An Atom-Economical Approach to Conformationally Constrained Tricyclic Nitrogen Heterocycles via Sequential and Tandem Ugi/Intramolecular Diels-Alder Reaction of Pyrrole

Article abstract of DOI:10.1021/jo030231z

An efficient approach to rigid tricyclic nitrogen heterocycles via sequential and tandem Ugi/intramolecular Diels-Alder (IMDA) cycloaddition of pyrrole is described. The one-pot Ugi four-component condensation (4CC) reaction was used as the key transforma

Full text of DOI:10.1021/jo030231z

An Atom -Econ om ica l Ap p r oa ch to Con for m a tion a lly Con str a in ed
Tr icyclic Nitr ogen Heter ocycles via Sequ en tia l a n d Ta n d em
Ugi/In tr a m olecu la r Diels-Ald er Rea ction of P yr r ole1,2
K. Paulvannan*,†
Affymax Research Institute, 3410 Central Expressway, Santa Clara, California 95051
kpaulvannan@sunesis.com
Received J uly 17, 2003
An efficient approach to rigid tricyclic nitrogen heterocycles via sequential and tandem Ugi/
intramolecular Diels-Alder (IMDA) cycloaddition of pyrrole is described. The one-pot Ugi four-
component condensation (4CC) reaction was used as the key transformation to prepare trienes
with a carboxamide substituent on the tether. The use of acrylic acid (21) and N-propyl- and N-ben-
zylmaleamic acids (24b and 24C) as the acid components provided trienes 22, 25b, and 25c,
respectively, which upon heating at 120 °C for 12 h yielded the corresponding [4 + 2] cycloaddition
products. In the case of maleic acid derivative 24a , heating the reaction mixture at 60 °C for 6 h
promoted the cycloaddition reaction and provided the desired product 26a in 78% yield. In contrast,
fumaric acid monoethyl ester (27a ) and 3-acetyl- and 3-(4-methylbenzoyl) acrylic acids (27b-c)
directly yielded the corresponding Ugi/IMDA cycloaddition products 29a -c in high yields at room
temperature without any trace of initially formed trienes 28a -c. The IMDA cycloaddition reactions
proceed with excellent stereoselectivity with the formation of five stereogenic centers and three
rings.
In tr od u ction
benzylfurfurylamine 1 with fumaric anhydride 2 (Scheme
1).4a Acylation of amine 1 with anhydride 2 initially pro-
vided triene 3, which immediately underwent IMDA cy-
cloaddition to provide tricyclic compound 4 at room tem-
perature. As an extension of this work, we set out to ex-
amine the intramolecular Diels-Alder reaction employ-
ing pyrrole as a diene partner to prepare tricyclic mole-
cules possessing a 7-azabicyclo[2,2,2]hept-2-ene moiety.
Although significant progress has been recorded on the
intermolecular Diels-Alder cycloaddition reaction of
The intramolecular Diels-Alder (IMDA) [4 + 2] cy-
cloaddition reaction employing a cyclic diene partner has
been established as a powerful synthetic tool for the con-
struction of tricyclic ring system in a stereo- and regio-
controlled manner3 and has been widely used in the prep-
aration of a wide range of carbocyclic and heterocyclic
compounds. Furan is one of the commonly used electron-
rich diene partners known to undergo IMDA cycloaddi-
tion reaction with various alkene dienophiles to provide
molecules with a 7-oxabicyclo[2.2.1]hept-2-ene (7-oxanor-
bornene) ring system.4 Recently, we reported a one-pot
approach to tricyclic compound 4 via acylation of N-
(4) (a) Paulvannan, K.; J acobs, J . W. Tetrahedron 1999, 55, 7433.
(b) Paulvannan, K.; Chen, T.; J acobs, J . W. Synlett 1999, 1609. (c) Akai,
S.; Naka, T.; Omura, S.; Tanimoto, K.; Imanishi, M.; Takebe, Y.;
Matsugi, M. Kita, Y. Chem. Eur. J . 2002, 8, 4255. (d) Mance, A. D.;
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Heterocycl. Chem. 1997, 34, 1315. (e) Hudlicky, T.; Butora, G.;
Fearnley, S. P.; Gum, A. G.; Persichini, P. J ., III; Stabile, M. R.; Merola,
J . S. J . Chem. Soc., Perkin Trans. 1 1995, 2393. (f) Pedrosa, R.; Andres,
C.; Nieto, J . J . Org. Chem. 2000, 65, 831. (g) J acobi, P. A.; Li, Y. J .
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B.; Satake, K.; Wu, T. J . Org. Chem. 1999, 64, 3595. (i) Padwa, A.;
Brodney, M. A.; Lynch, S. M. J . Org. Chem. 2001, 66, 1716. (j) Padwa,
A.; Straub, C. S. J . Org. Chem. 2003, 68, 227. (k) Claeys, S.; Van Haver,
D.; De Clercq, P. J .; Milanesio, M.; Viterbo, D. Eur. J . Org. Chem. 2002,
1051. (l) Lee, M.; Moritomo, H.; Kanematsu, K. Tetrahedron 1996, 52,
8169. (m) Padwa, A.; Ginn, J . D.; Bur, S. K.; Eidell, C. K.; Lynch, S.
M. J . Org. Chem. 2002, 67, 3412. (n) Parker, K. A.; Adamchuk, M. R.
Tetrahedron Lett. 1978, 19, 1689. (o) Zylber, J .; Tubul, A,; Brun, P.
Tetrahedron: Asymmetry 1995, 6, 377. (p) J ung, M. E.; Street, L. J . J .
Am. Chem. Soc. 1984, 106, 8327. (q) J ung, M. E.; Kiankarimi, M. J .
Org. Chem. 1998, 63, 2968. (r) Rogers, C.; Keay, B. A. Can. J . Chem.
1993, 71, 611. (s) Hunt, I. R.; Rauk, A.; Keay, B. A. J . Org. Chem.
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1982, 23, 303. (u) Sternbach, D. D.; Rossana, D. M.; Onan, K. D. J .
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dron Lett. 1988, 29, 2493.
† Current address: Sunesis Pharmaceuticals, Inc., 341 Oyster Point
Blvd, South San Francisco, CA 94080.
(1) Dedicated to all the employees who worked at Affymax Research
Institute, 3410 Central Expressway, Santa Clara, CA 95051.
(2) Presented at The First International Conference on Multi-
Component Reactions, Combinatorial and Related Chemistry, Oct 5,
2000, Munich.
(3) For reviews on Diels-Alder reaction, see: (a) Petrzilka, M.;
Grayson, J . I. Synthesis 1981, 753. (b) Pindur, U.; Lutz, G.; Otto, C.
Chem. Rev. 1993, 93, 741. (c) Cycloaddition Reactions in Organic
Synthesis; Kobayashi, S., J orgensen, K. A., Eds.; Wiley-VCH: Wein-
heim, 2002. (d) Carruthers, W. Cycloaddition Reactions in Organic
Synthesis; Tetrahedron Organic Chemistry Series; Pergamon Press:
New York, 1990; Vol. 8. (e) Fringuelli, F.; Taticchi, A. The Diels-Alder
Reaction: Selected Practical Methods; J ohn Wiley & Sons: New York,
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A. G. Can. J . Chem. 1984, 62, 183. (h) Ciganek, E. Org. React. 1984,
32, 1. (i) Craig, D. Chem. Soc. Rev. 1987, 16, 187. (j) Lipshutz, B. H.
Chem. Rev. 1986, 86, 795. (k) Kappe, C. O.; Murphree, S. S.; Padwa,
A. Tetrahedron 1997, 53, 14179. (l) Vogel, P.; Cossy, J .; Plumet, J .;
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Gasparini, F.; LeDrain, C. Synlett 1990, 173. (n) Chiu, P.; Lautens,
M. In Topics in Current Chemistry; Metz, P., Ed.; Springer-Verlag:
Berlin, 1997; Vol. 190, pp 1-85.
10.1021/jo030231z CCC: $27.50 © 2004 American Chemical Society
Published on Web 01/27/2004
J . Org. Chem. 2004, 69, 1207-1214
1207

Paulvannan
SCHEME 1
SCHEME 3
SCHEME 2
SCHEME 4
N-protected pyrroles,5,6 IMDA cycloaddition reactions
employing pyrrole as a diene partner have received very
little attention. Furthermore, in comparison to the nu-
merous work reported on IMDA reaction of furan only a
few reports describing IMDA cycloaddition of pyrrole
have appeared,7,8 which may be due to the aromatic
character of the pyrrole ring (resonance energy: pyrrole
) 21 kcal mol-1; furan ) 16 kcal mol-1).9 The first
example of IMDA cycloaddition of pyrrole was reported
by the J ung group (Scheme 2).7 Acylation of 1-hydroxy-
pyrrole (5) with fumaroyl chloride 6 provided triene 7,
which upon heating provided the tricyclic compound 8.
Later, Takayama and co-workers reported the prepara-
tion of azanorbonanes 11a and 11b via IMDA cycload-
dition of pyrrole followed by SO2 extrusion (Scheme 3).8
Despite the great potential of the IMDA reaction of
pyrrole to prepare polycyclic nitrogen heterocycles, the
synthetic usefulness of IMDA reaction of pyrrole has not
been fully exploited. Herein, we disclose our effort on the
preparation of novel tricyclic molecules possessing a
7-azabicyclo[2.2.1]hept-2-ene ring system via IMDA reac-
tion employing pyrrole as a diene partner.
Resu lts a n d Discu ssion
The amine prepared from aldehyde 14 and amine 15a
was chosen as the initial test substrate for our IMDA
cycloaddition study (Scheme 4). Condensation of aldehyde
14, prepared from 12 and 13, with benzylamine 15a
followed by reduction of the imine 16a with sodium
triacetoxyborohydride (Na(OAc)3BH) provided amine 17a.
Acylation of the crude amine 17a with anhydride 2 gave
triene 18a as the only product in 69% overall yield for a
two-step reaction sequence. Upon heating in toluene at
80 °C for 15 h, triene 18a underwent the IMDA cycload-
dition to provide the desired tricylic compound 19a as a
single diastereoisomer in quantitative yield. Compound
19a was fully characterized by 1H and 13C NMR and mass
spectrometry. The relative trans stereochemistry at C-3
(5) (a) Drew, M. G. B.; George, A. V.; Isaacs, N. S.; Rzepa, H. S. J .
Chem. Soc., Perkin Trans. 1 1985, 1277. (b) Keijsers, J .; Hams, B.;
Kruse, C.; Scheeren, H. Heterocycles 1989, 29, 79. (c) Saito, K.; Ito, K.;
Takahashi, K. Heterocycles 1989, 29, 2135. (d) Bennes, R.; Babiloni,
M. S.; Hayes, W.; Philp, D. Tetrahedron Lett. 2001, 42, 2377. (e) Sha,
C.-K.; Chuang, K.-S.; Young, J .-J . J . Chem. Soc., Chem. Commun. 1984,
1552. (f) Bansal, R. C.; McCulloch, A. W.; McInnes, A. G. Can. J . Chem.
1969, 47, 2391. (g) Rajakumar, P.; Kannan, A. Ind. J . Chem. 1993,
32B, 1275. (h) Bansal, R. C.; McCulloch, A. W.; McInnes, A. G. Can.
J . Chem. 1970, 48, 1472. (i) Ando, K.; Kankake, M.; Suzuki, T.;
Takayama, H. J . Chem. Soc., Chem. Commun. 1992, 1100. (j) Alten-
bach, H.-J .; Bleck, B.; Marco, J . A.; Vogel, E. Angew. Chem., Int. Ed.
Engl. 1982, 21, 778. (k) Chen, Z.; Trudell, M. L. Tetrahedron Lett. 1994,
35, 9649. (l) Zhang, C.; Trudell, M. L. Tetrahedron 1998, 54, 8349. (m)
Zhang, C.; Ballay, C. J ., II; Trudell, M. L. J . Chem. Soc., Perkin Trans.
1 1999, 675. (n) Singh, S.; Basmadjian, G. P. Tetrahedron Lett. 1997,
38, 6829. (o) J ones, C. D.; Simpkins, N. S.; Giblin, G. M. P. Tetrahedron
Lett. 1998, 39, 1021.
(6) For review on cycloaddition reaction of pyrrole diene, see: Chen,
Z.; Trudell, M. L Chem. Rev. 1996, 96, 1179.
(7) J ung, M. E.; Rohloff, J . C. J . Chem. Soc., Chem. Commun. 1984,
630.
(8) Suzuki, T.; Takayama, H. J . Chem. Soc., Chem. Commun. 1995,
807.
(9) (a) Smith, M. B.; March, J . Advanced Organic Chemistry
Reactions, Mechanisms, and Structure; J ohn Wiley & Sons: New York,
2001. (b) J oule, J . A.; Mills, K. Heterocyclic Chemistry; Blackwell
Sciences: 2001. (c) J ones, R. A.; Bean, G. P. The Chemistry of Pyrroles;
Academic Press, Inc.: New York, 1977; pp 256-264.
and C-4 of 19a was assigned based on the vicinal coupling
1
constant of H3 and H4 in the H NMR spectrum (J 3,4
)
4.1 Hz). It is also interesting to mention that the
examination of the 1H NMR spectrum and LCMS of
triene 18a obtained at various time intervals over a
period of 10 weeks clearly indicated that triene 18a was
slowly undergoing the cycloaddition reaction when stored
at room temperature to give the cycloadduct 19a . How-
ever, storing the triene 18a at lower temperatures (<0
°C) slowed the rate of the cycloaddition and only a trace
of the cycloaddition product formation was detected by
1H NMR even after several weeks.
To examine the influence of a sterically bulky N-
substituent on the cycloaddition reaction, triene with an
1208 J . Org. Chem., Vol. 69, No. 4, 2004

Conformationally Constrained Tricyclic Nitrogen Heterocycles
SCHEME 5
SCHEME 6
SCHEME 7
N-isopropyl substituent was prepared (Schemes 4 and 5).
The presence of a bulky N-isopropyl substituent in 18b
was expected to increase the steric hindrance and simul-
taneously bring both the diene and dienophile closer to
promote the cycloaddition under milder reaction condi-
tions compared to the triene 18a with a N-benzyl sub-
stituent. Treatment of crude amine 17b with anhydride
2 yielded triene 18b and cycloadduct 19b in 74% and 6%
yields, respectively. Heating the triene 18b in toluene
at 65 °C for 12 h promoted the cycloaddition and
furnished compound 19b as a single isomer in quantita-
tive yield. When stored at room temperature, similar to
triene 18a , triene 18b slowly (>8 weeks) undergoes
IMDA cycloaddition to give the cyclized product 19b.
Comparison of the temperatures required to promote the
cycloaddition reaction of trienes 18a and 18b (80 °C for
18a and 65 °C for 18b) clearly indicate that the presence
of a N-isopropyl substituent slightly enhanced the rate
of the cycloaddition reaction of triene 18b compared to
that of the triene 18a with a N-benzyl group.
Having studied the cycloaddition reaction of pyrrole
with N-benzyl and N-isopropyl trienes, attention was
then turned to examine the impact of a substituent on
the tether connecting the pyrrole diene and dienophile
on the cycloaddition reaction. The J ung group and other
research groups4p-w previously reported that a substitu-
ent on the tether accelerated the rate of IMDA cycload-
dition due to the “internal angle compression effect”4q by
bringing the diene and dienophile somewhat closer
compared to a similar system with no substituent on the
tether. Encouraged by the above reports and to examine
the internal angle compression effect in our system, we
proceeded to prepare trienes with a carboxamide sub-
stituent on the tether using the one-pot Ugi four-
component condensation reaction (4CC).10,11 The one-pot
Ugi 4CC approach would provide triene with a carboxa-
mide substituent on the tether in a single step and
eliminate the need for a reductive amination and acyla-
tion reaction sequence.
used as the solvent. Stirring a mixture of aldehyde 14,
benzylamine (15a ), benzyl isocyanide (20), and acrylic
acid (21) in MeOH at room temperature for 36 h provided
triene 22 as a 74:26 mixture of amide rotational isomers
in 80% combined yield (Scheme 6). Heating triene 22 in
DMSO at 120 °C for 12 h promoted the cycloaddition and
yielded the desired tricyclic lactam 23 as a single dias-
tereoisomer in 98% yield.
Encouraged with these results, we next examined the
influence of electronically and geometrically different
dienophile acids 24a -c and 27a -c on the Ugi/ IMDA
reaction sequence (Schemes 7 and 8). Condensation of
doubly activated dienophile acid 24a with aldehyde 14,
amine 15a , and isocyanide 20 in MeOH at room temper-
ature provided the Ugi/IMDA reaction product 26a as a
(11) Four-component condesation: (a) J anvier, P.; Sun, X.; Bi-
enayme, H.; Zhu, J . J . Am. Chem. Soc. 2002, 124, 2560. (b) Nixey, T.;
Kelly, M.; Hulme, C. Tetrahedron Lett. 2000, 41, 8729. (c) Floyd, C.
D.; Harnett, L. A.; Miller, A.; Patel, S.; Saroglou, L.; Whittaker, M.
Synlett 1998, 637. (d) Park, S. J .; Keum, G.; Kang, S. B.; Koh, H. Y.;
Kim, Y.; Lee, D. H. Tetrahedron Lett. 1998, 39, 7109. (e) Kompa, C.
H.; Ugi, I. Tetrahedron Lett. 1998, 39, 2725. (f) Bienayme, H.; Bouzid,
K. Tetrahedron Lett. 1998, 39, 2735. (g) Hulme, C.; Morrissette, M.
M.; Volz, F. A.; Burns, C. J . Tetrahedron Lett. 1998, 39, 1113. (h) Pitlik,
J .; Townsend, C. A. Bioorg. Med. Chem. Lett.1997, 7, 3129. (i) Short,
K. M.; Ching, B. W.; Mjalli, A. M. M. Tetrahedron 1997, 53, 6653. (j)
Ugi, I.; Demharter, A.; Horl, W.; Schmid, T. Tetrahedron 1996, 52,
11657. (k) Keating, T. A.; Armstrong, R. W. J . Org. Chem. 1996, 61,
8935. (l) Failli, A.; Immer, H.; Gotz, M. Can. J . Chem. 1979, 57, 3257.
(m) Paulvannan, K. Tetrahedron Lett. 1999, 40, 1851. (n) Lee, D.; Sello,
J . K.; Schreiber, S. L. Org. Lett. 2000, 2, 709.
Our initial optimization study was carried out using
acrylic acid (21) as the acid component and MeOH was
(10) For reviews on multi-component condensation reactions, see:
(a) Ugi, I.; Lohberger, S.; Karl, R. The Passerini and Ugi Reactions.
In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I.,
Heathcock, C., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, pp 1083-
1109. (b) Ugi, I.; Domling, A.; Horl, W. Endeavour 1994, 18, 115. (c)
Armstrong, R. W.; Combs, A. P.; Tempest, P. A.; Brown, S. D.; Keating,
T. A. Acc. Chem. Res. 1996, 29, 123. (d) Domling, A. Curr. Opin. Chem.
Biol. 2002, 6, 306. (e) Bienayme, H.; Hulme, C.; Oddon, G.; Schmitt,
P. Chem. Eur. J . 2000, 6, 3321. (f) Weber, L. Curr. Med. Chem. 2002,
9, 1241. (g) Zhu, J . Eur. J . Org. Chem. 2003, 1133.
J . Org. Chem, Vol. 69, No. 4, 2004 1209

Paulvannan
SCHEME 8
F IGURE 1. Chem3D representation of the X-ray crystal
structure of 29a .
single diastereoisomer, albeit only in 27% yield after a
tedious chromatographic purification due to unreacted
starting materials and unidentified impurities. Recovery
of the unreacted aldehyde 14 clearly revealed that there
was incomplete imine formation, which is a key step in
the Ugi reaction. In an alternative approach, the imine
16a , prepared from aldehyde 14 and amine 15a was
dissolved in MeOH and allowed to react with isocyanide
20 and dienophile acid 24a to undergo the Ugi/IMDA
reaction sequence (Scheme 7). Examination of the 1H
NMR of an aliquot of the crude reaction mixture indicated
the presence of a 1:1 mixture of triene 25a and the
desired cycloaddition product 26a and the triene 25a was
present as a 81:19 mixture of amide rotational isomers.
The reaction mixture was heated at 60 °C for 6 h in order
to drive the cycloaddition reaction to completion. The
above approach (preformed imine and heating) sup-
pressed the side product formation and yielded the
cycloaddition product 26a as a single isomer in 78% yield.
The cycloaddition reaction of triene 25a proceeded with
excellent control of diastereoselectivity and no trace of
minor isomer was detected. This is the first reported
example of IMDA reaction employing pyrrole as a diene
partner to undergo IMDA cycloaddition under mild
reaction conditions (rt to 60 °C) without the use of any
Lewis acids or higher temperatures and pressures. The
relative cis stereochemistry at C-3 and C-4 of 26a was
assigned based on the vicinal coupling constant of H3 and
H4 in the 1H NMR spectrum (J 3,4 ) 9.9 Hz), and the
relative stereochemistry of compound 26a was assigned
based on the X-ray crystal structure of compound 29a .
Reaction of electronically different maleamic acids 24b
and 24c with imine 16a and isocyanide 20 provided only
trienes 25b and 25c as 81:19 and 80:20 mixture of amide
rotational isomers in 70% and 80% yields, respectively
(Scheme 7). No expected cycloaddition products 26b and
26c were detected in the reaction mixture, which could
be attributed to the fact that an amide group is less
electron withdrawing than an ester group that makes
maleamic acids 24b and 24c poor dienophiles compared
to the dienophile acid 24a . Hence, the reaction stopped
at the Ugi reaction stage to yield only the trienes 25a
and 25b without further undergoing the IMDA cycload-
dition. However, heating the trienes 25b and 25c in
DMSO at 120 °C for 10 h promoted the cycloaddition to
give the corresponding tricyclic products 26b and 26c,
respectively, as single isomers (Scheme 7). Comparison
of the above results clearly indicate that the success of
the IMDA cycloaddition reaction of a pyrrole diene
tethered to a dienophile partner depends on the nature
of the electron-withdrawing substituent at the â-position
of the dienophile acid (ester vs amide substituent).
In contrast to dienophile acids 24a -c with Z-geometry,
condensation of fumaric acid monoethyl ester (27a ) with
imine 16a and isocyanide 20 in MeOH provided the
corresponding Ugi/IMDA reaction product 29a as a single
isomer in 72% yield. No trace of the presumed triene
intermediate 28a was detected in the reaction mixture,
1
as judged by the H NMR spectrum of the crude reaction
mixture, which clearly indicated that the triene 28a
containing a dienophile with E-geometry underwent the
IMDA cycloaddition reaction faster than the triene 24a
containing dienophile with Z-geometry. The relative
trans stereochemistry at C-3 and C-4 of 29a was assigned
on the basis of the vicinal coupling constant of H3 and
H4 in the 1H NMR spectrum (J 3,4 ) 4.0 Hz). Our attempts
to determine the relative stereochemistry of the carbox-
amide substituent at C-9 stereocenter of 29a using
1
various H NMR experiments met with failure. However,
the structure of the compound 29a was unambiguously
assigned based on the single-crystal X-ray analysis.
Figure 1 shows the chem.3D representation of the X-ray
crystal structure of compound 29a . Comparison of the
temperatures required to effect the IMDA cycloaddition
reactions of trienes 18a and 28a (80 °C for 18a and room
temperature for 28a (Schemes 5 and 8) clearly indicates
that the presence of a carboxamide substituent on the
tether influences the triene 28a to undergo IMDA cy-
clization at room temperature. The Ugi/ IMDA reaction
can be conveniently carried out on a multigram scale to
afford compound 29a in synthetically useful yield (>65%).
In the case of large-scale synthesis, removal of the solvent
followed by a diethyl ether wash and MeOH trituration
provided compound 29a in analytically pure form. To the
best of our knowledge, this is the first example of
1210 J . Org. Chem., Vol. 69, No. 4, 2004

Conformationally Constrained Tricyclic Nitrogen Heterocycles
SCHEME 9
stereocontrolled construction of conformationally rigid
tricyclic molecule with five stereocenters from readily
available achiral starting materials under mild reaction
conditions via Ugi 4CC and IMDA cycloaddition of
pyrrole in a tandem fashion.12,13 Since all the atoms,
except one water molecule, of the reactants were incor-
porated into the final product in a regio- and stereocon-
trolled manner, this tandem Ugi 4CC/ IMDA cycloaddi-
tion approach is an excellent illustration for Trost’s “atom
economy” concept.14 Similar to furmaric acid derivative,
condensation of trans-3-acetyl- and 3-(4-methylbenzoy-
l)acrylic acids (27b,c) with imine 16a and isocyanide 20
readily furnished the corresponding cycloaddition prod-
ucts 29b and 29c as single diastereoisomers in 75% and
66% yields, respectively (Scheme 8). In general, reactions
involving doubly activated dienophile acids with trans
geometry were remarkably clean and provided the de-
sired Ugi/ IMDA cycloaddition products in good yields.
To demonstrate the versatility and to expand the
synthetic scope of the sequential and tandem Ugi/ IMDA
reaction strategy, the reaction was next examined using
propiolic acid (30) as the acid component (Scheme 9).15
Stirring a mixture of acid 30, imine 16a , and isocyanide
20 in MeOH at room temperature for 36 h provide the
triene 31 as the Ugi condensation product as a 57:43
mixture of amide rotational isomers in 85% yield (Scheme
9). The structure of the triene 31 was unambiguously
confirmed by the characteristic chemical shifts of the
alkyne carbons in the 13C NMR spectrum (major isomer,
76.4 and 82.5 ppm; minor isomer, 75.8 and 83.2 ppm).
The isomeric mixture of triene 31 in toluene was heated
at 110 °C for 18 h to promote the triene to undergo
cycloaddition reaction. To our disappointment, under the
reaction conditions, no desired tricyclic lactam 32 was
isolated. Instead, isoindolone 33 was isolated in 65%
yield. Presumably, the initially formed rigid cycloaddition
product 32, rearranges to a bicyclic compound at higher
temperature via a sequential ring-opening/aromatization
pathway.16 The structure of compound 33 was deter-
mined on the basis of 1H and 13C NMR spectra. The
presence of an additional broad singlet (sulfonamide
proton) at 11.5 ppm and the disappearance of the vinylic
protons in the NMR spectrum clearly indicated the
absence of the tricyclic ring skeleton. This synthetic
approach could be used as a complementary route to the
currently existing routes to isoindolones.
A recent report from the Schreiber group11n led us to
initiate a synthetic effort to further elaborate compound
29a into a tetracyclic compound 37 using a ring opening
and ring closing metathesis (RORCM)17,18 reaction se-
quence. The proposed synthetic approach to compound
37 is shown in Scheme 10. Hydrolysis of ester 29a
followed by coupling with amine 15a gave amide 35 in
58% overall yield for two steps. To our disappointment,
allylation of amide 35 under various reaction conditions
failed to yield pure bis-allyl compound 36. When the
impure bis-allyl compound 36 was subjected to the
RORCM reaction following Schreiber’s reaction condi-
tions using Grubb’s second-generation catalyst19 no de-
sired tetracyclic product 37 was detected by LCMS. At
this point, we strongly believe that the incompatibility
of 2-nitrophenylsulfonyl protecting group (Ns) and the
bases used in the allylation reaction may have attributed
for the failure to isolate the pure bis-allyl compound.20
We are currently examining alternative synthetic routes
to bis-allyl compound 36, and our results will be reported
in due course.
(12) For reviews on tandem reactions, see: (a) Tietze, L. F.; Haunert,
F. In Stimulating Concepts in Chemistry; Vogtle, F., Stoddart, J . F.,
Shibasaki, M., Eds.; Wiley-VCH: Weiheim, 2000; pp 39-64. (b) Bunce,
R. A. Tetrahedron 1995, 51, 13103. (c) Ho, T. L. Tandem Organic
Reactions; Wiley: New York, 1992. (d) Waldmann, H. In Domino
Reactions in Organic Synthesis Highlight II; Waldmann, H., Ed.;
VCH: Weinheim, 1995; pp 193-202. (e) Wender, P. A., Ed. Frontiers
in Organic Synthesis. Chem. Rev. 1996, 96, 1-600. (f) Neuschutz, K.;
Velker, J .; Neier, R. Synthesis 1998, 227. (g) Heathcock, C. H. Angew.
Chem., Int. Ed. Engl. 1992, 31, 665. (h) Padwa, A. In Topics in Current
Chemistry; Metz, P., Ed.; Springer-Verlag: Berlin, 1997; Vol. 189, pp
21-158.
(13) (a) Paulvannan, K.; Hale, R.; Mesis, R.; Chen, T. Tetrahedron
Lett. 2002, 43, 203. (b) Nair, V.; Sreekanth, A. R.; Abhilash, N.;
Bhadbhade, M. M.; Gonnade, R. C. Org. Lett. 2002, 4, 3575. (c) Padwa,
A.; Diana, M. D.; Hardcastle, K. I.; McClure, M. S. J . Org. Chem. 2003,
68, 929. (d) Denmark, S. E.; Gomez, L. Org. Lett. 2001, 3, 2907. (e)
Neuschutz, K.; Simone, J .-M.; Thyrann, T.; Neier, R. Helv. Chim. Acta
2000, 83, 2712. (f) Shindo, M.; Fukuda, Y.-I.; Shishido, K. Tetrahedron
Lett. 2000, 41, 929. (g) Brosius, A. D.; Overman, L. E.; Schwink, L. J .
Am. Chem. Soc. 1999, 121, 700. (h) Ruel, R.; Deslongchamps, P. Can.
J . Chem. 1992, 70, 1939. (i) Ruggeri, R. B.; Hansen M. M.; Heathcock,
C. H. J . Am. Chem. Soc. 1988, 110, 8734. (j) Ihara, M.; Taniguchi, T.;
Makita, K.; Takano, M.; Ohnishi, M.; Taniguchi, N.; Fukumoto, K.;
Kabuto, C. J . Am. Chem. Soc. 1993, 115, 8107. (k) Grigg, R.; Sridharan,
V.; Suganthan, S.; Bridge, A. W. Tetrahedron 1995, 51, 295.
(14) For reviews on atom-economy, see: (a) Trost, B. M. Acc. Chem.
Res. 2002, 35, 695. (b) Trost, B. M. Angew. Chem., Int. Ed. 1995, 34,
259. (c) Trost, B. M. Science 1991, 254, 1471.
(16) For similar transformations, see: (a) J eevanandam, A.; Srini-
vasan, P. C. J . Chem. Soc., Perkin Trans. 1 1995, 2663. (b) Sha, C.;
Chuang, K.; Wey, S. J . Chem. Soc., Perkin Trans. 1 1987, 977.
(17) For reviews on olefin metathesis, see: (a) Trnka, T. M.; Grubbs,
R. H. Acc. Chem. Res. 2001, 34, 18. (b) Roy, R.; Das, S. K. Chem.
Commun. 2000, 519. (c) Furstner, A. Angew. Chem., Int. Ed. 2000,
39, 3012. (d) Yet, L. Chem. Rev. 2000, 100, 2963. (e) Wright, D. L.
Curr. Org. Chem. 1999, 3, 211. (f) Phillips, A. J .; Abell, A. D. Aldrichim.
Acta 1999, 32, 75.
(18) For recent applications of RCM-ROM, see: (a) Mehta, G.
Nandakumar, J . Tetrahedron Lett. 2002, 43, 699. (b) Lee, C. W.; Choi,
T.-L.; Grubbs, R. H. J . Am. Chem. Soc. 2002, 124, 3224. (c) Buschmann,
N.; Ruckert, A.; Blechert, S. J . Org. Chem. 2002, 67, 4325. (d) Blechert,
S.; Stapper, C. Eur. J . Org. Chem. 2002, 2855. (e) Stragies, R.; Blechert,
S. J . Am. Chem. Soc. 2000, 122, 9584. (f) Voigtmann, U.; Blechert, S.
Org. Lett. 2000, 2, 3971. (g) Stragies, R.; Blechert, S. Tetrahedron 1999,
55, 8179. (h) Stragies, R.; Blechert, S. Synlett, 1998, 169.
(19) (a) Scholl, M.; Ding, S.; Lee, C. W.; Grubbs, R. H. Org. Lett.
1999, 1, 953. (b) Chatterjee, A. K.; Grubbs, H. Org. Lett. 1999, 1, 1751.
(c) Huang, J .; Stevens, E. D.; Nolan, S. P.; Petersen, J . L. J . Am. Chem.
Soc. 1999, 121, 2674. (d) Scholl, M.; Trnka, T. M.; Morgan, J . P.;
Grubbs, R. H. Tetrahedron Lett. 1999, 40, 2247.
(15) For similar reaction with furaldehyde, see: Wright, D. L.;
Robotham, C. V.; Aboud, K. Tetrahedron Lett. 2002, 43, 943.
J . Org. Chem, Vol. 69, No. 4, 2004 1211

Paulvannan
SCHEME 10 a
Gen er a l P r oced u r e for th e P r ep a r a tion of Com p ou n d s
19a a n d 19b. Rep r esen ta tive P r oced u r e for Com p ou n d
19b. To a solution of aldehyde 14 (3.0 g, 10.68 mmol, 1 equiv)
in TMOF (55 mL) was added isopropylamine (15b) (0.7 g, 11.74
mmol, 1.1 equiv), and the reaction mixture was stirred at room
temperature for 24 h. Removal of TMOF under vacuum gave
the crude imine 16b, which was used in the next step without
further characterization. To a solution of imine 16b in dichlo-
roethane (DCE, 55 mL) were added Na(OAc)3BH (3.4 g, 16.02
mmol, 1.5 equiv) and HOAc (1.6 mL), and the reaction was
stirred at rt. After 1 h, solvent was removed, and the residue
was carefully neutralized with saturated aqueous NaHCO3 and
extracted with EtOAc (2 × 150 mL). The combined organic
layer was dried (MgSO4) and evaporated to give the crude
amine 17b. To a solution of the crude amine 17b (10.68 mmol,
1.0 equiv) in CH2Cl2 (30 mL) were added DIEA (2.10 g, 16.02
mmol, 1.5 equiv), fumaric anhydride (12.82 mmol,1.2 equiv)
in CH2Cl2 (20 mL), and DMAP (cat.), and the reaction mixture
was stirred at rt for 10 h. The reaction mixture was washed
saturated aqueous NaHCO3 and 10% HCl, dried (MgSO4), and
evaporated to give a residue, which was purified to give triene
18b (3.6 g, 74%). A solution of triene 18b (100 mg) in toluene
was heated at 65 °C for 12 h. Evaporation of the solvent
provided compound 19b in quantitative yield.
a
Reagents and conditions: (a) LiOH, THF/H2O, rt, 10 h; (b)
DIC, BnNH2, DMAP DMF; (c) LHMDS, allyl bromide, -78 °C,
THF.
1
Com p ou n d 18a : H NMR (CDCl3) (mixture of isomers) δ
1.29 (t, J ) 7.1 Hz, 3H), 4.25 (m, 2H), 4.59 (s, 1H), 4.63 (s,
2H), 4.70 (s, 1H), 6.18 (b, 1H), 6.32 (dt, J ) 15.2, 4.4 Hz, 0.5
H), 6.36 (dt, J ) 15.2, 4.4 Hz, 0.5 H), 6.86 (d, J ) 15.2 Hz, 0.5
H), 6.90 (d, J ) 15.2 Hz, 0.5 H), 7.08-7.36 (m, 8H), 7.65-7.82
(m, 2H), 7.86-7.91 (m, 1H); 13C NMR (CDCl3) (mixture of
isomers) δ 14.5, 43.2, 45.1, 49.5, 51.5, 61.5, 61.6, 112.3, 112.7,
114.2, 115.1, 124.9, 125.1, 125.6, 125.9, 126.7, 128.0, 128.2,
128.3, 128.5, 128.9, 129.0, 129.2, 130.4, 131.1, 132.7, 133.0,
133.1, 133.2, 133.4, 133.6, 133.8, 135.1, 135.4, 135.8, 136.4,
147.4, 165.4, 165.5, 165.6; MS (EI) m/z 498 (M+).
Con clu sion s
In summary, the preparation of rigid tricyclic nitro-
gen heterocyles via sequential and tandem 4CC/IMDA
reaction employing pyrrole as a diene partner is described.
The key to the success of the Ugi/ IMDA cycloaddition
strategy is the selection of N-protected pyrrole aldehyde
and activated dienophile acid as the aldehyde and acid
components, respectively. The attractive feature of this
approach is the stereocontrolled generation of five ste-
reocenters, including a quaternary center, and two rings
in a single chemical transformation from readily avail-
able achiral starting materials. Considering the mild
reaction conditions, and convergent and stereochemical
control associated with the Ugi/IMDA cycloaddition reac-
tion sequence, we strongly believe that this methodology
will find widespread use in organic synthesis for the
preparation of polycylic drug- and natural product-like
molecules. Furthermore, this study represents a promis-
ing starting point for further expansion of the relatively
unexplored IMDA cycloaddition reaction employing pyr-
role as a diene partner in organic synthesis.
1
Com p ou n d 18b: H NMR (CDCl3) (mixture of isomers) δ
1.07 (d, J ) 6.8 Hz, 3H), 1.22 (d, J ) 6.8 Hz, 3H), 1.28 (t, J )
6.8 Hz, 1.5H), 1.33 (t, J ) 6.8 Hz, 1.5 H), 4.19 (q, J ) 6.8 Hz,
1 H), 4.27 (q, J ) 6.8 Hz, 1H), 4.49 (s, 1H), 4.54 (s, 1H), 4.85
(m, 1H), 6.09 (d, J ) 1.6 Hz, 0.5 H), 6.18 (d, J ) 1.6 Hz, 0.5
H), 6.31 (t, J ) 3.4 Hz, 0.5 H) 6.35 (t, J ) 3.4 Hz, 0.5 H), 6.73
(d, J ) 15.6 Hz, 0.5 H), 6.85 (d, J ) 15.2 Hz, 0.5 H), 6.97 (d,
J ) 15.2 Hz, 1H), 7.14 (dd, J ) 7.2, 1.6 Hz, 1H), 7.22 (b, 0.5
H), 7.29 (b, 0.5 H), 7.47 (d, J ) 15.6 Hz, 0.5 H), 7.74 (m, 1H),
7.83 (m, 1H), 7.96 (m, 1H); 13C NMR (CDCl3) (mixture of
isomers) δ 14.1, 14.2, 20.0, 21.2, 38.8, 40.7, 46.4, 49.7, 61.0,
61.2, 112.3, 112.5, 113.1, 114.6, 123.5, 124.5, 125.4, 125.7,
128.3, 128.7, 131.1, 132.2, 132.8, 133.3, 133.4, 133.5, 133.7,
133.8, 134.1, 134.4, 134.5, 135.0, 165.0, 165.2, 165.6; MS (EI)
m/z 450 (M+).
Com p ou n d 19a : 1H NMR (CDCl3) δ 1.28 (t, J ) 7.0 Hz,
3H), 2.96 (d, J ) 4.1 Hz, 1H), 3.6 (t, J ) 4.3 Hz, 1H), 3.78 (d,
J ) 14.5 Hz, 1H), 3.89 (d, J ) 12.5 Hz, 1H), 4.16 (m, 2H), 4.21
(d, J ) 12.5 Hz, 1H), 4.95 (d, J ) 14.5 Hz, 1H), 5.22 (dd, J )
4.3, 2.0 Hz, 1H), 6.04 (dd, J ) 5.8, 2.0 Hz, 1H), 6.39 (d, J )
5.8 Hz, 1H), 7.23-7.37 (m, 5H), 7.65-7.76 (m, 3H), 7.91 (dd,
J ) 7.8, 1.4 Hz, 1H); 13C NMR (CDCl3) δ 14.6, 44.1, 47.4, 47.6,
54.8, 62.0, 67.1, 77.5, 124.9, 128.2, 128.5, 129.2, 131.0, 132.6,
132.9, 133.4, 135.0, 136.1, 136.2, 148.3, 170.1, 171.5; MS (EI)
m/z 498 (M+).
Com p ou n d 19b: 1H NMR (CDCl3) δ 0.88 (d, J ) 6.9 Hz,
3H), 1.16 (d, J ) 6.9 Hz, 3H), 1.28 (t, J ) 7.0 Hz, 3H), 2.92 (d,
J ) 4.1 Hz, 1H), 3.56 (dd, J ) 4.1, 4.2 Hz, 1H), 3.88 (d, J )
12.5 Hz, 1H), 4.16 (q, J ) 7.0 Hz, 2H), 4.30 (d, J ) 12.5 Hz,
1H), 4.34 (m, 1H), 5.20 (b, 1H), 6.04 (d, J ) 5.6 Hz, 1H), 6.48
(d, J ) 5.6 Hz, 1H), 7.65-7.73 (m, 3H), 7.99 (m, 1H); 13C NMR
(CDCl3) δ 14.5, 19.5, 20.3, 42.4, 43.2, 43.8, 55.3, 61.9, 67.4,
77.4, 124.9, 130.9, 132.6, 133.1, 134.8, 136.4, 148.2, 170.2,
170.5; MS (EI) m/z 450 (M+).
Exp er im en ta l Section
Ald eh yd e 14. To a solution of pyrrole-2-carboxaldehyde (12)
(20.00 g, 210.30 mmol, 1.1 equiv) in CH2Cl2 (750 mL) were
added TEA (29.00 g, 286.77 mmol, 1.5 equiv), 2-nitroben-
zenesulfonyl chloride (13) (42.40 g, 191.18 mmol, 1.0 equiv),
and DMAP (cat), and the reaction mixture was stirred at rt
for 15 h. Solvent was removed, and the residue was purified
by column chromatography (CH2Cl2/EtOAc) to give aldehyde
14 (42.3 g, 79%): 1H NMR (DMSO-d6) δ 6.67 (t, J ) 3.3 Hz,
1H), 7.49 (dd, J ) 3.3, 1.8 Hz, 1H), 7.86 (m, 1H), 7.92 (td, J )
7.7, 1.1 Hz, 1H), 8.01 (m, 2H), 8.13 (dd, J ) 7.7, 1.1 Hz, 1H),
9.55 (s, 1H); 13C NMR (DMSO-d6) δ 112.7, 125.3, 129.1, 130.2,
131.0, 131.6, 133.2, 133.3, 136.3, 147.2, 178.2; MS (EI) m/z 281
(M+).
(20) (a) Sinhababu, A. K.; Borchardt, R. T. J . Org. Chem. 1983, 48,
1941. (b) Ng, F. W.; Lin, H.; Danishefsky, S. J . J . Am. Chem. Soc.
2002, 124, 9812. (c) Buck, P.; Kobrich, G. Tetrahedron Lett. 1967, 8,
1563.
Com p ou n d 23. To a solution of aldehyde 14 (500 mg, 1.79
mmol, 1.0 equiv) in MeOH (15 mL) were added amine 15a (190
mg, 1.79 mmol, 1 equiv), isocyanide 20 (210 mg, 1.79 mmol, 1
1212 J . Org. Chem., Vol. 69, No. 4, 2004

Conformationally Constrained Tricyclic Nitrogen Heterocycles
equiv), and acid 21 (130 mg, 1.79 mmol, 1 equiv), and the
reaction mixture was stirred at rt for 36 h. Evaporation of the
solvent followed by column chromatography purification (EtOAc/
hexane) provided the triene 22 (800 mg, 80% yield). Heating
a solution of triene 22 (100 mg) in DMSO at 120 °C for 12 h
followed by removal of the solvent gave the cycloaddition
product 23.
1H), 8.56 (t, 6.0 Hz, 1H), 9.33 (t, J ) 6.4 Hz, 1H); 13C NMR
(major) (CDCl3) δ 11.6, 22.6, 41.6, 44.1, 50.4, 55.1, 112.4, 119.7,
125.0, 125.4, 126.2, 126.5, 127.2, 128.0, 128.4, 128.5, 128.6,
129.2, 130.1, 133.2, 133.8, 134.3, 134.8, 136.4, 139.1, 147.3,
164.4, 168.2, 169.6; HRMS (FAB) calcd for C33H34N5O7S (M +
H) 644.2179, found 644.2188.
Com p ou n d 25c: 1H NMR (DMSO-d6) (major isomer) δ
4.18-4.36 (m, 4H), 4.46 (d, J ) 17.6 Hz, 1H), 4.69 (d, J ) 17.6
Hz, 1H), 6.11 (d, J ) 11.7 Hz, 1H), 6.24 (t, J ) 3.5 Hz, 1H),
6.40 (s, 1H), 6.48 (s, 2H), 6.89 (m, 2H), 6.98 (m, 2H), 7.08-
7.32 (m, 12 H), 7.81 (t, J ) 7.7 Hz, 1H), 7.94 (t, J ) 7.7 Hz,
1H), 8.18 (d, J ) 8.0 Hz, 1H), 9.09 (t, J ) 5.5 Hz, 1H), 9.30 (t,
J ) 5.5 Hz, 1H); 13C NMR (CDCl3) (major isomer) δ 43.6, 44.1,
50.4, 55.0, 112.3, 119.5, 124.7, 125.3, 125.6, 126.3, 127.0, 127.5,
127.6, 128.0, 128.2, 128.4, 128.5, 128.6, 129.8, 133.1, 133.5,
133.7, 134.1, 134.7, 136.0, 137.8, 138.8, 146.9, 164.1, 168.0,
169.8; HRMS (FAB) calcd for C37H34N5O7S (M + H) 692.2179,
found 692.2175.
Com p ou n d 31: 1H NMR (DMSO-d6) (mixture of isomers)
δ 4.00-4.31 (m, 3H), 4.36 (d, J ) 17.2 Hz, 0.43H), 4.56 (s,
0.57H), 4.57 (s, 0.43H), 4.70 (d, J ) 17.2 Hz, 0.57H), 4.74 (d,
J ) 17.2 Hz, 0.43H), 4.97 (d, J ) 17.2 Hz, 0.57H), 6.31 (m,
1H), 6.40 (m, 1H), 6.50 (m, 1H), 6.89-7.34 (m, 11H), 7.75 (m,
1H), 7.93 (m, 1H), 8.16 (m, 1H), 8.75 (t, J ) 5.9 Hz, 0.57 H),
8.81 (t, J ) 5.9 Hz, 0.43 H); 13C NMR (mixture of isomers)
(DMSO-d6) δ 42.4, 42.8, 47.0, 50.2, 53.7, 58.7, 75.8, 76.4, 82.5,
83.2, 112.47, 112.5, 118.1, 118.5, 125.5, 125.6, 125.7, 125.8,
126.4, 126.6, 126.7, 126.8, 126.86, 126.9, 127.1, 127.2, 127.3,
127.6, 127.7, 128.0, 128.2, 128.4, 129.5, 130.4, 131.7, 132.0,
133.8, 133.9, 135.8, 136.0, 136.5, 136.9, 138.6, 138.8,146.5,
146.7, 154.1, 154.6, 166.9, 167.2; HRMS (FAB) calcd for
1
Com p ou n d 22: H NMR (DMSO-d6) (mixture of isomers)
δ 3.85-4.31 (m, 3H), 4.58-4.77 (m, 2H), 5.62 (minor) (d, J )
10.4 Hz, 0.26H), 5.68 (major) (d, J ) 10.4 Hz, 0.74H), 5.87-
6.67 (m, 5H), 6.92-7.28 (m, 11H), 7.74 (m, 1H), 7.92 (t, J )
7.7 Hz, 1H), 8.16 (d, J ) 8.1 Hz, 1H), 8.69 (major) (b, 0.76H),
8.77 (minor) (b, 0.24H); 13C NMR (CDCl3) (major isomer) δ
43.7, 49.1, 54.3, 111.8, 119.4, 125.4, 126.1, 127.1, 127.5, 127.6,
128.0, 128.5, 128.7, 130.1, 130.5, 133.3, 135.3, 137.1, 137.9,
147.4, 161.4, 168.0, 168.3; (minor isomer) δ 33.2, 42.1, 60.6,
112, 125.5, 125.6, 127.1, 127.8, 127.9, 128.2, 128.3, 128.6,
128.7, 128.8, 128.9, 130.3, 131.3, 132.6, 132.7, 135.4, 136.7,
137.8, 165.0, 166.1, 172.0; HRMS (FAB) calcd for C29H27N4O6S
(M + H) 559.1651, found 559.1653.
Com p ou n d 23:. 1H NMR (DMSO-d6) δ 1.52 (t, J ) 11.4
Hz, 1H), 2.39 (dt, J ) 11.4, 3.7 Hz, 1H), 2.84 (dd, J ) 9.5, 3.7
Hz, 1H), 4.19 (dd, J ) 14.7, 5.5 Hz, 1H), 4.32 (dd, J ) 14.7,
5.5 Hz, 1H) 4.40 (d, J ) 14.7 Hz, 1H), 4.53 (d, J ) 14.7 Hz,
1H), 4.92 (s, 1H), 4.96 (s, 1H), 6.09 (m, 1H), 6.39 (m, 1H),
7.11 (d, J ) 7.0 Hz, 2H), 7.20 (m, 8 H), 7.55 (d, J ) 7.7 Hz,
1H), 7.64 (m, 1H), 7.85 (d, J ) 7.7 Hz, 1H); 13C NMR (CDCl3)
δ 26.0, 43.7, 47.0, 49.8, 61.3, 65.7, 78.1, 124.1, 127.6, 127.8,
127.9, 128.57, 128.6, 128.7, 131.2, 132.0, 132.4, 132.6, 134.1,
134.7, 135.4, 137.7, 148.0, 167.5, 173.9; HRMS (FAB) calcd
C
29H27N4O6S (M + H) 559.1651, found 559.1664.
P r ep a r a tion of Com p ou n d 26a . To a solution of aldehyde
C
29H25N4O6S (M + H) 557.1497, found 557.1509.
14 (1.0 g, 3.57 mmol, 1 equiv) in benzene (20 mL) was added
benzylamine (15a ) (380 mg, 3.57 mmol, 1 equiv), and the
reaction mixture was stirred at rt for 15 h. Removal of benzene
provided the crude imine 16a . To a solution of the crude imine
16a in MeOH (20 mL) were added isocyanide 20 (420 mg, 3.57
mmol, 1 equiv) and acid 24a (510 mg, 3.57 mmol, 1 equiv),
and the reaction mixture was stirred at room temperature.
After 36 h, the reaction flask was heated at 65 °C for 6 h to
drive the IMDA reaction to completion. Removal of MeOH
provided the crude material, which was purified by column
(CH2Cl2/EtOAc) to give the lactam 26a as a solid (1.75 g, 78%
yield).
Com p ou n d 26a : mp 219-221 °C; 1H NMR (DMSO-d6) δ
1.21 (t, J ) 7.0 Hz, 3H), 2.63 (d, J ) 9.9 Hz, 1H), 3.27 (d, J )
9.9 Hz, 1H), 4.09 (m, 3H), 4.29 (dd, J ) 15.0, 5.9 Hz, 1H), 4.34
(s, 2H), 4.90 (d, J ) 2.2 Hz, 1H), 5.08 (s, 1H), 5.73 (d, J ) 5.5
Hz, 1H), 6.11 (dd, J ) 5.5, 2.2 Hz, 1H), 7.17 (d, J ) 7.0 Hz,
2H), 7.28 (m, 8H), 7.63 (td, J ) 8.0, 1.1 Hz, 1H), 7.87 (td, J )
8.0, 1.1 Hz, 1H), 7.94 (d, J ) 8.0 Hz, 1H), 8.13 (dd, J ) 8.0,
1.1 Hz, 1H), 9.31 (t, J ) 5.9 Hz, 1H); 13C NMR (DMSO-d6) δ
13.9, 41.4, 42.7, 46.0, 52.1, 59.9, 60.3, 67.6, 76.7, 124.3, 127.1,
127.3, 127.5, 127.8, 128.2, 128.4, 130.9, 132.2, 133.1, 135.1,
135.2, 135.8, 138.5, 147.8, 167.1, 170.2, 170.5; HRMS (FAB)
calcd for C32H31N4O8S (M + H) 631.1863, found 631.1880.
Gen er a l P r oced u r e for th e P r ep a r a tion of Tr ien es
25b, 25c, a n d 31. Rep r esen ta tive P r oced u r e for Tr ien e
25c. To a solution of the crude imine 16a (1.63 mmol, 1 equiv),
prepared as before, in MeOH (10 mL) were added benzyl
isocyanide (20) (171 mg, 1.63 mmol, 1 equiv) and N-benzyl-
maleamic acid (24c) (334 mg, 1.63 mmol, 1 equiv), and the
reaction mixture was stirred at room temperature for 36 h.
Removal of MeOH gave the crude material, which was then
purified by column (hexane and EtOAc) to give the triene 25c
as a solid (900 mg, 80%).
Com p ou n d 25b: 1H NMR (DMSO-d6) (major) δ 0.79 (t, J
) 7.3 Hz, 3H), 1.37 (m, 2H), 2.98 (m, 2H), 4.34 (d, J ) 6.4 Hz,
2H), 4.46 (d, J ) 17.2 Hz, 1H), 4.67 (d, J ) 17.2 Hz, 1H), 6.05
(d, J ) 11.7 Hz, 1H), 6.24 (m, 1H), 6.42 (d, J ) 11.7 Hz, 1H),
6.48 (m, 1H), 6.88 (m, 2H), 6.99 (m, 1H), 7.09-7.33 (m, 11H),
7.82 (m, 1H), 7.94 (t, J ) 7.7 Hz, 1H), 8.17 (d, J ) 8.0 Hz,
Gen er a l P r oced u r e for th e P r ep a r a tion of Com p ou n d s
26b a n d 26c. Rep r esen ta tive P r oced u r e for Com p ou n d
26c. A solution of triene 25c (100 mg) in DMSO (10 mL) was
heated at 120 °C for 10 h to undergo IMDA reaction. Evapora-
tion of the solvent provided the lactam 26c (100 mg, 100%
crude yield).
Com p ou n d 26b: 1H NMR (DMSO-d6) δ 0.88 (t, J ) 7.5 Hz,
3H), 1.45 (m, 2H), 2.48 (d, J ) 9.9 Hz, 1H), 3.05 (m, 2H), 3.10
(d, J ) 9.9 Hz, 1H), 4.08 (dd, J ) 14.7, 5.5 Hz, 1H), 4.26 (s,
2H), 4.27 (dd, J ) 14.7, 5.5 Hz, 1H), 4.85 (d, J ) 2.0 Hz, 1H),
4.97 (s, 1H), 5.78 (d, J ) 5.9 Hz, 1H), 6.20 (dd, J ) 5.9, 2.0
Hz, 1H), 7.18 (m, 4H), 7.29 (m, 6H), 7.64 (td, J ) 8.0, 1.1 Hz,
1H), 7.79 (t, J ) 5.5 Hz, 1H), 7.86 (td, J ) 8.0, 1.1 Hz, 1H),
7.94 (dd, J ) 8.0, 1.1 Hz, 1H), 8.33 (dd, J ) 8.0, 1.1 Hz, 1H),
9.25 (t, J ) 5.9 Hz, 1H); 13C NMR (DMSO-d6) δ 11.7, 22.3,
40.4, 40.8, 42.1, 42.6, 45.9, 51.5, 59.7, 68.0, 76.4, 124.1, 126.9,
127.0, 127.3, 127.5, 127.9, 128.1, 130.8, 131.2, 132.0, 133.2,
134.7, 135.5, 135.7, 138.2, 147.4, 166.9, 168.0, 170.5; HRMS
(FAB) calcd for C33H34N5O7S (M + H) 644.2179, found 644.2181.
Com p ou n d 26c: 1H NMR (DMSO-d6) δ 2.57 (d, J ) 9.9 Hz,
1H), 3.14 (d, J ) 9.9 Hz, 1H), 4.08 (dd, J ) 15.0, 5.5 Hz, 1H),
4.28 (m, 4H), 4.41 (dd, J ) 15.0, 5.5 Hz, 1H), 4.89 (d, J ) 1.8
Hz, 1H), 4.97 (s, 1H), 5.79 (d, J ) 5.5 Hz, 1H), 6.23 (dd, J )
5.5, 1.8 Hz, 1H), 7.15-7.36 (m, 12H), 7.39 (d, J ) 7.7 Hz, 1H),
7.64 (t, J ) 7.7 Hz, 1H), 7.86 (t, J ) 7.7 Hz, 1H), 7.94 (d, J )
7.7 Hz, 1H), 8.36 (m, 2H), 9.26 (t, J ) 5.5 Hz, 1H); 13C NMR
(DMSO-d6) δ 42.1, 42.5, 42.6, 45.9, 51.5, 59.7, 68.0, 76.4, 124.1,
126.5, 126.8, 127.0, 127.1, 127.3, 127.5, 127.9, 128.0, 128.1,
130.7, 131.3, 132.0, 133.2, 134.6, 135.6, 138.2, 138.9, 147.4,
166.9, 168.3, 170.6; HRMS (FAB) calcd for C37H34N5O7S (M +
H) 692.2179, found 692.2181.
Gen er a l P r oced u r e for th e P r ep a r a tion of Com p ou n d s
29a -c. Rep r esen ta tive P r oced u r e for La cta m 29a . To a
solution of the crude imine 16a (1.63 mmol, 1 equiv), prepared
as before, in MeOH (10 mL) were added benzyl isocyanide (20)
(171 mg, 1.63 mmol, 1 equiv) and fumaric acid monoethyl ester
(27a ) (235 mg, 1.63 mmol, 1 equiv), and the reaction mixture
was stirred at room temperature for 36 h. Removal of MeOH
J . Org. Chem, Vol. 69, No. 4, 2004 1213

Paulvannan
gave the crude material, which was then purified by column
(EtOAc/hexane) to give the lactam 29a as a solid (720 mg,
72%).
LiOH‚H2O (1.0 g, 23.81 mmol, 3.0 equiv), and the reaction
mixture was stirred at rt for 12 h. THF was removed under
vacuum, and additional H2O (50 mL) was added to the reaction
mixture. The reaction mixture was washed with ether and
then acidified with 10% HCl, and the aqueous layer was
extracted with EtOAc (2 × 150 mL). The combined organic
layer was dried (MgSO4) and evaporated to give the acid 34
(4.8 g, 100%), which was used in the next step without
purification. To a solution of the acid 34 (2.0 g, 3.32 mmol, 1
equiv) in DCM (30 mL) were added amine 15a (430 mg, 3.99
mmol, 1.2 equiv), DIC (503 mg, 3.99 mmol, 1.2 equiv), and
DMAP (cat.), and the reaction mixture was stirred for 12 h.
Solvent was removed, and the reaction mixture was purified
by column chromatography (EtOAc/hexane) to give the amide
35 (1.4 g, 61% yield).
1
Com p ou n d 29a : mp 212-214 °C; H NMR (CDCl3) δ 1.26
(t, J ) 7.0 Hz, 3H), 3.25 (d, J ) 4.0 Hz, 1H), 3.60 (dd, J ) 4.4,
4.0 Hz, 1H), 4.14 (q, J ) 7.0 Hz, 2H), 4.27 (m, 2H), 4.38 (d, J
) 15.0 Hz, 1H), 4.61 (d, J ) 15.0 Hz, 1H), 4.93 (s, 1H), 5.21
(dd, J ) 4.4, 2.0 Hz, 1H), 5.98 (dd, J ) 5.5, 2.0 Hz, 1H), 6.17
(d, J ) 5.5 Hz, 1H), 6.36 (b, 1H), 7.12 (m, 2H), 7.28 (m, 8H),
7.60 (m, 1H), 7.70 (m, 2H), 7.91 (m, 1H); 13C NMR (CDCl3) δ
14.5, 44.1, 44.5, 47.6, 53.7, 61.6, 61.9, 66.9, 78.9, 124.2, 127.8,
127.9, 128.0, 128.7, 128.8, 128.9, 131.3, 132.3, 132.4, 133.1,
134.3, 134.4, 135.1, 137.2, 147.9, 166.9, 169.5, 172.4; HRMS
(FAB) calcd for C32H31N4O8S (M + H) 631.1863, found 631.1874.
Com p ou n d 29b: mp 204-206 °C; 1H NMR (CDCl3) δ 2.26
(s, 3H), 3.12 (d, J ) 4.6 Hz, 1H), 3.62 (t, J ) 4.6 Hz, 1H), 4.29
(d, J ) 5.5 Hz, 2H), 4.49 (s, 2H), 4.89 (s, 1H), 5.12 (m, 1H),
5.99 (dd, J ) 5.9, 1.8 Hz, 1H), 6.05 (d, J ) 5.9 Hz, 1H), 6.59 (t,
J ) 5.5 Hz, 1H), 7.13-7.33 (m, 10H), 7.59 (dd, J ) 7.7, 1.5
Hz, 1H), 7.69 (m, 2H), 7.88 (dd, J ) 7.7, 1.5 Hz, 1H); 13C NMR
(CDCl3) δ 28.9, 44.1, 47.5, 53.0, 53.1, 61.6, 66.7, 78.9, 124.5,
128.0, 128.2, 128.92, 128.94, 129.0, 131.4, 132.5, 132.8, 133.5,
134.0, 134.4, 135.2, 137.3, 147.9, 167.3, 172.7, 204.9; HRMS
(FAB) calcd for C31H29N4O7S (M + H) 601.1757, found 601.1764.
Com p ou n d 34: 1H NMR (DMSO-d6) δ 3.15 (d, J ) 4.4 Hz,
1H), 3.31 (t, J ) 4.4 Hz, 1H), 4.06 (dd, 14.8, 5.6 Hz, 1H), 4.20
(d, J ) 15.2 Hz, 1H), 4.25 (dd, J ) 14.8, 5.6 Hz, 1H), 4.36 (d,
J ) 15.2 Hz, 1H), 4.97 (dd, J ) 4.4, 2.0 Hz, 1H), 5.00 (s, 1H),
5.84 (d, J ) 5.6 Hz, 1H), 6.01 (dd, J ) 5.6, 2.0 Hz, 1H), 7.11-
7.29 (m, 10 H), 7.63 (td, J ) 7.2, 1.2 Hz, 1H), 7.85 (td, J ) 7.2,
1.2 Hz, 1H), 7.93 (d, J ) 7.2 Hz, 1H), 8.08 (dd, J ) 7.2, 1.2 Hz,
1H), 9.26 (t, J ) 5.6 Hz, 1H), 13.0 (b, 1H); 13C NMR (DMSO-
d6) δ:43.3, 44.7, 46.9, 53.8, 61.3, 67.1, 79.0, 125.2, 127.7, 128.0,
128.2, 128.5, 128.9, 129.0, 131.2, 131.4, 133.0, 133.6, 134.6,
136.2, 136.5, 139.0, 148.3, 167.7, 171.5, 172.8; HRMS (FAB)
calcd C30H26N4O8S (M + H) 603.1549, found 603.1550.
Com p ou n d 35: 1H NMR (CDCl3) δ 3.12 (d, J ) 5.1 Hz,
1H), 3.40 (m, 1H), 4.19-4.47 (m, 6H), 4.91 (s, 1H), 5.12 (d, J
) 3.7 Hz, 1H), 6.07 (S, 2H), 6.68 (t, J ) 5.9 Hz, 1H), 6.82 (t, J
) 5.9 Hz, 1H), 7.12-7.31 (m, 15 H), 7.53 (dd, J ) 7.7, 1.5 Hz,
1H), 7.58-7.67 (m, 2H), 7.88 (dd, J ) 7.7, 1.5 Hz, 1H); 13C
NMR (CDCl3) δ 43.9, 44.1, 45.7, 47.3, 55.6, 61.8, 67.4, 78.7,
124.3, 127.5, 127.67, 127.7, 127.8, 127.9, 128.6, 128.7, 128.8,
131.2, 132.3, 132.5, 133.0, 134.1, 134.2, 134.9, 137.2, 137.7,
147.5, 166.9, 169.0, 173.0; HRMS (FAB) calcd C37H33N5O7S (M
+ H) 692.2180, found 692.2178.
1
Com p ou n d 29c: mp 205-208 °C; H NMR (CDCl3) δ 2.40
(s, 3H), 3.35 (d, J ) 4.4 Hz, 1H), 4.10 (dd, J ) 15.0, 5.6 Hz,
1H), 4.29 (dd, J ) 15.0, 5.6 Hz, 1H), 4.34 (d, J ) 15.6 Hz, 1H),
4.38 (t, J ) 4.4 Hz, 1H), 4.43 (d, J ) 15.6 Hz, 1H), 5.11 (s,
1H), 5.12 (dd, J ) 4.4, 1.8 Hz, 1H), 5.77 (d, J ) 5.9 Hz, 1H),
5.94 (dd, J ) 5.9, 1.8 Hz, 1H), 7.16 (d, J ) 8.0 Hz, 1H), 7.24-
7.33 (m, 8H), 7.39 (d, J ) 8.0 Hz, 2H), 7.66 (t, J ) 8.0 Hz,
1H), 7.87 (t, J ) 8.0 Hz, 1H), 7.94 (d, J ) 8.0 Hz, 1H), 8.13
(m, 3H), 9.33 (t, J ) 5.6 Hz, 1H); 13C NMR (CDCl3) 22.0, 44.0,
47.6, 49.2, 53.3, 61.3, 67.9, 79.6, 124.5, 127.9, 128.0, 128.2,
128.9, 129.0, 129.5, 129.8, 131.4, 132.5, 132.8, 132.9, 134.4,
135.2, 135.3, 137.3, 145.2, 147.9, 167.3, 173.1, 196.2; HRMS
(FAB) calcd for C37H33N4O7S (M + H) 677.2070, found 677.2057.
P r ep a r a tion of Com p ou n d 33. Heating a solution of
triene 31 (200 mg) in toluene (20 mL) at 110 °C for 18 h
followed by evaporation of the solvent and purification (EtOAc/
hexane) provided compound 33 (130 mg, 65% yield).
Ack n ow led gm en t. I thank Dr. Ted Baer, Dr. Mike
Needles, Dr. Dennis Solas, Dr. Ron Hale, and Dr.
William Fitch for their helpful suggestions and Ms. Tao
Chen for her contribution to this work. I also thank Dr.
Peter White, Department of Chemistry, University of
North Carolina at Chapel Hill, for obtaining the X-ray
crystal structure.
Com p ou n d 33: 1H NMR (DMSO-d6) δ 3.97 (d, J ) 15.3 Hz,
1H), 4.23 (dd, J ) 15.0, 5.9 Hz, 1H), 4.35 (dd, J ) 15.0, 5.9
Hz, 1H), 4.90 (s, 1H), 5.16 (d, J ) 15.3 Hz, 1H) 7.16-7.44 (m,
13 H), 7.85 (m, 2H), 8.01 (m, 2H), 9.06 (t, J ) 5.9 Hz, 1H),
11.13 (s, 1H); 13C NMR (DMSO-d6) δ 42.5, 44.5, 61.9, 114.1,
123.4, 123.7, 124.6, 126.8, 127.0, 127.3, 127.7, 128.1, 128.5,
129.6, 131.0, 132.2, 132.5, 134.6, 136.2, 137.1, 137.3, 138.4,
147.6, 165.9, 166.9; HRMS (FAB) calcd for C29H25N4O6S (M +
H) 557.1497, found 557.1504.
Su p p or tin g In for m a tion Ava ila ble: Complete X-ray
crystallography data for compound 29a and photocopies of 1H
and 13C NMR spectra. This material is available free of charge
via the Internet at http://pubs.acs.org.
Com p ou n d s 35. To a solution of ester 29a (5.0 g, 7.94
mmol, 1 equiv) in 3:1 THF/H2O (45 mL/15 mL) was added
J O030231Z
1214 J . Org. Chem., Vol. 69, No. 4, 2004