A one-pot coupling/hydrolysis/condensation process to pyrrolo[1,2-a] quinoxaline

Article abstract of DOI:10.1021/jo8008098

(Chemical Equation Presented) CuI/L-proline-catalyzed coupling of 2-halotrifluoroacetanilides with pyrrole-2-carboxylate esters in DMSO at 80-90 °C followed by in situ hydrolysis at 60°C afforded pyrrolo[1,2-a] quinoxalines. Indole-2-carboxylate esters underwent the same process smoothly to provide the corresponding tetracyclic products.

Full text of DOI:10.1021/jo8008098

A One-Pot Coupling/Hydrolysis/Condensation
Process to Pyrrolo[1,2-a]quinoxaline
Qiliang Yuan† and Dawei Ma*,‡
Department of Chemistry, Fudan UniVersity,
Shanghai 200433, China, State Key Laboratory of
Bioorganic and Natural Products Chemistry, Shanghai
Institute of Organic Chemistry, Chinese Academy of
Sciences, 354 Fenglin Lu, Shanghai 200032, China
madw@mail.sioc.ac.cn
ReceiVed April 11, 2008
FIGURE 1. Structures of some pharmaceutically important pyrrolo[1,2-
a]quinoxalines.
inconvenient operation and a limited number of suitable
substrates for diverse synthesis. Recently, Beccalli and co-
workers described a Pd-catalyzed intramolecular C-N bond
formation strategy to assemble these tricyclic compounds from
2-haloanilines and pyrrole-2-carboxylic acids.6 However, pre-
liminary methylation of the commercially available 2-haloa-
nilines is required. This additional manipulation limits the scope
of application of this method.
We recently revealed that there exists an ortho-substitution
effect caused by NHCOR groups in some CuI/amino acid-
catalyzed Ullmann-type coupling reactions.7 On the basis of this
discovery we have developed new cascade processes for the
assembly of benzimidazoles,7c 1,3-dihydrobenzimidazol-2-ones,8
and indoles.7d,9 In connection with these investigations, we
envisioned that the coupling reaction of pyrrole-2-carboxylate
esters 6 with 2-halotrifluoroacetanilides 5 would proceed
smoothly to deliver the coupling products 7,10,11 which upon
liberation of the amine group by hydrolysis and subsequent
intramolecular condensation would provide pyrrolo[1,2-a]qui-
noxaline compounds (Scheme 1).
With this idea in mind, we first attempted the CuI/L-proline-
catalyzed coupling of 2-iodotrifluoroacetanilide 5a and pyrrole-
2-carboxylate methyl ester 6a. As expected, this reaction worked
well in DMSO at 80 °C to afford coupling product 7a in 96%
yield (Scheme 2). Under the same conditions the coupling of
2-iodoacetanilide 10 with 6a gave only 10% yield of product
12, while 2-iodoanisole 11 gave no coupled product at all. These
results indicated that an ortho-substitution effect directed by
NHCOR groups also exists for the present coupling reaction,
and that NHCOCF3 has a significantly better accelerating ability
than NHCOCH3, which is consistent with our previous
observations.7a Further evidence was provided by the fact that
CuI/L-proline-catalyzed coupling of 2-halotrifluoroacetanil-
ides with pyrrole-2-carboxylate esters in DMSO at 80-90
°C followed by in situ hydrolysis at 60 °C afforded
pyrrolo[1,2-a]quinoxalines. Indole-2-carboxylate esters un-
derwent the same process smoothly to provide the corre-
sponding tetracyclic products.
The pyrrolo[1,2-a]quinoxaline moiety has been found in many
pharmaceutically important molecules, including antipsychotic
agent 1,1 anti-HIV agent 2,2 adenosine A3 receptor modulator
3,3 and antitumor agent 44 (Figure 1). In addition, pyrrolo[1,2-
a]quinoxaline compounds have served as key intermediates for
the assembly of several heterocycles that displayed a wide range
of biological activities.5
The common method for the construction of pyrrolo[1,2-
a]quinoxalines starts from 2-nitroanilines and proceeds in three
steps (pyrrole ring formation, nitro group reduction, and
cyclization with triphosgene).5 This approach suffers from
† Fudan University.
‡ Chinese Academy of Sciences.
(1) Campiani, G.; Butina, S.; Fattorusso, C.; Trotta, F.; Franceschina, S.; De
Angelis, M.; Nielsen, K. S. WO2006072608.
(2) Campiani, G.; Aiello, F.; Fabbrini, M.; Morelli, E.; Ramunno, A.;
Armaroli, S.; Nacci, V.; Garofalo, A.; Greco, G.; Novellino, E.; Maga, G.;
Spadari, S.; Bergamini, A.; Ventura, L.; Bongiovanni, B.; Capozzi, M.;
Bolacchi, F.; Marini, S.; Coletta, M.; Guiso, G.; Caccia, S. J. Med. Chem.
2001, 44, 305.
(3) Schann, S.; Mayer, S.; Gardan, S. EP1798233.
(4) Milne, J.; Normington, K. D.; Milburn, M. WO2006094210.
(5) (a) Grande, F.; Aiello, F.; De Grazia, O.; Brizzi, A.; Garofalo, A.; Neamati,
N. Bioorg. Med. Chem. 2007, 15, 288. (b) Guillon, J.; Forfar, I.; Mamani-
Matsuda, M.; Desplat, V.; Salie`ge, M.; Thiolat, D.; Massip, S.; Tabourier, A.;
Le´ger, J.-M.; Dufaure, B.; Haumont, G.; Jarrt, C.; Mossalayi, D. Bioorg. Med.
Chem. 2007, 15, 194. (c) Guillon, J.; Grellier, P.; Labaied, M.; Sonnet, P.; Le´ger,
J.-M.; De´prez-Poulain, R.; Forfar-Bares, I.; Dallemagne, P.; Lemaitre, N.;
Pe´hourcq, F.; Rochette, J.; Sergheraert, C.; Jarry, C. J. Med. Chem. 2004, 47,
1997. (d) Campiani, G.; Morelli, E.; Gemma, S.; Nacci, V.; Butini, S.; Hamon,
M.; Novellino, E.; Greco, G.; Cagnotto, A.; Goegan, M.; Cervo, L.; Valle, F. D.;
Fracasso, C.; Caccia, S.; Mennini, T. J. Med. Chem. 1999, 42, 4362.
(6) Abbiati, G.; Beccalli, E. M.; Broggini, G.; Paladino, G.; Rossi, E. Synthesis
2005, 2881.
(7) (a) Cai, Q.; Zou, B.; Ma, D. Angew. Chem., Int. Ed. 2006, 45, 1276. (b)
Xie, X.; Chen, Y.; Ma, D. J. Am. Chem. Soc. 2006, 128, 16050. (c) Zou, B.;
Yuan, Q.; Ma, D. Angew. Chem., Int. Ed. 2007, 46, 2598. (d) Liu, F.; Ma, D. J.
Org. Chem. 2007, 72, 4884.
(8) Zou, B.; Yuan, Q.; Ma, D. Org. Lett. 2007, 9, 4291.
(9) (a) Chen, Y.; Xie, X.; Ma, D. J. Org. Chem. 2007, 72, 9329. (b) Chen,
Y.; Wang, Y.; Sun, Z.; Ma, D. Org. Lett. 2008, 10, 625.
(10) (a) Ma, D.; Cai, Q. Synlett 2004, 1, 128. (b) Zhang, H.; Cai, Q.; Ma, D.
J. Org. Chem. 2005, 70, 5164.
10.1021/jo8008098 CCC: $40.75
Published on Web 06/04/2008
2008 American Chemical Society
J. Org. Chem. 2008, 73, 5159–5162 5159

SCHEME 1. Coupling/Hydrolysis/Condensation Approach
to Pyrrolo[1,2-a]quinoxaline
and pyrrole-2-carboxylate esters. The electronic properties of
pyrrole-2-carboxylate esters obviously had little influence on
this process, as is evident from the fact that both electron-rich
and electron-deficient pyrrole-2-carboxylate esters afforded good
yields of tricyclic products (entries 2-5). However, only
electron-rich 2-iodotrifluoroacetanilides gave rise to the desired
products in excellent yields (Table 1, entries 6 and 7), while
electron-deficient 2-iodotrifluoroacetanilides gave good to mod-
erate yields (Table 1, entries 8, 9, and 17). In the latter case,
the problem should result from the sluggish coupling reaction,
demonstrating that electron-deficient 2-halotrifluoroacetanilides
are less reactive than electronic-rich ones. These phenomena
have also been observed in our previous studies,7a,b although
the reason is not fully clear yet.
Disubstituted pyrrolo[1,2-a]quinoxalines 9j-l could be elabo-
rated from the corresponding substituted coupling partners in
good yields (Table 1, entries 10-12). Starting from 9l, some
new analogues of antitumor agent 4 could be prepared.
2-Bromotrifluoroacetanilides also worked well in our process,
although slightly higher reaction temperatures were required
during the coupling step (Table 1, entries 13-16). Noteworthy
is that pyrido-fused heterocycles 9o and 9p (Table 1, entries
15 and 16) were obtained from N-(2,6-dibromopyridin-3-yl)-
2,2,2-trifluoroacetamide 5i. The exclusive isolation of one isomer
in these two reactions illustrated that the coupling only occurred
at the ortho-position of the amide group. This result gave
additional evidence for the proposed ortho-substitution effect
in the coupling step. The bromide moiety in 9o and 9p allows
further coupling manipulations for the elaboration of more
diverse compounds, e.g., amination of 9o would afford ana-
logues of adenosine A3 receptor modulator 3.
SCHEME 2. CuI/L-Proline-Catalyzed Couplings of
Ortho-Substituted Iodobenzenes with Pyrrole-2-carboxylate
Methyl Ester
coupling of 2-iodoaniline 14 with 6a furnished the coupling/
condensative cyclization product 9a in only 25% yield, together
with 61% of recovered 14 and 8% of aniline (dehalogenation
product).
We next investigated the applicability of indole-2-carboxylate
esters and imidazole-2-carboxylate esters as substrates. As
shown in Scheme 3, the coupling reaction of methyl 1H-indole-
2-carboxylate (15) with iodide 5e and bromide 5k proceeded
smoothly to afford fused tetracyclic compounds 16 in good
yields after hydrolysis and subsequent intramolecular condensa-
tion. However, the reaction of methyl 1H-imidazole-2-carboxy-
late 17 with iodide 5c under the same coupling conditions gave
only a poor conversion. The reason for this unsatisfactory result
is not clear yet.
In conclusion, we have developed a one-pot coupling/
hydrolysis/intramolecular condensation process to assemble
pyrrolo[1,2-a]quinoxalines from pyrrole-2-carboxylate esters. A
wide range of these fused heterocycles bearing different
functional groups such as ketone, ester, methoxy, bromo, and
chloro could be elaborated from suitable substrates, thereby
providing a versatile and reliable method for the elaboration of
these pharmaceutically important compounds. Indole-2-car-
boxylate esters were compatible with this process, giving the
corresponding fused tetracyclic compounds, while imidazole-
2-carboxylate esters gave low yields of the desired coupling
products. Further attempts to improve this process are in
progress, as well as its application to the synthesis of special
target compounds.
For the coupling of 2-iodoaniline 14 with 6a, exclusive
isolation of 9a indicated that the intramolecular condensative
cyclization was much faster than the coupling, which implied
that a one-pot process for the assembly of pyrrolo[1,2-
a]quinoxalines could be developed if the trifluoroacetyl group
was selectively removed after coupling of 5 and 6. Conse-
quently, the conditions for the deprotection step were closely
investigated. After careful experimentation, we were pleased
to find that the addition of water to the coupling reaction mixture
followed by heating to 60 °C could provide the cyclization
product 9a in excellent yield (Table 1, entry 1). These conditions
were then examined for a variety of 2-halotrifluoroacetanilides
(11) For selected examples about Cu-catalyzed couplings of aryl halides with
N-containing heterocycles from other groups, see: (a) Klapars, A.; Antilla, J. C.;
Huang, X.; Buchwald, S. L. J. Am. Chem. Soc. 2001, 123, 7727. (b) Antilla,
J. C.; Klapars, A.; Buchwald, S. L. J. Am. Chem. Soc. 2002, 124, 11684. (c)
Cristau, H.-J.; Cellier, P. P.; Spindler, J.-F.; Taillefer, M. Chem. Eur. J. 2004,
10, 5607. (d) Zhang, Z.; Mao, J.; Zhu, D.; Wu, F.; Chen, H.; Wan, B. Tetrahedron
2006, 62, 4435. (e) Rao, H.; Jin, Y.; Fu, H.; Jiang, Y.; Zhao, Y. Chem. Eur. J.
2006, 12, 3636. (f) Altman, R. A.; Buchwald, S. L. Org. Lett. 2006, 8, 2779. (g)
Taillefer, M.; Xia, N.; Ouali, A. Angew. Chem., Int. Ed. 2007, 46, 934. (h) Chang,
J.; Xu, X.; Chan, P. Tetrahedron Lett. 2007, 48, 245. (i) Correa, A.; Bolm, C.
AdV. Synth. Catal. 2007, 349, 2673. (j) Zhu, L.; Cheng, L.; Zhang, Y.; Xie, R.;
You, J. J. Org. Chem. 2007, 72, 2737. (k) Lv, X.; Bao, W. J. Org. Chem. 2007,
72, 3863. (l) Verma, A. K.; Singh, J.; Sankar, V. K.; Chaudhary, R.; Chandra,
R. Tetrahedron Lett. 2007, 48, 4207. (m) Kantam, M. L.; Yadav, J.; Laha, S.;
Sreedhar, B.; Jha, S. AdV. Syn. Catal. 2007, 349, 1938. (n) Sprotto, E.; de Vries,
J. G.; van Klink, G. P. M.; van Koten, G. Tetrahedron Lett. 2007, 48, 7368. (o)
Ma, H.; Jiang, X. J. Org. Chem. 2007, 72, 8943. (p) Chen, W.; Zhang, Y.; Zhu,
L.; Lan, J.; Xie, R.; You, J. J. Am. Chem. Soc. 2007, 129, 13879. (q) Song, R.;
Deng, C.; Me, Y.; Li, J. Tetrahedron Lett. 2007, 48, 7845. (r) Chouhan, G.;
Wang, D.; Alper, H. Chem. Commun. 2007, 4809. (s) Altman, R.; Koval, E. P.;
Buchwald, S. L. J. Org. Chem. 2007, 72, 6190. (t) Huang, Y.; Gao, J.; Ma, H.;
Miao, H.; Xu, J. Tetrahedron Lett. 2008, 49, 948. (u) Mao, J.; Guo, J.; Song,
H.; Ji, S. Tetrahedron 2008, 64, 2471. (v) Maheswaran, H.; Krishna, G. G.;
Prasanth, K. L.; Srinivas, V.; Chaitanya, G. K.; Bhanuprakash, K. Tetrahedron
2008, 64, 2471.
Experimental Section
General Procedure for Synthesis of Substituted Pyrrolo[1,2-
a]quinoxalines. A Schlenk tube was charged with pyrrole-2-
carboxylate ester (0.25 mmol), aryl iodide (0.375 mmol), CuI (5
mg, 0.025 mmol), L-proline (6 mg, 0.05 mmol), and K2CO3 (104
mg, 0.75 mmol), evacuated, and backfilled with argon. After DMSO
5160 J. Org. Chem. Vol. 73, No. 13, 2008

TABLE 1. Synthesis of Pyrrolo[1,2-a]quinoxalines via CuI/L-Proline Catalyzed Coupling of 2-Halotrifluoroacetanilides 5 with
Pyrrole-2-carboxylate Esters 6a
a Reaction conditions: 2-halotrifluoroacetanilide 5 (0.37 mmol), pyrrole-2-carboxylate ester 6 (0.25 mmol), CuI (0.025 mmol), L-proline (0.05 mmol),
K2CO3 (0.75 mmol), DMSO (0.5 mL), 80 °C (90 °C for bromides); then adding 1.5 mL of water, 60 °C. b Isolated yield.
(0.5 mL) was injected, the reaction mixture was stirred at 80 °C
until pyrrole-2-carboxylate ester disappeared monitored by TLC.
To the cooled solution was added 1.5 mL of water. The mixture
was then heated at 60 °C for 8-15 h. The mixture was cooled to
J. Org. Chem. Vol. 73, No. 13, 2008 5161

SCHEME 3. Assembly of Fused Tetracyclic Compounds 16
Methyl 7-Methoxy-4-oxo-4,5-dihydropyrrolo[1,2-a]-quinoxaline-
2-carboxylate (9l). 1H NMR (400 MHz, DMSO-d6) δ 11.33 (s, 1H),
8.68 (d, J ) 1.4 Hz, 1H), 8.13 (d, J ) 10.1 Hz, 1H), 7.20, (d, J )
1.4 Hz, 1H), 6.80-6.72 (m, 2H), 3.78 (s, 3H), 3.75 (s, 3H); 13C
NMR (100 MHz, DMSO-d6) δ 164.16, 158.37, 155.38, 130.75,
124.18, 121.60, 118.62, 117.57, 116.63, 111.72, 109.72, 101.43,
56.01, 51.98; EI-MS m/z 272 (M+), 257, 241, 229; EI-HRMS calcd
for C14H12N2O4 (M+) 272.0797, found 272.0796.
2-Ethyl-8-methoxypyrrolo[1,2-a]quinoxalin-4(5H)-one (9m). 1H
NMR (400 MHz, DMSO-d6) δ 11.00 (s, 1H), 8.01 (d, J ) 0.9 Hz,
1H), 7.51 (d, J ) 2.8 Hz, 1H), 7.15 (d, J ) 9.2 Hz, 1H), 6.86-6.81
(m, 2H), 3.79 (s, 3H), 2.57 (q, J ) 7.3 Hz, 2H), 1.21 (t, J ) 7.3
Hz, 3H); 13C NMR (100 MHz, DMSO-d6) δ 155.65, 154.95, 130.55,
123.62, 122.47, 117.82, 116.06, 112.66, 111.23, 100.16, 56.35,
20.30, 15.52; EI-MS m/z 242 (M+), 227, 212, 199, 184; EI-HRMS
calcd for C14H14N2O2 (M+) 242.1055, found 242.1058.
1
2-Acetyl-7-ethylpyrrolo[1,2-a]quinoxalin-4(5H)-one (9n). H
room temperature and diluted with 150 mL of ethyl acetate, washed
with water, dried over Na2SO4, and concentrated in vacuo. The
residue was purified by column chromatography on silica gel
(eluting with 3:1 to 1:10 petroleum ether/ethyl acetate) to provide
the desired product.
NMR (400 MHz, DMSO-d6) δ 11.35 (s, 1H), 8.82 (d, J ) 1.8 Hz,
1H), 8.09 (d, J ) 7.8 Hz, 1H), 7.29 (d, J ) 1.8 Hz, 1H), 7.10-7.05
(m, 2H), 2.61 (q, J ) 7.3 Hz, 2H), 2.48 (s, 3H), 1.17 (t, J ) 7.3
Hz, 3H); 13C NMR (100 MHz, DMSO-d6) δ 193.54, 155.58, 143.25,
129.58, 128.10, 124.82, 123.04, 121.78, 120.69, 116.17, 115.98,
110.98, 28.29, 28.06, 15.90; EI-MS m/z 254 (M+), 239, 226, 211,
196, 183; EI-HRMS calcd for C15H14N2O2 (M+) 254.1055, found
254.1048.
Pyrrolo[1,2-a]quinoxalin-4(5H)-one (9a). 1H NMR (400 MHz,
DMSO-d6) δ 11.22 (s, 1H), 8.15 (dd, J ) 2.8, 1.4 Hz, 1H), 8.01
(d, J ) 7.8 Hz, 1H), 7.27-7.22 (m, 2H), 7.18-7.14 (m, 1H), 6.99
(dd, J ) 4.1, 1.4 Hz, 1H), 6.65 (dd, J ) 3.7, 2.8 Hz, 1H); 13C
NMR (100 MHz, DMSO-d6) δ 155.53, 129.04, 126.15, 123.78,
123.11, 123.07, 118.57, 116.99, 115.53, 113.25, 111.89; EI-MS m/z
184 (M+), 155, 129; EI-HRMS calcd for C11H8N2O (M+) 184.0637,
found 184.0642.
Methyl 2-Bromo-6-oxo-5,6-dihydropyrido[3,2-e]pyrrolo-[1,2-a]-
1
pyrazine-8-carboxylate (9o). H NMR (400 MHz, DMSO-d6) δ
11.63 (s, 1H), 8.25 (d, J ) 1.8 Hz, 1H), 7.60 (d, J ) 8.2 Hz, 1H),
7.53 (d, J ) 8.2 Hz, 1H), 7.24 (d, J ) 1.8 Hz, 1H), 3.79 (s, 3H);
13C NMR (100 MHz, DMSO-d6) δ 163.70, 154.65, 134.48, 131.30,
128.04, 127.13, 125.42, 125.26, 120.14, 119.84, 112.86, 52.26; EI-
MS m/z 323 (M+, 81Br), 321 (M+, 79Br), 292, 290, 262, 234; EI-
HRMS calcd for C12H8BrN3O3 (M+, 79Br) 320.9749, found
320.9747.
2-Ethylpyrrolo[1,2-a]quinoxalin-4(5H)-one (9b). 1H NMR (400
MHz, DMSO-d6) δ 11.15 (s, 1H), 7.96 (d, J ) 1.4 Hz, 1H), 7.93
(d, J ) 7.8 Hz, 1H), 7.27-7.11 (m, 3H), 6.85 (d, J ) 1.4 Hz, 1H),
2.58 (q, J ) 7.3 Hz, 2H), 1.20 (t, J ) 7.3 Hz, 3H); 13C NMR (100
MHz, DMSO-d6) δ 155.34, 130.61, 128.86, 125.68, 123.46, 123.02,
116.89, 115.86, 115.23, 111.27, 20.26, 15.55; EI-MS m/z 212 (M+),
197, 184, 168; EI-HRMS calcd for C13H12N2O (M+) 212.0950,
found 212.0959.
2-Acetylindolo[1,2-a]quinoxalin-6(5H)-one (16a). 1H NMR
(400 MHz, DMSO-d6) δ 11.83 (s, 1H), 8.75 (s, 1H), 8.33 (d, J )
8.7 Hz, 1H), 7.92 (d, J ) 8.3 Hz, 1H), 7.88 (d, J ) 8.2 Hz, 1H),
7.60 (t, J ) 8.7 Hz, 1H), 7.49 (s, 1H), 7.41-7.34 (m, 2H), 2.65 (s,
3H); 13C NMR (100 MHz, DMSO-d6) δ 196.84, 156.41, 134.35,
132.90, 131.93, 129.03, 128.75, 126.57, 125.75, 125.27, 123.73,
123.18, 117.01, 114.99, 114.59, 106.77, 27.15; EI-MS m/z 276
(M+), 261, 214, 199, 171; EI-HRMS calcd for C17H12N2O2 (M+)
276.0899, found 276.0887.
8-Methoxypyrrolo[1,2-a]quinoxalin-4(5H)-one (9f). 1H NMR
(400 MHz, DMSO-d6) δ 11.07 (s, 1H), 8.19 (dd, J ) 2.8, 1.4 Hz,
1H), 7.59 (d, J ) 2.3 Hz, 1H), 7.18 (d, J ) 8.7 Hz, 1H), 6.97 (dd,
J ) 3.7, 1.4 Hz, 1H), 6.88 (dd, J ) 8.7, 2.3 Hz, 1H), 6.64 (dd, J
) 3.7, 2.8 Hz, 1H), 3.80 (s, 3H); 13C NMR (100 MHz, DMSO-d6)
δ 155.67, 155.13, 123.93, 123.67, 122.66, 118.79, 117.92, 113.18,
112.97, 111.81, 100.64, 56.39; EI-MS m/z 214 (M+), 199, 171,
143; EI-HRMS calcd for C12H10N2O2 (M+) 214.0742, found
214.0746.
Acknowledgment. The authors are grateful to the Chinese
Academy of Sciences, National Natural Science Foundation of
China (grants 20321202 and 20572119) for their financial
support.
2-Acetyl-8-methylpyrrolo[1,2-a]quinoxalin-4(5H)-one (9k). 1H
NMR (400 MHz, DMSO-d6) δ 11.33 (s, 1H), 8.83 (d, J ) 1.4 Hz,
1H), 8.04 (s, 1H), 7.28 (d, J ) 1.4 Hz, 1H), 7.17-7.11 (m, 2H),
2.48 (s, 3H), 2.35 (s, 3H); 13C NMR (100 MHz, DMSO-d6) δ
193.51, 155.38, 132.89, 128.17, 128.07, 127.27, 125.06, 122.36,
121.85, 117.03, 116.25, 110.89, 28.02, 21.08; EI-MS m/z 240 (M+),
225, 197, 169, 112; EI-HRMS calcd for C14H12N2O2 (M+)
240.0899, found 240.0904.
Supporting Information Available: Analytical data of
1
compounds 9c-e, 9g-j, 9p, and 16b, and the copies of H
NMR and 13C NMR spectra for all new products. This material
is available free of charge via the Internet at http://pubs.acs.org.
JO8008098
5162 J. Org. Chem. Vol. 73, No. 13, 2008