization of ortho-
substituted 1-aryl-1,7-octadiynes with benzonitrile. The scope of the reaction with respect to the ortho substituents (OMe, Me, COOMe,
NHCOMe, F, etc.) was investigated. Three potentially atropoisomeric arylpyridines were prepared and one of them was converted into the
corresponding N-oxide and resolved into its enantiomers. The absolute configuration of the N-oxide was established by X-ray crystal
structure analysis. Preliminary results of its application in asymmetric organocatalysis are presented.
q 2005 Elsevier Ltd. All rights reserved.
1. Introduction
catalysts was pioneered by Wakatsuki,7 Vollhardt,8 and
9
¨
Bonnemann. Over the years a number of other transition
metal compounds such as Ti,10 Zr,11 Fe,12 Ta,13 and Rh14
were shown to catalyze or mediate the cyclotrimerization.
Recently, a Ru-based catalyst has been shown to be suitable
for cyclotrimerization of diynes with electron-deficient
nitriles.15,16 Cocyclotrimerization has also been used for
preparation of oligopyridines (namely bipyridines) either by
cocyclotrimerization of diynes with dinitriles,17 or alkynyl-
nitriles with diynes,18 or cyanopyridines with alkynes.19
The synthesis of chiral pyridines is based either on
cyclotrimerization with chiral nitriles20 or enantioselective
cyclotrimerization by treatment with chiral cyclopenta-
dienyl cobalt complexes.21 Herein, we report on the cobalt-
catalyzed cyclotrimerization of substituted aryldiynes with
nitriles to potentially atropoisomeric pyridines, conversion
The interest in the field of organocatalysis (acceleration of a
reaction by a catalytic amount of an organic compound) has
increased in the last few years. In particular, organocatalysis
is gaining importance in asymmetric synthesis, comple-
menting bio- and metal-catalysis.1 Out of several concepts
of organocatalysis, a significant role is played by activation
of a Lewis acid by a Lewis base. One type of the typical
Lewis base organocatalysts are pyridine N-oxides with a
biaryl framework.2–5 Since pyridine N-oxides are easily
accessible from pyridines, there is general interest in the
development of new synthetic methods for pyridine
preparation. One of them is based on [2C2C2] cocyclo-
trimerization of two C–C-triple bonds with a nitrile.6 The
use of the most widely and generally utilized cobalt
Scheme 1. Preparation of diynes 2 and their cocyclotrimerization with nitriles to arylpyridines 3 under Co-catalysis.
Keywords: Pyridine; Cocyclotrimerization; Cobalt; Catalysis; Organocatalysis.
*
Corresponding author. Tel.: C420 221 951 334; fax: C420 221 951 326; e-mail: kotora@natur.cuni.cz
0040–4020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2005.10.034

R. Hrdina et al. / Tetrahedron 62 (2006) 968–976
969
Table 1. Cobalt-catalyzed cocyclotrimerization of diynes 2 with benzonitrile to arylpyridines 3
Entry
Diyne 2a
Product 3
Conditionsa
Yield %b
1
A
54
2
3
4
A
A
A
35
76
33
5
6
7
8
A
91
A
46
A, B, C
30, 25, 62
A, B, C
75 (54)c, 67, 0
9
A, B, C
30, 69, 48
a Conditions: AZCpCo(CO)2 (20 mol%), PPh3 (40 mol%), 140 8C, 48 h; BZCpCo(COD) (20 mol%), 140 8C, 48 h; CZCpCo(CH2]CH2)2 (10 mol%),
20 8C, 30 min.
b Isolated yields.
c CpCo(CO)2 (10 mol%), 140 8C, 48 h.

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R. Hrdina et al. / Tetrahedron 62 (2006) 968–976
of one of them into a pyridine N-oxide, its resolution into
enantiomers, and preliminary results of its application in
enantioselective additions to benzaldehyde.
about the bond connecting two aromatic rings were far more
intriguing (entries 7–9). The reaction of the methoxy-
methyl substituted diyne 2g afforded the desired product 3g
in 30% yield (entry 7, conditions A). The use of
CpCo(COD) under the same reaction conditions afforded
the product in a similar yield of 25% (conditions B). A
considerably different result was obtained when the Jonas
catalyst (condition C) was used. The full conversion of the
starting material was observed within 30 min and 3g was
isolated in good 62% yield. The structure of 3g was
unequivocally confirmed by crystalographic analysis
(Fig. 1).
2. Results and discussion
We envisioned that one of the possible pathways to
potentially atropoisomeric arylpyridines could be based on
the reaction of nitriles with properly substituted a,u-
diynes,22,23 such as 1-(ortho-substituted-aryl)-1,7-octa-
diynes (Scheme 1). This strategy is similar to that used by
Heller et al.21 but its scope is limited only to a methoxy
group as the substituent in the ortho-position. It is
reasonable to assume that ortho-substitution may affect
the course of cyclotrimerization by steric and electronic
effects. These effects are important in the search for new
synthetic methods for preparation of potentially atropoiso-
¨
meric biaryls. Recently, they have been studied in the Dotz
reaction of ortho-substituted arylalkynes with chromium
carbenes24 and in the CuCl mediated reaction of zircona-
cyclopentadienes with ortho-substituted arylpropynoates.25
Furthermore, the synthetic usefulness of the commercially
available CpCo(CO)2 was explored.
The required ortho-substituted 1-aryl-1,7-octadiynes were
prepared by palladium-catalyzed Krause modification26 of
the Sonogashira coupling27 of 1,7-octadiyne with arylha-
lides 1 (Scheme 1). Usually, the coupling proceeded
smoothly to afford the desired diynes 2 in moderate to
reasonable isolated yields (24–62%) and selectivity. To
accomplish the cyclotrimerization of the diynes with
nitriles, the standard conditions (20 mol% of commercially
available CpCo(CO)2, 40 mol% of PPh3 as a ligand, 140 8C,
2 days) were used (Scheme 1). It has been shown that the
catalytically active species are formed in a reasonable
reaction rate at this temperature.6a Other cobalt complexes
such as CpCo(COD) and CpCo(CH2]CH2)2 (Jonas
catalyst)28,29 were used in order to compare the catalytic
activity. The cocyclotrimerizations were carried out in
benzonitrile as solvent to minimize homocyclotrimerization
of diyne, to ensure a high selectivity ratio for pyridine
formation.
Figure 1. An ORTEP diagram of 3g. Displacement parameters are shown at
the 50% probability level.
The cyclotrimerization of diyne 2g was also carried out on
10 mmol scale and the product 3g was isolated in 45% yield.
In addition, it was possible to isolate the compound 4 in 6%
yield, which was the product of the cocyclotrimerization of
two molecules of 2g with benzonitrile (Scheme 2). As
expected, the reaction with the methoxynaphthyldiyne 2h
furnished the corresponding product 3h in very good yield
of 75% (entry 8, conditions A), which is close to the yield
obtained by Heller under different reaction conditions.21
The similar result was observed under conditions B (67%
yield). Surprisingly, the reaction carried out in the presence
of the Jonas catalyst did not proceed and the starting
material was quantitatively recovered (entry 8, conditions
C). The reaction with methylnaphthyldiyne 2i gave the
corresponding product 3i in rather low yield of 30% (entry
9, conditions A). Again the use the Jonas catalyst
(conditions C) resulted in increase of the reaction rate and
the conversion of the starting material; the product 3i was
isolated in 48% yield. However, in this instance
CpCo(COD) proved to be the catalyst of choice, because
The results of cocyclotrimerizations are presented in
Table 1. The reaction with the diyne bearing an ester
group 2a afforded the corresponding product 3a in
acceptable yield of 54% (entry 1). In the case of the diyne
with a nitrogen substituent such as 2b, the reaction
proceeded only in moderate yield of 35% (entry 2). The
cocyclotrimerizations with alkynes bearing methoxy 2c and
methoxymethyl substituents 2d differed considerably
(entries 3 and 4); the product 3c was obtained in good
yield of 76%, whereas the arylpyridine 3d was isolated in
significantly lower yield of 33%. In the case of 1-(ortho-
tolyl)-1,7-octadiyne 2e the arylpyridine 3e was furnished in
high yield of 91% (entry 5). The cocyclotrimerization of the
fluorine substituted diyne 2f with benzonitrile also
proceeded to give the corresponding arylpyridine 3f in
moderate 46% yield (entry 6).
Cocyclotrimerizations of diynes that were expected to give
sterically hindered arylpyridines with restricted rotation

R. Hrdina et al. / Tetrahedron 62 (2006) 968–976
971
Scheme 2. Formation of 4 in cocyclotrimerization of 2g and benzonitrile.
its use afforded the corresponding product in 69% yield
(conditions B).
example methyl group occupies larger space than methoxy
or ester groups.30 Although we do not have any spectro-
scopic evidence for the following hypothesis, it is sensible
to assume that the course of the reaction is influenced
(retarded) by the strengh of the coordination of the lone
electron pair on the heteroatom of the ortho-substituent to
the cobalt atom in the intermediate cobaltacyclopentadiene.
The question is what factors are mainly responsible for the
observed difference in the yields of the arylpyridines in
entries 1–6. Obviously, the differences cannot be simply
explained by steric factors, since it is known that for
Since our initial impetus for this work was to develop an
alternative method for the preparation of chiral pyridine
oxides as potential organocatalysts, we chose pyridine 3g
for further investigation in this direction. Its oxidation with
m-chloroperoxobenzoic acid (MPCBA) proceeded
smoothly to give the corresponding N-oxide 6 in 54%
isolated yield (Scheme 3). The N-oxide 6 was resolved by
cocrystallization with (S)-(K)-binol 7 (binolZ2,20-di-
hydroxy-1,10-binaphthyl),2–5 which gave the crystalline
Scheme 3. Oxidation of the pyridine 3g to 6.
Figure 2. An ORTEP diagram illustrating the interaction of (R)-(C)-6 (on the left) with (S)-(K)-7 (right), in particular the hydrogen bonding N–O/H–O;
˚
O(1)/O(4a) 2.606(2) A, O(1)/H–O(4a) 176(2)8. Displacement parameters are shown at the 50% probability level.

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R. Hrdina et al. / Tetrahedron 62 (2006) 968–976
material containing (S)-(K)-binol 7 and (C)-6 (in 1:1
ratio), while (K)-6 remained in the solution. This
cocrystallization, followed by a chromatographic separation
of (C)-6 from (S)-(K)-binol 7, furnished pure (C)-6 of
95% ee (as detected by chiral HPLC, Chiracel OD-H) in
30% yield. The absolute configuration was found to be (R)-
(C)-6 by crystallographic analysis of the molecular crystal
of (C)-6 with (S)-(K)-7 (Fig. 2) of known absolute
configuration. The configurational stability of the com-
pound (R)-(C)-6 was quantitatively evaluated by an
analytical chiral HPLC. Preliminary data were obtained by
heating samples of (R)-(C)-6 and injecting them on the
chiral column. The (R)-(C)-6 showed no racemization in
toluene at 110 8C after 12 h.
rule out the synthetic utility of the pyridine N-oxide (R)-(C)-6
at this moment. Further experiments investigating its
reactivity and structural modifications will follow in the near
future.
4. Experimental
All reactions were carried out under a protective atmosphere
of Ar in 20 mL Schlenk flasks. Unless mentioned, reagents
were used as obtained without further purification.
4.1. General procedure for catalytic cyclotrimerization
of aryl-substituted 1,7-octadiynes with benzonitrile
1-Aryl-1,7-octadiyne (0.4 mmol) and PPh3 (42 mg,
0.16 mmol) were added to a dry Schlenk tube under argon
and dissolved in benzonitrile (2 mL, 19.4 mmol). Then
CpCo(CO)2 (14 mg, 0.08 mmol) was added. The reaction
mixture was heated for 48 h at 140 8C. After cooling down it
was quenched with water and volatiles were removed under
reduced pressure. Column chromatography on silica gel was
used to isolate products.
The catalytic activity of the pyridine N-oxide (R)-(C)-6
(5 mol%) was preliminarly tested in the addition of
allytrichlorosilane 8 to benzaldehyde 7 in dichloromethane
(Scheme 4). The attempt to carry out the reaction under
usual conditions (K40 8C)5 was not successful. The
reaction proceeded at room temperature only, but even
then the reaction rate was rather low, 50% yield of the
corresponding alcohol 9 was obtained after 72 h with the
modest asymmetric induction of 20% ee. The enantioselec-
tivity of (R)-(C)-6 was also tested in the reaction of
diethylzinc 10 with benzaldehyde 7.31 The resulting
asymmetric induction was again modest (17% ee).
4.1.1. Methyl 2-(5,6,7,8-tetrahydro-3-phenylisoquinolin-
1-yl)benzoate (3a). Column chromatography on silica gel
(7:1 hexane/EtOAc) afforded 192 mg (54%) of the title
compound as a viscous liquid: 1H NMR (400 MHz, CDCl3)
d 1.74–1.84 (m, 4H), 2.44–2.47 (m, 2H), 2.87–2.90 (m, 2H),
3.61 (s, 3H), 7.30–7.47 (m, 6H), 7.54–7.59 (m, 1H),
7.93–7.95 (m, 2H), 7.99–8.01 (m, 1H); 13C NMR
(100 MHz, CDCl3) d 22.4, 23.0, 26.7, 29.5, 52.0, 119.8,
126.9 (2C), 127.7, 128.1, 128.4 (2C), 129.4, 130.0, 130.1,
130.3, 131.6, 139.7, 142.3, 146.6, 153.1, 159.0, 167.7; IR
(CHCl3) n 3523, 3367, 3064, 3005, 2952, 1721, 1590, 1576,
1434, 1295, 1275, 1130, 1084, 1052, 966, 908 cmK1
;
FAB-MS m/z 241 (MCHC), 225, 165, 128, 115; HR-MS
(FAB) calculated for C16H17O2 (MCHC) 241.1239, found
241.1229.
4.1.2. N-(2-(5,6,7,8-Tetrahydro-3-phenylisoquinolin-1-
yl)phenyl)acetamide (3b). Column chromatography on
silica gel (1:1 hexane/EtOAc) afforded 96 mg (35%) of the
title compound as a pale yellow solid: mp 130–132 8C
(hexane); 1H NMR (400 MHz, CDCl3) d 1.72–1.76 (m, 2H),
1.83–1.89 (m, 2H), 1.92 (s, 3H), 2.66–2.69 (m, 2H),
2.92–2.95 (m, 2H), 7.13–7.17 (m, 1H), 7.35–7.51 (m, 6H),
8.01–8.03 (m, 2H), 8.33 (d, JZ8.4 Hz, 1H), 9.61 (br s, 1H);
13C NMR (100 MHz, CDCl3) d 22.1, 22.9, 24.8, 27.6, 29.7,
119.7, 122.4, 123.0, 126.2 (2C), 128.4, 128.7 (2C), 128.8,
128.9, 129.9, 131.5, 135.8, 138.5, 149.5, 152.5, 156.0,
168.1; IR (CHCl3) n 3325, 3065, 3011, 2943, 2864, 1682,
1590, 1521, 1448, 1303, 1242 cmK1; EI-MS m/z (% relative
intensity) 342 (MC, 100), 327 (95), 299 (28), 284 (20), 271
(9), 225 (16), 171 (8), 149 (32), 105 (86), 77 (52), 57 (26),
55 (19), 43 (27); HR-MS calculated for C23H22N2O
342.1732, found 342.1749.
Scheme 4. Enantioselective additions to benzaldehyde 7.
3. Conclusion
This work has shown that cobalt-catalyzed [2C2C2]
cocyclotrimerization of diynes with benzonitrile is a con-
venientandstraightforwardmethodforpreparationofnotonly
mono-ortho-substituted arylpyridines but also potentially
atropoisomeric bis-ortho-substituted arylpyridines (entries
7–9, Table 1) in reasonable yields. The starting diynes are
easilyprepared from the corresponding substitutedarylhalides
and 1,7-octadiyne in good yields and the use of the
commercially available CpCo(CO)2 catalysts gave good
yields of the cyclotrimerization products in most cases.
Other types of CpCo(ligand)n (ligandZethylene, COD)
catalysts were tested in cyclotrimerization with bis-ortho-
substituted aryldiynes but their activity was highly dependent
on the structure of the substrate. Last but not least, the racemic
arylpyridine-N-oxide 6 was resolved into enantiomers and its
absolute configuration was unequivocally determined by
X-ray structure analysis. Despite the fact that the result of
enantioselective additions were not too high, it is premature to
4.1.3. 5,6,7,8-Tetrahydro-1-(2-methoxyphenyl)-3-phenyl-
isoquinoline (3c). Column chromatography on silica gel
(4:1 hexane/EtOAc) afforded 97 mg (76%) of the title
compound as a viscous liquid: 1H NMR (400 MHz, CDCl3)
d 1.65–1.85 (m, 4H), 2.33–2.40 (m, 1H), 2.60–2.66 (m, 1H),

R. Hrdina et al. / Tetrahedron 62 (2006) 968–976
973
2.85–2.90 (m, 2H), 3.77 (s, 3H), 6.95–6.97 (m, 1H),
7.04–7.07 (m, 1H), 7.30–7.42 (m, 6H), 7.96–7.98 (m, 2H);
13C NMR (100 MHz, CDCl3) d 22.4, 22.9, 25.7, 29.6, 55.5,
110.8, 120.0, 120.7, 127.0 (2C), 128.1, 128.4 (2C), 129.2,
130.4, 130.7, 131.0, 139.9, 146.5, 153.6, 156.6, 157.0; IR
(CHCl3) n 3530, 3063, 2940, 2863, 2837, 1697, 1589, 1555,
138–139 8C (hexane); 1H NMR (400 MHz, CDCl3) d
1.69–1.83 (m, 4H), 2.03 (s, 3H), 2.04–2.27 (m, 1H), 2.43–
2.49 (m, 1H), 2.86–2.89 (m, 2H), 3.71 (s, 3H), 6.81 (d, JZ
8.4 Hz, 1H), 6.91 (d, JZ7.6 Hz, 1H), 7.23–7.27 (m, 1H),
7.31–7.42 (m, 4H), 7.94–7.97 (m, 2H); 13C NMR
(100 MHz, CDCl3) d 19.7, 22.3, 22.8, 25.4, 29.6, 55.6,
108.4, 120.1, 122.7 (2C), 127.1, 128.2, 128.3, 128.4 (2C),
128.6, 131.1, 137.6, 139.8, 146.9, 153.7, 156.4, 156.7; IR
(CHCl3) n 3065, 3025, 3016, 2941, 2863, 2839, 2357, 1591,
1581, 1556, 1470, 1434, 1422, 1387, 1297, 1261, 1230,
1221, 1212, 1087 cmK1; EI-MS m/z (% relative intensity)
329 (MC, 29), 314 (20), 298 (12), 284 (10), 256 (15), 242
(6), 148 (31), 135 (9), 123 (10), 111 (13), 97 (24), 81 (42),
69 (100), 57 (67), 43 (77); HR-MS calculated for C23H23NO
329.1780, found 329.1784. EA calculated for C23H23NO C,
83.85; H, 7.04; N, 4.25. Found C, 83.59; H, 7.08; N, 3.99.
1495, 1463, 1278, 1244, 1180, 1109, 1027, 955 cmK1
;
EI-MS m/z (% relative intensity) 315 (MC, 100), 298 (10),
284 (30), 210 (13); HR-MS calculated for C22H21NO
315.1623, found 315.1638.
4.1.4. 5,6,7,8-Tetrahydro-1-(2-(methoxymethyl)phenyl)-
3-phenylisoquinoline (3d). Column chromatography on
silica gel (5:2 hexane/EtOAc) afforded 56 mg (33%) of the
1
title compound as a viscous liquid: H NMR (400 MHz,
CDCl3) d 1.71–1.88 (m, 4H), 2.35–2.58 (m, 2H), 2.87–2.91
(m, 2H), 3.25 (s, 3H), 4.33 (s, 3H), 7.16–7.43 (m, 7H),
7.56–7.57 (m, 1H), 7.95–7.97 (m, 2H); 13C NMR
(100 MHz, CDCl3) d 22.3, 23.0, 26.7, 29.6, 58.3, 72.2,
119.9, 125.3, 126.8, 127.2, 127.9, 128.1, 128.2, 128.3, 128.5
(2C), 128.8, 129.0, 130.2, 136.3, 139.4, 153.1, 158.3; IR
(CHCl3) n 3063, 3008, 2935, 2862, 1589, 1432, 1090,
956 cmK1; EI-MS m/z (% relative intensity) 329 (MC, 16),
314 (100), 277 (9), 149 (11), 69 (25), 55 (20), 43 (23);
HR-MS calculated for C23H23NO 329.1780, found
329.1768.
4.1.8. 5,6,7,8-Tetrahydro-1-(2-methoxynaphthalen-1-yl)-
3-phenylisoquinoline (3h). Spectral characteritics were in
agreement with the previously published data.21
4.1.9. 5,6,7,8-Tetrahydro-1-(2-methylnaphthalen-1-yl)-
3-phenylisoquinoline (3i). Column chromatography on
silica gel (10:1 hexane/EtOAc) afforded 125 mg (30%) of
the title compound as a white solid: mp 175–176 8C
(hexane); 1H NMR (400 MHz, CDCl3) d 1.63–1.69 (m,
2H), 1.77–1.83 (m, 2H), 2.13–2.22 (m, 2H), 2.22 (s, 3H),
2.91–2.94 (m, 2H), 7.22–7.24 (m, 1H), 7.29–7.50 (m, 7H),
7.79–7.84 (m, 2H), 7.96–7.98 (m, 2H); 13C NMR
(100 MHz, CDCl3) d 20.0, 22.3, 22.9, 25.6, 29.7, 120.1,
124.7, 125.1, 126.0, 126.9 (2C), 127.6, 127.9, 128.3, 128.5
(2C), 128.8, 131.0, 131.9, 132.1, 133.1, 136.6, 139.8, 147.2,
154.3, 158.1; IR (CHCl3) n 3059, 3024, 3015, 2941, 2356,
1591, 1556, 1508, 1494, 1381, 1315, 1260, 1229, 1219,
1205, 1198, 1085, 915, 866, 813 cmK1; EI-MS m/z
(% relative intensity) 349 (MC, 100), 334 (65), 320 (16),
307 (14), 256 (7), 166 (8), 149 (46), 139 (8), 111 (10), 97
(16), 83 (24), 69 (42), 57 (56), 43 (59); HR-MS calculated
for C26H23N 349.1830, found 349.1839. EA calculated for
C26H23N C, 89.36; H, 6.63; H 4.01. Found C, 88.86; H,
6.67; H, 3.76.
4.1.5. 5,6,7,8-Tetrahydro-3-phenyl-1-o-tolylisoquinoline
(3e). Column chromatography on silica gel (4:1 hexane/
EtOAc) afforded 110 mg (91%) of the title compound as a
1
viscous liquid: H NMR (400 MHz, CDCl3) d 1.71–1.83
(m, 4H), 2.14 (s, 3H), 2.30–2.45 (m, 2H), 2.86–2.89 (m,
2H), 7.19–7.29 (m, 4H), 7.33–7.42 (m, 4H), 7.95–7.98 (m,
2H); 13C NMR (100 MHz, CDCl3) d 19.6, 22.3, 23.0, 26.5,
29.6, 119.7, 125.5, 126.8 (2C), 127.6, 128.2, 128.5 (2C),
128.6, 129.7, 130.2, 135.7, 139.8, 140.5, 147.1, 153.5,
159.5; IR (CHCl3) n 3523, 3063, 2942, 2863, 1692, 1589,
1580, 1554, 1432, 1387, 1247, 1178, 1072, 1026 cmK1
;
EI-MS m/z (% relative intensity) 299 (MC, 100), 284 (65),
270 (20), 257 (26), 165 (9), 128 (8), 103 (8), 84 (27), 49 (7);
HR-MS calculated for C22H21N 299.1674, found 299.1672.
4.1.6. 5,6,7,8-Tetrahydro-1-(2-fluorophenyl)-3-phenyl-
isoquinoline (3f). Column chromatography on silica gel
(4:1 hexane/EtOAc) afforded 122 mg (46%) of the title
compound as a viscous liquid: 1H NMR (400 MHz, C6D6) d
1.41–1.46 (m, 4H), 2.41–2.50 (m, 4H), 2.60–2.66 (m, 1H),
6.63–6.67 (m, 1H), 6.79–6.83 (m, 1H), 6.90–6.96 (m, 2H),
7.16–7.20 (m, 1H), 7.24–7.29 (m, 2H), 7.40–7.45 (m, 1H),
8.16–8.19 (m, 2H); 13C NMR (100 MHz, C6D6) d 23.3,
23.8, 27.0, 30.3, 116.9, 121.5, 125.7 (d, JZ3 Hz), 128.6
(2C), 130.2 (2C), 131.2, 132.4, 133.4 (d, JZ18 Hz), 141.4,
148.5, 155.5, 156.2, 161.7 (d, JZ246 Hz); IR (CHCl3) n
2941, 1713, 1617, 1590, 1580, 1553, 1494, 1452, 1432,
1423, 1386, 1226, 1099 cmK1; EI-MS m/z (% relative
intensity) 303 (35), 133 (10), 103 (MC, 100), 76 (32), 50
(16); HR-MS calculated for C21H18FN 303.1423, found
303.1435.
4.1.10. (G)-5,6,7,8-Tetrahydro-1-(2-methoxy-6-methyl-
phenyl)-3-phenylisoquinoline-N-oxide (6). To a solution
of pyridine 3f (160 mg, 0.48 mmol) in dichloromethane
(2 mL) was added MCPBA (purity 70%) (220 mg,
0.93 mmol) at 0 8C. After stirring of the resulting mixture
at room temperature for 1 h it was quenched by the saturated
water solution of NaHCO3 (1 mL) and the crude product
was extracted with dichloromethane (5 mL). The organic
layer was separated and column chromatography on silica
gel (ethyl acetate) afforded 90 mg (54%) of the title
compound 6 as a viscous liquid: 1H NMR (400 MHz,
C6D6) d 1.32–1.44 (m, 4H), 2.06–2.14 (m, 2H), 2.16 (s, 3H),
2.26–2.33 (m, 2H), 3.25 (s, 3H), 6.56 (d, JZ8.2 Hz, 1H),
6.91 (d, JZ7.6 Hz, 1H), 7.01–7.06 (m, 1H), 7.10–7.22 (m,
4H), 7.96–7.98 (m, 2H); 13C NMR (100 MHz, CDCl3) d
19.9, 23.1, 23.3, 27.1, 29.2, 56.2, 109.8, 123.6, 123.9, 126.8,
128.6 (2C), 129.5, 130.3, 130.6 (2C), 134.0, 134.7, 135.4,
139.5, 146.9, 148.0, 158.0; IR (CHCl3) n 3614, 3010, 2971,
1582, 1467, 1387, 1257, 1127, 1080, 945 cmK1; EIS-MS
m/z 346 (MCCH), 352 (MCKOCNa), 368 (MCCNa).
4.1.7.
5,6,7,8-Tetrahydro-1-(2-methoxy-6-methyl-
phenyl)-3-phenylisoquinoline (3g). Column chromato-
graphy on silica gel (4:1 hexane/EtOAc) afforded 121 mg
(30%) of the title compound as a white solid: mp

974
R. Hrdina et al. / Tetrahedron 62 (2006) 968–976
4.1.11. (R)-(C)-5,6,7,8-Tetrahydro-1-(2-methoxy-6-
methylphenyl)-3-phenylisoquinoline-N-oxide ((R)-(C)-6).
To a solution of (S)-(K)-binol 7 (293 mg, 0.99 mmol) and
racemic 5,6,7,8-tetrahydro-1-(2-methoxy-6-methylphenyl)-
3-phenylisoquinoline-N-oxide 6 (340 mg, 0.99 mmol) in
dichloromethane (5 mL) heptane (10 mL) was added, the
flask was closed with a septum with a needle and set aside to
allow slow evaporation of dichloromethane through the
needle. The molecular complex (R)-(C)-6$(S)-(K)-7
crystallized within 5 days as colorless needles that were
collected by suction filtration. Individual components were
collected by column chromatography on silica gel (ethyl
acetate), which afforded 105 mg (30%) of (R)-(C)-6.
Chiral HPLC (Chiralcel OD-H, 0.46!25 cm, 8:1 heptane/
2-propanol, 1.2 mL minK1) showed 95% ee depending on
the batch (tSZ8.01 min, tRZ9.12 min).
were recalculated into idealised positions (riding model)
and assigned displacement parameter either Hiso(H)Z
1.2 Ueq(pivot atom) or Hiso(H)Z1.5 Ueq(pivot atom) for
methyl moiety. The refinement converged (D/smaxZ0.001)
to RZ0.0447 for observed reflections and wRZ0.124, SZ
1.038 for 229 parameters and all 4076 reflections. The final
difference map displayed no peaks of chemical significance
(DrmaxZ0.252, Drmin K0.246 eAK3).
˚
Crystal data for (R)-(C)-6$(S)-(K)-7: C23H23NO2$C20-
˚
H14O2, MZ631.74, monoclinic, P21, aZ11.5900(3) A,
˚
˚
bZ9.0280(2) A, cZ16.0570(4) A, bZ104.4160(13)8, VZ
1627.22(7) A , ZZ2, DxZ1.289 Mg mK3. A colorless
3
˚
plate of dimensions 0.37!0.2!0.15 mm was mounted
on glass capillary with epoxy glue and measured at
Nonius KappaCCD diffractometer by monochromatized
˚
Mo Ka radiation (lZ0.71073 A) at 150(2) K. An
absorption was neglected (mZ0.082 mmK1); a total of
19962 measured reflections in the range hZK15 to 15,
kZK11 to 11, lZK20 to 20 (qmaxZ27.58), from which
7408 were unique (RintZ0.028), 6678 observed according
to the IO2s(I) criterion. The structure was solved by
direct methods (SIR92)32 and refined by full-matrix least
squares based on F2 (SHELXL97).33 The absolute
configuration of the crystal has been assigned by
reference of known configuration of (S)-(K)-binol 7.
The hydrogen atoms were found on difference Fourier
map, those on carbon atoms were recalculated into
idealised positions (riding model) and assigned displace-
ment parameter either Hiso(H)Z1.2 Ueq(pivot atom) or
Hiso(H)Z1.5 Ueq(pivot atom) for methyl moiety. The
hydrogen of the hydroxyl moiety was refined isotropi-
cally. The refinement converged (D/smaxZ0.000) to RZ
0.0378 for observed reflections and wRZ0.0956, SZ
1.001 for 443 parameters and all 7408 reflections. The
final difference map displayed no peaks of chemical
4.2. Enantioselective allylation of benzaldehyde with
allyltrichlorosilane to (R)-(C)-1-phenyl-but-3-en-1-ol (9)
To a solution of (R)-(C)-6 (5 mg, 0.014 mmol) in dichloro-
methane (1.4 mL) were added benzaldehyde (40 mL,
0.4 mmol), diisopropylethylamine (87 mL, 0.5 mmol), and
allyltrichlorosilane (75 mL, 0.47 mmol) at 0 8C. The reaction
mixture was stirred at 20 8C for 72 h. The reaction was
quenched with saturated aqueous NaHCO3 (1 mL), the layers
wereseparatedanddriedoverMgSO4. GCyieldof9was50%.
Chiral GC (HP-Chiral b 30 m!0.25 mm, oven: 80 8C for
15 min, then 1 8C/min to 1508C, 5 min at that temperature)
showed 20% ee (tRZ57.55 min, tSZ56.03 min).
4.3. Enantioselective alkylation of benzaldehyde with
diethylzinc to (R)-(C)-1-phenyl-1-propanol (11)
To a solution of (R)-(C)-6 (7 mg, 0.02 mmol) in toluene
(0.6 mL) 1 M solution of diethyl zinc hexane (0.68 mL,
0.68 mmol) was added at 0 8C and the reaction mixture was
stirred for 20 min. Then benzaldehyde (33 mL, 0.33 mmol),
was added and the reaction mixture was stirred for 72 h at
20 8C. The reaction was quenched with 10% H2SO4 (0.5 mL),
the organic layer was separated and the aqueous phase was
extracted with diethylether, the combined organic layers were
dried over MgSO4. GC yield of the 1-phenyl-1-propanol was
62%. Chiral GC (HP-Chiral b 30 m!0.25 mm, oven: 80 8C
for15 min, then1 8C/minto150 8C, 5 minatthattemperature)
showed 17% ee (tRZ49.78 min, tSZ51.09 min).
significance (DrmaxZ0.259, Drmin K0.181 eAK3).
˚
Crystallographic data for structural analysis have been
deposited with the Cambridge Crystallographic Data Centre,
CCDC no. 283868 and 283869 for 3g and (R)-(C)-6$(S)-
(K)-7, respectively. Copies of this information may be
obtained free of charge from The Director, CCDC, 12 Union
Road, Cambridge CB2 1EY, UK (fax: C44 1223 336033;
e-mail: deposit@ccdc.cam.ac.uk or www: http://www.ccdc.
cam.ac.uk).
4.4. Crystallography
Acknowledgements
Crystal data for: 3g. C23H23NO, MZ329.42, monoclinic,
We gratefully acknowledge financial support from the
Czech Science Foundation (Grant No. 203/05/0102).
˚
˚
˚
P21/n, aZ13.1910(3) A, bZ8.6090(2) A, cZ16.4300(4) A,
3
˚
bZ107.1860(11)8, VZ1782.50(7) A , ZZ4, DxZ
1.228 Mg mK3. A colorless prism dimensions 0.5!0.25!
0.2 mm was mounted on glass capillary with epoxy glue and
measured at Nonius KappaCCD diffractometer by mono-
ˇ
Authors would like to thank Dr. Iva Tislerova for NMR
and Mr. Miroslav Kvasnica for IR measurements, and
´
´
Dr. Irena Valtrova for ee determination by GC.
˚
chromatized Mo Ka radiation (lZ0.71073 A) at 150(2) K.
An absorption was neglected (mZ0.074 mmK1); a total of
26146 measured reflections in the range hZK17 to 17,
kZK11 to 11, lZK21 to 21 (qmaxZ27.58), from which
4076 were unique (RintZ0.015), 3294 observed according to
the IO2s(I) criterion. The structure was solved by direct
methods (SIR92)32 and refined by full-matrix least squares
based on F2 (SHELXL97).33 The hydrogen atoms
Supplementary data
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.tet.2005.10.
034. Preparation and spectral characteristics of the starting
1-aryl-1,7-diynes 2 and the pyridine 4.

R. Hrdina et al. / Tetrahedron 62 (2006) 968–976
975
´
12. Fe-mediated. Ferre, K.; Toupet, L.; Guerchais, V. Organome-
tallics 2002, 21, 2578–2580.
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