Au(I)-catalyzed cascade reaction involving formal double hydroamination of alkynes bearing tethered carboxylic groups: An easy access to fused dihydrobenzimidazoles and tetrahydroquinazolines

Article abstract of DOI:10.1021/jo1013228

A process involving gold(I)-catalyzed formal double hydroamination of alkynes, bearing a tethered carboxylic group, for the synthesis of fused dihydrobenzimidazoles and tetrahydroquinazolines has been developed. A series of transition metal catalysts have been screened for this transformation, and a catalyst system consisting of Ph₃PAuCl (1 mol %) and AgOTf (1 mol %) was found to be the best. The procedure entails the reaction of easily accessible starting materials such as alkynoic acids and 1,2-diaminobenzenes/2- aminobenzylamines in the presence of the catalyst in 1,2-dichloroethane at 100 °C. In the case of α-substituted alkynoic acids, the corresponding products were obtained in high diastereoselectivities; the structure of the diastereomers has been unambiguously characterized by NMR techniques. The mechanism of the reaction is discussed, and the origin of the diastereoselectivities is addressed. It was observed that under the microwave irradiation conditions, the reaction time is significantly shortened (0.5 h).

Full text of DOI:10.1021/jo1013228

pubs.acs.org/joc
Au(I)-Catalyzed Cascade Reaction Involving Formal Double
Hydroamination of Alkynes Bearing Tethered Carboxylic Groups: An
Easy Access to Fused Dihydrobenzimidazoles and Tetrahydroquinazolines
Nitin T. Patil,*,† Anil Kumar Mutyala,† Pediredla G. V. V. Lakshmi,† Balakrishna Gajula,†
Balasubramanian Sridhar,‡ Gurava Reddy Pottireddygari,§ and
Tadikamalla Prabhakar Rao§
†Organic Chemistry Division II, ‡Laboratory of X-ray Crystallography, and §Center for Nuclear Magnetic
Resonance, Indian Institute of Chemical Technology, Hyderabad 500 607, India
patilnitint@yahoo.com; nitin@iict.res.in
Received July 5, 2010
A process involving gold(I)-catalyzed formal double hydroamination of alkynes, bearing a tethered
carboxylic group, for the synthesis of fused dihydrobenzimidazoles and tetrahydroquinazolines has been
developed. A series of transition metal catalysts have been screened for this transformation, and a catalyst
system consisting of Ph3PAuCl (1 mol %) and AgOTf (1 mol %) was found to be the best. The procedure
entails the reaction of easily accessible starting materials such as alkynoic acids and 1,2-diaminobenzenes/
2-aminobenzylamines in the presence of the catalyst in 1,2-dichloroethane at 100 °C. In the case of
R-substituted alkynoic acids, the corresponding products were obtained in high diastereoselectivities; the
structure of the diastereomers has been unambiguously characterized by NMR techniques. The mechan-
ism of the reaction is discussed, and the origin of the diastereoselectivities is addressed. It was observed that
under the microwave irradiation conditions, the reaction time is significantly shortened (0.5 h).
Introduction
ship of the molecule is restricted and therefore a specific
biological activity would be expected. Such compounds are
characterized by their ability to bind to a multitude of recep-
tors through a variety of favorable interactions. Therefore,
the nitrogen-containing compounds are considered as attr-
active templates for drug discovery. Among various N-con-
taining heterocycles, fused dihydrobenzimidazoles1 and tet-
rahydroquinazolines2 are important structural motifs found
in numerous natural products and/or pharmaceutically im-
portant compounds. General and convenient methods for
the constructionofthesecompounds bearing multiple reactive
sites for further functionalization would be of great interest
to the synthetic organic chemists. The ideal way to access
these molecules would be to implement metal-catalyzed re-
action cascade3 using easily available starting materials in
one-pot fashion without isolating any intermediates.4
As a result of the rigid conformation of nitrogen-contain-
ing polycyclic compounds, the three-dimensional relation-
(1) For syntheses and/or SAR studies of fused dihydrobenzimidazoles,
ꢀ
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DOI: 10.1021/jo1013228
r
Published on Web 08/13/2010
J. Org. Chem. 2010, 75, 5963–5975 5963
2010 American Chemical Society

Patil et al.
JOCArticle
The catalytic hydroamination of alkynes5 has emerged as a
highly atom-economical6 and broadly applicable transform-
ation.7 In general, primary or secondary amines can undergo
addition reactions with alkynes to give imines or enamines.
Very recently, we expanded the alkyne hydroamination stra-
tegy beyond the example of imines/enamines formation and
further developed cascade reactions involving formal double
hydroamination of alkynes (Figure 1, path a).8 In this case, a
proximal hydroxyl group was proved to be necessary for the
reaction to occur. Interestingly, when PtCl2 was used as a
catalyst, double hydroamination product A was obtained;
on the other hand, using PtCl4 as a catalyst, cyclic fused
compound A0 was obtained. Later, we reported Au(I)-cata-
lyzed direct double hydroamination of terminal alkynes
having no hydroxyl group in the proximity.9 Dixon and co-
workers reported conceptually different Au(I)-catalyzed for-
mal hydroamination-hydroarylation of alkynes bearing
tethered carboxylic group.10 They utilized alkyonic acids
and amino-aromatics as starting materials, and the process
led to the efficient synthesis of complex multiring hetero-
cyclic compounds. Recently, Liu and co-workers broadened
the scope of the reaction to a formal double hydroamination
process for the synthesis of pyrrolo/pyrido[2,1-a]quinazoli-
nones and pyrrolo/pyrido[2,1-a][1,3]benzoxazinones.11 It
should be further emphasized that although formal or direct
hydroalkoxylation-hydroarylation,12 double hydroalkoxyl-
ation,13 hydroamination-hydroarylation,10 double hydro-
arylation,14 and hydroamination-hydroalkoxylation15 of al-
kynes have recently been reported, only few reports exist on
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published online July 13, 2010, DOI: 10.1002/ejoc.201000389.
5964 J. Org. Chem. Vol. 75, No. 17, 2010

Patil et al.
JOCArticle
FIGURE 1. Concept of the double hydroamination of alkynes.
TABLE 1. Optimization Studies
double hydroamination process of the starting alkynoic acids
and would provide an easy access to pharmaceutically important
molecules such as pyrrolo/pyrido[1,2-a]benzimidazol-1-ones
and pyrrolo/pyrido[2,1-b]quinazolin-1-ones in an appar-
ently very simple way.
Results and Discussion
At the outset of this study, our efforts were directed to find
an appropriate catalyst and reaction conditions to perform
the proposed reaction. We commenced our study of the
metal-catalyzed reaction with readily accessible benzene-
1,2-diamine (1a) and pent-4-ynoic acid (2a). The results of
this study are summarized in Table 1. We focused our
attention on the use of platinum salts as they have proved
to be efficient catalysts in related reactions.8 The substrate 1a
was treated with 1 equiv of pent-4-ynoic acid (2a) in the
presence of 1 mol % PtCl2 in DCE at 100 °C for 24 h. Indeed,
the desired product 3a was obtained in 91% yield (entry 1).
The use of PtCl4 as a catalyst gave 3a in 90% yield (entry 2).
Although we had satisfactory results in hand, we were
curious to know the activity of other metal catalysts for the
present transformation. When AgOTf and Cu(OTf)2 cata-
lysts were employed independently, 3a was obtained in 40%
and 45% yields, respectively (entries 3 and 4). Among the
gold catalysts examined (AuCl, Ph3PAuCl, Ph3PAuOTf,
and Ph3PAuNTf2) (entries 5-8), Ph3PAuOTf afforded the
highest yield of 3a (entry 7). Interestingly, even copper(I)
catalysts such as CuBr and CuI provided 3a in moderate
yields (entry 9 and 10). Since the catalyst Ph3PAuOTf was
found to be superior (entry 7), we next examined the effect of
various solvents and quickly came to the conclusion that the
reaction is sensitive to the solvents employed. The yield
dropped significantly when toluene, THF and 1,4-dioxane
were used (entries 11-13). On the other hand, solvents such
as nitromethane and N,N0-dimethylformamide were com-
entry
catalysta
PtCl2
PtCl4
AgOTf
Cu(OTf)2
AuCl
Ph3PAuCl
Ph3PAuCl/AgOTf
Ph3PAuNTf2
CuBr
solvent
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
toluene
THF
1,4-dioxane
MeNO2
DMF
DCE
yield (%)b
1
2
3
4
5
6
7
8
91
90
40
45
50
60
95
92
9
65
10
11
12
13
14
15
16
CuI
70
Ph3PAuCl/AgOTf
Ph3PAuCl/AgOTf
Ph3PAuCl/AgOTf
Ph3PAuCl/AgOTf
Ph3PAuCl/AgOTf
TfOH
30c
40
30
trace
trace
51
aAll reactions were carried out using 1 mol % metal catalysts (MLn),
0.46 mmol of 1a, and 0.46 mmol of 2a in 2 mL of DCE at 100 °C for 24 h.
bIsolated yields. cThe starting material 1a was partly soluble in toluene at
100 °C.
pletely ineffective and did not lead to the formation of 3a
(entries 14 and 15). It is interesting to note that when TfOH
was used as catalyst, 3a was obtained only in 51% yields
(entry 16).
The substrate scope toward this cascade reaction was
further investigated, and the results are summarized in Table 2.
Gratifyingly, the reaction was proved to be very general
under the optimized conditions, performing well in most of
the cases examined. At first, the scope of the reaction with
various alkynoic acids was studied using 1a as a model
substrate. The alkynoic acids bearing sterically demanding
substituents in the tether such as 2b, 2c, and 2d reacted well,
giving corresponding products 3b, 3c, and 3d in 92%, 84%,
and 91% yields, respectively (entries 1-3). As can be judged
from entries 4 and 5, hexynoic acids 2e and 2f on reaction
with 1a gave products 3e18 and 3f in 79% and 96% yields,
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(18) X-ray crystallographic data of 3e is given in Supporting Information
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TABLE 2. Ph3PAuOTf -Catalyzed Reactions of Alkynoic Acids with Benzene-1,2-diaminesa
aReactions were performed in DCE (2 mL) employing 1 (0.46 mmol), 2 (0.46 mmol) and 1 mol % Ph3PAuOTf at 100 °C for 24 h. bIsolated yields.
d
e
f
cObtained as a single regioisomer. Inseperable mixture (70:30) of regioisomers. Inseperable mixture (90:10) of regioisomers. Inseperable mixture
(80:20) of regioisomers. gStarting material 1a was recovered in quantitiative yields.
respectively. Interestingly, 2-ethynylbenzoic acid (2g) also
reacted well, giving fused polycyclic compound 3g in 73%
yield (entry 6). Even internal alkynes such as 2h and 2i were
found to be useful substrates, giving the corresponding pro-
ducts 3h and 3e in 85% and 81% yields, respectively (entries 7
and 8). Particularly noteworthy is the fact that in the latter
case only one regioisomer 3e was obtained, indicating that 2i
cyclized in 6-endo-dig fashion (entry 8). Next, the scope of the
reaction with differentially substituted benzene-1,2-diamines
was studied. When 3-methylbenzene-1,2-diamine (1b) was
treated with 2a and 2f, the products 3i and 3j were obtained
as single regioisomers in 73% and 78% yields (entries 9 and
10).19 The reason for excellent regioselectivity might be attri-
buted to the steric hindrance created by the methyl group.
The amine group, located ortho to methyl group, should be
less nucleophilic than the one at meta position. As shown in
(19) See Supporting Information for NOE details.
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TABLE 3. Ph3PAuOTf-Catalyzed Reactions of Alkynoic Acids with 2-(Aminomethyl)benzenaminesa
aReactions were performed in DCE (2 mL) employing 1 (0.46 mmol), 2 (0.46 mmol), and 1 mol % Ph3PAuOTf at 100 °C for 24 h. bIsolated yields. cA
mixture of regioisomers 5e and 5g in a ratio of 90:10 was obtained as judged by 1H NMR spectra of crude product. dStarting material 1a was recovered in
quantitiative yield.
entry 11, the reaction of 4-ethoxybenzene-1,2-diamine (1c)
with 2a gave 3k in 86% yield as single regioisomer. The
observed regioselectivity could be due to the resonance effect
of the -OEt group, which make the amine located at the para
position more nucleophilic than the one at meta position.
However, in the case of 1d, 1e, 1f, and 1g the desired products
3l, 3m, 3n and 3o were obtained as inseparable mixtures of
regioisomers in variable ratios (entries 12-15). It should be
noted that heptynoic acids are not viable substrates for this
transformation; for instance, the reaction between 1a and 2j
did not give 3p under the optimized reaction conditions
(entries 16).
The applicability of benzene-1,2-diamines as a bisnucleo-
phile having been established, for a formal double hydro-
amination cascade, the scope of the reaction has been
extended to 2-aminobenzylamines. The results are summar-
ized in Table 3. Treatment of 4a with pent-4-ynoic acid (2a)
in the presence of 1 mol % Ph3PAuOTf in DCE at 100 °C
gave fused tetrahydroquinazolines 5a, as a single regioi-
somer, in 96% yield (entry 1). The observed regioselectivity
could be due to the higher nucleophilicity of -CH2NH2
compared to that of Ar-NH2 (see Mechanistic Studies).
The alkynoic acids 2b and 2d on reaction with 4a gave the
expected products 5b and 5c in 82% and 75% yields,
respectively (entries 2 and 3). 2-Ethynylbenzoic acid (2g)
also reacted well with 4a, for this cascade transformation, to
give 5d in 96% yield (entry 4). Internal alkynes such as hex-3-
ynoic acid (2h) and dodec-3-ynoic acid (2k) on reaction with
4a gave 5e and 5f in 82% and 74% yields, respectively (entries
5 and 6). However, in the case of hex-4-ynoic acid (2i) a
mixture of regioisomers 5e and 5g in the ratio of 90:10 was
obtained; each of the regioisomers was separated by column
chromatography (entry 7). As can be judged from entries
8-13, various substituents such as -Me, -OMe, -Cl, and -F in
J. Org. Chem. Vol. 75, No. 17, 2010 5967

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TABLE 4. Diastereoselectivity Studiesa
acid (2l) and 1a was conducted under earlier optimized
reaction conditions. Pleasingly, the reaction was found to
be very diastereoselective and 3q was obtained as a single 1,3-
trans diastereomer in 78% yield (Table 4, entry 1). In the case
of 2-ethyl-pent-4-ynoic acid (2m), a mixture of diastereomers
3r and 3r0 was obtained favoring more of 1,3-trans isomer
(3r:3r0 = 90:10). This observation suggests that the steric
bulk of the R-substituent plays an important role in deciding
the diastereoselectivity (vide infra). Interestingly, in the case
of disubstituted alkynoic acid 2n only a single diastereomer
3s was obtained in 92% yield (entry 3). An X-ray crystal
structure analysis of 3s unambiguously allowed the determi-
nation of relative stereochemistry.22 When 2-(aminomethyl)-
benzenamine (4a) was treated with 2l, the product 5p was
obtained as a single 1,3-cis diastereomer in 74% yield (entry
4). As anticipated, a mixture of diastereomers 5q and 5q0 in
the ratio of 90:10 was obtained when 2m was treated with 4a
(entry 5). Similar observation was noticed in the case of 2n; a
mixture of diastereomers was obtained (5r:5r0 = 95:05) in
82% yield (entry 6). The relative stereochemistries of the
diastereomers 3q, 3q0 (vide infra), 3r, 3r0, 5p, 5p0 (vide infra),
5q, 5q0, 5r, and 5r0 were unambiguously determined by
examining the nuclear Overhauser effect (NOE) enhance-
ments (Figure 2).
Mechanistic Studies
A mechanism involving multiple catalytic cycles23 for the
gold-catalyzed formal double hydroamination of alkynes,
which is presumably analogous to that reported by Dixon10
and Liu,11 is outlined in Figure 3. The first step would be the
complexation of Au(I) catalyst to the alkyne function in 2e,
which leads to an intermediate 6 (Figure 3, cycle A). The
cyclization may then occur directly by the attack of proximal
hydroxyl group to form the vinylgold intermediate 7.24 The
next step would be the proto-demetalation to generate
exocyclic enol lactone 8 with the release of catalyst.25 Once
8 is formed, it enters another catalytic cycle B where Ph3-
PAuOTf acts as a Lewis acid. Thus, the Lewis acidic Au(I)
complex catalyzes the formation of oxonium ion 9 from 8.
Intermolecular nucleophilic addition of the benzene-1,2-
diamine (1a) to 9 (cf. 10) followed by proto-demetalation
would lead to the keto amide 11 with the liberation of the
catalyst. The keto amide 11 would then be poised to under-
go N-acyl iminium ion26 formation 12b, which could be
derived from 12a, in the presence of Au(I) catalyst.27 The
aReactions were performed in DCE (2 mL) employing 1/4 (0.46
mmol), 2 (0.46 mmol), and 1 mol % Ph3PAuOTf at 100 °C for 24 h.
c
bIsolated yields. Structures of diastereomers were unambigiously de-
termined by NOE studies (Figure 2) except 3s, whose structure was
d
1
confirmed by X-ray crystallography. The H NMR of crude product
showed 90:10 mixture of diastereomers. eThe 1H NMR of crude product
showed 95:05 mixture of diastereomers.
(22) X-ray crystallographic data of 3s is given in Supporting
Information
(23) (a) Shindoh, N.; Takemoto, Y.; Takasu, K. Chem.-Eur. J. 2009, 15,
12168–12179. (b) Wasilke, J.-C.; Obrey, S. J.; Baker, R. T.; Bazan, G. C.
Chem. Rev. 2005, 105, 1001–1020.
2-aminobenzylamines were well tolerated in the reaction
(4b-g f 5h-m).20 The reaction of 4h with 2f afforded 5n
in 73% yield (entry 14). As anticipated, the reaction between
4a and 2j did not give 5o under the optimized reaction con-
ditions (entry 15).
(24) For reports on vinyl gold intermediates, see: (a) Hashmi, A. S. K.;
€
€
Dopp, R.; Lothschutz, C.; Rudolph, M.; Riedel, D.; Rominger, F. Adv.
Synth. Catal. 2010, 352, 1307–1314. (b) Hashmi, A. S. K.; Schuster, A. M.;
Rominger, F. Angew. Chem., Int. Ed. 2009, 48, 8247–8249. (c) Seidel, G.;
€
Mynott, R.; Furstner, A. Angew. Chem., Int. Ed. 2009, 48, 2510–2513.
As a part of continuing work, we next planned to inves-
tigate the diastereoselectivity of the reaction, and therefore
R-substituted alkynoic acids such as 2l, 2m, and 2n were
prepared.21 The reaction between 2-phenyl-pent-4-ynoic
(d) Liu, L.-P.; Xu, B.; Mashuta, M. S.; Hammond, G. B. J. Am. Chem.
Soc. 2008, 130, 17642–17643.
(25) The reaction between 1a and 4a with 2a; independently, were carried
out in the absence and presence of Ph3PAuOTf at 50 °C for 24 h. In the
absence of catalyst, both the starting materials remained intact; while, in the
presence of catalyst, formation of small amounts of 3a/5a, corresponding
ketoamides and unreacted 1a/4a were obtained as judged by 1H NMR
spectra of crude product.
(20) X-ray crystallographic data of 5m is given in Supporting
Information
€
(26) For an excellent review on iminium ion catalysis, see: Erkkila, A.;
Majander, I.; Pihko, P. M. Chem. Rev. 2007, 107, 5416–5470.
(21) See Supporting Information for the preparation of 2l, 2m
and 2n.
5968 J. Org. Chem. Vol. 75, No. 17, 2010

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FIGURE 2. Structure elucidation of diastereomers by NOE studies.
FIGURE 3. Mechanistic proposal for the formation of 3e from 1a and 2e.
intramolecular trapping of N-acyl iminium ion in 12b by
tethered amine would produce final product 3e (cf. 13) with
the regeneration of catalyst.
To determine the role of TfOH, which could be generated
from Ph3PAuOTf in the presence of in situ generated water,
in catalytic cycles B and C, the reaction was conducted
between 1a and 8 in the presence of 1 mol % TfOH in
DCE at 100 °C (eq 1). The product 3e was obtained in 93%
yield. This suggests that residual TfOH may be responsible
for cycles B and C. Interestingly, the same transformation
was also catalyzed by Ph3PAuOTf, leading to the formation
of 3e in 91% yield. It should be noted that in the absence of
(27) The possibility of Brønsted acid catalysis assisted by a Lewis acid,
which results from the use of Au catalysts in the presence of water, cannot be
ruled out completely. An example of this type of catalysis, see: (a) Ishihara,
K.; Ishibashi, H.; Yamamoto, H. J. Am. Chem. Soc. 2002, 124, 3647–3655.
Such type of activation has been envisaged for other reactions, see:
ꢁ
ꢁ
~
(b) Barluenga, J.; Fernandez, A.; Dieguez, A.; Rodrıguez, F.; Fananas,
ꢁ
F. J. Chem.-Eur. J. 2009, 15, 11660–11667. (c) ref 8b (d) ref 10b.
J. Org. Chem. Vol. 75, No. 17, 2010 5969

Patil et al.
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€
SCHEME 1. Diastereomerization of 3q/5p under Bronsted Acid
SCHEME 2. Diastereomerization of 3q and 5p
Catalysisa
aReaction conditions: 5 mol % pTSA H2O, DCE, rt, 12 h.
3
any catalyst the reaction of 1a with 8 is sluggish and the
desired product 3e was formed only in 20% yield (eq 1).
€
SCHEME 3. Diastereomerization of 3s/5r under Bronsted Acid
Catalysisa
Kinetic versus Thermodynamic Control and Origin of Diaster-
eoselectivity
It is evident that only a single diastereomer (3q and 5p) was
obtained when 2-phenyl-pent-4-ynoic acid (2l) was reacted
with 1a and 4a, independently (Table 4, entry 1 and 4). At this
€
stage, we were intrigued to study the effect of Bronsted acid
on diastereomerization of 3q and 5p. Accordingly, 3q was
aReaction conditions: 5 mol % pTSA H2O, DCE, rt, 12 h.bInseperable
mixture of diastereomers.
treated with 5 mol % pTSA H2O in DCE at rt for 12 h. The
3
3
reaction furnished a mixture of diastereomers 3q and 3q0 in
the ratio of 70:30 (Scheme 1). In an analogous manner, dia-
stereomerization of 5p occurred (5p:5p0 = 70:30). This clearly
establishes the mildness of gold-mediated reactions as com-
SCHEME 4. Diastereomerization of 3/5 under Ph3PAuOTf
Catalysisa
€
pared to Bronsted acid mediated reactions. The plausible
mechanism for the diastereomerization of 3q/3q0 and 5p/5p0
is given in Scheme 2. In path a, the intermediacy of N-acyl
iminium ion I was proposed, which after trapping with pro-
ximal amine would give the products. On the other hand,
path b explains the intermediacy of the amidoenolate II,
which on transannular cyclization would furnish products
3q0/5p0. At present, we do not have any conclusive evidence
to prove which pathway is operating. The other possibility,
that the stereogenic center R to the amide group undergoes
epimerization by the Lewis acidic Au catalyst, can be ruled
out completely. The treatment of 3s/5r, which do not possess
hydrogen at the R position of the carbonyl group, with
aReaction conditions: 1 mol % Ph3PAuOTf, DCE, 100 °C
SCHEME 5. Controlled Experiments
5 mol % pTSA H2O in DCE at rt afforded a mixture of
3 0
regioisomer 3s/3s and 5r/5r0 (Scheme 3).
In order to shed some light on the kinetic and thermo-
dynamic aspects of the gold-catalyzed reactions, the follow-
ing experiments were conducted. When 3q and 3q0 were
independently subjected to gold catalysis, 3q remained un-
changed, whereas 3q0 was converted completely into 3q
(Scheme 4). A controlled experiment was conducted between
1a and 2l under standard gold-catalyzed conditions (Scheme 5,
eq 2) and the progress of the reaction was followed by
analyzing the samples at end of 12 h intervals by 1H NMR.
The analysis of the sample after 12 h showed the presence of
1a, 3q, and 3q0, while the sample after 24 h showed the
presence of 3q alone. This establishes that 3q0 is kinetic-
ally controlled product, while 3q is a thermodynamically
controlled product. In the case of 5p and 5p0, the former
remain unchanged while the latter converted into 5p when
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TABLE 5. Ph3PAuOTf-Catalyzed Reactions of Alkynoic Acids with
Diamines under MW Conditionsa
entry
1/4
2
3/5
yield (%)b
1
2
3
4
5
6
7
8
1a
1a
1a
4a
4a
4a
1a
4a
2a
2g
2d
2a
2d
2k
2l
3a
3g
3d
5a
5c
5f
75
79
76
81
85
73
3q þ 3q0
70c
73d
2l
5p þ 5p0
aA solution of the aminoaromatics 1/4 (0.46 mmol), alkynoic acids 2
(0.46 mmol), and Ph3PAuOTf (1 mol %) in DCE (0.8 mL) was subjected
to microwave irradiation at 150 °C (P = 40-80 W) for 30 min (Biotage,
Initiator Eight, single-mode reactor). bIsolated yield. c75:25 mixture of
diastereomers favoring 3q. d70:30 mixture of diastereomers favoring 5p.
FIGURE 4. Proposed model for observed diastereoselectivity of
3q/3q0 and 5p/5p0.
Effect of Microwave Irradiation
Considering the advantages of microwave-assisted re-
action28 over conventional heating in terms of efficiency,
we became interested in testing the feasibility of the present
reaction under MW irradiation. Indeed, a significant rate
enhancement was observed when the reactions were con-
ducted under microwave conditions (Table 5). Reactions of
1a with 2a in the presence of 1 mol % Ph3PAuOTf under
microwave conditions for 30 min afforded 3a in 75% yield
(entry 1).29 The reaction of 2g and 2d with 1a furnished 3g
and 3d in 79% and 76% yields, respectively (entries 2 and 3).
Similarly, 4a on reaction with 2a, 2d, and 2k under the
microwave-assisted conditions gave 5a, 5c, and 5f in 81%,
85%, and 73% yields, respectively (entries 4-6). Unfortu-
nately, R-substituted alkynoic acid 2l afforded a mixture of
diastereomers when reacted independently with 1a and 4a
(entries 7 and 8).
FIGURE 5. Plausible reason for the stability of 3s over 3s0.
treated under standard Ph3PAuOTf catalyzed conditions
(Scheme 4). Next, we carefully monitored the progress of
the reaction between 4a and 2l, and the results are presented
in Scheme 5 (eq 3). This suggests that 5p0 is akinetically con-
trolled product, whereas 5p is a thermodynamically con-
trolled product.
Our proposed model for explaining the stability of dia-
stereomers is shown in Figure 4 and is based on the steric
hindrance created by the substituents present at the position
R to the carbonyl groups. In the case of 3q and 3q0, we suggest
that the latter one is highly disfavored because of severe steric
interactions between the methyl and phenyl groups. Simi-
larly, in the case of 5p and 5p0, the latter one is disfavored
because of possible steric interactions of the phenyl group
with either hydrogen (of hexahydropyrimidine ring) or
nitrogen lone pair (Figure 4). The stability of 3s over 3s0
can be attributed to the possible preference of the -Ar ring to
rotate in order to relieve the steric interaction with methyl
group (Figure 5), which is further evidenced by the examina-
tion of the X-ray crystal structure of 3s.22
Conclusion
In conclusion, we have developed a Au(I)-catalyzed cas-
cade reaction involving formal double hydroamination of
alkynes bearing tethered carboxylic groups. The method
provides facile access to fused dihydrobenzimidazoles and
tetrahydroquinazolines under very mild reaction conditions
with high yields and excellent diastereo-/regioselectivities
(wherever applicable). Furthermore, we have proven that
this reaction could easily be performed in a microwave-
assisted conditions, opening the way for the generation of
number of these compounds in efficient manner.30 Further
investigation on the formal or direct double hydroamination
reactions of alkynes, for the synthesis of structurally diverse
biologically important scaffolds, is currently underway in
our laboratory.
Experimental Section
(28) Selected reviews on microwave assisted reactions in organic synthesis
see: (a) Appukkuttan, P.; Mehta, V. P.; Van der Eycken, E. Chem. Soc. Rev.
2010, 39, 1467–1477. (b) Kappe, C. O.; Dallinger, D. Mol. Divers. 2009, 13,
71–193. (c) Appukkuttan, P.; Van der Eycken, E. Eur. J. Org. Chem. 2008,
1133–1155. (d) Kappe, C. O. Chem. Soc. Rev. 2008, 37, 1127–1139. (e) Das,
S. K. Synlett 2004, 915–932. (f) de la Hoz, A.; Dıaz-Ortiz, A.; Moreno, A.
€
Chem. Soc. Rev. 2005, 34, 164–178. (g) Lidstrom, P.; Tierney, J.; Wathey, B.;
Westman, J. Tetrahedron 2001, 57, 9225–9283.
Ph3PAuOTf Catalyzed Cascade Reactions Involving Formal
Double Hydroamination of Alkynes (Tables 1-4). The preparation
(29) The reaction between 1a and 2a under gold catalysis in a preheated
oil bath at 150 °C for 15 min gave 3a only in 20% yield.
(30) (a) Schreiber, S. L. Chem. Eng. News 2003, 81, 51–61. (b) Schreiber,
S. L. Science 2000, 287, 1964–1969.
ꢁ
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of 3a is representative. To a DCE (2 mL) solution of 1a (0.050 g,
0.46 mmol) and 2a (0.045 g, 0.46 mmol) in a screw cap vial were
added Ph3PAuCl (2.3 mg, 1 mol %) and AgOTf (1.2 mg, 1 mol %)
under nitrogen atmosphere. The mixture was stirred at 100 °C for
24 h. Then, the reaction mixture was filtered through a pad of silica
gel with ethyl acetate as an eluent, and the solvent was removed
under reduced pressure. The residue was purified by flash silica gel
column chromatography using hexane/ethyl acetate (70/30) as
eluent to obtain 3a (0.082 g, 95%).
2.32 (ABq, J = 12.8 Hz, 2H), 1.89-1.58 (m, 6H), 1.55 (s, 3H),
1.51-1.34 (m, 4H); 13C NMR (75 MHz, CDCl3) δ 179.9, 142.9,
129.1, 125.3, 119.8, 116.3, 110.3, 82.8, 48.8, 46.6, 35.3, 33.8, 28.7,
25.2, 22.5, 21.9; IR (KBr) νmax 3282, 3056, 2932, 2854, 1683,
1490, 1256, 1053, 740 cm-1; HRMS calcd for C16H21N2O
(Mþ þ H) 257.1653, found 257.1663.
4a-Methyl-1,2,3,4,4a,5-hexahydrobenzo[4,5]imidazo[1,2-a]pyri-
din-1-one (3e). White solid; mp = 146-148 °C; Rf = 0.62
1
(DCM/MeOH = 95/05); H NMR (300 MHz, CDCl3) δ 7.83
General Procedure for pTSA Catalyzed Diastereomerization
of 3q/3s/5p/5r (Schemes 1 and 3). To a DCE (0.8 mL) solution of
3q/3s/5p/5r (0.18 mmol) was added pTSA H2O (5 mol %)
under nitrogen atmosphere. The mixture was stirred at rt for
12 h. Then, the reaction mixture was filtered through a pad of
silica gel with ethyl acetate as an eluent, and the solvent was
removed under reduced pressure. The residue was purified by
flash silica gel column chromatography using hexane/ethyl
acetate (70/30) as eluent to obtain products as a mixture of
diastereomers.
General Procedure for Ph3PAuOTf Catalyzed Cascade Reac-
tions Involving Formal Double Hydroamination of Alkynes under
Microwave-Assisted Conditions (Table 5). A solution of the
aminoaromatic compound 1/4 (0.46 mmol), alkynoic acid 2
(0.46 mmol), Ph3PAuCl (2.3 mg, 1 mol %), and AgOTf (1.2 mg,
1 mol %) in DCE (2 mL) was sealed under nitrogen in a reaction
vial and irradiated in a microwave reactor (Biotage, initiator 8,
single-mode reactor) for 30 min at 150 °C. On cooling of the
reaction to ambient temperature, the solvent was removed
under reduced pressure, and the residue was purified by flash
silica gel column chromatography using hexane/ethyl acetate
(70/30) as eluent to afford 3/5.
(dd, J = 7.6, 1.5 Hz, 1H), 6.88 (dt, J = 7.6, 1.5 Hz, 1H), 6.80 (dt,
J = 7.6, 1.5 Hz, 1H), 6.64 (dd, J = 7.6, 1.5 Hz, 1H), 3.91 (brs,
1H), 2.63-2.41 (m, 2H), 2.16-1.87 (m, 4H), 1.49 (s, 3H); 13C
NMR (75 MHz, CDCl3) δ 166.8, 139.2, 131.3, 124.6, 120.4,
117.2, 110.7, 80.1, 34.7, 30.6, 26.2, 17.5; IR (KBr) νmax
3
3253, 2966, 2917, 1638, 1592, 1266, 1207, 1081, 740 cm-1
;
HRMS calcd for C12H15N2O (Mþ þ H) 203.1184, found
203.1181.
10a-Methyl-3,4,10,10a-tetrahydro-1H-benzo[4,5]imidazo[2,1-
c][1,4]oxazin-4-one (3f). Yellow solid; mp = 182-184 °C; Rf =
0.31 (hexane/EtOAc = 50/50); 1H NMR (300 MHz, CDCl3) δ
7.72 (d, J = 7.6 Hz, 1H), 6.93 (t, J = 7.6 Hz, 1H), 6.82 (t, J = 7.6
Hz, 1H), 6.67 (d, J = 7.6 Hz, 1H), 4.26 (ABq, J = 17.4 Hz, 2H),
3.81 (ABq, J = 10.6 Hz, 2H), 3.75 (brs, 1H), 1.63 (s, 3H); 13
C
NMR (75 MHz, CDCl3) δ 163.8, 139.3, 129.8, 125.5, 120.7,
117.2, 110.6, 77.9, 72.2, 66.9, 24.9; IR (KBr) νmax 3248, 2976,
2880, 1652, 1491, 1236, 1104, 941, 751 cm-1; HRMS calcd for
C11H13N2O2 (Mþ þ H) 205.0977, found 205.0968.
4b-Methyl-4b,11-dihydro-5H-benzo[4,5]imidazo[2,1-a]isoindol-
11-one (3g). White solid; mp = 186-188 °C; Rf = 0.56 (hexane/
EtOAc = 30/70); 1H NMR (300 MHz, CDCl3) δ 7.82 (d, J = 7.6
Hz, 1H), 7.60-7.45 (m, 4H), 6.96-6.83 (m, 2H), 6.67 (d, J = 7.6
Hz, 1H), 4.20 (brs, 1H), 1.81 (s, 3H); 13C NMR (75 MHz,
CDCl3) δ 170.7, 149.6, 145.1, 133.4, 132.0, 130.6, 129.6, 125.4,
125.1, 121.9, 120.9, 117.2, 111.4, 86.1, 26.8; IR (KBr) νmax 3355,
3056, 2922, 2853, 1702, 1601, 1482, 1324, 1123, 1015, 738, 697
cm-1; HRMS calcd for C15H13N2O (Mþ þ H) 237.1028, found
237.1021.
3a-Methyl-2,3,3a,4-tetrahydro-1H-benzo[d]pyrrolo[1,2-a]imi-
dazol-1-one (3a). Brown solid; mp = 106-108 °C; Rf = 0.39
(hexane/EtOAc = 70/30); 1H NMR (300 MHz, CDCl3) δ 7.38
(dd, J = 7.6, 1.5 Hz, 1H), 6.90 (dt, J = 7.6, 1.5 Hz, 1H), 6.77
(t, J = 6.8 Hz, 1H), 6.60 (d, J = 6.8 Hz, 1H), 4.11 (brs, 1H), 2.76-
2.67 (m, 1H), 2.54-2.32 (m, 3H), 1.51 (s, 3H); 13C NMR (75
MHz, CDCl3) δ 173.7, 142.7, 126.5, 125.2, 120.1, 115.3, 110.5,
85.5, 37.6, 33.6, 26.1; IR (KBr) νmax 3320, 2969, 1692, 1603,
1491, 1202, 1163, 1050, 746 cm-1; HRMS calcd for C11H13N2O
(Mþ þ H) 189.1027, found 189.1029.
3a-Ethyl-2,3,3a,4-tetrahydro-1H-benzo[d]pyrrolo[1,2-a]imidazol-
1-one (3h). Brown solid; mp = 118-120 °C; Rf = 0.47 (hexane/
EtOAc = 70/30); 1H NMR (300 MHz, CDCl3) δ 7.36 (d, J = 7.6
Hz, 1H), 6.87 (t, J = 7.6 Hz, 1H), 6.73 (t, J = 7.4 Hz, 1H), 6.57
(d, J = 7.6 Hz, 1H), 4.32 (brs, 1H), 2.76-2.64 (m, 1H),
2.50-2.20 (m, 3H), 1.87-1.68 (m, 2H), 0.96 (t, J = 7.4 Hz,
3H); 13C NMR (75 MHz, CDCl3) δ 174.3, 142.9, 129.7, 125.1,
119.8, 115.3, 109.8, 87.8, 35.6, 33.4, 32.9, 17.8; IR (KBr) νmax
2,2,3a-Trimethyl-2,3,3a,4-tetrahydro-1H-benzo[d]pyrrolo[1,2-a]-
imidazol-1-one (3b). Brown solid; mp = 148-150 °C; Rf = 0.46
(hexane/EtOAc = 70/30); 1H NMR (300 MHz, CDCl3) δ 7.36
(d, J = 7.6 Hz, 1H), 6.91 (t, J = 7.6 Hz, 1H), 6.78 (t, J = 7.6 Hz,
1H), 6.59 (d, J = 8.3 Hz, 1H), 4.12 (brs, 1H), 2.27 (ABq, J =
12.8 Hz, 2H), 1.56 (s, 3H), 1.39 (s, 3H), 1.23 (s, 3H); 13C NMR
(75 MHz, CDCl3) δ 179.9, 142.9, 128.8, 125.3, 119.6, 116.1,
110.2, 82.3, 50.9, 44.2, 28.0, 26.6, 26.5; IR (KBr) νmax 3299, 2965,
2862, 1690, 1493, 1255, 1193, 828, 741 cm-1; HRMS calcd for
C13H17N2O (Mþ þ H) 217.1341, found 217.1332.
3326, 2969, 1698, 1601, 1490, 1210, 1153, 1051, 747 cm-1
;
HRMS calcd for C12H15N2O (Mþ þ H) 203.1184, found
203.1191.
3a,5-Dimethyl-2,3,3a,4-tetrahydro-1H-benzo[d]pyrrolo[1,2-a]-
imidazol-1-one (3i). Red solid; mp = 164-166 °C; Rf = 0.32
1
(DCM/MeOH = 95/05); H NMR (500 MHz, CDCl3) δ 7.25
3a-Methyl-3a,4-dihydrospiro[benzo[d]pyrrolo[1,2-a]imidazole-
2,10-cyclopentan]-1(3H)-one (3c). White solid; mp = 180-182 °C;
Rf = 0.71 (hexane/EtOAc = 80/20); 1H NMR (300 MHz,
CDCl3) δ 7.37 (d, J = 7.2 Hz, 1H), 6.90 (t, J = 7.6 Hz, 1H),
6.78 (t, J = 7.5 Hz, 1H), 6.59 (d, J = 7.6 Hz, 1H), 3.89 (brs, 1H),
2.32 (ABq, J = 12.5 Hz, 2H), 2.31-2.22 (m, 1H), 2.14-2.03 (m,
1H), 1.96-1.59 (m, 5H), 1.55 (s, 3H), 1.51-1.42 (m, 1H); 13C
NMR (75 MHz, CDCl3) δ 179.6, 142.9, 128.9, 125.1, 119.9,
115.8, 110.3, 82.6, 54.2, 51.4, 39.0, 37.8, 28.0, 26.0, 25.2; IR
(KBr) νmax 3303, 3062, 2953, 2862, 1687, 1601, 1491, 1469, 1425,
1261, 1054, 736 cm-1; HRMS calcd for C15H19N2O (Mþ þ H)
243.1497, found 243.1503.
(dd, J = 6.8, 2.3 Hz, 1H), 6.76-6.69 (m, 2H), 3.78 (brs, 1H),
2.83-2.65 (m, 1H), 2.54-2.31 (m, 3H), 2.12 (s, 3H), 1.52 (s, 3H);
13C NMR (75 MHz, CDCl3) δ 173.6, 141.0, 128.0, 126.4, 120.1,
120.0, 112.8, 85.4, 37.7, 33.5, 26.3, 16.4; IR (KBr) νmax 3282,
3055, 2958, 1662, 1592, 1483, 1387, 1329, 1227, 1180, 898, 740
cm-1; HRMS calcd for C12H15N2O (Mþ þ H) 203.1184, found
203.1175.
9,10a-Dimethyl-3,4,10,10a-tetrahydro-1H-benzo[4,5]imidazo-
[2,1-c][1,4]oxazin-4-one (3j). Yellow solid; mp = 186-188 °C;
Rf = 0.36 (DCM/MeOH = 95/05); 1H NMR (300 MHz,
CDCl3) δ 7.58 (dd, J = 6.0, 3.0 Hz, 1H), 6.79-6.73 (m, 2H),
4.25 (ABq, J = 16.6 Hz, 2H), 3.84 (ABq, J = 10.6 Hz, 2H), 3.50
(brs, 1H), 2.15 (s, 3H), 1.63 (s, 3H); 13C NMR (75 MHz, CDCl3)
δ 163.4, 137.6, 129.6, 126.8, 121.0, 120.0, 115.0, 77.8, 72.3, 67.0,
25.5, 16.5; IR (KBr) νmax 3273, 2963, 2923, 2860, 1651, 1587,
1479, 1393, 1224, 1159, 948, 757 cm-1; HRMS calcd for C12H14-
N2O2Na (Mþ þ H) 241.0943, found 241.0952.
3a-Methyl-3a,4-dihydrospiro[benzo[d]pyrrolo[1,2-a]imidazole-
2,10-cyclohexan]-1(3H)-one (3d). Yellow solid; mp = 186-188 °C;
Rf = 0.56 (hexane/EtOAc = 70/30); 1H NMR (300 MHz,
CDCl3) δ 7.37 (d, J = 7.6 Hz, 1H), 6.91 (t, J = 7.6 Hz, 1H),
6.79 (t, J = 7.6 Hz, 1H), 6.62 (d, J = 7.6 Hz, 1H), 4.03 (brs, 1H),
5972 J. Org. Chem. Vol. 75, No. 17, 2010

Patil et al.
6-Ethoxy-3a-methyl-2,3,3a,4-tetrahydro-1H-benzo[d]pyrrolo-
JOCArticle
(d, J = 7.5 Hz, 1H), 4.07 (brs, 1H), 4.06 (dd, J = 10.7, 2.2 Hz,
1H), 2.92 (dd, J = 12.8, 10.7 Hz, 1H), 2.45 (dd, J = 12.8, 2.2 Hz,
1H), 1.35 (s, 3H); 13C NMR (75 MHz, CDCl3) δ 174.7, 142.9,
139.4, 128.8, 127.4, 127.1, 125.7, 120.3, 116.5, 110.5, 85.2, 50.8,
44.4, 28.5; IR (KBr) νmax 3324, 2965, 2928, 2871, 1691, 1603,
1490, 1416, 1256, 743 cm-1; HRMS calcd for C17H17N2O
(Mþ þ H) 265.1341, found 265.1343.
[1,2-a]imidazol-1-one (3k). Darkbrownsolid; mp= 122-124 °C;
Rf = 0.37 (hexane/EtOAc = 70/30); 1H NMR (300 MHz,
CDCl3) δ 7.24 (d, J = 8.3 Hz, 1H), 6.26 (dd, J = 8.3, 2.3 Hz,
1H), 6.19 (d, J = 2.3 Hz, 1H), 4.03 (brs, 1H), 3.93 (q, J = 6.9 Hz,
2H), 2.87-2.67 (m, 1H), 2.53-2.27 (m, 3H), 1.51 (s, 3H), 1.38 (t,
J = 6.9 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ 173.5, 157.4,
144.1, 122.3, 115.6, 104.3, 98.9, 86.1, 63.8, 37.4, 33.5, 26.1, 14.9;
IR (KBr) νmax 3268, 2971, 2923, 1680, 1610, 1499, 1343, 1161,
1045, 836, 782, 738 cm-1; HRMS calcd for C13H17N2O2 (Mþ þ
H) 233.1290, found 233.1292.
(2R,3aR)-2-Ethyl-3a-methyl-2,3,3a,4-tetrahydro-1H-benzo[d]-
pyrrolo[1,2-a]imidazol-1-one (3r). Brown solid; mp = 142-144
°C; Rf = 0.62 (hexane/EtOAc = 70/30); 1H NMR (300 MHz,
CDCl3) δ 7.37 (d, J = 7.6 Hz, 1H), 6.89 (dt, J = 7.6, 1.1 Hz, 1H),
6.77 (dt, J = 7.6, 1.1 Hz, 1H), 6.60 (d, J = 7.6 Hz, 1H), 4.10 (brs,
1H), 2.75-2.65 (m, 1H), 2.52-2.46 (m, 1H), 2.07-1.89 (m, 1H),
1.50 (s, 3H), 1.46-1.34 (m, 1H), 0.97 (t, J = 7.6 Hz, 3H); 13C
NMR (75 MHz, CDCl3) δ 175.2, 142.6, 128.6, 124.9, 120.1,
115.4, 110.5, 82.9, 45.8, 44.1, 26.1, 23.1, 11.6; IR (KBr) νmax
(3l). A mixture of regioisomers (70:30); thick liquid; Rf = 0.34
(hexane/EtOAc = 70/30); 1H NMR (300 MHz, CDCl3) δ 7.26-
7.19 (m, 1H), 6.71-6.20 (m, 2H), 4.06 (brs, 1H), 2.82-2.66 (m,
1H), 2.54-2.24 (m, 3H), 1.49 (s, 3H); 13C NMR (75 MHz,
CDCl3) δ 173.6, 143.0, 140.4, 135.2, 126.3, 125.4, 120.3, 116.1,
115.0, 111.5, 110.6, 85.8, 37.6, 36.0, 33.8, 33.6, 29.7, 26.0, 21.5,
21.0; IR (film) νmax 3311, 2970, 2921, 1690, 1500, 1463, 1393,
1202, 1085, 982, 858, 802, 753, 659 cm-1; HRMS calcd for
C12H12F3N2O (Mþ þ H) 257.0902, found 257.0913.
3276, 2964, 2928, 1683, 1604, 1492, 1258, 1056, 743, 681 cm-1
;
HRMS calcd for C13H17N2O (Mþ þ H) 217.1341, found
217.1339.
(2S,3aR)-2-Ethyl-3a-methyl-2,3,3a,4-tetrahydro-1H-benzo[d]-
pyrrolo[1,2-a]imidazol-1-one (3r0). Brown solid; mp =94-96 °C;
Rf = 0.61 (hexane/EtOAc = 70/30); 1H NMR (500 MHz,
CDCl3) δ 7.34 (d, J = 8.4 Hz, 1H), 6.89 (t, J = 7.3 Hz, 1H),
6.75 (t, J = 7.3 Hz, 1H), 6.60 (d, J = 7.3 Hz, 1H), 4.40 (brs, 1H),
2.60-2.55 (m, 1H), 2.53 (ABq, J = 10.5 Hz, 2H), 1.95-1.86 (m,
1H), 1.63-1.54 (m, 1H), 1.49 (s, 3H), 1.02 (t, J = 7.3 Hz, 3H);
13C NMR (75 MHz, CDCl3) δ 177.8, 142.8, 129.3, 125.5,
120.1, 116.5, 110.5, 84.9, 47.0, 40.5, 29.2, 26.1, 12.3; IR (KBr)
νmax 3286, 3056, 2942, 1680, 1596, 1484, 1232, 1034, 745, 693
cm-1; HRMS calcd for C13H17N2O (Mþ þ H) 217.1341, found
217.1339.
(2R,3aR)-2-(4-Isobutylphenyl)-2,3a-dimethyl-2,3,3a,4-tetra-
hydro-1H-benzo[d]pyrrolo[1,2-a]imidazol-1-one (3s). White so-
lid; mp = 158-160 °C; Rf = 0.81(hexane/EtOAc = 70/30);
1H NMR (500 MHz, CDCl3) δ 7.53 (d, J = 7.3 Hz, 1H), 7.36 (d,
J = 8.4 Hz, 2H), 7.13 (d, J = 8.4 Hz, 2H), 6.97 (t, J = 8.4 Hz,
1H), 6.85 (t, J = 7.3 Hz, 1H), 6.67 (d, J = 7.3 Hz, 1H), 4.05 (brs,
1H), 2.92 (d, J = 12.5 Hz, 1H), 2.61 (d, J = 12.5 Hz, 1H), 2.46
(d, J = 7.3 Hz, 2H), 1.89-1.81 (m, 1H), 1.53 (s, 3H), 1.13 (s,
3H), 0.89 (s, 3H), 0.88 (s, 3H); 13C NMR (75 MHz, CDCl3) δ
176.5, 143.0, 141.6, 140.0, 129.4, 128.9, 125.7, 125.4, 119.8,
116.1, 110.3, 89.2, 82.6, 52.9, 44.9, 30.2, 28.3, 26.6, 22.5; IR
(KBr) νmax 3290, 3062, 2927, 1667,1497, 1380, 1261, 1156, 1028,
756, 691 cm-1; HRMS calcd for C22H27N2O (Mþ þ H)
335.2123, found 335.2126.
(3m). A mixture of regioisomers (90:10); brown solid; mp =
1
110-112 °C; Rf = 0.37 (hexane/EtOAc = 70/30); H NMR
(300 MHz, CDCl3) δ 7.27 (dd, J = 8.3, 5.3 Hz, 1H), 6.43 (dt, J =
9.1, 2.3 Hz, 1H), 6.32 (dd, J = 9.1, 2.3 Hz, 1H), 4.42 (brs, 1H),
2.79-2.65 (m, 1H), 2.53-2.29 (m, 3H), 1.51 (s, 3H); 13C NMR
(75 MHz, CDCl3) δ 173.8, 162.5, 159.3, 144.0, 124.5, 115.5,
115.4, 110.5, 110.4, 105.3, 104.9, 98.7, 98.3, 86.4, 37.6, 37.4, 33.4,
33.2, 26.0; IR (KBr) νmax 3302, 2976, 2919, 1692, 1614, 1500,
1349, 1138, 1087, 971, 833, 792, 715, 625 cm-1; HRMS calcd for
C11H12FN2O (Mþ þ H) 207.0934, found 207.0923.
(3n). A mixture of regioisomers (80:20); pale Yellow solid;
mp =92-94 °C; Rf = 0.33 (hexane/EtOAc = 70/30); 1H NMR
(300 MHz, CDCl3) δ 7.37 (d, J = 1.5 Hz, 0.3H), 7.28 (d, J = 8.3
Hz, 0.8H), 6.87 (dd, J = 8.3, 2.3 Hz, 0.2H), 6.75 (dd, J = 8.3, 2.3
Hz, 0.8H), 6.58 (d, J = 1.5 Hz, 0.8H), 6.52 (d, J = 7.6 Hz, 0.2H),
4.18 (brs, 1H), 2.84-2.68 (m, 1H), 2.56-2.30 (m, 3H), 1.52 (s,
3H); 13C NMR (75 MHz, CDCl3) δ 173.9, 144.0, 130.3, 127.2,
124.9, 119.4, 115.8, 110.9 110.6, 86.2, 37.7, 37.6, 33.4, 26.2, 26.1;
IR (KBr) νmax 3265, 2969, 2921, 1700, 1606, 1498, 1334, 1262,
1049, 932, 778, 658 cm-1; HRMS calcd for C11H12ClN2O (Mþ
þ H) 223.0638, found 223.0629.
(3o). A mixture of regioisomers (70:30); dark red solid; mp =
1
136-138 °C; Rf = 0.57 (hexane/EtOAc = 70/30); H NMR
(300 MHz, CDCl3) δ 7.50 (d, J = 1.5 Hz, 0.3H), 7.23 (d, J = 8.3
Hz, 0.7H), 7.01 (dd, J = 8.3, 2.3 Hz, 0.3H), 6.89 (dd, J = 8.3, 2.3
Hz, 0.7H), 6.74 (d, J = 1.5 Hz, 0.7H), 6.47 (d, J = 8.3 Hz, 0.3H),
4.30 (brs, 1H), 2.77-2.67 (m, 1H), 2.61-2.34 (m, 3H), 1.52 (s,
3H); 13C NMR (75 MHz, CDCl3) δ 173.9, 144.2, 127.9, 127.6,
122.5, 118.4, 117.9, 116.3, 113.4, 111.5, 86.2, 37.9, 37.6, 33.4,
27.7, 26.2; IR (KBr) νmax 3302, 2972, 2921, 1680, 1595, 1474,
1328, 1078, 980, 744, 655 cm-1; HRMS calcd for C11H12N2OBr
(Mþ þ H) 267.0133, found 267.0132.
3a-Methyl-1,2,3,3a,4,9-hexahydropyrrolo[2,1-b]quinazolin-1-
one (5a). Brown solid; mp = 138-140 °C; Rf = 0.52 (hexane/
EtOAc = 30/70); 1H NMR (300 MHz, CDCl3) δ 7.01-6.97 (m,
2H), 6.73 (t, J = 7.6 Hz, 1H), 6.49 (d, J = 8.1 Hz, 1H), 4.56
(ABq, J = 16.9 Hz, 2H), 3.74 (brs, 1H), 2.59-2.38 (m, 2H),
2.15-2.01 (m, 2H), 1.54 (s, 3H); 13C NMR (75 MHz, CDCl3) δ
174.2, 141.7, 127.4, 126.7, 119.0, 117.1, 116.3, 71.8, 38.5, 32.7,
29.6, 25.4; IR (KBr) νmax 3294, 3057, 2908, 1718, 1484, 1383,
1094, 755, 700 cm-1; HRMS calcd for C12H15N2O (Mþ þ H)
203.1184, found 203.1191.
(2S,3aR)-3a-Methyl-2-phenyl-2,3,3a,4-tetrahydro-1H-benzo-
[d]pyrrolo[1,2-a]imidazol-1-one (3q). Yellow solid; mp = 178-
1
180 °C; Rf = 0.42 (hexane/EtOAc = 70/30); H NMR (500
MHz, CDCl3) δ 7.49-7.25 (m, 6H), 6.94 (t, J = 6.9 Hz, 1H),
6.82 (t, J = 6.9 Hz, 1H), 6.65 (d, J = 7.7 Hz, 1H), 4.15 (brs, 1H),
4.02 (dd, J = 13.0, 7.6 Hz, 1H), 2.77 (dd, J = 12.3, 7.6 Hz, 1H),
2.59 (dd, J = 12.5, 7.5 Hz, 1H), 1.60 (s, 3H); 13C NMR (75 MHz,
CDCl3) δ 173.3, 142.7, 137.1, 128.7, 128.5, 127.3, 125.2, 120.0,
115.5, 110.5, 82.5, 50.6, 47.2, 25.6; IR (KBr) νmax 3298, 3052,
2963, 2861, 1690, 1490, 1253, 1191, 738 cm-1; HRMS calcd for
C17H17N2O (Mþ þ H) 265.1341, found 265.1337.
2,2,3a-Trimethyl-1,2,3,3a,4,9-hexahydropyrrolo[2,1-b]quinazolin-
1-one (5b). Brown solid; mp = 148-150 °C; Rf = 0.68 (hexane/
EtOAc = 30/70); 1H NMR (300 MHz, CDCl3) δ 6.99-6.97 (m,
2H), 6.71 (t, J = 8.3 Hz, 1H), 6.47 (d, J = 7.6 Hz, 1H), 4.51
(ABq, J = 16.6 Hz, 2H), 3.78 (brs, 1H), 1.99 (ABq, J = 13.6 Hz,
2H), 1.54 (s, 3H), 1.24 (m, 6H); 13C NMR (75 MHz, CDCl3) δ
178.7, 141.7, 127.4, 126.8, 118.9, 117.3, 116.2, 69.2, 48.5, 40.5,
38.7, 26.7, 26.5; IR (KBr) νmax 3322, 2966, 2925, 1667, 1494,
1226, 1062, 747 cm-1; HRMS calcd for C14H19N2O (Mþ þ H)
231.1497, found 231.1495.
(2R,3aR)-3a-Methyl-2-phenyl-2,3,3a,4-tetrahydro-1H-benzo-
[d]pyrrolo[1,2-a]imidazol-1-one (3q0). Yellow solid; mp
=
1
174-176 °C; Rf = 0.41 (hexane/EtOAc = 70/30); H NMR
(500 MHz, CDCl3) δ 7.45 (d, J = 7.5 Hz, 1H), 7.40-7.20
(m, 5H), 6.93 (t, J = 8.5 Hz, 1H), 6.79 (t, J = 8.1 Hz, 1H), 6.30
3a0-Methyl-30,3a0,40,90-tetrahydro-10H-spiro[cyclohexane-1,20-
pyrrolo[2,1-b]quinazolin]-10-one (5c). Pale yellow solid; mp =
1
200-202 °C; Rf = 0.32 (hexane/EtOAc = 30/70); H NMR
J. Org. Chem. Vol. 75, No. 17, 2010 5973

Patil et al.
JOCArticle
(300 MHz, CDCl3) δ 6.99-6.95 (m, 2H), 6.71 (t, J = 7.6 Hz,
1H), 6.47 (d, J = 8.3 Hz, 1H), 4.58 (ABq, J = 16.6 Hz, 2H), 3.70
(brs, 1H), 2.02 (ABq, J = 12.8 Hz, 2H), 1.87-1.60 (m, 6H), 1.54
(s, 3H), 1.42-1.23 (m, 4H); 13C NMR (75 MHz, CDCl3) δ 178.4,
141.8, 127.4, 126.8, 118.9, 117.3, 116.1, 69.6, 45.4, 44.7, 38.5,
35.0, 33.5, 26.8, 25.2, 22.2, 22.1; IR (KBr) νmax 3323, 2926, 2849,
1664, 1490, 1251, 1207, 1096, 746 cm-1; HRMS calcd for
C17H23N2O (Mþ þ H) 271.1810, found 271.1816.
IR (KBr) νmax 3341, 2964, 2924, 1678, 1489, 1398, 1228, 1101,
1029, 636 cm-1; HRMS calcd for C14H19N2O (Mþ þ H)
231.1497, found 231.1494.
7-Methoxy-3a-methyl-1,2,3,3a,4,9-hexahydropyrrolo[2,1-b]-
quinazolin-1-one (5j). Brown solid; mp = 104-106 °C; Rf = 0.48
(hexane/EtOAc = 30/70); 1H NMR (300 MHz, CDCl3) δ 6.63-
6.49 (m, 3H), 4.53 (ABq, J = 17.4 Hz, 2H), 3.72 (s, 3H), 3.48
(brs, 1H), 2.58-2.39 (m, 2H), 2.15-1.99 (m, 2H), 1.50 (s,
3H); 13C NMR (75 MHz, CDCl3) δ 174.0, 153.3, 135.2, 118.9,
118.3, 114.1, 111.4, 72.0, 55.6, 38.7, 32.9, 29.5, 25.0; IR (KBr)
4b-Methyl-4b,5,10,12-tetrahydroisoindolo[1,2-b]quinazolin-12-
one (5d). Pale yellow solid; mp =222-224 °C; Rf = 0.32
(hexane/EtOAc = 30/70); 1H NMR (500 MHz, DMSO-d6)
δ 7.80-7.76 (m, 2H), 7.63 (t, J = 6.7 Hz, 1H), 7.52 (t, J = 6.7
Hz, 1H), 7.10 (d, J = 8.1 Hz, 1H), 7.05 (t, J = 8.1 Hz, 1H), 6.77
(t, J = 8.1 Hz, 1H), 6.70 (d, J = 8.1 Hz, 1H), 5.85 (brs, 1H), 4.83
(ABq, J = 17.5 Hz, 2H), 1.70 (s, 3H); 13C NMR (75 MHz,
DMSO-d6) δ 165.1, 147.6, 140.5, 131.4, 130.3, 128.4, 127.0,
126.1, 123.0, 120.7, 118.1, 116.2, 116.0, 70.5, 37.2, 23.0; IR
(KBr) νmax 3291, 2955, 2923, 2864, 1677, 1495, 1393, 1206, 1098,
1016, 841, 744, 694 cm-1; HRMS calcd for C16H15N2O (Mþ þ
H) 251.1184, found 251.1170.
νmax 3307, 2964, 1674, 1504, 1229, 1180, 1034, 834, 665 cm-1
;
HRMS calcd for C13H17N2O2 (Mþ þ H) 233.1290, found
233.1298.
7-Chloro-3a,5-dimethyl-1,2,3,3a,4,9-hexahydropyrrolo[2,1-b]-
quinazolin-1-one (5k). Darkbrownsolid;mp=144-146 °C; Rf =
0.33 (hexane/EtOAc = 30/70); 1H NMR(300 MHz, CDCl3) δ6.89
(s, 1H), 6.87 (s, 1H), 4.42 (ABq, J = 17.2 Hz, 2H), 3.63 (brs, 1H),
2.55-2.42 (m, 2H), 2.18-2.20 (m, 2H), 2.07 (s, 3H), 1.51 (s, 3H);
13C NMR (75 MHz, CDCl3) δ 174.1, 138.5, 128.4, 125.3, 124.1,
123.2, 118.1, 71.9, 38.3, 32.9, 29.4, 25.7, 16.9; IR (KBr) νmax 3336,
2964, 1678, 1482, 1396, 1227, 1169, 865, 723 cm-1; HRMS calcd for
C13H16ClN2O (Mþ þ H) 251.0951, found 251.0968.
3a-Ethyl-1,2,3,3a,4,9-hexahydropyrrolo[2,1-b]quinazolin-1-one
(5e). Brown solid; mp = 148-150 °C; Rf = 0.53 (hexane/EtOAc =
70/30); 1H NMR (300 MHz, CDCl3) δ 7.00-6.95 (m, 2H), 6.72
(t, J = 7.6 Hz, 1H), 6.49 (d, J = 7.6 Hz, 1H), 4.52 (ABq,
J = 16.6 Hz, 2H), 4.05 (brs, 1H), 2.59-2.38 (m, 2H), 2.18-2.08
(m, 1H), 1.94-1.78 (m, 3H), 0.94 (t, J = 7.5 Hz, 3H); 13C NMR
(75 MHz, CDCl3) δ 174.6, 141.6, 127.6, 126.9, 119.1, 117.6,
116.3, 74.7, 38.8, 29.8, 29.5, 29.4, 7.7; IR (KBr) νmax 3290, 2964,
2932, 1679, 1608, 1441, 1160, 983, 746 cm-1; HRMS calcd for
C13H17N2O (Mþ þ H) 217.1340, found 217.1341.
8-Chloro-3a-methyl-1,2,3,3a,4,9-hexahydropyrrolo[2,1-b]qui-
nazolin-1-one (5l). Yellow solid; mp = 128-130 °C; Rf = 0.36
(hexane/EtOAc = 30/70); 1H NMR (300 MHz, CDCl3) δ 6.93
(t, J = 7.7 Hz, 1H), 6.76 (d, J = 7.9 Hz, 1H), 6.39 (d, J = 7.9 Hz,
1H), 4.51 (ABq, J = 17.6 Hz, 2H), 4.00 (brs, 1H), 2.51-2.44 (m,
2H), 2.09-2.04 (m, 2H), 1.53 (s, 3H); 13C NMR (75 MHz,
CDCl3) δ 174.4, 143.6, 128.2, 126.9, 119.5, 116.4, 114.5, 71.9,
37.6, 32.6, 29.5, 25.3; IR (KBr) νmax 3292, 2975, 1682, 1395,
1233, 1200, 821, 780 cm-1; HRMS calcd for C12H14ClN2O (Mþ þ
H) 237.0795, found 237.0793.
3a-Octyl-1,2,3,3a,4,9-hexahydropyrrolo[2,1-b]quinazolin-1-one
(5f). Brown solid; mp =98-100 °C; Rf = 0.76 (hexane/EtOAc =
70/30); 1H NMR (500 MHz, CDCl3) δ 6.99-6.95(m, 2H), 6.71 (t,
J = 7.8 Hz, 1H), 6.47 (d, J = 7.8 Hz, 1H), 4.51 (ABq, J = 16.6
Hz, 2H), 2.53-2.39 (m, 2H), 2.15-2.01 (m, 1H), 1.92-1.80 (m,
1H), 1.80-1.69 (m, 2H), 1.35-1.23 (m, 12H), 0.86 (t, J = 6.8 Hz,
3H); 13C NMR (75 MHz, CDCl3) δ 174.5, 141.6, 127.5, 126.8,
119.0, 117.4, 116.1, 74.3, 38.7, 37.2, 31.7, 29.9, 29.5, 29.4, 29.1,
23.4, 22.5, 14.0; IR (KBr) νmax 3307, 2926, 2854, 1673, 1449, 1260,
1198, 813, 745 cm-1; HRMS calcd for C19H29N2O (Mþ þ H)
301.2280, found 301.2287.
8-Fluoro-3a-methyl-1,2,3,3a,4,9-hexahydropyrrolo[2,1-b]quina-
zolin-1-one (5m). Pale yellow solid; mp = 140-142 °C; Rf =
0.36 (hexane/EtOAc = 30/70); H NMR (300 MHz, CDCl3)
1
δ 6.95 (dd, J = 8.2, 6.4 Hz, 1H), 6.44 (t, J = 8.3 Hz, 1H), 6.27 (d,
J = 8.1 Hz, 1H), 4.57 (ABq, J = 17.4 Hz, 2H), 4.05 (brs, 1H),
2.58-2.40 (m, 2H), 2.12-2.02 (m, 2H), 1.50 (s, 3H); 13C NMR
(75 MHz, CDCl3) δ 174.4, 161.8, 158.6, 143.5, 131.9, 128.3,
128.2, 111.3, 105.2, 104.9, 71.6, 33.9, 32.6, 29.4, 25.3; IR (KBr)
ν
max 3300, 2965, 1681, 1500, 1391, 1233, 1199, 1079, 1025, 763
5a-Methyl-5,6,7,8,9,11-hexahydro-5aH-pyrido[2,1-b]quinazolin-
9-one (5g). Yellow solid; mp = 156-158 °C; Rf = 0.50 (hexane/
EtOAc = 30/70); 1H NMR (500 MHz, CDCl3) δ 6.95-6.92 (m,
2H), 6.69-6.66 (m, 1H), 6.47 (d, J = 7.4 Hz, 1H), 4.22 (ABq,
J = 17.5 Hz, 2H), 3.80 (brs, 1H), 2.44-2.26 (m, 2H), 1.98-1.88
(m, 3H), 1.78-1.67 (m, 1H), 1.47 (s, 3H); 13C NMR (75 MHz,
CDCl3) δ 169.0, 141.0, 128.4, 127.4, 126.8, 119.3, 116.1, 68.3,
39.7, 37.3, 32.9, 26.8, 16.8; IR (KBr) νmax 3293, 2941, 2862, 1619,
1491, 1271, 1113, 749, 541 cm-1; HRMS calcd for C13H17N2O
(Mþ þ H) 217.1341, found 217.1346.
cm-1; HRMS calcd for C12H14FN2O (Mþ þ H) 221.1090, found
221.1097.
11,11a-Dimethyl-1,3,4,6,11,11a-hexahydro[1,4]oxazino[3,4-b]-
quinazolin-4-one (5n). Brown solid; mp = 192-194 °C; Rf =
0.32 (DCM/MeOH = 95/05); 1H NMR (300 MHz, CDCl3)
δ 7.13 (t, J = 7.6 Hz, 1H), 7.04 (d, J = 7.4 Hz, 1H), 6.80 (t, J =
7.4 Hz, 1H), 6.71 (d, J = 8.1 Hz, 1H), 4.70 (ABq, J = 16.8 Hz,
2H), 4.12 (ABq, J = 4.1 Hz, 2H), 3.92 (ABq, J = 11.7 Hz, 2H),
2.82 (s, 3H), 1.45 (s, 3H) ; 13C NMR (75 MHz, CDCl3) δ 165.2,
144.1, 128.0, 126.3, 121.2, 119.5, 114.5, 72.2, 68.0, 39.3, 33.0,
29.8, 19.8; IR (KBr) νmax 2923, 1670, 1605, 1494, 1458, 1397,
1296, 1110, 1067, 981, 837, 600 cm-1; HRMS calcd for
C13H17N2O2 (Mþ þ H) 233.1290, found 233.1296.
3a,8-Dimethyl-1,2,3,3a,4,9-hexahydropyrrolo[2,1-b]quinazolin-
1-one (5h). Brown solid; mp = 156-158 °C; Rf = 0.53 (hexane/
EtOAc = 30/70); 1H NMR (300 MHz, CDCl3) δ 6.91 (t, J = 8.3
Hz, 1H), 6.59 (d, J = 7.6 Hz, 1H), 6.36 (d, J = 8.3 Hz, 1H), 4.45
(ABq, J = 16.6 Hz, 2H), 3.75 (brs, 1H), 2.54-2.46 (m, 2H), 2.23
(s, 3H), 2.11-2.02 (m, 2H), 1.54 (s, 3H); 13C NMR (75 MHz,
CDCl3) δ 174.1, 141.7, 135.7, 127.2, 120.8, 115.9, 114.1, 71.4,
37.4, 32.7, 29.5, 25.2, 18.5; IR (KBr) νmax 3319, 2969, 2923, 1675,
1236, 1200, 1099, 778, 673 cm-1; HRMS calcd for C13H17N2O
(Mþ þ H) 217.1340, found 217.1347.
(2R,3aR)-3a-Methyl-2-phenyl-1,2,3,3a,4,9-hexahydropyrrolo-
[2,1-b]quinazolin-1-one (5p). Pale yellow solid; mp = 170-172 °C;
Rf = 0.46 (hexane/EtOAc = 30/70); 1H NMR (500 MHz,
CDCl3) δ 7.37-7.18 (m, 5H), 7.02-6.97 (m, 2H), 6.74 (t, J =
7.6 Hz, 1H), 6.49 (d, J = 8.1 Hz, 1H), 4.40 (ABq, J = 16.8 Hz,
2H), 3.84 (t, J = 9.6 Hz, 1H), 3.82 (brs, 1H), 2.53 (dd, J =
13.0, 9.6 Hz, 1H), 2.12 (dd, J = 13.0, 9.6 Hz, 1H), 1.62 (s, 3H);
13C NMR (75 MHz, CDCl3) δ 174.9, 141.9, 139.1, 128.8,
128.1, 127.5, 127.1, 126.8, 119.2, 117.5, 116.4, 70.0, 47.1,
42.7, 39.0, 25.8; IR (KBr) νmax 3303, 2974, 1680, 1489, 1228,
1119, 1076, 751, 696 cm-1; HRMS calcd for C18H19N2O
(Mþ þ H) 279.1497, found 279.1508.
3a,5,7-Trimethyl-1,2,3,3a,4,9-hexahydropyrrolo[2,1-b]quina-
zolin-1-one (5i). Pale yellow solid; mp = 136-138 °C; Rf = 0.37
(hexane/EtOAc = 30/70); 1H NMR (300 MHz, CDCl3) δ 6.71
(s, 1H), 6.68 (s, 1H), 4.46 (ABq, J = 16.8 Hz, 2H), 3.39 (brs, 1H),
2.59-2.39 (m, 2H), 2.20 (s, 3H), 2.15-2.09 (m, 2H), 2.05 (s, 3H),
1.50 (s, 3H); 13C NMR (75 MHz, CDCl3) δ 173.8, 137.3, 129.4,
128.0, 124.8, 123.7, 116.9, 71.9, 38.6, 33.2, 29.5, 25.7, 20.4, 16.9;
(2S,3aR)-3a-Methyl-2-phenyl-1,2,3,3a,4,9-hexahydropyrrolo-
[2,1-b]quinazolin-1-one (5p0). Yellow solid; mp = 122-124 °C;
5974 J. Org. Chem. Vol. 75, No. 17, 2010

Patil et al.
JOCArticle
Rf = 0.70 (hexane/EtOAc = 30/70); 1H NMR (500 MHz, CDCl3)
δ 7.24-7.19 (m, 4H), 7.18-7.14 (m, 1H), 7.02-6.97 (m, 2H), 6.75
(t, J = 7.2 Hz, 1H), 6.54 (d, J = 7.2 Hz, 1H), 4.37 (ABq, J = 17.6
Hz, 2H), 3.78 (t, J = 9.3 Hz, 1H), 2.63 (dd, J = 13.5, 9.3 Hz, 1H),
2.15 (dd, J = 13.5, 3.1 Hz, 1H), 1.49 (s, 3H); 13C NMR (75 MHz,
CDCl3) δ 172.7, 141.2, 128.6, 128.3, 127.6, 127.0, 126.9, 119.3,
116.3, 70.1, 47.6, 43.2, 38.9, 25.2; IR (KBr) νmax 3326, 2994, 2826,
1692, 1497, 1253, 1181, 1074, 753, 695 cm-1; HRMS calcd for
C18H19N2O (Mþ þ H) 279.1497, found 279.1509.
172-174 °C; Rf = 0.74 (hexane/EtOAc =70/30); 1H NMR
(500 MHz, CDCl3) δ 7.28-7.25 (m, 2H), 7.07-6.97 (m, 4H),
6.74 (t, J = 7.6 Hz, 1H), 6.50 (d, J = 8.3 Hz, 1H), 4.68 (ABq,
J = 17.4 Hz, 2H), 3.85 (brs, 1H), 2.39 (ABq, J = 13.6 Hz, 2H),
2.43 (d, J = 6.8 Hz, 2H), 1.90-1.77 (m, 1H), 1.61 (s, 3H), 1.47 (s,
3H), 0.91 (s, 3H), 0.89 (s, 3H); 13C NMR (75 MHz, CDCl3) δ
176.7, 142.5, 141.5, 139.9, 129.2, 127.5, 126.9, 125.7, 119.1,
117.3, 116.1, 69.4, 50.5, 48.7, 44.9, 38.8, 30.1, 26.4, 26.3, 22.4;
IR (KBr) νmax 3296, 3027, 2925, 2854, 1675, 1607, 1487, 1399,
1239, 769, 750 cm-1; HRMS calcd for C23H29N2O (Mþ þ H)
349.2280, found 349.2277.
(2S,3aR)-2-(4-Isobutylphenyl)-2,3a-dimethyl-1,2,3,3a,4,9-hex-
ahydropyrrolo[2,1-b]quinazolin-1-one (5r0). White solid; mp =
128-130 °C; Rf = 0.72 (hexane/EtOAc =70/30); 1H NMR (500
MHz, CDCl3) δ 7.14 (d, J = 8.4 Hz, 2H), 6.96-6.95 (m, 4H),
6.69 (t, J = 7.5 Hz, 1H), 6.36 (d, J = 8.4 Hz, 1H), 4.61 (ABq,
J = 16.8 Hz, 2H), 2.36 (ABq, J = 13.9 Hz, 2H), 2.33 (d, J = 6.5
Hz, 2H), 1.78-1.70 (m, 1H), 1.57 (s, 3H), 1.50 (s, 3H), 0.82 (s,
3H), 0.80 (s, 3H); 13C NMR (75 MHz, CDCl3) δ 176.5, 142.2,
141.5, 139.8, 129.1, 127.5, 126.9, 125.9, 119.2, 117.3, 116.7, 69.4,
50.8, 48.4, 44.9, 39.0, 30.0, 26.9, 26.7, 22.3; IR (KBr) νmax 3313,
2955, 2866, 1676, 1609, 1489, 1410, 1213, 771, 749 cm-1; HRMS
calcd for C23H29N2O (Mþ þ H) 349.2280, found 349.2276.
(2S,3aR)-2-Ethyl-3a-methyl-1,2,3,3a,4,9-hexahydropyrrolo-
[2,1-b]quinazolin-1-one (5q). Yellow solid; mp = 130-132 °C; Rf
= 0.58 (hexane/EtOAc = 30/70); 1H NMR (500 MHz, CDCl3)
δ 6.99-6.95 (m, 2H), 6.72 (t, J = 8.3 Hz, 1H), 6.47 (d, J = 8.3
Hz, 1H), 4.45 (ABq, J = 16.6 Hz, 2H), 3.73 (brs, 1H), 2.58-2.48
(m, 1H), 2.21 (dd, J = 12.8, 9.0 Hz, 1H), 2.05-1.87 (m, 1H), 1.70
(dd, J = 12.8, 9.0 Hz, 1H), 1.55 (s, 3H), 1.51-1.39 (m, 1H), 0.97
(t, J = 7.6 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ 176.5, 141.9,
127.4, 126.8, 119.1, 117.6, 116.3, 70.2, 42.0, 39.0, 38.6, 25.9, 23.9,
11.4; IR (KBr) νmax 3331, 2963, 2925, 2869, 1680, 1487, 1399,
1231, 1032, 747, 695 cm-1; HRMS calcd for C14H19N2O (Mþ þ
H) 231.1497, found 231.1506.
(2R,3aR)-2-Ethyl-3a-methyl-1,2,3,3a,4,9-hexahydropyrrolo-
[2,1-b]quinazolin-1-one (5q0). Yellow solid; mp = 100-102 °C;
Rf = 0.56 (hexane/EtOAc = 70/30); 1H NMR (500 MHz,
CDCl3) δ 7.00-6.96 (m, 2H), 6.73 (t, J = 7.6 Hz, 1H), 6.50
(d, J = 8.7 Hz, 1H), 4.53 (ABq, J = 17.0 Hz, 2H), 3.86 (brs, 1H),
2.53-2.42 (m, 1H), 2.32 (dd, J = 12.5, 7.0 Hz, 1H), 1.97-1.84
(m, 1H), 1.79 (dd, J = 12.5, 7.0 Hz, 1H), 1.57-1.42 (m, 1H), 1.49
(s, 3H), 0.98 (t, J = 7.4 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ
174.7, 141.4, 127.6, 127.0, 119.2, 117.1, 116.2, 70.3, 42.7, 39.7,
38.5, 25.4, 24.7, 11.8; IR (KBr) νmax 3309, 2964, 2927, 2867,
1676, 1490, 1408, 1308, 1175, 752, 707 cm-1; HRMS calcd for
C14H19N2O (Mþ þ H) 231.1497, found 231.1506.
Acknowledgment. We gratefully acknowledge financial
support by the Council of Scientific and Industrial Research,
India. N.T.P. is grateful to Dr. J. S. Yadav, Director, IICT
and Dr. V. V. N. Reddy, Head, Org-II Division for their
support and encouragement.
Supporting Information Available: All experimental proce-
dures, analytical data, copies of 1H and 13C NMR spectra of all
newly synthesized products, and CIF files. This material is
available free of charge via the Internet at http://pubs.acs.org.
(2R,3aR)-2-(4-Isobutylphenyl)-2,3a-dimethyl-1,2,3,3a,4,9-hexa-
hydropyrrolo[2,1-b]quinazolin-1-one (5r). White solid; mp =
J. Org. Chem. Vol. 75, No. 17, 2010 5975