Efficient enantioselective syntheses of sertraline, 2-epicatalponol and catalponol from tetralin-1,4-dione

Article abstract of DOI:10.1002/adsc.201000384

Tetralin-1,4-dione, the stable tautomer of dihydroxynaphthalene, was reduced with catecholborane in the presence of 3,3-diphenyl-1-butyltetrahydro- 3H-pyrrolo[1,2-c][1,3,2]oxazaborole as catalyst to give enantiomerically highly enriched 4-hydroxy1-tetralone (99% ee) in an efficient one-pot procedure. The R-enantiomer provided a rapid access to sertraline while the S-enantiomer was converted into 2-epicatalponol and catalponol. A more selective enantioselective route to the antithermitic catalponol made use of the planar chiral tricarbonylchromium complex of hydroxytetralone. Its precursor chromium(tricarbonyl)[η⁶-(1-4,4a,8a)-tetralin-5,8dione] was obtained via direct complexation of 1,4-dihydroxynaphthalene using chromium(tricarbonyl)tris(ammonia) and boron trifluoride etherate as source of the chromium(tricarbonyl) fragment. Enolate prenylation was best carried out in the presence of a tetraamine ligand. Complete inversion of the stereogenic center bearing the prenyl group of the initially obtained tetralone complex was achieved via enolate formation followed by protonation.

Full text of DOI:10.1002/adsc.201000384

FULL PAPERS
DOI: 10.1002/adsc.201000384
Efficient Enantioselective Syntheses of Sertraline, 2-Epicatalponol
and Catalponol from Tetralin-1,4-dione
Alvaro Enriquez Garcia,a Souad Ouizem,a Xin Cheng,a Patrick Romanens,a
and E. Peter Kꢀndiga,*
a
Department of Organic Chemistry, University of Geneva, 30 Quai Ernest Ansermet, 1211 Geneva 4, Switzerland
Fax : (+41)-22-379-3215; e-mail: peter.kundig@unige.ch
Received: May 16, 2010; Published online: September 8, 2010
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/adsc.201000384.
Abstract: Tetralin-1,4-dione, the stable tautomer of dione] was obtained via direct complexation of 1,4-
dihydroxynaphthalene, was reduced with catechol- dihydroxynaphthalene using chromium(tricarbonyl)-
borane in the presence of 3,3-diphenyl-1-butyltetra- tris
ACHTUNGTRENUN(NG ammonia) and boron trifluoride etherate as
hydro-3H-pyrrolo[1,2-c][1,3,2]oxazaborole as catalyst source of the chromium(tricarbonyl) fragment. Eno-
A
ACHTUNGTRENNUNG
to give enantiomerically highly enriched 4-hydroxy- late prenylation was best carried out in the presence
1-tetralone (99% ee) in an efficient one-pot proce- of a tetraamine ligand. Complete inversion of the
dure. The R-enantiomer provided a rapid access to stereogenic center bearing the prenyl group of the
sertraline while the S-enantiomer was converted into initially obtained tetralone complex was achieved via
2-epicatalponol and catalponol. A more selective enolate formation followed by protonation.
enantioselective route to the antithermitic catalponol
made use of the planar chiral tricarbonylchromium
complex of hydroxytetralone. Its precursor Keywords: arene complexes; asymmetric reduction;
chromium(tricarbonyl)
G
chromium tricarbonyl; prenylation; tautomerism
Introduction
reducing agent.[2] Of special interest to the study de-
scribed in this paper is the finding that a two-step,
Tetralin-1,4-dione (1) is readily obtained by tautome- one-pot enantioselective mono-reduction of 1 to give
rization of 1,4-dihydroxynaphthalene (2) in trifluoro- (À)-(R)-3 can be achieved (Scheme 1).[2,3]
acetic acid.[1] In the solid as well as in solution in the
4-Hydroxy-1-tetralone (rac-3) is a naturally occur-
absence of acid or base, 1 and 2 do not interconvert ring compound isolated from Ampelocera edentula
unless heated at >1008C. Dione 1 can be reduced with activity against cutaneous Leishmaniasis.[4]
with fair to excellent selectivity to give either the cis-
In this article we report on (i) the application of
diol or the trans-diol preferentially depending on the highly enantiomerically enriched (R)-3 to a formal,
Scheme 1. Two-step, asymmetric mono-reduction of tetralin-1,4-dione.
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Efficient Enantioselective Syntheses of Sertraline, 2-Epicatalponol and Catalponol
efficient synthesis of sertraline; (ii) a new one-step
enantioselective catalytic reduction of 1 to 3; (iii) the
application of (S)-3 to a synthesis of catalponol and 2-
epicatalponol; (iv) an improved synthesis of the chro-
mium tricarbonyl complex of 1 and its enantioselec-
tive mono-reduction; and (v) an enantioselective syn-
thesis of catalponol via desymmetrization of
[Cr(arene)(CO)3] complex.
a
ACHTUNGTRENNUNG
Results and Discussion
The
antidepressant
sertraline
[(+)-cis-(1S,4S)-
4-(3,4-dichlorophenyl)-(1-4)-tetrahydronaphthalene-1-
amine] is a popular target of asymmetric synthesis.[5,6]
The route reported by Lautens and Rovis involves
the key intermediate (R)-5.[6h] This was synthesized
via a six-step sequence from oxaACHTUNTRGNEUNGbenzonorbornadiene.
Although the reported synthesis was efficient, the
ready access of (R)-3 suggested to us that the route to
(R)-5 and hence to sertraline may be shortened con-
siderably. The realization of this project is shown in
Scheme 2.[7]
Scheme 3. One-step enantioselective mono-reduction of tet-
ralin-1,4-dione (1).
In the course of these studies we reinvestigated the
mono-reduction of dione 1. We were pleased to find
that by switching from borane to catecholborane and
using (S)-6 as catalyst, the transformation of 1 to (R)- sor.[8] While this is elegant and of interest, our new
3 could be carried out in toluene in good yield with one-step asymmetric mono-reduction of 1 (Scheme 3)
high asymmetric induction (Scheme 3). Hence passing is more efficient and operationally simpler than the
via the cyanohydrin intermediate (Scheme 1) is not two-step double reduction/mono-oxidation sequence.
required and this shortens further the access to highly
Several natural products contain the 4-hydroxy-1-
enantioenriched 4-hydroxy-1-tetralone. Its enantiomer tetralone unit (Figure 1). Examples include catalpo-
was also synthesized via this route and a further im- nol,[9] epicatalponol,[9] isocatalponol,[10] junglanoside
provement was realized by increasing the quantity of A,[11] and isoshinanolone.[12] The rapid access to both
catecholborane from 1.2 to 1.5 mol equivalents enantiomers of highly enantioenriched 3 opens the
(Scheme 3).
way to efficient syntheses of these products. In this
Shortly before submission of this manuscript an ar- paper we will focus attention on catalponol. Catalpo-
ticle appeared reporting access to (R)-3 via (1R,4R)- nol [(2R,4S)-4-hydroxy-2-(3-methylbut-2-enyl)tetralin-
tetralindiol[1a,2] and Ru-catalyzed transfer-dehydrogen- 1-one][9] was isolated from the wood of Catalpa ova-
ation.[8] The authors showed that the oxidation of the ta.[9d–g] Its correct structure as shown in Figure 1 was
first alcohol function was faster than that of the established by Inoue et al.[9c] and its antithermitic ac-
second, and this provided a different access to (R)-3 tivity was documented by McDaniel.[9b] Catalponol is
which was then transformed into a sertraline precur- also reported to enhance dopamine biosynthesis and
Scheme 2. Synthesis of sertraline intermediate (R)-5.
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Scheme 4. alpha-Prenylation of (S)-4.
Figure 1. Natural products with
a 4-hydroxy-1-tetralone
motif.
epicatalponol. (Scheme 5). The ratio of 11/12 is differ-
ent from that of the precursors 8/9 raising the possi-
bility of isomerization during desilylation.
to protect against l-DOPA-induced cytotoxicity in
While this demonstrated the feasibility of the route
PC12 cells.[13] To the best of our knowledge, the syn- starting from tetralin-1,4-dione, we felt that catalpo-
thesis of catalponol has not been reported.
nol could be obtained with a higher selectivity than
With (+)-(S)-3 in hand, the synthesis of catalponol that shown in Scheme 4. Turning to chiral enolates or
requires alcohol protection, prenylation a to the enamines would have been a likely successful route to
ketone and removal of the protecting group.
achieve this goal.
Initial attempts at mono-prenylation of (S)-4
We chose instead a different approach, one that
(LDA/THF/prenyl bromide) were plagued by low builds on our long-standing interest in asymmetric
yields of the sought after monoprenylated products 8 synthesis using [Cr
AHCTUNGTRENNUNG
and 9, competitive bis-prenylation and partial recov- tion metal p-complexes of arenes with different sub-
ery of starting material. Similar findings have been re- stituents in the ortho- or meta-positions are chiral.
ported by Koga and co-workers in the allylation of This and the fact that additions to [CrACTHNUTRGNEG(NU arene)(CO)3]
tetralone.[14] Taking our cue from their work by complexes occur predominantly exo to the metal then
switching to DME as solvent and adding the tetraden- offer opportunities in asymmetric synthesis.
tate amine 7 to the Li-enolate before the addition of
For the problem at hand, a rapid access to
prenyl bromide gave an 83% yield of a 52:48 mixture [Cr(CO)3(tetralin-5,8-dione)] (14) is important. The
of the cis and trans diastereoisomers (8 and 9, respec- two published methods for the synthesis of its precur-
tively), together with 4% of diprenylated compound sor 13 both start with the readily available 1,4-dihy-
10 and 9% of recovered 4 (Scheme 4).
droxynaphthalene (2) and both use a protection/com-
Not unexpectedly, the pseudoequatorial OTBS plexation/deprotection sequence.[1a,15] We have dem-
group at the C-4 stereogenic center did not result in onstrated earlier that 13 readily tautomerizes to the
significant diastereoselection of the enolate prenyla- dione 14.[1a,15b] While this last part of the sequence is
tion. Nevertheless, after treating the mixture of dia- efficient, the protection/deprotection sequence is not
stereoisomers 8 and 9 with TBAF, chromatographic very economical but appeared necessary.
separation allowed the isolation of catalponol and 2-
Scheme 5. Catalponol and 2-epicatalponol.
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Efficient Enantioselective Syntheses of Sertraline, 2-Epicatalponol and Catalponol
Scheme 6. New access to 14 and its asymmetric mono-reduction and silylation.
We now report that 1,4-dihydroxynaphthalene (2) [C-6-H-C-8-H coupling in (6S,8S)-20, but not in
can be complexed directly to give, after tautomeriza- (6R,8S)-19], and on comparison of spectral data of
tion, the tetralindione complex 14. Enantioselective compounds obtained after desilylation/decomplexa-
reduction of 14 afforded the requisite complex 15 tion with those of 11 and 12. On treating rac-18 with
which was silylated to give 16 (Scheme 6).
Optimized conditions of enolate formation and pre- give, after 15 h, an equilibrium mixture of exo-prenyl/
nylation were first established for [Cr(CO)3A(tetralin)] endo-prenyl product in a 1:4 ratio. The same ratio was
Na2CO3 in MeOH at 08C, epimerization occured to
CTHUNGTRENNUNG
(rac-17) (Scheme 7) using in-situ IR spectroscopy (see observed by Jaouen and Meyer for the methyltetr-
supporting information) to yield rac-18 as a single dia- alone complex.[18]
stereoisomer. As noted above for 4, prenylation is
best carried out in the presence of tetraamine 7.
In order to obtain the endo complex (Sp,6R,8S)-20
selectively we took recourse to enolate formation and
When applied to the catalponol precursor (S)-16, exo-protonation with citric acid at À408C. As shown
the Cr(CO)3 complex of the TMS ether of epicatalpo- in Scheme 8, this was successful. Ether hydrolysis and
nol was formed selectively. It is well established in re- decomplexation then delivered enantiomerically pure
actions of arene tricarbonylchromium complexes that catalponol.
nucleophilic and electrophilic reagents approach the
complexed arene on the face opposite to the
metal[16,17] The structural assignment of 19 rests on the Conclusions
precedence of diastereoselective methylation of the
enolate of complex 17,[18] on NOESY measurements In conclusion, the efficient enantioselective mono-re-
duction of tetralin-1,4-dione, the stable tautomer of
1,4-dihydroxynaphthalene, provides access to a highly
useful chiral building block. This is shown here in the
rapid syntheses of the three title products. Reactions
of the corresponding Cr(CO)3 complex demonstrate
the power of complexation to access selectively and
at will one or the other highly enantioenriched diaste-
reoisomeric product.
Experimental Section
General
Reactions and manipulations involving organometallics or
moisture-sensitive compounds were carried out under an at-
mosphere of N2 in dry glassware. Solvents were degassed
and dried by filtration on Al2O3 (Solvtekꢁ) or distillation
Scheme 7. Prenylation of rac-[Cr(CO)3(tetralone)] (rac-17)
and of (S)-16.
from Na/benzophenone ketyl. Chemicals were obtained
from Aldrich, Acros, and Strem and used as received unless
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Alvaro Enriquez Garcia et al.
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Scheme 8. Inversion of configuration at C-6 in 19, desilylation and decomplexation to give catalponol.
noted. All chromium complexes were kept away from light.
Reactions were followed by analytical TLC [Al-sheet, silica
gel 60 F254 (Merck)]/UV. Yields given are of material puri-
fied by crystallization or flash column chromatography (f.c)
40.1 min [minor, (R)-3], 42.0 min [major, (S)-3]; [a]2D3: +23.2
(c 1.01, MeOH); H NMR (400 MHz, CDCl3): d=7.86 (d,
J=7.8 Hz, 1H), 7.56–7.44 (m, 2H), 7.30 (t, J=7.1 Hz, 1H),
4.89–4.81 (m, 1H), 4.01 (bs, 1H), 2.85–2.73 (m, 1H), 2.53–
2.40 (m, 1H), 2.32–2.21 (m, 1H), 2.12–1.99 (m, 1H).
1
1
[Aldrich silica gel 60 ꢂ (230–400 mesh)]. H and 13C NMR
(room temperature) were recorded on Brucker AMX-500,
AMX-400, or AMX-300. Chemical shifts are given in ppm,
int d-lock. Coupling constants J are given in Hertz. Multi-
plicities are indicated as follows: singlet (s), doublet (d),
triplet (t), quartet (q), multiplet (m). IR spectra were taken
on a Perkin–Elmer Spectrum 100/Golden Gate accessory.
HR-MS were obtained with a QSTAR Pulsar (AB/MDS
Sciex). For HPLC, Agilent 1100/Chiracel-OD-H or OJ-H
columns were used. Optical rotations (208C) were measured
on a JACSO P-1030 polarimeter with a quartz cell (l=
10 cm), l=589 nm. Melting points were determined on a
Bꢀchi 510. 1,4-Naphthoquinone was purified by recrystalli-
zation. 1,4-dihydroxynaphthalene (2),[19] tetralin-1,4-dione
(1),[2] (S)- and (R)-3,3-diphenyl-1-butyltetrahydro-3H-
(4R)-4-(tert-Butyldimethylsilyloxy)-1-tetralone [(R)-
4]
A two-neck round-bottomed flask equipped with a condens-
er was charged under N2 with (R)-4-hydroxy-1-tetralone
[(R)-3][2] (400 mg, 2.49 mmol, 95% ee), CH2Cl2 (18 mL), (i-
Pr)2EtN (2.17 mL, 12.45 mmol), DMAP (60 mg, 0.50 mmol)
and TBSCl (1.495 g, 9.96 mmol). The clear solution was re-
fluxed for 60 h, quenched with H2O (20 mL) and stirred at
room temperature for 3 h. The reaction mixture was extract-
ed with CH2Cl2 (3ꢃ) and the combined organic layers dried
with Na2SO4. Evaporation of the solvent under reduced
pressure and purification of the residue by f.c. (Et2O/pen-
tane 1:15) gave 4-(tert-butyldimethylsiloxy)-1-tetralone [(R)-
4] as a white solid; yield: 605 mg (88%); [a]2D0: +2 (c 1.12
CH2Cl2). Spectral data agreed with literature values.[23]
pyrrolo
A
ACHTUNGTRENNUNG ,
[1,3,2]oxazaborole [(R)-6], its (S)-antipode[20]
[Cr(CO) CHTUNGTRENNUNG
thesized according to the cited literature procedures.
1,1,4,10,10-Hexamethyltriethylenetetramine was filtered on
Al2O3 and prenyl bromide was dried over CaH2 and distilled
prior to use.
(+)-(1R)-4-(3,4-Dichlorophenyl)-1,2-dihydro-
naphthalen-1-ol [(R)-5]
A two-neck round-bottomed flask equipped with condenser
was charged under N2 with Mg (50 mg, 2.06 mmol), a crystal
of I2 and Et2O (1.6 mL). A solution of 4-bromo-1,2-dichloro-
benzene (264 mL, 2.06 mmol) in 2.5 mL of Et2O was added
dropwise under stirring over 5 min while heating gently to
maintain reflux. This suspension was further refluxed during
1 h to give a clear solution. Then, a solution of (R)-4
(285 mg, 1.03 mmol, 95% ee) in Et2O (2.5 mL) was added
dropwise and the mixture was refluxed for 19 h. The reac-
tion was quenched with saturated aqueous NH4Cl and ex-
tracted with Et2O (3ꢃ). The combined organic phases were
dried over Na2SO4 and volatiles were removed under re-
duced pressure. The crude product was dissolved in CH2Cl2
(8.6 mL, 08C) under N2. A solution of Et3N (724 mL,
5.16 mmol) in CH2Cl2 (8.6 mL, 08C) and a solution of MsCl
(319 mL, 4.12 mmol) in CH2Cl2 (8.6 mL, 08C) were added se-
(4S)-4-Hydroxy-1-tetralone [(S)-(3)]
Under N2, a Schlenk tube was charged with tetralin-1,4-
dione (1) (561 mg, 3.50 mmol) and dry toluene (15 mL). The
solution was cooled to À788C before adding a solution
of (R)-3,3-diphenyl-1-butyl tetrahydro-3H-pyrroloACTHNUGTRNEUNG[1,2-c]-
ACHTUNGTRENNUNG[1,3,2]oxazaborole (3.5 mL, 0.1M in toluene, 0.35 mmol).
Catecholborane (5.3 mL, 1M in toluene, 5.3 mmol) was
added after 2 h via a syringe over 15 min. After stirring at
À788C for 40 h the reaction mixture was quenched with
MeOH (4 mL) and diluted with AcOEt. Volatiles were re-
moved under reduced pressure and the residue was purified
by f.c. on silica gel (eluent: pentane/Et2O=1/1) to afford
(S)-(3) as a liquid; yield: 443 mg (78%); 99.3% ee deter-
mined by HPLC analysis (Chiralcel OJ, hexane/i-PrOH=99/
1, gradient to 90/10 over 60 min, 1 mL. minÀ1, 254 nm): tR =
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Efficient Enantioselective Syntheses of Sertraline, 2-Epicatalponol and Catalponol
quentially. After further stirring at 08C for 2 h and at room
temperature, for 2 h, the reaction was quenched with satu-
rated aqueous NaHCO3 and extracted with Et2O (3ꢃ). The
organic phases were combined, dried with Na2SO4 and the
solvent evaporated under reduced pressure. This residue
was dissolved in THF (10 mL) and a solution of TBAF (1M
in THF, 1.55 mL, 1.55 mmol) was added at room tempera-
ture. The mixture was stirred for 1 h, diluted with Et2O,
washed with saturated aqueous NaHCO3 and extracted with
Et2O (3ꢃ). The organic phases were combined, dried with
MgSO4 and evaporated under reduced pressure. Purification
by f.c. (AcOEt/pentane 1:4) furnished (R)-5 as a white solid;
yield: 237 mg (79%); 95% ee; mp 107–1098C (CH2Cl2/cyclo-
hexane); [a]2D0: +35 (c 0.47, CH2Cl2). Spectral data agreed
with literature values.[6h] RF =0.30 (Et2O/pentane, 1: 4); IR
(neat): n=3346, 3060, 2928, 2857, 2824, 1547, 1468, 1380,
2.39–2.18 (m, 8 and 9 together, 4H), 2.09 (ddd, J=13.1, 9.7,
3.4 Hz, 9, 1H), 1.88 (q, J=12.5 Hz, 8, 1H), 1.72 (s, 8 and 9
together, 6H), 1.65 (s, 8, 3H), 1.63 (s, 9, 3H), 1.00 (s, 8,
9H), 0.89 (s, 9, 9H), 0.23 (s, 8, 3H), 0.19 (s, 8, 3H), 0.17 (s,
9, 3H), 0.10 (s, 9, 3H); 13C NMR (100 MHz, CDCl3): d=
199.6, 198.4, 147.3, 144.6, 133.7, 133.5, 133.4, 133.3, 131.12,
131.06, 127.9, 127.2, 127.1, 126.9, 125.6, 121.7, 121.2, 69.2,
67.0, 46.4, 42.8, 38.7, 36.3, 28.0, 27.8, 25.8, 25.7, 25.6, 18.1,
17.9, 17.78, 17.76, À4.3, À4.7, À4.9; MS (ESI): m/z (%)=
345 ([M+H]+), 367 ([M+Na]+); HR-MS (ESI): m/z=
367.2073, calcd. for C21H32O2NaSi ([M+Na]+): 367.2063.
(S)-10: IR (neat): n=2929, 1683, 1601, 1453, 1377, 1255,
1132, 1079 cmÀ1 1H NMR (400 MHz, CDCl3): d=8.03 (d,
;
J=7.8 Hz, 1H), 7.62–7.55 (m, 2H), 7.41–7.33 (m, 1H), 5.26–
5.18 (m, 1H), 5.11–5.01 (m, 2H), 2.57 (dd, J=14.3, 6.2 Hz,
1H), 2.35 (dd, J=14.9, 7.8 Hz, 1H), 2.29–2.06 (m, 4H), 1.74
(s, 3H), 1.64 (s, 3H), 1.62 (s, 3H), 1.60 (s, 3H), 1.00 (s, 9H),
0.23 (s, 3H), 0.18 (s, 3H); 13C NMR (100 MHz, CDCl3): d=
200.9, 146.4, 134.8, 134.2, 133.4, 130.6, 127.6, 127.4, 125.9,
119.9, 118.9, 66.0, 50.1, 40.4, 34.9, 34.4, 26.1, 25.9, 25.8, 18.1,
18.0, 17.9, À4.3, À4.9; MS (ESI): m/z (%)=413 ([M+H]+),
435 ([M+Na]+); HR-MS (ESI): m/z=413.2876, calcd. for
C26H41O2Si ([M+H]+): 413.2870.
1333, 1198, 1131, 1029 cmÀ1 1H NMR (400 MHz, CDCl3):
;
d=7.32–7.28 (m, 3H), 7.12 (td, J=7.3 and 1.3 Hz, 1H), 7.07
(td, J=7.5 and 1.4 Hz, 1H), 7.01 (dd, J=8.2 and 0.0 Hz,
1H), 6.86 (d, J=7.5 Hz, 1H), 5.83 (t, J=4.5 Hz, 1H), 4.65
(t, J=5.9 Hz, 1H), 2.52–2.47 (m, 2H), 1.99 (broad s, 1H);
13C NMR (100 MHz, CDCl3): d=140.4, 137.8, 137.7, 133.0,
132.7, 131.7, 130.9, 130.6, 128.5, 128.47, 128.43, 127.0, 125.9,
125.6, 68.0, 33.0; HR-MS (EI): m/z=272.0156, calcd. for
C16H10OCl2 [MÀH2O]+: 272.0159; HPLC (Chiralcel OJ, F=
1 mL·minÀ1, hexane/i-PrOH=99:1 gradient to 90/10 over
60 min, l=254 nm): tR =30.3 min [(4R)-enantiomer] and
33.6 min [(4S)-enantiomer].
Catalponol (11) and 2-Epicatalponol (12)
To a solution of a mixture of 8 and 9 (1.08:1) (278 mg,
0.81 mmol) in dry THF (17 mL) was added TBAF (1.7 mL,
1.0M in toluene, 1.70 mmol) under N2 at room temperature.
The reaction mixture was stirred for 15 min, then concen-
trated and the residue was purified by f.c. on silica gel
(eluent: pentane/Et2O=2/1) to afford first 39 mg of catalpo-
nol and then 123 mg of a mixture of catalponol and 2-epica-
talponol. This 123 mg mixture was chromatgraphed on silica
gel (eluent: pentane/Et2O=4/1) for the second time to
afford another 70 mg of catalponol and 48 mg of 2-epicatal-
ponol.
ACHTUNGTRENNUNG(2R,4S)-4-(tert-Butyldimethylsilyloxy)-2-(3’-
methylbut-2’-en-1-yl)-1,2,3,4-tetrahydronaphthalene-
1-one (8)
ACHTUNGTRENNUNG(2S,4S)-4-(tert-Butyldimethylsilyloxy)-2-(3’-
methylbut-2’-en-1-yl)-1,2,3,4-tetrahydronaphthalene-
1-one (9)
(4S)-4-(tert-Butyldimethylsilyloxy)-2,2-bis(3’-
methylbut-2’-en-1-yl)-1,2,3,4-tetrahydronaphthalene-
1-one (10)
Catalponol (11): liquid, yield: 109 mg (59%); 99.3% ee
determined by HPLC analysis (Chiralcel OJ, hexane/i-
PrOH=99/1, gradient to 90/10 over 60 min, 1 mL·minÀ1,
254 nm): tR =30.4 min (major), 32.6 min (minor); [a]2D3:
+10.6 (c 1.2, MeOH); IR (neat): n=3432, 2916, 1679, 1601,
Under an atmosphere of N2, a solution of n-BuLi (0.609
mL, 1.6M in hexane, 1.10 mmol) was added to a stirred so-
lution of diisopropylamine (170 mL, 1.21 mmol) in DME
(5 mL) at À788C (dry ice/EtOH). After 1 h, a solution of
(S)-4 (276 mg, 1.00 mmol) in DME (5 mL) was added drop-
wise via a syringe over 5 min at À788C. Tetraamine 7
(0.550 mL, 2.02 mmol) was then added in one portion and
the mixture was stirred for 2 h. After this time, prenyl bro-
mide (620 mL, 95%, 5.06 mmol) was added in one portion
and the reaction mixture was brought from À788C to room
temperature over the course of a 15 h period. The resulting
mixture was diluted with CH2Cl2, filtered, concentrated, and
the residue was purified by f.c. on silica gel (eluent: pen-
tane/Et2O first 50/1 then 10/1) to afford a 1.08:1 mixture of
diastereoisomers 8 and 9 (yield: 286 mg, 83%, determined
by 1H NMR) and 10 (yield: 15 mg, 4%).
1
1454, 1336, 1271, 1220, 1074, 1042 cmÀ1; H NMR (400 MHz,
CDCl3): d=8.01 (d, J=7.6 Hz, 1H), 7.72 (d, J=7.8 Hz, 1H),
7.59 (t, J=7.5 Hz, 1H), 7.39 (t, J=7.6 Hz, 1H), 5.18–5.11
(m, 1H), 5.00 (dd, J=11.2, 3.9 Hz, 1H), 2.75–2.66 (m, 1H),
2.56–2.46 (m, 2H), 2.34 (bs, 1H), 2.34–2.21 (m, 1H), 1.79 (q,
J=13.0, 1H), 1.71 (s, 3H), 1.64 (s, 3H); 13C NMR
(100 MHz, CDCl3): d=198.7, 146.5, 134.0, 133.7, 131.1,
127.8, 127.1, 125.7, 121.2, 68.4, 46.5, 38.6, 27.9, 25.9, 17.9;
MS (ESI): m/z (%)=231 ([M+H]+), 253 ([M+Na]+); HR-
MS (ESI): m/z=253.1189, calcd. for C15H18O2Na ([M+
Na]+): 253.1199; HPLC (Chiracel OJ-H, F=1 mL·minÀ1,
hexane/i-PrOH: 99:1 to 90:10 gradient over 60 min, l=
254 nm): tR =28.0 min (2S,4R)-4-hydroxy-2-prenyl-3,4-dihy-
dronaphthalenone) and tR =29.9 min (2R,4S)-4-hydroxy-2-
prenyl-3,4-dihydronaphthalenone (11), [a]3D4: +118 (c 1.2,
MeOH, > 98% ee). Ref.[9d] [a]3D4: +118 (c 1.2, MeOH).
2-Epicatalponol (12): liquid; yield: 48 mg (26%); 99.1%
ee determined by HPLC analysis (Chiralcel OJ, hexane/i-
PrOH=99/1, gradient to 90/10 over 60 min, 1 mL·minÀ1,
254 nm): tR =28.8 min (minor), 32.4 min (major); IR (neat):
8 and 9: IR (neat): n=2929, 1686, 1601, 1455, 1362, 1253,
1131, 1077 cmÀ1 1H NMR (400 MHz, CDCl3): d=8.01 (d,
;
J=7.6 Hz, 8 and 9 together, 2H), 7.63–7.51 (m, 8 and 9 to-
gether, 3H), 7.42–7.33 (m, 8 and 9 together, 3H), 5.20–5.12
(m, 8 and 9 together, 2H), 4.99 (dd, J=11.1, 4.5 Hz, 8, 1H),
4.96 (dd, J=5.8, 3.3 Hz, 9, 1H), 3.10–3.00 (m, 9, 1H), 2.74–
2.64 (m, 8, 1H), 2.64–2.55 (m, 9, 1H), 2.55–2.46 (m, 8, 1H),
Adv. Synth. Catal. 2010, 352, 2306 – 2314
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Alvaro Enriquez Garcia et al.
FULL PAPERS
n=3421, 2919, 1674, 1600, 1454, 1377, 1332, 1277, 1227,
(8S)-15; anal. calcd. for C13H10O5Cr: C 52.36%, H 3.38%;
found: C 52.56%, H 3.35%; [a]2D0: +684 (c 0.2, CH2Cl2).
1
1049 cmÀ1; H NMR (400 MHz, CDCl3): d=8.03 (dd, J=7.8,
1.3 Hz, 1H), 7.62–7.54 (m, 1H), 7.49–7.39 (m, 2H), 5.21–
5.12 (m, 1H), 5.04–4.96 (m, 1H), 3.06–2.97 (m, 1H), 2.65–
2.55 (m, 1H), 2.36–2.22 (m, 2H), 2.15 (ddd, J=13.9, 10.6,
3.3 Hz, 1H), 2.03 (d, J=3.8 Hz, 1H), 1.71 (s, 3H), 1.63 (s,
3H); 13C NMR (100 MHz, CDCl3): d=199.5, 143.6, 133.92,
133.86, 131.3, 128.8, 128.3, 127.4, 121.3, 66.7, 42.4, 35.7, 28.0,
25.8, 17.9; MS (ESI): m/z (%)=231 ([M+H]+).
[(+)-(Sp,8S)-Cr(CO)3(h6-8-trimethylsilyloxy-5-
tetralone)] [(Sp,8S)-16]
A
Schlenk tube was charged with (8S)-15 (620 mg,
2.08 mmol), imidazole (424.82 mg, 6.24 mmol) and CH2Cl2
(23 mL). TMSCl (0.55 mL, 4.16 mmol) was added to this so-
lution and the mixture was stirred for 3 h under N2. The re-
action was then quenched with saturated aqueous NH4Cl
(30 mL) and the mixture extracted with CH2Cl2 (3ꢃ30 mL).
The organic layers were washed with brine (30 mL) and
then dried over anhydrous MgSO4. The solvent was evapo-
rated under vacuum and the residue was purified by f.c.
over SiO2 (eluent: Et2O) to give (8S)-16 as an orange solid;
yield: 771 mg (>99%); >98% ee; mp 96–988C. IR
{Cr(CO)3[h6(1-4,4a,6a)tetralin-5,8-dione]} (14)[1a,2]
A Carius tube was charged with 1,4-dihydroxynaphthalene
[19]
(687 mg, 4.29 mmol), Cr(CO)3(NH)3 (536 mg, 2.86 mmol),
Et2O (30 mL) and BF3·Et2O (2.17 mL, 17.16 mmol). The
yellow suspension was stirred at room temperature under N2
for 5d. The contents were cooled with an ice/NaCl bath and
Et2O (40 mL) was added followed by aqueous saturated
NaHCO3 (160 mL). The organic layer was transferred via
canula to another Schlenk tube containing MgSO4 and the
aqueous layer was extracted three times with small portions
of Et2O (30 mL). The combined organic layers were filtered
and then all volatiles were removed under vacuum. The
orange residue was taken up in toluene (42 mL) and
CF3COOH (440 mL, 5.72 mmol). The suspension was de-
gassed three times by freeze-pump-thaw cycles and stirred
at room temperature for 14 h. A colour change from orange
to dark red was observed. The reaction mixture was then
cooled to 08C, filtered via canula to a Schlenk tube and all
volatiles were removed under vacuum. The crude product
was recrystallized, under N2, from boiling, i-Pr2O (30 mL) to
give 14 as a deep red solid; yield: 554 mg (65%).
(CH2Cl2): n=1981, 1912, 1685 cmÀ1 1H NMR (400 MHz,
;
C6D6): d=5.74 (dd, J=0.8 and 6.8 Hz, 1H), 5.05 (d, J=
6.6 Hz, 1H), 4.64 (t, J=6.6 Hz, 1H), 4.37 (t, J=6.8 Hz, 1H),
4.10 (dd, J=4.8 and 10.9 Hz, 1H), 2.29–2.23 (m, 1H), 1.85–
1.48 (m, 3H), 0.05 (s, 9H); 13C NMR (75 MHz, C6D6): d=
231.5, 193.9 , 119.3, 93.4, 92.7, 90.2, 89.2, 86.9, 66.7, 35.7,
32.2, 0.1; HR-MS (ESI): m/z=371.0399, calcd. for
C16H19CrO5Si [M+H]+: 371.0401; HPLC (Chiracel OD-H,
F=1 mL·minÀ1, hexane/i-PrOH: 90/10 iso over 60 min, l=
254 nm): tR =11.5 min (8R)-16 and tR =23.9 min (8S)-16;
anal. calcd. for C16H18Cr1O5Si: C 51.88%, H 4.90%;found; C
51.97%, H 4.97%; [a]2D0: +729 (c 0.2, CH2Cl2).
A
(h6-6-(3’-methylbut-2’-enyl)-5-tetralone]
3ACHTUNGTRENNUNG
To a cooled solution of (Æ)-[Cr(CO)3(h6-tetralone)] (17)
(197.5 mg, 0.7 mmol) in dry and degassed DME (8.5 mL)
was added dropwise at À408C a freshly prepared solution of
LDA (1 mL, 1M in DME, 1 mmol), followed by addition
[(+)-(Sp,8S)-Cr(CO)3(h6-8-hydroxy-5-tetralone)]
[(Sp,8S)-15][2]
A dry Schlenk tube charged with 14 (300 mg, 1.01 mmol)
and dry toluene (5 mL) was cooled to À788C. To the stirred
solution was added (R)-3,3-diphenyl-1-butyltetrahydro-3H-
of
1,1,4,10,10-hexamethyltriethylenetetramine
(484 mL,
2.1 mmol). The orange solution turned first yellow and then
red. Freshly distilled prenyl bromide (0.7 mL, 5.6 mmol) was
then slowly injected to the mixture. After 2 h of stirring at
À408C, the reaction was quenched with 30 mL of aqueous
citric acid (40%) and extracted three times with CH2Cl2 (3ꢃ
30 mL). The organic extracts were washed with saturated
aqueous NaHCO3 (30 mL), and with brine (30 mL). Organic
layers were dried over anhydrous MgSO4 and filtered. The
filtrate was evaporated under vacuum and the residue was
purified by f.c. (Et2O/pentane: 1/1) to give (Æ)-[Cr(CO)3(h6-
6-prenyl-5-tetralone)] (18); yield: 190 mg (78%). IR (meth-
pyrroloACHTUNGTRENNUNG[1,2-c]ACHTUNGTRENNUNG
[1,3,2]oxazaborole[18] (1.0 mL, 0.1M in toluene,
0.10 mmol) dropwise. After 40 min of stirring at À788C, a
solution of catecholborane (1.5 mL, 1M in toluene,
1.52 mmol) was added during 20 min. After stirring for 24 h
at À788C, the red solution turned to orange. The mixture
was then quenched with saturated aqueous NaHCO3
(10 mL) and the separated org. phase was washed with satu-
rated aqueous NaHCO3 (3ꢃ10 mL). After extraction with
Et2O (30 mL), the combined organic layers were dried over
MgSO4 and all volatiles were removed under reduced pres-
sure. This residue was purified by f.c. (eluent: Et2O) to give
(S)-15 as an orange solid; yield: 297 mg (>99%), >98% ee;
mp 1848C (dec. under N2) (hexane/i-PrOH). IR (CH2Cl2):
n=3602, 3063, 2929, 1981, 1914, 1688, 1523, 1454, 1421,
ylcyclohexane): n=1987, 1930, 1914, 1694 cmÀ1 1H NMR
;
(300 MHz, CDCl3): d=6.21 (d, J=6.7 Hz, 1H), 5.64 (t, J=
6.2 Hz, 1H), 5.23 (t, J=6.4 Hz, 1H), 5.13 (m, 1H), 3.00–2.90
(m, 1H), 2.81–2.71 (m, 1H), 2.65–2.43 (m, 2H), 2.26–2.14
(m, 2H), 1.91–1.82 (m, 1H), 1.72 (s, 3H), 1.62 (s, 3H);
13C NMR (400 MHz, C6D6): d=231.6, 121.6, 94.3, 91.4, 89.9,
89.5, 79.5, 47.6, 41.8, 28.5, 28.0, 26.8, 26.0.
1326 cmÀ1
;
1H NMR (400 MHz, C6D6): d=5.70 (d, J=
6.6 Hz, 1H), 5.00 (d, J=6.8 Hz, 1H), 4.56 (t, J=6.8 Hz,
1H), 4.28 (t, J=6.1 Hz, 1H), 3.90–3.80 (m, 1H), 2.21–2.16
(m, 1H), 1.63–1.23 (m, 4H); 13C NMR (100 MHz, C6D6):
d=231.6, 193.8, 128.0, 100.4, 93.4, 92.9, 90.3, 87.0, 65.9, 35.9,
31.8; HR-MS (EI): m/z=299.0009, calcd. for C13H11O5Cr
[M+H]+: 299.0006; HPLC (Chiracel OD-H, F=
1 mL·minÀ1, hexane/i-PrOH: 90/10 iso over 60 min, l=
254 nm): tR =24.6 min. (À)-(8R)-15 and tR =28.8 min. (+)-
[(+)-(Sp,6S,8S)-Cr(CO)3ACHTNUTRGENUNG
(h6-6-(3’-methylbut-2’-enyl)-8-
trimethylsilyloxy-5-tetralone] [(Sp,6S,8S)-(19)]
To a cooled solution of (8S)-16 (680 mg, 1.84 mmol) in dry
and degassed DME (24 mL) was added dropwise at À408C
a freshly prepared solution of LDA (2.6 mL, 1M in DME,
2312
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ꢁ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2010, 352, 2306 – 2314

Efficient Enantioselective Syntheses of Sertraline, 2-Epicatalponol and Catalponol
2.6 mmol), followed by addition of 1,1,4,10,10-hexamethyl-
triethylenetetramine (1.55 mL, 5.5 mmol). The orange solu-
tion turned first yellow and then orange. Freshly distilled
prenyl bromide (1.2 mL, 9.2 mmol) was then slowly injected
into the mixture. After 2 h of stirring at À408C more prenyl
bromide (0.5 mL, 3.7 mmol) was added to the now red reac-
tion mixture. The reaction was monitored by TLC (Et2O/
pentane: 1:1). After 4 h at À408C, the reaction was
quenched with 30 mL of aqueous citric acid (40%) and ex-
tracted with CH2Cl2 (3ꢃ30 mL). The organic phase was
washed with saturated aqueous NaHCO3 (30 mL), and with
brine (30 mL). The organic phase was dried over anhydrous
MgSO4 and filtered. The filtrate was evaporated under
vacuum and the residue was purified by f.c. over SiO2
(Et2O/pentane: 1/1) to give (Sp,6S,8S)-19 as an orange oil;
yield:; 662 mg (82%); >98% ee. IR (CH2Cl2): n=3685,
with pentane/ether (1: 4) afforded (Sp)-21 as a red solid;
yield: 385 mg (75%); 98% ee; mp 113–1148C; IR (CH2Cl2):
1
n=1980, 1915, 1683, 1605 cmÀ1; H NMR (400 MHz, C6D6):
d=5.75 (d, J=5.8 Hz, 1H), 5.17 (t, J=7.6 Hz, 1H), 5.10 (d,
J=6.6 Hz, 1H), 4.58 (t, J=6 Hz, 1H), 4.29 (t, J=5.8 Hz,
1H), 4.00 (m, 1H), 2.50 (m, 2H), 1.71 (s, 3H), 1.60 (m, 1H),
1.51 (s, 3H); 13C NMR (100 MHz, C6D6): d=231.7, 195.7,
134.5, 128.3, 121.0, 119.3, 93.4, 90.5, 90.3, 86.8, 65.9, 46.0,
37.0, 28.3, 26.0, 17.9; HPLC (Chiracel OD-H, F=
1 mL·minÀ1, hexane/i-PrOH: 90/10 iso over 60 min, l=
254 nm): tR =18.4 min 21; anal. calcd. for C18H18CrO5: C
59.02%, H 4.95%; found: C 58.75%, H 4.72%; [a]2D0: +523
(c 0.5, CH2Cl2).
Catalponol (11)
2952, 2927, 2855, 1980, 1911, 1681, 1605, 1456 cmÀ1
;
A 250-mL round-bottom flask was charged with (Sp,6R,8S)-
21 (366 mg, 1 mmol) and CH3CN (150 mL) and was exposed
to sunlight and air. Decomplexation was monitored by TLC
(ether/pentane: 1:2). After 1 h, solvent was removed under
reduced pressure and the residue was dissolved in ether and
filtered over celite. F.c. of the crude product over SiO2
(ether/pentane: 1:8) afforded catalponol as a colourless oil;
yield: 200.4 mg (87%); >98% ee. Data see above.
1H NMR (400 MHz, C6D6): d=5.82 (d, J=6 Hz, 1H), 5.10
(d, J=6.8 Hz, 1H), 4.90 (m, 1H), 4.64 (t, J=6 Hz, 1H), 4.57
(dd, J=4.8, 10.4 Hz, 1H), 4.38 (t, J=6.4 Hz, 1H), 2.60–1.80
(m, 5H), 1.60 (s, 3H), 1.40 (s, 3H), 0.09 (s, 9H); 13C NMR
(100MHz, C6D6): d=231.5, 196.7, 134.2, 121.8, 119.1, 92.9,
92.8, 90.4, 89.4, 87.3, 63.4, 44.8, 35.4, 29.3, 25.8, 17.9, 0.1;
HR-MS (ESI): m/z=439.1007, calcd. for C21H27O5Si Cr
[M+H]+: 439.1027; anal. calcd. for C21H26Cr1O5Si:
C
57.52%, H 5.98%; found: C 57.15%, H 5.95%; [a]2D0: +329
(c 0.2, CH2Cl2).
Acknowledgements
{(+)-(Sp,6R,8S)-Cr(CO)3ACHTNUTRGENUNG
[h6--6-(3’-methylbut-2’-enyl)-
We thank Prof. Alexandre Alexakis and Dr. S. Belot for a
gift of (R)-(+)-a,a-diphenyl-2-pyrrolidinemethanol. Finan-
cial support of this project by the University of Geneva and
by the Swiss National Science Foundation (project
200020 119947) is gratefully acknowledged.
8-trimethylsilyloxy-5-tetralone]} [(Sp,6R,8S)-(20)]
To a cooled solution of (Sp,6S,8S)-19 (660 mg, 1.51 mmol) in
DME (20 mL) was added dropwise at À408C a freshly pre-
pared solution of LDA (2.2 mL, 1M in DME, 2.2 mmol).
The orange mixture was stirred at À408C for 1 h. Then a so-
lution of citric acid (1 mL, 1M in distilled water) was added
slowly at À408C. The mixture was allowed to warm up to
room temperature. After 30 min, distilled water (10 mL)
was added and the mixture was extracted three times with
Et2O (3ꢃ30 mL). The organic extracts were washed with sa-
turated aqueous NaHCO3 (40 mL), and with brine (40 mL).
The organic phase was dried over anhydrous MgSO4. Sol-
vents were removed under reduced pressure and the crude
product was purified by f.c. over SiO2 (Et2O/pentane: 1/2) to
give (Sp,6R,8S)-20 as an orange oil; yield: 636 mg (96%);
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with Et2O (3ꢃ30 mL). The combined organic layers were
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trated under reduced pressure. Purification by f.c. over SiO2
Adv. Synth. Catal. 2010, 352, 2306 – 2314
ꢁ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
2313

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