Facile synthesis of 1H, 4H-cyclopenta[c]pyrrolo[1,2-b]isoquinolin-2(3H)-one

Article abstract of DOI:10.3184/030823409X439690

A novel and facile method for the synthesis of 4H-cyclopenta[c]pyrrolo[1,2- b] isoquinolin-2(3H)-one has been developed by employing the [2, 3] Stevens rearrangement of methyl N-allyl-N-benzylpyrrolidine 2-carboxylate to methyl 2-allyl-l-benzyl-pyrrolidin

Full text of DOI:10.3184/030823409X439690

JOURNAL OF CHEMICAL RESEARCH 2009
APRILꢁꢀꢃꢄꢄ±257
RESEARCH PAPER 255
Facile synthesis of 1H, 4H-cyclopenta[c]pyrrolo[1,2-b]isoquinolin-2(3H)-one
Mo Ran Sun, Hong Tao Lu and Hua Yang*
School of Pharmaceutical Science, Zhengzhou University, Zhengzhou 450001, P.R. China
A novel and facile method for the synthesis of 4H-cyclopenta[c]pyrrolo[1,2-b] isoquinolin-2(3H)-one has been
developed by employing the [2, 3] Stevens rearrangement of methyl N-allyl-N-benzylpyrrolidine 2-carboxylate
to methyl 2-allyl-l-benzyl-pyrrolidine 2-carboxylate and acid-lactonisation as key transformations. The synthetic
strategy from readily available materials provided a model skeletal analogue of cephalotaxine and should have
general applicability in the synthesis of Cephalotaxus alkaloids.
Keywords: cephalotaxine, homoharringtonine, Stevens rearrangement, acid-lactonisation
Cephalotaxine (CET, 1) is the parent compound of the
harringtonine.1 As representative ester derivatives of CET,
harringtonine (2) and homoharringtonine (HHT, 3) (Fig. 1)
have been used as front-line drugs for acute myeloid leukaemia
for more than 20 years in China.2,3ꢀ,QꢀWKHꢀ86$ꢁꢀWKHꢀHI¿FLHQF\ꢀ
of HHT in the treatment of chronic myeloid leukaemia is
being evaluated in a large-scale study and the clinical trials
have reached phase III.4
Chemists have examined the relevant bioactivity of a large
number of natural and unnatural ester derivatives of CET
and the results indicate that esters with different acyl chains
display different levels of activity.5 Although the acyl moiety
is very important for expressing activity, little is known about
WKHꢀLQÀXHQFHꢀRIꢀWKHꢀFHSKDORWD[LQHꢀVNHOHWRQꢀXSRQꢀWKHꢀDFWLYLW\ꢂꢀ
,Wꢀ ZDVꢀ RXUꢀ DVVXPSWLRQꢀ WKDWꢀ PRGL¿FDWLRQꢀ RIꢀ FHSKDORWD[LQHꢀ
skeleton would be a rational approach towards designing
an alternative to 3 possessing a more promising biological
SUR¿OHꢂꢀ:HꢀSODQQHGꢀWRꢀPRGLI\ꢀWKHꢀULQJꢀ&ꢀRIꢀFHSKDORWD[LQHꢀWRꢀ
a six-membered ring analogue 4 (Fig. 1). In order to test the
feasibility of our approach for the construction of the tetracyclic
core ring system (BCDE), we have carried out preliminary
experiments to produce the tetracyclic ketone 5. The synthetic
route to 5 was applicable to the preparation of 4 following the
literature methods.6,7 We now report the results obtained from
this model study.
Our approach started with the proline derivative 7,8 which
was treated with benzyl bromide in CH3CN to smoothly afford
8 in 92% yield by a [2, 3]-Stevens rearrangement as described
O
O
O
N
N
A
N
5R
Skeletal
B
C
D
4S
O
E
modification
RO
1
3S
HO
2
OMe
O
OMe
4
1
5
1. Cephalotaxine
2. Harringtonine
HO
3. Homoharringtonine
O
O
OH
OH
3'
5'
3'
5'
HO
R =H
6'
R =
R =
1'
1'
2'R
2'R
4'
4'
CO2Me
CO2Me
Fig. 1 Modification of cephalotaxine skeleton.
1. SOCl2, MeOH
H2
N
2. allyl bromide,
K2CO3, DMF, rt
3.benzyl bromide,
CH3CN
N
N
CO2
CO2Me
CO2Me
89%
92%
7
6
OH
O
Bn
N
Bn
N
5. LiAlH4, THF,
0oC,
93%
Bn
6. DMSO, (COCl)2,
Et3N, CHCl2
CO2Me
4. TfOH, CH2Cl2,
95%
OH
N
O
8
13
14
O
Bn
N
N
N
7. KOtBu, THF, rt
50% , two steps
8. TfOH, CH2Cl2,
85%
O
5
16
15
O
O
Scheme 1 Synthesis of compound 5.
* Correspondent. E-mail: yanghua@zzu. edu.cn

256 JOURNAL OF CHEMICAL RESEARCH 2009
Bn
N
CO2Me
Experimental
General procedure
CO2Me O2, PdCl2(cat.)
CuCl, DMF-H2O
BnN
O
6LOLFDꢀJHOꢀꢅꢃꢉꢉ±ꢋꢉꢉꢀPHVKꢆꢀDQGꢀSHWUROHXPꢀHWKHUꢀꢅESꢂꢀꢌꢉ±ꢍꢉ°C) were
XVHGꢀIRUꢀWKHꢀSXUL¿FDWLRQꢀRIꢀSURGXFWVꢀE\ꢀÀDVKꢀFROXPQꢀFKURPDWRJUDSK\ꢂꢀ
$OOꢀ VROYHQWVꢀ ZHUHꢀ SXUL¿HGꢀ DQGꢀ GULHGꢀ E\ꢀ VWDQGDUGꢀ WHFKQLTXHVꢁꢀ DQGꢀ
distilled prior to use. All organic extracts were dried over MgSO4,
unless otherwise noted. IR spectra were recorded on a Nicolet IR200
LQVWUXPHQWꢀ XVLQJꢀ .%Uꢀ GLVNVꢀ LQꢀ WKHꢀ ꢎꢉꢉ±ꢎꢉꢉꢉꢀ FP-1 region. HRMS
were obtained on a Waters Micromass Q-Tof MicroTM instrument
using the ESI technique. Melting points were determined using a
XT5A apparatus and were uncorrected. 1H and 13C NMR spectra
were recorded on a Bruker AM-400 spectrometer with TMS as an
internal standard and CDCl3 as solvent.
18% yield
9
8
O2, PdCl2(cat.)
CHO
CHO
O
BnN
CuCl, DMF-H2O
10% yield
BnN
10
8
11
O
Bn
I
2 / CH2Cl2
O
N
I
Methyl 2-allyl-1-benzylpyrrolidine-2-carboxylate (8): Dry K2CO3
(4.8 g, 35 mmol) was added to a solution of 7 (2 g, 11.8 mmol) and
benzyl bromide (2 g, 11.8 mmol) in dry CH3CN (20 mL). After stirring
for 6 h at room temperature, the solvent was evaporated under reduced
pressure. Water (20 mL) and ethyl acetate (100 mL) were added. The
separated water phase was extracted by ethyl acetate (30 mL) and the
combined organic phase was washed by saturated brine (3 u 20 mL),
GULHGꢀ DQGꢀ FRQFHQWUDWHGꢂꢀ 3XUL¿FDWLRQꢀ E\ꢀ FROXPQꢀ FKURPDWRJUDSKꢀ
[petroleum ether: EtOAc = 4:1] gave the product 8 (2.75 g, 90%)
as a colourless oil: IR(KBr)Qmax 2950, 1726, 1639, 1452(cm-1).
1H NMR (400 MHz, CDCl3): Gꢀ ꢈꢂꢌꢉ±ꢈꢂꢏꢌꢀ ꢅPꢁꢀ ꢋ+ꢆꢁꢀ ꢃꢂꢉꢍ±ꢃꢂꢈꢏꢅPꢁꢀ
ꢈ+ꢆꢁꢀꢃꢂꢎꢎ±ꢃꢂꢄꢄꢅPꢁꢀꢃ+ꢆꢁꢀꢃꢂꢌꢋ±ꢃꢂꢌꢍꢅPꢁꢀꢈ+ꢆꢁꢀꢃꢂꢏꢃ±ꢃꢂꢍꢃꢅPꢁꢀꢈ+ꢆꢁꢀꢋꢂꢋꢈꢅGꢁꢀ
J = 13.5 Hz, 1H), 3.70(s, 3H), 3.95(d, J = 13.5 Hz, 1H), 5.06-5.12(m,
ꢃ+ꢆꢁꢀꢄꢂꢏꢋ±ꢄꢂꢍꢄꢅPꢁꢀꢈ+ꢆꢁꢀꢇꢂꢈꢄ±ꢇꢂꢃꢌꢅPꢁꢀꢄ+ꢆꢂꢀ+506ꢀꢅ(6,ꢆꢀm/z Found
260.1649 ([M + H]+), Calcd 260.1651 for C16H22NO2.
rt, 0% yield
12
Scheme 2 Failed Wacker oxidation and lactonisation.
in Scheme 1. Thus, we constructed a quaternary centre D to
the nitrogen of the pyrrolidine ring in one pot. In an alternative
method for generation of the quaternary carbon, the secondary
amine of a proline ester was protected using (Boc)2O, followed
by treatment with allyl bromide, in the presence of LHMDS
and anhydrous THF under argon atmosphere.9 In our hands,
the allyl and benzyl group were installed at suitable positions
in one pot under milder and more economical conditions.
Next, the Wacker oxidation of 8 with oxygen, palladium
FKORULGHꢀ DQGꢀ FRSSHUꢅǿꢆꢀ FKORULGHꢀ ZDVꢀ H[DPLQHGꢀ WRꢀ JLYHꢀ 9 in
only 18% yield, as shown in Scheme 2. Similar treatment
of compound 10 furnished 11 in poor yield. The iodine-
D-(1-Benzylpyrrolidine)-J -butyrolactone (13ꢆꢐꢀ7ULÀLFꢀDFLGꢀꢅꢄꢂꢄꢀJꢁꢀ
36.5 mmol) was added to a solution of compound 8 (1.9 g, 7.3 mmol)
in dry CH2Cl2 (10 mL). After stirring for 7 minutes at room
temperature, CH2Cl2 (100 mL) was added to the reaction mixture
and the system was washed successively with saturated Na2CO3
and brine. The organic phase was dried and concentrated. Column
chromatography [petroleum ether: EtOAc = 2:1] gave compound 13
(1.71 g, 95%) as a colourless oil: IR (KBr)Qmax 1726, 1449, 1216,
1175, 916(cm-1). 1H NMR (400 MHz, CDCl3): G 1.40 (d, J = 6.1 Hz,
ꢋ+ꢆꢁꢀꢈꢂꢇꢋ±ꢃꢂꢉꢍꢅPꢁꢀꢎ+ꢆꢁꢀꢃꢂꢈꢄ±ꢃꢂꢋꢌꢅPꢁꢀꢃ+ꢆꢁꢀꢃꢂꢇꢄ±ꢋꢂꢉꢉꢅPꢁꢀꢃ+ꢆꢁꢀꢋꢂꢇꢎꢅGꢁꢀ
J = 13.4, 1H), 3.83(d, Jꢀ ꢀꢈꢋꢂꢎꢁꢀꢈ+ꢆꢁꢀꢎꢂꢎꢌ±ꢎꢂꢄꢌꢅPꢁꢀꢈ+ꢆꢁꢀꢇꢂꢃꢎ±ꢇꢂꢎꢃꢅPꢁꢀ
5H). 13C NMR (100 MHz, CDCl3) G 178.3, 139.4, 128.4, 128.2, 127.1,
126.9, 73.5, 70.1, 53.2, 51.5, 41.1, 36.4, 21.9, 21.0. HRMS (ESI) m/z
Found 246.1494 ([M + H]+), Calcd 246.1494 for C15H20NO2.
induced lactonisation of D-amino-4-encarboxylate
8 in
dichloromethane failed.10-12
Unexpectedly, the desired acid-mediated spirolactionisation
occurred cleanly on treatment of 8 ZLWKꢀ WULÀLFꢀ DFLGꢀ DWꢀ
ambient temperature to give the spirolactone 13 (Scheme 1)
almost quantitatively (95%). Various acidic catalysts
(H2SO4, HCl, CH3SO3H, TsOH, CF3COOH and PPA) were
H[DPLQHGꢀ DQGꢀ SURYHGꢀ WRꢀ EHꢀ OHVVꢀ HI¿FLHQWꢀ RUꢀ LQHIIHFWLYHꢀ LQꢀ
this spirolactonisation. It is worth noting that, although the
acid-catalysed lactonisation of nitrogen-free substrates has
been reported for many years,13,14 this reaction of D-amino-
4-en-carboxylate has not to our knowledge been explored
previously. It may be attributed to the decomposition of D-
amino carboxylate in acidic conditions. The reaction must be
TXHQFKHGꢀZLWKLQꢀꢇ±ꢈꢉꢀPLQꢀDIWHUꢀWKHꢀDGGLWLRQꢀRIꢀWKHꢀWULÀLFꢀDFLGꢂ
Reduction of 13 with lithium aluminum hydride followed
by Swern oxidation of the resulting diol 14, afforded the
keto-aldehyde 15. Attempted oxidation of diol 14 with PCC
and PDC failed because D-amino aldehyde was sensitive
to decomposition in an acidic environment. For the same
reason, the crude product was subjected to the condensation
UHDFWLRQꢀZLWKRXWꢀWKHꢀSXUL¿FDWLRQꢀE\ꢀFROXPQꢀFKURPDWRJUDSK\ꢂꢀ
&RQVLGHUDEOHꢀGLI¿FXOW\ꢀZDVꢀHQFRXQWHUHGꢀLQꢀ¿QGLQJꢀFRQGLWLRQVꢀ
suitable for the base-catalysed adol condensation of 15.
Among the conditions (i.e. K2CO3/CH3OH, KOH/CH3OH,
NaOH/CH3OH) that were examined, the only effective reagent
was the KOtBu/THF system which furnished the amino spiro-
cyclopentenone 16 in 50% yield over two steps. Subsequently,
the protic acid mediated cyclisation of 16 proceeded to give
the tetracyclic ketone 5 according to the literature method.15
,Qꢀ VXPPDU\ꢁꢀ Dꢀ KLJKO\ꢀ HI¿FLHQWꢀ VWUDWHJ\ꢀ IRUꢀ WKHꢀ V\QWKHVLVꢀ
of compound 5 with [2, 3]-Stevens rearrangement and
spirolactonation as key steps has been developed. Through
eight-stage operation, the overall yield from L-proline to 5 is
ca 31%. The strategy should have general applicability in the
synthesis of amino cyclopentenones from readily available
amino acids. At the moment, this procedure is being used for
WKHꢀV\QWKHVLVꢀRIꢀVNHOHWDOO\ꢊPRGL¿HGꢀDQDORJXHVꢀRIꢀ&(7ꢂ
1-(1-Benzyl-2-(hydroxymethyl)pyrrolidin-2-yl) propan-2-ol (14):
Compound 13(1.7 g, 6.9 mmol) in dry THF (5 mL) was added to a
solution of LiAlH4 (0.39 g,10 mmol) suspended in dry THF (20 mL)
XQGHUꢀUHÀX[ꢂꢀ$IWHUꢀUHÀX[LQJꢀIRUꢀꢋꢉꢀPLQXWHVꢁꢀWKHꢀVROXWLRQꢀZDVꢀFRROHGꢀWRꢀ
room temperature. Then, H2O (0.39 mL), 15% NaOH (0.39 mL) and
H2O (1.17 mL) were added in succession. After stirring for 5 minutes,
WKHꢀ SUHFLSLWDWHꢀ ZDVꢀ ¿OWHUHGꢀ RIIꢀ DQGꢀ WKHꢀ ¿OWUDWHꢀ ZDVꢀ FRQFHQWUDWHGꢀ
under vacuum to give the diol 14 (1.62 g, 93%) as a colourless oil:
IR(KBr)Qmax 3338(OH), 2964,1453, 1128, 1048, 947, 733, 700(cm-1).
1H NMR(400 MHz, CDCl3): G 1.27(d, J = 6.0 Hz, 3H), 1.60(dd,
Jꢀ ꢀ ꢈꢎꢂꢎꢁꢀ ꢈꢂꢃꢀ +]ꢁꢀ ꢈ+ꢆꢁꢀ ꢈꢂꢌꢇ±ꢈꢂꢏꢃꢅPꢁꢀ ꢎ+ꢆꢁꢀ ꢈꢂꢍꢈ±ꢃꢂꢉꢉꢅPꢁꢀ ꢈ+ꢆꢁꢀ ꢃꢂꢄꢇ±
ꢃꢂꢌꢋꢅPꢁꢀꢈ+ꢆꢁꢀꢃꢂꢇꢈ±ꢃꢂꢇꢄꢀꢅPꢁꢀꢈ+ꢆꢁꢀꢋꢂꢎꢍ±ꢋꢂꢇꢄꢅPꢁꢀꢎ+ꢆꢁꢀꢋꢂꢍꢌ±ꢎꢂꢉꢋꢀꢅPꢁꢀꢈ+ꢆꢁꢀ
ꢎꢂꢃꢉ±ꢎꢂꢏꢉꢀꢅEUVꢁꢀꢃ+ꢆꢁꢀꢇꢂꢃꢈ±ꢇꢂꢃꢇꢅPꢁꢀꢈ+ꢆꢁꢀꢇꢂꢃꢇ±ꢇꢂꢋꢄꢅPꢁꢀꢎ+ꢆꢂꢀ+506ꢀꢅ(6,ꢆꢀ
m/z Found 250.1802 ([M + H]+), Calcd 250.1807 for C15H24NO2.
1-Benzyl azaspiro[4,4]non-8-en-7-one (16): A solution of oxalyl
dichloride (1.43 g, 11.2 mmol) in dry CH2Cl2 (8 mL) was added
WRꢀDꢀFRROHGꢀꢅ±ꢇꢏ°C) solution of DMSO (1.87 g, 24.0 mmol) in dry
CH2Cl2 (8 mL) over a period of 6 min. The mixture was stirred
for 10 min and then a solution of 14(2 g, 10 mmol) in dry CH2Cl2
ꢅꢈꢉꢀP/ꢆꢀZDVꢀDGGHGꢀDWꢀ±ꢇꢏ°C. The solution was stirred at the same
temperature for 15 min. Triethylamine (5 g, 50 mmol) was then
added, and the solution was allowed to warm to room temperature.
The mixture was diluted with water (10 mL) and the organic layer
was washed successively with saturated NaHCO3 and brine, dried
and concentrated. The residue was dissolved in anhydrous THF
ꢅꢈꢉꢀP/ꢆꢀZLWKRXWꢀIXUWKHUꢀSXUL¿FDWLRQꢀDQGꢀ.2tBu (1.12 g, 10 mmol)
was added. After stirring for 20 min at room temperature, the solution
was evaporated under vacuum. Water (15 mL) was added to the
residue and the solution was extracted with ethyl acetate (3 u 50 mL).
The combined organic phase was dried, concentrated and subjected
to column chromatography [petroleum ether: EtOAc = 10:1] to give
the enone 16 (1.12 g, 50%) as a colourless oil: IR (KBr) Qmax 2965,
2800, 1716, 1664, 1586, 1494, 1453 (cm-1). 1H NMR(400 MHz,
CDCl3): Gꢀꢈꢂꢇꢄ±ꢈꢂꢍꢃꢀꢅPꢁꢀꢋ+ꢆꢁꢀꢈꢂꢍꢏ±ꢃꢂꢉꢍꢅPꢁꢀꢈ+ꢆꢁꢀꢃꢂꢈꢄꢅGꢁꢀJ = 18.4 Hz,
ꢈ+ꢆꢁꢀꢃꢂꢎꢄ±ꢃꢂꢎꢍꢅPꢁꢀꢈ+ꢆꢁꢀꢃꢂꢄꢈꢅGꢁꢀJꢀ ꢀꢈꢏꢂꢏꢀ+]ꢁꢀꢈ+ꢆꢁꢀꢃꢂꢏꢋ±ꢃꢂꢍꢎꢅPꢁꢀꢈ+ꢆꢁꢀ
3.27(d, J = 13.2 Hz, 1H), 3.45(d, J = 13.2 Hz, 1H), 6.08(d, J = 5.6 Hz,
ꢈ+ꢆꢁꢀ ꢇꢂꢈꢃ±ꢇꢂꢃꢎꢅPꢁꢀ ꢄ+ꢆꢁꢀ ꢇꢂꢋꢏꢅGꢁꢀ J
=
5.6 Hz, 1H). 13C NMR

JOURNAL OF CHEMICAL RESEARCH 2009 257
References
(100.6 MHz, CDCl3) G 207.8, 167.8, 139.4, 134.0, 128.3, 127.0,
71.5, 53.3, 51.6, 41.1, 38.0, 21.7. HRMS (ESI) m/z Found 228.1385
([M + H]+), Calcd 228.1388 for C15H18NO.
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(0.42 g, 85%) as a colourless oil. The IR and 1H NMR were in complete
agreement with the literature.15 IR (KBr) Qmax 2968, 2909, 2809, 2773,
1744, 1488, 1455, 1380, 1267(cm-1). 1H NMR(400 MHz, CDCl3):
Gꢀ ꢈꢂꢏꢄ±ꢃꢂꢉꢏꢀ ꢅPꢁꢀ ꢄ+ꢆꢁꢀ ꢃꢂꢋꢈꢅGꢁꢀ Jꢀ ꢀ ꢈꢇꢂꢌꢀ +]ꢁꢀ ꢈ+ꢆꢁꢀ ꢃꢂꢌꢎ±ꢃꢂꢇꢃꢅPꢁꢀ ꢃ+ꢆꢁꢀ
ꢃꢂꢇꢇ±ꢃꢂꢏꢎꢅPꢁꢀꢈ+ꢆꢁꢀꢋꢂꢈꢋ±ꢋꢂꢃꢉꢀꢅPꢁꢀꢈ+ꢆꢁꢀꢋꢂꢎꢋꢅGꢁꢀJ = 8.4 Hz, 1H), 3.78(d,
J = 16.0 Hz, 1H), 4.03(d, Jꢀ ꢀꢈꢌꢂꢉꢀ+]ꢁꢀꢈ+ꢆꢁꢀꢇꢂꢉꢍ±ꢇꢂꢃꢇꢀꢅPꢁꢀꢎ+ꢆꢂꢀ+506ꢀ
(ESI) m/z Found 228.1378 ([M + H]+), Calcd 228.1382 for C15H18NO.
4
H.M. Kantarjian, M. Talpaz, V. Santini, A. Murgo, B. Cheson and
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9
ꢀꢈꢉꢀ .ꢂꢀ0DHGDꢁꢀ5ꢂ$ꢂꢀ0LOOHUꢁꢀ5ꢂ+ꢂꢀ6]XPLJDODꢁꢀ-Uꢂꢀ$OLꢀ6KD¿HHꢁꢀ6ꢂꢀ.DUDG\ꢀDQGꢀ
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2341.
We thank the National Natural Science Foundation (20502023)
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Received 23 January 2009; accepted 23 February 2009
Paper 09/0407 doi: 10.3184/030823409X439690
Published online: 29 April 2009
15 W.-D.Z. Li and X.-W. Wang, Org. Lett., 2007, 9, 1211.