Synthesis of 4-diphenylphosphanylmethyl- and 4-phenylthiomethyl-1,4-methano-11,11-dimethyl-1,2,3,4-tetrahydroacridine: new N-P and N-S camphor-derived chiral ligands for asymmetric catalysis

Article abstract of DOI:10.1016/j.tetasy.2006.05.012

A new procedure has been developed for the preparation of camphor-annulated quinoline with different substituents on the 1-methyl group of the (+)-camphor backbone. Amongst them, two new N-P and N-S ligands, namely the 4-(diphenylphosphanylmethyl)- and 4-

Full text of DOI:10.1016/j.tetasy.2006.05.012

Tetrahedron: Asymmetry 17 (2006) 1529–1536
Synthesis of 4-diphenylphosphanylmethyl- and 4-phenylthiomethyl-
1,4-methano-11,11-dimethyl-1,2,3,4-tetrahydroacridine: new N–P and
N–S camphor-derived chiral ligands for asymmetric catalysis
Giorgio Chelucci* and Salvatore Baldino
`
Dipartimento di Chimica, Universita di Sassari, via Vienna 2, I-07100 Sassari, Italy
Received 10 April 2006; accepted 15 May 2006
Abstract—A new procedure has been developed for the preparation of camphor-annulated quinoline with different substituents on the
1-methyl group of the (+)-camphor backbone. Amongst them, two new N–P and N–S ligands, namely the 4-(diphenylphosphanyl-
methyl)- and 4-(phenylthiomethyl)-1,4-methano-11,11-dimethyl-1,2,3,4-tetrahydroacridine, have been employed in asymmetric palla-
dium-catalyzed allylic substitution.
ꢀ 2006 Elsevier Ltd. All rights reserved.
1. Introduction
Our interest in pyridine ligands,9 prompted our investiga-
tions into camphor-based pyridine ligands containing an
additional ligand on the 1-methyl group of the camphor
backbone. Herein, we report the synthesis of 4-(diphenyl-
phosphanylmethyl)- and 4-(phenylthiomethyl)-1,4-meth-
ano-11,11-dimethyl-1,2,3,4-tetrahydroacridine 7a and 7b,
respectively, as representative examples of camphor-annu-
lated pyridines of type 6 (Scheme 1). Moreover, in order
to prove the ability of the new N–P and N–S ligands to
form complexes with transition metals, they have been
assessed in the asymmetric palladium-catalyzed allylic
substitution.
Optically active monoterpenes derived from naturally
occurring compounds have been widely used as chiral
building blocks for the synthesis of auxiliaries for asym-
metric synthesis and ligands for asymmetric catalysis.1 In
the middle of the monoterpenes, a prominent position is
occupied by optically active camphor, the framework of
which has been incorporated into a variety of chiral ligands
having homo- or heterodonor atoms.2 In this context,
many examples possess pyridine N-donors, such as 2,20-
bipyridines,3 1,10-phenthrolines,4 2,20:60,200-terpyridines,5
pyridine–phosphines,6 pyridine–thioethers7 and pyridine–
alcohols.8
2. Results and discussion
These pyridine ligands can be divided into two types; those
in which the camphor is annulated in the 2,3-positions to
the b-face of the pyridine ring such as the 2,20-bipyridine
13 or 1,10-phenanthroline 24b (Fig. 1) and those in which
the pyridine is contained as a pendant group on the C2,
such as hydroxy-pyridine 3,8d,e pyridine–phosphine 46b
and pyridine–thioether 55b (Fig. 1). Only this last type of
pyridine ligands bears a terpene skeleton containing
another donor atom, located on C2 or C3.
For the synthesis of ligands 7, we envisaged that a conve-
nient approach could involve the substitution of a proper
substituent on the 4-methyl group of tetrahydroacridine 8
with a diphenylphosphino or phenylthio group. Com-
pound 8 could, in turn, be obtained by Friedla¨nder-modi-
fied condensation10 between the camphor derivative 9
and 2-nitrobenzaldehyde 10 (Scheme 1).
Since the phosphorus derivative ligand 7a was chosen as
the target for our initial investigation, we examined the
possibility of introducing the diphenylphosphino group
via nucleophilic substitution of the trifluoromethanesulfo-
nate (Scheme 2, 8: X = OTf) with the diphenylphosphide
*
Corresponding author. Tel.: +39 079 229539; fax: +39 079 229559;
e-mail: chelucci@uniss.it
0957-4166/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2006.05.012

1530
G. Chelucci, S. Baldino / Tetrahedron: Asymmetry 17 (2006) 1529–1536
PR2
OH
N
N
N
N
N
N
1
2
3
4
SR
R
N
N
N
N
R1
SPh
PPh2
6
7a
7b
5
R = alkyl, aryl, heteroaryl, etc.
R1 = NR2, OR, SR, PR2, etc.
Figure 1.
OHC
+
N
X
N
O2N
O
Y
X
10
7a,b
8a-c
9a-c
a: X= OH, b: X= Br, c: X= I
a: Y= PPh2, b: Y= SPh
Scheme 1.
group. Accordingly, 10-hydroxycamphor 9a was prepared
in a three step sequence from (+)-camphor [(i) base-pro-
moted Tf2O rearrangement, (ii) LiAlH4 reduction of the
obtained 2-methylenenorbor-1-yl triflate and finally (iii)
m-CPBA-promoted rearrangement of reduced product 2-
methylenebornan-1-ol].11 Alternatively, 9a can be obtained
from 10-iodocamphor 9c (displacement of the iodide by
acetate ion followed by hydrolysis),12 which can be readily
obtained from 10-camphorsulfonic acid 12.13 The hydroxy
group of 9a was protected as a benzyl derivative (NaH,
BnBr, THF, reflux, 2 h, 95%) and then the resultant camp-
hor-derivative 13 was deprotonated by lithium diisoprop-
ylamide (LDA, ꢀ40 ꢁC, 2 h). The lithium enolate was
condensed with 2-nitrobenzaldehyde 10 to give the cross-
aldol product 14 as a single geometric isomer (72% yield).
The nitro group of 14 was then reduced by refluxing with
powdered iron in acetic acid/ethanol/water (2:2:1)14 to
afford, in good yield (87%), the corresponding amine 15 that
was finally converted into the camphor-fused quinoline 16
by heating at reflux in a degassed carbitol solution (cata-
lytic H2SO4, 200 ꢁC, 10 h, 89%). Unexpectedly, the removal
of the benzyl protecting group from 15 proved problematic
and after several failed attempts [(H2, Pd/C, EtOH, rt),
(Me3SiI, CH2Cl2, rt or 60 ꢁC, 48 h)15 and (SnCl4, CH2Cl2
or benzene, rt, 48 h)16] alcohol 8a was obtained in 26%
yield by treatment of 16 with boron trifluoride and sodium
iodide (MeCN, rt, 24 h).17
We next examined the possibility of obtaining 8a directly
from alcohol 9a, that would overcome the protection–
deprotection steps. Thus, treatment of 9a with two equiva-
lents of LDA and then treatment with 2-nitrobenzaldehyde
10 gave condensation product 19. The yield of the reaction
was low (37%), but the two next steps, carried out in the
usual way, were very successful (81% overall yield). Alco-
hol 8a was converted into the corresponding triflate 17
[(Tf2O, Et3N, ꢀ45 ꢁC to rt, 95%] which was then treated
with lithium diphenylphosphide (LiPPh2, ꢀ60 ꢁC to rt,
24 h). Unexpectedly, the reaction failed to give phosphine
7a. Therefore, to overcome these problems, temporary
protection of the phosphorus with BH3 was examined.18
Treatment of 17 with sodium diphenylphosphide–borane
[Na(PPh2–BH3), THF, ꢀ30 ꢁC to rt, 12 h)] gave in good
yield (77%) the phosphine–borane 18 which, by removal
of BH3 from the phosphorus with an excess of morpholine
(70 ꢁC, 2 h), afforded phosphine 7a in 96% yield.
Although we have been able to obtain the desired N,P-
ligand 7a, a low yield of 8a was restrictive. An alternative
to the triflate leaving group is iodide; thus we devoted
our attention to the possibility of obtaining 8c (Scheme
1) from 10-iodocamphor 9c, following the usual protocol
(Scheme 3). Notwithstanding the rather harsh conditions
required for the reduction and annulation steps (carbitol,
200 ꢁC, 1 h), the iodomethyl-tetrahydroacridine 8c was

G. Chelucci, S. Baldino / Tetrahedron: Asymmetry 17 (2006) 1529–1536
1531
b
O
O
I
SO3H
9c
c
12
e
a
d
NO2
O
O
O
O
OBn
13
OBn
11
OH
14
9a
m
f
n
NH2
NH2
NO2
O
OBn
O
O
20
19
15
OH
OH
o
g
h
i
N
N
N
OBn
OTf
OH
8a
17
16
k
l
j
N
N
PPh2
PPh2
H3B
7a
18
Scheme 2. Reagents and conditions: (a) (i) Tf2O, CH2Cl2, MTBMP, 95%, (ii) LiAlH4, Et2O, then hydrolysis, 95%, (iii) m-CPBA, CH2Cl2, rt, 24 h, 78%; (b)
(i) I2, PPh3, toluene, reflux, 16 h, 92%, (ii) KOH, MeOH, reflux, 6 h, 69%; (c) KOAc, AcOH, 180 ꢁC, 1.5 h, 88%; (d) NaH, BnBr, THF, reflux, 2 h, 95%; (e)
LDA, THF, ꢀ40 ꢁC, 2 h, then 2-nitrobenzaldehyde, 72%; (f) Fe, AcOH/EtOH/H2O (2:2:1), catalytic HCl, reflux, 15 min, 87%; (g) carbitol, catalytic
H2SO4, reflux, 10 h, 89%; (h) BF3, NaI, CH3CN, rt, 24 h, 26%; (i) Tf2O, Et3N, CH2Cl2, ꢀ45 ꢁC to rt, 12 h, 95%; (j) LiPPh2, THF, ꢀ60 ꢁC to rt, 24 h; (k)
LiPPh2(BH3), THF, rt, 48 h, 76%; (l) morpholine, 70 ꢁC, 2 h, 96%; (m) LDA (2.2 equiv), THF, ꢀ40 ꢁC, 2 h, then 2-nitro benzaldehyde, 37%; (n) Fe,
AcOH/EtOH/H2O (2:2:1), catalytic HCl, reflux, 15 min, 92%; (o) carbitol, catalytic H2SO4, reflux, 10 h, 88%.
obtained in a reasonable yield (58% from 9c). Treatment of
8c with sodium diphenylphosphide–borane [Na(PPh2–
BH3), THF, ꢀ30 ꢁC to rt, 48 h] also proved satisfactory
giving 76% yield of the phosphine–borane 18 that was
finally deprotected to give 7a in the usual way.
(Scheme 4). In the presence of 2.5% of bis(p-allylpalladium
chloride), both ligands 7a and 7b (Pd/ligand = 1:4) pro-
vided effective palladium catalysts to give the dimethyl
(R)-1,3-diphenylprop-2-enyl malonate 24 in good yields
(>90%) and reasonable reaction times (<20 h), although
in modest enantiomeric excesses (44% and 22%, respec-
tively). When the alkylation with ligand 7a was performed
using a Pd/ligand ratio of 1:2 and 1:1, similar reaction
times, yields and selectivities (43% and 42% ee, respec-
tively) were obtained. Allylic alkylation was also carried
out using the borane protected ligand 18 and 10 mol % of
palladium acetate (Pd/ligand = 1:1), which was employed
simultaneously to release the phosphorus from borane
and as the Pd(0) source for the catalytic reaction.22 The
reaction afforded (R)-24 in a longer time (60 h) and with
lower yield (66%) and enantioselectivity (34% ee) with
respect to the P-free ligand 7a.
Iodo-compound 8c was also converted in good yield (76%)
to phenylthiomethyl-acridine 7b by treatment with sodium
benzenethiolate in N,N-dimethylformamide (70 ꢁC, 5 h)
(Scheme 3).
The catalytic activity of the new N–P19 and N–S20 ligands
was tested in the palladium-catalyzed allylic substitution21
and, in particular, the alkylation of 1,3-diphenylprop-2-
enyl acetate 23 by using dimethyl malonate as the nucleo-
phile in the presence of N,O-bis(trimethylsilyl)acetamide
(BSA) and potassium acetate in methylene chloride

1532
G. Chelucci, S. Baldino / Tetrahedron: Asymmetry 17 (2006) 1529–1536
b
a
c
NO2
NH2
O
I
O
O
I
I
21
22
9c
d, e
N
N
PPh2
7a
I
8c
f
N
SPh
7b
Scheme 3. Reagents and conditions: (a) LDA, THF, ꢀ40 ꢁC, 2 h, then 2-nitrobenzaldehyde, 72%; (b) Fe, CH3COOH/EtOH/H2O (2:2:1), catalytic HCl,
reflux, 15 min, 87%; (c) carbitol, catalytic H2SO4, reflux, 1 h, 92%; (d) LiPPh2(BH3), THF, rt, 48 h, 76%; (e) morpholine, 70 ꢁC, 2 h, 96%; (f) NaSPh,
DMF, reflux, 5 h, 76%.
[Pd(η3-C3H5)Cl]2
or Pd(OAc)2 / L*
OCOCH3
C6H5
CH(COOCH3)2
C6H5
C6H5
CH2(COOCH3)2, BSA,
CH2Cl2, KOAc
C6H5
24
23
Scheme 4.
3. Conclusion
were performed on a Perkin–Elmer 240 B analyzer. Ethyl
acetate and petroleum ether were distilled before use.
THF was distilled from sodium–benzophenone ketyl and
CH2Cl2 from P2O5. Both solvents were degassed thor-
oughly with dry nitrogen directly before use. Alcohol 9a
was obtained from (+)-1111 or 9c.12
In conclusion, we have developed a procedure for the prep-
aration of camphor-annulated quinoline derivatives with
different substituents on the 10-methyl group of the cam-
phor backbone. Amongst them, the new bidentate N–P
and N–S ligands 7a and 7b, respectively, have proven their
catalytic activity in Pd-catalyzed allylic alkylation.
Although the stereochemical result has been modest, it is
premature to rule out the synthetic utility of these ligands
at this time. Further experiments to investigate their reac-
tivity and the conversion of the iodo-compound 8c and/
or hydroxy analogue 8a in other camphor-based ligands
are currently in progress.
4.2. (1R,4R)-1-Benzyloxymethyl-7,7-dimethylbicyclo-
[2.2.1]heptan-2-one 13
Alcohol 9a (2.16 g, 12.9 mmol) was added dropwise to a
mixture of NaH (0.324 g, 13.5 mol) in anhydrous THF
(100 mL). After 3 h, benzyl bromide (2.3 g, 13.5 mmol)
was added dropwise. The mixture was stirred at room tem-
perature for 1 h and then heated at reflux for 2 h. The sol-
vent was evaporated under vacuum and the residue taken
up in H2O and extracted with Et2O (2 · 50 mL). The com-
bined organic solution was dried over anhydrous Na2SO4
and the solvent evaporated. Purification of the residue by
distillation under vacuum gave 13: 3.1 g (95%), bp 150 ꢁC
4. Experimental
4.1. General methods
25
1
Melting points were determined on a Buchi 510 capillary
¨
at 0.1 mm Hg; ½aꢁD ¼ þ38:0 (c 1.77, CHCl3); H NMR: d
2.34–2.22 (m, 5H), 4.53 (s, 2H), 3.64 (d, 1H, J =
10.5 Hz), 3.59 (d, 1H, J = 10.5 Hz), 2.39 (dddd, 1H,
J = 18.3, 7.2, 4.2, 2.4 Hz), 2.15–2.92 (m, 3H), 1.84 (d,
1H, J = 18.3 Hz), 1.35 (d, 2H, J = 9.0 Hz), 1.07 (s, 3H),
0.95 (s, 3H). Anal. Calcd for C17H22O2: C, 79.03; H,
8.58. Found: C, 79.32; H, 8.61.
apparatus and are uncorrected. NMR spectra were
obtained with a Varian VXR-300 spectrometer at 300 MHz
for 1H, 75.4 MHz for 13C and 121.4 MHz for 31P. Chemical
shifts are reported in ppm downfield from internal Me4Si in
CDCl3. Optical rotations were measured with a Perkin–
Elmer 241 polarimeter in a 1 dm tube. Elemental analyses

G. Chelucci, S. Baldino / Tetrahedron: Asymmetry 17 (2006) 1529–1536
1533
4.3. (1R,4S)-3-(2-Nitrophenyl)methylene-1-benzyloxy-
methyl-7,7-dimethyl[2.2.1]bicycloheptan-2-one 14
7.22 (m, 6H), 4.71 (s, 2H), 4.33 (d, 1H, J = 10.5 Hz), 4.10
(d, 1H, J = 10.5 Hz), 2.87 (d, 1H, J = 3.9 Hz), 2.53–2.42
(m, 1H), 2.59–2.30 (m, 1H), 1.32–1.20 (m, 2H), 1.21 (s,
3H), 0.65 (s, 3H). Anal. Calcd for C24H25NO: C, 83.93;
H, 7.34; N, 4.08. Found: C, 83.73; H, 7.37; N, 4.06.
A solution of 13 (1.55 g, 6 mmol) in THF (5 mL) was
added dropwise over 15 min to a cooled (ꢀ40 ꢁC) solution
of LDA (6.6 mmol) in THF (90 mL) under an argon atmo-
sphere. The solution was stirred for 2 h at ꢀ78 ꢁC and then
a solution of 2-nitrobenzaldehyde (0.91 g, 6 mmol) in THF
(10 mL) was added dropwise over 10 min. The solution was
stirred at ꢀ40 ꢁC for 1 h and then allowed to warm to room
temperature overnight. Water (5 mL) was added and the
THF was evaporated under vacuum. The residue was
poured into H2O (50 mL) and the resulting mixture
extracted with ethyl acetate (3 · 50 mL). The combined
organic solution was dried over anhydrous Na2SO4 and
the solvent evaporated. Purification of the residue by flash
chromatography (petroleum ether/EtOAc = 8:2) gave 14
4.6. (1S,4S)-4-Hydroxymethyl-1,4-methano-11,11-dimethyl-
1,2,3,4-tetrahydroacridine 8a
Freshly distilled boron trifluoride–ether (1.46 g, 10.3
mmol) was added dropwise to a solution of 16 (1.41 g,
4.1 mmol) and NaI (1.54 g, 10.3 mmol) in acetonitrile
(20 mL). The mixture was stirred at room temperature
for 24 h and then poured into ice-cold water (40 mL). This
mixture was basified with 5% NaOH and extracted with
CH2Cl2 (3 · 30 mL). The combined organic extracts were
washed with H2O (3 · 20 mL) followed by brine
(2 · 20 mL). Evaporation of the solvent gave a residue
which was purified by flash chromatography (petroleum
ether/EtOAc = 7:3) to give 8a: 0.27 g (26%); oil,
1
(1.69 g, 72%): mp 107–109 ꢁC; H NMR: d 8.08 (d, 1H,
J = 8.1 Hz), 7.64 (t, 1H, J = 7.8 Hz), 7.57–7.22 (m, 7H),
7.34 (s, 1H), 4.58 (s, 2H), 3.77 (d, 1H, J = 10.5 Hz), 3.71
(d, 1H, J = 10.5 Hz), 2.69 (d, 1H, J = 3.9 Hz), 2.30–2.11
(m, 2H), 1.65–1.45 (m, 2H), 1.09 (s, 3H), 0.96 (s, 3H). Anal.
Calcd for C24H25NO4: C, 73.64; H, 6.44; N, 3.58. Found:
C, 73.85; H, 6.48; N, 3.56.
25
1
½aꢁD ¼ þ21:3 (c 0.72, CHCl3); H NMR: d 7.97 (d, 1H,
J = 8.1 Hz), 7.72 (s, 1H), 7.70 (d, 1H, J = 8.1 Hz), 7.57
(dt, 1H, J = 6.9, 0.9 Hz), 7.45 (dt, 1H, J = 6.9, 0.9 Hz),
4.76 (br s, 1H), 4.37 (d, 1H, J = 11.4 Hz), 4.01 (dd, 1H,
J = 11.4, 6.3 Hz), 2.93 (d, 1H, J = 3.9 Hz), 2.26–2.13 (m,
1H), 2.07 (dt, 1H, J = 12.6, 3.6 Hz), 1.61 (ddd, 1H,
J = 12.6, 9.0, 3.6 Hz), 1.17–1.11 (m, 1H), 1.06 (s, 3H),
0.66 (s, 3H). 13C NMR: d 171.5, 145.6, 139.6, 128.3,
127.7, 127.4, 127.4, 126.5, 125.3, 61.9, 57.4, 54.8, 51.7,
28.1, 25.8, 20.8, 19.0. Anal. Calcd for C17H19NO: C,
80.60; H, 7.56; N, 5.53. Found: C, 80.81; H, 7.53; N, 5.54.
4.4. (1R,4S)-3-(2-Aminophenyl)methylene-1-benzyloxy-
methyl-7,7-dimethyl[2.2.1]bicycloheptan-2-one 15
A mixture of 14 (0.78 g, 2 mmol), iron power (0.826 g,
14.9 mmol), concentrated HCl (two drops) and EtOH/
AcOH/H2O (2:2:1, 20 mL) was heated at reflux for
15 min and then stirred at room temperature for 20 min.
The solution was filtered, diluted with H2O (200 mL),
and extracted with ethyl acetate (3 · 100 mL). The com-
bined organic phase was washed with a 5% aqueous NaOH
solution (50 mL) and then with H2O (50 mL). The organic
solution was dried over anhydrous Na2SO4 and the solvent
evaporated. Purification of the residue by flash chromato-
graphy (petroleum ether/EtOAc = 8:2) gave 15 (0.63 g,
4.7. (1R,4S)-3-(2-Nitrophenyl)methylene-1-hydroxymethyl-
7,7-dimethyl[2.2.1]bicycloheptan-2-one 19
The procedure used for the preparation of 14, but using
2.2 equiv of LDA with respect to 9a, was followed. In this
way compound 19 was obtained by flash chromatography
(petroleum ether/EtOAc = 7:3 and then 1:1) in 37% yield:
mp 134–136 ꢁC; 1H NMR: d 8.10 (d, 1H, J = 7.8 Hz),
7.67 (t, 1H, J = 7.5 Hz), 7.55 (s, 1H), 7.53 (d, 1H,
J = 7.8 Hz), 7.41 (t, 1H, J = 7.8 Hz), 4.01 (d, 1H, J =
12.0 Hz), 3.76 (d, 1H, J = 12.0 Hz), 2.73 (d, 1H,
J = 3.9 Hz), 2.64 (br s, 1H), 2.24–2.09 (m, 1H), 1.96 (dt,
1H, J = 12.9, 3.6 Hz), 1.82–1.70 (m, 1H), 1.67–1.56 (m,
1H), 1.03 (s, 3H), 1.00 (s, 3H). Anal. Calcd for
C17H19NO4: C, 67.76; H, 6.36; N, 4.65. Found: C, 67.85;
H, 6.35; N, 4.68.
1
87%): mp 97–99 ꢁC; H NMR: d 7.37–7.19 (m, 6H), 7.35
(s, 1H), 7.15 (t, 1H, J = 7.5 Hz), 6.77 (t, 1H, J = 7.5 Hz),
6.70 (d, 1H, J = 7.5 Hz), 4.57 (s, 2H), 3.87 (br s, 2H),
3.77 (d, 1H, J = 10.5 Hz), 3.70 (d, 1H, J = 10.5 Hz), 2.94
(d, 1H, J = 3.3 Hz), 2.28–2.13 (m, 2H), 1.53–1.42 (m,
2H), 1.10 (s, 3H), 0.93 (s, 3H). Anal. Calcd for
C24H27NO2: C, 79.74; H, 7.53; N, 3.87. Found: C, 79.91;
H, 7.55; N, 3.84.
4.5. (1S,4S)-4-Benzyloxymethyl-1,4-methano-11,11-
dimethyl-1,2,3,4-tetrahydroacridine 16
4.8. (1R,4S)-2-(Aminophenyl)methylene-1-hydroxymethyl-
7,7-dimethyl[2.2.1]bicycloheptan-2-one 20
A solution of 15 (0.72 g, 2 mmol) in degassed carbitol
(9 mL) was heated at reflux under argon for 10 h. The
cooled solution was then poured into H2O (250 mL) and
the resulting mixture extracted with Et2O (3 · 100 mL).
The combined organic solution was washed with H2O
(5 · 100 mL), dried over anhydrous Na2SO4, and the sol-
vent evaporated to give an oil. Purification of this oil by
flash chromatography (petroleum ether/EtOAc = 7:3) gave
Following the procedure used for the preparation of 15,
compound 20 was obtained by flash chromatography
(petroleum ether/EtOAc = 7:3) in 92% yield: foam solid;
1H NMR: d 7.31 (s, 1H), 7.22 (d, 1H, J = 7.5 Hz), 7.15
(t, 1H, J = 7.5 Hz), 6.76 (t, 1H, J = 7.5 Hz), 7.71 (d, 1H,
J = 7.5 Hz), 4.02 (br s, 2H), 3.98 (d, 1H, J = 12.0 Hz),
3.75 (d, 1H, J = 12.0 Hz), 2.98 (d, 1H, J = 4.2 Hz), 2.94
(br s, 1H), 2.25–2.15 (m, 1H), 1.94 (dt, 1H, J = 13.2,
3.3 Hz), 1.76–1.58 (m, 2H), 1.03 (s, 3H), 0.96 (s, 3H). Anal.
25
1
16: 0.61 mg (89%); oil; ½aꢁD ¼ þ50:7 (c 3.22, CHCl3); H
NMR: d 8.04 (d, 1H, J = 8.4 Hz), 7.67 (dd, 1H, J = 7.5,
1.2 Hz), 7.59 (s, 1H), 7.56 (dt, 1H, J = 7.5, 1.5 Hz), 7.46–

1534
G. Chelucci, S. Baldino / Tetrahedron: Asymmetry 17 (2006) 1529–1536
Calcd for C17H21NO2: C, 75.25; H, 7.80; N, 5.16. Found:
C, 75.25; H, 7.80; N, 5.16.
28.0, 26.6, 22.6, 22.2, 20.1. 31P NMR: d 15.8–13.5 (br s).
Anal. Calcd for C29H31BNP: C, 80.01; H, 7.18; N, 3.22;
Found: C, 80.12; H, 7.19; N, 3.20.
4.9. (1S,4S)-4-Hydroxymethyl-1,4-methano-11,11-dimethyl-
1,2,3,4-tetrahydroacridine 8a
4.12. (1S,4S)-4-Diphenylphosphanylmethyl-1,4-methano-
11,11-dimethyl-1,2,3,4-tetrahydroacridine 7a
Following the procedure used for the preparation of 16,
the heating at reflux of the amine 20 for 1 h gave a crude
product that by flash chromatography (petroleum ether/
EtOAc = 7:3) afforded 8a in 88% yield. Spectroscopic data
of this compound were identical to all the data above.
A solution of the P-borane 18 (130.5 mg, 0.3 mmol) in mor-
pholine (2 mL) was heated under argon at 70 ꢁC for 2 h.
After the reaction mixture was cooled, the excess morphol-
ine was eliminated under vacuum and the residue purified
by flash chromatography (petroleum ether/EtOAc = 95:5)
to give 7a: 0.120 g, (96%); mp 47–52 ꢁC (sticky
solid); ½aꢁD ¼ þ29:4 (c 0.48, CHCl3); H NMR: d 8.00 (d,
1H, J = 8.4 Hz), 7.76–7.52 (m, 8H), 7.45–7.26 (m, 6H),
3.15 (d, 1H, J = 15.0, 3.6 Hz), 2.90 (d, 1H, J = 2.4 Hz),
2.45 (dd, 1H, J = 15.0, 2.7 Hz), 2.21–2.02 (m, 2H), 1.46–
1.38 (m, 1H), 1.32–1.21 (m, 1H), 1.12 (s, 3H), 0.59 (s,
3H). 13C NMR: d 171.2, 146.6, 139.6, 133.4–132.6 (m),
129.1, 128.4–127.3 (m), 125.8, 125.2, 56.7, 56.3, 56.1,
51.2, 29.7, 26.6, 20.1, 20.0. 31P NMR: d ꢀ21.6. Anal. Calcd
for C29H28NP: C, 82.63; H, 6.70; N, 3.32. Found: C, 82.81;
H, 6.74; N, 3.31.
4.10. (1S,4S)-4-Trifluoromethanesulfonyloxymethyl-1,4-
methano-11,11-dimethyl-1,2,3,4-tetrahydroacridine 17
25
1
Triflic anhydride (0.31 mL, 1.88 mmol) was added drop-
wise to a cooled (ꢀ45 ꢁC) solution of 8a (1.25 mmol) and
Et3N (0.21 mL, 1.5 mmol) in anhydrous CH2Cl2 (6 mL)
under nitrogen. The resulting solution was allowed to
warm to room temperature and stirred overnight. The mix-
ture was treated with a saturated aqueous Na2CO3 solution
and extracted with CH2Cl2. The organic phase was washed
with brine, dried over anhydrous Na2SO4 and the solvent
evaporated. The residue was purified by flash chromato-
graphy (petroleum ether/EtOAc = 8:2) to give 17: 0.460 g
4.13. (1R,4S)-3-(2-Nitrophenyl)methylene-1-iodomethyl-
7,7-dimethyl[2.2.1]bicycloheptan-2-one 21
1
(95%); yellow oil; H NMR: d 8.01 (d, 1H, J = 8.4 Hz),
7.73 (s, 1H), 7.72 (d, 1H, J = 8.4 Hz), 7.58 (t, 1H,
J = 6.9 Hz), 7.45 (t, 1H, J = 6.9 Hz), 5.40 (d, 1H,
J = 12.0 Hz), 5.15 (d, 1H, J = 12.0 Hz), 2.96 (d, 1H,
J = 3.6 Hz), 2.40–2.18 (m, 2H), 1.35–1.17 (m, 2H), 1.19
(s, 3H), 0.69 (s, 3H). Anal. Calcd for C18H18F3NO3S: C,
56.10; H, 4.71; N, 3.63. Found: C, 56.32; H, 4.75; N, 3.66.
Following the procedure used for the preparation of 14,
compound 21 was obtained after chromatographic purifi-
cation on neutral aluminum oxide (petroleum ether/ethyl
acetate = 9:1): 62%; mp 84–86 ꢁC; 1H NMR: d 8.08 (d,
1H, J = 8.1 Hz), 7.65 (t, 1H, J = 7.8 Hz), 7.55 (s, 1H),
7.39 (t, 1H, J = 7.8 Hz), 7.37 (d, 1H, J = 8.1 Hz), 3.44 (d,
1H, J = 10.5 Hz), 3.21 (d, 1H, J = 10.5 Hz), 2.78 (d, 1H,
J = 3.9), 2.22–2.09 (m, 2H), 1.80–1.70 (m, 1H), 1.70–1.55
(m, 1H), 1.09 (s, 3H), 0.92 (s, 3H). Anal. Calcd for
C17H18INO3: C, 49.65; H, 4.41; N, 3.41. Found: C, 49.83;
H, 4.43; N, 3.44.
4.11. Synthesis of the P-borane of (1S,4S)-4-diphenylphos-
phanylmethyl-1,4-methano-11,11-dimethyl-1,2,3,4-tetra-
hydroacridine 18
A
solution of diphenylphosphine borane (0.224 g,
1.22 mmol) in dry THF (3 mL) was added to a mixture
of oil-free NaH (36.6 mg, 1.22 mmol) in dry THF (7 mL)
at ꢀ30 ꢁC for 30 min. The mixture was then slowly warmed
at room temperature and stirring continued for 1 h. The
mixture was cooled again at ꢀ30 ꢁC and a solution of 17
(0.229 g, 0.61 mmol) in dry THF (3 mL) was added drop-
wise over 30 min. After addition, the cooling bath was
turned off and when the temperature reached room temper-
ature and the mixture was stirred for 12 h. The solvent was
evaporated under reduced pressure and the residue taken
up in H2O (10 mL) and extracted with CH2Cl2
(3 · 20 mL). The combined organic phase was dried on
anhydrous Na2SO4 and the solvent evaporated under
vacuum. The residue was purified by chromatography on
4.14. (1R,4S)-3-(2-Aminophenyl)methylene-1-iodomethyl-
7,7-dimethyl[2.2.1]bicycloheptan-2-one 22
Following the procedure used for the preparation of 15,
compound 22 was obtained in 73% yield after chromato-
graphic purification on neutral aluminum oxide (petroleum
1
ether/ethyl acetate = 9:1): oil; H NMR: d 7.31 (s, 1H),
7.23–7.08 (m, 2H), 6.80–6.66 (m, 2H), 4.00 (br s, 2H),
3.41 (d, 1H, J = 10.5 Hz), 3.05 (d, 1H, J = 10.5 Hz), 3.01
(d, 1H, J = 3.9 Hz), 2.25–2.15 (m, 2H), 1.75–1.55 (m,
2H), 1.08 (s, 3H), 0.87 (s, 3H). Anal. Calcd for C17H20INO:
C, 53.56; H, 5.29; N, 3.67. Found: C, 53.75; H, 5.31; N,
3.69.
neutral alumina (petroleum ether/EtOAc = 98:2) to give
25
18: 0.204 g (77%); mp 146–148 ꢁC; ½aꢁD ¼ ꢀ13:4 (c 0.65,
4.15. (1S,4S)-4-Iodomethyl-1,4-methano-11,11-dimethyl-
1,2,3,4-tetrahydroacridine 8c
CHCl3); 1H NMR: d 8.35–8.26 (m, 2H), 8.02 (d, 1H,
J = 8.4 Hz), 7.84–7.56 (m, 5H), 7.50–7.36 (m, 7H), 3.93
(t, 1H, J = 16.8 Hz), 2.91 (d, 1H, J = 3.9 Hz), 2.60 (dt,
1H, J = 13.8, 3.5 Hz), 2.30–2.10 (m, 2H), 1.40–0.70 (m,
3H, broad signals from BH3), 1.20 (s, 3H), 1.09 (dt, 1H,
J = 12.9, 3.5 Hz), 0.89–0.80 (m, 1H), 0.56 (s, 3H). 13C
NMR: d 170.0, 146.3, 139.4, 133.5–128.5 (m, PPh2),
128.4, 127.9, 127.7, 127.4, 126.2, 125.4, 57.6, 55.2, 50.3,
Following the procedure used for the preparation of 16, the
heating under reflux of the amine 22 for 1 h gave a crude
product that by chromatographic purification on neutral
alumina (petroleum ether/ethyl acetate = 95:5) afforded
25
8c in 92% yield: mp 100–102 ꢁC, ½aꢁD ¼ ꢀ49:3 (c 0.13,
1
CHCl3); H NMR: d 8.06 (d, 1H, J = 8.4 Hz), 7.76–6.69

G. Chelucci, S. Baldino / Tetrahedron: Asymmetry 17 (2006) 1529–1536
1535
(m, 1H), 7.72 (s, 1H), 7.60 (dt, 1H, J = 6.9, 1.5 Hz), 7.45
(dt, 1H, J = 6.9, 1.2 Hz), 4.02 (d, 1H, J = 10.5 Hz), 3.61
(d, 1H, J = 10.5 Hz), 3.01 (d, 1H, J = 3.9 Hz), 2.38–2.18
(m, 2H), 1.52–1.42 (m, 1H), 1.35–1.24 (m, 1H), 1.22 (s,
3H), 0.63 (s, 3H). 13C NMR: d 168.9, 146.4, 138.9, 129.1,
127.8, 127.7, 127.4, 126.2, 125.5, 65.8, 56.7, 55.4, 52.3,
32.4, 26.3, 20.3, 20.4. Anal. Calcd for C17H18IN: C,
56.21; H, 4.99; N, 3.86. Found: C, 56.42; H, 4.97; N, 3.89.
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)-enantio-
mer in excess, which was confirmed by comparing the spe-
cific rotation obtained with literature values.21
Acknowledgements
4.16. (1S,4S)-4-Phenylthiomethyl-1,4-methano-11,11-
dimethyl-1,2,3,4-tetrahydroacridine 7b
Financial support from MIUR (PRIN 2005035123- regio-
and enantioselective reactions mediated by transition metal
catalysts for innovative processes in fine chemicals synthe-
sis) and from the University of Sassari is gratefully
acknowledged by G.C.
Benzenethiol (0.165 g, 1.5 mmol) was added dropwise to a
mixture of oil-free NaH (36.0 mg, 1.5 mmol) in dry DMF
(3 mL) at 0 ꢁC. After 30 min at room temperature, a solu-
tion of 8c (0.181 g, 0.5 mmol) in dry DMF (2 mL) was
added dropwise and the resulting mixture heated under
nitrogen at 70 ꢁC for 5 h. After cooling the solution was
taken up in H2O (50 mL) and extracted with Et2O. The
organic phase was dried on anhydrous Na2SO4 and the sol-
vent evaporated under vacuum. The residue was purified
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25
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with dimethyl malonate: general procedure
A solution of the catalyst was prepared as follows: (a) with
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TLC analysis (petroleum ether/diethyl ether = 3:1). The
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