Easy one-pot synthesis of fused heterocycles from 1,2-diaza-1,3-dienes

Article abstract of DOI:10.1002/ejoc.201100340

A base-promoted chemoselective synthesis of 6a-hydroxy-6,6a-dihydro-1H- thieno[3,4-b]pyrrole-3,3a(4H)-dicarboxylates, 5-(2-furylmethyl)-6a-hydroxy-6- oxo-4,5,6,6a-tetrahydropyrrolo[3,4-b]pyrrole-3,3a(1H)-dicarboxylates, and 5-benzyl-7a-hydroxy-1,4,5,6,7,7

Full text of DOI:10.1002/ejoc.201100340

SHORT COMMUNICATION
DOI: 10.1002/ejoc.201100340
Easy One-Pot Synthesis of Fused Heterocycles from 1,2-Diaza-1,3-dienes
Orazio A. Attanasi,[a] Luca Bianchi,[a] Lucia De Crescentini,[a] Gianfranco Favi,[a] and
Fabio Mantellini*[a]
Keywords: Michael addition / Fused-ring systems / Nitrogen heterocycles / 1,2-Diaza-1,3-dienes / Cyclization
A base-promoted chemoselective synthesis of 6a-hydroxy-
[3,2-c]pyridine-3,3a-dicarboxylates starting from diazadienes
6,6a-dihydro-1H-thieno[3,4-b]pyrrole-3,3a(4H)-dicarboxyl-
and heterocycles containing an activated methine group has
ates, 5-(2-furylmethyl)-6a-hydroxy-6-oxo-4,5,6,6a-tetra- been developed. This transformations proceeds by Michael
hydropyrrolo[3,4-b]pyrrole-3,3a(1H)-dicarboxylates, and 5-
benzyl-7a-hydroxy-1,4,5,6,7,7a-hexahydro-3aH-pyrrolo-
addition/5-exo cyclization sequence.
rolo[3,2-c]pyridine moiety C has been a significant subject
of synthetic studies of biologically active compounds.[14]
Based on our experience, we have planned a new simple
methodology for the construction of pyrrolines containing
Introduction
Because of the widespread application of structurally
novel heterocycles in drug development, nitrogen-contain-
ing heterocyclic compounds have received considerable at-
tention due to their applications ranging from medicinal
chemistry[1] to materials science.[1a,2] Among them, the
pyrroline/pyrrolidine fragment is a common structural mo-
tif present in several inhibitors and antagonists.[3] For exam-
ple, the pyrroline/pyrrolidine core is contained in a series of
HIV-1 reverse transcriptases that display the greatest degree
of inhibition,[4] or in potent dopamine D4 antagonists that
are selective over D2 and in α1 receptors employed in the
treatment of various disorders such as ADHD, Parkinson’s
disease and sexual dysfunction,[5] or in histamine H3 recep-
tor antagonists.[6] Pyrrolines/pyrrolidines feature also in
fused polycyclic structures of many bioactive molecules: the
1H-thieno[3,4-b]pyrrole fragment A is present in inhibitors
of the biotin-dependent wheat acetyl-CoA carboxylase,[7] or
in an antitumor agent;[8] the pyrrolo[3,4-b]pyrrol-6(1H)-one
B is the core of a potent 5-HT2C agonist,[9] of a peptidyl
VLA-4 antagonist,[10] and of an inhibitor for glycosyl-
transferase enzymes (Scheme 1).[11] Particular attention is
turned to the 1H-pyrrolo[3,2-c]pyridine moiety C that is a
core structure in some biologically active natural products
such as martinellic acid and martinelline (Scheme 1).[12]
They are the first nonpeptide natural product bradykinin
receptor antagonists. These compounds also exhibit potent
antibiotic activities against both Gram-positive and Gram-
negative bacteria, and they also have an affinity for several
G-proteine coupled receptors.[13] Consequently, the 1H-pyr-
[a] Istituto di Chimica Organica, Università degli Studi di Urbino
“Carlo Bo”,
Via I Maggetti 24, 61029 Urbino (PU), Italy
Fax: +39-0722-303441
Scheme 1. Representative examples of fused polycyclic structures
containing a pyrroline/pyrrolidine core with relevant biological ac-
tivities.
E-mail: fabio.mantellini@uniurb.it
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201100340.
2924
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2011, 2924–2927

Fused Heterocycles from 1,2-Diaza-1,3-dienes
fused polycyclic structures that exploit the versatility of 1,2-
diaza-1,3-dienes (DDs) in the syntheses of several five- and
six-membered azaheterocycles.[15]
Results and Discussion
DDs 1a–g easily reacted in tetrahydrofuran (THF) at
room temperature with methyl 4-oxotetrahydrothiophene-
3-carboxylate (2a) or ethyl 1-(2-furylmethyl)-4,5-dioxopyr-
rolidine-3-carboxylate (2b) in the presence of a catalytic
amount of sodium hydride to give in a one-pot reaction 6a-
hydroxy-6,6a-dihydro-1H-thieno[3,4-b]pyrrole-3,3a(4H)-
dicarboxylates 4a–e, or 5-(2-furylmethyl)-6a-hydroxy-6-oxo-
4,5,6,6a-tetrahydropyrrolo[3,4-b]pyrrole-3,3a(1H)-dicarb-
oxylates 4f–i, respectively, in rather good yields (Scheme 3,
Table 1). Under the same conditions, the reaction between
DD 1a and methyl 1-benzyl-4-oxo-3-piperidinecarboxylate
hydrochloride (2c) did not work, and, by increasing the
amount of the sodium hydride until stoichiometric, a com-
plicated mixture was obtained. This occurrence is probably
due to the concomitant acid/base reaction of the hydrochlo-
ride of 2c with the base.
Then, different bases were tested for this reaction (see
Supporting Information). Sodium methoxide has shown the
same behaviour of sodium hydride, sodium acetate (1.0 and
2.0 equiv.) has reacted with DDs giving the corresponding
α-acetoxy-hydrazones, whereas potassium carbonate (2.0
and 5.0 equiv.) was ineffective. Only the strongly basic resin
Merck 104767 ion exchanger III has furnished the desired
3-ethyl 3a-methyl 1-[(aminocarbonyl)amino]-5-benzyl-7a-
hydroxy-2-methyl-1,4,5,6,7,7a-hexahydro-3aH-pyrrolo[3,2-c]-
pyridine-3,3a-dicarboxylate (4j). The best result in term of
yield (66%) and reaction time (2.0 h) was obtained by em-
ploying 1.5 equiv. of resin in THF, at room temperature.
Our analysis of the fused polycyclic structures
(Scheme 2) emphasizes two strategic disconnections of the
pyrrolidine ring, along the carbon–carbon C(3)–C(4) and
the carbon–nitrogen C(5)–N(1) bonds. This reveals two
subunits that trace the left half back to the pertinent hetero-
cyclic anion D and the right half to the zwitterionic hydraz-
one E. Fragment D can be correlated to the pertinent het-
erocycles 2 containing both an activated methine group and
a carbonyl moiety, and fragment E to the azo-ene system
of DD 1. The high reactivity of these latter compounds,
related to the electrophilicity of the terminal carbon atom
of the heterodiene system,[16] permits the C(3)–C(4) junc-
tion by 1,4-addition (Michael-type) of the activated methine
group of 2 to DD 1. Subsequent regioselective intramolecu-
lar cyclization by nucleophilic attack of one of the nitrogen
atoms deriving from the former azo group furnishes the sec-
ond connection C(5)–N(1).
Scheme 2. Retrosynthetic analysis of fused polycyclic structures
containing a pyrroline/pyrrolidine core.
Here, we have verified that our hypothesis to construct The use of these optimized conditions was then extended
the 1H-thieno[3,4-b]pyrrole fragment A, the pyrrolo[3,4-b]- to the reaction of other DDs 1b–d with 2c to obtain the
pyrrol-6(1H)-one moiety B, or the 1H-pyrrolo[3,2-c]pyr- corresponding 3aH-pyrrolo[3,2-c]pyridines 4k–m in 49, 52
idine core C is confirmed by allowing DDs to react, under and 55% yields, respectively (Scheme 3, Table 1).
basic conditions, with the pertinent heterocycles containing
The plausible mechanism of these reactions involves the
an activated methine group through a domino process.
preliminary nucleophilic attack (Michael-type) of the acti-
Scheme 3. Synthesis of 6a-hydroxy-6,6a-dihydro-1H-thieno[3,4-b]pyrrole-3,3a(4H)-dicarboxylates 4a–e, 5-(2-furylmethyl)-6a-hydroxy-6-
oxo-4,5,6,6a-tetrahydropyrrolo[3,4-b]pyrrole-3,3a(1H)-dicarboxylates 4f–i, and 5-benzyl-7a-hydroxy-1,4,5,6,7,7a-hexahydro-3aH-pyr-
rolo[3,2-c]pyridine-3,3a-dicarboxylates 4j–m. (i) NaH (0.1 equiv.), room temp., THF for the reaction between 1a–e with 2a and 1a,c,f, g
with 2b. Resin Merck 104767 ion exchanger III (1.5 equiv.), room temp., THF for the reaction between 1a–d with 2c.
Eur. J. Org. Chem. 2011, 2924–2927
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
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O. A. Attanasi, L. Bianchi, L. De Crescentini, G. Favi, F. Mantellini
SHORT COMMUNICATION
carboxylate (2a) or ethyl 1-(2-furylmethyl)-4,5-dioxopyrrolidine-3-
carboxylate (2b) in THF (20 mL) a catalytic amount of sodium
hydride (0.1 mmol) was added. In the case of the reactions between
DDs 1a–d with methyl 1-benzyl-4-oxo-3-piperidinecarboxylate hy-
drochloride (2c), DDs 1a–d and 2c were dissolved in THF (20 mL),
and the strongly basic resin Merck 104767 ion exchanger III
(1.5 equiv.) was added under gently magnetic stirring. The reaction
mixture was allowed to stand at room temperature until the starting
materials had disappeared (monitored by TLC). Then, the reaction
solvent was evaporated under reduced pressure, and the residues
were chromatographed (silica gel column; elution mixture: 0.8 ethyl
acetate/0.2 cyclohexane) to obtain the corresponding pure 6a-
hydroxy-6,6a-dihydro-1H-thieno[3,4-b]pyrrole-3,3a(4H)-dicarb-
oxylates 4a–e, 5-(2-furylmethyl)-6a-hydroxy-6-oxo-4,5,6,6a-tetra-
hydropyrrolo[3,4-b]pyrrole-3,3a(1H)-dicarboxylates 4f–i, and 5-
benzyl-7a-hydroxy-1,4,5,6,7,7a-hexahydro-3aH-pyrrolo[3,2-c]pyr-
idine-3,3a-dicarboxylates 4j–m that were crystallized from diethyl
ether/light petroleum ether (40–60 °C).
Table 1. Yields and reaction times for the synthesis of 6a-hydroxy-
6,6a-dihydro-1H-thieno[3,4-b]pyrrole-3,3a(4H)-dicarboxylates 4a–
e, 5-(2-furylmethyl)-6a-hydroxy-6-oxo-4,5,6,6a-tetrahydropyrrolo-
[3,4-b]pyrrole-3,3a(1H)-dicarboxylates 4f–i, and 5-benzyl-7a-
hydroxy-1,4,5,6,7,7a-hexahydro-3aH-pyrrolo[3,2-c]pyridine-3,3a-
dicarboxylates 4j–m.
Data for 3-Ethyl 3a-Methyl 1-[(Aminocarbonyl)amino]-6a-hydroxy-
2-methyl-6,6a-dihydro-1H-thieno[3,4-b]pyrrole-3,3a(4H)-dicarboxyl-
ate (4a): Yield 242.0 mg (70%), obtained as white solid, m.p. 174–
[a] Isolated yields based on starting DDs 1.
176 °C. IR (nujol): ν
= 3426, 3351, 3304, 3230, 1733, 1725,
˜
max
1703 cm–1. 1H NMR (400 MHz, CDCl3): δ = 1.20 (t, 3 H, J =
7.2 Hz, OCH2CH3), 2.21 (s, 3 H, CH3), 2.95 (d, 1 H, J = 12.8 Hz,
CHS), 3.00 (d, 1 H, J = 12.8 Hz, CHS), 3.12 (d, 1 H, J = 12.8 Hz,
CHS), 3.70 (s, 3 H, OCH3), 4.02–4.14 (m, 3 H, OCH2CH3 and
CHS), 5.98 and 6.08 (2 br. s, 2 H, NH2), 7.66 (br. s, 1 H, OH), 7.82
(br. s, 1 H, NH) ppm. 13C NMR (100 MHz, CDCl3): δ = 11.7 (q),
14.3 (q), 39.4 (t), 40.1 (t), 52.9 (q), 59.6 (t), 65.3 (s), 102.8 (s), 108.0
(s), 160.8 (s), 161.1 (s), 165.0 (s), 171.7 (s) ppm. MS: m/z (%) = 345
vated methine group of compounds 2a–c to the terminal
carbon atom of the azo-ene system of 1 with formation of
the non-isolable hydrazone intermediates 3 (Scheme 3). The
subsequent regioselective 5-exo cyclization that converts 3
into the final products 4a–m provides a further conjugate
nucleophilic attack of the hydrazone sp2-nitrogen atom to
the oxo function derived from the starting heterocycles 2.
This process is due to the base-promoted loss of the hydro- (12) [M+], 327 (15), 298 (7), 268 (100), 252 (12), 239 (14), 222 (27),
209 (21), 197 (24), 180 (22), 164 (26), 152 (25), 136 (35).
C13H19N3O6S (345.37): calcd. C 45.21, H 5.54, N 12.17; found C
45.32, H 5.49, N 12.24.
gen atom originally located in 4-position of the azo-ene sys-
tem, activated by the presence of electron-withdrawing
groups in α-position such as ester and hydrazone groups.
Data for Diethyl 1-[(Aminocarbonyl)amino]-5-(2-furylmethyl)-6a-
hydroxy-2-methyl-6-oxo-4,5,6,6a-tetrahydropyrrolo[3,4-b]pyrrole-
3,3a(1H)-dicarboxylate (4f): Yield 257.5 mg (59 %), obtained as
Conclusions
white solid, m.p. 142–144 °C. IR (nujol): ν
= 3457, 3293, 3205,
˜
max
An efficient domino one-pot methodology toward
chemoselective syntheses of 1H-thieno[3,4-b]pyrrolines 4a–
e, 6-oxo-pyrrolo[3,4-b]pyrrolines 4f–i, and pyrrolo[3,2-c]-
pyridines 4j–m by starting from DDs 1 and heterocycles
1
1749, 1721, 1689 cm–1. H NMR (400 MHz, CDCl3): δ = 1.17 (t,
3 H, J = 7.2 Hz, OCH2CH3), 1.25 (t, 3 H, J = 7.2 Hz, OCH2CH3),
2.28 (s, 3 H, CH3), 4.04–4.19 (m, 4 H, 2 OCH2CH3), 4.21–4.26 (m,
2 H, NCH2), 4.33 (d, 1 H, J = 11.6 Hz, NCH2furyl), 4.55 (d, 1 H,
containing an activated methine group 2 has been devel- J = 11.2 Hz, NCH2furyl), 5.64 (br. s, 1 H, NH2), 6.24 (d, 1 H, J =
3.2 Hz, furyl), 6.30 (dd, 1 H, J = 3.2 Hz, J = 2.0 Hz, furyl), 7.25
(br. s, 1 H, NH2), 7.35 (dd, 1 H, J = 1.6 Hz, J = 1.2 Hz, furyl),
8.39 (br. s, 1 H, OH), 9.68 (br. s, 1 H, NH) ppm. 13C NMR
(100 MHz, CDCl3): δ = 11.8 (q), 14.1 (q), 14.3 (q), 39.7 (t), 51.3
(t), 57.1 (s), 59.4 (t), 61.6 (t), 95.2 (s), 100.2 (s), 109.3 (s), 110.7 (d),
143.1 (d), 148.4 (d), 160.3 (s), 162.9 (s), 164.7 (s), 167.9 (s), 168.3
(s) ppm. MS: m/z (%) = 420 (4), 393 (10), 327 (12), 302 (17), 268
(100), 252 (18), 225 (45), 210 (43), 197 (44), 164 (57), 136 (67).
C19H24N4O8 (436.41): calcd. C 52.29, H 5.54, N 12.84; found C
52.38, H 5.57, N 12.75.
oped. This transformation proceeds by a Michael addition/
5-exo cyclization sequence. The obtained products represent
interesting scaffolds deployed with a variety of functional
groups as potential pharmacophores (ester, hydroxy, carba-
mate, urea etc.) that may exhibit enzyme or receptor-based
activity. All these reactions proceed under mild conditions
by using easily available starting materials without compli-
cated workup procedures.
Data for 3-Ethyl 3a-Methyl 1-[(Aminocarbonyl)amino]-5-benzyl-7a-
hydroxy-2-methyl-1,4,5,6,7,7a-hexahydro-3aH-pyrrolo[3,2-c]pyrid-
ine-3,3a-dicarboxylate (4j): Yield 285.5 mg (66%), obtained as
Experimental Section
General Procedure for the Synthesis of 6a-Hydroxy-6,6a-dihydro-
1H-thieno[3,4-b]pyrrole-3,3a(4H)-dicarboxylates 4a–e, 5-(2-Furyl-
methyl)-6a-hydroxy-6-oxo-4,5,6,6a-tetrahydropyrrolo[3,4-b]pyrrole-
3,3a(1H)-dicarboxylates 4f–i, and 5-Benzyl-7a-hydroxy-1,4,5,6,7,7a-
hexahydro-3aH-pyrrolo[3,2-c]pyridine-3,3a-dicarboxylates 4j–m: To
a magnetically stirred solution of DDs 1a–g (1.0 mmol) as a mix-
ture of (E)/(Z) isomers[17] and methyl 4-oxotetrahydrothiophene-3-
white solid, m.p. 142–144 °C. IR (nujol): ν
= 3457, 3345, 3189,
˜
max
1
1749, 1725, 1689 cm–1. H NMR (400 MHz, CDCl3): δ = 1.11 (t,
3 H, J = 7.2 Hz, OCH2CH3), 1.23–1.41 (m, 2 H, NCH2CH2), 1.88
(d, 1 H, J = 12.0 Hz, NCH2C), 2.18 (s, 3 H, CH3), 2.51–2.63 (m,
2 H, NCH2CH2), 2.79 (br. s, 1 H, OH), 3.46 (d, 1 H, J = 11.6 Hz,
NCH2C), 3.56 (s, 2 H, NCH2Ph), 3.71 (s, 3 H, OCH3), 4.11 (q, 2
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Fused Heterocycles from 1,2-Diaza-1,3-dienes
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H, J = 7.2 Hz, OCH2CH3), 5.66 (br. s, 2 H, NH2), 7.21–7.36 (m, 6
H, Ph and NH) ppm. 13C NMR (100 MHz, CDCl3): δ = 13.3 (q),
13.7 (q), 29.5 (t), 52.1 (q), 57.1 (t), 58.2 (t), 59.4 (s), 60.2 (t), 61.9
(t), 93.7 (s), 106.0 (s), 126.9 (d), 127.9 (d), 128.7 (d), 127.9 (s), 128.7
(d), 137.9 (s), 158.7 (s), 160.2 (s), 164.8 (s), 172.1 (s) ppm. MS: m/z
(%) = 432 (2) [M+], 414 (30), 373 (20), 355 (100), 342 (73), 310 (12),
295 (18), 249 (25), 224 (78), 205 (41), 191 (78), 178 (50), 164 (42),
148 (36), 118 (90). C21H28N4O6 (432.27): calcd. C 58.32, H 6.53, N
12.96; found C 58.23, H 6.56, N 13.03.
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Acknowledgments
This work was supported by the financial assistance from the Min-
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Received: March 10, 2011
Published Online: April 20, 2011
Eur. J. Org. Chem. 2011, 2924–2927
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