Chiral 2-(2-diphenylphosphinophenyl)-5,6,7,8-tetrahydroquinolines: New P-N ligands for asymmetric catalysis

Article abstract of DOI:10.1016/S0040-4020(01)01002-X

New chiral phosphorus-nitrogen ligands, specifically, 2-(2-diphenylphosphinophenyl)-5,6,7,8-tetrahydroquinolines were prepared and assessed in the enantioselective palladium catalyzed allylic substitution of 1,3-diphenylprop-2-enyl acetate with dimethyl m

Full text of DOI:10.1016/S0040-4020(01)01002-X

TETRAHEDRON
Pergamon
Tetrahedron 57 (2001) 9989±9996
Chiral 2- 2-diphenylphosphinophenyl)-5,6,7,8-
tetrahydroquinolines: new P±N ligands for asymmetric catalysis
Giorgio Chelucci,p Antonio Saba and Franco Soccolini
Á
Dipartimento di Chimica, Universita di Sassari, via Vienna 2, I-07100 Sassari, Italy
Received 20 April 2001; revised 13 September 2001; accepted 4 October 2001
AbstractÐNew chiral phosphorus±nitrogen ligands, speci®cally, 2-(2-diphenylphosphinophenyl)-5,6,7,8-tetrahydroquinolines were
prepared and assessed in the enantioselective palladium catalyzed allylic substitution of 1,3-diphenylprop-2-enyl acetate with dimethyl
malonate. Enantioselectivity up to 71% was obtained. q 2001 Published by Elsevier Science Ltd.
1. Introduction
examples of phosphinopyridines (1±5)4 are reported in
Scheme 1.
Enantioselective reactions using metal complexes with
ligands having hetero-donor atoms are an actively pursued
research area. The interest toward this type of ligand comes
from the fact that a control element for optimizing a par-
ticular catalytic system is the modulation of the electron
density on the metal both by changing the nature of the
heteroatoms and by modifying the electron donating or
accepting properties of the ligand by a proper choice of
the substituents bonded to it.1 The easier way to obtain
this goal is the use of ligands with different donating
atoms. This is the case of phosphorus±nitrogen (P±N)
ligands which are very successful in asymmetric catalysis.2
In this context, relatively few examples of bidentate P±N
ligands where the nitrogen atom is included in a pyridine
framework have been reported so far.3 Representative
Recently, Katsuki et al. reported the application of (phos-
phinoaryl)pyridine ligands 5 to palladium-catalyzed asym-
metric allylic alkylation.4f±l Although these ligands afforded
very good results in this process, their use is limited because
only small amount of these ligands are available. In fact,
their preparation requires a rather elaborate synthesis or the
separation of a racemic mixture by preparative chiral
HPLC.5 With the aim of obtaining similar ligands more
easily, we have prepared a series of (phosphinoaryl)pyri-
dines derived from naturally occurring compounds.
In this paper, we report the synthesis of the chiral 2-(2-
diphenylphosphinophenyl)-5,6,7,8-tetrahydroquinoline
ligands 9, 20, 25, 30 (Schemes 3 and 4) and the results
Scheme 1.
Keywords: phosphinopyridine ligands; palladium catalysts; enantioselective allylic substitution reactions.
Corresponding author. Tel.: 139-79-229-539; fax: 139-79-229-559; e-mail: chelucci@ssmain.uniss.it
p
0040±4020/01/$ - see front matter q 2001 Published by Elsevier Science Ltd.
PII: S0040-4020(01)01002-X

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G. Chelucci et al. / Tetrahedron 57 &2001) 9989±9996
Scheme 2. (a) I2, pyridine; (b) 10, AcOH, AcONH4, 1208C, 4 h, 46%; (c) KPPh2, THF.
obtained with these ligands in the enantioselective
palladium catalyzed allylic substitution of 1,3-diphenyl-
prop-2-enyl acetate with dimethyl malonate.
reaction of (2)-pinocarvone 10 with 1-phenacylpyridinium
iodide 12, in turn prepared by reaction of 2-methoxyaceto-
phenone 11 with iodine in pyridine (Scheme 3).10
Demethylation of the methyl ether 13 with boron tribromide
occurred in good yield (79%) to give the phenol 14 which
was converted into the tri¯uoromethansulphonate 15 with
(CF3CO2)2Oin pyridine (88%). Finally, treatment of tri¯ate
15 with diphenylphosphine in the presence of 10 mol% of
NiCl2(dppe) and 2 equiv. of 1,4-diazabicyclo[2.2.2]octane
(DABCO) in DMF at 1008C gave the corresponding
phosphinoquinoline ligands 9 (20%) with the corresponding
N-oxide (20%) and the phenyl derivative (16%). The last
one results from the reduction of the tri¯uoromethan-
sulphonate group.
2. Results and discussion
For the synthesis of this class of ligand, we considered that a
convenient approach could involve the nucleophilic
substitution of an electrophilic aryl ¯uoride with potassium
diphenylphosphide.6 Thus, as a substrate to test the
feasibility of this idea, the ¯uoro derivative 8 was prepared
È
(Scheme 2) following the Krohnke methodology which
demands the reaction of an a,b-unsaturated ketone with a
pyridinium salt.7 Thus, (2)-pinocarvone 108 underwent
annelation with the pyridinium iodide 7, prepared in turn
by reaction of 2-¯uoroacetophenone 6 with iodine in
pyridine, to give the ¯uoropyridine 8 in moderate yield.
Unfortunately, several attempts to convert 8 into the desired
phosphinoquinoline 9 failed.
Having obtained the desired phosphinoquinoline 9, this
protocol was extended to other a,b-methylene ketones
(Scheme 4). Thus, the ketones 16, 21, 26 obtained
from (2)-isopinocampheol,11 (2)-b-pinene12 and (1)-
camphor,12 respectively, yielded the methoxyquinolines
17, 22, 27 (46, 24, 24% yields, respectively). Cleavage of
the methyl ether afforded the phenols 18, 23, 28 (80, 86,
85% yields, respectively) which were converted into the
tri¯uoromethansulphonates 19, 24, 29 (82, 82, 79% yields,
respectively). Finally cross-coupling of 19, 24, 29 with
Therefore, we examined the possibility of introducing the
diphenylphosphino group by nickel(0)-catalyzed cross-
coupling of aryl sulfonates with chlorodiphenylphosphine.9
For this purpose, the methoxyquinoline 13 was prepared by
Scheme 3. (a) I2, pyridine; (b) 10, AcOH, AcONH4, 120±1408C, 4±20 h; (c) BBr3, CH2Cl2; (d) (CF3SO2)2O, pyridine, CH2Cl2; (e) HPPh2, 10 mol%
NiCl2(dppe), DABCO, DMF, 1008C.

G. Chelucci et al. / Tetrahedron 57 &2001) 9989±9996
9991
Scheme 4. (a) 12, AcOH, AcONH4, 120±1408C, 4±20 h; (b) BBr3, CH2Cl2; (c) (CF3SO2)2O, pyridine, CH2Cl2; (d) HPPh2, 10 mol% NiCl2(dppe), DABCO,
DMF, 1008C.
diphenylphosphine gave the corresponding phosphino-
quinoline ligands 20, 25, 30 in 32, 43, 19% yields, respec-
tively, with a variable quantity of the corresponding
N-oxides (16±20%) and the phenyl derivatives (16±39%).
C3H5)Cl]2 as procatalyst and a mixture of dimethyl
malonate, N,O-bis(trimethylsilyl)acetamide (BSA) and
potassium acetate in methylene chloride.14 The results of
the catalytic reactions are reported in Table 1.
As a model for the evaluation of the ability of the new P±N
ligands to provide asymmetric induction in catalytic
processes we selected the palladium-catalyzed allylic
substitutions and in particular, the alkylation of 1,3-di-
phenylprop-2-enyl acetate with dimethyl malonate, which
serves as a representative substrate to compare the outcome
of different ligands.13
Ligands 9, 20, 25, 30 were able to provide effective
palladium catalysts and to give the dimethyl 1,3-diphenyl-
prop-2-enyl malonate 32 in good yield and in low to
moderate enantiomeric excess. Both the reaction rate and
enantioselectivity were increased when the stereocenter is
closer to the tetrahydroquinoline nitrogen.
Thus, ligand 25, differing from 9 by the position of the
dimethylmethylene bridge, which in the former ligand is
Allylic substitutions were carried out employing [Pd(h3-

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G. Chelucci et al. / Tetrahedron 57 &2001) 9989±9996
Table 1. Allylic alkylation of 1,3-diphenylprop-2-enyl acetate with dimethyl malonate
Entry
Methoda
Ligand
Reaction time (h)
Yield (%)b
ee (%)c
Con®gurationd
1
2
3
4
5
6
A
A
A
B
C
A
9
96
15
70
0.3
90
12
87
95
92
96
88
96
37
68
70
71
66
50
S
S
S
S
S
S
20
25
25
25
30
a
Method A: reaction of the ligand (10 mol%) and [Pd(h3-C3H5)Cl]2 (2.5 mol%) with 1,3-diphenylprop-2-enyl acetate (0.4 mmol), CH2(COOMe)2 (1.2 mmol),
N,O-bis(trimethylsilyl)acetamide (BSA) (1.2 mmol) and KOAc (3.5 mol%) in CH2Cl2 (2 mL) at room temperature. Method B: reaction of the ligand
(10 mol%) and [Pd(h3-C3H5)Cl]2 (2.5 mol%) with 1,3-diphenylprop-2-enyl acetate (0.8 mmol), NaCH(COOMe)2 (1.2 mmol), 15-crown-5 (1.2 mmol) in
CH3CN (2.5 mL) at room temperature. Method C: reaction of the ligand (10 mol%) and [{Pd(h3-C3H5)Cl}2] (2.5 mol%) in CH2Cl2 (1 mL) for 30 min,
followed by a solution of 1,3-diphenylprop-2-enyl acetate (0.8 mmol) in CH2Cl2 (0.5 mL). Then, a solution of dimethyl malonate (2.4 mmol), BSA
(2.4 mmol) and tetrabutylammonium ¯uoride trihydrate (2.4 mmol) in CH2Cl2 (3.5 mL) was added over 1 h.
b
c
d
Isolated yields.
Determined by H NMR spectroscopy using Eu(hfc)3 as chiral shift reagent.
The assignment is based on the sign of the optical rotation, see Ref. 18.
1
in close proximity to the nitrogen donor center, increased
stereoselectivity of the reaction could be increased both
by the introduction of encumbering substituents on the
8-position of the tetrahydroquinoline ring and/or by
modifying the substituents on the phosphorus. Further
studies aimed at modifying the ligand design and applica-
tion to other catalytic asymmetric reactions are in progress.
both the reaction rate and the stereoselectivity of the reac-
tion. A similar improvement in the results were obtained
passing from ligand 9 to ligand 20 which are different due
to the presence of a methyl group on the 8-position of the
tetrahydroquinoline ring.
Surprisingly, both ligands 9 and 20, gave the reaction
product 32 with the same sense of chirality, even though
they have opposite con®gurations to the stereogenic centers
on the 5,7-positions of the tetrahydroquinoline ring indicat-
ing that the course of the reaction reasonably depends on the
stereogenic center bonded to the 8-position.
3. Experimental
3.1. General methods
Melting points were determined on a BuÈchi 510 capillary
apparatus and are uncorrected. The NMR spectra were
It has been reasoned that one of the critical factors in
controlling the selective addition of nucleophiles to p-
allyl palladium intermediates is the nature of the ion pair
of the attacking nucleophile.13,15 Thus, the complexation of
the cation with crown ether4f±l,16 or the use of tetraalkyl-
ammonium as a bulky counterion17 can have a dramatic
effect on the enantioselectivity of the process.
obtained with
a Varian VXR-300 spectrometer at
1
300 MHz for H and 101.4 MHz for 31P. Chemical shifts
are reported in ppm down®eld from internal Me4Si in
CDCl3. Optical rotations were measured with a Perkin±
Elmer 241 polarimeter in a 1 dm tube. Elemental analyses
were performed on a Perkin±Elmer 240 B analyzer.
(2)-Pinocarvone 10 was obtained by oxydation of (1R)-
(1)-a-pinene (90% ee by GLC, Aldrich).8 (1R,4S,5R)-
4,6,6-Trimethyl-2-methylenebicyclo[3.1.1]heptan-3-one 16,
(1R,5R)-6,6-dimethyl-3-methylene bicyclo[3.1.1] heptan-2-
one 21 and (1R,4S)-1,7,7-trimethyl-3-methylenebicyclo-
[2.2.1]heptan-2-one 26 were prepared from (2)-isopino-
campheol,11 (2)-b-pinene12 and (1)-camphor,12 respec-
tively. 1-[2-(2-Methoxy phenyl)-2-oxoethyl]pyridinium
iodide 12 was prepared according to a reported procedure.19
Therefore, in an effort to increase the enantioselectivity of
the reaction, we chose the best performing ligand 25 to test
other two methods for the generation of the malonate anion.
When the reaction was carried out in acetonitrile with
sodium malonate, generated using sodium hydride, in the
presence of 15-crown-5,16 a rapid reaction was observed
(the reaction was complete in less than 20 min), but the
enantioselectivity remained unchanged (Table 1, entry 4).
In contrast, the reaction in methylene chloride of tetrabutyl-
ammonium malonate, generated from dimethyl malonate
and using the BSA/tetrabutylammonium ¯uoride system
as the base,17 depressed both reaction rate and enantio-
selecivity (Table 1, entry 5).
3.1.1.
1-[2- 2-Fluorophenyl)-2-oxoethyl]pyridinium
iodide 7. 2-Fluoroacetophenone (25 g, 166.5 mmol) was
added dropwise to a mixture of iodine (46 g, 0.181 mol)
in pyridine (90 mL). Then the mixture was heated to
1008C for 45 min. After this period, the solution was cooled
in ice and the formed solid ®ltered off. Recrystallization
from methanol gave yellow crystals of 7: 23.4 g (38%);
In summary, we have prepared new chelating ligands of the
type P±N and demonstrated that they are worthy of attention
for their applications in the ®eld of asymmetric catalysis.20
The preliminary results obtained in enantioselective
palladium catalyzed allylic substitutions indicate that the
1
mp 183±1848C; H NMR (DMSO-d6) d 8.99 (d, 2H, Jˆ
6.0 Hz), 8.76 (t, 1H, Jˆ7.8 Hz), 8.29 (t, 2H, Jˆ7.2 Hz),
8.04 (m, 1H), 7.85 (m, 1H), 7.52 (m, 2H), 6.32 (d, 2H,

G. Chelucci et al. / Tetrahedron 57 &2001) 9989±9996
9993
Jˆ3.0 Hz). Anal. calcd for C13H11FINO: C, 45.48; H, 3.23;
Jˆ7.5 Hz), 3.85 (s, 3H), 3.26 (dq, 1H, Jˆ6.9, 2.4 Hz),
2.77 (t, 1H, Jˆ5.7 Hz), 2.59±2.52 (m, 1H), 2.18±2.13 (m,
1H), 1.44 (d, 3H, Jˆ7.5 Hz), 1.42 (s, 3H), 1.35 (d, 1H,
N, 4.08. Found: C, 45.59; H, 3.34; N, 4.15.
1
3.1.2. 5S,7S)- 1)-5,6,7,8-Tetrahydro-6,6-dimethyl-2- 2-
¯uorophenyl)-5,7-methanoquinoline 8. A mixture of 1-
Jˆ9.9 Hz), 0.69 (s, 3H). H NMR (minor isomer) d 7.87
(dd, 1H, Jˆ7.5, 1.8 Hz), 7.55 (d, 1H, Jˆ7.5 Hz), 7.33 (dt,
1H, Jˆ7.5, 1.8 Hz), 7.19 (d, 1H, Jˆ7.5 Hz), 7.07 (dt, 1H,
Jˆ7.5, 0.9 Hz), 6.95 (d, 1H, Jˆ7.5 Hz), 3.85 (s, 3H), 3.26
(dq, 1H, Jˆ6.9, 2.4 Hz), 2.77 (t, 1H, Jˆ5.7 Hz), 2.59±2.52
(m, 1H), 2.18±2.13 (m, 1H), 1.55 (d, 3H, Jˆ7.5 Hz), 1.42
(s, 3H), 1.35 (d, 1H, Jˆ9.9 Hz), 0.74 (s, 3H). Anal. calcd for
C20H23NO: C, 81.86; H, 7.91; N, 4.78. Found: C, 81.78; H,
7.686; N, 4.65.
[2-(2-¯uorophenyl)-2-oxoethyl]pyridinium
iodide
7
(23.4 g, 68 mmol), ammonium acetate (75 g) and glacial
acetic acid (260 mL) was heated at 1008C for 10 min.
Then a solution of (2)-pinocarvone (10.15 g, 68 mmol) in
glacial acetic acid (10 mL) was added dropwise and the
resulting solution was heated at 1208C for 4 h. After cool-
ing, the mixture was taken up in H2O(1 L) and extracted
with ethyl ether (3£200 mL). The combined organic phases
were dried over anhydrous Na2SO4, the solvent was evapo-
rated and the residue was puri®ed by ¯ash chromatography
(eluent: petroleum ether/ethyl acetateˆ9:1) to give pure 8 as
3.2.3. 6R,8R)- 1)-5,6,7,8-Tetrahydro-7,7-dimethyl-2- 2-
methoxyphenyl)-6,8-methanoquinoline 22. The reaction
was carried out at 1208C for 20 h using the a,b-methylene
ketone 21. Chromatographic eluent: petroleum ether/ethyl
acetateˆ7:3; 2.26 g (24%); colorless powder of mp 1038C;
25
a pale yellow oil: 8.32 g (46%); [a]D ˆ171.3 (c 1.8,
1
CHCl3); H NMR d 7.96 (dt, 1H, Jˆ7.8, 1.8 Hz), 7.51±
25
1
7.44 (m, 1H), 7.36±7.09 (m, 4H), 3.19 (d, 2H, Jˆ2.7 Hz),
2.80 (t, 1H, Jˆ5.7 Hz), 2.70 (m, 1H), 2.40 (m, 1H), 1.42 (s,
3H), 1.32 (d, 1H, Jˆ9.3 Hz), 0.70 (s, 3H). Anal. calcd for
C18H18FN: C, 80.86; H, 6.79; N, 5.24. Found: C, 80.99; H,
6.55; N, 5.11.
[a]D ˆ19.89 (c 2.1, CHCl3); H NMR d 7.79 (dd, 1H,
Jˆ7.8, 1.8 Hz), 7.54 (d, 1H, Jˆ7.8 Hz), 7.36 (dt, 1H,
Jˆ8.1, 1.8 Hz), 7.23 (d, 1H, Jˆ8.1 Hz), 7.06 (dt, 1H,
Jˆ7.8, 0.9 Hz), 6.98 (d, 1H, Jˆ8.1 Hz), 3.85 (s, 3H), 3.01
(t, 1H, Jˆ5.4 Hz), 2.98±2.90 (m, 2H), 2.78±2.72 (m, 1H),
2.42±2.32 (m, 1H), 1.44 (s, 3H), 1.34 (d, 1H, Jˆ9.9 Hz),
0.69 (s, 3H). Anal. calcd for C19H21NO: C, 81.67; H, 7.58;
N, 5.02. Found C, 81.55; H, 7.45; N, 5.13.
3.2. General procedure for the preparation of quinolines
13, 17, 22, 27
3.2.4. 5S,8R)- 2)-5,6,7,8-Tetrahydro-8,9,9-trimethyl-2-
The
A mixture of 1-[2-(2-methoxyphenyl)-2-oxoethyl]pyri-
dinium iodide 12 (12 g, 33.8 mmol), ammonium acetate
(20 g) and glacial acetic acid (46 mL) was heated at
1008C for 10 min. Then a solution of the a,b-methylene
ketone (33.8 mmol) in glacial acetic acid (5 mL) was
added dropwise and the resulting solution was heated at
120±1408C for 4±20 h. After cooling, the mixture was
taken up in H2O(1 L) and extracted with ethyl ether
(3£100 mL). The combined organic phases were dried
over anhydrous Na2SO4, the solvent was evaporated and
the residue was puri®ed by ¯ash chromatography.
2-methoxyphenyl)-5,8-methanoquinoline
27.
reaction was carried out at 1408C for 20 h using the
a,b-methylene ketone 26. Chromatographic eluent:
petroleum ether/ethyl acetateˆ20:1; 2.38 g (24%); colorless
25
powder of mp 106±1088C; [a]D ˆ230.6 (c 1.0, CHCl3);
1H NMR d 7.92 (dd, 1H, Jˆ7.5, 1.5 Hz), 7.58 (d, 1H,
Jˆ7.5 Hz), 7.34 (d, 1H, Jˆ7.5 Hz), 7.28 (dt, 1H, Jˆ7.5,
1.5 Hz), 7.06 (t, 1H, Jˆ7.5 Hz), 6.95 (d, 1H, Jˆ7.5 Hz),
3.82 (s, 3H), 2.84 (d, 1H, Jˆ3.9 Hz), 2.16±2.06 (m, 1H),
1.85 (dt, 1H, Jˆ3.3 Hz), 1.37 (s, 3H), 1.31±1.12 (m, 2H),
0.99 (s, 3H), 0.59 (s, 3H). Anal. calcd for C20H23NO: C,
81.86; H, 7.91; N, 4.78. Found: C, 81.78; H, 7.68; N, 4.65.
3.2.1. 5S,7S)- 1)-5,6,7,8-Tetrahydro-6,6-dimethyl-2- 2-
methoxyphenyl)-5,7-methanoquinoline 13. The reaction
was carried out at 1208C for 4 h using the a,b-methylene
ketone 10. Chromatographic eluent: petroleum ether/ethyl
acetateˆ7:3; 4.15 g (44%); colorless powder of mp 103±
3.3. General procedure for preparation of 2- 2-hydroxy-
phenyl)-5,6,7,8-tetrahydroquinolines 14, 18, 23, 28
25
1
1048C; [a]D ˆ163.7 (c 1.8, CHCl3); H NMR (CDCl3) d
7.77 (dd, 1H, Jˆ7.8, 1.8 Hz), 7.50 (d, 1H, Jˆ7.8 Hz), 7.33
(dt, 1H, Jˆ8.1, 1.8 Hz), 7.22 (d, 1H, Jˆ8.1 Hz), 7.06 (dt,
1H, Jˆ7.8, 0.9 Hz), 6.98 (d, 1H, Jˆ8.1 Hz), 3.85 (s, 3H),
3.18 (d, 2H, Jˆ3.0 Hz), 2.78 (t, 1H, Jˆ5.7 Hz), 2.69 (m,
1H), 2.38 (m, 1H), 1.42 (s, 3H), 1.33 (d, 1H, Jˆ9.6 Hz), 0.7
(s, 3H). Anal. calcd for C19H21NO: C, 81.67; H, 7.58; N,
5.02. Found: C, 81.76; H, 7.81; N, 5.11.
Boron tribromide (2.0 g, 8.0 mmol) was added dropwise by
a syringe to a cooled (08C) solution of 2-(2-methoxy-
phenyl)-5,6,7,8-tetrahydroquinolines 13, 17, 22, 27
(4.0 mmol) in anhydrous CH2Cl2 (20 mL) under nitrogen.
After stirring overnight to room temperature, water was
added cautiously at 08C. The resulting mixture was treated
with 5% sodium hydroxide then neutralized with glacial
acetic acid and ®nally extracted with CH2Cl2 (2£50 mL).
The organic phase was dried on anhydrous Na2SO4 and the
solvent was evaporated. The residue was puri®ed by ¯ash
chromatography to give pure phenol derivatives 14, 18, 23,
28.
3.2.2. 5R,7R,8S)-5,6,7,8-Tetrahydro-6,6,8-trimethyl-2-
The
2-methoxyphenyl)-5,7-methanoquinoline
17.
reaction was carried out at 1208C for 20 h using the
a,b-methylene ketone 16. Chromatographic eluent:
petroleum ether/ethyl acetateˆ7:3; 4.55 g (46%); this
compound was obtained as a distereomeric mixture of 17
3.3.1. 5S,7S)- 1)-5,6,7,8-Tetrahydro-6,6-dimethyl-2- 2-
hydroxyphenyl)-5,7-methanoquinoline 14. Chromato-
graphic eluent: petroleum ether/ethyl acetateˆ40:1; 0.98 g
1
(77%) and its epimer at the C8-carbon (23%). H NMR
25
(major isomer) d 7.87 (dd, 1H, Jˆ7.5, 1.8 Hz), 7.55 (d,
1H, Jˆ7.5 Hz), 7.33 (dt, 1H, Jˆ7.5, 1.8 Hz), 7.19 (d, 1H,
Jˆ7.5 Hz), 7.07 (dt, 1H, Jˆ7.5, 0.9 Hz), 6.95 (d, 1H,
(92%); white solid of mp 122±1248C; [a]D ˆ198.5 (c 0.7,
1
CHCl3); H NMR d 7.77 (d, 1H, Jˆ6.9 Hz), 7.62 (d, 1H,
Jˆ8.1 Hz), 7.37 (d, 1H, Jˆ8.1 Hz), 7.26 (m, 1H), 7.00 (d,

9994
G. Chelucci et al. / Tetrahedron 57 &2001) 9989±9996
1H, Jˆ7.8 Hz), 6.89 (t, 1H, Jˆ7.8 Hz), 3.14 (d, 2H,
Jˆ2.7 Hz), 2.84±2.68 (m, 2H), 2.40 (m, 1H), 1.43 (s, 3H),
1.31 (d, 1H, Jˆ9.6 Hz), 0.68 (s, 3H). Anal. calcd for
C18H19NO: C, 81.48; H, 7.22; N, 5.28. Found: C, 81.65;
H, 7.39; N, 5.15.
with brine, dried on anhydrous Na2SO4 and the solvent
was evaporated. The residue was puri®ed by ¯ash chromato-
graphy to give pure aryl sulfonates 15, 19, 24, 29.
3.4.1. 5S,7S)-5,6,7,8-Tetrahydro-6,6-dimethyl-2- 2-tri-
¯uoromethanesulfonyloxy)-5,7-methanoquinoline
15.
Chromatographic eluent: petroleum ether/ethyl acetateˆ
3.3.2. 5R,7R,8S)-5,6,7,8-Tetrahydro-6,6,8-trimethyl-2-
2-hydroxyphenyl)-5,7-methanoquinoline 18. Chromato-
graphic eluent: petroleum ether/ethyl acetateˆ8:2; 0.95 g
(85%); this compound was obtained as a distereomeric
mixture of 18 (85%) and its epimer at the C8-carbon
1
8:2; 2.45 g (98%); pale yellow oil; H NMR d 7.74±7.71
(m, 1H), 7.49±7.40 (m, 2H), 7.38±7.34 (m, 1H), 7.31 (d,
1H, Jˆ7.8 Hz), 7.31 (d, 1H, Jˆ7.8 Hz), 7.25 (d, 1H,
Jˆ7.8 Hz), 3.20 (d, 2H, Jˆ2.7 Hz), 2.82 (t, 1H,
Jˆ5.7 Hz), 2.72 (dt, 1H, Jˆ9.6, 5.7 Hz), 2.41±2.36 (m,
1H), 1.43 (s, 3H), 1.32 (d, 1H, Jˆ9.6 Hz), 0.69 (s, 3H).
Anal. calcd for C19H18F3NO3S: C, 57.42; H, 4.57; N, 3.53.
Found: C, 57.55; H, 4.66; N, 3.44.
1
(15%). H NMR (major isomer) d 7.76 (dd, 1H, Jˆ9.1,
1.5 Hz), 7.60 (d, 1H, Jˆ9.1 Hz), 7.34 (d, 1H, Jˆ9.1 Hz),
7.29±7.23 (m, 1H), 7.01 (dd, 1H, Jˆ9.1, 1.2 Hz), 6.88 (dt,
1H, Jˆ9.1, 1.2 Hz), 3.23 (dq, 1H, Jˆ6.9, 2.4 Hz), 2.79 (t,
1H, Jˆ6.0 Hz), 2.63±2.56 (m, 1H), 2.16 (dt, 1H, Jˆ6.0,
2.4 Hz), 1.43 (s, 3H), 1.41 (d, 3H, Jˆ6.9 Hz), 1.32 (d, 1H,
3.4.2. 5R,7R,8S)-5,6,7,8-Tetrahydro-6,6,8-trimethyl-2-
2-tri¯uoromethanesulfonyloxy)-5,7-methanoquinoline
19. Chromatographic eluent: petroleum ether/ethyl
acetateˆ8:2; 2.20 g (85%); pale yellow oil; this compound
was obtained as a distereomeric mixture of 19 (85%) and its
epimer to the C8-carbon (15%). 1H NMR (major isomer) d
7.80±7.50 (m, 1H), 7.49±7.41 (m, 2H), 7.38±7.35 (m, 1H),
7.30±7.24 (m, 2H), 3.29 (dq, 1H, Jˆ7.2, 2.4 Hz), 2.81 (t,
1H, Jˆ5.7 Hz), 2.59 (dt, 1H, Jˆ9.6, 5.7 Hz), 2.18 (dt, 1H,
Jˆ6.0, 2.4 Hz), 1.42 (d, 3H, Jˆ6.0 Hz), 1.35 (d, 1H,
1
Jˆ9.6 Hz), 0.66 (s, 3H). H NMR (minor isomer) d 7.78
(dd, 1H, Jˆ9.1, 1.5 Hz), 7.62 (d, 1H, Jˆ9.1 Hz), 7.36 (d,
1H, Jˆ9.1 Hz), 7.29±7.23 (m, 1H), 7.01 (dd, 1H, Jˆ9.1,
1.2 Hz), 6.88 (dt, 1H, Jˆ9.1, 1.2 Hz), 3.23 (dq, 1H, Jˆ6.9,
2.4 Hz), 2.79 (t, 1H, Jˆ6.0 Hz), 2.63±2.56 (m, 1H), 2.31
(dt, 1H, Jˆ6.0, 2.4 Hz), 1.53 (d, 3H, Jˆ6.9 Hz), 1.43 (s,
3H), 1.32 (d, 1H, Jˆ9.6 Hz), 0.71 (s, 3H). Anal. calcd for
C19H21NO: C, 81.67; H, 7.58; N, 5.02. Found: C, 81.58; H,
7.66; N, 5.15.
1
Jˆ9.6 Hz), 0.67 (s, 3H). H NMR (minor isomer) d 7.80±
3.3.3. 6R,8R)- 1)-5,6,7,8-Tetrahydro-7,7-dimethyl-2- 2-
hydroxyphenyl)-6,8-methanoquinoline 23. Chromato-
graphic eluent: petroleum ether/ethyl acetateˆ9:1; 1.0 g
7.50 (m, 1H), 7.49±7.41 (m, 2H), 7.38±7.35 (m, 1H), 7.30±
7.24 (m, 2H), 3.29 (dq, 1H, Jˆ7.2, 2.4 Hz), 2.81 (t, 1H,
Jˆ5.7 Hz), 2.59 (dt, 1H, Jˆ9.6, 5.7 Hz), 2.18 (dt, 1H,
Jˆ6.0, 2.4 Hz), 1.54 (d, 3H, Jˆ7.5 Hz), 1.35 (d, 1H,
Jˆ9.6 Hz), 0.74 (s, 3H). Anal. calcd for C20H20F3NO3S:
C, 58.38; H, 4.90; N, 3.41. Found: C, 58.48; H, 4.67; N,
3.33.
25
(95%); white solid of mp 153±1548C; [a]D ˆ148.5 (c
1
1.6, CHCl3); H NMR d 7.77 (d, 1H, Jˆ8.1 Hz), 7.70 (d,
1H, Jˆ8.1 Hz), 7.36 (d, 1H, Jˆ8.1 Hz), 7.26 (t, 1H,
Jˆ6.9 Hz), 7.00 (d, 1H, Jˆ8.1 Hz), 6.88 (t, 1H,
Jˆ8.1 Hz), 3.01 (t, 1H, Jˆ5.4 Hz), 2.98±2.90 (m, 2H),
2.78±2.72 (m, 1H), 2.42±2.32 (m, 1H), 1.44 (s, 3H), 1.34
(d, 1H, Jˆ9.9 Hz), 0.69 (s, 3H). Anal. calcd for C18H19NO:
C, 81.48; H, 7.22; N, 5.28. Found C, 81.56; H, 7.35; N, 5.19.
3.4.3. 6R,8R)-5,6,7,8-Tetrahydro-7,7-dimethyl-2- 2-tri-
¯uoromethanesulfonyloxy)-6,8-methanoquinoline
24.
Chromatographic eluent: petroleum ether/ethyl acetateˆ
1
95:5 and then 8:2; 2.04 g (82%); pale yellow oil; H NMR
3.3.4. 5S,8R)- 2)-5,6,7,8-Tetrahydro-8,9,9-trimethyl-2-
2-hydroxyphenyl)-5,8-methanoquinoline 28. Chromato-
graphic eluent: petroleum ether/ethyl acetateˆ8:2; 0.95 g
d 7.76±7.73 (m, 1H), 7.51 (d, 1H, Jˆ7.8 Hz), 7.46±7.42
(m, 2H), 7.37±7.34 (m, 2H), 3.10 (t, 1H, Jˆ5.1 Hz), 3.00 (d,
2H, Jˆ2.7 Hz), 2.75 (dt, 1H, Jˆ9.6, 6.0 Hz), 2.37±2.33 (m,
1H), 1.43 (s, 3H), 1.34 (d, 1H, Jˆ9.6 Hz), 0.70 (s, 3H).
Anal. calcd for C19H18F3NO3S: C, 57.42; H, 4.57; N, 3.53.
Found: C, 57.66; H, 4.55; N, 3.65.
25
(85%); white solid of mp 106±1078C; [a]D ˆ258.5 (c
1
0.8, CHCl3); H NMR d 7.50 (d, 1H, Jˆ7.8 Hz); 7.60 (d,
1H, Jˆ7.8 Hz); 7.51(d, 1H, Jˆ7.8 Hz); 7.25 (t, 1H,
Jˆ7.8 Hz); 7.00 (d, 1H, Jˆ7.8 Hz); 6.87 (t, 1H,
Jˆ7.2 Hz); 2.87 (d, 1H, Jˆ3.9 Hz); 2.20±2.09 (m, 1H);
1.95±1.87 (m, 1H); 1.36 (1, 3H); 1.26±1.14 (m, 3H); 1.00
(s, 3H); 0.58 (s, 3H). Anal. calcd for C19H21NO: C, 81.67; H,
7.58; N, 5.02. Found: C, 81.58; H, 7.66; N, 5.15.
3.4.4. 5S,8R)-5,6,7,8-Tetrahydro-8,9,9-trimethyl-2- 2-
tri¯uoromethanesulfonyloxy)-5,8-methanoquinoline 29.
Chromatographic eluent: petroleum ether/ethyl acetateˆ
1
8:2; 2.30 g (89%); pale yellow oil; H NMR d 7.82±7.77
(m, 1H), 7.57 (d, 1H, Jˆ7.8 Hz), 7.55±7.47 (m, 2H), 7.37±
7.34 (m, 2H), 3.05 (d, 1H, Jˆ3.9 Hz), 2.20±2.09 (m, 1H),
1.95±1.87 (m, 1H), 1.36 (s, 3H), 1.26±1.14 (m, 3H), 1.00 (s,
3H), 0.58 (s, 3H). Anal. calcd for C20H20F3NO3S: C, 58.38;
H, 4.90; N, 3.41. Found: C, 58.66; H, 4.62; N, 3.56.
3.4. General procedure for the preparation of 2- 2-tri-
¯uoromethanesulfonyloxy)-5,6,7,8-tetrahydro-quino-
lines 15, 19, 24, 29
Tri¯ic anhydride (1.6 mL, 8.1 mmol) was added dropwise
to a cooled (08C) solution of 2-(2-hydroxyphenyl)-5,6,7,8-
tetrahydroquinolines 14, 18, 23, 28 (6.3 mmol) and pyridine
(0.56 mL, 7.0 mmol) in anhydrous CH2Cl2 (8 mL) under
nitrogen. The resulting solution was allowed to warm to
room temperature and stirred overnight. The mixture was
treated with a saturated aqueous NH4Cl solution and
extracted with CH2Cl2. The organic phase was washed
3.5. General procedure for the preparation of 2- 2-
diphenylphosphinophenyl)-5,6,7,8-tetrahydroquinolines
9, 20, 25, 30
A mixture of NiCl2(dppe) (115 mg, 0.2 mmol) and di-
phenylphosphine (0.103 mL, 0.596 mmol) in degassed
DMF (2.5 mL) was heated at 1008C for 30 min under

G. Chelucci et al. / Tetrahedron 57 &2001) 9989±9996
9995
argon. Then a solution of tri¯uoromethansulphonates 15,
19, 24, 29 (2.0 mmol) and 1,4-diazabicyclo[2.2.2]octane
(4.0 mmol) in degassed DMF (2.5 mL) was added by a
syringe. Additional diphenylphosphine (0.311 mL,
1.74 mmol) was added and the resulting mixture was heated
at 1008C until conversion was complete (about 24 h) as
shown by TLC analysis [light petroleum/ethyl acetateˆ8:2].
After cooling the reaction mixture to room temperature,
most of the DMF was removed by vacuum distillation.
The residue was diluted with dichloromethane and washed
successively with 5% aqueous Na2S2O3, 10% aqueous citric
acid and ®nally with brine. The organic phase was dried
over anhydrous Na2SO4 and the solvent was evaporated.
The residue was puri®ed by ¯ash chromatography to give
1.22±1.04 (m, 2H), 0.91 (s, 3H), 0.87 (s, 3H), 0.45 (s, 3H).
31P NMR d 29.60. Anal. calcd for C31H30NP: C, 83.18; H,
6.76; N, 3.13. Found: C, 83.25; H, 6.65; N, 3.09.
3.6. Allylic alkylation of1,3-diphenyl-2-propenyl acetate
with dimethyl malonate: general procedure
Method A. A solution of ligand (0.04 mmol, 10 mol%) and
[Pd(h3-C3H5)Cl]2 (4 mg, 2.5 mol%) in dry CH2Cl2 (2 mL)
was stirred at room temperature for 1 h. This solution was
treated successively with a solution of rac-(E)-1,3-diphenyl-
2-propenyl acetate (0.4 mmol) in CH2Cl2 (1 mL), dimethyl
malonate (1.2 mmol), N,O-bis(trimethylsilyl)acetamide
(1.2 mmol) and anhydrous potassium acetate (3.5 mol%).
The reaction mixture was stirred until conversion was
complete as shown by TLC analysis [light petroleum/
etherˆ3:1]. The reaction mixture was diluted with ether
(25 mL) and washed with ice-cold saturated aqueous
ammonium chloride. The organic phase was dried
(Na2SO4) and concentrated under reduced pressure. The
residue was puri®ed by ¯ash chromatography [light
petroleum/etherˆ3:1] to afford dimethyl 1,3-diphenyl-
prop-2-enyl malonate. The enantiomeric excess was deter-
mined from the 1H NMR spectrum in the presence of
enantiomerically pure shift reagent Eu(hfc)3; splitting of
the signals for one of the two methoxy groups was observed.
If the right-hand peak of these two is larger, then this is
typical of the (S)-enantiomer in excess, which was
con®rmed by comparing the speci®c rotation obtained
with literature values.18
pure 2-(2-diphenylphosphinophenyl)-5,6,7,8-tetrahydro-
quinolines 9, 20, 25, 30.
3.5.1. 5S,7S)- 1)-5,6,7,8-Tetrahydro-6,6-dimethyl-2- 2-
diphenylphosphinophenyl)-5,7-methanoquinoline
9.
Chromatographic eluent: petroleum ether/ethyl acetateˆ
13:1; 0.173 g (20%); white solid of mp 136±1388C;
25
1
[a]D ˆ159.7 (c 0.9, CHCl3); H NMR d 7.60 (m, 1H),
7.40 (t, 1H, Jˆ6.6 Hz), 7.32±7.22 (m, 11H), 7.18 (d, 1H,
Jˆ7.8 Hz), 7.11 (d, 1H, Jˆ7.8 Hz), 6.70 (m, 1H), 2.84 (d,
2H, Jˆ2.4 Hz), 2.69 (t, 1H, Jˆ5.4 Hz), 2.62 (m, 1H), 2.28
(m, 1H), 1.36 (s, 3H), 1.23 (d, 1H, Jˆ7.5 Hz), 0.55 (s, 3H).
31P NMR d 28.35. Anal. calcd for C30H28NP: C, 83.10; H,
6.31; N, 3.23. Found: C, 83.17; H, 6.25; N, 3.33.
3.5.2. 5R,7R,8S)- 2)-5,6,7,8-Tetrahydro-6,6,8-trimethyl-
2- 2-diphenylphosphinophenyl)-5,7-methanoquino line
20. Chromatographic eluent: petroleum ether/ethyl
etherˆ9:1; 0.286 g (32%); white solid of mp 93±958C;
Method B. Rac-(E)-1,3-diphenyl-2-propenyl acetate
(0.8 mmol) was added by a syringe to a solution of sodium
dimethylmalonate (1.2 mmol) and 15-crown-5 (1.2 mmol)
in dry acetonitrile (1.2 mL). To this solution was added a
solution prepared by stirring the ligand (0.08 mmol,
10 mol%) and [Pd(h3-C3H5)Cl]2 (8 mg, 2.5 mol%) in dry
acetonitrile (2.5 mL) at room temperature for 1 h. The reac-
tion mixture was stirred until conversion was complete.
Acid acetic was added and then the solvent removed in
vacuo. The residue was diluted with ether and worked up
as described in the BSA procedure.
25
1
[a]D ˆ26.0 (c 0.4, CHCl3); H NMR d 7.62 (dq, 1H,
Jˆ5.2, 1.2 Hz), 7.41 (dt, 1H, Jˆ8.0, 1.2 Hz), 7.32±7.22
(m, 12H), 7.20±7.12 (m, 1H), 7.04 (dq, 1H, Jˆ5.2,
1.2 Hz), 2.98 (dq, 1H, Jˆ5.2, 2.4 Hz), 2.70 (t, 1H,
Jˆ5.7 Hz), 2.52±2.45 (m, 1H), 2.05 (dt, 1H, Jˆ6.0,
2.4 Hz), 1.38 (s, 3H), 1.26±1.23 (m, 1H), 0.98 (d, 3H,
Jˆ7.2 Hz), 0.58 (s, 3H). 31P NMR d 29.56. Anal. calcd
for C31H30NP: C, 83.18; H, 6.76; N, 3.13. Found: C,
83.29; H, 6.86; N, 3.07.
3.5.3. 6R,8R)- 1)-5,6,7,8-Tetrahydro-7,7-dimethyl-2- 2-
diphenylphosphinophenyl)-6,8-methanoquinoline
Method C. A solution of ligand (0.08 mmol, 10 mol%)
and [{Pd(h3-C3H5)Cl}2] (8 mg, 2.5 mol%) in dry CH2Cl2
(1 mL) was stirred at room temperature for 30 min. and
then a solution of rac-(E)-1,3-diphenyl-2-propenyl acetate
(0.8 mmol) in CH2Cl2 (0.5 mL). After 5 min, a solution
of dimethyl malonate (2.4 mmol), BSA (2.4 mmol) and
tetrabutylammonium ¯uoride trihydrate (2.4 mmol) in
CH2Cl2 (3.5 mL) was added over 1 h and stirring
continued at room temperature until conversion was
complete and then worked up as described in the BSA
procedure.
25.
Chromatographic eluent: petroleum ether/ethyl acetateˆ
13:1; 0.372 g (43%); white solid of mp 138±1408C;
25
1
[a]D ˆ128.6 (c 0.9, CHCl3); H NMR d 7.59 (dq, 1H,
Jˆ5.2, 1.2 Hz), 7.38 (dt, 1H, Jˆ7.5, 1.2 Hz), 7.31±7.20
(m, 13H), 7.05±7.02 (m, 1H), 2.87 (d, 2H, Jˆ2.4 Hz),
2.62±2.55 (m, 2H), 2.28±2.23 (m, 1H), 1.33 (s, 3H),
1.22±1.19 (m, 1H), 0.60 (s, 3H). 31P NMR d 29.74. Anal.
calcd for C30H28NP: C, 83.10; H, 6.31; N, 3.23. Found C,
83.22; H, 6.42; N, 3.15.
3.5.4. 5S,8R)- 2)-5,6,7,8-Tetrahydro-8,9,9-trimethyl-2-
2-diphenylphosphinophenyl)-7,8-methanoquinoline 8.
Chromatographic eluent: petroleum ether/ethyl etherˆ9:1;
0.170 g (19%); white solid of mp 132±1368C;
Acknowledgements
25
1
[a]D ˆ222.7 (c 0.5, CHCl3); H NMR d 7.60±7.57 (m,
1H), 7.39 (t, 1H, Jˆ7.5 Hz), 7.31 (d, 1H, Jˆ7.5 Hz), 7.26
(m, 11H), 7.16 (d, 1H, Jˆ7.5 Hz), 7.02±6.98 (m, 1H), 2.78
(d, 1H, Jˆ3.9 Hz), 2.09±2.02 (m, 1H), 1.77±1.69 (m, 1H),
Thanks are due to Mr Mauro Mucedda for experimental
assistance. Financial support by MURST and by Regione
Autonoma Sardegna are gratefully acknowledged.

9996
G. Chelucci et al. / Tetrahedron 57 &2001) 9989±9996
9. (a) Park, S. W.; Son, J. O.; Kim, S. G.; Ahn, K. H.
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