Stereochemistry as a tool in deciphering the processes of a tandem iminium cyclization and smiles rearrangement

Article abstract of DOI:10.1021/jo101798p

To understand the detailed mechanism of a recently reported tandem iminium cyclization and Smiles rearrangement, the reaction processes of a chiral substrate were investigated by monitoring its stereochemical courses. Under the tandem reaction conditions,

Full text of DOI:10.1021/jo101798p

pubs.acs.org/joc
Stereochemistry as a Tool in Deciphering the Processes of a Tandem
Iminium Cyclization and Smiles Rearrangement
Jinbao Xiang, Tong Zhu, Qun Dang,* and Xu Bai*
The Center for Combinatorial Chemistry and Drug Discovery, The School of Pharmaceutical Sciences and
The College of Chemistry, Jilin University, 1266 Fujin Road, Changchun, Jilin 130021, P. R. China
xbai@jlu.edu.cn; qdang@jlu.edu.cn
Received September 13, 2010
To understand the detailed mechanism of a recently reported tandem iminium cyclization and Smiles
rearrangement, the reaction processes of a chiral substrate were investigated by monitoring
its stereochemical courses. Under the tandem reaction conditions, chiral aldehyde 1 derived from
L-prolinol led to two surprising results. First, the iminium cyclization gave a diastereomeric mixture
with the cis-configured product as the predominant one. Second, Smiles rearrangement of both cis-
and trans-2 led to the same product 3a directly derived from the trans isomer. The former was
rationalized by the postulation of a Cram’s chelate transition state leading to the cis product as
kinetically favored. The latter was due to the equilibration between the trans/cis pair involving a
carbocation intermediate and the steric hindrance, which prevented the cis isomer from undergoing
the intramolecular nucleophilic substitution. This hypothesis was further supported by the results of
a competition experiment in which the addition of 1 equiv of p-methoxyaniline in the rearrangement
step led to a significant amount of anilinyl-exchanged rearrangement product.
Introduction
generation of reactions that may be more efficient or
stereospecific.2 Stereochemistry has often been used as a
powerful tool in elucidation of reaction processes.3
Recently, we reported a new tandem reaction entailing an
iminium cyclization followed by a Smiles rearrangement in a
N-pyrrolopyrimidine and analogous systems.4 As depicted
in Scheme 1, the reaction of aldehyde A with a primary amine
yields an exo iminium cyclization product diazepine B under
acidic conditions; subsequently, diazepine B may undergo an
Mechanistic studies have been an important area of
organic chemistry research1-3 which can provide insights
to reaction processes and facilitate the design of the next
ꢀ
ꢀ
ꢀ~
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DOI: 10.1021/jo101798p
r
Published on Web 11/09/2010
J. Org. Chem. 2010, 75, 8147–8154 8147
2010 American Chemical Society

Xiang et al.
JOCArticle
SCHEME 1. Tandem Iminium Cyclization and Smiles Rear-
rangement
acidic silica gel. Therefore, the crude aldehyde 1 was used
immediately for the iminium cyclization reaction without
further purification.
The cyclization reactions of aldehyde 1 with several
anilines under conditions of trifluoroacetic acid-dichlor-
oethane (TFA-Cl(CH2)2Cl) at ambient temperature were
investigated, and the results are summarized in Table 1. In
general, the iminium cyclizations proceeded in good to
excellent yields and with the cis cyclization product being
preferentially produced in most cases. The selectivity for cis
products are more pronounced with electron-rich anilines
(entry 1, Table 1) compared to electron-deficient anilines
(entries 4 and 5, Table 1). It is interesting to note that 24% of
the direct aldehyde cyclization product 6 was isolated when
p-nitroaniline was used, which indicated that the imine
formation reaction is much slower for the electron-deficient
aniline. The chiral aldehyde 1 was then subjected to the
current reaction conditions without an aniline present, which
produced the hydroxydiazepines 6 in excellent yield (entry 6,
Table 1). Moreover, the cyclization of aldehyde 1 was much
more stereoselective than imine cyclization (entry 6 vs entries
1-5, Table 1).
The acid-catalyzed ring closure reactions may be rationa-
lized by a combination of steric and electronic effects in the
two competing transition-state conformations as shown in
Figure 1. First, the pyrimidine (A) and pyrrole (B) rings are
likely to be nonplanar.8 Second, the π-orbitals of the B ring
should be periplanar to the ones of the reacting double
bond (carbonyl or iminium) in order to form a σ bond
(cyclization).9 Third, the approach of B ring to the double
bond should come from the less hindered H-atom side of the
pyrolidine ring (C). Therefore, the approaching direction of
B ring to the double bond was dictated by the configuration
of the stereogenic carbon in the C ring, and the orientation of
the double bond (iminium or carbonyl) could determine the
formation of the trans (Re-face attacked) cyclized product
or cis (Si-face attacked) one. It is postulated that the forma-
tion of a cyclic transition state via intramolecular hydrogen
bond between the pyrrolidinyl nitrogen and the proton of
either protonated imine or aldehyde10 made the Si-face
attack (Figure 1, chelate mode) kinetically favored following
Cram’s rule over the Re-face attack (Figure 1, open mode).
These rationalizations are consistent with the experimental
results. There is less steric hindrance within the cyclic transi-
tion state (via hydrogen bond) for the aldehyde over an
imine, which explains why the cyclization of aldehyde is more
stereoselective than the imine.
intramolecular nucleophilic displacement (Smiles rearrange-
ment) to produce pteridine derivative C. To the best of our
knowledge, this is the first reported cascade of reactions
consisting of both electrophilic cyclization and nucleophilic
substitution in a single molecular system. Although a plau-
sible mechanism was proposed for this reaction in our initial
disclosure,4b details of the reaction processes remained to be
investigated. Thus, further investigation of the reaction
mechanism is warranted. A molecular system with a stereo-
genic center next to the reaction centers in the substrate, was
designed to the study of the tandem reaction process. Herein,
the results of the investigations and rationalizations are
presented.
Results and Discussion
Design of the Molecular System. To study the stereochem-
ical transformations of the current tandem reaction, chiral
substrate 1 derived from L-prolinol was designed (Scheme 2).
Theoretically, aldehyde 1, without racemization, reacts with
an amine to give either trans-diazepine 2a (path a) or cis-2b
(path b) (via an imine intermediate),3a,5 subsequent Smiles
rearrangement of trans-diazepine 2a and cis-2b should form
epimers 3a and 3b, respectively, in an SN2 process. On the
other hand, racemization at either the iminium cyclization
step and/or Smiles rearrangement step would lead to more
complicated stereochemical outcomes in this tandem reac-
tion. Therefore, investigation of the stereochemical transi-
tions in this molecular system should reveal insights to the
reaction processes.
The Iminium Cyclization of Chiral Aldehyde 1 to Diaze-
pines 2. Aldehyde 1 was readily prepared according to
Scheme 3. Substitution of 4,6-dichloro-5-(1H-pyrrol-1-yl)-
pyrimidine 44a with L-prolinol produced intermediate 5 in
high yield, and subsequent Parikh-Doering oxidation of
alcohol 5 provided aldehyde 1.6 Attempted isolation of
aldehyde 1 using silica gel column led to hydroxydiazepines
6 resultimg from an intramolecular attack of the aldehyde by
the pyrrolyl group,4a,7 presumably promoted by the slightly
Do Diazepines 2 Come from Hydroxydiazepines 6 or Imine
Intermediate 7? The ease of self-cyclization of aldehyde 1
raised the question how diazepines 2 were formed. For
example, diazeines 2.4 could be formed from the direct
cyclization of the imine intermediate 7.4 or they could be
produced from the nucleophilic substitution of alcohol 6 by
p-chloroaniline (Scheme 4). Thus, hydroxydiazepines 6 were
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2008, 64, 9101. (c) Xiang, J.; Xie, H.; Wen, D.; Dang, Q.; Bai, X. J. Org.
Chem. 2008, 73, 3281.
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Huff, J. R. Org. Lett. 2000, 2, 3473. (c) Chihab-Eddine, A.; Daıch, A.; Jilale,
A.; Decroix, B. Tetrahedron Lett. 2001, 42, 573. (d) Mecozzi, T.; Petrini, M.;
Profeta, R. Tetrahedron: Asymmetry 2003, 14, 1171. (e) Damon, D. B.;
Dugger, R. W.; Magnus-Aryitey, G.; Ruggeri, R. B.; Wester, R. T.; Tu, M.;
Abramov, Y. Org. Process Res. Dev. 2006, 10, 464.
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Cyvin, S. J.; Samdal, S. J. Mol. Struct. 1985, 128, 59. (b) Tanabe, Y.;
Mizuhata, Y.; Tokitoh, N. Organometallics 2010, 29, 721.
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(b) Kawamoto, T.; Tomimatsu, K.; Ikemoto, T.; Abe, H.; Hamamura, K.;
Takatani, M. Tetrahedron Lett. 2000, 41, 3447.
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(b) Reetz, M. T.; Huellmann, M.; Seitz, T. Angew. Chem., Int. Ed. Engl.
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8148 J. Org. Chem. Vol. 75, No. 23, 2010

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SCHEME 2. Possible Stereochemical Paths in Tandem Iminium Cyclization and Smiles Rearrangement
SCHEME 3. Preparation of Chiral Aldehyde 1
TABLE 1. Cyclization Results (Schemes 2 and 3)
by flash chromatography. The structure of product 2.4b was
unambiguously determined as the cis configuration in the
diazepine ring by an X-ray diffraction analysis (Figure S-18,
Supporting Information).
entry
RNH2
2 or 6
yield (%)
trans/cis
1
2
3
4
5
6
p-MeOPhNH2
p-MePhNH2
PhNH2
p-ClPhNH2
p-NO2PhNH2
2.1
2.2
2.3
2.4
2.5
6
83
85
80
86
69a
86
1:9.1
1:3.7
1:3.2
1:2.1
1:1.0
1:28
Study of the Smiles Rearrangement. If the Smiles rearran-
gement follows the direct SN2 process, compounds 2.4a and
2.4b should yield products 3.4a and 3.4b, respectively
(Scheme 2). However, it is interesting to note that both
2.4a and 2.4b were converted to the same product 3.4a
(small amount of an elimination byproduct 8 was also iso-
lated) in similar yields in a modified rearrangement condition
of TFA/Cl(CH2)2Cl at 60 °C (Scheme 5). The conversion rate
for the trans isomer 2.4a was faster than for the cis isomer
2.4b, while the rate of the trans/cis mixture 2.4 fell between
those of trans-2.4a and cis-2.4b. The rearranged product 3.4a
a24% hydroxydiazepine 6 was also isolated.
1
was determined as the (S,S)-configuration by LC-MS, H
NMR, 13C NMR, and X-ray diffraction (Figure S-45, Sup-
porting Information).
To understand these observations, we examined a molec-
ular model of the isomers trans-2.4a and cis-2.4b. The aniline
moiety of trans-2.4a can readily access to the 6-position of
the pyrimidine nucleus for the Smiles rearrangement reac-
tion, while the steric hindrance (neighboring substituent on
the same side in the 7-membered ring) of the cis isomer 2.4b
prevented the aniline group from attacking the 6-position of
the pyrimidine ring. Therefore, we propose that cis-2.4b must
undergo conversion to the trans isomer 2.4a3c,d,9,11 before
proceeding with the Smiles rearrangement to give 3.4a under
the current reaction conditions. It is further hypothesized
that the conversion of compound 2.4b to compound 2.4a
involved a carbocation intermediate as illustrated in Scheme 6.
FIGURE 1. Transition-state conformations of the cyclization
reaction.
treated with p-chloroaniline for 10 min in TFA/Cl(CH2)2Cl
at room temperature (the exact cyclization condition), but no
diazepines 2.4 were observed, and instead 97% of compound
6 was recovered. Therefore, the results confirmed that dia-
zepines 2.4 were indeed produced via direct cyclization of
imine 7.4, not amine substitution of the hydroxyl group in 6
(Scheme 4).
Determination of the Absolute Configurations of Diazepines
2.4. A pure sample of the major product 2.4b was obtained by
recrystallization, while the minor product 2.4a was purified
(11) (a) Cox, E. D.; Hamaker, L. K.; Li, J.; Yu, P.; Czerwinski, K. M.;
Deng, L.; Bennett, D. W.; Cook, J. M. J. Org. Chem. 1997, 62, 44.
(b) Cabanal-Duvillard, I.; Berrien, J.-F.; Ghosez, L.; Husson, H.-P.; Royer,
J. Tetrahedron 2000, 56, 3763. (c) Cimarelli, C.; Palmieri, G.; Volpini, E.
Tetrahedron 2001, 57, 6089.
J. Org. Chem. Vol. 75, No. 23, 2010 8149

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SCHEME 4. Possible Reactions Leading to Diazepines 2.4
SCHEME 5. Smiles Rearrangement of 2.4
processes. For this reason, the reaction of diazepine 10 with
1 equiv of p-methoxyaniline was performed under the pre-
vious Smiles rearrangement conditions of TFA-DCM at
room temperature. Surprisingly, the reaction produced the
direct rearrangement product 11 in good yield (83%) and
only a trace amount of the anilinyl-exchanged rearrange-
ment product 12 (Scheme 8). This observation indicates that
the Smiles rearrangement of diazepine 10 is more facile than
the formation of the carbocation intermediate. The observed
difference in reactivity between diazepines 10 and 2.4 could
be attributed to the presence of the pyrrolidine moiety in
diazepines 2.4. It is likely that the steric hindrance and struc-
tural rigidity of the pyrrolidine ring slows down the Smiles
rearrangement reaction and diverts the reaction more down
the carbocation path in diazepine 2.4 (Scheme 6).
To further validate the reaction process, aldehyde 1 was
reacted with several aromatic amines under the current tandem
conditions (Scheme 9). In general, anilines with either electron-
withdrawing (Cl) or electron-donating (MeO, Me) groups led
to the desired pteridines 3a in good yields (59-74%). The
slightly higher yield for anilines with an electron-donating
group (MeO, Me) compared to that for p-chloroaniline is
consistent with formation of the imine intermediate as the key
to this tandem iminium cyclization and Smiles rearrangement.
Under the acidic conditions, loss of the aniline group in the cis
isomer 2.4b generates a carbocation 9, which is reassociated
with the aniline group via a SN1 mechanism to give either the
trans isomer 2.4a or the cis isomer 2.4b.3c,d,9,11a Subsequently,
trans isomer 2.4a proceeds to the Smiles rearrangement to give
product 3.4a, which drives the equilibrium to the direction of
2.4a. The small amount of byproduct 8wasformedeitherfrom
loss of a proton from intermediate 9 or direct aniline elimina-
tion of precursors 2.4a and 2.4b.12
Conclusion
To further validate our proposed carbocation process
depicted in Scheme 6, a competition experiment was per-
formed. Thus, the Smiles rearrangement reaction of the
diastereomeric mixture (trans/cis = 1:2.1) 2.4 was carried
out in the presence of 1 equiv of p-methoxyaniline, which
produced a mixture of products 3.4a and 3.1a in a combined
yield of 68% (3.4a:3.1a = 1.25:1) (Scheme 7). The formation
of p-methoxyaniline-incorporated product 3.1a provided the
evidence that the Smiles rearrangement might indeed take
place via carbocation intermediate 9 (the SN2 replacement of
p-chloroanilinyl by p-methoxyanilinyl had been excluded in
the earlier experiment). The significant amount of anilinyl-
exchanged product 3.1a indicated that formation of carbo-
cation 9 could be quite facile under the current rearrange-
ment conditions.
In comparison to our previously reported Smiles rearran-
gement conditions of TFA-dichloromethane (DCM) at
room temperature,4a the moderate elevation of reaction
temperature required for diazepines 2.4 suggested that the
presence of an additional ring in the substrate might increase
the activation energy in the transition state. Consequently,
the change of conditions could lead to the alteration reaction
Mechanistic investigations of the previously communi-
cated tandem iminium cyclization and Smiles rearrangement
reactions4 were carried out using a carefully designed chiral
substrate 1 as a tool. Insights to the mechanism of this
cascade reaction were obtained. First, the cascade reaction
is a highly stereospecific process starting from the homo-
chiral alcohol 5 and ending with a homochiral pteridine
product 3a in 59-74% overall yield for the three steps.
Second, the formation of the kinetically favored cis cycliza-
tion product over the thermodynamically favored trans
cyclization product could be rationalized by the formation
of a Cram’s chelate transition state (via intramolecular
hydrogen bond). Third, the cis-diazepine 2.4b must undergo
equilibration to the trans isomer 2.4a before proceeding to
the Smiles rearrangement reaction, and the equilibration
took place via a carbocation intermediate. Finally, the
Smiles rearrangement of diazepine 10 without the additional
pyrrolidine ring was much faster than the generation of a
carbocation since very little exchange of the anilinyl moiety
in the product was observed. These results reaffirmed the
initially proposed cascade reaction involving an iminium
cyclization followed by Smiles rearrangement in the unique
molecular systems. The knowledge gained in these experi-
ments could be useful in the design of new tandem reaction
sequences for the synthesis of complex organic molecules
from nature or with important biological activities. Further
(12) (a) Koiwa, M.; Hareau, G. P-J.; Morizono, D.; Sato, F. Tetrahedron
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Lett. 1999, 40, 4199. (b) Barluenga, J.;Tomas, M.;Ballesteros, A.;Santamarı
a-Granda, S.; Pinera-Nicolas, A.; Vazquez, J. T. J. Am.
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J.; Brillet, C.; Garcı
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Chem. Soc. 1999, 121, 4516.
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SCHEME 6. Proposed Rearrangement Processes
SCHEME 7. Competition Experiment 1
SCHEME 8. Competition Experiment 2
work is in progress to expand the strategy and methodo-
logy for the asymmetric synthesis of chiral heterocyclic
molecules.
br, broad. Coupling constants (J values) where noted are quoted
in hertz.
(S)-(1-(6-Chloro-5-(1H-pyrrol-1-yl)pyrimidin-4-yl)pyrrolidin-
2-yl)methanol (5). To a stirred solution of 4,6-dichloro-5-(1H-
pyrrol-1-yl)pyrimidine (4) (5.0 g, 23.47 mmol) and L-prolinol
(2.61 g, 25.82 mmol) in n-BuOH (80 mL) was added TEA (4.91
mL, 35.21 mmol). The resulting solution was stirred for 2 h at
reflux. Then n-BuOH was evaporated, and the residue was
diluted with DCM and washed with water. The organic layers
were dried over MgSO4, filtered, and concentrated in vacuo.
Purification by flash column chromatography (petroleum
ether/EtOAc = 4:1 to 2:1, v/v) afforded 6.08 g (93%) of 5 as a
Experimental Section
General Consideration. Dichloromethane (DCM) was dried
with P2O5 and distilled. All other commercial reagents were used
as received without additional purification. The melting point
was uncorrected. Mass spectra and HPLC data were recorded
on a LC/MS system with ELSD. Optical rotations were deter-
1
mined with a digital polarimeter. The H and 13C NMR data
were obtained on a 300 MHz NMR spectrometer with TMS as
the internal standard and CDCl3 as solvent unless otherwise
stated. Multiplicities are indicated as follows: s, singlet; d,
doublet; t, triplet; q, quartet; m, multiplet; dd, doubled doublet;
white solid: mp 84-85 °C; [R]18 -56.0 (c 1.0, CHCl3); 1H
D
NMR δ 8.30 (s, 1H), 6.70 (dd, 2H, J = 4.5, 2.7 Hz), 6.33 (dd, 2H,
J = 4.5, 2.4 Hz), 4.44 (br, 1H), 3.93 (br, 1H), 3.68 (d, 2H, J = 5.7
Hz), 2.93 (t, 2H, J = 6.3 Hz), 1.97-1.69 (m, 4H); 13C NMR δ
J. Org. Chem. Vol. 75, No. 23, 2010 8151

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SCHEME 9. Tandem Reaction of Aldehyde 1 with Anilines
160.0, 158.2, 155.7, 124.9, 124.3, 116.5, 110.0, 109.9, 65.1, 62.6,
45.9, 27.6, 24.5; MS (ESI) m/z 279.1 [M þ Hþ]. Anal. Calcd for
C13H15ClN4O: C, 56.02; H, 5.42; N, 20.10. Found: C, 55.89; H,
5.40; N, 20.10.
isomers of 2.3 to be 1:3.2 (2.3a/2.3b): 1H NMR δ 8.30 (s, 0.31H),
8.28 (s, 1.00H), 7.21-7.11 (m, 3.66H), 7.01-6.99 (m, 0.37H), 6.94
(t, 1.21H, J = 2.4), 6.78-6.64 (m, 5.75H), 6.19 (t, 0.54H, J = 1.5),
4.78 (s, 1.47H), 4.58 (d, 0.44H, J = 8.4), 4.09 (dd, 1.55H, J = 10.5,
5.4), 4.00-3.70 (m, 4.77H), 2.37-2.28 (m, 0.81H), 2.22-2.00 (m,
6.42H), 1.95-1.72(m,4.66H);MS(ESI) m/z352.1 [M þ Hþ].Anal.
Calcd for C19H18ClN5: C, 64.86; H, 5.16; N, 19.91. Found: C, 64.78;
H, 5.15; N, 19.83.
General Procedure for the Synthesis of Pyrimido[4,5-b]di-
pyrrolo[1,2-d:10,20-g][1,4]diazepin-9-amine (2). (S)-(1-(6-Chloro-5-
(1H-pyrrol-1-yl)pyrimidin-4-yl)pyrrolidin-2-yl)methanol (5) (139
mg, 0.50 mmol) in 6 mL of DMSO-DCM (1:1) was treated with
TEA (0.703 mL, 5.0 mmol). A solution of SO3-pyridine (481 mg,
3.0 mmol) in 4 mL of DMSO-DCM (3:1) was added, and the
mixture was stirred for 35 min at ambient temperature. The reaction
solution was then diluted with DCM (20 mL), washed twice with
10% citric acid and brine, dried over MgSO4, filtered, and concen-
trated in vacuo to give crude aldehyde 1. The crude 1 was dissolved
in Cl(CH2)2Cl (18 mL). To the resulting solution was added the
appropriate amine (0.6 mmol) followed by TFA (78 μL, 1.05 mmol).
The mixture was stirred for 10 min at room temperature, washed
with saturated aqueous Na2CO3, dried over MgSO4, and concen-
trated in vacuo. Purification by flash chromatography (petroleum
ether/EtOAc = 4:1 to 2:1, v/v) afforded the desired product 2.
(9aS)-4-Chloro-N-(4-methoxyphenyl)-9a,10,11,12-tetrahydro-
9H-pyrimido[4,5-b]dipyrrolo[1,2-d:10,20-g][1,4]diazepin-9-amine
(9aS)-4-Chloro-N-(4-chlorophenyl)-9a,10,11,12-tetrahydro-9H-
pyrimido[4,5-b]dipyrrolo[1,2-d:10,20-g][1,4]diazepin-9-amine (2.4).
Yield: 86%. 1H NMR (2.4a/2.4b, 8.30 ppm/8.27 ppm) indicated
the ratio of two isomers of 2.4 to be 1:2.1 (2.4a/2.4b): 1H NMR δ
8.30 (s, 0.48H), 8.27 (s, 1.00H), 7.14-7.05 (m, 3.77H), 7.03-6.99
(m, 0.60H), 6.93 (t, 1.14H, J=2.4 Hz), 6.66-6.51 (m, 4.22H),
6.23-6.16 (m, 3.24H), 6.01 (t, 0.62H, J = 1.8 Hz), 4.72 (d, 1.34H,
J = 5.7 Hz), 4.52 (t, 0.62H, J=9.0 Hz), 4.18-4.02 (m, 1.60H),
4.01-3.67 (m, 5.61H), 3.48 (d, 1.13H, J = 6.0 hz), 2.38-1.71 (m,
8.94H); MS (ESI) m/z 385.9 [M þ Hþ]. Anal. Calcd for C19H17-
Cl2N5: C, 59.08; H, 4.44; N, 18.13. Found: C, 58.94; H, 4.43; N,
18.05. A pure sample of major product 2.4b was obtained by
recrystallization from i-PrOH while the one of the minor product
2.4a was purified by flash chromatography (petroleum ether/
EtOAc=20:1 to 15:1, v/v). (9S,9aS)-4-Chloro-N-(4-chlorophenyl)-
9a,10,11,12-tetrahydro-9H-pyrimido[4,5-b]dipyrrolo[1,2-d:10,20-g]-
1
(2.1). Yield: 83%. H NMR (2.1a/2.1b, 8.29 ppm/8.27 ppm)
indicated the ratio of the two isomers of 2.1 to be 1:9.1 (2.1a/
1
2.1b): H NMR δ 8.29 (s, 0.11H), 8.27 (s, 1.00H), 6.99 (dd,
[1,4]diazepin-9-amine (2.4a): mp 79-82 °C; [R]23 þ83.6 (c 1.0,
D
0.10H, J=4.5, 1.5 Hz), 6.93 (dd, 1.35H, J=2.7, 1.5 Hz), 6.79-
6.58 (m, 8.90H), 6.21-6.13 (m, 3.21H), 6.06-6.04 (m, 0.08H),
4.67 (s, 1.67H), 4.46 (d, 0.05H, J = 7.8 Hz), 4.09-4.04 (m,
1.70H), 3.90-3.84 (m, 3.50H), 3.75 (s, 1.23H), 3.73 (s, 0.39H),
3.71 (s, 4.66H), 2.36-2.28 (m, 0.13H), 2.18-2.04 (m, 5.79H),
1.95-1.79 (m, 2.40H); MS (ESI) m/z 382.1 [M þ Hþ]. Anal.
Calcd for C20H20ClN5O: C, 62.91; H, 5.28; N, 18.34. Found: C,
63.17; H, 5.30; N, 18.29.
(9aS)-4-Chloro-N-(4-methylphenyl)-9a,10,11,12-tetrahydro-
9H-pyrimido[4,5-b]dipyrrolo[1,2-d:10,20-g][1,4]diazepin-9-amine (2.2).
Yield: 85%. 1H NMR (2.2a/2.2b, 8.29 ppm/8.27 ppm) indicated the
ratio of the two isomers of 2.2 to be 1:3.7 (2.2a/2.2b):1HNMRδ8.29
(s, 0.27H), 8.27 (s, 1.00H), 7.00-6.93 (m, 5.34H), 6.62-6.54 (m,
3.81H), 6.20-6.15 (m, 3.17H), 6.05-6.04 (m, 0.23H), 4.73 (s,
1.53H), 4.53 (d, 0.26H, J = 8.7), 4.07 (dd, 1.63H, J = 10.2, 5.7),
3.91-3.68 (m, 4.38H), 2.35-2.25 (m, 0.74H), 2.23 (s, 1.13H), 2.20
(s, 4.52H), 2.18-1.99 (m, 5.42H), 1.89-1.79 (m, 2.19H); MS (ESI)
m/z 366.1 [M þ Hþ]. Anal.Calcd for C20H20ClN5: C, 65.66; H, 5.51;
N, 19.14. Found: C, 65.55; H, 5.49; N, 19.08.
CHCl3); 1H NMR δ 8.30 (s, 1H), 7.14-7.10 (m, 2H), 7.01 (dd, 1H,
J = 2.7, 1.8 Hz), 6.64-6.59 (m, 2H), 6.20 (t, 1H, J = 3.3 Hz), 6.02
(d, 1H, J = 3.3 Hz), 4.52 (t, 1H, J = 9.0 Hz), 4.00-3.70 (m, 4H),
2.32-2.28 (m, 1H), 2.05-2.01 (m, 1H), 1.85-1.72 (m, 2H); 13
C
NMR δ 154.2, 153.9, 152.6, 145.3, 135.0, 129.2, 124.5, 123.1,
115.3, 114.9, 109.0, 105.5, 69.8, 53.9, 51.4, 32.5, 22.0; MS (ESI) m/z
386.1 [M þ Hþ]. Anal.Calcd for C19H17Cl2N5: C, 59.08; H, 4.44;
N, 18.13. Found: C, 58.87; H, 4.46; N, 18.09. (9R,9aS)-4-Chloro-
N-(4-chlorophenyl)-9a,10,11,12-tetrahydro-9H-pyrimido[4,5-b]-
dipyrrolo[1,2-d:10,20-g][1,4]diazepin-9-amine (2.4b): mp 171-
172 °C; [R]23D þ348.8 (c 1.0, CHCl3); 1H NMR δ 8.27 (s, 1H),
7.07 (d, 2H, J = 8.7), 6.93 (s, 1H), 6.57 (d, 2H, J = 8.7), 6.19 (d,
2H, J=1.8), 4.72 (d, 1H, J = 7.2), 4.11-4.06 (m, 1H), 3.90-3.85
(m, 2H), 3.47 (d, 1H, J=6.9), 2.20-1.83 (m, 4H); 13C NMR δ
154.1, 153.4, 152.0, 145.2, 133.0, 128.9, 125.0, 123.3, 115.7, 115.3,
109.0, 108.7, 66.7, 52.2, 51.4, 31.5, 22.2; MS (ESI) m/z 386.0
[M þ Hþ]. Anal. Calcd for C19H17Cl2N5: C, 59.08; H, 4.44; N,
18.13. Found: C, 58.98; H, 4.43; N, 18.08. Further recrystalliza-
tion of compound 2.4b by slow evaporation from DCM/MeOH
afforded a colorless crystal for X-ray diffraction analysis (see the
CIF in the Supporting Information).
(9aS)-4-Chloro-N-phenyl-9a,10,11,12-tetrahydro-9H-pyrimido-
[4,5-b]dipyrrolo[1,2-d:10,20-g][1,4]diazepin-9-amine (2.3).Yield: 80%.
1H NMR (2.3a/2.3b, 8.30 ppm/8.28 ppm) indicated the ratio of two
8152 J. Org. Chem. Vol. 75, No. 23, 2010

Xiang et al.
JOCArticle
(9aS)-4-Chloro-N-(4-nitrophenyl)-9a,10,11,12-tetrahydro-9H-
pyrimido[4,5-b]dipyrrolo[1,2-d:10,20-g][1,4]diazepin-9-amine (2.5).
Yield: 69%. 1H NMR (2.5a/2.5b, 8.31 ppm/8.28 ppm) indicated
the ratio of two isomers of 2.5 to be 1:1.0 (2.5a/2.5b): 1H NMR δ
8.31 (s, 1.00H), 8.28 (s, 1.00H), 8.10 (d, 2.77H, J = 9.0 Hz), 8.04
(d, 2.68H, J = 9.0 Hz), 7.05-7.04 (m, 1.18H), 6.98-6.96 (m,
1.21H), 6.70-6.64 (m, 6.32H), 6.31-6.29 (m, 1.47H), 6.24-6.20
(m, 2.77H), 6.02-6.01 (m, 1.63H), 4.88 (d, 1.29H, J = 6.3 Hz),
4.71-4.69 (m, 3.12H), 4.30 (d, 1.37H, J = 7.2Hz), 4.16-4.11 (m,
1.74H), 4.02-3.89 (m, 6.72H), 3.77 (dd, 2.28H, J = 12.3, 7.6
Hz), 2.34-2.22 (m, 4.00H), 2.12-1.80 (m, 13.63H); MS (ESI)
m/z 397.1 [M þ Hþ]. Anal. Calcd for C19H17ClN6O2: C, 57.51;
H, 4.32; N, 21.18. Found: C, 57.44; H, 4.31; N, 21.12.
(9aS)-4-Chloro-9a,10,11,12-tetrahydro-9H-pyrimido[4,5-b]di-
pyrrolo[1,2-d:10,20-g][1,4]diazepin-9-ol (6). (S)-(1-(6-Chloro-
5-(1H-pyrrol-1-yl)pyrimidin-4-yl)pyrrolidin-2-yl)methanol (5)
(139 mg, 0.50 mmol) in 6 mL of DMSO-DCM (1:1) was
treated with TEA (0.703 mL, 5.0 mmol). A solution of SO3-
pyridine (481 mg, 3.0 mmol) in 4 mL of DMSO-DCM (3:1)
was added, and the mixture was stirred for 35 min at ambient
temperature. The reaction solution was then diluted with
DCM (20 mL), washed twice with 10% citric acid and brine,
dried over MgSO4, filtered, and concentrated in vacuo to give
crude aldehyde 1. The crude 1 was dissolved in Cl(CH2)2Cl
(18 mL). To the above solution was added TFA (78 μL, 1.05
mmol). The mixture was stirred for 20 min at ambient tem-
perature, washed with saturated aqueous Na2CO3, dried over
MgSO4, and concentrated in vacuo. Purification by flash
chromatography (petroleum ether/EtOAc = 4:1 to 2:1, v/v)
afforded 4 mg (3%) of compound 6a and 114 mg (83%) of
compound 6b.
7.42 (d, 2H, J = 8.7 Hz), 7.36 (d, 2H, J = 8.7 Hz), 6.43 (t, 1H,
J = 3.3 Hz), 6.14-6.13 (m, 1H), 4.79 (d, 1H, J = 4.2 Hz),
3.58-3.52 (m, 1H), 2.74-2.69 (m, 1H), 2.38-2.33 (m, 1H),
1.84-1.74 (m, 1H), 1.54-1.41 (m, 4H); 13C NMR δ 154.2,
151.6, 142.4, 140.6, 132.8, 129.6, 128.9, 125.4, 120.0, 118.2,
111.5, 107.1, 63.5, 61.4, 46.7, 29.0, 25.9; MS (ESI) m/z 386.0
[M þ Hþ]. Compound 2.4 (2.4a/2.4b = 1:2.1) as starting mate-
rial: 3.4a, 69%; mp 110-112 °C; [R]21D þ405.6 (c 1.0, CHCl3);
1H NMR δ 8.09 (s, 1H), 7.97 (dd, H, J = 3.0, 1.5 Hz), 7.42 (d,
2H, J = 8.7 Hz), 7.36 (d, 2H, J = 9.0 Hz), 6.43(t, 1H, J=3.3 Hz),
6.13 (dd, 1H, J = 3.3, 1.2 Hz), 4.79 (d, 1H, J = 4.2 Hz), 3.58-
3.52 (m, 1H), 2.74-2.67 (m, 1H), 2.38-2.31 (m, 1H), 1.83-1.74
(m, 1H), 1.57-1.37 (m, 4H); 13C NMR δ 154.2, 151.6, 142.4,
140.6, 132.8, 129.6, 128.9, 125.3, 120.0, 118.2, 111.5, 107.2, 63.4,
61.4, 46.6, 29.0, 25.9; MS (ESI) m/z 386.0 [M þ Hþ]. Recrys-
tallization of compound 3.4a by slow evaporation from DCM/
hexane/Et2O afforded a colorless crystal for X-ray diffraction
analysis (see the CIF in the Supporting Information).
(Z)-4-Chloro-11,12-dihydro-10H-pyrimido[4,5-b]dipyrrolo[1,2-
1
d:10,20-g][1,4]diazepine (8): 5-8% yield; oil; H NMR δ 8.12 (s,
1H), 6.75 (d, 1H, J = 3.0 Hz), 6.24 (t, 1H, J = 3.3 Hz), 5.91-5.90
(m, 1H), 5.59 (s, 1H), 3.75 (t, 2H, J = 6.9 Hz), 2.50 (t, 2H, J = 7.5
Hz), 1.98-1.89 (m, 2H); MS (ESI) m/z 259.1 [M þ Hþ].
Competition Experiment 1. To a stirred solution of 2.4 (2.4a/
2.4b =1:2.1) (97 mg, 0.25 mmol) in Cl(CH2)2Cl (9 mL) were
added p-methoxyaniline (31 mg, 0.25 mmol) and TFA (40 μL,
0.525 mmol). After the mixture was stirred for 35 h at 60 °C, the
solvent was removed in vacuo, and DCM (40 mL) was added.
The organic layers were washed with saturated aqueous NaH-
CO3 (20 mL), dried over MgSO4, and concentrated in vacuo to
afford a crude mixture of 3.4a and 3.1a (1H NMR of 8.09 ppm/
8.06 ppm indicated the ratio of 3.4a and 3.1a to be 1.25:1). The
residue was purified by flash column chromatography (petro-
leum ether/EtOAc=2:1, v/v) to afford 66 mg (68%) of a mix-
ture of 3.4a and 3.1a (ratio 1.25:1) and 3 mg (5%) of 8.
(9S,9aS)-4-Chloro-9a,10,11,12-tetrahydro-9H-pyrimido[4,5-b]-
dipyrrolo[1,2-d:10,20-g][1,4]diazepin-9-ol (6a): mp 172-174 °C; 1H
NMR δ 8.25 (s, 1H), 7.04-7.02 (m, 1H), 6.27 (t, 1H, J = 3.0 Hz),
6.24-6.22 (m, 1H), 4.71 (d, 1H, J = 8.4 Hz), 3.96-3.86 (m, 1H),
3.75-3.62 (m, 2H), 2.38-2.34 (m, 1H), 2.12-2.03 (m, 1H),
1.90-1.73 (m, 3H); MS (ESI) m/z 277.1 [M þ Hþ].
Synthesis of 5-Benzyl-1-chloro-N-(4-chlorophenyl)-6,7-dihy-
dro-5H-pyrimido[4,5-b]pyrrolo[1,2-d][1,4]diazepin-7-amine (10).
6-[N-Benzyl(2-ethanol)amino]-4-chloro-5-pyrrol-1-yl-pyrimidine4a
(984 mg, 3.0 mmol) in 20 mL of DMSO-DCM (1:1) was treated
with TEA (4.2 mL, 30 mmol). A solution of SO3-pyridine (2.8 g,
18.0 mmol) in 20 mL of DMSO-DCM (1:1) was added, and the
mixture was stirred for 35 min at ambient temperature. The reaction
solution was then diluted with DCM (60 mL), washed twice with
10% citric acid and brine, dried over MgSO4, and filtered to give
crude aldehyde1a in DCM. To the above solution was added
p-chloroaniline (383 mg, 3.0 mmol). The mixture was stirred for
1 h at ambient temperature, washed with saturated aqueous
Na2CO3, dried over MgSO4, and concentrated in vacuo. Purifica-
tion by flash chromatography (petroleum ether/EtOAc = 4:1 to
2:1, v/v) afforded 770 mg (59%) of product 10: mp 203-204 °C;
1H NMR δ 8.35 (s, 1H), 7.31-7.23 (m, 5H), 7.01-6.97 (m, 3H),
6.37 (d, 2H, J = 8.7 Hz), 6.25 (t, 1H, J = 3.3 Hz), 6.12 (dd, 1H,
J = 3.3, 1.2 Hz), 4.94 (br, 1H), 4.87 (br, 1H), 4.69-4.63 (m, 1H),
3.77-3.73 (m, 2H), 3.65-3.58 (m, 1H); 13C NMR (DMSO-d6)
δ 156.8, 153.4, 152.5, 145.8, 136.8, 134.2, 128.42, 128.39, 127.4,
127.1, 123.5, 120.1, 116.5, 114.6, 108.5, 104.8, 58.8, 54.1, 47.1; MS
(ESI): m/z 436.1 [M þ Hþ]. Anal. Calcd for C23H19Cl2N5: C,
63.31; H, 4.39; N, 16.05. Found: C, 63.22; H, 4.38; N, 15.99.
Competition Experiment 2. To a stirred solution of 5-benzyl-
1-chloro-N-(4-chlorophenyl)-6,7-dihydro-5H-pyrimido[4,5-b]-
pyrrolo[1,2-d][1,4]diazepin-7-amine (10) (43.6 mg, 0.1 mmol) in
DCM (3 mL) were added p-methoxyaniline (12.3 mg, 0.1 mmol)
and TFA (13 μL, 0.18 mmol). The mixture was stirred for 36 h at
room temperature (a trace amount with molecular ion corre-
sponding to 1-chloro-5,6-dihydro-6-[(benzylamino)methyl]-5-
(4-methoxyphenyl)pyrrolo[1,2-f]pteridine (12) was detected by
LC-MS) and then washed with saturated aqueous NaHCO3
(1.5 mL), dried over MgSO4, and concentrated in vacuo.
(9R,9aS)-4-Chloro-9a,10,11,12-tetrahydro-9H-pyrimido[4,5-b]-
dipyrrolo[1,2-d:10,20-g][1,4]diazepin-9-ol (6b): mp 238-239 °C;
[R]23D þ459.0 (c 1.0, CHCl3); 1H NMR δ 8.20 (s, 1H), 7.03 (dd,
1H, J = 3.0, 1.8), 6.18 (t, 1H, J = 3.3), 6.14 (dd, 1H, J = 3.6, 1.5),
4.96 (s, 1H), 3.89-3.74 (m, 3H), 2.16-2.00 (m, 4H), 1.86-1.76
(m, 1H);13CNMR (DMSO-d6) δ155.0, 152.9, 150.1, 135.5, 124.8,
116.2, 108.4, 107.0, 67.8, 64.2, 51.4, 30.8, 21.9; MS (ESI) m/z 277.0
[M þ Hþ]. Anal. Calcd for C13H13ClN4O: C, 56.42; H, 4.74; N,
20.25. Found: C, 56.17; H, 4.72; N, 20.27.
General Procedure for the Synthesis of Pyrrolo[1,2-f]pteridine
3.4a via Smiles Rearrangement. To a stirred solution of 2.4a,
2.4b, or 2.4 (2.4a/2.4b = 1:2.1) (193 mg, 0.5 mmol) in Cl(CH2)2Cl
(18 mL) was added TFA (78 μL, 1.05 mmol). After the mixture
was stirred for the corresponding time at 60 °C, the solvent was
removed in vacuo and DCM (30 mL) was added. The organic
layers were washed with saturated aqueous NaHCO3 (15 mL),
dried over MgSO4, concentrated in vacuo, and purified by flash
chromatography (MeOH/DCM=100:1 to 20:1, v/v) toaffordthe
desired products 3.4a and 8.
(S)-1-Chloro-5-(4-chlorophenyl)-6-((S)-pyrrolidin-2-yl)-5,6-di-
hydropyrrolo[1,2-f]pteridine 3.4a. Compound 2.4a as starting
material: 3.4a, 76%; mp 111-113 °C; [R]21 þ423.2 (c 1.0,
D
CHCl3); 1H NMR δ 8.09 (s, 1H), 7.96 (d, 1H, J=1.5 Hz), 7.42
(d, 2H, J = 8.4 Hz), 7.36 (d, 2H, J = 8.1 Hz), 6.43 (t, 1H, J = 2.7
Hz), 6.13 (t, 1H, J = 1.5 Hz), 4.79 (d, 1H, J = 4.2 Hz), 3.58-3.52
(m, 1H), 2.74-2.67 (m, 1H), 2.38-2.31 (m, 1H), 1.83-1.74 (m,
1H), 1.56-1.35 (m, 4H); 13C NMR δ 154.1, 151.5, 142.4, 140.6,
132.8, 129.5, 128.8, 125.3, 119.9, 118.1, 111.5 107.2, 63.4, 61.3,
46.6, 29.0, 25.9; MS (ESI) m/z 386.1 [M þ Hþ]. Compound 2.4b
as starting material: 3.4a, 75%; mp 110-112 °C; [R]21D þ411.8
(c 1.0, CHCl3); 1H NMR δ 8.09 (s, 1H), 7.97 (d, 1H, J = 1.8 Hz),
J. Org. Chem. Vol. 75, No. 23, 2010 8153

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JOCArticle
Purification by flash chromatography (petroleum ether/EtOAc=
4:1 to 2:1, v/v) afforded 36 mg (83%) of 1-chloro-5,6-dihydro-
6-[(benzylamino)methyl]-5-(4-chlorophenyl)pyrrolo[1,2-f ]-
pteridine (11): mp 138-140 °C; H NMR δ 8.12 (s, 1H), 7.98
(dd, 1H, J = 3.3, 1.2), 7.38-7.33 (m, 2H), 7.33-7.22 (m, 3H),
7.21-7.15 (m, 2H), 7.10 (dd, 2H, J = 7.5, 1.8), 6.44 (t, 1H,
J = 3.3), 6.15 (dd, 1H, J = 3.6, 1.5), 5.02 (dd, 1H, J = 6.3, 3.9),
3.69 (A of AB, 1H, J = 13.2), 3.60 (B of AB, 1H, J = 13.2), 2.96
(dd, 1H, J = 12.3, 3.9), 2.86 (dd, 1H, J=12.3, 6.3); MS (ESI)
m/z 436.1 [M þ Hþ].
6.11 (d, 1H, J = 2.4 Hz), 4.78 (d, 1H, J = 3.9 Hz), 3.59-3.55
(m, 1H), 2.74-2.66 (m, 1H), 2.39-2.31 (m, 4H), 1.78-1.72 (m,
1H), 1.54-1.40 (m, 4H); 13C NMR δ 154.5, 151.7, 141.9, 139.3,
137.4, 130.0, 127.6, 125.4, 119.8, 117.7, 111.4, 106.9, 63.5, 61.2,
46.6, 28.9, 25.9, 21.2; MS (ESI): m/z 365.9 [M þ Hþ]; Anal.
Calcd for C20H20ClN5: C, 65.66; H, 5.51; N, 19.14. Found: C,
65.44; H, 5.53; N, 19.13.
(S)-1-Chloro-5-phenyl-6-((S)-pyrrolidin-2-yl)-5,6-dihydro-
pyrrolo[1,2-f]pteridine (3.3a): 66% yield; mp 118-120 °C;
[R]21D þ444.0 (c 1.0, CHCl3); 1H NMR δ 8.09 (s, 1H), 7.97 (d,
1H, J = 1.8 Hz), 7.48-7.30 (m, 5H), 6.43 (t, 1H, J = 3.3 Hz),
6.12 (d, 1H, J = 2.4 Hz), 4.82 (d, 1H, J = 3.9 Hz), 3.62-3.56
(m, 1H), 2.75-2.67 (m, 1H), 2.39-2.32 (m, 1H), 1.81-1.73
(m, 1H), 1.52-1.40 (m, 4H); 13C NMR δ 154.3, 151.6, 142.1,
129.3, 127.5,127.3, 125.5, 119.8, 117.9,111.4, 106.9, 63.4,
61.3, 46.6, 28.9, 25.8; MS (ESI) m/z 351.9 [M þ Hþ]. Anal.
Calcd for C19H18ClN5: C, 64.86; H, 5.16; N, 19.91. Found: C,
64.66; H, 5.14; N, 19.86.
1
General Procedure for the Synthesis of 5,6-Dihydropyrrolo-
[1,2-f]pteridine 3a via Tandem Iminium Cyclization and Smiles
Rearrangement. (S)-(1-(6-Chloro-5-(1H-pyrrol-1-yl)pyrimidin-
4-yl)pyrrolidin-2-yl)methanol (5) (139 mg, 0.50 mmol) in 6 mL
of DMSO-DCM (1:1) was treated with TEA (0.703 mL, 5.0
mmol). A solution of SO3-pyridine (481 mg, 3.0 mmol) in 4 mL
of DMSO-DCM (3:1) was added, and the mixture was stirred
for 35 min at ambient temperature. The reaction solution was
then diluted with DCM (20 mL), washed twice with 10% citric
acid and brine, dried over MgSO4, filtered, and concentrated in
vacuo to give crude aldehyde 1. The crude 1 was dissolved in
Cl(CH2)2Cl (18 mL). To the resulting solution was added the
appropriate amine (0.6 mmol) followed by TFA (78 μL, 1.05
mmol). After the mixture was stirred for the corresponding time
at 60 °C, the solvent was removed in vacuo and DCM (30 mL)
was added. The organic layers were washed with saturated
aqueous NaHCO3 (15 mL), dried over MgSO4, concentrated in
vacuo, and purified by flash chromatography (MeOH/DCM =
100:1 to 20:1, v/v) to afford the desired products 3a and 8.
(S)-1-Chloro-5-(4-chlorophenyl)-6-((S)-pyrrolidin-2-yl)-5,6-
dihydropyrrolo[1,2-f]pteridine (3.4a): 59% yield; mp 110-
D
112 °C; [R]21 þ416.2 (c 1.0, CHCl3); 1H NMR δ 8.09 (s,
1H), 7.97 (d, 1H, J=1.5 Hz), 7.42 (d, 2H, J =8.4 Hz), 7.36 (d,
2H, J=8.7 Hz), 6.43 (t, 1H, J = 3.3 Hz), 6.13 (d, 1H, J = 2.1
Hz), 4.78 (d, 1H, J = 3.9 Hz), 3.57-3.52 (m, 1H), 2.72-2.67
(m, 1H), 2.37-2.32 (m, 1H), 1.80-1.74 (m, 1H), 1.52-1.40 (m,
4H); 13C NMR δ 154.2, 151.6, 142.4, 140.6, 132.8, 129. 6,
128.9, 125.4, 120.0, 118.2, 111.5, 107.1, 63.5, 61.3, 46.6, 29.0,
25.9; MS (ESI) m/z 386.0 [M þ Hþ]. Anal. Calcd for C19H17
-
Cl2N5: C, 59.08; H, 4.44; N, 18.13. Found: C, 58.87; H, 4.42; N,
18.05.
(S)-1-Chloro-5-(4-methoxyphenyl)-6-((S)-pyrrolidin-2-yl)-5,6-
dihydropyrrolo[1,2-f]pteridine (3.1a): 74%; mp: 60-62 °C;
D
1
[R]21 þ382.2 (c 1.0, CHCl3); H NMR δ 8.06 (s, 1H), 7.97
Acknowledgment. This paper is dedicated to the memory
of Professor Ernest L. Eliel at the University of North
Carolina at Chapel Hill. This work was supported by the
National Natural Science Foundation of China (No.
20902036), National Science & Technology Major Project
“Key New Drug Creation and Manufacturing Program” of
China (No. 2009ZX09501-010), and Changchun Discovery
Sciences, Ltd.
(d, 1H, J = 2.1 Hz), 7.31 (d, 2H, J = 8.7 Hz), 6.97 (d, 2H, J =
9.0 Hz), 6.43 (t, 1H, J = 3.0 Hz), 6.11 (d, 1H, J = 2.4 Hz), 4.75
(d, 1H, J = 3.6 Hz), 3.84 (s, 3H), 3.58-3.54 (m, 1H), 2.74-2.67
(m, 1H), 2.40-2.34 (m, 1H), 1.78-1.72 (m, 1H), 1.52-1.40 (m,
4H); 13C NMR δ 158.6, 154.6, 151.7, 141.8, 134.5, 129.2, 125.4,
119.9, 117.5, 114.6, 111.4, 106.9, 63.7, 61.1, 55.5, 46.6, 28.9,
25.9; MS (ESI) m/z 382.3 [M þ Hþ]; Anal. Calcd for C20H20-
ClN5O: C, 62.91; H, 5.28; N, 18.34. Found: C, 62.67; H, 5.30;
N, 18.31.
(S)-1-Chloro-5-(4-methylphenyl)-6-((S)-pyrrolidin-2-yl)-5,6-
dihydropyrrolo[1,2-f]pteridine (3.2a): 71% yield; mp 68-70 °C;
[R]21D þ376.8 (c 1.0, CHCl3); 1H NMR δ 8.07 (s, 1H), 7.97 (d,
1H, J = 1.5 Hz), 7.34-7.10 (m, 4H), 6.43 (t, 1H, J = 3.0 Hz),
Supporting Information Available: Copies of LC-MS and
NMR spectra for all products and crystallographic data of 2.4b
and 3.4a (CIF). This material is available free of charge via the
Internet at http://pubs.acs.org.
8154 J. Org. Chem. Vol. 75, No. 23, 2010