Synthesis of (-)-coniine and (-)-pipecoline using ruthenium catalyzed ring closing metathesis

Article abstract of DOI:10.1016/S0022-328X(00)00930-X

Ring closing metathesis employing the well-known Grabbs' ruthenium catalyst has been used as the key step in the synthesis of piperidine alkaloids, (-)-coniine and (-)-pipecoline, and the asymmetric induction has been performed by using (R)-α-methyl benzy

Full text of DOI:10.1016/S0022-328X(00)00930-X

Journal of Organometallic Chemistry 624 (2001) 359–363
www.elsevier.nl/locate/jorganchem
Communication
Synthesis of (−)-coniine and (−)-pipecoline using ruthenium
catalyzed ring closing metathesis
Kandasamy Pachamuthu, Yashwant D. Vankar *
Department of Chemistry, Indian Institute of Technology, Kanpur 208 016, India
Received 3 October 2000; accepted 6 December 2000
Dedicated to Professor J.-F. Normant on the occasion of his 65th birthday
Abstract
Ring closing metathesis employing the well-known Grubbs’ ruthenium catalyst has been used as the key step in the synthesis
of piperidine alkaloids, (−)-coniine and (−)-pipecoline, and the asymmetric induction has been performed by using (R)-a-methyl
benzylamine as an auxiliary. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Grubbs’ ruthenium catalyst; Ring closing metathesis; Synthesis; Piperidine alkaloids; (R)-a-methyl benzylamine
lowing chiron approach (starting with properly func-
tionalized allene) [6h,i], and by chiral catalysis [4].
1. Introduction
In this note we describe short syntheses of (−)-coni-
ine (8) and (−)-pipecoline (9) starting from imines 2a
and 2b which were, in turn, derived from butanal and
acetaldehyde respectively using (R)-a-methyl benzy-
lamine as a chiral auxiliary (Scheme 1). In the initial
studies allylation of imine 2a [4] was attempted using
indium [9], magnesium [10], and zinc [11a], however,
zinc based reaction in dry THF gave the best yield
(82%) of the desired product 4a whose reaction with
allyl bromide in the presence of NaH and n-BuN+I−
(catalytic amounts) in refluxing THF for 8 h led to the
diene 5a. The intermediate 3, in all cases, could also be
directly converted into the bis allylated products (5a–
5c) by quenching the reactions with allyl bromide, thus
saving one step in the synthetic operations. Yields of
the dienes 5a–5c obtained in this manner were com-
parable to the stepwise allylation.
Recently ring closing metathesis (RCM) reaction us-
ing a ruthenium complex such as 1 (Scheme 1) has been
shown [1] to be of great potential in organic synthesis.
Several kinds of ring structures, including heterocycles,
have been synthesized [2] by this approach. Coniine (8)
belongs to a class of piperidine ring based alkaloids and
numerous reports for its synthesis, in both the enan-
tiomeric forms, have appeared in the recent past [3].
Strategies to form such a six-membered ring alkaloid
include aza-Diels–Alder reaction [4], Mannich–
Michael reaction [5], intramolecular cyclization through
an appropriately attached nucleophilic nitrogen atom
[6], condensation [7] of terminally bifunctionalized
molecule with a nitrogen containing species and modi-
fying an already available six membered nitrogen hete-
rocycle [3,8]. The enantioselectivity has been induced
mainly by starting with a chiral auxiliary containing
substrate [5,6a–c,f,g,7,8], by enzymatic resolution [6d],
using Sharpless asymmetric dihydroxylation [6e], fol-
Ring closing metathesis using ruthenium catalyst 1
gave the expected heterocycle 7a which on treatment
with 10% Pd–C/H2 at room temperature for 8 h gave
(−)-coniine (8). For comparison purpose, coniine was
isolated as its HCl salt by reacting it with dry HCl gas
in ether which showed a melting point of 209°C and its
* Corresponding author. Tel.: +91-512597169; Fax: +91-512-
590007.
E-mail address: vankar@iitk.ac.in (Y.D. Vankar).
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(00)00930-X

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K. Pachamuthu, Y.D. Vankar / Journal of Organometallic Chemistry 624 (2001) 359–363
Scheme 1.
1H- and 13C-NMR spectral data were comparable with
the literature [8a] values. It may be noted that although
the two diastereomers were inseparable at the stage of
the diene 5a they could be separated after the cycliza-
tion and the major product 7a was further transformed
into (−)-coniine. The diastereoemeric ratio was deter-
mined to be 85:15 which was also confirmed by finding
out the enantiomeric excess of 8 [12]1 from its Mosher’s
ester. Since the substitution at two-position is depen-
dent on the initial imine we have also synthesized
pipecoline 9 [13] in 71% ee from the imine 2b following
the same strategy which permitted incorporation of
methyl side chain readily. Likewise, two chromato-
graphically separable diasteroemers 6c and 7c (ratio
17:83) were synthesized from benzaldehyde derived
imine 2c and the major isomer 7c was converted into
2-phenyl piperidine (10) [14].
internal standard. The 13C-NMR spectra were recorded
on JNM LA-400 spectrometers at 100 Hz. IR spectra
were recorded on Perkin–Elmer 1320 spectrophotome-
ter. Mass spectra were recorded on GC-MS (FINNI-
GAN VOYAGER). Optical rotations were measured
using Autopol II Rudolph polarimeter. All the experi-
ments were performed under an atmosphere of dry
argon unless otherwise specified. The products were
purified by column chromatography on silica gel (100–
200 mesh). Melting points were determined in a Fischer
John melting point apparatus.
Compound 2 was prepared according to a literature
procedure [4].
2.2. Preparation of secondary amines (4a–c)
A mixture of imine 2 (5 mmol), allyl bromide (6
mmol), activated zinc powder (6 mmol) and
CeCl3·7H2O (0.5 mmol) in 5 ml of THF was stirred at
room temperature (r.t.) for 1 h. Usually the exothermal
reaction proceeded readily and the metal disappeared
within 10–20 min. The reaction mixture was extracted
with ethyl acetate and the organic layer was worked up
as usual. Purification of the crude product by column
chromatography gave secondary amines 4a–c.
In summary, the present approach of imine allylation
followed by N-allylation either stepwise or in-situ and
further followed sequentially by ring closing metathesis
and hydrogenolysis/hydrogenation is flexible and we
expect it to be useful in the synthesis of two-substituted
based piperidine alkaloids.
2. Experimental
2.2.1. (R)-(+)-N-[(R)-h-Methybenzyl]-hept-1-ene-4-
amine (4a)
2.1. General
Yield, 82%. [h]D= +24° (c 1.05, CHCl3),
1H-NMR spectra (400 MHz) were recorded on JEOL
JNM LA-400 FT NMR spectrometers with Me4Si as
1
IR(CH2Cl2): 1635 cm−1. H-NMR (CDCl3): l 0.78 (t,
J=8.6 Hz, 3H, –CH2CH3), 1.27–1.50 (m, 5H, –
CH2CH2CH3, –NCH–), 1.33 (d, J=7 Hz, 3H, –CH
CH3), 2.15–2.42 (m, 3H, –NH, –CH2CH:CH2), 3.87–
1 Optical purity of (−)-coniine was determined from the analysis
of the 1H-NMR (400 MHz) spectrum of the amide prepared by
treatment of 7 with (R)-(+)-a-methoxy-a-(trifluoromethyl) pheny-
lacetyl chloride.
3.92 (m, 1H, PhCH–), 5.02–5.18 (m, 2H,
–
CH2CH:CH2), 5.6–5.9 (m, 1H, –CH2CH:CH2),

K. Pachamuthu, Y.D. Vankar / Journal of Organometallic Chemistry 624 (2001) 359–363
361
7.2–7.33 (m, 5H, aromatic). 13C-NMR(CDCl3): l
13.88, 19.05, 24.89, 37.05, 37.66, 53.43, 54.90, 116.93,
126.43, 126.48, 126.7, 127.62, 128, 128.33, 135.48. Mass
m/z (%): 218 (3) [M++1], 217 (12) [M+]. Anal. Calc.
for C15H23N: C, 82.89; H, 10.66; N, 6.44. Found: C,
82.79; H, 10.50; N, 6.40%.
–NCH2CH:CH2), 3.95 (q, J=10.5 Hz, 1H, PhCH–),
4.81–5.2 (m, 4H, 2× –CH2CH:CH2), 5.55–5.9 (m,
2H, 2× –CH2CH:CH2), 7.19–7.33 (m, 5H, aromatic).
13C-NMR(CDCl3): l 14.08, 20.16, 20.69, 34.6, 35.71,
48.75, 57.2, 58.43, 114.74, 115.27, 126.4, 126.6, 127.72,
127.75, 127.9, 128.0, 137.82, 140.0. Mass m/z (%): 257
(10) [M+]. Anal. Calc. for C18H27N: C, 83.99; H, 10.57;
N, 5.44. Found: C, 83.0; H, 10.6; N, 5.42%.
2.2.2. (R)-(+)-N-[(R)-h-Methybenzyl]-pent-1-ene-4-
amine (4b)
2.3.2. (R)-(+)-N-Allyl,
Yield, 80%. [h]D= +18 (c 0.65, CH2Cl2),
IR(CH2Cl2): 1632 cm−1 1H-NMR (CDCl3): l 0.95 (d,
J=6.6 Hz, 3H, –CHCH3), 1.32 (d, J=8.52 Hz, 3H,
PhCHCH3), 1.5 (br s, 1H, –NH), 2.05–2.64 (m, 3H,
–CHCH2CH:CH2), 3.89 (q, J=2.68 Hz, 1H, PhCH–),
5.03–5.1, 5.6–5.81 (m, 3H, –CH2CH:CH2–), 7.18–
7.34 (m, 5H, aromatic). 13C-NMR(CDCl3): l 21.08,
24.58, 40.27, 49.66, 55.09, 117.02, 126.38–128.33 (6C)
135.47. Mass m/z (%): 189 (10) [M+]. Anal. Calc. for
C13:H19N: C, 82.48; H, 10.12; N, 7.39. Found: C, 82.28;
H, 10.16; N, 7.28%.
N-[(R)-h-methylbenzyl]-pent-1-ene-4-amine (5b)
Yield, 75%. IR (CH2Cl2): 1630 cm−1. [h]D= +10° (c
0.95, CH2Cl2). 1H-NMR (CDCl3): l 0.99 (d, J=6.6
Hz, 3H, –CHCH3), 1.34 (d, J=6.84 Hz, 3H,
PhCHCH3), 1.80–2.33 (m, 2H, –CH2CH:CH2), 2.88 (q,
J=6.56 Hz, 1H, –NCHCH3), 3.06–3.28 (m, 2H, –
NCH2CH:CH2), 4.0 (q, J=6.6 Hz, 1H, PhCHCH3),
4.80–5.21 (m, 4H, 2× –CH2CH:CH2), 5.58–5.90 (m,
2H, 2× –CH2CH:CH2), 7.18–7.39 (m, 5H, aromatic).
13C-NMR(CDCl3): l 17.19, 18.63, 39.32, 48.70, 52.94,
57.36, 115.04, 115.26, 126.36, 126.44, 127.48, 127.62,
127.91, 128.0, 137.5, 139.63. Mass m/z (%): 230 (5)
[M++1], 229 (20) [M+]. Anal. Calc. for C16H23N: C,
83.79; H, 10.11; N, 6.11. Found: C, 83.82; H, 10.18; N,
6.30%.
2.2.3. (R)-(+)-N-[(R)-h-Methybenzyl]-4-phenyl-
but-1-ene-4-amine (4c)
Yield, 89%. [h]D= +35.6 (c 3.15, CH2Cl2): IR
(CH2Cl2): 1620 cm−1 1H-NMR (CDCl3): l 1.26 (d,
.
J=6.84 Hz, 3H, PhCHCH3), 1.74 (brs, 1H, –NH),
2.25–2.55 (m, 2H, –CH2CH:CH2), 3.30–3.50 (m, 1H,
PhCH–), 3.72 (q, J–6.8 Hz, 1H, PhCHCH3), 4.98–
5.05(m, 2H, –CH2CH:CH2), 5.60–5.72 (m, 1H, –
CH2CH:CH2), 7.11–7.32 (m, 10H, aromatic).
13C-NMR(CDCl3): l 24.82, 43.26, 54.80, 58.98, 117.27,
126.53,–128.29 (12C), 135.65. Mass m/z (%): 252 (5)
[M++1], 251 (10) [M+]. Anal. Calc. for C18H21N: C,
86.0; H, 8.42; N, 5.57. Found: C, 86.03; H, 8.40; N,
5.42%.
2.3.3. (R)-(+)-N-Allyl, N-[(R)-h-methylbenzyl]-
4-phenyl-but-1-ene-4-amine (5c)
Yield, 86%. IR (CH2Cl2): 1625 cm−1. [h]D= +13.8°
1
(c 2.65, CH2Cl2). H-NMR (CDCl3): l 1.11 (d, J=6.84
Hz, 3H, PhCHCH3), 2.40–3.43 (m, 4H, 2×
–
CH2CH:CH2), 3.86–4.10 (m, 2H, PhCHCH3,
PhCHCH2–), 4.84–5.15 (m, 4H, 2× –CH2CH:CH2),
5.55–5.86 (m, 2H, 2× –CH2CH:CH2), 7.15–7.45 (m,
10H, aromatic). 13C-NMR(CDCl3): l 20.15, 36.83,
49.56, 56.05, 62.73, 115.38, 115.94, 126.40, 126.47,
126.74, 126.79, 127.56, 127.69, 127.86, 127.96, 128.04,
128.07, 128.42, 128.79, 136.70, 141.39. Mass m/z (%):
292 (6) [M++1], 291 (10) [M+]. Anal. Calc. for
C21H25N: C, 86.55; H, 8.65; N, 4.81. Found: C, 86.6; H,
8.75; N, 4.75%.
2.3. Preparation of dienes (5a–c):
To a suspension of NaH (2 mmol) in THF at 0°C
was added secondary amine 4 (1 mmol) dropwise and
stirred for 15 min. To this reaction mixture was added
allyl bromide (1.2 mmol) and n-butyl ammonium iodide
(0.2 mmol) and the reaction mixture refluxed for 8 h. It
was quenched with satd. NH4Cl solution and extracted
with ether, washed with water and brine. The organic
layer was dried over anhydrous Na2SO4. The crude
material after concentration was purified by column
chromatography gave dienes (5a–c).
2.4. Ring closing metathesis: preparation of cyclic
olefins (7a–c)
To a solution of diene 5 (1 mmol) in CH2Cl2 was
added the Grubb’s catalyst 1 (10 mol%) under nitrogen
and stirred at room temperature for 24 h. The reaction
mixture was filtered through Celite and washed with
CH2Cl2 and evaporation of solvent to give a crude
products (7a–c) which were purified by coloumn
chromatography.
2.3.1. (R)-(+)-N-Allyl,
N-[(R)-h-methylbenzyl]-hept-1-ene-4-amine (5a)
Yield, 70%. IR (CH2Cl2): 1630 cm−1. [h]D= +24° (c
1
1, CHCl3). H-NMR (CDCl3): l 0.83 (t, J=9.2 Hz,
2.4.1. 2R-(+)-4,5-Didehydro-N-[(R)-h-
methylbenzyl]-2-propyl-piperidine (7a)
3H, –CH2CH2CH3), 1.23–1.49 (m, 5H, –CH2CH2CH3,
–NCH–), 1.34 (d, J=6.84 Hz, 3H, –CHCH3), 1.77–
1.99 (m, 2H, –CHCH2CH:CH2), 3.08–3.29 (m, 2H,
Yield, 64%. IR (CH2Cl2): 1632 cm−1. [h]D= +6° (c
1.25, CHCl3). IR (CH2Cl2): 1630 cm−1 1H-NMR
,

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K. Pachamuthu, Y.D. Vankar / Journal of Organometallic Chemistry 624 (2001) 359–363
(CDCl3): l 0.92 (t, J=7.08 Hz, 3H, –CH2CH2CH3),
1.23–1.51 (m, 4H, –CH2CH2CH3), 1.31 (d, J=6.56,
3H, –CHCH3), 1.77–1.99 (m, 1H, –NCH–), 2.27–3.1
(m, 4H, –NCH2CH:CH–, –NCHCH2CH:CH–), 3.68
(q, J=6.84 Hz, 1H, PhCH–), 5.54–5.70 (m, 2H,
–CH2CH:CHCH2–), 7.18–7.37 (m, 5H, aromatic).
13C-NMR(CDCl3): l 14.41, 20.1, 20.79, 27.84, 28.42,
45.17, 51.18, 60.29, 123.48, 125.42, 126.59, 127.36,
127.40, 128.19, 128.2, 146.313. Mass m/z (%): 230 (5)
[M++1], 229 (10) [M+]. Anal. Calc. for C16H23N: C,
83.79; H, 10.11; N, 6.11. Found: C, 83.7; H, 10.14; N,
6.13%.
201 (30) [M+], 186 (95) [M+−15]. Anal. Calc. for
C14H19N: C, 83.53; H, 9.51; N, 6.96. Found: C, 83.54;
H, 9.41; N, 6.80%.
2.4.5. 2R-(+)-4,5-Didehydro-N-[(R)-h-methylbenzyl]-
2-phenyl-piperidine (7c)
Yield, 72%. IR (CH2Cl2): 1635 cm−1. [h]D= +67.3
1
(c 2.05, CH2Cl2) H-NMR (CDCl3): l 1.21 (d, J=9
Hz, 3H, PhCHCH3), 2.30-3.16 (m, 4H,
–
CH2CH:CHCH2–), 3.82 (dd, J=5.12, 8 Hz, 1H,
PhCH–), 3.92, (q, J=1.65 Hz, 1H, PhCHCH3), 5.63–
5.77 (m, 2H, –CH2CH:CHCH2–), 7.16–7.48 (m, 10H,
aromatic).). 13C-NMR (CDCl3): l 10.59, 35.26, 43.57,
55.87, 60.19, 124.32–128.5 (12C), 143.58, 144.27. Mass
m/z (%): 264 (2) [M++1], 265 (10) [M+]. Anal. Calc.
for C19H21N: C, 86.65; H, 8.04; N, 5.32. Found: C,
83.76; H, 8.23; N, 5.45%.
2.4.2. 2R-(−)-4,5-Didehydro-N-[(R)-h-
methylbenzyl]-2-propyl-piperidine (6a)
Yield, 14%. IR (CH2Cl2): 1630 cm−1. [h]D= −6° (c
,
1.25, CHCl3) IR (CH2Cl2): 1630 cm−1 1H-NMR
(CDCl3): l 0.82 (t, J=7.08 Hz, 3H, –CH2CH2CH3),
1.16–1.55 (m, 4H, –CH2CH2CH3), 1.33 (d, J=6.6 Hz,
3H, PhCHCH3), 1.7–1.83 (m, 1H, –NCH–), 2.20–3.30
(m, 4H, –CH2CH:CHCH2–), 3.7 (q, J=6.32 Hz, 1H,
PhCH–), 5.64–5.72 (m, 2H, –CH2CH:CHCH2–),
7.19–7.36 (m, 5H, aromatic). 13C-NMR (CDCl3): l
14.30, 20.19, 22.38, 26.92, 28.18, 44.76, 51.38, 60.49,
123.93, 125.49, 126.68, 127.24, 127.24, 128.30, 128.3
146.39. Mass m/z (%): 230 (3) [M++1], 229 (8) [M+].
Anal. Calc. for C16H23N: C, 83.79; H, 10.11; N, 6.11.
Found: C, 83.74; H, 10.18; N, 6.0%.
2.4.6. 2R-(−)-4,5-Didehydro-N-[(R)-h-methylbenzyl]-
2-phenyl-piperidine (6c)
Yield, 18%. IR (CH2Cl2): 1635 cm−1. [h]D= −67.3
1
(c 2.05, CH2Cl2). H-NMR (CDCl3): l 1.34 (d, J=6.84
Hz, 3H, PhCHCH3), 2.2–3.18 (m, 4H,
–
CH2CH:CHCH2–), 3.75 (t, J=5.36 Hz, 1H, PhCH–),
3.80 (q, J=6.8 Hz, 1H, PhCHCH3), 5.77–5.86 (m, 2H,
–CH2CH:CHCH2–), 7.22–7.48 (m, 10H, aromatic).
13C-NMR (CDCl3): l 20.99, 29.67, 33.60, 44.01, 58.32,
124.49–128.38 (12C), 142.43, 142.94. Mass m/z (%):
264 (10) [M++1], 263 (2) [M+]. Anal. Calc. for
C19H21N: C, 86.65; H, 8.04; N, 5.32. Found: C, 83.77;
H, 8.13; N, 5.55%.
2.4.3. 2R-(+)-4,5-Didehydro-N-[(R)-h-methylbenzyl]-
2-methyl-piperidine (7b)
Yield, 62%. IR (CH2Cl2): 1605 cm−1. [h]D= +5.6°
1
(c 0.45, CH2Cl2). H-NMR (CDCl3): l 1.02 (d, J=6.8
Acknowledgements
Hz, 3H, –CHCH3), 1.32 (d, J=6.8 Hz, 3H,
PhCHCH3), 1.82–2.91 (m, 4H, –CH2CH:CHCH2–),
3.3–3.9 (m, 1H, –CHCH3), 3.65 (q, J=6.8 Hz, 1H,
PhCHCH3), 5.48–5.63 (m, 2H, –CH2CH:CHCH2–),
7.19–7.38 (m, 5H, aromatic). 13C-NMR (CDCl3): l
11.75, 19.22, 32.98, 45.28, 46.54, 60.37, 123.17, 123.17,
125.13, 126.64, 127.49, 127.49, 128.23, 128.23. Mass
m/z (%): 202 (10) [M++1], 201 (45) [M+], 186 (80)
[M+−15], 96 (25) [M+−105]. Anal. Calc. for
C14H19N: C, 83.53; H, 9.51; N, 6.96. Found: C, 83.74;
H, 9.42; N, 6.90%.
We thank the Department of Science and Technol-
ogy and the Council of Scientific and Industrial Re-
search (CSIR), New Delhi, for financial support. KP
thanks the CSIR for a senior research fellowship.
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