Copper-mediated cyclization-halogenation and cyclization-cyanation reactions of β-hydroxyalkynes and o -alkynylphenols and anilines

Article abstract of DOI:10.1021/jo1005119

The CuX (X = I, Br, Cl, CN)-mediated cyclization-halogenation and cyclization-cyanation reactions of β-hydroxyalkynes and o-alkynylphenol and -aniline derivatives give rise to 3-halo- and 3-cyanofuro[3,2-b]pyrroles, 3-iodo-, 3-bromo-, and 3-cyanobenzofurans, and 3-cyanoindoles, respectively.

Full text of DOI:10.1021/jo1005119

pubs.acs.org/joc
Copper-Mediated Cyclization-Halogenation and
Cyclization-Cyanation Reactions of β-Hydroxyalkynes and
o-Alkynylphenols and Anilines
Nalivela Kumara Swamy, Arife Yazici, and Stephen G. Pyne*
School of Chemistry, University of Wollongong, Wollongong, New South Wales 2522, Australia
spyne@uow.edu.au
Received March 18, 2010
The CuX (X = I, Br, Cl, CN)-mediated cyclization-halogenation and cyclization-cyanation reactions
of β-hydroxyalkynes and o-alkynylphenol and -aniline derivatives give rise to 3-halo- and 3-cyanofuro-
[3,2-b]pyrroles, 3-iodo-, 3-bromo-, and 3-cyanobenzofurans, and 3-cyanoindoles, respectively.
Introduction
alkaloids.3 We recently reported an efficient synthesis of this
latter heterocyclic class of compounds, for example, 2 (R =
H, Ph, Scheme 1), via metal-catalyzed cycloisomerization of
4,5-cis-hydroxyalkynylpyrrolidin-2-ones 1 using Agþ, Auþ,
or Pd2þ/Cuþ as catalyst.4 Related cycloisomerization reac-
tions have been developed to prepare benzofurans and
indoles.5 This type of transformation would be made more
valuable if the initially formed cyclized organometallic inter-
mediate A could be utilized to introduce further useful
functional groups into the cyclized products and provide,
for example, 3-functionalized furo[3,2-b]pyrroles, like 3
(Scheme 1). Such useful functional groups could include
halogen and cyano that have well-documented utility in
organic synthesis for the formation of new C-Y bonds (Y =
C, N, S and O) and the preparation of other key functional
groups (e.g., keto, formyl, CH2NH2, and CH2OH groups),
respectively.6
The benzofuran and indole ring structures are common to
many bioactive and natural product molecules, and there-
fore efficient methods for the synthesis of substituted deri-
vatives are highly desirable.1,2 The less common furo[3,2-
b]pyrrole heterocyclic system is a key structural feature
of the bioactive fungal metabolite lucilactaene and related
(1) McCallion, G. D. Curr. Org. Chem. 1999, 3, 67–76.
(2) ROMPP Encylopedia Natural Products; Steglich, W., Fugmann, B.,
Lang-Fugmann, S., Eds.; Thieme Verlag: Stuttgart, 2000; pp 314-316.
(3) Bashyal, B. P.; Faeth, S. H.; Gunatilaka, A. A. L. Nat. Prod. Commun.
2007, 2, 547-550 and references cited therein.
(4) Jury, J. C.; Swamy, N. K.; Yazici, A.; Willis, A.; Pyne, S. G. J. Org.
Chem. 2009, 74, 5523–5527.
(5) For reviews on metal-catalyzed cyclization reactions, see: Nakamura,
I.; Yamamoto, Y. Chem. Rev. 2004, 104, 2127–2198. Zeni, G.; Larock, R. C.
Chem. Rev. 2006, 106, 4644–4680. Hashmi, A. S. K.; Hutchings, G. J. Angew.
Chem., Int. Ed. 2006, 45, 7896–7936. Hashmi, A. S. K. Chem. Rev. 2007, 107,
3180–3211. Fuerstner, A.; Davies, P. W. Angew. Chem., Int. Ed. 2007, 46,
3410–3449. Shen, H. C. Tetrahedron 2008, 64, 3885–3903. Shen, H. C.
Tetrahedron 2008, 64, 7847–7870. Alvarez-Corral, M.; Munoz-Dorado,
M.; Roderiguez-Garcia, I. Chem. Rev. 2008, 108, 3174–3198. Patil, N. T.;
Yamamoto, Y. Chem. Rev. 2008, 108, 3395–3442. Gorin, D. J.; Sherry, B. D.;
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108, 3266–3325. Li, Z.; Brouwer, C.; He, C. Chem. Rev. 2008, 108, 3239–
3265. Yamamoto, Y.; Gridnev, I. D.; Patil, N. T.; Jin, T. Chem. Commun.
2009, 5075–5087.
The organometallic intermediates formed in the cyclo-
isomerization reactions of related o-alkynylphenols and
anilines have been shown to undergo further metal-mediated
(6) Comprehensive Organic Transformations, 2nd ed.; Larock, R. C., Ed.;
Wiley: New York, 1999.
3412 J. Org. Chem. 2010, 75, 3412–3419
Published on Web 04/21/2010
DOI: 10.1021/jo1005119
r
2010 American Chemical Society

Swamy et al.
JOCArticle
SCHEME 1. Synthesis of Furo[3,2-b]pyrroles 2 and 3
In principle, compounds 3 could be prepared from reduc-
tive elimination of the cyclization intermediate A (X =
halogen or CN) (Scheme 1). In fact, Ma has demonstrated
that CuCl2 and CuBr2 are effective reagents for the halo-
lactonization of 2,3-allenoic acids.12 Presumably, these reac-
tions occur via a reductive elimination pathway of a RCu-
(II)X (X = Cl or Br) intermediate. This type of reaction
has been further developed employing Pd/Cu catalysis, using
PdX2 (5 mol %) and CuX2 (3 equiv) [X = Cl, Br or I], for the
cyclization-halogenation reactions of o-alkynylphenols and
N-acetyl-o-alkynylanilines to give 3-halo-2-substituted benzo-
furans and indoles, respectively.13 These reactions, however,
often gave mixtures of 3-unsubstituted-2-substituted benzo-
furans and indoles (cycloisomerization products) and
3-halo-2-substituted benzofurans and indoles (cyclization-
halogenation products). We report here a novel and direct
method for the synthesis of 3-halo- and 3-cyanofuro[3,2-
b]pyrroles, 3-iodo, 3-bromo-, and 3-cyanobenzofurans, and
3-cyanoindoles from the CuX (X = I, Br, Cl, CN)-promoted
sequential cyclization-reductive elimination reactions of
the cis-4-hydroxy-5-phenylethynylpyrrolidinones 1 (R =
Ph, n-Pent) and O- and N-protected o-alkynylphenols and
-anilines, respectively.
reactions with alkenes or CO/MeOH, or reductive elimina-
tion when the cyclization catalyst is RPd(II), to provide
3-substituted benzofurans and indoles through subsequent
C-C bond-forming reactions.5 Further, methods that in-
volve migration of the initial O- or N-substituent of the
phenol and aniline precursors, respectively, to the C-3 posi-
tion during the cyclization process have also been reported.7
Metal-catalyzed procedures for the direct cyclization-
cyanation reaction of these and related substrates, however,
have not been reported.8
While the synthesis of 2-substituted 3-iodobenzofurans
and indoles has been achieved from the cyclization reactions
of o-alkynylphenols9 (or their O-protected derivatives)10 and
anilines11 with electrophilic iodine reagents, the synthesis of
the valuable nitrile products in a direct process requires a
different synthetic strategy. Further, these iodonium ion
induced cyclization reactions are sometimes complicated
due to competing 1,2-addition reactions to the triple bond
of the starting substrates.11b Indeed, treatment of 1 (R = Ph)
with I2/NaHCO3/CH2Cl2 gave a complex mixture of pro-
ducts while the reaction of 1 (R = Ph) with NIS/CH2Cl2
resulted in an 81:19 mixture of 3 (R = Ph, X = I, 71%
isolated yield) and the 1,2-diiodo addition product 4 (X=I,
13% isolated yield), Scheme 1.
Results and Discussion
Under the Ma conditions,12 the reaction of 1 (R = Ph)
with CuBr2 (2 equiv) in acetone/water at 70 °C resulted in
only recovered 1, while the same reaction with 6 equiv of
CuBr2 in DMF with heating at 70 °C for 12 h gave the 1,2-
dibromo derivative 4 (X = Br) in 67% yield (Scheme 1).
When 1 (R = Ph) was treated with CuI (1.5 equiv) in DMF at
rt, no reaction occurred; however, when the mixture was
heated at 80 °C under a nitrogen atmosphere for 16 h, a 68:32
mixture of 3 and 2 (R = Ph) was obtained from which 3 (R =
Ph, X = I) could be isolated after column chromatography
in 46% yield (Table 1, entry 1). We assumed that intermedi-
ate A (M = Cu(I), m = 0) was formed initially and under-
went oxidation by a redox reaction with CuI to the
corresponding Cu(II), or possibly Cu(III),14 intermediate A
(M = Cu(II), m = 1), which then gave the desired product 3
(R = Ph). Consistent with this hypothesis was the fact that
increasing the amount of CuI to 3 and 6 equiv gave higher
ratios of 3:2, the latter modification giving only 3 (R = Ph,
X = I) in 71% isolated yield (Table 1, entries 2 and 3, res-
pectively). The addition of base (Et3N) resulted in formation
of only the cyclized product 2 (R = Ph). The amount of CuI
could be reduced to 1.1 equiv if the reaction was performed
under an oxygen atmosphere (balloon) providing iodide 3
(R = Ph, X = I) in 85% yield (Table 1, entry 4). The reac-
tions under an oxygen atmosphere required heating at 100 °C
to ensure complete conversion in 16 h. Similar results were
obtained using 1 (R = Ph) and 1.1 equiv of CuBr or CuCl
under an oxygen atmosphere (Table 1, entries 5 and 6)
providing the corresponding 3-bromo- and 3-chloro-cyclized
products. The cyano derivative 3 (R = Ph, X = CN) was ob-
tained in 76% yield when the amount of CuCN was increased
(7) See, for example: Cacchi, S.; Fabrizi, G.; Pace, P. J. Org. Chem. 1998,
63, 1001–1011. Shimada, T.; Nakamura, I.; Yamamoto, Y. J. Am. Chem.
Soc. 2004, 126, 10546–10547.
(8) For some recent methods to prepare 3-cyanofurans and indoles using
strategies different from that described here, see: Shi, Z.; Zhang, C.; Li, S.;
Pan, D.; Ding, S.; Cui, Y.; Jiao, N. Angew. Chem., Int. Ed. 2009, 48, 4572–
4576. Li, X.; Du, Y.; Liang, Z.; Li, X.; Pan, Y.; Zhao, K. Org. Lett. 2009, 11,
2643–2646. Yu, W.; Du, Y.; Zhao, K. Org. Lett. 2009, 11, 2417–2420. Huang,
X.-C.; Liu, Y.-L.; Liang, Y.; Pi, S.-F.; Wang, F.; Li, J.-H. Org. Lett. 2008, 10,
1525–1528. Wacker, D. A.; Kasireddy, P. Tetrahedron Lett. 2002, 43, 5189–
5191. Chen, C.-y.; Domer, P. G. J. Org. Chem. 2005, 70, 6964–6967.
(9) Arcardi, A.; Cacchi, S.; Fabrizi, G.; Marinelli, F.; Moro, L. Synlett
1999, 1432–1434.
(10) (a) Yue, D.; Yao, T.; Larock, R. C. J. Org. Chem. 2005, 70, 10292–
10296. (b) Okitsu, T.; Nakazawa, D.; Taniguchi, R.; Wada, A. Org. Lett.
2008, 10, 4967–4970.
(11) (a) Barluenga, J.; Trincado, M.; Rubino, E.; Gonzalez, J. M. Angew.
Chem., Int. Ed. 2003, 42, 2406–2409. (b) Yue, D.; Yao, T.; Larock, R. C.
J. Org. Chem. 2006, 71, 62–69.
(12) Ma, S.; Wu, S. J. Org. Chem. 1999, 64, 9314–9317.
(13) (a) Liang, Y.; Tang, S.; Zhang, X.-D.; Mao, L.-Q.; Xie, Y.-X.; Lie,
J.-H. Org. Lett. 2006, 8, 3017–3020. (b) Tang, S.; Xie, Y.-X.; Li, J.-H.; Wang,
N.-X. Synthesis 2007, 1841–1847.
(14) Ley, S. V.; Thomas, A. W. Angew. Chem., Int. Ed. 2003, 42, 5400–
5449.
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TABLE 1. Synthesis of Furo[3,2-b]pyrroles 3a,b
TABLE 2. Synthesis of 3-Substituted Benzofurans 7a
entry
1 (R)
CuX (equiv)
atm
ratio 2:3
yield (%) of 3
1
2
3
4
5
6
7
8
9
Ph
Ph
Ph
Ph
Ph
Ph
Ph
n-Pent
n-Pent
CuI (1.5)
CuI (3.0)
CuI (6.0)
CuI (1.1)
CuBr (1.1)
CuCl (1.1)
CuCN (2.2)d
CuI (1.1)
N2
N2
N2
O2
O2
O2
O2
O2
O2
32:68
25:75
0:100
0:100
0:100
0:100
7:93
46
50
71
85
87
77c
76
72
79
0:100
0:100
CuCN (2.2)
aReactions under N2 were performed in DMF at 80 °C for 16 h.
bReactions under O2 were performed in DMF at 100 °C for 16 h. cThis
product was obtained in approximately 90% purity. dWhen 1.1 equiv
was used the ratio of 2:3 was 28:72 and the yield of 3 was 50%.
to 2.2 equiv (Table 1, entry 7). Quenching of the CuCl reaction
mixture with water after 2 h at 80°C afforded only the product
2 (R=Ph). This result suggested that cyclization of 1 (R =
Ph) to a Cu(I) intermediate A (M = Cu(I), m = 0) was
relatively fast and that its further oxidation by O2 to A (M =
Cu(II), m=1) and/or reductive elimination to give 3 was a
much slower process. The nonaromatic substrate 1 (R =
n-Pent) reacted with CuI and CuCN to provide the iodinated
and cyanated derivatives 3 (R = n-Pent, X = I or CN) in
respective yields of 72% and 79% (Table 1, entries 8 and 9).
In order to further examine the scope of these CuX-
mediated reactions, the related o-alkynylphenols and
-anilines were examined as substrates. The o-alkynylphenol 5
(R = H, R1 = Ph) underwent similar CuI- and CuCN-
mediated reactions to provide mixtures of 7a or 7c and the
cycloisomerization product 8 (R=H, R1=Ph). Often, the
products 7 and 8 were difficult to separate. For example,
treatment of 5 (R = H, R1 = Ph) with CuI (1.1 equiv) under
an oxygen atmosphere as described above gave an insepar-
able 86:14 mixture of 7a and the benzofuran 8 (R = H, R1 =
Ph) in a combined yield of 82%. The starting o-alkynyl-
phenol 5 (R=H, R1=Ph) was, as previously noted,10a an
unstable substrate and underwent cyclization to benzofuran
8 (R=H, R1 =Ph) on storage and had to be prepared or
purified fresh before each reaction.
Because of these difficulties, attention was focused on the
more stable O-acetyl derivatives 6. These substrates required
higher reaction temperatures (135-140 °C) than 5 in their
reactions with CuX but provided much higher ratios of 7:8
(usually 7:8 = 100:0, see Table 2, footnote a) and allowed
for the isolation of pure products 7 (Table 2). We found that
2.2 equiv of CuX was required in these cases to ensure
good conversions to 7 in 16 h. The parent compound 6 (R =
H, R1 = Ph) gave the desired 3-substituted benzofurans
7a-c exclusively and in good yields (Table 2, entries 1-3),
while its reaction with CuCl gave a complex mixtures of
aReactions were performed under O2 in DMF at 135-140 °C for 16 h.
The ratio of 7:8 was 100:0, except entry 4 (93:7) and entry 9 (92:8).
bA complex mixture of products was obtained that included 7f, which
could not be obtained pure. cReaction performed at 100 °C for 16 h.
products. The reactions of substrates 6 having electron-
withdrawing (Table 2, entries 5 and 7) and electron-donating
(Table 2, entry 4) substituents work equally well in their
reactions with CuCN as did the parent compound 6 (R = H,
R1=Ph). The methoxy derivative 6 (R=OMe, R1 = Ph),
however, produced a complex mixture of products. The
1-alkylalkynyl substrate 6 (R = H, R1 = n-Pent) also reacted
efficiently with CuI and CuCN to give the respective benzo-
furan products 7h and 7i in 76% and 69% yields, respectively
(Table 2, entries 8 and 9).
An attempt to perform the cyclization-iodination reac-
tion on 6 (R = H, R1 = Ph) using CuI in a catalytic amount
(0.1 equiv) in the presence of LiI (3 equiv) and TMEDA (1
equiv) under an oxygen atmosphere gave an inseparable
49:51 mixture of 7a and 8 (R = H, R1 = Ph) in a combined
yield of 73%.
The N-Ts and N-TFA o-alkynylanilines 9 (R = H, R1 =
Ph) underwent CuCN-mediated cyclization-cyanation re-
actions upon heating at 100 °C for 16 h to provide the
3-cyano, N-Ts, and N-unsubstituted indoles 10a and 10b in
yields of 74% and 80%, respectively (Table 3, entries 1 and 2)
when 3.0 equiv.of CuCN was used. The aforementioned
reaction also produced a small amount (3%) of the less
substituted indole 11 (R = H, R1 = Ph, R2 = Ts), while the
reaction of the latter substrate resulted in clean formation of
the N-unprotected indole product 10b with efficient loss of
the N-TFA group. Attempts to cyclize the N-unprotected
compound 9 (P = H, R = H, R1 = Ph) resulted in a complex
mixture of products, while the reaction of its N-Cbz analo-
gue 9 (P = Cbz, R = H, R1 = Ph) returned only unreacted
starting material. These results may suggest that only the
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TABLE 3. Synthesis of 3-Cyanoindoles 10a
cyanation reactions of cis-4-hydroxy-5-phenylethynylpyrro-
lidinones 1 and O- and N-protected o-alkynylphenols 6 and
-anilines 9, respectively. Although cyclization-halogenation
reactions of similar substrates have been reported using
electrophilic halogenation reagents,10,11 the CuX (X = I,
Br, Cl) method reported here will be useful in cases where
the aforementioned reagents give poor yields of cyclized
products due to competing intermolecular addition reactions
of the alkyne moiety or halogenation of the aromatic ring.
While the cyanation reactions of alkynes are known,16 the
sequential cyclization-cyanation reactions of these sub-
strates has not been reported. Furthermore, this method
allows for the synthesis of 3-cyanobenzofurans and indoles
in a one-step process that otherwise would require two
sequential steps from the same starting substrates, that is,
iodonium ion induced cyclization followed by a classical
Rosenmund-von Braun reaction with CuCN17 or its more
recent and milder Pd-catalyzed versions,18 on the resulting
3-iodobenzofurans or 3-iodoindoles.10,11 As a comparison,
the 3-cyanobenzofuran 7c was obtained in 65% overall yield
from the two-step method, which employed in the second
step a Pd-catalyzed Rosenmund-von Braun reaction which
required heating at 120 °C for 36 h,13a while this compound
was obtained in 78% yield using this new method at a similar
reaction temperature (135 °C) in 16 h. The majority of
reactions that provided the 3-cyanoindoles 10, using this
new one-step process, however, proceeded efficiently under
much milder conditions at 100 °C. Further, this new method
is also more cost-effective when one compares the relatively
higher costs per mole of iodine and NIS with the less
expensive CuCN.
aReactions were performed under O2 in DMF at 100 °C for 16 h. The
ratio of 7:8 was 100:0, except entry 1 (98:2), entry 6 (30:70), and entry 9
(70:30). bCompound11 was also isolated in 3% yield. cAt 130 °C for 16 h.
dCompound 11 was also isolated in 38% yield. eCompound 11 was also
isolated in 24% yield.
While the exact mechanism of these reactions is not
known, the difference in the results of the reaction of 1
(R = Ph) with CuBr2 (alkyne dibromination) and CuBr
(cyclization-bromination) (Scheme 1) suggests that a Cu(II)
species is not involved in the initial cyclization reaction.
We suggest that, in the reactions of CuX with 1 under an
oxygen atmosphere, the intermediate A (M = Cu(I), m = 0)
in Scheme 1 is formed initially via cyclization of an electro-
philic Cu(I)-alkyne complex intermediate5 which then
undergoes oxidation by molecular oxygen to the correspond-
ing Cu(II) or Cu(III) species before reductive elimination to give
products 3.
softer amine nucleophiles (NHTFA and NHTS compared
to NH2) were suitable for cyclization with the relatively
soft electrophilic Cu-alkyne complex intermediate.15 In con-
trast, the reactions of 9 (P = Ts R = H, R1 = Ph) with CuX
(X = I, Br, Cl) were unsuccessful and resulted in the return of
unreacted starting material. The reactions of substrates 9
having electron-withdrawing (Table 3, entries 4, 6, and 7)
and electron-donating (Table 2, entry 3) substituents work
equally well as 9 (P = Ts or TFA, R = H, R1 = Ph) with
CuCN. The methoxy-substituted substrate 9 (P = TFA, R =
OMe, R1 = Ph), however, required heating at 130 °C to
obtain 100% consumption of 9 in 16 h, resulting in a 78%
isolated yield of indole 10e (Table 3, entry 5). The N-TFA pro-
tected, 1-alkylalkynyl substrate 9 (P = TFA, R = H, R1 =
n-Pent) reacted efficiently with CuCN to give the 3-cyanated
indole product 10i in 73% yield (Table 3, entry 8), while its
N-Ts analogue 9 (P = TsR = H, R1 = n-Pent) gave a mixture
of 10i (55% isolated yield) and 11 (R = Ts R = H, R1 =
n-Pent, 24% isolated yield) (Table 3, entry 9).
Experimental Section
General Details. See the Supporting Information. Safety
Note. While we have experienced no problems, care must be
taken when heating DMF above its flash point (58 °C) under an
oxygen atmosphere.
Cyclization-Iodination Reaction of 1 (R = Ph) Using N-
Iodosuccinimide. (3aR,6aS)-4-Benzyl-3-iodo-2-phenyl-6,6a-di-
hydro-3aH-furo[3,2-b]pyrrol-5(4H)-one (3, R=Ph, X=I) and
(4S,5R)-1-Benzyl-5-((E)-1,2-diiodo-2-phenylvinyl)-4-hydroxypyr-
rolidin-2-one (4, X = I). To a solution of 1 (R = Ph)4 (25 mg,
0.085 mmol) and NIS (57 mg, 0.25 mmol) in CH2Cl2 (3 mL) was
added NaHCO3 (21 mg, 0.25 mmol), and stirring was continued
Conclusions
In conclusion, we have developed a direct and convenient
method for the cyclization-halogenation and cyclization-
(16) Arai, S.; Sato, T.; Koike, Y.; Hayashi, M.; Nishida, A. Angew.
Chem., Int. Ed. 2009, 48, 4528–4531.
(15) A reviewer has suggested that the NTs or NTFA aniline substrates
may undergo initial deprotonation prior to cyclization, and hence, they are
more reactive than their N-unsubstituted aniline counterparts. While this
may be a possibility, the absence of a base in these reactions would suggest
that this is less likely.
(17) Beletskaya, I. P.; Cheprakov, A. V. Coord. Chem. Rev. 2004, 248,
2337–2364.
(18) (a) Okitsu, T.; Nakazawa, D.; Taniguchi, R.; Wada, A. Org. Lett.
2008, 10, 4967–4970. (b) Hatsuda, M.; Seki, M. Tetrahedron 2005, 61,
9908–9917. and references cited therein.
J. Org. Chem. Vol. 75, No. 10, 2010 3415

Swamy et al.
JOCArticle
at rt for 16 h under a N2 atmosphere. The reaction mixture was
diluted with water (8 mL), quenched with saturated sodium
thiosulfate solution (1 mL), and extracted with EtOAc (2 ꢀ
10 mL). The combined organic extracts were dried (MgSO4),
and the solvent was removed in vacuo. The crude product was
chromatographed on silica gel (1:2 EtOAc/petroleum ether) to
give 3 (R=Ph, X= I) as a white crystalline solid (26 mg, 71%)
and 4 (X = I) as a white solid (6 mg, 13%).
properties of 3 (R = Ph, X = I) were the same as those described
above.
(3aR,6aS)-4-Benzyl-3-bromo-2-phenyl-6,6a-dihydro-3aH-furo-
[3,2-b]pyrrol-5(4H)-one (3, R = Ph, X = Br). Prepared from 1
(R = Ph) (50 mg, 0.17 mmol) and CuBr (27 mg, 0.19 mmol) ac-
cording to the general procedure A described above. Purification
via flash chromatography (1:1 EtOAc/petroleum ether) provided
the title compound as a colorless gum (55.3 mg, 87%): Rf = 0.72
(1:1 EtOAc/petroleum ether); [R]24 þ2.6 (c 0.87, CHCl3); IR
3 (R = Ph, X = I): mp 140-142 °C; Rf = 0.71 (1:1 EtOAc/
D
(neat, νmax/cm-1) 1674, 1438, 1226, 1068, 922 and 753; δH
7.86-7.29 (10H, m, ArH), 5.18 (1H, d, J = 15.0 Hz, CHHPh),
5.16 (1H, m, HC-6a), 4.73 (1H, d, J = 7.9 Hz, HC-3a), 4.43 (1H,
d, J = 15.0 Hz, CHHPh), 2.97-2.87 (2H, m, H2C-6). δC 172.1
(CO), 154.9 (2-C), 136.1 (C), 130.1 (CH), 128.8 (CH), 128.7 (CH),
128.6 (C), 128.4 (CH), 128.2 (CH), 127.7 (CH), 87.9 (3-C), 76.3
(6a-C), 68.7 (3a-C), 44.8 (CH2Ph), 37.9 (6-C); ESIMS m/z 370
[(MHþ), 79Br, 100], 372 [(MHþ), 81Br, 100]; HREIMS calcd. for
C19H16NO279Br (Mþ) 369.0365, found 369.0364.
petroleum ether); [R]24 þ6.1 (c 1.8, CHCl3); IR (neat, νmax
/
D
cm-1) 1672, 1406, 1218, 916, 862, 756; δH 7.82-7.29 (10H, m,
H), 5.18 (1H, m, HC-6a), 5.15 (1H, d, J = 15.2 Hz, CHHPh),
4.70 (1H, dd, J = 7.8, 0.7 Hz, HC-3a), 4.54 (1H, d, J = 15.2 Hz,
CHHPh), 2.96-2.86 (2H, m, H2C-6). δC 172.34 (CO), 159.2 (2-
C), 136.2 (C), 130.2 (CH), 129.3 (CH), 128.6 (CH), 128.4 (CH),
128.3 (CH), 128.1 (CH), 127.6 (C), 77.4 (6a-C), 71.1 (3a-C), 52.3
(3-C), 44.8 (CH2Ph), 37.6 (6-C); EIMS m/z 417 [(Mþ) 50];
HREIMS calcd for C19H16NO2I (Mþ) 417.0225, found
417.0211.
(3aR,6aS)-4-Benzyl-3-chloro-2-phenyl-6,6a-dihydro-3aH-furo-
[3,2-b]pyrrol-5(4H)-one (3, R = Ph, X = Cl). Prepared from 1
(R = Ph) (50 mg, 0.17 mmol) and CuCl (19 mg, 0.19 mmol) ac-
cording to the general procedure A described above. Purification
via flash chromatography (1:1 EtOAc/petroleum ether) provided
the title compound as an off white solid (43 mg, 77%). This
compound was approximately 90% pure from NMR analysis:
4 (X = I): mp 166-168 °C; Rf = 0.75 (1:1 EtOAc/petroleum
ether); [R]24D -0.9 (c 1.28, CHCl3); IR (neat, νmax/cm-1) 3232,
1675, 1408, 1261, 1045, 744 and 703; δH 7.88-7.31 (10H, m, H),
5.40 (1H, d, J = 15.0 Hz, CHHPh), 4.83 (1H, m, HC-4), 4.61
(1H, d, J = 8.1 Hz, HC-5), 4.30 (1H, d, J = 15.0 Hz, CHHPh),
3.47 (1H, s, OH), 2.93 (1H, dd, J = 18.0, 9.3 Hz, HC-3), 2.80
(1H, dd, J = 18.0, 5.3 Hz, HC-3). δC 173.3 (CO), 139.0 (C),
135.3 (C), 129.9 (CH), 128.9 (CH), 128.8 (CH), 127.9 (CH),
127.8 (CH), 127.6 (CH), 107.2 (IC=CI), 75.1 (ICdCI and 5-C),
72.1 (4-C), 45.0 (CH2Ph), 37.5 (3-C); ESIMS m/z 562 [(M þ
NH3)þ 100]; HRESIMS calc. for C19H20N2O2I2 (M þ NH3)þ
561.9459, found 561.9503.
mp 158-160 °C; Rf = 0.74 (1:1 EtOAc/petroleum ether); [R]25
D
þ21.2 (c 0.80, CHCl3); IR (neat, νmax/cm-1): 1692, 1485, 1398,
1227, 1028, 937 and 768; δH 7.83-7.81 (2H, m, ArH), 7.41-7.25
(8H, m, ArH), 5.20 (1H, d, J=15.0 Hz, CHHPh), 5.15-5.12 (1H,
m, HC-6a), 4.68(1H, d, J =7.5Hz, HC-3a), 4.34(1H, d, J = 15.0
Hz, CHHPh), 2.95-2.88 (2H, m, H2C-6). δC 172.0 (CO), 152.6
(2-C), 136.0(C), 130.0 (CH), 128.7(CH), 128.4(CH), 128.3 (CH),
128.2 (CH), 127.7 (C), 127.2 (CH), 102.5 (3-C), 75.5 (6a-C), 67.4
(3a-C), 44.8 (CH2Ph), 37.9 (6-C); ESIMS m/z 326 [(MHþ), 35Cl,
100]; HREIMS calcd. for C19H16NO235Cl (Mþ) 325.0872, found
325.0869.
Reaction of 1 (R = Ph) with CuBr2. (4S,5R)-1-Benzyl-5-((E)-
1,2-dibromo-2-phenylvinyl)-4-hydroxypyrrolidin-2-one (4, X =
Br). A mixture of 1 (R = Ph) (20 mg, 0.068 mmol) and CuBr2
(90 mg, 0.4 mmol) in anhydrous DMF (2 mL, Aldrich) was
stirred at 70 °C for 12 h under a N2 atmosphere. The reaction
mixture was cooled to rt, diluted with water (10 mL), and
extracted with EtOAc (2 ꢀ 10 mL). The combined organic
extracts were dried (MgSO4), and the solvent was removed
under vacuo. The crude product was chromatographed on silica
gel (1:2 EtOAc/petroleum ether) to give the title compound as a
white powder (20 mg, 67%): mp 178-180 °C; Rf = 0.75 (1:1
(3aR,6aS)-4-Benzyl-3-iodo-2-pentyl-6,6a-dihydro-3aH-furo-
[3,2-b]pyrrol-5(4H) one (3, R = n-Pent, X = I). Prepared from 1
(R = n-Pent) (50 mg, 0.21 mmol) and CuI (44 mg, 0.23 mmol)
according to the general procedure A described above. Purifica-
tion via flash chromatography (1:2 EtOAc/petroleum ether)
provided the title compound 3 (R = Pent, X = I) as a light
yellow gum (52 mg, 72%): Rf = 0.82 (1:2 EtOAc/petroleum
ether); [R]25D -25.2 (c 4.0, CHCl3); IR (neat, νmax/cm-1) 2945,
2924, 1681, 1408, 1219, 1040, 958, 860 and 702; δH 7.36-7.26
(5H, m, ArH), 5.12 (1H, d, J = 15.0 Hz, CHHPh), 5.02-4.98
(1H, td, J = 1.5, 8.0 Hz, HC-6a), 4.52 (1H, d, J = 8.0 Hz, HC-
3a), 4.40 (1H, d, J = 15.0 Hz, CHHPh), 2.90-2.84 (1H, dd, J =
7.5, 18.5 Hz, HHC-3), 2.75 (1H, d, J = 18.5 Hz, HHC-3),
2.27(2H, t, J = 7.5 Hz, H2C-pent), 1.53-1.47 (2H, m, H2C-
pent), 1.35-1.25 (4H, m, -H2C-H2C-pent), 0.90 (3H, t, J=7.0
Hz, H3C-pent). δC 172.2 (CO), 164.6 (2-C), 136.1 (C), 128.6
(CH), 128.3 (CH), 127.6 (CH), 77.5 (3-C), 68.8 (6a-C), 53.6 (3a-
C), 44.7 (CH2Ph), 37.8 (6-C), 31.1, 28.0, 25.8, 22.3, and 13.9
(pent-C); EIMS m/z 411 [(M)þ, 30]; HRESIMS calcd for
C18H23NO2I (MHþ) 412.0761, found 412.0774.
(3aS,6aS)-4-Benzyl-5-oxo-2-phenyl-4,5,6,6a-tetrahydro-3aH-
furo[3,2-b]pyrrole-3-carbonitrile (3, R = Ph, X = CN). Prepared
from 1 (R = Ph) (25 mg, 0.085 mmol) and CuCN (17 mg, 0.19
mmol) and anhydrous DMF (1.5 mL), according to the general
procedure A described above. The crude product (93: 07 ratio of
3 (R = Ph, X = CN):2 (R = Ph) was chromatographed on silica
gel (1:1 EtOAc/petroleum ether) to give the title compound as a
colorless gum (20.4 mg, 76%) and 2 (R = Ph)4 (1.6 mg, 6%).
Data for 3 (R = Ph, X = CN): Rf = 0.65 (1:2 EtOAc/petroleum
ether); [R]24D þ26.1 (c 0.42, CHCl3); IR (neat, νmax/cm-1) 2194,
1692, 1618, 1233, 1019 and 750; δH 7.96-7.32 (10H, m, ArH),
5.30-5.29 (1H, m, HC-6a), 5.23 (1H, d, J = 15.0 Hz, CHHPh),
EtOAc/petroleum ether); [R]24 -17.7 (c 1.69, CHCl3); IR
D
(neat, νmax/cm-1) 3230, 1669, 1428, 1215, 1044, 1017 and 754;
δ
H 7.80-7.32 (10H, m, H), 5.36 (1H, d, J = 14.9 Hz, CHHPh),
4.85-4.84 (1H, m, HC-4), 4.80 (1H, d, J = 8.3 Hz, HC-5), 4.15
(1H, d, J = 14.9 Hz, CHHPh), 3.70 (1H, s, OH), 2.84 (1H, dd,
J = 17.9, 8.6 Hz, HC-3), 2.76 (1H, dd, J = 17.9, 5.2 Hz, HC-3);
δC 173.0 (CO), 137.3 (C), 135.3 (C), 129.9 (CH), 128.9 (CH),
128.7 (CH), 128.0 (CH), 127.7 (CH), 127.5 (CH), 107.7, 73.2
(BrCdCBr), 72.3, 71.5 (5-C, 4-C), 45.0 (CH2Ph), 37.1 (3-C);
ESIMS m/z 450 [(MHþ), 79Br, 10%]; HRESIMS calcd for
C19H18NO279Br2 (MHþ) 449.9642, found 449.9704.
General Procedure (A) for the Cyclization-halogenation and
Cyclization-cyanation Reactions. The preparation of 3 (R =
Ph, X = I) is representative. To a solution of 1 (R = Ph) (50 mg,
0.17 mmol) in anhydrous DMF (2 mL, Aldrich) under an O2
atmosphere (balloon) was added CuI (36 mg, 0.19 mmol), and
the reaction flask was inserted into a preheated oil bath at 100 °C
(see the safety note above). Stirring was continued for 16 h at the
same temperature, until the reaction was complete as deter-
mined by TLC. The reaction mixture was cooled to rt, diluted
with water (15 mL), and extracted with ethyl acetate (2 ꢀ
30 mL). The combined organic extracts were dried (MgSO4),
and the solvent was removed in vacuo. The crude product
was chromatographed on silica gel (1:2 EtOAc/petroleum
ether) to give compound 3 (R = Ph, X = I) as a white crystalline
solid (61 mg, 85%). The spectroscopic data and physical
3416 J. Org. Chem. Vol. 75, No. 10, 2010

Swamy et al.
JOCArticle
4.87 (1H, d, J = 7.5 Hz, HC-3a), 4.18 (1H, d, J = 15.0 Hz,
CHHPh), 3.01-2.92 (2H, m, H2C-6). δC 171.0 (CO), 170.5
(2-C), 135.2 (C), 132.6 (CH), 128.9 (CH), 128.85 (CH), 128.7
(CH), 128.0 (CH), 127.6 (CH), 126.8 (C), 80.9 (CN), 79.3 (6a-C),
64,5 (3a-C), 44.3 (CH2Ph), 37.1 (6-C); ESIMS m/z 317 [(MHþ)
100]; HREIMS calcd for C20H16N2O2, (Mþ) 316.1220, found
316.1211.
according to the general procedure B described above. The
crude product (ratio of 7d:8d was 93:7) was chromatographed
on silica gel (1:8, EtOAc/petroleum ether) to give 7d as a white
solid (31.3 mg, 67%) and 2-(4-methoxyphenyl)benzofuran (8d)
as a white solid (1 mg, 3%).
7d: mp 138-140 °C; Rf = 0.65 (1:4 EtOAc/petroleum ether);
IR (neat, νmax/cm-1) 2225, 1608, 1506, 1266, 1024, 831 and 738;
(3aR,6aS)-4-Benzyl-5-oxo-2-pentyl-4,5,6,6a-tetrahydro-3aH-
furo[3,2-b]pyrrole-3-carbonitrile (3, R = n-Pent, X = CN). Pre-
pared from 1 (R = Pent) (60 mg, 0.21 mmol) and CuCN (41 mg,
0.46 mmol) according to the general procedure A described
above. Purification via flash chromatography (1:2 EtOAc/
petroleum ether) provided the title compound as a light yellow
gum (52 mg, 79%): Rf = 0.63 (1:2 EtOAc/petroleum ether);
[R]25D-42.8 (c 4.5, CHCl3); IR (neat, νmax/cm-1) 2960, 2924,
2207, 1692, 1632, 1239, 994, 772, and 731. δH 7.35-7.26 (5H, m,
ArH), 5.20 (1H, d, J = 15.0 Hz, CHHPh), 5.15 (1H, t, J = 7.5
Hz, HC-6a), 4.68 (1H, d, J = 7.5 Hz, HC-3a), 4.05 (1H, d, J =
15.0 Hz, CHHPh), 2.94-2.88 (1H, dd, J = 7.5, 18.5 Hz, HHC-
3), 2.81 (1H, d, J = 18.5 Hz, HHC-3), 2.43-2.40 (2H, m, H2C-
pent), 1.61-1.56 (2H, m, H2C-pent), 1.35-1.30 (4H, m,
-H2C-H2C-pent), 0.90 (3H, t, J = 6.5 Hz, H3C-pent). δC
179.3 (CO), 170.4 (2-C), 135.2 (C), 128.9 (CH), 128.7 (CH),
128.1 (CH), 115.9 (3-C), 83.8 (CN), 80.1 (6a-C), 63.3 (3a-C), 44.3
(CH2Ph), 37.1 (6-C), 31.0, 28.0, 25.7, 22.1, and 13.8 (pent-C).
EIMS m/z 310 [(Mþ) 40]; HREIMS calcd for C19H22N2O2 (Mþ)
310.1687, found 310.1681.
General Procedure (B) for the Synthesis of Substituted 3-Halo-
and 3-Cyanobenzo[b]furans. The preparation of 3-iodo-2-
phenylbenzofuran is representative. To a mixture of 6 (R = H,
R1 = Ph) (50 mg, 0.21 mmol) in anhydrous DMF (2 mL) under
an O2 atmosphere (balloon) was added CuI (88 mg, 0.46 mmol),
and the reaction flask was inserted in to a preheated oil bath at
135-140 °C (see the safety note above). Stirring was continued
for 16 h at the same temperature until complete consumption of
starting material as determined by TLC. The reaction mixture
was cooled to rt, diluted with water (8 mL), and extracted with
EtOAc (2 ꢀ 10 mL). The combined organic extracts were dried
(MgSO4), and the solvent was removed in vacuo. The crude
product was chromatographed on silica gel (petroleum ether)
to give the product 7a as a yellow oil (47 mg, 70%): Rf = 0.82
(1:4 EtOAc/petroleum ether); δH 8.19 (2H, d, J = 8.0 Hz),
7.28 -7.51 (7H, m); EIMS m/z 320 [(Mþ) 100]. The analytical
and spectroscopic data matched with those reported in the
literature.10a
3-Bromo-2-phenylbenzofuran (7b). Prepared from 6 (R = H,
R1 = Ph) (50 mg, 0.21 mmol) and CuBr (66 mg, 0.46 mmol) ac-
cording to the general procedure B described above. The crude
product was chromatographed on silica gel (petroleum ether) to
give the title compound 7b as a colorless solid (35 mg, 62%): mp
62-64 °C (lit.7 mp 62-63 °C); Rf = 0.83 (1:4 EtOAc/petroleum
ether); δH 8.17 (2H, d, J = 7.5 Hz), 7.58-7.31 (7H, m); EIMS m/
z 272 [(Mþ), 79Br, 100], 274 [(Mþ), 81Br, 98]. The analytical and
spectroscopic data matched with those reported in the
literature.13a
2-Phenylbenzofuran-3-carbonitrile (7c). Prepared from 6
(R = H, R1 = Ph) (50 mg, 0.21 mmol) and CuCN (41 mg,
0.46 mmol) according to the general procedure B described
above. The crude product was chromatographed on silica gel
(9:1, petroleum ether/EtOAc) to give 7c as a colorless solid
(36 mg, 78%): mp 58-60 °C (lit.8 mp 57.5-59.4 °C); Rf = 0.69
(1:4 EtOAc/petroleum ether); δH 8.19 (2H, d, J = 7.5 Hz),
7.70 (1H, d, J = 7.5 Hz), 7.57-7.36 (6H, m); EIMS m/z 219
[(Mþ) 100]. The analytical and spectroscopic data matched
with those reported in the literature.10b
δH 8.14 (2H, d, J = 9.0 Hz), 7.66 (1H, dd, J = 2.5, 6.5 Hz), 7.52
(1H, dd, J = 2.5, 6.5 Hz), 7.37 - 7.34 (2H, m), 7.03 (2H, d, J =
9.0 Hz), 3.88 (3H, s, OMe); δC 162.0 (2-C), 161.8 (C), 153.0 (C),
128.3 (CH), 127.4 (C), 125.8 (CH), 124.5 (CH), 120.4 (C), 119.6
(CH), 114.7 (C), 114.5 (CH), 111.5 (CH), 86.2 (CN), 55.4 (OMe);
EIMS m/z 249 [(Mþ) 100]; HREIMS calcd for C16H11NO2 (Mþ)
249.0784, found 249.0789.
8d: colorless solid; mp 142-144 °C (lit.19 mp 143 °C); δH 7.81
(2H, d, J = 8.5 Hz), 7.56 (1H, d, J = 7.0 Hz), 7.50 (1H, d, J =
8.0 Hz), 7.26-7.20 (3H, m), 6.99 (2H, d, J = 8.9 Hz), 6.89
(1H, s), 3.87 (3H, s, OMe); EIMS m/z 224 [(Mþ) 80]. The
analytical and spectroscopic data matched with those reported
in the literature.19
2-(4-Fluorophenyl)benzofuran-3-carbonitrile (7e). Prepared
from 6 (R = H, R1 = p-FPh) (50 mg, 0.19 mmol) and CuCN
(39 mg, 0.43 mmol) according to the general procedure (B)
described above. The crude product was chromatographed on
silica gel (9:1, petrol/EtOAc) to give 7e as a colorless solid (34.5
mg, 74%): mp 124-126 °C; Rf = 0.68 (1:4 EtOAc/petroleum
ether); IR (neat, νmax/cm-1) 2226, 1606, 1503, 1236, 1040, 835 and
748; δH 8.19-8.16 (2H, dd, J = 5.5, 9.0 Hz), 7.69 (1H, d, J = 7.5
Hz), 7.55 (1H, d, J = 8.5 Hz), 7.42-7.35 (2H, m), 7.21 (2H, t, J =
8.5 Hz); δC 164.2 (C, d, J = 251.7 Hz), 160.7 (C), 153.2 (C), 128.7
(CH, d, J = 9.2 Hz), 127.0 (C), 126.4 (CH), 124.7 (CH), 124.1 (C,
d, J = 3.7 Hz), 120.0 (CH), 116.4 (CH, d, J = 22.2 Hz), 114.2 (C),
111.6 (CH), 87.8 (CN); EIMS m/z 237 [(Mþ) 100%]; HREIMS
calcd. for C15H8FNO (Mþ) 237.0589, found 237.0589.
2-Phenylbenzofuran-3,5-dicarbonitrile (7g). To a solution of 6
(R = CN, R1 = Ph) (50 mg, 0.19 mmol) in anhydrous DMF
(2 mL) under an O2 atmosphere (balloon) was added CuCN
(39 mg, 0.42 mmol), and the reaction flask was inserted into a
preheated oil bath at 100 °C. Stirring was continued for 16 h at
the same temperature, until complete consumption of starting
material as determined by TLC. Workup was according to the
general procedure B described above. The crude product was
chromatographed on silica gel (5:1 petrol/EtOAc) to give 7g
as a colorless solid (37.3 mg, 80%): mp 168-170 °C; Rf = 0.51
(1:4 EtOAc/petroleum ether); IR (neat, νmax/cm-1) 2230, 1562,
1465, 1448, 1169, 897, 817 and 770; δH 8.18 (2H, dd, J = 1.5, 5.5
Hz), 8.02 (1H, s), 7.69 (2H, s), 7.58-7.57 (3H, m); δC 163.8
(2-C), 154.6 (C), 132.2 (CH), 129.9 (CH), 129.3 (CH), 128.0 (C),
126.8 (CH), 126.7 (C), 124.6 (CH), 118.2 (C), 113.0 (CH), 112.9
(C), 109.0 (CN), 87.8 (CN); EIMS m/z 244 [(Mþ) 100]; HREIMS
calcd. for C16H8N2O (Mþ) 244.0640, found 244.0636.
3-Iodo-2-pentylbenzofuran (7h). Preparedfrom6(R =H, R1 =
n-Pent) (50 mg, 0.21 mmol) and CuI (90 mg, 0.47 mmol) accord-
ing tothegeneralprocedureBdescribed above. The crude product
was chromatographed on silica gel (petroleum ether) to give 7h as
a pale yellow gum (51 mg, 76%): Rf = 0.75 (1:4 EtOAc/petroleum
ether); IR (neat, νmax/cm-1) 2955, 2919, 1582, 1449, 1014 and 742;
δH 7.38-7.24 (4H, m), 2.84 (2H, t, J = 7.5 Hz), 1.75-1.72 (2H,
m), 1.36-1.33 (4H, m), 0.90 (3H, t, J = 7.5 Hz); δC 159.1 (2-C),
154.2 (C), 131.0 (C), 124.4 (CH), 123.0 (CH), 120.7 (CH), 110.9
(CH), 62.5 (3-C), 31.1, 28.0, 27.5, 22.3, and 13.9 (pent-C); EIMS
m/z 314 [(Mþ) 40]; HREIMS calcd for C13H15OI (Mþ) 314.0166,
found 314.0167.
2-Pentylbenzofuran-3-carbonitrile (7i) and 2-Pentylbenzofuran
(8i). Prepared from 6 (R = H, R1 = n-Pent) (50 mg, 0.21 mmol)
2-(4-Methoxyphenyl)benzofuran-3-carbonitrile (7d) and 2-(4-
Methoxyphenyl)benzofuran (8d). Prepared from 6 (R = H, R1 =
p-MeOPh) (50 mg, 0.18 mmol) and CuCN (37 mg, 0.41 mmol)
(19) Razler, T. M.; Hsiao, Y.; Qian, F.; Fu, R.; Khan, R. K.; Doubleday,
W. J. Org. Chem. 2009, 74, 1381–1384.
J. Org. Chem. Vol. 75, No. 10, 2010 3417

Swamy et al.
JOCArticle
and CuCN (43 mg, 0.47 mmol) according to the general proce-
dure B described above. The crude product (ratio of 7i:8i was
92:8) was chromatographed on silica gel (1:8, EtOAc/petroleum
ether) to give 7i as a pale yellow gum (51 mg, 76%) and
2-pentylbenzofuran (8i) as a colorless oil (2 mg, 5%).
purified by column chromatography (silica gel, 1:3 EtOAc/
petroleum ether) to give the title compound (0.059 g, 80%)
as a white solid: Rf = 0.22 (1:3 EtOAc/petroleum ether); mp
224-226 °C; IR (neat, νmax/cm-1) 3221, 2361, 2335, 2217, 1654,
1490, 1451, 1424, 1250, 732; δH (acetone-d6) 11.5 (1H, br s, NH),
8.05-8.02 (2H, m, ArH), 7.71-7.68 (1H, m, ArH), 7.61-7.56
(4H, m, ArH), 7.35-7.26 (2H, m, ArH); δC (acetone-d6) 145.5
(C), 136.6 (C), 130.7 (C), 130.6 (CH), 130.1 (CH), 129.7 (C), 127.8
(CH), 124.8 (CH), 122.9(CH), 119.4 (CH), 117.1(C), 113.2 (CH),
83.7 (CN), ESIMS m/z 218 [(MH)þ, 100]; HRESIMS calcd for
C15H10N2 (MH)þ 218.0846, found 218.0843.
2-(4-Methoxyphenyl)-1H-indole-3-carbonitrile (10c). Using
the general indole preparation procedure C above, a mixture
of 9 (R=H, R1=4-MeOC6H4-, P=TFA) (0.100 g, 0.32 mmol),
DMF (4 mL), and CuCN (0.086 g, 0.95 mmol) was stirred at
100 °C for 16 h. Workup procedure B was applied. The crude
product was purified by column chromatography (silica gel,
EtOAc) to give the title compound (0.061 g, 77%) as a white
solid: Rf = 0.15 (3:1 EtOAc/petroleum ether); mp 99-101 °C;
IR (neat, νmax/cm-1) 3257, 2212, 1613, 1499, 1446, 1255, 1245,
1173, 1040, 836; δH (acetone-d6) 11.4 (1H, br s, NH), 7.99 (2H, d,
J =8.5 Hz, ArH), 7.67 (1H, d, J = 7.5 Hz, ArH), 7.53 (1H, d,
J =7.5 Hz, ArH), 7.30-7.24 (2H, m, ArH), 7.15 (2H, d, J = 8.5
Hz, ArH), 3.89 (3H, s, CH3O); δC (acetone-d6) 161.3 (C), 145.1
(C), 135.8 (C), 129.1 (C), 128.7 (CH) 123.8 (CH), 122.4 (C),
122.1 (CH), 118.6 (CH), 116.8 (C), 114.9 (CH), 112.3 (CH), 81.9
(CN), 55.2 (CH3O); EIMS m/z 248 [(M)þ, 80]; HREIMS calcd
for C16H12N2O (M)þ 248.0943, found 248.0949.
2-(4-Fluorophenyl)-1H-indole-3-carbonitrile (10d). Using the
general indole preparation procedure C above, a mixture of 9
(R = H, R1 = 4-FC6H4-, P = TFA) (0.080 g, 0.26 mmol), DMF
(3 mL), and CuCN (0.072 g, 0.79 mmol) was stirred at 100 °C for
16 h. Workup procedure B was applied. The crude product was
purified by column chromatography (silica gel, 1:3 EtOAc/
petroleum ether) to give the title compound (0.041 g, 65%)
as a white solid: Rf = 0.26 (1:3 EtOAc/petroleum ether); mp
239-241 °C; (neat, νmax/cm-1) 3257, 2213, 1675, 1613, 1498,
1448, 1241, 1173, 830; δH (acetone-d6) 11.5 (1H, br s, NH),
8.08-8.06 (2H, m, ArH), 7.69 (1H, d, J=7.5 Hz, ArH), 7.56
(1H, d, J = 7.5 Hz, ArH), 7.39-7.34 (2H, m. ArH), 7.32-7.27
(2H, m, ArH); δC (acetone-d6) 164.2 (C, d, J = 247.6 Hz), 144.5
(C), 136.6 (C), 130.2 (CH, d, J = 8.5 Hz), 129.5 (C), 127.3 (C),
124.9 (CH), 122.9 (CH), 119.4 (CH), 116.9 (CH, d, J = 7.1 Hz),
116.5 (C, d, J = 3.1 Hz), 113.1 (CH), 83.7 (CN); EIMS m/z 236
[(M)þ, 100]; HREIMS calcd for C15H9N2F (M)þ 236.0760,
found 236.0749.
5-Methoxy-2-phenyl-1H-indole-3-carbonitrile (10e). Using the
general indole preparation procedure C above, a mixture of 9
(R = OMe, R1 = Ph, P = TFA) (0.100 g, 0.32 mmol), DMF
(4 mL), and CuCN (0.086 g, 0.95 mmol) was stirred at 100 °C for
16 h at 130 °C. Workup procedure B was applied. The crude
product was purified by column chromatography (silica gel, 1:3
EtOAc/petroleum ether) to give the title compound (0.062 g,
78%) as a white solid: Rf = 0.35 (1:3 EtOAc/petroleum ether);
mp 120-122 °C; IR (neat, νmax/cm-1) 3216, 2965, 2909, 2358,
2341, 2217, 1685, 1652, 1558, 1540, 1456, 1055, 752; δH (acetone-
d6) 11.4 (1H, brs, NH), 8.01 (2H, d, J = 7.0 Hz, ArH), 5.95 (2H, t,
J =7.0 Hz, ArH), 7.53 (1H, d, J =7.0 Hz, ArH), 7.46 (1H, d, J =
8.5 Hz, ArH), 7.16 (1H, s, ArH), 6.94 (1H, d, J = 8.5 Hz, ArH),
3.90 (3H, s, CH3O); δC (acetone-d6) 156.7 (C), 145.1 (C), 131.2
(C), 130.5 (C), 130.3 (CH), 130.2 (CH), 129.8 (CH), 127.3 (CH),
117.1 (C), 115.1 (CH), 113.8 (C), 100.4 (CH), 83.2 (CN), 55.6
(CH3O); EIMS m/z 248 [(M)þ, 100]; HREIMS calcd for
C16H12N2O (M)þ 248.0938, found 248.0949.
7i: Rf = 0.69 (1:4 EtOAc/petroleum ether); IR (neat, νmax
/
cm-1) 2960, 2924, 2233, 1593, 1454, 1178 and 747; δH 7.62-7.33
(4H, m), 2.96 (2H, t, J = 7.5 Hz), 1.83 (2H, t, J = 7.5 Hz), 1.39-
1.37 (4H, m), 0.91 (3H, t, J = 7.5 Hz); δC 168.7 (2-C), 153.6 (C),
126.0 (C), 125.4 (CH), 124.2 (CH), 119.5 (CH), 113.4 (3-C),
111.5 (CH), 90.6 (CN), 31.1, 28.1, 27.1, 22.3, and 13.8 (pent-C);
EIMS m/z 213 [(Mþ) 40]; HREIMS calcd for C14H15NO (Mþ)
213.1154, found 213.1153.
8i: δH 7.47(1H, d, J = 7.0 Hz), 7.40 (d, J = 8.0 Hz, 1H), 7.20-
7.16 (2H, m), 6.36 (s, 1H), 2.75 (2H, t, J = 7.0 Hz), 1.76-1.73
(2H, m), 1.39-1.36 (4H, m), 0.90 (3H, t, J = 7.0 Hz); EIMS m/z
188 [(Mþ) 90]. The analytical and spectroscopic data matched
with those reported in the literature.20
General Procedure (C) for the Synthesis of 3-Cyanoindoles. To
a solution of the 2-ethynylaniline derivative (0.30 mmol) in
anhydrous DMF (4 mL) under an oxygen atmosphere (balloon)
was added CuCN (0.90 mmol), and the reaction vessel was
inserted into a preheated oil bath at 100 °C (see the safety note
above). The reaction mixture was stirred at this temperature for
16 h. Two different workup procedures were followed. Workup
procedure A: Water (5 mL) was added and the aqueous layer was
extracted with EtOAc (3 ꢀ 5 mL), dried (MgSO4), filtered, and
concentrated in vacuo. The crude product was purified by column
chromatography. Workup procedure B: The solvent was removed
in vacuo at 60 °C. The crude residue was purified by column
chromatography.
2-Phenyl-1-(4-methylbenzenesulfonyl)-1H-indole-3-carbonitrile
(10a) and 2-Phenyl-1-(4-methylbenzenesulfonyl)-1H-indole (11; R =
H, R1 = Ph, R2 = Ts). Using the general indole preparation pro-
cedure C above, a mixture of 9 (R = H, R1 = Ph, P = Ts)
(0.100 g, 0.288 mmol), DMF (4 mL), and CuCN (0.080 g,0.86
mmol) was stirred at 100 °C for 16 h. Workup procedure A was
applied. The crude product was purified by column chromato-
graphy (silica gel, 1:5 EtOAc/petroleum ether) to give the
compound 10a (0.080 g, 74%) as a white solid and compound 11
(R = H, R1 = Ph, R2 = Ts) (0.003 g, 3%) as a colorless solid.
10a: Rf = 0.35 (1:5 EtOAc/petroleum ether); mp 148-150 °C;
IR (neat, νmax/cm-1) 2361, 1342, 2230, 1451, 1375, 1197, 1178;
δ
H 8.36 (1H, d, J = 8.5 Hz, ArH), 7.65 (1H, d, J = 7.5 Hz, ArH),
7.55-754 (1H, m, ArH), 7.51-7.46 (5H, m, ArH), 7.42 (1H, t,
J=7.5 Hz, ArH), 7.28 (2H, d, J = 8.0 Hz, ArH), 7.10 (2H, d,
J=8.0 Hz, ArH), 2.33 (3H, s, CH3); δC 148.6 (C),145.8 (C),
136.4 (C), 134.6 (C), 130.9 (CH), 130.5 (CH), 129.7 (CH), 128.3
(C), 127.9 (CH), 127.8 (C), 126.9 (CH), 126.6 (CH), 125.3 (CH),
119.6 (CH), 116.3 (CH), 113.9 (C), 96.7 (CN), 21.6 (CH3); EIMS
m/z 372 [(M)þ, 65]; HREIMS calcd for C22H16N2O2S (M)þ
372.0935, found 372.0932.
11 (R = H, R1 = Ph, R2 = Ts): Rf = 0.52 (1:3 EtOAc/petro-
leum ether); mp 144-146 °C (lit.11 mp 146-148 °C); IR (neat,
ν
max/cm-1) 1598, 1449, 1367, 1306, 1167, 1060, 978, 809; δH 8.31
(1H, d, J = 8.5 Hz, ArH), 7.50-7.48 (2H, m, ArH), 7.43 (4H, m,
ArH), 7.35 (1H, t, J = 7.5 Hz, ArH), 7.27-7.24 (3H, m, ArH),
7.03 (2H, d, J = 8.5 Hz, ArH), 6.54 (1H, s, ArH), 2.28 (3H, s,
CH3); EIMS m/z 348 [(M)þ, 100]; HREIMS calcd. for C21H18-
NO2S (M)þ 348.1042, found 348.1058.
2-Phenyl-1H-indole-3-carbonitrile (10b). Using the general
indole preparation procedure C above, a mixture of 9 (R = H,
R1 = Ph, P = TFA) (0.100 g, 0.34 mmol), DMF (4 mL), and
CuCN (0.093 g, 1.02 mmol) was stirred at 100 °C for 16 h.
Workup procedure A was applied. The crude product was
2-Phenyl-1-(4-methylbenzenesulfonyl)-1H-indole-3,5-dicarbo-
nitrile (10f) and 2-Phenyl-1-(4-methylbenzenesulfonyl)-1H-in-
dole-5-carbonitrile (11; R = CN, R1 =Ph, R2 = Ts). Using the
general indole preparation procedure above, a mixture of 9
(20) Furstner, A.; Davies, P. W. J. Am. Chem. Soc. 2005, 127, 15024–
15025.
3418 J. Org. Chem. Vol. 75, No. 10, 2010

Swamy et al.
JOCArticle
(R = CN, R1 = Ph, P = Ts) (0.100 g, 0.26 mmol), DMF (4 mL),
and CuCN (0.072 g, 0.78 mmol) was stirred at 100 °C for 16 h.
Workup procedure A was applied. The crude product was
purified by column chromatography (silica gel, 1:4 EtOAc/
petroleum ether) to give the compound 11 (R = CN, R1 =
Ph, R2 = Ts) (0.037 g, 38%) and compound 10f (0.023 g, 22%)
both as a white solid.
10f: Rf = 0.32 (1:4 EtOAc/petroleum ether); mp 131-133 °C;
IR (neat, νmax/cm-1) 2228, 1598, 1465, 1378, 1260, 1378, 1260,
1175, 1091, 819; δH 8.50 (1H, d, J=8.5 Hz, ArH), 7.99 (1H, s,
ArH), 7.59 (1H, t, J =7.0 Hz, ArH), 7.74 (1H, d, J =8.5 Hz,
ArH), 7.49 (2H, t, J =7.0 Hz, ArH), 7.42 (2H, d, J = 7.0 Hz,
ArH), 7.25 (2H, d, J = 8.0 Hz, ArH), 7.14 (2H, d, J = 8.0 Hz,
ArH), 2.36 (3H, s, CH3); δC 150.6 (C), 146.6 (C), 138.0 (C), 134.1
(C), 131.3 (CH), 130.2 (CH), 129.6 (CH), 128.3 (CH), 127.7 (C),
127.3 (CH), 124.4 (CH), 118.2 (C), 117.4 (CH), 112.7 (C), 109.1
(CN), 96.0 (CN), 21.6 (CH3); ESIMS m/z 398 [(MH)þ, 100];
HRESIMS calcd for C23H16N3O2S (MH)þ 398.0944, found
398.0963.
1557, 1490, 1452, 1332, 1239, 742; δH 8.70 (1H, br s, NH), 7.65
(1H, d, J = 8.5 Hz, ArH), 7.38 (1H, d, J = 8.5 Hz, ArH), 7.25-
7.22 (2H, m, ArH), 2.94 (2H, t, J = 7.0 Hz, CH2), 1.80-1.78
(2H, m, CH2), 1.38-1.35 (4H, m, 2 ꢀ CH2), 0.90 (3H, t, J = 7.0
Hz, CH3); δC 149.3 (C), 134.5 (C), 127.6 (C), 123.3 (CH), 121.9
(CH), 118.9 (CH), 116.4 (C), 111.3 (CH), 84.7 (CN), 31.1 (CH2),
28.7 (CH2), 27.5 (CH2), 22.2 (CH2), 13.8 (CH3); ESIMS m/z 213
[(MH)þ, 100]; HREIMS calcd for C14H17N2 (MH)þ 213.1360,
found 213.1392.
2-Pentyl-1-(4-methylbenzenesulfonyl)-1H-indole-3-carbonitrile
(10i) and 2-Pentyl-1-(4-methylbenzenesulfonyl)-1H-indole (11;
R = H, R1 = n-Pent, R2 = Ts). Using the general indole pre-
paration procedure C above, a mixture of 9 (R = H, R1 =
n-Pentyl, R2 =Ts) (0.0.080 g, 0.23 mmol), DMF (3 mL), and
CuCN (0.063 g, 0.69 mmol) was stirred at 100 °C for 16 h.
Workup procedure A was applied. The crude product was
purified by column chromatography (silica gel, 1:5 EtOAc/
petroleum ether) to give the compound 10i (0.046 g, 55%) as
a colorless oil and compound 11 (R = H, R1 = Pent, R2 = Ts)
(0.019 g, 24%) as a white solid. 10i: Rf = 0.42 (1:5 EtOAc/
petroleum ether); (neat, νmax/cm-1) 2955, 2924, 2863, 2228, 1598,
1451, 1384, 1191, 1178, 1155, 1098, 969; δH 8.17 (1H, d, J = 8.5
Hz, ArH), 7.65 (1H, d, J = 8.5 Hz, ArH), 7.58 (1H, d, J = 8.0Hz,
ArH) 7.39-7.33 (2H, m, ArH), 7.25 (3H, d, J = 8.0 Hz, ArH),
3.20 (2H, t, J = 7.5 Hz, CH2), 2.37 (3H, s, CH3), 1.82-1.77 (2H,
m, CH2), 1.43-1.35 (4H, m, 2 ꢀ CH2), 0.91 (3H, t, J = 7.5 Hz,
CH3); δC 151.4 (C), 145.9 (C), 135.6 (C), 135.3 (C), 130.2 (CH),
127.2 (C), 126.4 (CH), 125.7 (CH), 124.8 (CH), 119.1 (CH), 115.1
(CH), 114.1 (C), 94.5 (CN), 31.4 (CH2), 30.4 (CH2), 28.5 (CH2),
22.2 (CH2), 21.6 (CH3), 13.9 (CH3); ESIMS m/z 367 [(MH)þ,
100]; HRESIMS calcd for C21H23N2O2S (MH)þ 367.1470, found
367.1480.
11 (R = CN, R1 = Ph, R2 = Ts): Rf = 0.34 (1:4 EtOAc/petro-
leumether); mp78-80 °C;IR(neat, νmax/cm-1) 2970, 2361, 1340,
2223, 1654, 1375, 1173, 1091, 1081, 756; δH 8.42 (1H, d, J = 8.0
Hz, ArH), 7.70 (1H, s, ArH), 7.60 (1H, dd, J = 1.5, 8.0 Hz, ArH),
7.45-7.42 (5H, m, ArH), 7.24 (2H, d, J = 7.0 Hz, ArH), 7.07
(2H, d, J = 7.0 Hz, ArH), 6.56 (1H, s, ArH), 2.31 (3H, s, CH3); δC
145.3 (C), 144.1 (C), 139.8 (C), 134.5 (C), 130.5 (CH), 129.5 (CH),
129.2 (CH), 127.7 (CH), 127.5 (CH), 126.9 (CH), 125.3 (CH),
123.5 (C), 119.2 (C), 117.0 (CH), 111.9 (CH), 107.6 (CN), 21.6
(CH3); ESIMS m/z 373 [(MH)þ, 100]; HRESIMS calcd for
C22H17N2O2S (MH)þ 373.1018, found 373.1011.
Phenyl-1H-indole-3,5-dicarbonitrile (10g). Using the general
indole preparation procedure C above, a mixture of 9 (R = CN,
R1 = Ph, P = TFA) (0.070 g, 0.21 mmol), DMF (3 mL), and
CuCN (0.059 g, 0.64 mmol) was stirred at 100 °C for 16 h.
Workup procedure B was applied. The crude product was
purified by column chromatography (silica gel, 2:1 EtOAc/
petroleum ether) to give the title compound (0.031 g, 60%) as
a white solid: Rf = 0.64 (EtOAc); mp 265-267 °C; IR (neat,
11 (R = H, R1 = Pent, R2 = Ts): Rf = 0.55 (1:5 EtOAc/
petroleum ether); mp 57-59 °C; IR (neat, νmax/cm-1) 2955,
2924, 2356, 2330, 1444, 1369, 1224, 1170, 1139, 1092, 1060, 804;
δ
H 8.16 (1H, d, J = 8.0 Hz, ArH), 7.61 (2H, d, J = 8.0 Hz, ArH),
7.39 (1H, d, J = 8.0 Hz, ArH), 7.25-7.16 (4H, m, ArH), 6.37
(1H, s, ArH), 2.97 (2H, t, J = 7.5 Hz, CH2), 2.32 (3H, s, CH3),
1.75-1.72 (2H, m, CH2), 1.39-1.35 (4H, m, 2 ꢀ CH2), 0.91 (3H,
t, J = 7.5 Hz, CH3); δC 144.2 (C), 142.5 (C), 137.1 (C), 136.2 (C),
129.7 (CH), 126.6 (CH), 126.2 (C), 123.7 (CH), 123.4 (CH),
119.9 (CH), 114.7 (CH), 108.5 (CH), 31.5 (CH2), 28.9 (CH2),
28.5 (CH2), 22.4 (CH2), 21.5 (CH3), 14.0 (CH3); EIMS m/z 341
[(M)þ, 50]; HREIMS calcd for C20H23NO2S (M)þ 341.1451,
found 341.1449.
ν
max/cm-1) 3231, 2360, 2335, 2224, 1685, 1654, 1475, 1449, 1367,
1255, 1070, 906; δH (acetone-d6) 12.1 (1H, br s, NH), 8.13 (1H, d,
J = 1.5 Hz, ArH), 8.06 (2H, dd, J = 1.5, 7.0 Hz, ArH), 7.76 (1H,
d, J = 7.0 Hz, ArH), 7.68-7.59 (4H, m, ArH); δC (acetone-d6)
147.8 (C), 138.0 (C), 131.1 (CH), 130.0 (CH), 129.4 (C), 129.0
(C), 127.8 (CH), 127.4 (CH), 124.3 (CH), 119.7 (C), 115.7 (C),
114.2 (CH), 106.0 (CN), 84.1 (CN); EIMS m/z 243 [(M)þ, 100];
HREIMS calcd for C16H9N3 (M)þ 243.0813, found 243.0796.
2-Pentyl-1H-indole-3-carbonitrile (10h). Using the general
indole preparation procedure C above, a mixture of 9 (R =
H, R1 = n-Pentyl, P = TFA) (0.100 g, 0.32 mmol), DMF
(4 mL), and CuCN (0.088 g, 0.96 mmol) was stirred at 100 °C for
16 h. Workup procedure A was applied. The crude product was
purified by column chromatography (silica gel, 1:3 EtOAc/
petroleum ether) to give the title compound (0.050 g, 73%)
as a white solid: Rf = 0.31 (1:3 EtOAc/petroleum ether); mp
49-51 °C; IR (neat, νmax/cm-1) 3262, 2955, 2929, 2858, 2208,
Acknowledgment. We thank the Australian Research
Council and the University of Wollongong for financial
support.
Supporting Information Available: Full experimental and
spectroscopic details for the synthesis of the substrates 1 (R =
n-Pentyl), 5, 6, and 9 and copies of the 1H and 13C NMR spectra
of all new compounds. This information is available free of
charge via the Internet at http://pubs.acs.org.
J. Org. Chem. Vol. 75, No. 10, 2010 3419