Carbamoyl radicals from carbamoylxanthates: a facile entry into isoindolin-1-ones

Article abstract of DOI:10.1016/j.tetlet.2007.09.142

It has been found that carbamoylxanthates derived from secondary t-butyl amines are stable compounds which function as efficient sources of carbamoyl radicals. The carbamoylxanthates derived from t-butylbenzylamines can be efficiently transformed into 2-t

Full text of DOI:10.1016/j.tetlet.2007.09.142

Available online at www.sciencedirect.com
Tetrahedron Letters 48 (2007) 8285–8289
Carbamoyl radicals from carbamoylxanthates:
a facile entry into isoindolin-1-ones
*
´
´
´
´
German Lopez-Valdez, Simon Olguın-Uribe and Luis D. Miranda
Instituto de Quı´mica, Universidad Nacional Auto´noma de Me´xico, Circuito Exterior S.N., Ciudad Universitaria,
Coyoacan, Me´xico D.F. 04510, Mexico
Received 20 February 2007; revised 20 September 2007; accepted 22 September 2007
Available online 26 September 2007
Abstract—It has been found that carbamoylxanthates derived from secondary t-butyl amines are stable compounds which function
as efficient sources of carbamoyl radicals. The carbamoylxanthates derived from t-butylbenzylamines can be efficiently transformed
into 2-t-butylisoindolin-1-ones via an oxidative radical cyclization process. The carbamoylxanthates derived from N-t-butylamino
olefins underwent the expected cyclization/xanthate-transfer process to afford the corresponding pyrrolidones and piperidones
under thermally induced DLP fragmentation conditions and in the presence of catalytic Et3B in air, at room temperature.
Ó 2007 Elsevier Ltd. All rights reserved.
Acyl radicals can be grouped into three major classes:
alkanoyl radicals 1, alkoxycarbonyl radicals 2, and car-
bamoyl radicals 3 (Fig. 1).1 Alkanoyl radicals easily lose
carbon monoxide to produce an alkyl radical, neverthe-
less this class of radicals is by far the most extensively
studied, and has been used for synthetic purposes.1
Alkoxylcarbonyl radicals also ought to be prone to frag-
mentation (loss of carbon dioxide), but these species
have received little attention. Carbamoyl radicals 3,
which should be comparatively long lived species, since
decarbonylation would afford high energy aminyl radi-
cals, have been considerably less studied than have alka-
noyl radicals 1. Presumably, the paucity of convenient
methods of generating 3 has been a factor contributing
to this situation. Nevertheless, carbamoyl radical addi-
tions to double bonds,2 aromatic systems,3 and oxime
ethers4 have been reported. The synthetic potential of
these radicals has been recently illustrated in the synthe-
sis of the complex natural product stephacidin B.5
In connection with our studies on the addition of alkyl
and acyl radicals to aromatic and heteroaromatic sys-
tems,6 it became of interest to examine the feasibility
of effecting oxidative cyclization of carbamoyl radicals
onto aromatic systems. Given the versatility of alkyl
radical generation from dithiocarbonates, developed
by Zard et al.7 we entertained the possibility of using
the related carbamoyl xanthates (carbamoyldithio-
carbonates) as carbamoyl radical sources.8 We fully
recognized that such species might have stability pro-
blems and could lose carbon oxysulfide to generate thio-
carbamates.2g Indeed, Grainger and Innocenti2g recently
encountered this problem and resorted to the use of
the more stable carbamoyldithiocarbamates as car-
bamoyl radical sources. Our endeavors in this area
commenced with the reaction of the carbamoyl chlo-
rides 5a–c (Scheme 1) with potassium ethyl xanthate
(0.9 equiv; see Ref. 7c for rationalization) in acetonitrile
at room temperature. Whereas carbamoyl xanthates 6a
and 6b were very unstable and rapidly decomposed to
complex mixtures, the N-t-butyl substituted congener
6c was isolated as a remarkably stable, crystalline
compound, the structure of which was verified by X-
ray crystallography (Fig. 2).9 Indeed, 6c remained
unchanged after two hours in chlorobenzene at reflux
temperature. When 6c was, however, submitted to one
of the typical Zard radical generation conditions, that
is, portionwise addition of 1.2 equiv of lauroyl peroxide
to a refluxing solution in 1,2-dichlorethane, isoindoli-
none 9 was isolated as the only product in good yield
O
O
O
R1
N
R
O
R
R2
1
2
3
Figure 1. Acyl radicals.
*
Corresponding author. Tel.: +52 55 56 22 44 40; fax: +52 55 56 16 22
17; e-mail: lmiranda@servidor.unam.mx
0040-4039/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2007.09.142

8286
G. Lo´pez-Valdez et al. / Tetrahedron Letters 48 (2007) 8285–8289
O
Cl
R
Furthermore, we realized that the N-unsubstituted cong-
eners ought to be accessible by the removal of the t-butyl
group in acidic media. One of the reported11 conditions
(catalytic trifluoromethanesulfonic acid; TFMSA)
failed, however, to effect this transformation. Neverthe-
less, after some experimentation it was found that the
removal of the N-t-butyl moiety from compounds 9
and 20–24 was accomplished simply by stirring solutions
thereof in neat TFMSA at room temperature or neat
trifluoroacetic acid (TFA) at reflux temperature. The
trifluoroacetic acid procedure gave NH isoindolones
39–44 in excellent yields (Table 2) including compounds
43 and 44, which were obtained somewhat less efficiently
by the TFMSA procedure. It is worth pointing out that
the NH isoindolinones are potential isoindole precursors
whose utility in Diels–Alder reactions is well estab-
lished.12 In addition, many isoindolinone derivatives
possess a variety of significant biological activities,
including antidopaminergic and protein kinase inhibit-
ing activities.13
R
O
S
R
OEt
KSC(S)OEt,
Triphosgene,
NH
N
N
S
CH3CN,
15 min,
0 °C.
Et3N, CH2Cl2,
r. t., 10 min
Ph
Ph
Ph
4a R = Me
6a R = Me (0%)
5a R = Me
4b R =
4c R =
i
-Pr
6b R =
6c R =
i
-Pr (0%)
5b R =
5c R =
i
-Pr
t
-Bu
t
-Bu, (77%)
t
-Bu
t-Bu
t-Bu
N
N
O
Lauroyl
O
peroxide
S
S
OEt
(72%) 9
DLP
6c
t-Bu
N
N
t-Bu
O
O
8
7
Scheme 1. Preparation and radical reaction of carbamoyl xanthate 6c.
How does the N-t-butyl group confer such notable sta-
bility upon the carbamoyl xanthates? This stability
may be a consequence of conformational effects (fixed
conformation and a high NCO rotational barrier) or
steric hindrance in the vicinity of the NCO moiety, but
at the present time we have no convincing data in this
regard. Why do the N-t-butylcarbamoyl radicals derived
from the above carbamoylxanthates undergo such effi-
3f
cient oxidative cyclization, which with one exception
has not been observed before, even in substrates where
it might have been expected to occur?2c,g In all of the
previously reported substrates the carbamoyl radical
could select between intramolecular addition to a double
bond or to the ortho sites of a benzenoid nucleus.
Radical addition to a double bond is generally a lower
energy process and is expected to be favored over addi-
tion to an aromatic system. We are currently studying
the synthetic consequences of, and the mechanistic ques-
tions which have been raised by the results described
above.
Figure 2. Computer generated perspective drawing of 6c.
(Scheme 1).10 Thus, the generation of carbamoyl radical
7, its cyclization to 8, and the dilauroyl peroxide (DLP)
mediated oxidation6a,b of radical 8 to isoindolinone 9 all
must take place with high efficiency.
To further explore the potential utility of the t-butyl-
carbamoylxanthates, we examined the possibility of
intramolecular addition of the derived carbamoyl radi-
cals to a double bond. We were pleased to observe that
the N-t-butylamino olefins 45 and 46 gave the thermally
stable carbamoylxanthates 47 and 48, respectively
(Scheme 2). These compounds underwent the expected
cyclization/xanthate-transfer process to afford the
corresponding pyrrolidone 49 and piperidone 50 under
thermally induced DLP fragmentation conditions. The
c-lactam 49 was obtained in slightly lower yield (76%)
than that observed with the related dithiocarbamate
reported before (80%).2g The reaction of xanthate 68
under the same conditions, afforded piperidone 50 in
62%, as the only product (Scheme 2). In contrast,
in the similar reported experiment (using a related
dithiocarbamate), a mixture (8.4:1) of the piperidone
derivative and a seven-membered lactam (formed by a
7-endo cyclization), was obtained in 65% yield.2g In
addition, products 49 and 50 could also be generated
at room temperature from xanthates 47 and 48, albeit
On the basis of this observation, several ring substituted
t-butylbenzylamines were converted into the corre-
sponding stable and isolable carbamoyl xanthates,
which were then subjected to the above carbamoyl rad-
ical generation conditions. In every case the ring substi-
tuted N-t-butylisoindolinone was obtained in excellent
yield (Table 1, entry 1), independent of the nature of
the benzenoid substituent(s). Interestingly, 3,4-methyl-
enedioxy compound 26 and 3-bromo compound 36 gave
mixtures of isoindolinones in which the products derived
from cyclization at C-6, the less hindered position (27
and 37, respectively), were only slightly favored over
those derived from attack at C-2 (28 and 38, respec-
tively). The data in Table 1 convincingly show that a
variety of structurally diverse isoindolinones, a relatively
rare class of compounds, are now readily available.

G. Lo´pez-Valdez et al. / Tetrahedron Letters 48 (2007) 8285–8289
Table 1. Synthesis of 2-t-butylisoindolin-1-ones from t-butylbenzylamines
8287
Entry
Amine
Xanthatea
Product
N
t
-Bu
O
NH
Nt-Bu
t-Bu
R
Xtht
R
R
O
10 R = Me
11 R = Cl
12 R = Br
13 R = OMe
14 R = COOMe
15 R = Me (81%)
16 R = Cl (71%)
17 R = Br (82%)
18 R = OMe (80%)
19 R = COOMe (85%)
20 R = Me (77%)
21 R = Cl (86%)
22 R = Br (92%)
23 R = OMe (72%)
24 R = COOMe (91%)
1
O
Nt-Bu
O
O
O
N
t
-Bu
O
O
NH
-Bu
27 (44%)
O
t
Xtht
2
O
Nt-Bu
25
26 (85%)
O
O
O
28 (36%)
R
R
R
NH
Nt-Bu
Nt-Bu
t-Bu
3
Xtht
O
O
33 R = Cl (85%)
34 R = F (90%)
29 R = Cl
30 R = F
31 R = Cl (84%)
32 R = F (65%)
Br
Nt-Bu
Br
O
N
t
-Bu
Br
NH
-Bu
37 (49%)
4
Xtht
O
t
Br
O
35
36 (60%)
Nt-Bu
38 (33%)
a Xtht = SC(S)OEt.
OEt
Table 2. Removal of the t-butyl group
S(C)SOEt
1) Triphosgene,
Et3N, CH2Cl2
Cond.
S
S
t-Bu NH
N
tBu
N H
R
R
n
O
O
n
N
n
2) KSC(S)OEt,
CH3CN
N
O
O
t-Bu
t-Bu
Subs.
R
Prod.
Cond. A
Cond. B
47 n = 1 (75%)
48 n = 2 (63%)
45 n = 1
46 n = 2
DLP (cat.) Cl(CH2)2Cl
49 n = 1 (76%)
Time (h) Yield Time (h) Yield
50 n = 2 (62%)
1
2
3
4
5
6
9
20
21
22
23
24
H
Me
Cl
Br
OMe
39
40
41
42
43
0.5
0.5
24
24
3
0.5
98
97
100
100
74
72
72
72
72
96
96
100
100
100
100
96
Et3B/air (cat.) CH2Cl2, r. t.
49 n = 1 (63%)
50 n = 2 (56%)
Scheme 2. Cyclization of carbamoyl radicals onto C–C double
bonds.2g
CO2Me 44
42
95
Conditions: (A) neat TFMSA, rt; (B) neat TFA, reflux.
In summary, we have demonstrated that carbamoylx-
anthates derived from secondary t-butyl-amines are
stable compounds that serve as efficient sources of
carbamoyl radicals both by thermally induced DLP
in somewhat lower yields, by means of catalytic triethyl
borane in an aerial atmosphere.

8288
G. Lo´pez-Valdez et al. / Tetrahedron Letters 48 (2007) 8285–8289
addition of Et3N (3.4 mmol). The mixture was stirred for
10 min at room temperature. The solvent was removed
under reduced pressure to give the crude carbamoyl
chloride. This compound was used in the next step
without further purification. A solution of the crude
carbamoyl chloride in acetonitrile (5.0 mL) was treated
with the O-ethylxanthic acid, potassium salt (0.95 mmol).
The reaction was stirred for 15 min, at room temperature,
quenched with water and extracted with CH2Cl2. The
organic layer was dried over Na2SO4 and the solvent
removed under reduced pressure. The carbamoylxanthate
was purified by a silica gel column chromatography
(hexanes/EtOAc, 98:2) to afford the pure xanthate.
Selected spectral data. Compound (6c): A yellow oil; IR
(film) cmÀ1 m: 2983, 2967, 2933, 1679; 1H NMR (200 MHz,
CDCl3): d 1.44 (s, 9H), 1.46 (t, 3H), 4.66 (q, 2H), 4.78 (s,
2H), 7.18–7.40 (m, 5H); 13C NMR (50.3 MHz, CDCl3): d
207.3, 160.2, 138.2, 128.7, 127.3, 125.8, 70.6, 60.7, 51.1,
28.3, 13.5.; HRMS (FAB+) calcd for C15H22NO2S2:
[M+1] 312.1092, found: 312.1091. Compound (15): A
fragmentation and at room temperature in the presence
of catalytic Et3B in air. Carbamoylxanthates derived
from t-butyl-benzylamines are transformed into 2-t-
butylisoindolin-1-ones by oxidative radical cyclization
of the derived carbamoyl radical onto the benzenoid sys-
tem, a process scarcely exploited so far.
Acknowledgments
We thank CONACYT (J42673Q) for financial support
and Dr. Joseph M. Muchowski for many helpful discus-
´
sions. We also thank R. Patino, J. Perez, L. Velasco, H.
˜
Rios, N. Zavala, E. Huerta and A. Pena, for technical
˜
support and Dr. A. Toscano for X-ray crystallography.
S.O.-U in a sabatical leave from Universidad Autonoma
Metropolitana.
1
yellow oil, IR (film) cmÀ1 m: 2978, 2927, 1691; H NMR
(200 MHz, CDCl3): d 1.42 (s, 9H), 1.45 (t, 3H), 4.65 (c,
2H), 4.73 (s, 2H), 7.14 (d, J = 8.4 Hz, 2H), 7.31 (d,
J = 8.2 Hz, 2H); 13C NMR (50.3 MHz, CDCl3): d 207.3,
160.1, 136.9, 135.1, 129.3, 125.7, 70.5, 60.6, 50.8, 28.3,
20.9, 13.5.; HRMS (FAB+) calcd for C16H24O2NS2:
[M+1] 326.1248, found: 326.1247. Compound (16): A
References and notes
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2. (a) Gill, G. B.; Pattenden, G.; Reynolds, S. J. Tetrahedron
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Reynolds, S. J. J. Chem. Soc., Perkin Trans. 1 1994, 369;
(c) Bella, A. F.; Jackson, L. V.; Walton, J. C. J. Chem.
Soc., Perkin Trans. 2 2002, 1839; (d) Bella, A. F.; Jackson,
L. V.; Walton, J. C. Org. Biomol. Chem. 2004, 2, 421; (e)
Scanlan, E. M.; Slawin, A. M. Z.; Walton, J. C. Org.
Biomol. Chem. 2004, 2, 716; (f) Ribby, J. H.; Danca, D.
M.; Horner, J. H. Tetrahedron Lett. 1998, 39, 8413; (g)
Grainger, R. S.; Innocenti, P. Angew. Chem., Int. Ed. 2004,
43, 3445.
3. (a) Minisci, F.; Recupero, F.; Punta, C.; Gambarotti, C.;
Antonietti, F.; Fontana, F.; Gian, F. Chem. Commun.
2002, 2496; (b) Biyouki, M. A. A.; Smith, R. A. J.;
Bedford, J. J.; Leader, J. P. Synth. Commun. 1998, 28,
3817; (c) Nagata, K.; Itoh, T.; Okada, M.; Takahashi, O.
A. Heterocycles 1991, 32, 2015; (d) Leardini, R.; Tundo,
A.; Zanardi, G. J. Chem. Soc., Perkin Trans. 1 1981, 3164;
(e) Minisci, F.; Gardini, G. P.; Galli, R.; Bertini, F.
Tetrahedron Lett. 1970, 1, 15; (f) Minisci, F.; Fontana, F.;
Coppa, F.; Yan, Y. M. J. Org. Chem. 1995, 60, 5430.
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2005, 7, 155.
1
yellow oil; IR (film) cmÀ1 m: 2979, 2933, 1692; H NMR
(200 MHz, CDCl3): d 1.43 (s, 9H), 1.45 (t, 3H), 2.33 (s,
3H), 4.65 (c, 2H), 4.73 (s, 2H), 7.08 (d, J = 8.2 Hz, 2H),
7.15 (d, J = 8.2 Hz, 2H); 13C NMR (50.3 MHz, CDCl3): d
206.6, 160.0, 136.7, 132.9, 128.7, 127.1, 70.6, 60.6, 50.3,
28.2, 13.4; HRMS (FAB+) calcd for C15H21O2NClS2:
[M+1] 346.0702, found: 346.0704. Compound (17): A
1
yellow oil; IR (film) cmÀ1 m: 2976, 2932, 1692; H NMR
(200 MHz, CDCl3): d 1.43 (s, 9H), 1.46 (t, 3H), 4.63 (c,
2H), 4.71 (s, 2H), 7.09 (d, J = 8.4 Hz, 2H), 7.48 (d,
J = 8.4 Hz, 2H); 13C NMR (50.3 MHz, CDCl3):
d
206.7, 160.2, 137.3, 131.8, 127.5, 121.1, 70.7, 60.7, 50.4,
28.3, 13.5; HRMS (FAB+) calcd for C15H21O2NBrS2:
[M+1] 390.0197, found: 390.0196. Compound (18): IR
(film) cmÀ1 m: 2978, 2934, 1690; 1H NMR (200 MHz,
CDCl3): d 1.43 (s, 9H), 1.45 (t, 3H), 3.79 (s, 3H) 4.66 (c,
2H), 4.71 (s, 2H), 6.88 (d, J = 8.8 Hz, 2H), 7.12 (d,
J = 8.8 Hz, 2H); 13C NMR (50.3 MHz, CDCl3): d 207.3,
160.0, 158.8, 130.0, 127.0, 114.0, 70.5, 60.5, 55.2, 50.4,
28.3, 13.5; HRMS (CI+) calcd for C16H23NO3S2: [M+]
341.1119, found: 341.1111. Compound (19): A yellow oil;
1
IR (film) cmÀ1 m: 2980, 2955, 2930, 1723, 1694; H NMR
5. Herzon, S. B.; Myers, A. G. J. Am. Chem. Soc. 2005, 127,
5342.
6. (a) Osornio, Y. M.; Cruz-Almanza, R.; Jimenez-Montano,
˜
(200 MHz, CDCl3): d 1.43 (s, 9H), 1.46 (t, 3H), 3.92 (s,
3H) 4.66 (c, 2H), 4.82 (s, 2H), 7.29 (d, J = 8.6 Hz, 2H),
8.03 (d, J = 8.8 Hz, 2H); 13C NMR (50.3 MHz, CDCl3): d
206.7, 166.5, 160.1, 143.5, 130.0, 129.2, 125.7, 70.6, 60.7,
52.0, 50.8, 28.2, 13.4; HRMS (FAB+) calcd for
C17H24NO4S2: [M+1] 370.1147, found: 370.1150.
´
V.; Miranda, L. D. Chem. Commun. 2003, 2316; (b)
´
Menes-Arzate, M.; Martınez, R.; Cruz-Almanza, R.;
Osornio, Y. M.; Muchowski, J. M.; Miranda, L. D. J.
Org. Chem. 2004, 69, 4001; (c) Miranda, L. D.; Cruz-
10. General procedure for the synthesis of isoindolin-1-ones. A
deaerated solution of the corresponding xanthate
(1.0 mmol) in 1,2-dichloroethane (10 mL) was heated at
reflux, and 1.2 mmol of dilauroyl peroxide was added
portionwise (0.3 mmol/h). After completion (4 h) the
solution was cooled and the 1,2-dichloroethane evapo-
rated under reduced pressure. In order to precipitate the
by-products derived from DLP, the reaction crude was
suspended in acetonitrile (10 mL). The residue was puri-
fied by a silica gel column chromatography (Hexanes/
EtOAc, 90:10) to afford the corresponding isoindolin-1-
one. Selected spectral data. Compound (9): A yellowish
´
Almanza, R.; Pavon, M.; Alva, E.; Muchowski, J. M.
Tetrahedron Lett. 1999, 40, 7153.
7. (a) Quiclet-Sire, B.; Zard, S. Z. Top. Curr. Chem. 2006,
264, 201; (b) Zard, S. Z. In Radicals in Organic Synthesis;
Renaud, P., Sibi, M. P., Eds.; Wiley VCH: Weinhem,
2001; p 90; (c) Zard, S. Z. Angew. Chem., Int. Ed. 1997, 36,
672.
8. For generation of alkoxycarbonyl radical from S-acylx-
anthates see: Forbes, J. E.; Saicic, R. N.; Zard, S. Z.
Tetrahedron 1999, 55, 3791.
9. General procedure for the preparation of carbamoylxanth-
ates. To a stirred solution of triphosgene (0.7 mmol) in
CH2Cl2 (5.0 mL), at 5 °C the corresponding t-butylbenzyl-
amine (1.0 mmol) was added, followed by dropwise
1
solid; IR (film) cmÀ1 m: 3013, 2956, 2923, 2854, 1660; H
NMR (200 MHz, CDCl3): d 1.57 (s, 9H), 4.45 (s, 2H),

G. Lo´pez-Valdez et al. / Tetrahedron Letters 48 (2007) 8285–8289
8289
7.37–7.54 (m, 3H), 7.78 (dt, J = 6.8, 1.6 Hz, 1H); 13C
NMR (50.3 MHz, CDCl3): d 168.8, 140.6, 134.4, 130.8,
127.7, 123.0, 122.2, 54.2, 48.4, 27.9; HRMS (FAB+) calcd
for C12H16NO: [M+1] 190.1232, found: 190.1236. Com-
pound (20): A yellowish solid; IR (film) cmÀ1 m: 3010,
2970, 2918, 2869, 1671; 1H NMR (200 MHz, CDCl3): d
1.56 (s, 9H), 2.42 (s, 3H), 4.41 (s, 2H), 7.29 (2H), 7.58 (s,
1H); 13C NMR (50.3 MHz, CDCl3): d 169.0, 137.9, 137.7,
134.5, 131.8, 123.3, 122.0, 54.3, 48.2, 27.9, 21.3; HRMS
(FAB+) calcd for C13H18NO: [M+1] 204.1383, found:
204.1388. Compound (21): A yellowish solid; IR (film)
cmÀ1 m: 3065, 2982, 2958, 2869, 1672; 1H NMR (200 MHz,
CDCl3): d 1.56 (s, 9H), 4.43 (s, 2H), 7.33 (dd, J = 8.0,
0.6 Hz, 1H), 7.46 (dd, J = 8.0, 2.0 Hz, 1H) 7.74 (d,
J = 2.0 Hz, 1H); 13C NMR (50.3 MHz, CDCl3): d 167.4,
138.7, 136.2, 134.1, 131.0, 123.6, 123.3, 54.6, 48.1, 27.9;
HRMS (CI+) calcd for C12H14ClNO: [M+] 223.0764,
found: 223.0781. Compound (22): A yellowish solid; IR
(film) cmÀ1 m: 3061, 2980, 1671; 1H NMR (200 MHz,
CDCl3): d 1.56 (s, 9H), 4.41 (s, 2H), 7.29 (dd, J = 7.4,
0.6 Hz, 1H), 7.61 (dd, J = 8.0, 2.0 Hz, 1H) 7.90 (d,
J = 1.8 Hz, 1H); 13C NMR (50.3 MHz, CDCl3): d 167.3,
139.2, 136.5, 133.8, 126.3, 123.9, 121.9, 54.6, 48.1, 27.9;
HRMS (CI+) calcd for C12H15BrNO: [M+1] 268.0332,
found: 268.0283. Compound (23): A yellowish solid; IR
(film) cmÀ1 m: 3065, 2963, 2923, 2855, 1679; 1H NMR
(200 MHz, CDCl3): d 1.56 (s, 9H), 3.84 (s, 3H), 4.38 (s,
2H), 7.06 (dd, J = 8.2, 2.4 Hz, 2H), 7.29 (dd, J = 6.0,
0.6 Hz, 1H); 13C NMR (50.3 MHz, CDCl3): d 159.8,
135.7, 132.8, 123.1, 119.4, 105.7, 55.5, 54.3, 48.0, 29.6,
27.9; HRMS (FAB+) calcd for C13H18NO2: [M+1]
220.1332, found: 220.1338. Compound (24): A yellowish
solid; IR (film) cmÀ1 m: 2972, 2931, 1725, 1666; 1H
NMR (200 MHz, CDCl3): d 1.58 (s, 9H), 3.94 (s, 3H), 4.51
(s, 2H), 7.48 (dd, J = 7.8, 0.6 Hz, 1H), 8.20 (dd, J = 8.2,
1.8 Hz, 1H), 8.44 (dd, J = 0.8 Hz, 1H); 13C NMR
(50.3 MHz, CDCl3): d 168.1, 166.5, 145.1, 132.1, 130.3,
124.7, 122.5, 54.5, 52.2, 48.5, 27.9; HRMS (FAB+) Calcd
for C14H18NO3: [M+1] 248.1281, found: 248.1287.
11. Earle, M. J.; Fairhurst, R. A.; Heaney, H.; Papageorgiou,
G. Synlett 1990, 621.
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