Total synthesis of quinolizidine (-)-217A

Article abstract of DOI:10.1021/jo101668k

We report here the construction of quinolizidine ring systems by intramolecular cyclization of suitable functionalized piperidines via a reductive amination sequence. This reaction proceeds with a total stereocontrol at C4. The preparation of the piperidi

Full text of DOI:10.1021/jo101668k

pubs.acs.org/joc
Total Synthesis of Quinolizidine (-)-217A
ꢀ
Mouloud Fellah, Marco Santarem, Gerard Lhommet,* and Virginie Mouries-Mansuy*
ꢁ
ꢀ
UPMC Univ Paris 06, Institut Parisien de Chimie Moleculaire (UMR CNRS 7201), C. 43,
ꢀ ꢀ
Equipe Heterocycle, 4 place Jussieu, 75005 Paris, France
gerard.lhommet@upmc.fr; virginie.mansuy@upmc.fr
Received August 30, 2010
We report here the construction of quinolizidine ring systems by intramolecular cyclization of
suitable functionalized piperidines via a reductive amination sequence. This reaction proceeds with a
total stereocontrol at C4. The preparation of the piperidine precursors is based on a chain elongation
of a piperidine aldehyde either by aldolization or by Wittig reaction. We applied this second route to
the total synthesis of quinolizidine (-)-217A from (S )-methyl 2-((S )-1-((R)-1-phenylethyl)piperidin-
2-yl)propanoate 5.
Introduction
(-)-217A. The key step is a highly stereoselective synthesis of
a trisubstituted tetrahydropyridine obtained by intramolecular
imine crotylation.5 The synthesis of alkaloid (-)-217A was
accomplished in 11 steps and 19% overall yield from (2R,3S,
E)-methyl 2-amino-3-(dimethyl(phenyl)silyl)hex-4-enoate pre-
pared in six steps from racemic butyn-2-ol.6 Finally Danheiser’s7
group performed the synthesis of quinolizidine (-)-217A
through an intramolecular iminoacetonitrile [4 þ 2] cycload-
dition function to generate the quinolizidine skeleton. This
synthesis supports the preparation of significant quantities of
the target alkaloid but requires a resolution step. Amphibian
alkaloid 217A was obtained in 12 steps and 7% overall yield
from 5-hexenol.
Our goal was to develop a simple and efficient procedure
providing an easy access to natural quinolizidine 217A in
sufficient amounts from readily accessible compounds and
without a resolution step. As part of a program aimed at the
synthesis of alkaloids using cyclic aminoesters as versatile
synthons, we report herein a highly stereoselective synthesis
of quinolizidine (-)-217A from a chiral piperidine ester. Our
approach to the synthesis of the target alkaloid 1 is outlined
in Scheme 1. It is based on the use of the chiral methyl
Alkaloids containing saturated six-membered nitrogen het-
erocycles such as piperidines,1 indolizidines, and quinolizi-
dines2 are abundant in nature. Many of these alkaloids exhibit
interesting and potent biological activities and are important
targets in organic synthesis. Alkaloid 217A, a 1,4-disubstituted
quinolizidine, was isolated as a major component from the
Madagascan frog Mantella baroni by Daly in 1993.3 Because of
the scarcity of this natural product, its biological activities
remain largely unexplored. To date, only three syntheses of
this alkaloid have been reported in the literature. The racemic
synthesis of quinolizidine 217A described by Pearson’s group4
in 1998 has confirmed the relative stereochemistry of this
natural product. This synthesis is based on a double cyclization
of a chloro azidoalkene to generate the quinolizidine system.
More recently Panek5 and co-workers resolved the absolute
configuration by an asymmetric synthesis of quinolizidine
(1) Schneider, M. J. Alkaloids: Chemical and Biological Perspectives, 1st
ed.; Pelletier, S. W., Ed.; Pergamon: New York, 1996; Vol. 10, Chapter 2, pp
155-299.
(2) Daly, J. W.; Garraffo, H. M.; Spande, T. F. Alkaloids: Chemical and
Biological Perspectives, 1st ed.; Pelletier, S. W., Ed.; Pergamon: Oxford, U.
K., 1999; Vol. 13, Chapter 1, pp 1-161.
(3) (a) Garraffo, H. M.; Caceres, J.; Daly, J. W.; Spande, T. F.;
Andriamaharavo, N. R.; Andriantsiferana, M. J. Nat. Prod 1993, 56,
1016–1038. (b) Jain, P.; Garraffo, H. M.; Yeh, H. J. C.; Spande, T. F.; Daly,
J. W.; Andriamaharavo, N. R.; Andriantsiferana, M. J. Nat. Prod. 1996, 59,
1174–1178.
(4) Pearson, W. H.; Suga, H. J. Org. Chem. 1998, 63, 9910–9918.
(5) Huang, H.; Spande, T., F.; Panek, J., S. J. Am. Chem. Soc. 2003, 125,
626–627.
(6) This amino silyl hexenoate was prepared by mild acid hydrolysis of a
triphenylphosphine imine intermediate obtained from the corresponding
azido silyl hexenoate. The latter was synthetized in five steps and 21% overall
yield from racemic butyn-2-ol. See: (a) Beresis, R. T.; Solomon, J. S.; Yang,
M. G.; Jain, N. F.; Panek, J. S. Org. Synth. 1998, 75, 78–86. (b) Panek, J. S.;
Beresis, R.; Xu, F.; Yang, M. J. Org. Chem. 1991, 56, 7341–7344. (c) Panek,
J. S.; Zhang, J. J. Org. Chem. 1993, 58, 294–296.
(7) Maloney, K. M.; Danheiser, R., L. Org. Lett. 2005, 7, 3115–3118.
DOI: 10.1021/jo101668k
r
Published on Web 10/25/2010
J. Org. Chem. 2010, 75, 7803–7808 7803
2010 American Chemical Society

Fellah et al.
JOCArticle
SCHEME 1. Retrosynthetic Analysis for Quinolizidine (-)-217A
SCHEME 2. Synthesis of (2S,20S)-Methyl-2-piperidin-2-ylpropanoate 5
SCHEME 3. Synthesis of Quinolizidine 13
piperidin-2-ylpropanoate 5 that was obtained by a diaster-
eodivergent synthesis from piperidine enaminoester 7.8
We envisioned that quinolizidine (-)-217A could stem from
quinolizidine 2, the stereocontrol at C4 being expected to be
obtained in the intramolecular cyclization of piperidine 3.9
Elaboration of the appropriate side chain of piperidine 3 could
arise from aldehyde 4. The latter would be obtained from (S)-
methyl 2-((S)-1-((R)-1-phenylethyl)piperidin-2-yl)propanoate 5.
Indeed, compound 5 was easily prepared as outlined in
Scheme 2. Methyl 7-chlorohept-2-ynoate6 (obtained fromthe
commercially available chlorohexyne) underwent halogen
exchange with sodium iodide to afford methyl 7-iodohept-2-
ynoate. The latter was condensed with (R)-1-phenylethyla-
mine to provide (R,E)-methyl 2-(1-(1-phenylethyl)piperidin-
2-ylidene)acetate 7.10 A two-step reduction/alkylation procedure
afforded chiral piperidine 5 by a method previously described
for its enantiomer.8
Wittig reaction was conducted on a racemic model, the com-
mercially avalaible Cbz-N protected aldehyde 8. As a first
attempt, we performed an aldolization reaction between alde-
hyde 8 and the dianion of methyl acetoacetate. This reaction
failed and only led to degradation products. We then turned
our attention toward the vinylogous Mukaiyama aldol reaction
between aldehyde 8 and the dioxanone-derived dienol ether 9
(Scheme 3).11 This condensation carried out in the presence of
boron trifluoride-diethyl ether provided the expected piper-
idine 10 as a 1:1 mixture of diastereomers in a 62% isolated
yield. Thermolysis of the latter in a refluxing toluene/methanol
mixture afforded the desired piperidine 11 as a 1:1 mixture of
diastereomers in 70% isolated yield. Dehydration reaction
attempted in acidic medium (PTSA in refluxing toluene)
provided the undesired corresponding decarboxylation prod-
uct. This result is probably due to the formation of water
during the process. It is noteworthy that the reaction in the
presence of PTSA in toluene at room temperature or in the
presence of molecular sieves in refluxing toluene left compound
11 unchanged. To solve this problem a two-step procedure was
envisaged. The expected ethylenic β-ketoester moiety was
obtained via the corresponding acetate prepared by treatment
of piperidine 11 with acetyl chloride in pyridine followed by
subsequent elimination of the acetate group in the presence of
triethylamine in refluxing toluene.12 Piperidine 12 was then
obtained in a 56% isolated yield as a single E isomer. Finally
compound 12was submitted to both benzyl carbamate removal
It is noteworthy that this strategy could allow the diaster-
eoselective introduction of various alkyl groups giving access
to chiral piperidine 5 analogues.
Results and Discussion
We initially focused our attention on the construction of a
piperidine substituted by an appropriate functionalized side
chain and its subsequent intramolecular cyclization into a
quinolizidine. An elongation study based on aldolization or
ꢁ
(8) Pereira, J.; Calvet-Vitale, S.; Fargeau-Bellassoued, M.-C.; Mouries-
Mansuy, V.; Vanucci-Bacque, C.; Lhommet, G. Heterocycles 2007, 71, 437–444.
ꢀ
(9) For an example of aza annulation involving the formation of a
tetrahydropyridine followed by subsequent reduction of the imine function
see: Evans, D. A.; Adams, D. J. J. Am. Chem. Soc. 2007, 129, 1048–1049.
(10) David, O.; Fargeau-Bellassoued, M.-C.; Lhommet, G. Tetrahedron
Lett. 2002, 43, 3471–3474.
(11) (a) Denmark, S. E.; Beutner, G. L. J. Am. Chem. Soc. 2003, 125,
7800–7801. (b) Munakata, R.; Katakai, H.; Ueki, T.; Kurosaka, J.; Takao,
K.; Tadano, K. J. Am. Chem. Soc. 2003, 125, 14722–14723.
(12) White, J. D.; Skeean, R. W.; Trammell, G. L. J. Org. Chem. 1985, 50,
1939–1948.
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SCHEME 4. Synthesis of Phosphorane 16
TABLE 1. Catalytic Hydrogenation of 17
entry
conditionsa
pressure (bar)
product (% yield)
1
2
3
4
MeOH
MeOH
AcOH
MeOH, HClO4
1
10
1
18a (87)
18a (90)
18a (85)
18b (90)
b
1
and reductive amination in a one-pot procedure to afford
quinolizidine 13 as a single diastereoisomer in 90% isolated
yield.
aH2, 10% Pd/C. b3 equiv of 60% aqueous acid.
The second route to build the side chain was then inves-
tigated. The Wittig reaction was first performed from race-
mic aldehyde 8 and methyl-4-(triphenylphosphoranylidene)
acetoacetate. Unfortunately this condensation in basic con-
ditions (NaH,13 NaHMDS14) failed and yielded intractable
mixtures.
We then turned our attention to the use of 4-benzyloxy-
1-(triphenyl-λ5-phosphanylidene)-butan-2-one 16 in which
the acetate group is replaced by a benzyl ether moiety. This
compound is prepared as outlined in Scheme 4.
Our study clearly showed that this second route is very
effective to generate the quinolizidine ring system. Thus,
quinolizidine 13 was prepared via the aldolization route in a
19% overall yield from aldehyde 8 whereas quinolizidine 18b
was obtained via the Wittig reaction in a 67% overall yield.
Therefore we decided to prepare quinolizidine (-)-217A
through this second methodology. The requisite aldehyde 4
was prepared in four steps from (2S,20S )-methyl-2-piperidin-
2-ylpropanoate 5 (Scheme 6).
Reduction of the ester moiety of piperidine 5 with lithium
aluminum hydride afforded the corresponding piperidine
alcohol 19 in quantitative yield. The latter was submitted to
a debenzylation/carbamatation sequence to give N-Cbz-pro-
tected piperidine 21 in a 77% isolated yield from 19. Swern
oxidation of piperidine 21 led to the enantiopure aldehyde 4,
which was subjected to a Wittig reaction with ylide 16 (as in
Scheme 5) to afford unsaturated ketone 3a as a single E alkene
isomer in 70% isolated yield in two steps. Piperidine 3a was
then submitted to catalytic hydrogenation (Table 1, entry 4) to
give the quinolizidine alcohol 2a as a single isomer in quanti-
tative yield. This compound was converted into aldehyde 22
(Swern oxidation), which was submitted without purification
to the Yamamoto’s olefination to provide enyne 23.16 Finally
desilylation of the terminal alkyne5 with potassium carbonate
provided quinolizidine (-)-217A 1 in a 95% isolated yield.
The spectral characteristics and the optical rotation of 1
Reaction of the anion of (2-oxopropyl)triphenylphos-
phorane 14 with benzyl chloromethyl ether afforded 16 in
50% isolated yield. Condensation of aldehyde 8 with this
new more reactive phosphorane 16 performed in toluene
(80 °C) provided the expected piperidine 17 as a single E
alkene isomer in 74% isolated yield (Scheme 5).
Catalytic hydrogenation of precursor 17 was then tested in
the presence of Pd/C (10%) in order to obtain the correspond-
ing O-deprotected quinolizidine. This reaction performed
either in methanol under 1 or 10 bar of H2 (Table 1, entries
1 and 2) or in acetic acid (entry 3) exclusively afforded
quinolizidine 18a in which the alcohol function remained
protected. However, when the reaction was conducted in a
HClO4/MeOH15 mixture (entry 4) the expected debenzylated
quinolizidine 18b was obtained as a single isomer in 90%
isolated yield.
SCHEME 5. Synthesis of Quinolizidine 18
SCHEME 6. Total Synthesis of Quinolizidine (-)-217A
J. Org. Chem. Vol. 75, No. 22, 2010 7805

Fellah et al.
JOCArticle
([R]20 -14.0 (c 0.8, CHCl3)) were in complete agree-
ment with those reported in the literature for the natural
(s, 2H), 3.73 (s, 3H), 3.81 (br s, 1H), 4.05 (br d, J = 14.7 Hz, 1H),
C
D
4.28 (br s, 1H), 4.50 (m, 1H), 5.14 (s, 2H), 7.31-7.40 (m, 5H); 13
product.3,5,7
NMR (62.5 MHz, CDCl3) δ 19.2, 25.5, 29.4, 37.4, 39.5, 47.3, 49.6,
50.1, 52.4, 64.4, 67.7, 128.0, 128.3, 128.7, 136.6, 157.1, 167.8, 202.4.
11b: 1H NMR (250 MHz, CDCl3) δ 1.20-1.70 (m, 7H), 1.86-2.10
(m, 1H), 2.62 (dd, J = 7.5, 17.5 Hz, 1H), 2.71-2.98 (m, 2H), 3.24-
3.56 (m, 3H), 3.71 (s, 3H), 3.92-4.12 (m, 2H), 4.32-4.49 (m, 1H),
5.09 (s, 2H), 7.24-7.40 (m, 5H); 13C NMR (62.5 MHz, CDCl3) δ
18.9, 25.4, 29.0, 36.9, 39.4, 48.1, 49.4, 49.5, 52.4, 65.7, 67.1, 127.8,
128.0, 128.5, 136.8, 155.7, 167.4, 203.3; HRMS (ESI) m/z calcd for
C20H27NO6Na (MNaþ) 400.1730, found 400.1724.
Conclusion
In summary, we have achieved a simple and efficient
synthesis of quinolizidine (-)-217A via enantiopure methyl
piperidine propanoate 5 in 13 steps and 15% overall yield.
Our synthesis was based on two strategic steps: a chain
elongation by the Wittig reaction between two readily avail-
able precursors, the enantiopure aldehyde 4 and the novel
ylide 16, and a totally strereocontrolled aza-annulation
into quinolizidine 2. Considering that the starting material
is the 7-chlorohept-2-ynoate 6, our approach represents
the most efficient synthesis of quinolizidine (-)-217A to
date. Further applications of this strategy toward more
complex biologically active alkaloids are currently under
investigation.
Benzyl 2-(6-Methoxy-4,6-dioxohex-2-enyl)piperidine-1-car-
boxylate (12). To a solution of 11 (0.187 g, 0.50 mmol) in
CH2Cl2 (6 mL), cooled at 0 °C, were successively added drop-
wise pyridine (0.046 mL, 0.57 mmol) and AcCl (0.037 mL,
0.52 mmol). The reaction was warmed to room temperature
and stirred for 24 h. The mixture was diluted with Et2O (15 mL),
then washed with water (2 ꢀ 10 mL). The organic layers were
dried over anhydrous Na2SO4, filtered, and concentrated under
reduced pressure to give crude acetate (0,173 g) as a yellow oil
that was used in the next step without purification.
The crude 11 acetate was dissolved in toluene (6 mL) and
Et3N (0.065 mL, 0.50 mmol) was added. The mixture was stirred
for 2 h at 110 °C then cooled to 0 °C, diluted with Et2O (15 mL),
and washed with water (2 ꢀ 10 mL). The organic layers were
dried over anhydrous Na2SO4, filtered, and concentrated under
reduced pressure. Purification by silica gel chromatography with
20% EtOAc/cyclohexane afforded 12 (0.099 g, 56% over 2 steps)
as a colorless oil: IR (neat) 1690, 1430 cm-1; 1H NMR (250 MHz,
CDCl3) δ 1.20-1.74 (m, 6H), 2.26-2.88 (m, 3H), 3.47 (m, 1.4H),
3.70 (s, 2.1H), 3.72 (s, 0.9H), 3.99-4.14 (m, 1H), 4.48 (br s, 1H),
4.96 (s, 0.3H), 5.09 (s, 2H), 5.80 (d, J= 15.0 Hz, 0.3H), 6.12 (d, J=
15.0 Hz, 0.7H), 6.57 (dt, J = 7.5, 15.0 Hz, 0.3H), 6.75 (dt, J = 7.5,
15.0 Hz, 0.7H), 7.26-7.39 (m, 5H), 11.76 (d, J = 2.5 Hz, 0.3H);
13C NMR (62.5 MHz, CDCl3) δ 18.8, 25.3, 28.2, 33.3, 33.4, 39.3,
46.3, 49.9, 50.3, 51.3, 52.4, 67.2, 90.3, 126.4, 127.9-128.1, 128.5,
128.6, 131.5, 136.7, 136.8, 137.2, 146.3, 155.4, 155.5, 167.8, 169.0,
173.3, 192.0; HRMS (ESI) m/z calcd for C20H25NO5Na (MNaþ)
382.1630, found 382.1615.
Methyl 2-(Octahydro-1H-quinolizin-4-yl)acetate (13). To a
solution of 12 (0.091 g, 0.25 mmol) in MeOH (6 mL) was added
10% Pd/C (0.091 g). The reaction flask was purged with H2 and
the reaction was stirred for 14 h at room temperature under H2
balloon (1 atm). The reaction mixture was filtered through a pad
of Celite. The cake was washed with MeOH (3 ꢀ 10 mL) and the
combined filtrates were evaporated under reduced pressure.
Purification by silica gel chromatography with 90% EtOAc/
MeOH afforded 13 (0.048 g, 90%) as a colorless oil: IR (neat)
1713 cm-1; 1H NMR (250 MHz, CDCl3) δ 1.10-1.93 (m, 14H),
2.20 (dd, J = 6.5, 15.2 Hz, 1H), 2.36-2.49 (m, 1H), 2.72 (dd, J =
5.2, 15.5 Hz, 1H), 3.03 (m, 1H), 3.64 (s, 3H); 13C NMR (62.5
MHz, CDCl3) δ 24.2, 24.5, 26.3, 33.3, 33.6, 33.9, 40.1, 51.7, 51.9,
60.4, 63.2, 173.4; HRMS (ESI) m/z calcd for C12H22NO2 (MHþ)
212.1645, found 212.1645.
Experimental Section
The preparation and characterization of the starting materi-
als 5 and 7 are described in the Supporting Information.
Benzyl 2-(3-(2,2-Dimethyl-4-oxo-4H-1,3-dioxin-6-yl)-2-hydroxy-
propyl)piperidine-1-carboxylate (10). To a solution of aminoalde-
hyde 8 (1.36 g, 5.2 mmol) in CH2Cl2 (25 mL), cooled at -78 °C,
were successively added dropwise BF3 Et2O (0.504 mL, 5.47 mmol)
3
and silyl derivative11a 9 (1.43 g, 5.57 mmol). The reaction mixture
was stirred for 2 h at -78 °C. The reaction was then warmed to
room temperature and quenched with a saturated NaHCO3 solu-
tion (50 mL). The aqueous layer was extracted with CH2Cl2 (3 ꢀ
40 mL), and the combined organic layers were dried over anhydrous
Na2SO4, filtered, and concentrated under reduced pressure. Purifi-
cation by silica gel chromatography with 50% EtOAc/cyclohexane
afforded 10 as a 1:1 mixture of diastereomers (1.29 g, 62%) as a
colorless oil. 10a: IR (neat) 3420, 1750, 1690 cm-1; 1H NMR (250
MHz, CDCl3) δ 1.20-1.85 (m, 14H), 2.00 (dt, J = 1.7, 13 Hz, 1H),
2.22-2.43 (m, 2H), 2.72 (t, J = 12.5 Hz, 1H), 3.57 (m, 1H), 4.06 (d,
J = 15.0 Hz, 1H), 4.46 (br d, J = 12.2 Hz, 1H), 5.04-5.20 (m, 2H),
5.29 (s, 1H), 7.28-7.35 (m, 5H); 13C NMR (62.5 MHz, CDCl3) δ
19.2, 24.6, 25.3, 25.4, 29.3, 37.6, 39.4, 40.8, 47.2, 64.5, 67.5, 94.9,
106.4, 127.8, 128.6, 136.4, 157.0, 161.2, 169.3. 10b: IR (neat) 3420,
1
1750, 1690 cm-1; H NMR (250 MHz, CDCl3) δ 1.27-1.75 (m,
13H), 1.86 (m, 1H), 2.20-2.50 (m, 2H), 2.86 (t, J = 12.5 Hz, 1H),
3.59-4.15 (m, 3H), 4.42 (m, 1H), 5.09 (s, 2H), 5.27 (s, 1H),
7.21-7.42 (m, 5H); 13C NMR (62.5 MHz, CDCl3) δ 18.7, 24.4,
25.2, 28.7, 37.5, 39.4, 41.3, 48.2, 66.5, 67.0, 94.8, 106.3, 127.6, 127.9,
128.3, 129.4, 136.4, 155.6, 161.2, 169.4; HRMS (ESI) m/z calcd for
C22H29NO6Na (MNaþ) 426.4580, found 426.4575.
Benzyl 2-(2-Hydroxy-6-methoxy-4,6-dioxohexyl)piperidine-1-
carboxylate (11). A degassed solution of 10 (0.252 g, 0.63 mmol)
in toluene/MeOH (8:2, 10 mL) was stirred in a sealed tube for 16 h
at 110 °C.9b After the mixture was cooled to room temperature, the
solvents were removed under reduced pressure. Purification by
silica gel chromatography with 20% EtOAc/cyclohexane afforded
11 (0.162 g, 70%) as a colorless oil: IR (neat) 1690, 1430 cm-1. 11a:
1H NMR (250 MHz, CDCl3) δ 1.17-1.86 (m, 7H), 1.97-2.15
(m, 1H), 2.56 (dd, J = 5.2, 16.0 Hz, 1H), 2.70-2.91 (m, 2H), 3.51
4-Benzyloxy-1-(triphenyl-λ5-phosphanylidene)butan-2-one (16).
To a solution of (2-oxopropyl)triphenylphosphorane 14 (3.65 g,
11.5 mmol) in THF (100 mL) was added dropwise n-BuLi
(5.04 mL of a 2.5 M solution in hexane, 12.6 mmol) at -78 °C.
The reaction was stirred for 2 h at the same temperature and benzyl
chloromethyl ether 15 (1.97 g, 12.6 mmol) was then added drop-
wise. The reaction mixture was warmed to 0 °C and stirred for 16 h.
The reaction was quenched with a mixture of Et2O/H2O (1/2,
100 mL) and stirred over 30 min. The organic solvents were removed
under reduced pressure and the aqueous layer was extracted with
ethyl acetate (5 ꢀ 50 mL). The organic layers were dried over
anhydrous Na2SO4, filtered, and evaporated under reduced pres-
sure. Purification by silica gel chromatography (EtOAc) afforded 16
(2.52 g, 50%) as a yellow solid: mp 106-107 °C; IR (neat) 1530,
(13) Pietrusiewicz, K. M.; Monkiewicz, J. Tetrahedron Lett. 1986, 27,
739–742.
(14) Ceccarelli, S. M.; Piarulli, U.; Gennari, C. Tetrahedron 2001, 57,
8531–8542.
(15) Fujimoto, R.; Kishi, Y.; Blount, J. F. J. Am. Chem. Soc. 1980, 102,
7154–7156.
(16) Yamakado, Y.; Ishiguro, M.; Ikeda, N.; Yamamoto, H. J. Am.
Chem. Soc. 1981, 103, 5568–5570.
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1480, 1440 cm-1; 1H NMR (250 MHz, CDCl3) δ 2.68 (t, J = 7.5
Hz, 2H), 3.87 (t, J= 7.5 Hz, 2H), 4.56 (s, 2H), 7.15-7.72 (m, 21H);
13C NMR (62.5 MHz, CDCl3) δ41.7 (d, J = 18.7 Hz), 52.3 (d, J =
106.2 Hz), 68.4, 72.9, 126.2, 127.2, 127.5, 127.7, 128.2, 128.6, 128.8,
138.9, 190.5; HRMS (ESI) m/z calcd for C29H27O2P (MHþ)
439.1821, found 439.1813.
General Procedure for the Wittig Reaction. A solution of
aminoaldehyde (1.0 equiv) and ylide 16 (1.4 equiv) in toluene
(10 mL) was stirred for 19 h at 80 °C. The reaction mixture was
cooled to room temperature and the solvent was removed under
reduced pressure. The residue was purified by silica gel chro-
matography with 20% EtOAc/cyclohexane.
The reaction was cooled at 0 °C and quenched by addition of
saturated aqueous Na2SO4 solution. The mixture was filtered
through a pad of Celite and the cake was washed with ethyl acetate
(3 ꢀ 15 mL). The combined filtrates were dried over anhydrous
Na2SO4, filtered, and concentrated under reduced pressure. Puri-
fication by silica gel chromatography with 20% EtOAc/cyclohex-
ane afforded 19 (3.22 g, 93%) as a colorless oil: [R]20 þ64.3
D
(c 1.60, CHCl3); IR (neat) 3380, 2928, 2858 cm-1; 1H NMR (250
MHz, CDCl3) δ 0.52 (d, J = 7.5 Hz, 3H), 1.22-1.34 (m, 2H), 1.37
(d, J = 7.5 Hz, 3H), 1.50-1.86 (m, 4H), 2.31-2.47 (m, 2H),
3.06-3.25 (m, 3H), 3.49 (dd, J = 2.5, 10.0 Hz, 1H), 4.17 (q, J =
7.5 Hz, 1H), 6.88 (br s, 1H), 7.22-7.42 (m, 5H); 13C NMR
(62.5 MHz, CDCl3) δ 14.6, 19.5, 20.0, 22.0, 31.5, 42.2, 57.8, 61.6,
71.0, 127.3, 127.4, 128.8, 145.3; HRMS (ESI) m/z calcd for
C16H26NO (MHþ) 248.2009, found 248.2003.
(E)-Benzyl 2-(6-(Benzyloxy)-4-oxohex-2-enyl)piperidine-1-
carboxylate (17). This compound was prepared from the ami-
noaldehyde 8 (0.258 g, 0.99 mmol) and ylide 16 (0.609 g,
1.38 mmol) to yield 17 (0.308 g, 74%) as a colorless oil: IR
(neat) 1690, 1430 cm-1; 1H NMR (250 MHz, CDCl3) δ 1.31-
1.76 (m, 6H), 2.28-2.92 (m, 6H), 3.74 (t, J = 7.5 Hz, 2H),
3.98-4.16 (m, 1H), 4.49 (s, 2H), 5.09 (s, 2H), 6.10 (d, J = 15.0
Hz, 1H), 6.74 (dt, J = 7.5, 15.0 Hz, 1H), 7.23-7.43 (m, 10H);
13C NMR (62.5 MHz, CDCl3) δ 18.7, 25.2, 28.0, 33.2, 39.3, 44.4,
49.9, 65.4, 67.0, 73.1, 127.6-128.5 (10C), 132.5, 136.7, 138.2,
144.1, 155.4, 198.2; HRMS (ESI) m/z calcd for C26H31NO4Na
(MNaþ) 444.2145, found 444.2138.
4-(2-(Benzyloxy)ethyl)octahydro-1H-quinolizine (18a). To a
solution of 17 (0.292 g, 0.69 mmol) in MeOH (10 mL) was
added 10% Pd/C (0.146 g). The reaction flask was purged with
H2 and the reaction was stirred for 12 h at room temperature
under H2 balloon (1 atm). The reaction mixture was filtered
through a pad of Celite. The cake was washed with MeOH (3 ꢀ
10 mL) and the solvent was removed under reduced pressure.
Purification by silica gel chromatography with 90% EtOAc/
MeOH afforded 18a (0.164 g, 87%) as a colorless oil: IR (neat)
2984, 1461 cm-1; 1H NMR (250 MHz, CDCl3) δ 1.13-1.90 (m,
16H), 1.91-2.16 (m, 2H), 3.26 (br d, J = 10.0 Hz, 1H), 3.52 (br t,
J = 7.5 Hz, 1H), 4.48 (s, 2H), 7.18-7.44 (m, 5H); 13C NMR
(62.5 MHz, CDCl3) δ 24.2, 24.3, 26.0, 31.9, 33.3, 33.4, 33.6, 51.4,
61.2, 63.3, 67.7, 72.8, 127.4, 127.5, 128.2, 138.4; HRMS (ESI) m/
z calcd for C18H28NO (MHþ) 274.4205, found 274.4201.
General Procedure for the Synthesis of O-Deprotected Quino-
lizidine. To a solution of piperidine olefin (1.0 equiv) in MeOH
(10 mL) was added 10% Pd/C (0.5 equiv w/w). The reaction
flask was purged with H2 and the reaction was stirred for 3 h at
room temperature under H2 balloon (1 atm). A 60% HClO4
aqueous solution (3 equiv) was then added. The reaction
mixture was stirred for 16 h at room temperature and then
filtered through a pad of Celite. The cake was washed with
MeOH (3 ꢀ 10 mL) and the solvent was removed under reduced
pressure. Saturated NaHCO3 solution (20 mL) was added and
the aqueous layer was extracted with CH2Cl2 (7 ꢀ 20 mL), dried
over anhydrous Na2SO4, filtered, and concentrated under re-
duced pressure. The residue was purified by silica gel chroma-
tography with 90% EtOAc/cyclohexane.
(S )-2-((S )-Piperidin-2-yl)propan-1-ol (20). To a solution of 19
(3.40 g, 13.7 mmol) in MeOH (30 mL) was added 10% Pd/C
(0.68 g). The reaction flask was purged with H2 and the reaction
was stirred for 6 h at room temperature under H2 balloon
(1 atm). The reaction mixture was filtered through a pad of
Celite. The cake was washed with MeOH (3 ꢀ 20 mL) and the
combined filtrates were evaporated under reduced pressure.
Purification by silica gel chromatography with 90% EtOAc/
MeOH afforded 20 (1.96 g, 100%) as a white solid: mp 61-
D
1
62 °C; [R]20 þ4.9 (c 1.00, CHCl3); IR (neat) 3455 cm-1; H
NMR (250 MHz, CDCl3) δ 0.81 (d, J = 7.5 Hz, 3H), 1.00-1.62
(m, 5H), 1.66-1.91 (m, 2H), 2.39-2.63 (m, 2H), 2.96-3.08 (m,
1H), 3.48 (dd, J = 10.0, 12.5 Hz, 1H), 3.71 (dd, J = 5.0, 10.0 Hz,
1H); 13C NMR (62.5 MHz, CDCl3) δ 14.1, 24.7, 27.3, 31.5, 39.3,
46.6, 63.5, 69.6; HRMS (ESI) m/z calcd for C8H18NO (MHþ)
144.1383, found 144.1379.
(S )-Benzyl 2-((S )-1-Hydroxypropan-2-yl)piperidine-1-carbox-
ylate (21). To a solution of 20 (1.85 g, 14.3 mmol) in CH2Cl2
(60 mL) cooled at 0 °C were successively added K2CO3 (2.97 g,
21.5 mmol) and benzyl chloroformate (2.23 mL, 15.8 mmol). The
reaction mixture was stirred for 16 h at 0 °C. The mixture was
filtered and concentrated under reduced pressure. Purification
by silica gel chromatography with 20% EtOAc/cyclohexane
afforded 21 (3.26 g, 83%) as a colorless oil: [R]20 -23.9
D
(c 1.00, CHCl3) IR (neat) 3455, 1670, 1430 cm-1 1H NMR
;
(250 MHz, CDCl3) δ 1.03 (d, J = 7.5 Hz, 3H), 1.37-1.70 (m, 5H),
1.75-2.11 (m, 2H), 2.76 (br t, J = 12.5 Hz, 1H), 3.12-3.58 (m,
3H), 3.94-4.23 (m, 2H), 5.03-5.24 (m, 2H), 7.27-7.41 (m, 5H);
13C NMR (62.5 MHz, CDCl3) δ 14.9, 18.9, 25.5, 25.9, 32.7, 40.0,
52.2, 64.2, 67.6, 128.0, 128.2, 128.7, 136.7, 156.9; HRMS (ESI) m/
z calcd for C16H23NO3Na (MNaþ) 300.1570, found 300.1578.
General Procedurefor the Swern Oxidation. To a cooled -60 °C
solution of oxalyl chloride (2.1 equiv of a 2 M solution
in CH2Cl2) in CH2Cl2 (80 mL) was added dropwise DMSO
(4.2 equiv). The mixture was stirred at this temperature for
15 min, then a solution of alcohol (1 equiv) in dry CH2Cl2
(10 mL) was added dropwise. The resulting solution was stirred
at -60 °C for 1 h. Finally, triethylamine (6 equiv) was added
dropwise. The reaction mixture was allowed to warm to room
temperature over 3 h. The reaction was quenchedwith a saturated
aqueous NaHCO3 solution (60 mL). The aqueous layer was
extracted with AcOEt (4 ꢀ 40 mL), and the combined organic
layers were dried over anhydrous Na2SO4, filtered, and concen-
trated under reduced pressure. The residue was purified by silica
gel chromatography with 20% EtOAc/cyclohexane.
2-(Octahydro-1H-quinolizin-4-yl)ethanol (18b). This com-
pound was prepared from the piperidine olefin 17 (0.150 g,
0.36 mmol), 10% Pd/C (0.075 g), and 60% HClO4 aqueous
solution (0.055 mL, 1.70 mmol) to yield 18b (0.059 g, 90%) as a
1
colorless oil: IR (neat) 3427, 1461 cm-1; H NMR (250 MHz,
CDCl3) δ 1.08-1.95 (m, 16H), 2.18-2.41 (m, 2H), 3.42-3.76
(m, 2H), 4.03 (dt, J = 5.0 Hz, 12.5 Hz, 1H); 13C NMR (62.5
MHz, CDCl3) δ 24.1, 24.6, 26.1, 30.1, 31.9, 33.7, 34.1, 52.4, 60.3,
61.7, 63.8; HRMS (ESI) m/z calcd for C11H22NO (MHþ)
184.1696, found 184.1692.
(S )-2-((S)-1-((R)-1-Phenylethyl)piperidin-2-yl)propan-1-ol (19).
To a suspension of LiAlH4 (1.17 g, 30.8 mmol) in dry THF (30 mL)
cooled at 0 °C was added dropwise a solution of aminoester 58
(3.85 g, 14.0 mmol) in THF (10 mL). The reaction mixture was
then warmed to room temperature and stirred for 1 h and 30 min.
(S )-Benzyl 2-((S )-1-Oxopropan-2-yl)piperidine-1-carboxylate
(4). This compound was prepared from oxalyl chloride (12.1 mL
of a 2 M solution in CH2Cl2, 24.2 mmol,), DMSO (3.44 mL,
48.5 mmol), alcohol 21 (3.20 g, 11.5 mmol) and triethylamine
(10.0 mL, 1.5 mmol) to yield 4 (3.00 g, 95%) as a white solid:
mp 54-55 °C; [R]20D -38.4 (c 1.00, CHCl3); IR (neat) 1750, 1690
1
cm-1; H NMR (250 MHz, CDCl3) δ 1.09 (d, J=7.5 Hz, 3H),
1.31-1.89 (m, 6H), 2.74-3.14 (m, 2H), 4.06 (m, 1H), 4.45 (m, 1H),
J. Org. Chem. Vol. 75, No. 22, 2010 7807

Fellah et al.
JOCArticle
5.10 (s, 2H), 7.27-7.50 (m, 5H), 9.47 (d, J = 2.5 Hz, 1H); 13
C
was added at -78 °C. The reaction mixture was stirred for 10 min
and a solution of the crude aldehyde 22 previously prepared in
THF (2 mL) was added dropwise. The resulting mixture was
stirred at -78 °C for 1 h, -20 °C for 1 h, and at room temperature
for 1 h. The reaction was quenched by addition of a saturated
aqueous NH4Cl solution (30 mL) and the mixture was extracted
with AcOEt (4 ꢀ 20 mL). The combined organic layers were
dried over anhydrous Na2SO4, filtered, and concentrated under
reduced pressure. Purification by silica gel chromatography
with 50% EtOAc/cyclohexane afforded 23 (0.352 g, 48% over
2 steps) as a colorless oil: [R]25D -17.0 (c 0.31, CHCl3); IR (neat)
2850 cm-1; 1H NMR (250 MHz, CDCl3) δ 0.14 (s, 9H), 0.81 (d,
J = 5.0 Hz, 3H), 0.85-1.78 (m, 12H), 1.81-2.07 (m, 2H),
2.33-2.66 (m, 2H), 3.26 (br d, J = 10.0 Hz, 1H), 5.50 (d, J =
10.0 Hz, 1H), 6.00 (m, 1H); 13C NMR (62.5 MHz, CDCl3) δ 0.1,
19.3, 24.7, 26.3, 26.4, 30.2, 32.0, 33.9, 35.0, 36.4, 51.9, 63.5, 69.7,
98.9, 102.3, 110.4, 142.8; HRMS (ESI) m/z calcd for C18H32NSi
(MHþ) 290.2299, found 290.2298.
NMR (62.5 MHz, CDCl3) δ 12.1, 18.9, 25.2, 25.4, 39.9, 45.2,
52.2, 67.4, 128.0, 128.1, 128.6, 136.7, 155.5, 203.7; HRMS
(ESI) m/z calcd for C16H21NO3Na (MNaþ) 298.1414, found
298.1407.
(S )-Benzyl 2-((R,E)-7-(Benzyloxy)-5-oxohept-3-en-2-yl)-
piperidine-1-carboxylate (3a). This compound was prepared
according to the Wittig reaction general procedure from ami-
noaldehyde 4 (0.667 g, 2.42 mmol) and ylide 16 (3.11 g, 3.39
mmol) to yield 3a (0.781 g, 74%) as a colorless oil: [R]20
D
-28.8 (c 0.95, CHCl3); IR (neat) 1690, 1430 cm-1; H NMR
1
(250 MHz, CDCl3) δ 1.01 (d, J = 5.0 Hz, 3H), 1.32-1.67 (m,
6H), 1.70-1.87 (m, 1H), 2.50-2.91 (m, 4H), 3.59-3.79 (m, 2H),
3.92-4.28 (m, 2H), 4.45 (s, 2H), 5.05 (s, 1H), 6.02 (d, J = 15.0
Hz, 1H), 6.55-6.76 (m, 1H), 7.12-7.44 (m, 10H); 13C NMR
(62.5 MHz, CDCl3) δ 17.2, 18.5, 25.0, 25.2, 26.6, 36.1, 38.7, 39.4,
54.7, 65.1, 66.7, 72.7, 127.2, 127.3, 127.5, 127.6, 128.0, 128.2,
128.0, 130.1, 136.6, 138.0, 150.2, 155.2, 198.2; HRMS (ESI) m/z
calcd for C27H33NO4Na (MNaþ) 458.2302, found 458.2289.
2-((1R,4S,9aS )-1-Methyloctahydro-1H-quinolizin-4-yl)etha-
nol (2a). This compound was prepared according to the general
procedure for the synthesis of O-deprotected quinolizidine from
the piperidine olefin 3a (0.494 g, 1.13 mmol), 10% Pd/C (0.148 g),
and 60% HClO4 aqueous solution (0.171 mL, 1.70 mmol) to
(1R,4S,9aS )-1-Methyl-4-((Z)-pent-2-en-4-ynyl)octahydro-
1H-quinolizine (-)-217A (1). To a solution of 23 (0.274 g, 0.95
mmol) in MeOH (16 mL) was added K2CO3 (0.144 g, 1.04 mmol).
The reaction mixture was stirred for 2 h at room temperature. The
reaction was quenched with water (30 mL) and the mixture was
extracted with Et2O (4 ꢀ 15 mL). The combined organic layers
were dried over anhydrous Na2SO4, filtered, and concentrated
under reduced pressure. Purification by silica gel chromatography
with 50% EtOAc/cyclohexane afforded 1 (0.195 g, 95%) as a
yield 2a (0.223 g, 100%) as a white solid: mp 49-50 °C; [R]20
D
-32.8 (c 1.0, CHCl3); IR (neat) 3427, 1461 cm-1; 1H NMR (250
MHz, CDCl3) δ 0.78 (d, J = 5.0 Hz, 3H), 0.88-2.01 (m, 14H),
2.04-2.42 (m, 2H), 3.33-3.70 (m, 2H), 3.83-4.06 (m, 1H), 4.74
(br s, 1H); 13C NMR (62.5 MHz, CDCl3) δ 19.2, 24.5, 25.9, 29.7,
30.2, 32.5, 33.3, 35.6, 51.9, 60.3, 61.5, 69.8; HRMS (ESI) m/z calcd
for C12H24NO (MHþ) 198.1852, found 198.1848.
colorless oil: [R]25 -14.0 (c 0.8, CHCl3); IR (neat) 3312, 2972,
D
1452 cm-1; 1H NMR (250 MHz, CDCl3) δ 0.82 (d, J = 5.0 Hz,
3H), 0.86-1.80 (m, 12H), 1.81-1.93 (m, 1H), 1.96-2.08 (m, 1H),
2.40-2.67 (m, 2H), 3.05 (m, 1H), 3.18-3.29 (m, 1H), 5.48 (m,
1H), 6.07 (dt, J = 7.5, 10.0 Hz, 1H); 13C NMR (62.5 MHz,
CDCl3) δ 19.3, 24.7, 26.2, 30.2, 31.8, 33.9, 35.0, 36.3, 51.8, 63.1,
69.6, 80.7, 81.7, 109.4, 143.4; HRMS (ESI) m/z calcd for C15H24N
(MHþ) 218.1903, found 218.1897.
(1R,4S,9aS )-1-Methyl-4-((Z)-5-(trimethylsilyl)pent-2-en-4-
ynyl)octahydro-1H-quinolizine (23). The aldehyde 22 was first
prepared according to the general Swern oxidation procedure
from oxalyl chloride (2.66 mL, 5.32 mmol, 2 M in CH2Cl2
solution), DMSO (0.751 mL, 8.05 mmol), alcohol 2a (0.50 g,
2.53 mmol), and triethylamine (2.20 mL, 15.7 mmol) to afford
the crude aldehyde 22 (0.498 g) as a pale yellow oil that was used
immediately in the next step without purification.
Acknowledgment. We thank Dr. Marie-Claude Fargeau-
Bellassoued for fruitful discussions during this work.
To a solution of 3-(tert-butyldimethylsilyl)-1-(trimethylsilyl)-
1-propyne14 (0.573 g, 2.53 mmol) in THF (5 mL) cooled at -78 °C
was added dropwise t-BuLi (2.06 mL of a 1.6 M solution in
hexane, 3.29 mmol). After 1 h Ti(Oi-Pr)4 (0.97 mL, 3.29 mmol)
Supporting Information Available: Characterization data
and 1H and 13C NMR spectra of new compounds. This material
is available free of charge via the Internet at http://pubs.acs.org.
7808 J. Org. Chem. Vol. 75, No. 22, 2010