Photochemistry of 2-indolyl aryl ethers: An unexpected rearrangement leading to C-C bond formation

Article abstract of DOI:10.3987/com-03-9762

Two types of 2-(p-tolyloxy)indole were prepared and their reactivity was studied under photochemical conditions. The expected electrocyclization was not observed. Instead, unprecedented rearrangement products were obtained. The reaction outcome was found to depend on the viscosity of the media.

Full text of DOI:10.3987/com-03-9762

HETEROCYCLES, Vol. 60, No. 7, 2003, pp. 1615 - 1623
Received, 12th March, 2003, Accepted, 6th May, 2003, Published online, 12th May, 2003
PHOTOCHEMISTRY
OF
2-INDOLYL
ARYL
ETHERS:
AN
UNEXPECTED REARRANGEMENT LEADING TO C-C BOND
FORMATION
Ken S. Feldman* and Daniela Boneva Vidulova
Department of Chemistry, The Pennsylvania State University, University Park,
PA 16802, USA
e-mail: ksf@chem.psu.edu
Abstract – Two types of 2-(p-tolyloxy)indole were prepared and their reactivity
was studied under photochemical conditions. The expected electrocyclization
was not observed. Instead, unprecedented rearrangement products were obtained.
The reaction outcome was found to depend on the viscosity of the media.
Irradiation of aryl systems bearing pendant unsaturated functionality can lead to diverse modes of
cyclization/rearrangement. In particular, six-electron systems containing a heteroatom are suitable
substrates for photochemical promotion of electrocyclization, a process that leads to heterocycle
formation in favorable cases.1 For example, this type of reaction with diaryl or aryl vinyl ether
substrates affords dihydrobenzofurans, a transformation of some value in the synthesis of cognate
naturally occurring materials.2
The possibility that 2-indolyl aryl ethers (1) (Scheme 1) might participate in similar electrocyclizations
prompted the investigations described below. Successful electrocyclization of this species might yield a
tetracycle of the general type (3), a product that could further an ongoing project in natural products
synthesis. Enthusiasm for the prospects for success in this transformation was tempered by the fact that
(1) most high-yielding aryl vinyl ether electrocyclizations utilize substrates bearing an electron-stabilizing
substituent at C(2) (cf. 1), and (2) a highly strained trans bicyclo[3.3.0]octane skeleton (3) would result.
Nevertheless, these points can only be settled by experiment, and so the photochemical reaction chemistry
of 1 was explored. As it transpired, products of the type (3) were not observed. Rather, a completely
different skeletal reorganization occurred, leading to 2-arylindole products (4) in a process reminiscent of

a formal photo-Fries rearrangement.3 A description of this process, along with a discussion of the
experimental evidence that addresses possible mechanistic pathways for the reaction, follows.
CH
CH
3
3
CH
3
H
CH O C
3
CH
CH O C
3
2
CH O C
3
CH O C
3
3
2
2
2
–
suprafacial
1,4 H-shift
hu
hu
O
O
O
+
2
conrotatory
cyclization
N
R
N
R
N
R
N
R
H
HO
4
observed
1
2
3
not observed
Scheme 1. Exploratory photochemistry of 2-indoyl aryl ethers.
RESULTS AND DISCUSSION
The syntheses of ether substrates (1a) and (1b) are outlined in Scheme 2. Commercially available methyl
indole-3-carboxylate (5) was chlorinated at C(2) at slightly elevated temperatures (45 – 50 ºC).4 The
chloro derivative (6) was protected at the indole nitrogen as its methoxymethyl ether (7). Substitution of
the chloride with a p-tolyloxy group via an addition-elimination mechanism was accomplished under
o
basic conditions at 85 - 90 C in N,N-dimethylacetamide, leading to the formation of 1a in good yield.5
Substrate (1b) was synthesized from 1a via MOM group removal and reprotection of the indole nitrogen
as its BOC derivative.
CH3
1) BBr3
CH3
CH3O2C
CH3O2C
N
CH3O2C
N
CH3O2C
NaH
p-cresol
2) NH4OAc,
NaOCH3
NCS
68%
Cl
O
O
3) LiNTMS2,
BOC2O
78%
N
R
N
H
MOM
BOC
LiNTMS2, MOMCl
~ 100%
6 R = H
66%
1b
5
1a
7 R = MOM
Scheme 2. Synthesis of substrates (1a) and (1b).
Diaryl ethers (1a) and (1b), independently, were irradiated at various wavelengths (254 and 300 nm),
through different media (pyrex glass (300 nm irradiations) or quartz (254 nm irradiations)), at different
concentrations (0.005 M – 0.5 M) and in different solvents (acetonitrile, methanol, benzene, acetone, 1,2-
dichloroethane and cyclohexane). However, no set of reaction conditions led to any detectable levels
of electrocyclization products of the type (3). Rather, a mixture of compounds (4a/b), (8a/b) and (9) was
obtained in all cases, although in widely varying yields depending upon conditions (Scheme 3 and Table
1).

CH3
CH3O2C
CH3O2C
CH3
+
CH3O2C
CH3
hu
O
H
+
see Table 1
for conditions
and yields
N
R
N
R
N
R
HO
HO
1a R = MOM
1b R = BOC
4a R = MOM
4b R = BOC
8a R = MOM
8b R = BOC
9
Scheme 3. Irradiation of 2-indole aryl ethers (1a) and (1b).
trial substrate
solvent
viscosity
(mPa•s)
acetone-d6
(0.306)
acetonitrile-d3
(0.369)
methanol-d4
(0.544)
conc. wavelength
4
8
9
M
(nm)
300
(%) (%) (%)
1
2
3
4
1a
1a
1a
1a
0.05
29
30
25
25
25
25
12
8
0.03
0.05
0.06
300
300
300
20a 12
benzene-d6
(0.604)
37
8
5
6
7
8
9
10
11
12
13
1a
1a
1a
1a
1a
1b
1b
1b
1b
methanol-d4
acetonitrile-d3
Cl(CH2)2Cl
cyclohexane-d12
CH3OD
acetone-d6
acetonitrile-d3
methanol-d4
benzene-d6
0.005
0.07
0.07
0.07
0.06
0.06
0.50
0.05
0.03
300
254
254
254
300
300
300
300
300
19
37
43
26
19
10
22
12
19
10
22
12
18
20
15
7
35a 18
20
21
23
30
20
15
7
10
10
a mixture of 4a and the corresponding lactone.
Table 1. Results of irradiation studies with diaryl ethers (1a) and (1b).
Several conclusions emerge from consideration of these data. First, the nature of the indole nitrogen
protecting group (electron donating as in 1a or electron withdrawing as in 1b) does not have a large
impact on the course of the reaction. Second, irradiation of substrate (1a) at the shorter wavelength led
to modest improvements in yield of 4a when compared to the 300 nm run (e.g., trial 2 vs. trial 6).
Variations in the concentration of substrate (within the range explored) did not lead to dramatic changes
in the product yields or ratios. The most noticeable change in product yield accompanied the solvent
studies. There appears to be a correlation between solvent viscosity (trials 1-4) and the ratio of Ar-Ar
bonded product (4a) to Ar-H reduction product (8a). A similar trend is observed with the N-BOC
substrate (1b) (trials 10-13). For both of these substrates, as the solvent viscosity increases, the ratio of 4
to 8 increases as well. These results, taken together, suggest that there are evident limitations to

developing this C–O-to-C–C bond shift as a useful method for 2-arylindole synthesis. However, they do
provide some insight into the possible mechanistic course of the transformation.
Two mechanistic hypotheses for the formation of 4 were considered (Scheme 4). One hypothesis (#1)
invokes a pathway proceeding through the intermediacy of the desired benzofuran derivative (3) en route
to 4. In this scenario, the inherent strain of the trans bicyclo[3.3.0]octane framework induces a
fragmentation/recyclization to furnish 11, which then suffers retro-Mannich cleavage to deliver 4. This
mechanistic model does not directly address the formation of reduction products (8) and (9), but variable
yields of 8/9 formation (cf. Table 1) raised the possibility that these species resulted from alternative
competitive processes whose occurrence were condition dependent. A second mechanistic hypothesis
(#2) explicitly acknowledges a route for 8/9 production within the context of a radical-based pathway to 4
from 1. In this scheme, an initial light-induced single electron transfer reaction within 1 would provide a
diradical species (13) susceptible to cleavage of the scissile C-O bond. The resulting diradical pair could
partition in one of several ways. Recombination within the solvent cage might afford 4, whereas cage
escape might provide opportunities for radical reduction to provide 8 and 9.
Hypothesis #1:
H3C
H3C
H3C
CH3O2C
CH3O2C
CH3
CH3
CH3O2C
H
CH3O2C
CH3O2C
O –
O
N
R
N
+
O
R
N
R
N +
R
N
R
– O
H
HO
3
10
11
12
4
CH3O2C
CH3
Hypothesis #2:
recombination
CH3
CH3
CH3
N
CH3O2C
CH3O2C
CH3O2C
N
R
+
HO
•
hu
–
+
•
4
O
O
•
N
R
•
SET
N
R
CH3O2C
CH3
R
O
14
15
(D)
H
1
13
cage escape
N
R
H source
8
HO
9
Scheme 4. Two mechanistic hypothesis for the rearrangement of 1 into 4.
A series of experiments designed to probe this mechanistic dichotomy were conducted. Irradiation of 1a
in the presence of a cation trap (Et3Si-H) might, in principle, divert some of the intermediate (10) if
mechanism #1 was operational. However, the results of this experiment did not lend any support to a
proposal that required cationic intermediates. More telling was the outcome of the series of experiments
that used solvents of varying viscosities (Table 1).6 The observed trend that higher solvent viscosity

scaled with greater yield of the internal trapping product (4) is consistent with a cage recombination/cage
escape mechanism such as that described in hypothesis #2 of Scheme 4. Finally, the results of a set of
deuterium labeling experiments provide further insight into this mechanistic puzzle. When CD3OD was
1
used as solvent, deuterium incorporation at C(2) in 8 was detected to the extent of 75% (by MS and H
NMR spectroscopy). However, when the reaction was run in CH3OD, no deuterium incorporation was
detected. These results are again completely consistent with a radical mediated mechanism featuring the
radical pair (14)/(15) as the key branch point.
In summary, an unprecedented photochemical rearrangement of 2-(p-tolyloxy)indoles has been observed.
The products are 2-(indol-2-yl)-4-methylphenol and methyl indol-3-carboxylate. The product distribution
was dependent on the solvent viscosity. These results, in conjunction with deuterium labeling studies,
support a mechanistic hypothesis that features SET-induced bond cleavage/recombination as the primary
source of the 2-arylindole products.
ACKNOWLEDGMENTS
We thank the National Institutes of Health (GM 35727) for support of this work.
EXPERIMENTAL
THF was distilled from sodium/benzophenone under Ar immediately before use. CH2Cl2 and MeOH
were dried by CaH2 and Mg, respectively, and distilled under Ar immediately before use. Oxygen- and
moisture-sensitive reactions were performed in flame-dried glassware under an Ar atmosphere. Flash
chromatography7 was carried out using 32 – 63 mm silica gel and the indicated solvent system. The
chromatography solvents hexanes, Et2O and CH2Cl2 were distilled from CaH2, whereas benzene was used
without further purification (EM Science). ESI-MS, APCI-MS and HRMS spectra were obtained from
the Mass Spectroscopy Laboratory at The Pennsylvania State University. All melting points are
uncorrected. Combustion analyses were performed by Midwest Microlab, Indianapolis, IN.
Methyl 2-Chloro-1H-indole-3-carboxylate (6).8
N-Chlorosuccinimide (1.15 g, 8.63 mmol) was added in one portion to a solution of 1H-indole-3-
carboxylic acid methyl ester (5) (1.16 g, 6.64 mmol) in 40 mL of CCl4 and 40 mL of THF. The mixture
was heated to 45 °C for 10 h. Aftercooling to rt, the reaction solution was poured into saturated NaHCO3
solution and extracted with Et2O (3 x 30 mL). The combined organic layers were dried over Na2SO4,
filtered, and concentrated in vacuo to give an off-white solid. Purification of this residue by flash column
chromatography using 100% CH2Cl2 as eluent gave 0.94 g (68%) of indole (6) as transparent crystals, mp
1
183 °C (recrystallized from EtOAc/hexane). IR (CCl4) 3462 (NH), 1710 (C=O) cm-1. H-NMR (360

MHz, CD3COCD3) d: 11.86 (br s, 1H); 8.07 (m, 1H); 7.43 (dddd, J=7.1, 3.5, 1.5, 0.7 Hz, 1H); 7.23 (m,
2H); 3.90 (s, 3H). 13C-NMR (90 MHz, CD3COCD3) d: 164.5, 135.4, 130.8, 127.3, 124.1, 122.9, 121.9,
112.1, 104.5, 51.2. MS m/z (relative intensity) 210 (MH+, 100). HRMS Calcd for C10H8NO2Cl 209.0244,
found 209.0263. Anal. Calcd for C10H8NO2Cl: C, 57.30; H, 3.85; N, 6.68; Cl, 16.91. Found: C, 57.18; H,
3.84; N, 6.54; Cl, 16.86.
Methyl 2-Chloro-1-methoxymethyl-1H-indole-3-carboxylate (7).
Lithium hexamethyldisilazide (1.0 M in THF, 1.17 mL, 1.17 mmol) was added slowly to a solution of 6
(245 mg, 1.17 mmol) in 12 mL of THF at 0 °C. The reaction solution was stirred at 0 °C for 30 min and
then chloromethyl methyl ether (108 mL, 1.42 mmol) was added dropwise. The solution was allowed to
warm to rt, stirred for 3 h, and then poured into 15 mL of H2O. The aqueous layer was neutralized with 1
mL 1 M H3PO4 and extracted with Et2O (3 x 10 mL). The combined organic layers were dried over
Na2SO4, filtered, and concentrated in vacuo to give an orange oil. Purification of the residue by flash
column chromatography using 20% Et2O in hexanes as eluent gave 293 mg (99%) of 7 as a white
amorphous solid, mp 36 - 37 °C. IR (thin film) 1712 (C=O) cm-1. 1H-NMR (300 MHz, CDCl3) d: 8.13
(ddd, J=5.0, 2.6, 0.7 Hz, 1H); 7.47 (ddd, J=5.0, 2.6, 0.7 Hz, 1H); 7.30 (m, 2H); 5.60 (s, 2H); 3.97 (s, 3H);
3.31 (s, 3H). 13C-NMR (90 MHz, CDCl3) d: 164.4, 135.5, 132.2, 125.9, 123.9, 123.1, 121.7, 110.3, 105.2,
74.2, 56.5, 51.4. MS m/z (relative intensity) 254 (MH+, 100). HRMS Calcd for C12H12NO3Cl 253.0506,
found 253.0521. Anal. Calcd for C12H12NO3Cl: C, 56.81; H, 4.77; N, 5.52; Cl, 13.98. Found: C, 56.72;
H, 4.59; N, 5.48; Cl, 14.09.
Methyl 1-Methoxymethyl-2-(4-methylphenoxy)-1H-indole-3-carboxylate (1a).
Dimethylacetamide (DMA) (2 mL) was added to sodium hydride (89 mg, 2.24mmol, 60% in oil)
previously washed with 2 x 1 mL hexanes. After the suspension was stirred for 5 min, p-cresol (260 mL,
2.48 mmol) was added one portion. The mixture was stirred until no evolution of gas was observable.
A solution of 7 (272.0 mg, 1.07mmol) in 10 mL of DMA was added dropwise at rt and the reaction was
heated at 85 °C overnight. The solvent was removed in vacuo and the residual brown oil was partitioned
between water and CH2Cl2. The organic layer was washed with brine, dried over Na2SO4, concentrated,
and the residue was purified by flash column chromatography, eluting with 20% Et2O in hexanes. The
pure product (1a) was recovered as a clear oil (272 mg, 78%) which solidified upon standing, mp 50 - 54
1
°C. IR (CCl4) 1709 (C=O) cm-1. H-NMR (400 MHz, CD3CN) d: 8.10 (ddd, J=5.9, 1.8, 0.7 Hz, 1H); 7.54
(ddd, J=5.8, 1.7, 0.7 Hz, 1H); 7.31 (m, 2H); 7.13 (dd, J=8.8, 0.7 Hz, 2H); 6.87 (br d, J=8.7 Hz, 2H); 5.41
(s, 2H); 3.64 (s, 3H); 3.22 (s, 3H); 2.29 (s, 3H). 13C-NMR (90 MHz, CD3CN) d: 164.4, 156.9, 151.6,
134.0, 133.0, 131.1, 126.0, 124.1, 123.7, 122.2, 116.2, 111.6, 95.0, 73.9, 56.9, 51.2, 20.6. MS m/z

(relative intensity) 326 (MH+, 100). HRMS Calcd for C19H19NO4 325.1314, found 325.1299. Anal. Calcd
for C19H19NO4: C, 70.14; H, 5.89; N, 4.31. Found: C, 69.77; H, 5.93; N, 4.46.
Methyl 2-(4-Methylphenoxy)-1-tert-butyloxycarbonyl-1-H-indole-3-carboxylate (1b).
Boron tribromide (1.0 M in CH2Cl2, 2.85 mL, 2.85 mmol) was added dropwise to a –75 °C solution of 1a
(459 mg, 1.41 mmol) in 14.2 mL of CH2Cl2. The reaction mixture was stirred for 30 min, warmed to rt,
and then poured into ice cold water. The two layers were separated, and the organic phase was dried over
Na2SO4 and concentrated in vacuo. The recovered off-white solids were dissolved in 28.2 mL CH2Cl2
and NH4OAc (446 mg, 578 mmol) was added in one portion. The mixture was stirred for 3 h and then the
solvent was removed in vacuo. MeOH (28.2 mL) was added followed by NaOMe (541 mg, 10.0 mmol).
The reaction mixture was stirred for 2 h and then poured into ice cold water. The aqueous layer was
acidified with 1 M H3PO4 and extracted with Et2O. The combined organic extracts were dried over
MgSO4 and concentrated. Purification of the residue via flash column chromatography using 100%
CH2Cl2 as eluent gave 321 mg (81%) of the free N-H indole as a white solid, mp 167 °C (recrystallized
from Et2O/hexane). IR (thin film) 3228 (NH), 1681 (C=O) cm-1. 1H-NMR (360 MHz, CD3CN) d: 9.72
(br s, 1H); 8.01 (dddd, J=8.2, 5.9, 2.7, 0.8 Hz, 1H); 7.30 (dddd, J=8.1, 5.9, 2.6, 0.7 Hz, 1H); 7.20 (m, 4H);
6.98 (dd, J=6.5, 2.1 Hz, 2H); 3.74 (s, 3H); 2.33 (s, 3H). 13C-NMR (90 MHz, CDCl3) d: 164.6, 153.7,
152.4, 134.4, 130.5, 129.9, 125.9, 122.4, 122.2, 121.2, 117.7, 110.7, 92.0, 50.9, 20.7. MS m/z (relative
intensity) 282 (MH+, 100) 250 (M - CH3O, 55). HRMS Calcd for C17H15NO3 281.1052, found 281.1074.
Anal. Calcd for C17H15NO3: C, 72.58; H, 5.37; N, 4.98. Found: C, 72.36; H, 5.41; N, 4.95.
Lithium hexamethyldisilazide (1.0 M in THF, 44 mL, 0.44 mmol) was added slowly to a 0 °C solution of
the indole from above (124 mg, 0.44 mmol) in 4.5 mL of THF. The mixture was stirred for 30 min and
then BOC2O (100 mg, 0.46 mmol) was added in one portion. The reaction mixture was allowed to warm
slowly to rt while stirred for 6 h. The solution was washed with water and the aqueous phase was further
extracted with EtOAc. The combined organic layers were dried over Na2SO4, concentrated in vacuo, and
the residue was purified by flash column chromatography using 10% Et2O in hexanes as eluent. The
product (1b) was recovered as a colorless oil (136 mg, 81%) which solidified upon standing, mp 64 °C.
1
IR (thin film) 1743 (C=O), 1708 (C=O) cm-1. H-NMR (400 MHz, CDCl3) d: 8.16 (m, 2H); 7.36 (m, 2H);
7.08 (dt, J=11.6, 2.9 Hz, 2H); 6.79 (dt, J=11.6, 3.0 Hz, 2H); 3.76 (s, 3H); 2.30 (s, 3H); 1.40 (s, 9H). 13C-
NMR (100 MHz, CDCl3) d: 163.7, 156.3, 149.6, 148.5, 132.3, 131.9, 130.1, 125.0, 124.9, 124.3, 121.5,
115.0, 114.8, 99.6, 85.4, 51.5, 27.9, 20.9. MS m/z (relative intensity) 382 (MH+, 30) 326 (MH+ - iC4H8,
60) 294.1 (MH+ - iC4H8 - CH3OH, 5) 282.1 (MH+ - iC4H8 - CO2, 100) 250.0 (MH+ - iC4H8 - CH3OH - CO2,
47). HRMS Calcd for C22H23NO5 381.1576, found 381.1590. Anal. Calcd for C22H23NO5: C, 69.28; H,
6.08; N, 3.67. Found: C, 68.97; H, 6.30; N, 3.68.

General Procedure for Photochemistry.
In a typical procedure, the starting ether (1a) or (1b) was dissolved in the indicated solvent at the
indicated concentration and transferred into either a pyrex or quartz NMR-tube. The solution was
degassed either by three freeze-pump-thaw cycles or by bubbling Ar through for 30 min (both methods
led to equivalent results). The sample was placed into a Rayonet photochemical reactor equipped with
either 254-nm or 300-nm bulbs. The mixture was irradiated until no further conversion of the starting
1
material was detected by H-NMR monitoring. The reaction mixture was concentrated in vacuo and
purified by preparative TLC eluting with the indicated solvent system.
Methyl 2-(2-Hydroxy-5-methyl-phenyl)-1-methoxymethyl-1H-indole-3-carboxylate (4a).
Following the general procedure and using the indicated solvent/concentration/wavelength, 1a was
converted to 4a, 8a, and 9, which were separated by preparative TLC eluting with 10% Et2O in benzene.
Crystallization was induced by scratching the wall of the glass vessel containing the initially formed oil,
and then cooling at 4 oC overnight. Compound (4a) was isolated as transparent crystals, mp 217 °C. IR
(CCl4) 3551, 3258 (OH), 1709 (C=O), 1682 (C=O) cm-1. 1H-NMR (400 MHz, CD3CN) d: 8.15 (m, 1H);
7.61 (m, 1H), 7.32 (m, 2H); 7.19 (ddd, J=8.3, 2.2, 0.5 Hz, 1H); 7.08 (dd, J=2.2, 0.5 Hz, 1H); 6.87 (d,
J=8.3, 1H); 6.74 (br s, 1H); 5.39 (d, J=11.0 Hz, 1H); 5.19 (d, J=11.0 Hz, 1H); 3.71 (s, 3H); 3.05 (s, 3H);
2.29 (s, 3H). 13C-NMR (90 MHz, CD3CN) d: 166.2, 154.0, 144.3, 137.8, 133.4, 132.5, 129.9, 128.0,
124.2, 123.3, 122.6, 119.1, 117.0, 112.1, 108.0, 75.8, 56.5, 51.4, 20.5. MS m/z (relative intensity) 326
(MH+, 15%) 294 (M - CH3O, 100). HRMS Calcd for C19H19NO4 325.1314, found 325.1249.
Methyl 1-Methoxymethyl-1H-indole-3-carboxylate (8a).9
mp 58 - 60 °C (recrystallized from Et2O/hexane). IR (CHCl3) 1702 (C=O) cm-1. 1H-NMR (360 MHz,
CDCl3) d: 8.19 (ddd, J=4.4, 2.7, 0.7 Hz, 1H); 7.89 (s, 1H); 7.52 (ddd, J=4.5, 2.7, 0.7 Hz, 1H); 7.31 (m,
2H); 5.47 (s, 2H), 3.93 (s, 3H); 3.26 (s, 3H). 13C-NMR (75 MHz, CDCl3) d: 165.5, 136.7, 134.5, 127.1,
123.6, 122.7, 122.0, 110.8, 108.5, 76.8, 56.4, 51.31. MS m/z (relative intensity) 220 (MH+, 100). HRMS
Calcd for C12H13NO3 219.0895, found 219.0911. Anal. Calcd for C12H13NO3: C, 65.74; H, 5.98; N, 6.39.
Found: C, 65.54; H, 6.00; N, 6.32.
Methyl 2-(2-Hydroxy-5-methyl-phenyl)-1-tert-butyloxycarbonyl-1-H-indole-3-carboxylate (4b).
Following the general procedure and using the indicated solvent/concentration/wavelength, 1b was
converted into 4b, 8b, and 9, which were separated by preparative TLC eluting with 10% Et2O in
hexanes. Compound (4b) was isolated as colorless oil. IR (thin film) 1739 (C=O), 1720 (C=O) cm-1. 1H-

NMR (300 MHz, CDCl3) d: 7.63 (d, J=7.6 Hz, 2H); 7.44 (dd, J=1.3, 0.6 Hz, 1H); 7.26 (dt, J=7.8, 1.4 Hz,
1H); 7.16 (br s, 1H); 7.04 (dt, J=7.6, 1.0 Hz, 1H); 6.98 (ddd, J=8.2, 2.0, 0.7 Hz, 1H); 6.76 (d, J=8.1 Hz,
1H); 3.85 (s, 3H); 2.32 (s, 3H); 1.66 (s, 9H). 13C-NMR (90 MHz, CDCl3) d: 169.9, 156.3, 152.4, 141.1,
131.2, 130.5, 129.6, 129.6, 126.6, 124.8, 124.6, 123.6, 115.5, 110.2, 110.0, 98.7, 82.3, 53.5, 28.6, 21.1.
MS m/z (relative intensity) 382 (MH+, 1) 326 (MH+ - iC4H8, 15) 294 (MH+ - iC4H8 - CH3OH, 100) 282
(MH+ - iC4H8 - CO2, 90) 250 (MH+ - iC4H8 - CH3OH - CO2, 95).
Methyl 1-tert-Butyloxycarbonyl-1-H-indole-3-carboxylate (8b). 9
White crystals, mp 117 - 120 °C (recrystallized from hexane). IR (thin film) 1746 (C=O), 1716 (C=O)
cm-1. 1H-NMR (300 MHz, CDCl3) d: 8.27 (s, 1H); 8.17 (m, 2H); 7.36 (m, 2H); 3.94 (s, 3H); 1.69 (s, 9H).
13C-NMR (75 MHz, CDCl3) d: 164.83, 149.11, 135.72, 132.24, 127.67, 125.29, 124.11, 121.82, 115.34,
112.36, 85.21, 51.62, 28.26. MS m/z (relative intensity) 276 (MH+, 10) 220 (MH+ - iC4H8, 100) 176 (MH+
- iC4H8 - CO2, 35) 144 (MH+ - iC4H8 - CO2- CH3OH, 15). Anal. Calcd for C15H17NO4: C, 65.44; H, 6.22;
N, 5.09. Found: C, 65.56; H, 6.32; N, 5.10.
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