Synthesis of lactams via copper-catalyzed intramolecular vinylation of amides

Article abstract of DOI:10.1021/ol0505555

(Chemical Equation Presented) Copper-catalyzed intramolecular vinylation of iodoenamides were investigated for the first time. With Cul as the catalyst and N,W-dimethylethyienediamine as the ligand, a number of iodoenamides underwent cyclization in dioxane leading to the formations of five- to seven-membered lactams in moderate to excellent yields.

Full text of DOI:10.1021/ol0505555

ORGANIC
LETTERS
2
005
Vol. 7, No. 10
035-2038
Synthesis of Lactams via
Copper-Catalyzed Intramolecular
Vinylation of Amides
2
Tianshun Hu and Chaozhong Li*
Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences,
354 Fenglin Road, Shanghai 200032, P. R. China
clig@mail.sioc.ac.cn
Received March 14, 2005
ABSTRACT
Copper-catalyzed intramolecular vinylation of iodoenamides were investigated for the first time. With CuI as the catalyst and N,N′-
dimethylethylenediamine as the ligand, a number of iodoenamides underwent cyclization in dioxane leading to the formations of five- to
seven-membered lactams in moderate to excellent yields.
Lactams are of considerable interest in a number of areas
ranging from drug discovery to polymer industry. Prepara-
tions of lactams have long been an important topic in organic
provide a facile route for the synthesis of lactams of various
ring sizes. However, to our surprise, such a process had never
previously been reported in the literature. Only a few
examples of the palladium-catalyzed intramolecular vinyla-
tion of amides were reported, which led to the formation of
1
chemistry and continue to be actively pursued. We report
here that the copper-catalyzed intramolecular vinylation of
amides provides an efficient and general entry to five- to
seven-membered lactams.
6
cyclic amines rather than lactams. Due to the importance
of lactams in organic synthesis, we carried out the following
The formation of aryl C-X bonds (X ) O, S, N, etc.) via
copper-catalyzed coupling between aryl halides and hetero-
centered nucleophiles has drawn a great deal of attention in
the past few years.2 The high stability and low costs of
copper catalysts enable these transformations to be a useful
complement to the more extensively investigated palladium-
(
3) For the latest examples, see: (a) Klapars, A.; Parris, S.; Anderson,
K. W.; Buchwald, S. L. J. Am. Chem. Soc. 2004, 126, 3529. (b) Antilla, J.
C.; Baskin, J. M.; Barder, T. E.; Buchwald, S. L. J. Org. Chem. 2004, 69,
578. (c) Son, S. U.; Park, I. K.; Park, J.; Hyeon, T. Chem. Commun. 2004,
78. (d) Cristau, H.-J.; Cellier, P. P.; Spimdler, J.-F.; Taillefer, M. Eur. J.
Org. Chem. 2004, 695. (e) Hosseinzadeh, R.; Tajbakhsh, M.; Mohadjerani,
M.; Mehdinejad, H. Synlett 2004, 1517. (f) Kim, K.-Y.; Shim, J.-T.; Lee,
K.-S.; Cho, C.-G. Tetrahedron Lett. 2004, 45, 117. (g) Nandakumar, M.
V. Tetrahedron Lett. 2004, 45, 1989. (h) Deng, W.; Wang, Y.-F.; Zou, Y.;
Liu, L.; Guo, Q.-X. Tetrahedron Lett. 2004, 45, 2311. (i) Li, C. S.; Dixon,
D. D. Tetrahedron Lett. 2004, 45, 4257. (j) Taniguchi, N.; Onami, T. J.
Org. Chem. 2004, 69, 915.
5
7
,3
4
catalyzed processes. More recently, this methodology was
successfully extended to the synthesis of enamides by
5
coupling of amides with vinyl halides. It could be envisioned
(4) For reviews, see: (a) Muci, A. R.; Buchwald, S. L. Top. Curr. Chem.
that, if the vinylation could proceed intramolecularly, it might
2
002, 219, 131. (b) Hartwig, J. F. In Handbook of Organopalladium
Chemistry for Organic Synthesis; Negichi, E.-i., Ed.; Wiley: New York,
2002; Vol. 1, p 1051. (c) Littke, A. F.; Fu, G. C. Angew. Chem., Int. Ed.
2002, 41, 4176. (d) Prim, D.; Campagne, J. M.; Joseph, D.; Andrioletti, B.
Tetrahedron 2002, 58, 2041. (e) Yang, B. Y.; Buchwald, S. L. J. Organomet.
Chem. 1999, 576, 125. (f) Wolfe, J. P.; Wagaw, S.; Marcoux, J. F.;
Buchwald, S. L. Acc. Chem. Res. 1998, 31, 805. (g) Hartwig, J. F. Angew.
Chem., Int. Ed. 1998, 37, 2046. (h) Hartwig, J. F. Acc. Chem. Res. 1998,
31, 852.
(
1) For recent review articles, see: (a) Nubbemeyer, U. Top. Curr. Chem.
2
9
(
001, 216, 125. (b) Groaning, M. D.; Meyers, A. I. Tetrahedron 2000, 56,
843. (c) Shiraki, R.; Tadano, K.-I. ReV. Heteroat. Chem. 1999, 20, 283.
d) Robin, S.; Rousseau, G. Tetrahedron 1998, 54, 13681. (e) Ley, S. V.;
Cox, L. R.; Meek, G. Chem. ReV. 1996, 96, 423.
2) For reviews, see: (a) Kunz, K.; Scholz, U.; Ganzer, D. Synlett 2003,
428. (b) Ley, S. V.; Thomas, A. W. Angew. Chem., Int. Ed. 2003, 42, 5400.
(
2
1
0.1021/ol0505555 CCC: $30.25
© 2005 American Chemical Society
Published on Web 04/09/2005

investigation to explore the scope and limitation of this
possible methodology.
Table 2. Synthesis of Lactams 2a-k
Thus, we prepared (Z)-5-iodo-N-phenylpent-4-enamide
(1a) as the prototypical substrate to screen the experimental
conditions (eq 1). The substrate concentration was set at 0.03
M for ease of comparison. The results are summarized in
Table 1. As the use of an appropriate ligand would allow a
Table 1. Optimization of Experimental Conditions for 1a
a
Isolated yield based on 1a. b Refluxing temperature.
a
Reaction conditions: substrate (0.03 M), CuI:8 ) 1:2, Cs2CO3 (2 equiv),
dioxane, reflux, 20 h. b Isolated yield based on 1. c Compound 9 was also
obtained in 25% yield.
5
mild procedure for the C-N bond formations, we carried
out an initial ligand screen with CuI (20 mol %) as the
catalyst and Cs CO (2 equiv) as the base in dioxane at re-
2 3
fluxing temperature. To our delight, among the six frequently
base was switched to K
was lowered (entries 8 and 9, Table 1). Changing the solvent
to THF or CH CN also gave very low yields of product
2 3 3 4
CO or K PO , the product yield
3
used ligands (3-8) examined, N,N′-dimethylethylenediamine
probably because their boiling points were not high enough
(entries 10 and 11, Table 1). This was evidenced by running
(8) gave the best result (entries 1-7, Table 1). When the
2036
Org. Lett., Vol. 7, No. 10, 2005

the reaction in dioxane at 80 °C, which gave only a trace
amount of 2a (entry 12, Table 1). Reducing the amount of
CuI to 10 mol % afforded 2a in a slightly lower yield (91%).
The above trend was also observed when we used (Z)-6-
iodohex-5-enamide (1c) as the model substrate. Thus, we
concluded that the optimized combination for this reaction
was to use dioxane as the solvent, Cs CO as the base, and
2 3
N,N′-dimethylethylenediamine 8 as the ligand.
We then synthesized a number of iodoenamides to explore
the scope of intramolecular vinylation under the optimized
conditions. The amount of CuI used was either 10 or 20 mol
these could be easily prepared from the corresponding
alkynes by reaction with TMSCl/NaI. Compound 1e gave
9
the corresponding γ-lactam 2e in almost quantitative yield
(entry 5, Table 1). Moreover, the reactions of substrates 1f
and 1h led to the formation of δ-lactam 2f and caprolactam
2h with an exocyclic double bond in high yield (entries 6
and 8, Table 2). In comparison, their N-unsubstituted
analogues 1g and 1i gave lactams 2g and 2i in 86 and 46%
yields, respectively, probably because the expected products
with an exocyclic double bond were less stable than 2f or
2h and underwent isomerization under the experimental
conditions (entries 7 and 9, Table 2).
%, depending on the ease of cyclization. The results are
summarized in Table 2.
As illustrated in Table 2, we first tested the substrates
As an extension, we synthesized iodoenamides 1j and 1k
and subjected them to the same experimental conditions as
above. Bicyclic compounds 2j and 2k were achieved in 83
and 45% yields, respectively (entries 10 and 11, Table 2).
This result illustrated the potential application of the above
methodology in natural product synthesis because the bicyclic
benzazepine skeleton is widely embedded in a number of
1a-d with terminal (Z)-vinylic iodine substitution, which
were readily prepared from the corresponding alkynes by
7
2 2
reaction with BuLi/I followed by reduction with TsNHNH /
8
NaOAc. The corresponding six- and seven-membered lac-
tams with an internal double bond could be achieved (entries
1
0
1-4, Table 2). The N-phenyl-substituted substrate 1b gave
alkaloids such as Stenine.
the seven-membered lactam 2b in excellent yield. With
N-unsubstituted substrate 1c, the expected product, caprolac-
tam 2c, was obtained in moderate yield along with the 14-
membered lactam 9 in 25% yield, whose structure was unam-
biguously established by its X-ray diffraction analysis (Figure
1). Compound 9 apparently resulted from the bimolecular
Our attempt to further extend the methodology to the
synthesis of eight-membered lactams via the reaction of
substrate 10 or 11 was unsuccessful under the optimized
experimental conditions.
The above results clearly demonstrated that the Cu(I)-
catalyzed intramolecular vinylation of iodoenamides is a
viable method for the synthesis of lactams. The intramo-
lecular vinylation also showed a different reactivity pattern
from that of the intermolecular vinylation. As reported by
Buchwald et al., the coupling of acetamide with ordinary
2 3
vinyl iodides with Cs CO as the base and diamine 8 as the
ligand proceeded in high efficiency at 50 °C or even at room
5
d
temperature. In contrast, the cyclization of iodoenamides
a-k required reaction temperatures higher than 80 °C.
1
While the intermolecular amidation of vinyl bromides worked
Figure 1. ORTEP drawings of compounds 9 and 13.
well in dioxane with N,N-dimethylglycine HCl salt 3 as the
5
h
additive, bromoenamides are unlikely to be a good choice
reaction of 1c. For N-methyl-substituted substrate 1d, the
cyclized product 2d was isolated in only 14% yield, while
most of the starting material remained unchanged. This trend
(
6) (a) Kozawa, Y.; Mori, M. Tetrahedron Lett. 2002, 43, 111. (b)
Kozawa, K.; Mori, M. J. Org. Chem. 2003, 68, 3064. (c) Willis, M. C.;
Brace, G. N.; Holmes, I. P. Angew. Chem., Int. Ed. 2005, 44, 403.
(7) Cossy, J.; Tresnard, L.; Pardo, D. G. Eur. J. Org. Chem. 1943, 8,
(Ph > H > Me) might probably be attributed to the different
1
925.
basicities of the nucleophiles (NH) in the starting amides.
We next screened the substrates 1e-k having an iodine
substituent on the internal side of the CdC double bond;
(8) Coleman, R. S.; Garg, R. Org. Lett. 2001, 3, 3487.
(9) Gras, J.; Kong, W. C.; You, Y.; Bertrand, M. Tetrahedron Lett. 1982,
3, 3571.
2
1
(10) (a) Wipf, P.; Rector, S. R.; Takahashi, H. J. Am. Chem. Soc. 2002,
24, 14848. (b) Morimoto, Y.; Iwahashi, M.; Kinoshita, T.; Nishida, K.
(
5) (a) Ogawa, T.; Kiji, T.; Hayami, K.; Suzuki, H. Chem. Lett. 1991,
Chem. Eur. J. 2001, 7, 4107. (c) Rigby, J. H.; Laurent, S.; Cavezza, A.;
Heeg, M. J. J. Org. Chem. 1998, 63, 5587. (d) Wipf, P.; Kim, Y.; Goldstein,
D. M. J. Am. Chem. Soc. 1995, 117, 11106. (e) Harada, H.; Irie, H.; Masaki,
N.; Osaki, K.; Uyeo, S. Chem. Commun. 1967, 460.
(11) Relatively low concentration is necessary for cyclization in some
cases. For example, the reaction of 1c at 0.5 M concentration afforded the
expected product 2c in only 14% yield along with the formation of the
dimer 9 in 55% yield.
1
443. (b) Shen, R.; Porco, J. A., Jr. Org. Lett. 2000, 2, 1333. (c) Shen, R.;
Lin, C. T.; Porco, J. A., Jr. J. Am. Chem. Soc. 2002, 124, 5650. (d) Jiang,
L.; Job, G. E.; Klapars, A.; Buchald, S. L. Org. Lett. 2003, 5, 3667. (e)
Wang, X.; Porco, J. A., Jr. J. Am. Chem. Soc. 2003, 125, 6040. (f) Han, C.;
Shen, R.; Su, S.; Porco, J. A., Jr. Org. Lett. 2004, 6, 27. (g) Coleman, R.
S.; Liu, P.-H. Org. Lett. 2004, 6, 577. (h) Pan, X.; Cai, Q.; Ma, D. Org.
Lett. 2004, 6, 1809.
Org. Lett., Vol. 7, No. 10, 2005
2037

of substrate for intramolecular vinylation. For example,
-bromo-N-phenylhex-5-enamide, the bromo analogue of 1f,
5
gave only 14% yield of the cyclized product 2f under the
optimized conditions. An obvious reason for these differences
is that the intramolecular reactions operate at low concentra-
tions in order to avoid the competing intermolecular reac-
tions,11 while intermolecular couplings are run at high
5
concentrations (such as 1 M). More importantly, the steric
iodoenamides, allowing the convenient preparations of five-,
six-, and seven-membered N-vinylic lactams. In addition,
macrocyclic lactams (such as 13) can also be achieved via
this method, which should be of important application in
organic synthesis.
requirement could play a key role in the intramolecular
vinylation of amides. This is further exemplified by the
reaction of iodoenamide 12 shown in eq 2. Treatment of 12
with CuI and diamine 8 in dioxane (0.03 M) at refluxing
temperature for 4 h afforded the 14-membered lactam 13
exclusively in 86% yield rather than the expected caprolac-
1
2
tam. The X-ray structure of 13 is presented in Figure 1.
The formation of 13 and 9 are particularly interesting, which
indicates that this method might be applied to the efficient
synthesis of certain macrocyclic lactams.
Acknowledgment. This project was supported by the
National Natural Science Foundation of China (Nos. 20325207
and 20472109) and by the Shanghai Municipal Scientific
Committee (No. 04QMH1418).
In conclusion, we have developed a mild and efficient
protocol for the copper-catalyzed intramolecular coupling of
Supporting Information Available: Synthesis and char-
acterizations of compounds 1a-k, 2a-k, 12, and 13 and
X-ray crystal data of 9 and 13 in CIF format. This material
is available free of charge via the Internet at http://pubs.acs.org.
(12) When a catalytic amount of CuI (10 mol %) was employed, only a
trace amount of 13 could be detected along with unidentified decomposition
products, probably because 13 was not very stable under the reaction
conditions for a prolonged time. An alternative explanation might be that
Cu(I) acted as a chelating template for the formation of 13.
OL0505555
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Org. Lett., Vol. 7, No. 10, 2005