Intramolecular cyclization reactions of unsaturated amino Fischer chromium carbenes forming indoles and quinolines

Article abstract of DOI:10.1016/j.tet.2003.09.028

A thermally induced intramolecular annulation reaction of N-(2-alkenylphenyl)amino substituted Fischer chromium carbenes has been extensively examined. The carbene complexes were prepared in moderate to good yields by reaction of 2-aminostyrenes with intermediately formed acyloxy substituted carbenes. Upon heating, the thermally labile carbenes decomposed producing indoles and quinolines as the major products. The product distribution was found to be highly dependent on the substitution pattern and electronic properties of the starting material, and on the solvent used.

Full text of DOI:10.1016/j.tet.2003.09.028

Tetrahedron 59 (2003) 8775–8791
Intramolecular cyclization reactions of unsaturated amino
Fischer chromium carbenes forming indoles and quinolines
a
a
a
a
,
*
¨
¨
Bjorn C. G. Soderberg, James A. Shriver, Seth H. Cooper, Timothy L. Shrout,
E. Scott Helton,b Lucinda R. Austin,b Herman H. Odens,b Brian R. Hearn,b Paula C. Jones,b
Tiara N. Kouadio,b Tan H. Ngi,b Rachel Baswell,b H. John Caprara,b Mark D. Meritta
and Than T. Maib
aDepartment of Chemistry, West Virginia University, PO Box 6045, Morgantown, WV 26506-6045, USA
bDepartment of Chemistry, University of South Alabama, Mobile, AL 36688, USA
Received 16 July 2003; revised 10 September 2003; accepted 10 September 2003
Abstract—A thermally induced intramolecular annulation reaction of N-(2-alkenylphenyl)amino substituted Fischer chromium carbenes has
been extensively examined. The carbene complexes were prepared in moderate to good yields by reaction of 2-aminostyrenes with
intermediately formed acyloxy substituted carbenes. Upon heating, the thermally labile carbenes decomposed producing indoles and
quinolines as the major products. The product distribution was found to be highly dependent on the substitution pattern and electronic
properties of the starting material, and on the solvent used.
q 2003 Published by Elsevier Ltd.
1. Introduction
addition, synthesis of bicyclo[5.3.0]decanones,30 and cyclo-
pentene derivatives,31–35 have also been reported.
A number of synthetically attractive annulation reactions of
Fischer carbene complexes have been developed over the
last two decades.1 Probably the most explored and utilized
reaction is the thermally promoted benzannulation of aryl or
a,b-unsaturated alkoxy Fischer chromium carbene com-
plexes with alkynes forming, primarily, quinone/hydro-
quinone derivatives.2,3 In contrast, related amino Fischer
carbenes usually produce cyclopentanones, and cyclo-
hexadienones upon reaction with alkynes.4,5 Other
alkyne–carbene annulations have been developed affording
a variety of products such as, b-lactones,6 lactams and
pyrroles,7–9 2-azabicyclo[3.1.0]hexanes,10 bicyclo[3.2.1]-
hexanes,11 bicyclo[3.1.1]heptanones,12 bicyclo[5.3.0]decanes,13
bicylo[4.1.0]heptanes,14 spiro[4.4]nonatrienes,15 [4.3.1]pro-
pellanes,16 cyclopentenones and cyclopentadienes,11,13,17–19
cyclooctatrienes,20 steroid ring-system,21 and indolines.22
Annulation reactions of Fischer carbenes with carbon–
carbon or carbon–nitrogen double bonds have also been
extensively studied. Perhaps the two most synthetically
useful reactions are photochemically23,24 driven [2þ2]-
cycloadditions forming cyclobutanones25,26 and b-lac-
tams27 and thermally promoted cyclopropanations.28,29 In
We have communicated a novel thermal annulation reaction
of N-(2-alkenylphenyl)amino substituted Fischer chromium
carbenes affording indole or quinoline derivatives.36 For
example, thermolysis of carbene complex 1, in toluene at
1208C for 20 h, gave indole 2 in 60% isolated yield (Scheme
1). In sharp contrast, thermal decomposition of complex 3
produced a mixture of quinoline 4 and tetrahydroquinoline
5, in 34 and 22% yields, respectively (Scheme 2).
Scheme 1.
Keywords: Fischer carbenes; indoles; quinolines.
*
Corresponding author. Address: Department of Chemistry, West
Virginia University, PO Box 6045, Morgantown, WV 26506-6045,
USA. Tel.: þ1-3042933435; fax: þ1-3042934904;
Scheme 2.
e-mail: bjorn.soderberg@mail.wvu.edu
0040–4020/$ - see front matter q 2003 Published by Elsevier Ltd.
doi:10.1016/j.tet.2003.09.028

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8776
Table 1. Synthesis of amino carbene complexes
R¼Me
18 (74%)
19 (88%)
1 (65%)
20 (87%)
21 (62%)
22 (82%)
23 (69%)
24 (43%)
25 (70%)a
26 (75%)
3 (61%)
27 (88%)
28 (89%)
29 (76%)
30b
R¼Ph
R¼Me, Y¼3-CO2Me
R¼Me, Y¼4-CO2Me
R¼Me, Y¼5-CO2Me
R¼Me, Y¼6-CO2Me
R¼Me, Y¼4-OMe
R¼Me, Y¼5-OMe
R¼R3¼Me
Scheme 3.
¨
Dotz and Woodgate have independently reported intramo-
lecular cyclization reactions of related alkyne functionalized
N-phenylamino Fischer carbenes forming, for example,
9H-carbazoles or 11H-benzo[a]carbazoles depending on the
starting material.37–40 For example, thermal decomposition
of complex 6 gave the 11H-benzo[a]carbazole 7 in 65%
yield (Scheme 3).
R¼R1¼R3¼Me
R2¼R¼Me
R2¼Me R¼Ph
R2¼Me R¼Cyclopropyl
R2¼Me R¼2-Furyl
R2¼H R¼OCH2OC6H3
Considering the difference in products formed from
decomposition of complexes 1 and 3, a more in-depth
study of this annulation reaction was warranted. Herein is
presented an account of the scope and limitation of the
thermal annulation reaction of N-(2-alkenylphenyl)amino
substituted Fischer chromium carbenes. The electronic and
steric properties of the carbenes and, to some extent, the
solvent have been varied to evaluate their influence on the
ratio and yield of products. In addition, mechanistic
rationales for the formation of the different products are
proposed.
a
A 1:1 mixture of double bond isomers.
Not isolated.
b
able, prepared according to literature procedures, or
synthesized as described herein. Thus, four 2-aminostyrenes
(8–11), having an electron withdrawing methyl ester
substituent, were readily prepared by reduction of the
corresponding 2-nitrostyrenes using Fe/HCl in methanol
(Scheme 4).
In order to compare and contrast the influence of the
electronic properties of the aromatic ring, methoxy-
substituted 2-aminostyrenes were also prepared. Reaction
of two isomeric methoxy-substituted 2-bromobenzene-
amines with, in sequence, ethyl chloroformate, tri-n-butyl
vinyltin in the presence of a palladium(0) catalyst,41 and
potassium hydroxide gave aminostyrenes 14 and 17
(Scheme 5). A more direct two-step route to these
compounds consisting of a Stille cross-coupling of meth-
oxy-substituted 2-bromo-1-nitrobenzenes with tri-n-butyl
vinyltin followed by reduction of the nitro group to an
amine was also pursued. Although the palladium catalyzed
coupling reaction gave the corresponding nitrostyrenes
in good to excellent yield,42 the subsequent reduction
employing, for example, Fe/HCl/MeOH, Fe/AcOH/EtOH,
or SnCl2/EtOH, gave either a very low yield or a complex
mixture of products.
2. Results and discussion
In order to examine the scope and limitation of the thermal
decomposition of N-(2-alkenylphenyl)amino substituted
Fischer chromium carbenes, a number of novel substituted
complexes, in addition to 1 and 3, were synthesized from
2-aminostyrenes according to standard procedures. The
2-aminostyrenes, in turn, were either commercially avail-
With a number of 2-aminostyrenes in hand, the desired
carbenes were prepared by acylation of the corresponding
tetramethylammonium pentacarbonyl[1-oxyalkyl]chro-
mate(1-) salt, in dichloromethane at 2408C, with acetyl
Scheme 4.
Scheme 5.

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B. C. G. Soderberg et al. / Tetrahedron 59 (2003) 8775–8791
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Table 2. Thermal decomposition of Fischer chromium aminocarbene complexes
Entry
Carbene
Products (yield)
1
2
18a
18b
18a (5%)
18b (15%)
18b (49%)
18c (21%)
18c (8%)
18d (12%)
3
4
5
19a
19b
19c
19b (17%)
19c (39%)
19c (50%)
19c (36%)
19d (17%)
19d (23%)d
19d (16%)
6
7
8
1a
1b
2 (60%)
2 (34%)
1d (63%)
1c,e
9
10
20b
20c
20b (95%)
20a (70%)
20c (18%)
11
12
21b,f
21c.g
21a (4%)
21a (7%)
21b (7%)
21b (38%)
21d (70%)
13
14
22b,h
22c,i
22a (7%)
22a (65%)
22b (24%)
22d (18%)
22d (4%)
15
16
23b
23c
23b (20%)
23b (20%)
23c (42%)
23c (57%)
a
In toluene at 908C.
In acetonitrile at 908C.
Contaminated by a small amount (,5%) of 3-methyl-2-phenyl-indole.
In hexanes at 908C.
Also, 61% of 8.
Also, 11% of 10.
Also, 33% of 10.
Also, 38% of 11.
Also, 18% of 11.
b
d
c
e
f
g
h
i

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8778
Table 3. Thermal decomposition of Fischer chromium aminocarbene complexes
Entry
Carbene
Products (yield)
1
2
3
25a
25b
25c
25a (62%)
25a (25%)
25a (47%)
25b (60%)
4
5
26b,d
26c,e
26a (8%)
6
7
3a
4 (34%)
4 (22%)
5 (22%)f
3b,g
8
9
10
11
27a
27b
27e
27c (26%)
27c (61%)
27c (55%)
27c (20%)
27d (9%)
27c
27b,h,i
12
13
28b
28c
28e (23%)
28e (25%)
28c (14%)
28c (31%)
14
15
29b
29c
29c
29c
a
In toluene at 908C.
In acetonitrile at 908C.
In hexanes at 908C.
Only 31 (13%).
b
c
d
e
f
Also, 44% of 2-(2-methylpropenyl)benzenamine.
Isomer ratio¼4.4:1.
g
h
i
Also, 41% of 2-(2-propenyl)benzenamine.
In acetonitrile at 908C under 3 atm of CO.
Also, 22% of imine 32.
1
chloride or bromide. The in situ formed acyloxy-substituted
complexes were subsequently treated, at 2408C, with the
appropriate 2-aminostyrene to afford carbenes 1, 3, and
18–30 in 43–89% yield after column chromatography
(Table 1). The isolated amino carbenes were found to be
thermally unstable, even as neat compounds, and a
substantial amount of decomposition was observed after a
few hours at ambient temperature. In most cases, H NMR
of the carbenes showed broad unresolved peaks due to rapid
partial decomposition in solution forming interfering
chromium species.
As expected, based on our initial experiments, thermal
decomposition of the isolated Fischer chromium carbenes

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8779
produced a variety of substituted indoles and quinolines.
The results of these reactions have been summarized in
Tables 2 and 3. In our preliminary communication, toluene
was used as the solvent for the thermolysis reaction
producing compounds having either an indole or a quinoline
type structure.36 However, careful examination of the crude
reaction mixture obtained from reaction of complex 18,
unsubstituted on both the aromatic ring and the pendant
alkene, revealed a more complex product mixture. It was
found that thermolysis of 18, in toluene at 908C, produced
2-methylindole (18a) and 2,3-dimethylindole (18b) in
addition to the previously reported products 2-methylquino-
line (18c), and 2-methyl-1,2,3,4-tetrahydroquinoline (18d)
(entry 1). Similar treatment of the phenyl-substituted
complex 19 also produced a mixture of products among
them, 3-methyl-2-phenylindole (19b) (entry 3). Formation
of 18b and 19b is noteworthy in that 2,3-disubstituted
indoles were previously not observed from reactions of
Fischer amino-carbene complexes. The products 18a–d
were partially separated by chromatography on silica gel
Thermolysis of complexes 1 and 20–23 produced all of the
products discussed above, 2-methyl-indoles, 2,3-dimethyl-
indoles, 2-methylquinolines, and 2-methyl-1,2,3,4-tetra-
hydroquinolines, in varying amounts and product ratios. It
is apparent from these results that electronic factors play an
important role in the thermal reaction of the amino carbenes.
Unfortunately, no clear trends can be discerned from the
results obtained. The product ratio and type of annulation
product for a given carbene is, as far as we can tell,
unpredictable; however, in some cases selective or exclu-
sive formation of one product was observed. For example,
reactions of carbenes 1 and 22 in hexanes or toluene
afforded a 2-substituted indole; reaction of carbene 20
in acetonitrile gave a 2,3-disubstituted indole, and reac-
tion of complexes
tetrahydroquinoline.
1 in acetonitrile produced a
One major side product was isolated from the thermally
induced annulation reactions. 2-Aminostyrenes correspond-
ing to the immediate precursor of the carbene examined
were obtained in up to 80% yield. In the case of the
5-methoxy-substituted complex 24, 2-ethenyl-5-methoxy-
benzenamine (17) was the only product isolated (not
included in Table 2). No trace of annulation product was
1
and identified by comparison with literature H and 13C
NMR data. In all other cases, unless otherwise stated, the
yields reported in Tables 2 and 3 are for pure isolated
compounds.
1
observed by H NMR of the crude reaction mixture.
Toluene proved to be somewhat cumbersome to use as a
solvent due to its relatively high boiling point, making it
hard to remove from the crude reaction mixtures. In
addition, formation of chromium tricarbonyl toluene com-
plex interfered with the purification of the products in a few
cases. Two additional solvents were examined in order to
evaluate the effect of solvent on the yield and selectivity
for a given product, and mainly to simplify the workup
procedure. Upon thermolysis of 18 in acetonitrile, only
indole 18b and quinoline 18c were isolated, the former in a
substantially higher yield compared to the reaction per-
formed in toluene (entries 1 and 2). Pronounced solvent
effects are not unusual in Fischer carbene chemistry and
have previously been observed, for example, in a number of
benzannulation reactions.3 In contrast to the results obtained
using complex 18, only quinolines were isolated from
reaction of 19 both in acetonitrile and hexanes (entries 4 and
5). Comparable yields of quinolines were obtained in all
three solvents.
The influence of a methyl substituent(s) on the alkene
moiety of the carbene was examined next (Table 3).
Complex 25 with one methyl group in the b-position of
the alkene gave exclusively indoles 25a–b in all three
solvents examined (entries 1 and 3). In the case of the
b,b-dimethyl substituted carbene 26, a sluggish reaction
took place in both acetonitrile and hexanes, and only a
minor amount of indole 26a was isolated in the latter case
(entries 4 and 5). Interestingly, reaction of 26 in acetonitrile
gave an amide 31, a product previously not observed
(Fig. 1).
In contrast to the b-substituted complexes, the a-methyl
substituted complexes 3 and 27–29 yielded only substituted
quinolines after purification (entries 6 and 7). For the phenyl
and cyclopropyl substituted carbenes 27 and 28 (entries 8,
and 12–13), 3-hydroxy quinolines (27e–28e) were isolated.
The annulation reaction was significantly inhibited in the
presence of carbon monoxide (entry 11). Thus, thermolysis
of complex 27 under 3 atm of CO gave a 20% yield of 27c, a
significant decrease from 61% in the absence of CO. In
addition to the expected product, the imine 32 was isolated
in 22% yield (Fig. 1).
Considering the relatively clean formation of quinolines
from the phenyl-substituted carbene 19 in hexanes and
acetonitrile having no substituent of the alkene, we
Figure 1.
Scheme 6.

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B. C. G. Soderberg et al. / Tetrahedron 59 (2003) 8775–8791
8780
Scheme 7.
Scheme 8.
envisioned a short synthesis of the quinoline alkaloid
dubamine from carbene 30. However, complex 30 proved to
be by far the most thermally labile complex examined.
Extensive decomposition was observed upon purification;
1H NMR of the product revealed only broad unresolved
peaks. Thermal reaction of crude 30 in acetonitrile gave the
expected product dubamine (30c) albeit in a low isolated
yield (Scheme 6). The major product was identified as
piperonal obtained in 51% yield.
The amide was most likely formed by air-oxidation of the
chromium carbon double bond of the thermally and
oxidatively labile complex 34.
3. Mechanistic considerations
Plausible mechanistic rationales for the formation of the
array of products obtained from thermal decomposition of
the carbenes are depicted in Schemes 8–12. Loss of one of
the chromium-bound carbon monoxide ligands from the
carbene complex enables the pendant double bond to
coordinate to the metal followed by formation of a
metallacyclobutane. Two possible intermediates can be
obtained from this intramolecular [2þ2]cycloaddition, an
indole or a quinoline fused metallacyclobutane, 36 and 37,
As the final carbene examined, the N-methyl substituted
complex 33 was prepared in 89% yield by deprotonation of
1 with sodium hydride followed by alkylation with
iodomethane (Scheme 7). Thermolysis of 33, under similar
reaction conditions as described above, gave a mixture of
indole 34 and amide 35 in 21 and 30% yield, respectively.
Scheme 9.

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B. C. G. Soderberg et al. / Tetrahedron 59 (2003) 8775–8791
8781
Scheme 10.
respectively (Scheme 8). A related [2þ2]cycloaddition has
been proposed for a manganese carbene intermediate.43
Moreover, similar fused [3.2.0] and bridged [3.1.1] ring
systems have been isolated in a number of cases from related
intramolecular [2þ2]cycloadditions between ketenes and
alkenes.44,45 In the case of complex 36, direct metathesis
wouldafforda2-substitutedindole38havinglosttheb-carbon
of the original alkene. The highly unstable and very reactive
pentacarbonyl(alkylidene)chromium complex 39, the second
‘half’ of the metathesis reaction, has not been isolated and is
tentatively proposed as a product.13,46,47 However, the amide
31, isolated from thermolysis of carbene 26 (entry 4, Table 3),
can be envisioned to be formed via nucleophilic addition of
aniline 40 to ketene 41.23,24 Ketene 41, in turn, is probably
derived from dimethyl carbene 39 formed by metathesis of
metallacyclobutane 42 (Scheme 9). The origin of the aniline
will be discussed below.
For obvious reasons, a metathesis mechanism cannot be
in operation for the formation of 2,3-dialkylindoles (i.e.
18b–23b and 25b) wherein the b-carbon of the starting
material remains in the product after the reaction. A couple
of different mechanistic possibilities can be invoked.
b-Hydride elimination either from the alkyl group attached
to the former carbene carbon and/or, in the case of complex
36 (R1¼CH3), from the terminal methyl group of the
propenyl substituent would give complex 43 and 44,
respectively (Scheme 10). Reductive elimination at this
point would afford 45 and 46 that upon isomerization
produces the observed 2,3-dialkyl substituted indoles.
In addition to the latter mechanism, an ionic mechanism is
also possible for the formation of indoles via the
zwitterionic complex 47. Proton shift affording 48 and/or
49 followed by reductive elimination (for 48) or reductive
Scheme 11.
Scheme 12.

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B. C. G. Soderberg et al. / Tetrahedron 59 (2003) 8775–8791
8782
1
elimination–isomerization (for 49) completes the mecha-
nism (Scheme 11).
parentheses. For H NMR, the assignments are: q¼quartet,
t¼triplet, d¼doublet, s¼singlet, br¼broad, and m¼
multiplet. Multiplet refers to unresolved resonances from
1
The quinoline-fused metallacyclobutane 37 can be envi-
sioned to undergo similar mechanistic steps, b-elimination
or ionic cleavage, as outlined for the formation of indoles in
Schemes 10 and 11.48 It should be noted that a related
mechanism, including a twisted mode of cycloaddition
followed by b-elimination, has been suggested for the
formation of 3,4-dihydropyranes via intramolecular reaction
of Fischer carbenes having a tethered alkene.5 The
intermediates from the eliminations are either compounds
isomeric to the quinoline product and/or dihydroquinolines.
The latter readily undergo disproportionation reactions to
form quinolines and tetrahydroquinolines. A similar
reduction of double bonds in the presence of chromium
complexes has been reported.49 The isolation of 2-phenyl
quinoline (19c) and 2-phenyl-1,2,3,4-tetrahydroquinoline
(19c) from thermolysis of 19, substrates lacking
b-hydrogens available for elimination, supports the ionic
mechanism. We are presently unable to give a reasonable
rationale for the formation of the hydroxyquinolines 27e
and 28e.
one or more protons having intractable H–1H coupling
constants.
Tetrahydrofuran (THF), 1,4-dioxane, toluene, and diethyl
ether were distilled from sodium benzophenone ketyl prior
to use. Pyridine, hexanes, acetonitrile, and ethyl acetate
were distilled from calcium hydride. Chemicals prepared
according to literature procedures have been footnoted first
time used; all other reagents were obtained from commer-
cial sources and used as received. All reactions were
performed in oven-dried glassware. The theromolysis
experiments were performed in ACE-glass pressure tubes
capped with an ACE-glass teflon plug. Solvents were
removed on a rotary evaporator at water aspirator pressure
unless otherwise stated. The following ‘air-oxidation’
procedure was employed in order to remove chromium
residues from the crude products. A flask containing a
solution (suspension) of the crude product in hexanes–
EtOAc (1:1, 30–75 mL) was irradiated (250 W lamp), open
to the air, until a clear colorless solution was formed. A
large amount of a brown-green precipitate was usually
obtained which was removed by filtration (Celite). Elemen-
tal analyses were performed by Atlantic Microlab Inc.,
Norcross, GA. High Resolution Mass Spectra (HRMS) were
performed at University of California Riverside Mass
Spectrometry Center.
A fairly straightforward mechanistic explanation for the
formation of the aminostyrenes is shown in Scheme 12.
Thermally induced b-hydride elimination would give an
imine, which subsequently undergoes hydrolysis to the
amine. Related eliminations forming both imines and the
corresponding amine have previously been observed.50
Imine 32 was isolated in low yield from thermolysis of
complex 27 under 3 atm of carbon monoxide. The
b-hydride elimination was especially pronounced in the
case of the substituted carbene 30. This carbene could not be
isolated, and the corresponding aldehyde, piperonal
(Scheme 6), was obtained in quantitative yield upon
standing for a few hours at ambient temperature.
4.1.1. Methyl 3-amino-2-ethenylbenzoate (8). To a
solution of methyl 2-ethenyl-3-nitrobenzoate42 (13.05 g,
63.0 mmol) in MeOH (260 mL) and HCl (37%, 10.4 mL)
was added Fe (powder, 14.07 g, 252 mmol). The resulting
slurry was heated (1008C, oil-bath temp) for 27 h. After
cooling to ambient temperature, the grey slurry was diluted
with water (400 mL), and the mixture was extracted with
EtOAc (3£150 mL). The aqueous phase was made basic
(pH ca. 9) with NH4OH (saturated, aqueous) and extracted
with EtOAc (3£150 mL). The combined organic phases
were dried (MgSO4), filtered, and the solvents were
removed. The crude product was purified by chromatog-
raphy (hexanes–EtOAc, 4:1) to give 8 (8.62 g, 48.6 mmol,
77%) as faint yellow oil. 1H NMR d 7.17 (dd, J¼7.7, 1.0 Hz,
1H), 7.03 (t, J¼7.9 Hz, 1H), 6.89 (dd, J¼18.1, 11.6 Hz, 1H),
6.77 (dd, J¼7.9, 1.2 Hz, 1H), 5.49 (dd, J¼11.6, 2.0 Hz, 1H),
5.37 (dd, J¼18.0, 1.7 Hz, 1H), 4.05 (br s, 2H), 3.78 (s, 3H);
13C NMR d 168.3 (þ), 144.3 (þ), 133.3 (2), 130.3 (þ),
127.2 (2), 123.6 (þ), 119.1 (2), 118.5 (þ), 118.4 (2), 51.5
In conclusion, thermal decomposition of N-(2-alkenyl-
phenyl)amino substituted Fischer chromium carbenes
affords indoles and/or quinolines. The yield and ratio of
products are highly dependant on the solvent used and
electronic and steric factors. The major competing side
reaction is formation of 2-aminostyrenes, compounds
derived from b-hydride elimination-hydrolysis of the
starting Fischer carbenes.
4. Experimental
(2); IR (neat), 3470, 3374, 1716, 1613, 1310, 1266 cm21
.
Anal. calcd for C10H11NO2: C, 67.78; H, 6.26. Found: C,
67.68; H, 6.34.
4.1. General procedures
All NMR spectra were determined in CDCl3 at 270 MHz
(1H NMR) and 67.5 MHz (13C NMR) unless otherwise
stated. The chemical shifts are expressed in d values relative
4.1.2. Methyl 4-amino-3-ethenylbenzoate (9). Methyl
3-ethenyl-4-nitrobenzoate42,51 (3.14 g, 15.17 mmol) was
reacted with Fe (2.43 g, 43.46 mmol) in MeOH (61 mL)
in the presence of HCl (37%, 2.5 mL), as described above
(49 h). Extraction and chromatography (hexanes–EtOAc,
4:1) gave, 9 (1.65 g, 9.44 mmol, 62%) as faint yellow
crystals. Mp 92–938C. 1H NMR d 7.96 (d, J¼2.0 Hz, 1H),
7.74 (dd, J¼8.3, 2.0 Hz, 1H), 6.67 (dd, J¼17.4, 11.0 Hz,
1H), 6.61 (d, J¼8.3 Hz, 1H), 5.66 (dd, J¼17.4, 1.4 Hz, 1H),
5.32 (dd, J¼11.1, 1.2 Hz, 1H), 4.29 (br s, 2H), 3.83 (s, 3H);
1
to Me4Si (0.0, H and 13C) or CDCl3 (77.0, 13C) internal
standards. 1H–1H coupling constants are reported as
calculated from spectra; thus, a slight difference between
Ja,b and Jb,a is usually obtained. Results of APT (attached
proton test)—13C NMR experiments are shown in paren-
theses, where relative to CDCl3, (2) denotes CH3 or CH and
(þ) denotes CH2 or C. Multiplicities observed in off-
resonance decoupled 13C NMR experiments are shown in

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8783
13C NMR d 167.1 (þ), 148.1 (þ), 131.6 (2), 130.3 (2),
129.3 (2), 122.6 (þ), 119.5 (þ), 116.7 (þ), 114.9 (2), 51.5
(2); IR (neat) 3460, 3358, 1674, 1257 cm21. Anal. calcd for
C10H11NO2: C, 67.78; H, 6.27. Found: C, 67.63; H, 6.29.
vinyl tri-n-butyltin (4.31 g, 13.60 mmol) in toluene
(100 mL) was added, under a positive flow of nitrogen,
bis(dibenzylideneacetone)palladium, (356 mg, 0.62 mmol)
and triphenylphosphine (647 mg, 2.47 mmol). The reaction
mixture was heated (1208C, oil bath temp, 23H), and
allowed to cool to ambient temperature followed by solvent
removal to give a black oil. The oil was dissolved in CH2Cl2
(100 mL), washed with NH4OH (3£150 mL, 10%, aq.), and
dried (MgSO4). Filtration and removal of solvent gave a
brown oil that was purified by chromatography (hexanes–
EtOAc, 8:2 followed by hexanes–EtOAc, 1:1) producing 13
(1.60 g, 7.24 mmol, 59%) as faint yellow crystals. Mp 748C.
1H NMR d 7.47 (br s, 1H), 6.95 (d, J¼2.7 Hz, 1H), 6.84–
6.74 (overlapping m, 2H), 6.56 (s, 1H), 5.62 (d, J¼17.9 Hz,
1H), 5.31 (d, J¼11.0 Hz, 1H), 4.17 (q, J¼7.1 Hz, 2H), 3.74
(s, 3H), 1.25 (t, J¼7.1 Hz, 3H); 13C NMR (22.5 MHz) d
156.8 (s), 154.6 (s), 132.5 (s), 132.0 (d), 127.5 (d), 125.6 (s),
116.5 (t), 113.7 (d), 110.8 (d), 60.9 (t), 55.1 (q), 14.3 (q); IR
(neat) 3425, 1728, 1518 cm21; GC-MS (EI) m/z 221 (Mþ)
148, 134, 133; HRMS (EI) calcd for C12H15NO3 (Mþ)
221.1052. Found: 221.1052.
4.1.3. Methyl 3-amino-4-ethenylbenzoate (10). Methyl
4-ethenyl-3-nitrobenzoate42,51 (6.37 g, 30.8 mmol) was
reacted with Fe (6.87 g, 123.1 mmol) in MeOH (125 mL)
in the presence of HCl (37%, 5.0 mL), as described above
(45 h). Extraction and chromatography (hexanes–EtOAc,
9:1) gave 10 (3.89 g, 22.0 mmol, 71%) as faint yellow
crystals. Mp 46–478C. 1H NMR d 7.38 (dd, J¼7.9, 1.5 Hz,
1H), 7.35 (br s, 1H), 7.29 (d, J¼8.2 Hz, 1H), 6.73 (dd, J¼
17.3, 11.1 Hz, 1H), 5.67 (dd, J¼17.3, 1.2 Hz, 1H), 5.35 (dd,
J¼11.1, 1.2 Hz, 1H), 3.93 (br s, 2H), 3.84 (s, 3H); 13C NMR
d 166.9 (þ), 143.6 (þ), 131.7 (2), 129.7 (þ), 127.9 (þ),
126.9 (2), 119.5 (2), 117.3 (þ), 116.8 (2), 51.8 (2); IR
(neat) 3434, 3364, 1688, 1243 cm21. Anal. calcd for
C10H11NO2: C, 67.78; H, 6.26. Found: C, 67.86; H, 6.30.
4.1.4. Methyl 2-amino-3-ethenylbenzoate (11). Methyl
3-ethenyl-2-nitrobenzoate42,51 (1.07 g, 5.17 mmol) was
reacted with Fe (823 mg, 14.82 mmol) in MeOH (21 mL)
in the presence of HCl (37%, 0.84 mL), as described above
(23.5 h). Extraction and chromatography (hexanes–EtOAc,
4:1) gave 11 (580 mg, 3.31 mmol, 64%) as faint yellow oil
followed by recovered starting material (269 mg,
1.30 mmol, 25%). 1H NMR d 7.81 (dd, J¼7.9, 1.5 Hz,
1H), 7.38 (dd, J¼7.4, 1.2 Hz, 1H), 6.74 (dd, J¼17.3,
10.9 Hz, 1H), 6.65 (t, J¼7.9 Hz, 1H), 6.00 (br s, 2H), 5.62
(dd, J¼17.3, 1.2 Hz, 1H), 5.36 (dd, J¼11.1, 1.2 Hz, 1H),
3.87 (s, 3H); 13C NMR (22.5 MHz) d 168.6 (þ), 147.8 (þ),
132.2 (2), 132.1 (2), 130.9 (2), 125.3 (þ), 117.1 (þ),
115.8 (2), 110.9 (þ), 51.5 (2); IR (neat) 3480, 3364, 1691,
1247 cm21. Anal. calcd for C10H11NO2: C, 67.78; H, 6.27.
Found: C, 67.69; H, 6.29.
4.1.7. 2-Ethenyl-4-methoxybenzenamine (14). A solution
of KOH (80%, 3.00 g, 42.8 mmol) in absolute ethanol
(30 mL) was added to a round-bottomed flask containing 13
(1.18 g, 5.40 mmol). The resulting solution was heated at
reflux (16 h). The reaction mixture was allowed to cool to
ambient temperature, water (40 mL) was added, and the
mixture was extracted with CH2Cl2 (3£40 mL). The
combined organic phase was dried (MgSO4), and filtered
followed by solvent removal on a rotary evaporator
affording dark red oil. The crude oil was purified by
chromatography (hexanes–EtOAc, 7:3) producing 14
1
(736 mg, 4.93 mmol, 91%) as faint red oil. H NMR d
6.8–6.5 (m, 3H), 5.60 (dd, J¼17.7, 1.5 Hz, 1H), 5.28 (dd,
J¼10.8, 1.5 Hz, 1H), 3.73 (s, 3H), 3.46 (br s, 2H); 13C NMR
(22.5 MHz) d 152.8 (s), 137.5 (s), 132.5 (d), 125.0 (s), 112.4
(d), 115.5 (t), 114.9 (d), 111.9 (d), 55.7 (q); IR (CH2Cl2)
3445, 3378, 2908, 2853, 1630, 1504, 1037 cm21. Anal.
calcd for C9H11NO: C, 72.45; H, 7.43. Found: C, 72.21; H,
7.43.
4.1.5. 2-Bromo-4-methoxyphenyl carbamic acid ethyl
ester (12). Ethyl chloroformate (2.26 mL, 23.60 mmol)
dissolved in THF (25 mL) was added dropwise to a solution
of 2-bromo-4-methoxybenzenamine,52 (4.35 g, 21.54 mmol)
and pyridine (3.46 mL, 42.87 mmol) in THF (50 mL). The
reaction mixture was stirred at ambient temperature (16 h)
producing faint pink solution containing a white precipitate.
The solvent was removed on a rotary evaporator; the oily
residue was dissolved in CH2Cl2 (50 mL) and washed
with aqueous HCl (10%, 3£50 mL) followed by water
(3£50 mL). The organic phase was dried (MgSO4), and
filtered, followed by solvent removal to give a colorless oil.
The crude material was purified by chromatography
(hexanes–EtOAc, 8:2) affording 12 (4.56 g, 16.64 mmol,
4.1.8. 2-Bromo-5-methoxyphenyl carbamic acid ethyl
ester (15). Ethyl chloroformate (3.06 mL, 32.0 mmol)
dissolved in THF (25 mL) was added drop vise to a solution
of 2-bromo-5-methoxybenzenamine,53 (6.85 g, 30.0 mmol)
and pyridine (5.09 mL, 63.0 mmol) in THF (100 mL). The
reaction mixture was stirred at ambient temperature (24 h).
The solvent was removed on a rotary evaporator giving an
oily residue that was dissolved in CH2Cl2 (50 mL) and
washed with aqueous HCl (10%, 3£50 mL) followed by
water (2£50 mL). The organic phase was dried (MgSO4),
and filtered followed by solvent removal to give faint yellow
oil. The crude material was purified by chromatography
(hexanes–EtOAc, 8:2) affording 15 (6.78 g, 24.8 mmol,
83%) as faint yellow oil. 1H NMR d 7.79 (s, 1H), 7.30–7.09
(m, 2H), 6.41 (d, J¼8.8 Hz, 1H), 4.17 (q, J¼6.9 Hz,
2H), 3.71 (s, 3H), 1.26 (t, J¼7.1 Hz, 3H); 13C NMR
(22.5 MHz) d 159.2 (s), 152.6 (s), 136.2 (s), 131.8 (d),
110.0 (d), 105.0 (d), 102.2 (s), 61.0 (t), 54.8 (q), 14.0 (q);
IR (neat) 3400, 2990, 1725, 1585, 1210 cm21. Anal. calcd
for C10H12BrNO3: C, 43.81; H, 4.41. Found: C, 43.82; H,
4.44.
1
78%) as white crystals. Mp 50–538C. H NMR d 7.89 (d,
J¼9.1 Hz, 1H), 7.04 (d, J¼2.9 Hz, 1H), 6.81 (dd, J¼8.9,
2.9 Hz, 1H), overlapping 6.8 (br s, 1H), 4.21 (q, J¼7.1 Hz,
2H), 3.72 (s, 3H), 1.29 (t, J¼7.1 Hz, 1H); 13C NMR d
155.8 (s), 153.5 (s), 129.0 (s), 122.2 (d), 117.3 (d), 113.8 (s),
113.7 (d), 61.3 (t), 55.5 (t), 14.2 (q); IR (neat) 3380,
2970, 1705, 1505, 1200, 1065, 1030 cm21. Anal. calcd
for C10H12BrNO3: C, 43.81; H, 4.41. Found: C, 43.56; H,
4.33.
4.1.6. 2-Ethenyl-4-methoxyphenyl carbamic acid ethyl
ester (13). To a solution of 12 (3.38 g, 12.44 mmol) and

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8784
1
4.1.9. 2-Ethenyl-5-methoxyphenyl carbamic acid ethyl
ester (16). To a solution of 15 (2.73 g, 9.97 mmol) and vinyl
n-tributyltin (3.80 g, 12.0 mmol) in toluene (150 mL) was
added, under a positive flow of nitrogen, triphenyl
phosphine (525 mg, 2.00 mmol) and bis(dibenzylidene-
acetone)palladium (288 mg, 0.50 mmol). The yellow reac-
tion mixture was put under a nitrogen atmosphere and
heated (oil-bath temperature 1308C, 20 h). The solvent was
removed on a rotary evaporator. The residue was redis-
solved in CH2Cl2 (50 mL), filtered through a Celite pad, and
the pad was washed with CH2Cl2 (50 mL). The organic
solution was washed with NH4OH (10% aq, 3£50 mL),
water (3£50 mL), and dried (MgSO4). Filtration and solvent
removal followed by chromatography using hexanes–
EtOAc (8:2) as eluent gave 16 (1.39 g, 6.28 mmol, 63%)
as faint yellow oil. The oil slowly formed faint yellow
a 3:1 ratio (1H NMR). Mp: softens at 458C then dec. H
NMR d 10.18 (br s, major, 1H), 9.99 (br s, minor, 1H), 7.66
(d, J¼7.2 Hz, 1H), 7.48–7.34 (m, 2H), 7.08 (d, J¼7.2 Hz,
1H), 6.66 (dd, J¼17.4, 10.9 Hz, 1H), 5.80 (d, J¼17.4 Hz,
1H), 5.47 (d, J¼10.9, 1H), 3.04 (s, minor, 3H), 2.51 (s, 3H);
13C NMR (APT for major isomer) d 289.9 (2), 287.4, 222.8
(2, trans –CO), 217.6 (2, cis –CO), 217.0, 139.2, 136.3
(2), 134.9, 133.6 (2), 130.8, 130.5 (þ), 129.9, 129.5
(þ), 128.9 (þ), 128.3, 126.8, 126.3 (þ), 118.9 (þ),
118.3, 46.3, 37.6 (þ); IR (neat) 2050, 1995 cm21. Anal.
calcd for C15H11CrNO5: C, 53.42; H, 3.29. Found: C, 53.60;
H, 3.32.
4.1.12. Pentacarbonyl(1-N-(2-(2-ethenyl)phenyl)amino-
1-phenylmethylidene)chromium (19). Reaction of tetra-
methylammonium pentacarbonyl(benzoyl)chromate(1-)55
(3.49 g, 9.41 mmol) in CH2Cl2 (200 mL) with acetyl
bromide (696 mL, 9.41 mmol) and 2-ethenyl benzenamine
(1.12 g, 9.41 mmol), as described above, gave after
chromatography (hexanes–EtOAc, 6:4), 19 (3.30 g,
8.27 mmol, 88%) as a orange crystals. Only one rotamer
was observed by 1H NMR. Mp 72–768C. 1H NMR d 10.53
(br s, 1H), 7.60–6.50 (m, 10H), 5.82 (d, J¼17.2 Hz, 1H),
5.60 (d, J¼11.3 Hz, 1H); 13C NMR d 290.4 (2), 223.3
(2, trans –CO), 217.0 (2, cis –CO), 149.8 (2), 137.3 (2),
132.7 (2), 130.8 (þ), 128.7 (þ), 128.5 (þ), 128.1 (þ),
127.8 (þ), 127.2 (þ), 127.1 (þ), 127.0 (þ), 126.5 (þ),
1
crystals upon storage at 2188C. Mp 46–488C. H NMR d
7.44–6.57 (m, 5H), 5.51 (d, J¼17.1 Hz, 1H), 5.24 (d,
J¼10.8 Hz, 1H), 4.19 (q, J¼7.1 Hz, 2H), 3.75 (s, 3H), 1.27
(t, J¼7.1 Hz, 3H); 13C NMR (22.5 MHz) d 159.6 (s), 153.6
(s), 135.6 (s), 131.3 (d), 127.5 (d), 121.5 (s), 115.6 (t), 110.5
(d), 106.3 (d), 61.1 (t), 55.0 (q), 14.3 (q); IR (neat) 3440,
3070, 3000, 1730, 1270, 1225, 1060, 900, 740 cm21. Anal.
calcd for C12H15NO3: C, 65.14; H, 6.83. Found: C, 64.87;
H, 6.75.
4.1.10. 2-Ethenyl-5-methoxybenzenamine (17).54 A solu-
tion of KOH (3.36 g, 47.9 mmol) in absolute ethanol
(30 mL) was added to a round-bottomed flask containing
16 (1.01 g, 4.56 mmol). The resulting solution was heated at
reflux (21H). Water (50 mL) was added, and the mixture
was extracted with CH2Cl2 (2£30 mL). The combined
organic phase was dried (MgSO4) and filtered followed by
solvent removal on a rotary evaporator affording dark red oil
(744 mg). The crude oil was purified by chromatography
(hexanes–EtOAc, 8:2) producing 17 (522 mg, 3.50 mmol,
120.6 (2), 119.4 (þ); IR (neat) 2058, 1976, 1908 cm21
.
4.1.13. Pentacarbonyl(1-N-(3-carbomethoxy-2-ethenyl-
phenyl)aminoethylidene)chromium (1). Reaction of tetra-
methylammonium pentacarbonyl(acetyl)chromate(1-) (1.43 g,
4.63 mmol) in CH2Cl2 (50 mL) with acetyl chloride
(345 mL, 4.00 mmol) and 8 (820 mg, 4.63 mmol), as
described above, gave after chromatography (hexanes–
CH2Cl2, 1:1 followed by hexanes–CH2Cl2, 3:7) 1 (1.19 g,
3.01 mmol, 65%) as a yellow crystals. Two rotamers were
1
77%) as faint red oil. H NMR d 7.18 (d, J¼8.8 Hz, 1H),
1
6.67 (dd, J¼17.2, 10.8 Hz, 1H), 6.31 (dd, J¼8.6, 2.5, 1H),
6.17 (d, J¼2.0 Hz, 1H), 5.48 (d, J¼17.4 Hz, 1H), 5.15 (d,
J¼10.3 Hz, 1H), 3.78 (br s, 2H), 3.69 (s, 3H); 13C NMR
(22.5 MHz) d 160.1 (s), 144.8 (s), 132.0 (d), 128.2 (d), 117.0
(s), 113.2 (t), 104.6 (d), 101.1 (d), 55.0 (q); IR (neat) 3440,
3350, 2990, 2940, 2820, 1600, 1490, 1435, 1205, 1165,
obtained in a 7:2 ratio (1H NMR). H NMR (300 MHz,
major rotamer): d 10.29 (br s, 1H), 7.88 (d, J¼6.9 Hz, 1H),
7.42 (t, J¼7.8 Hz, 1H), 7.25 (d, J¼7.2 Hz, 1H), 6.89 (dd,
J¼17.9, 11.6 Hz, 1H), 5.64 (d, J¼11.5 Hz, 1H), 5.29 (d, J¼
18.1 Hz, 1H), 3.90 (s, 3H), 2.60 (s, 3H). 1H NMR
(300 MHz, minor rotamer, partial spectra) d 10.05 (br s,
1H), 7.94 (d, J¼8.8 Hz, 1H), 7.59 (d, J¼7.4 Hz, 1H), 7.50
(t, J¼7.8 Hz, 1H), 5.87 (d, J¼10.8 Hz, 1H), 5.27 (d, J¼
17.9 Hz, 1H), 3.88 (s, 3H), 3.01 (s, 3H); 13C NMR (75 MHz)
d 289.5, 287.0, 223.0, 222.7, 217.5, 217.0, 167.3, 167.1,
136.8, 135.4, 132.1, 131.8, 131.1, 130.9, 130.6, 129.9,
128.1, 128.0, 122.2, 121.4, 52.5, 52.4, 46.4, 37.7; IR
1015, 900, 830 cm21
.
4.1.11. Pentacarbonyl(1-N-(2-ethenylphenyl)aminoethyl-
idene)chromium (18). Acetyl bromide (1.04 mL,
14.06 mmol) was added to a 2408C cold solution of
tetramethylammonium pentacarbonyl(acetyl)chromate(1-)55
(4.94 g, 14.06 mmol) in CH2Cl2 (350 mL) under an
atmosphere of nitrogen. Upon addition, the color immedi-
ately turned brown-red. The mixture was allowed to warm
slowly to 2308C over a 30 min period where after it was
cooled to 2408C, and 2-ethenyl benzenamine56 (1.70 g,
14.06 mmol), dissolved in CH2Cl2 (10 mL), was added via a
pipette under a positive flow of nitrogen. The reaction
mixture was allowed to stir at 2408C (30 min) then at
ambient temperature (30 min). The solvent was removed
from the resulting orange mixture using a high vacuum
pump producing brown-orange oil.57 The oil was purified by
chromatography (hexanes–CH2Cl2, 1:1) giving 18 (3.52 g,
10.45 mmol, 74%) as yellow crystals after solvent removal
using a high vacuum pump. Two rotamers were obtained in
(CH2Cl2) 2049, 1929, 1714 cm21
.
4.1.14. Pentacarbonyl(1-N-(4-carbomethoxy-2-ethenyl-
phenyl)aminoethylidene)chromium (20). Reaction of
tetramethylammonium pentacarbonyl(acetyl)chromate(1-)
(1.85 g, 6.00 mmol) in CH2Cl2 (160 mL) with acetyl
chloride (427 mL, 6.00 mmol) and 9 (1.06 g, 6.00 mmol),
as described above, gave after chromatography (hexanes–
EtOAc, 4:1 followed by hexanes–EtOAc, 1:1), 20 (2.06 g,
5.20 mmol, 87%) as yellow crystals. Two rotamers were
1
obtained in an 8:1 ratio (1H NMR). Mp 104–1058C. H
NMR d 10.42 (br s, 1H), 10.0 (br s, minor rotamer), 8.31 (s,
1H), 8.00 (d, J¼7.7 Hz, 1H), 7.16 (d, J¼7.9 Hz, 1H), 6.68
(dd, J¼17.0, 11.4 Hz, 1H), 5.93 (d, J¼17.3 Hz, 1H), 5.59 (d,

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B. C. G. Soderberg et al. / Tetrahedron 59 (2003) 8775–8791
8785
J¼11.1 Hz, 1H), 3.96 (s, 3H), 3.10 (s, minor rotamer), 2.56
(s, 3H); 13C NMR d 292.3 (þ), 222.6 (þ), 217.5 (þ), 165.8
(þ), 139.4 (þ), 134.1 (þ), 131.4, 129.8 (2), 129.7 (2),
128.4 (2), 126.8 (2), 120.4 (þ), 52.4 (2), 38.0 (2); IR
(neat) 3279, 2055, 1906, 1713 cm21. Anal. calcd for
C17H13CrNO7: C, 51.66; H, 3.32. Found: C, 51.71; H, 3.32.
134.8 (s), 130.7 (d), 129.6 (s), 127.4 (d), 118.9 (t), 114.4 (d),
111.3 (d), 55.5 (q), 37.5 (q); IR (neat) 3320, 2970, 2025,
1895 cm21
.
4.1.18. Pentacarbonyl(1-N-(5-methoxy-2-ethenylphenyl)-
aminoethylidene)chromium (24). Reaction of tetramethyl-
ammonium pentacarbonyl(acetyl)chromate(1-) (2.16 g,
7.00 mmol) in CH2Cl2 (180 mL) with acetyl chloride
(498 mL, 7.00 mmol) and 17 (1.04 g, 7.00 mmol), as
described above, gave after chromatography (hexanes–
CH2Cl2; 7:3 followed by hexanes–CH2Cl2; 1:1), 24 (1.10 g,
3.00 mmol, 43%) as yellow crystals. Two rotamers were
4.1.15. Pentacarbonyl(1-N-(5-carbomethoxy-2-ethenyl-
phenyl)aminoethylidene)chromium (21). Reaction of
tetramethylammonium pentacarbonyl(acetyl)chromate(1-)
(1.55 g, 5.01 mmol) in CH2Cl2 (130 mL) with acetyl
chloride (356 mL, 5.01 mmol) and 10 (886 mg,
5.00 mmol), as described above, gave after chromatography
(hexanes–CH2Cl2, 1:2) 21 (1.23 g, 3.10 mmol, 62%) as
yellow crystals. Two rotamers were obtained in a 4:3 ratio
1
obtained in a 7:2 ratio (1H NMR). Mp 86–878C. H NMR
(90 MHz) d 10.18 (br s, 1H), overlapping 10.01 (br s, 1H,
minor isomer), 7.56 (d, J¼9.1 Hz, 1H), 7.01–6.41 (m, 3H),
5.66 (d, J¼18.4 Hz, 1H), 5.34 (d, J¼11.8 Hz, 1H), 3.84 (s,
3H), 3.05 (s, 3H, minor isomer), 2.54 (s, 3H), 2.14 (s, 3H,
minor isomer); 13C NMR (22.5 MHz) d 290.2 (s), 287.5 (s,
minor), 222.7 (s), 217.6 (s), 217.2 (s, minor), 159.9 (s),
137.2 (s), 130.3 (d, minor), 130.0 (d), 127.8 (d), 126.1 (s),
116.7 (t), 116.2 (d, minor), 115.7 (d), 112.7 (d, minor),
111.2 (d), 55.7 (q), 46.4 (q, minor), 37.6 (q), 30.9 (q, minor);
1
(1H NMR). Mp 100–1208C (slow dec.) H NMR (major
rotamer) d 10.24 (br s, 1H), 8.07 (d, J¼7.4 Hz, 1H), 7.73 (s,
1H), 7.69 (d, J¼6.7 Hz, 1H), 6.70 (dd, J¼16.1, 11.4 Hz,
1
1H), 5.92 (m, 1H), 3.93 (s, 3H), 2.55 (s, 3H). H NMR
(minor rotamer, partial spectra) d 10.0 (br s, 1H), 8.38 (d,
J¼5.4 Hz, 1H), 7.86 (d, J¼8.4 Hz, 1H), 7.43 (s, 1H), 6.50
(dd, J¼17.3, 11.4 Hz, 1H), 5.58 (m, 1H), 1.70 (s, 3H); 13C
NMR (major rotamer) d 292.8 (þ), 217.5 (þ), 213.7 (þ),
163.7 (þ), 138.0 (þ), 136.3(þ), 130.0 (2), 129.8 (2), 127.6
(2), 126.9 (2), 121.4 (þ), 117.1 (þ), 52.6 (2), 37.9 (2);
13C NMR (minor rotamer) d 222.6 (þ), 217.4 (þ), 134.8
(þ), 132.4 (2), 130.7 (2), 130.5 (þ), 127.8 (2), 126.4 (2),
119.7 (þ), 52.4 (2), 21.4 (2); IR (neat) 2049, 1929,
IR (neat) 3326, 2054, 1904 cm21
.
4.1.19. Pentacarbonyl(1-N-(2-(1-propenyl)phenyl)amino-
ethylidene)chromium (25). Reaction of tetramethyl-
ammonium pentacarbonyl(acetyl)chromate(1-) (442 mg,
3.17 mmol) in CH2Cl2 (60 mL) with acetyl bromide
(234 mL, 3.17 mmol) and 2-(1-propenyl)benzenamine58,59
(980 mg, 3.17 mmol), as described above, gave after
chromatography (hexanes–CH2Cl2; 1:1) 25 (782 mg,
2.23 mmol, 70%) as yellow crystals. Four inseparable
1714 cm21
.
4.1.16. Pentacarbonyl(1-N-(6-carbomethoxy-2-ethenyl-
phenyl)aminoethylidene)chromium (22). Reaction of
tetramethylammonium pentacarbonyl(acetyl)chromate(1-)
(2.42 g, 7.84 mmol) in CH2Cl2 (245 mL) with acetyl
chloride (557 mL, 7.84 mmol) and 11 (1.39 g, 7.84 mmol),
as described above, gave after chromatography (hexanes–
EtOAc, 3:2 followed by hexanes–EtOAc, 1:1) 22 (2.34 g,
6.43 mmol, 82%) as a orange oil. Two rotamers were
obtained in a 3:1 ratio (1H NMR). 1H NMR (major rotamer)
d 10.58 (br s, 1H), 7.83 (d, J¼6.9 Hz, 1H), 7.38 (d, J¼
5.9 Hz, 1H), 6.65 (t, J¼6.9 Hz, 1H), 5.97 (m, 1H), 5.62 (d,
J¼17.3 Hz, 1H), 5.37 (d, J¼10.4 Hz, 1H), 3.86 (s, 3H), 2.42
(s, 3H). 1H NMR (minor rotamer, partial spectra) d 10.44 (br
s, 1H), 3.93 (s, 3H), 2.16 (s, 3H); 13C NMR (major rotamer)
d 289.7 (þ), 217.6 (þ), 211.4 (þ), 168.7 (þ), 147.8 (þ),
132.2 (2), 132.0 (2), 130.9 (2), 125.3 (þ), 117.2 (þ),
115.9 (2), 110.9 (þ), 51.5 (2), 37.5 (2); 13C NMR (minor
rotamer) d 289.5 (þ), 222.8 (þ), 213.4 (þ), 165.6 (þ),
148.9 (þ), 130.5 (2), 130.4 (2), 129.1 (2), 119.6 (þ),
115.5 (þ), 52.9 (2), 17.3 (2); IR (neat) 3494, 3364, 2054,
1
isomers–rotamers were obtained. Mp 41–438C. H NMR
(broad unresolved signals) d 10.16 (br s), 9.93 (br s), 7.57–
7.20 (m), 7.08 (d, J¼7.5 Hz), 7.03 (d, J¼7.7 Hz), 6.27 (m),
6.00 (m), 3.06 (s, minor), 3.01 (s, minor), 2.56 (s), 2.52 (s),
1.92–1.75 (m); 13C NMR d 288.8 (2), 287.9 (2), 222.9
(2), 217.7 (2), 217.7 (2), 136.8 (2), 135.8 (2), 133.9 (2),
133.4 (2), 131.3 (þ), 131.1 (þ), 130.7 (þ), 129.4 (þ),
128.8 (þ), 128.0 (þ), 127.9 (þ), 127.7 (þ), 126.8 (þ),
126.1 (þ), 125.9 (þ), 124.7 (þ), 124.3 (þ), 37.5 (þ), 37.3
(þ), 18.8 (þ), 14.4 (þ); IR (neat) 2040, 1920 cm21
.
4.1.20. Pentacarbonyl(1-N-(2-(2-methyl-1-propenyl)-
phenyl)aminoethylidene)chromium (26). Reaction of
tetramethylammonium pentacarbonyl(acetyl)chromate(1-)
(2.16 g, 7.00 mmol) in CH2Cl2 (180 mL) with acetyl
chloride (498 mL, 7.00 mmol) and 2-(2-methylpropenyl)-
benzeneamine60 (1.24 g, 7.00 mmol), as described above,
gave after chromatography (hexanes–CH2Cl2, 1:1) 26
(1.91 g, 5.23 mmol, 75%) as a red oil.61 Two rotamers
1916, 1724, 1694 cm21
.
1
were obtained in a 4:1 ratio (1H NMR). H NMR (broad
4.1.17. Pentacarbonyl(1-N-(4-methoxy-2-ethenylphenyl)-
aminoethylidene)chromium (23). Reaction of tetramethyl-
ammonium pentacarbonyl(acetyl)chromate(1-) (553 mg,
1.79 mmol) in CH2Cl2 (60 mL) with acetyl bromide
(132 mL, 1.79 mmol) and of 14 (267 mg, 1.79 mmol), as
described above, gave after chromatography (hexanes–
EtOAc; 1:1) 23 (456 mg, 1.24 mmol, 69%) as yellow
unresolved signal for the major isomer) d 10.17 (br s, 1H),
7.07 (m, 4H), 6.17 (s, 1H), 2.08 (s, 3H), 1.97 (s, 3H), 1.71 (s,
3H); 13C NMR (major isomer) d 286.5 (þ), 220.5 (þ), 211.4
(þ), 145.2 (þ), 140.8 (þ), 130.7 (2), 127.9 (2), 127.2 (þ),
123.9 (2), 118.9 (2), 118.3 (2), 25.7 (2), 19.2 (2), 14.1
(2); IR (CH2Cl2) 3355, 2054, 1922 cm21
.
1
crystals. Mp 33–358C. H NMR d 10.09 (br s, 1H), 7.24–
4.1.21. Pentacarbonyl(1-N-(2-(2-propenyl)phenyl)amino-
ethylidene)chromium (3). Reaction of tetramethyl-
ammonium pentacarbonyl(acetyl)chromium (1-) (1.236 g,
4.00 mmol) in CH2Cl2 (60 mL) with acetyl bromide
6.90 (m, 3H), 6.63 (dd, J¼17.6, 10.8 Hz, 1H), 5.77 (d, J¼
17.4 Hz, 1H), 5.47 (d, J¼11.9 Hz, 1H), 3.86 (s, 3H), 2.51 (s,
3H); 13C NMR d 290.0 (s), 222.8 (s), 217.7 (s), 159.9 (s),

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8786
(296 mL, 4.00 mmol) and of 2-(2-propenyl)benzenamine
(545 mL, 4.48 mmol), as described above, gave after
(þ), 144.3 (2), 142.1 (þ), 140.5 (þ), 138.8 (þ), 129.4 (2),
128.1 (2), 128.0 (2), 125.3 (2), 117.6 (þ), 113.9 (2), 23.7
(2); IR (neat) 3289, 1982, 1912 cm21
.
chromatography (hexanes–CH2Cl2; 1:1),
2.46 mmol, 61%) as a yellow oil. Two rotamers were
3
(863 mg,
1
obtained in a 5:1 ratio (1H NMR). H NMR d 10.24 (br s,
4.1.25. Tetramethylammonium pentacarbonyl(5-(1,3-
benzodioxol)carbonyl)chromate(1-). To a 2788C cold
solution of 5-bromo-1,3-benzodioxole (1.20 mL, 10.0 mmol)
in Et2O (15 mL) was added t-butyllithium (11.8 mL,
20.1 mmol, 1.7 M in hexanes) via a cannula. The solution
was stirred for 30 min at 2788C then 45 min at ambient
temperature. The solution was transferred via a cannula to a
08C cold slurry of Cr(CO)6 (2.20 g, 10.0 mmol) in Et2O
(25 mL). After being stirred for 30 min at 08C then at
ambient temperature for 30 min, the solvents were removed
from the brown reaction mixture. The resulting solid residue
was treated with a solution of tetramethylammonium
bromide (3.07 g, 20.0 mmol) in degassed, distilled water
(50 mL) for 20 min. The resulting yellow slurry was
extracted with CH2Cl2 (3£50 mL), dried (MgSO4), filtered
(Celite), and evaporated to dryness affording tetramethyl-
ammonium pentacarbonyl(1-(1,3-benzodioxol-5-yl)methyl-
idene)chromium (1-) (2.45 g, 5.87 mmol, 59%) as a yellow
1H), 7.37 (m, 3H), 7.10 (m, 1H), 5.36 (s, 1H), 4.98 (s, 1H),
2.93 (s, minor), 2.62 (s, 3H), 2.04 (s, 3H); 13C NMR d 287.5,
284.8 (minor), 222.9, 217.6, 216.5 (minor), 141.57, 139,
135.4, 129.5, 129.3, 128.1, 126.3, 118.0, 46.6 (minor), 37.4,
23.4; IR (neat) 2045, 1895 cm21
.
4.1.22. Pentacarbonyl(1-N-(2-ethenylphenyl)amino-1-
phenylmethylidene)chromium (27). Reaction of 2.97 g
(8.00 mmol) of tetramethylammonium pentacarbonyl-
(benzoyl)chromate(1-) in CH2Cl2 (120 mL) with 591 mL
(8.00 mmol) of acetyl bromide and 1.09 mL (8.00 mmol) of
2-(2-propenyl)benzenamine, as described above, gave after
chromatography (hexanes–CH2Cl2, 1:1) and solvent
removal on a high vacuum pump, 2.90 g (7.03 mmol,
88%) of 27 as orange crystals. Two rotamers were obtained
in a 4:1 ratio (1H NMR). Mp: 65–678C. 1H NMR d 10.73 (br
s, 1H), 9.97 (br s, 1H, minor), 7.60–6.81 (m, 8H), 6.48 (d,
J¼7.1 Hz, 1H), 5.59 (s, 1H), 5.36 (s, 1H, minor), 5.22 (s,
1H), 5.05 (s, 1H, minor), 2.19 (s, 3H), 2.14 (s, 3H, minor);
13C NMR d 286.8 (s), 286.3 (s, minor), 223.4 (s), 216.9 (s),
216.5 (s, minor), 155.6 (s), 150.0 (s), 141.7, 141.4, 140.5,
138.8, 137.6, 135.8, 129.9, 129.4, 128.6, 128.2, 127.7,
127.2, 125.2, 120.8, 118.7, 117.8, 24.0 (q); IR (neat) 2058,
1
solid. Mp 90–1058C (dec.) H NMR d 7.05 (d, J¼7.9 Hz,
1H), 6.85 (d, J¼7.9 Hz, 1H), 6.79 (s, 1H), 5.98 (s, 2H), 3.09
(br s, 12H); 13C NMR d 283.8 (þ), 227.6 (þ), 223.0 (þ),
149.2 (þ), 147.0 (þ), 146.5 (þ), 120.4 (2), 106.7 (2),
104.1 (2), 111.8 (þ), 54.8 (2); IR (neat) 2030, 1887,
1859 cm21
.
1979, 1928 cm21
.
4.1.26. Pentacarbonyl(1-N-methyl-N-(2-(2-propenyl)-
phenyl)amino-1-ethylidene)chromium (33). To a slurry
of 103 mg (2.57 mmol, 80%, washed with 5 mL of hexanes)
of sodium hydride in 10 mL of THF was added 848 mg
(2.15 mmol) of 1 dissolved in 6 mL of THF. After 15 min,
200 mL (3.22 mmol) of iodomethane was added by syringe.
The resulting mixture was stirred for 2.5 h followed by
solvent removal on a rotary evaporator at water aspirator
pressure to give an orange oil. The crude product was
purified by chromatography (hexanes then hexanes–
CH2Cl2, 1:1) to give, after solvent removal, 775 mg
(1.90 mmol, 89%) of 33 as yellow-orange oil. The oil
rapidly decomposes at room temperature, and it was
immediately used in the next step. Two rotamers were
4.1.23. Pentacarbonyl(1-N-(2-(2-propenyl)phenyl)amino-
1-cyclopropylmethylidene)chromium (28). Reaction of
tetramethylammonium pentacarbonyl(cyclopropylcarbonyl)-
chromate(1-)62 (1.344 g, 4.00 mmol) in CH2Cl2 (60 mL)
with acetyl bromide (300 mL, 4.06 mmol) and 2-(2-pro-
penyl)benzenamine (545 mL, 4.01 mmol), as described
above, gave after chromatography (hexanes–CH2Cl2, 1:1)
and solvent removal on a rotary evaporator, 28 (1.346 g,
3.57 mmol, 89%) as yellow-green oil. Two rotamers were
1
obtained in a 5:3 ratio (1H NMR). H NMR d 10.09 (br s,
major, 1H), 9.70 (br s, minor, 1H), 7.39 (br m, 4H), 5.36
(s, major, 1H), 5.30 (s, minor, 1H), 5.02 (s, major, 1H), 4.95
(s, minor, 1H), 3.05 (apparent quintet, J¼7.0 Hz, 1H), 2.05
(s, 3H), overlapping 2.0 (m, 1H), 1.5–0.9 (m, 4H); 13C
NMR d 285.3, 284.1, 223.5, 222.0, 217.9, 217.2, 142.0,
141.5, 140.2, 139.8, 138.5, 136.3, 129.4, 128.9, 127.0,
126.7, 117.9, 117.3, 36.7, 29.4, 23.9, 23.6, 14.0, 10.2; IR
1
obtained in a 1:1 ratio (1H NMR). H NMR (300 MHz) d
7.83 (d, J¼7.7 Hz), 7.53–7.42 (m, 1H), 7.16 (d, J¼7.8 Hz),
6.91–6.75 (m), 5.52 (d, J¼11.6 Hz), 5.41 (d, J¼17.8 Hz),
4.02 (s), 3.90 (s), 3.85 (s), 3.48 (s), 2.93 (s), 2.49 (s); 13C
NMR (75 MHz, partial) d 283.7, 280.9, 223.4, 217.6, 217.0,
167.5, 167.2, 150.1, 145.0, 134.4, 132.9, 131.5, 130.8,
130.6, 130.1, 130.0, 129.9, 128.9, 128.6, 128.2, 120.4,
120.3, 52.5, 52.4, 52.2, 45.4, 42.2, 40.8; IR (neat) 2053,
(neat) 2045, 1910 cm21
.
4.1.24. Pentacarbonyl(1-N-(2-(2-propenyl)phenyl)amino-
1-(2-furyl)methylidene)chromium (29). Reaction of
tetramethylammonium pentacarbonyl(2-furylcarbonyl)chro-
mate(1-)63 (3.62 g, 10.0 mmol) in CH2Cl2 (250 mL) with
acetyl chloride (711 mL, 10.0 mmol) and 2-(2-propenyl)-
benzenamine (1.37 mL, 10.0 mmol), as described above,
gave after chromatography (hexanes–CH2Cl2, 1:1) and
solvent removal on a rotary evaporator, 29 (2.66 mg,
7.55 mmol, 76%) as brown-red crystals. Two rotamers
1967, 1915, 1727 cm21
.
4.1.27. 2-Methylindole (18a),64 2,3-dimethylindole (18b),64
2-methylquinoline (18c),64 and 2-methyl-1,2,3,4-tetra-
hydroquinoline (18d).56,65 A solution of 18 (674 mg,
2.00 mmol) in toluene (20 mL) was heated at 1208C (oil-
bath temperature) for 19 h under a nitrogen atmosphere. The
resulting brown reaction mixture was cooled to ambient
temperature and filtered through a 0.5 cm Celite pad. The
pad was washed with toluene (20 mL). The solvent
was removed from the filtrate and the crude product was
purified by chromatography (hexanes–EtOAc, 9:1 then
1
were obtained in a 3:1 ratio (1H NMR). Mp 86–898C. H
NMR d 10.59 (br s, 1H), 9.80 (br s, minor, 1H), 7.70–6.66
(m, 7H), 5.26 (s, 1H), 5.02 (s, 1H), 2.22 (s, minor, 3H), 2.02
(s, 3H); 13C NMR d 258.4 (þ, minor), 250.9 (þ), 222.8
(þ, minor), 217.5 (þ), 213.4 (þ, minor), 211.3 (þ), 158.4

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8787
hexanes–EtOAc, 8:2) to give, in order of elution, 18d
(36 mg, 0.25 mmol, 12%) as faint yellow oil, a mixture of
18a (12 mg, 0.09 mmol, 5%) and 18b (44 mg, 0.30 mmol,
15%) as faint yellow crystals, and 18c (60 mg, 0.42 mmol,
21%) as faint yellow crystals. Spectral data for 18a–d were
in complete accordance with literature values. Additional
spectral data for 18d: 13C NMR (22.5 MHz) d 129.2, 126.7,
120.8, 118.9, 117.2, 114.1, 47.2, 30.0, 26.5, 22.5.
acetonitrile (5 mL) at 908C (oil-bath temperature) for 19 h,
as described above, gave after air oxidation (5 h) and
chromatography (hexanes–EtOAc, 9:1), 1d (72 mg, 0.36
1
mmol, 63%) as faint yellow oil. H NMR d 7.16 (d, J¼
6.9 Hz, 1H), 6.99 (t, J¼7.9 Hz, 1H), 6.60 (d, J¼7.9 Hz, 1H),
3.85 (s, 3H), 3.82 (br s, 1H), 3.39 (m, 1H), 3.16 (ddd, J¼
17.8, 5.2, 3.9 Hz, 1H), 2.98 (ddd, J¼17.8, 11.4, 5.8 Hz, 1H),
1.96 (m, 1H), 1.52 (m, 1H), 1.21 (d, J¼6.2 Hz, 3H); 13C
NMR d 168.5 (þ), 145.3 (þ), 130.3 (þ), 126.1 (2), 122.3
(þ), 119.1 (2), 117.8 (2), 51.7 (2), 46.5 (2), 29.9 (þ), 25.0
A solution of 18 (337 mg, 1.00 mmol) in acetonitrile
(10 mL) was heated at 908C (oil-bath temperature) for 2 h,
under an argon atmosphere, as described above to give
yellow-orange solution. Solvent evaporation and chroma-
tography (hexanes–EtOAc, 8:2) gave, in order of elution,
18b (71 mg, 0.49 mmol, 49%) as faint yellow crystals,
followed by a fraction containing 18c, partially complexed
to chromium. The latter fraction was redissolved in
hexanes–EtOAc (1:1), air-oxidized (6 h), filtered (Celite),
and evaporated in vacuo to give 18c (11 mg, 0.08 mmol,
8%) as faint yellow oil.
(þ), 22.4 (2); IR (neat) 3388, 1718, 1649, 1593, 1281 cm21
(EI) calcd for C12H15NO2 (Mþ) 205.1103. Found: 205.1103.
;
GC-MS (EI) m/z 205 (Mþ), 190 (100%), 158, 130; HRMS
4.1.31. Methyl 2-methylindole-4-carboxylate (2) and
methyl-3-amino-2-ethenylbenzoate (8). Thermolysis of 1
(395 mg, 1.00 mmol) in hexanes (10 mL) at 908C (oil-bath
temperature) for 46 h, as described above, gave after air-
oxidation (16 h), and chromatography (hexanes–EtOAc,
9:1 then hexanes–EtOAc, 7:3), 2 (64 mg, 0.34 mmol, 34%)
as faint yellow crystals followed by 8 (108 mg, 0.61 mmol,
61%) as faint yellow oil.
4.1.28. 3-Methyl-2-phenylindole (19b),66 2-phenylquino-
line (19c),64 and 2-phenyl-1,2,3,4-tetrahydroquinoline
(19d).67 Thermolysis of 19 (391 mg, 0.98 mmol) in toluene
(10 mL) at 1008C (oil-bath temperature) for 4 h, as
described above, gave after air oxidation (20 h), and
chromatography (hexanes–EtOAc, 9:1 then hexanes–
EtOAc, 7:3) 19b (35 mg, 0.17 mmol, 17%) as a colorless
oil followed by 19c (78 mg, 0.38 mmol, 39%) as faint
yellow crystals, and 19d (34 mg, 0.17 mmol, 17%) as faint
yellow oil. Additional spectral data for 19d: 13C NMR
(22.5 MHz) d 144.8, 129.3, 128.5, 127.4, 126.9, 126.5,
125.1, 122.3, 117.1, 113.9, 56.3, 31.0, 26.3.
4.1.32. Methyl 2,3-dimethylindole-5-carboxylate (20b).70
Thermolysis of 20 (285 mg, 0.72 mmol) in MeCN (7 mL) at
908C (oil-bath temperature) for 6 h gave after air-oxidation
(12H), and chromatography (hexanes–EtOAc, 49:1), 20b
(139 mg, 0.68 mmol, 95%) as white crystals.
4.1.33. Methyl 2-methylindole-5-carboxylate (20a)71 and
methyl 2-methylquinoline-6-carboxylate (20c).72 Ther-
molysis of 20 (395 mg, 1.00 mmol) in hexane (10 mL) at
908C (oil-bath temperature) for 6 h gave after air-oxidation
(14 h), and chromatography (hexanes–EtOAc, 49:1), 20a
(133 mg, 0.70 mmol, 70%) followed by 20c (35 mg,
0.18 mmol, 18%), both as faint yellow crystals.
Thermolysis of 19 (399 mg, 1.00 mmol) in hexanes (10 mL)
at 908C (oil-bath temperature) for 2 h, as described above,
gave after air oxidation (1.5 h) and chromatography
(hexanes–CH2Cl2, 8:2 then hexanes–CH2Cl2, 1:1), 19d
(33 mg, 0.16 mmol, 16%) as a colorless oil followed by
19c (73 mg, 0.36 mmol, 36%) as faint yellow crystals.
4.1.34. Methyl 2-methylindole-6-carboxylate (21a),
methyl 2,3-dimethylindole-6-carboxylate (21b),73 and
methyl 2-methyl-1,2,3,4-tetrahydroquinoline-7-carboxyl-
ate (21d), and methyl 3-amino-4-ethenylbenzoate (10).
Thermolysis of 21 (395 mg, 1.00 mmol) in MeCN (10 mL)
at 908C (oil-bath temperature) for 6 h gave after air-
oxidation (14 h), and chromatography (hexanes–EtOAc,
9:1), 21d (142 mg, 0.70 mmol, 70%) as white crystals
followed by 41 mg of a mixture74 of 21a (0.04 mmol, 4%),
21b (0.07 mmol, 7%), and 10 (0.11 mmol, 11%).
Thermolysis of 19 (399 mg, 1.00 mmol) in acetonitrile
(10 mL) at 908C (oil-bath temperature) for 0.5 h, as
described above, gave after air-oxidation (30 h), and
chromatography (hexanes–EtOAc, 9:1 then hexanes–
EtOAc, 7:3), 19c (49 mg, 0.23 mmol, 23%) as a colorless
oil followed by 19d (103 mg, 0.50 mmol, 50%) as faint
yellow crystals. A fraction containing a small amount of
impure 19b was also isolated (,5%).
1
Spectral data for 21d. Mp 76–778C. H NMR d 7.25 (d,
J¼7.9 Hz, 1H), 7.13 (s, 1H), 6.99 (d, J¼7.9 Hz, 1H), 3.86
(s, 3H), 3.83 (br s, 1H), 3.42 (m, 1H), 2.93–2.70 (m, 2H),
1.99–1.90 (m, 1H), 1.65–1.50 (m, 1H), 1.22 (d, J¼6.2 Hz,
3H); 13C NMR d 167.5 (þ), 144.7 (þ), 129.1 (2), 128.6
(þ), 126.2 (þ), 117.9 (2), 114.7 (2), 51.8 (2), 47.1 (2),
4.1.29. Methyl 2-methylindole-4-carboxylate (2).68
Thermolysis of 1 (395 mg, 1.00 mmol) in toluene (10 mL)
at 1208C (oil-bath temperature) for 1 h, as described above,
gave after chromatography (hexanes–EtOAc, 3:1), tri-
carbonyl chromium toluene complex69 (62 mg, 0.27 mmol,
27%) as yellow crystals followed by 2 (114 mg, 0.60 mmol,
60%) as faint yellow crystals. Additional spectral data for 2:
13C NMR (300 MHz) d 168.4 (s), 137.8 (s), 136.9 (s), 128.7
(s), 124.3 (d), 120.1 (s), 119.9 (d), 115.0 (d), 101.7 (d), 51.6
(q), 13.7 (q).
29.6 (þ), 26.7 (þ), 22.5 (2); IR (neat) 3384, 1708 cm21
;
GC-MS (EI) m/z 205; HRMS (EI) exact mass calcd for
C12H15NO2 m/z 205.1103, obsd 205.1099.
4.1.35. Methyl 2-methylindole-6-carboxylate (21a),
methyl 2,3-dimethylindole-6-carboxylate (21b), and
methyl 3-amino-4-ethenylbenzoate (10). Thermolysis of
21 (135 mg, 0.34 mmol) in MeCN (4 mL) at 908C (oil-bath
temperature) for 45 h gave after air-oxidation (12H),
4.1.30. Methyl 2-methyl-1,2,3,4-tetrahydroquinoline-5-
carboxylate (1d). Thermolysis of 1 (198 mg, 0.50 mmol) in

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8788
and chromatography (hexanes–EtOAc, 19:1) 41 mg of a
mixture74 of 21a (0.02 mmol, 7%), 21b (0.13 mmol, 38%),
and 10 (0.11 mmol, 33%).
Thermolysis of 24 (184 mg, 0.50 mmol) in MeCN (5 mL) at
908C (oil-bath temperature) for 3 h gave, after air-oxidation
(14 h) and chromatography (hexanes–EtOAc, 9:1), 17
(40 mg, 0.27 mmol, 54%).
4.1.36. Methyl 2-methylindole-7-carboxylate (22a),71
methyl 2,3-dimethylindole-7-carboxylate (22b),72 methyl
2-methyl-1,2,3,4-tetrahydroquinoline-8-carboxylate
(22d), methyl 2-amino-3-ethenylbenzoate (11), and
methyl 2-amino-3-ethylbenzoate. Thermolysis of 22
(395 mg, 1.00 mmol) in MeCN (10 mL) at 908C (oil-bath
temperature) for 6.5 h gave in order of elution, after air-
oxidation (12H) and chromatography (hexanes–EtOAc,
19:1), 22d (38 mg, 0.18 mmol, 18%) as faint yellow oil, a
2:1 mixture of 11 and methyl 2-amino-3-ethylbenzoate75
(67 mg, ca. 26 and 12%, respectively), a 1:2 mixture of 22a
and 22b (62 mg, ca. 7 and 24%, respectively) as faint yellow
crystals.
4.1.40. 2-Methylindole (25a).64 Thermolysis of a solution
of 25 (351 mg, 1.00 mmol) in toluene (10 mL, 1208C, 2H),
as described above, gave after air-oxidation (72H), and
chromatography (hexanes–EtOAc, 9:1), 25a (82 mg,
0.62 mmol, 62%) as faint yellow crystals.
4.1.41. 2-Methylindole (25a) and 3-ethyl-2-methylindole
(25b).78 Thermolysis of a solution of 25 (197 mg,
0.56 mmol) in acetonitrile (10 mL, 908C, 16.5 h), as
described above, gave after chromatography (hexanes–
EtOAc, 4:1), 25b (53 mg, 0.33 mmol, 60%) followed by
25a (18 mg, 0.14 mmol, 25%), both as faint yellow crystals.
Additional data for 25b: 13C NMR d 135.1 (2), 130.1 (2),
128.3 (2), 120.6 (þ), 118.8 (þ), 118.0 (þ), 113.7 (2),
110.2 (þ), 17.3 (2), 15.4 (þ), 11.3 (þ).
1
Spectral data for 22d. H NMR d 7.70 (d, J¼7.4 Hz, 1H),
overlapping 7.7 (s, 1H), 7.06 (d, J¼7.4 Hz, 1H), 6.45 (t,
J¼7.4 Hz, 1H), 3.84 (s, 3H), 3.54–3.40 (m, 1H), 2.83–2.61
(m, 2H), 1.93–180 (m, 1H), 1.55–1.40 (m, 1H), 1.28 (d, J¼
6.2 Hz, 3H); 13C NMR d 169.3 (þ), 148.4 (þ), 133.6 (2),
129.3 (2), 121.9 (þ), 113.6 (2), 108.2 (þ), 51.3 (2), 46.7
(2), 28.8 (þ), 27.1 (þ), 22.6 (2); IR (neat) 3372, 1677,
1254 cm21; GC-MS (EI) m/z 205 (Mþ), 190, 158 (100%),
130; HRMS (EI) calcd for C12H15NO2(Mþ), 205.1103.
Found: 205.1102.
4.1.42. 2-Methylindole (25). Thermolysis of a solution of
25 (197 mg, 0.56 mmol) in hexanes (10 mL, 908C, 48 h), as
described above, gave after chromatography (hexanes–
EtOAc, 4:1), 25a (36 mg, 0.27 mmol, 47%) as faint yellow
crystals.
4.1.43. N-(2-(2-Methyl-1-propen-1-yl)phenyl) 2-methyl-
propanamide (31). Thermolysis of 26 (365 mg,
1.00 mmol) in MeCN (10 mL) at 908C (oil-bath tempera-
ture) for 24 h gave, after air-oxidation (48 h) and chroma-
tography (hexanes–EtOAc, 9:1), 31 (28 mg, 0.13 mmol,
13%) as yellow crystals. Mp 65–668C. 1H NMR d 8.28 (d,
J¼8.2 Hz, 1H), 7.31 (br s, 1H), 7.25 (t, J¼8.4 Hz, 1H), 7.07
(s, 1H), 7.05 (t, J¼9.1 Hz, 1H), 6.11 (s, 1H), 2.51 (septet,
J¼6.9 Hz, 1H), 1.96 (s, 3H), 1.64 (s, 3H), 1.24 (d, J¼
6.9 Hz, 1H); 13C NMR d 174.7 (þ), 140.1 (þ), 135.6 (þ),
129.5 (2), 128.0 (þ), 127.5 (2), 123.4 (2), 120.2 (2),
120.0 (2), 36.9 (2), 25.7 (2), 19.6 (-, 2C), 19.4 (2); IR
(neat) 3246, 1658 cm21; GC-MS (EI) m/z 217 (Mþ), 147,
146 (100%), 132; HRMS (EI) calcd for C14H19NO (Mþ),
217.1467. Found: 217.1470.
Spectral data for methyl 2-amino-3-ethylbenzoate from the
1
mixture with 11. H NMR d 7.70 (dd, J¼6.4, 1.5 Hz, 1H),
7.12 (d, J¼7.4 Hz, 1H), 6.55 (t, J¼7.9 Hz, 1H), 3.78 (s, 3H),
2.42 (q, J¼7.7 Hz, 2H), 1.18 (t, J¼7.4 Hz, 3H).
4.1.37. Methyl 2-methylindole-7-carboxylate (23a),
methyl 2-methyl-1,2,3,4-tetrahydroquinoline-8-carboxyl-
ate (23d), and methyl 2-amino-3-ethenylbenzoate (11).
Thermolysis of 22 (410 mg, 1.04 mmol) in hexanes
(10.5 mL) at 908C (oil-bath temperature) for 6.5 h gave in
order of elution, after air-oxidation (12H) and chroma-
tography (hexanes–EtOAc, 19:1), 22d (9 mg, 0.04 mmol,
4%) as faint yellow oil, 11 (34 mg, 0.19 mmol, 18%), and
22a (129 mg, 0.68 mmol, 65%) as faint yellow oil.
4.1.44. 2-Methylindole (26a) and 2-(2-methyl-1-propenyl)-
benzenamine. Thermolysis of 26 (365 mg, 1.00 mmol) in
hexanes (10 mL) at 908C (oil-bath temperature) for 24 h
gave, after air-oxidation (48 h) and chromatography (hex-
anes–EtOAc, 9:1), a 75 mg of a mixture of 2-(2-methyl-1-
propenyl)benzenamine (64 mg, 0.44 mmol, 44%) and 26a
(11 mg, 0.08 mmol, 8%).74
4.1.38. 5-Methoxy-2,3-dimethylindole (23b)76 and
5-methoxy-2-methylquinoline (23c).77 Thermolysis of 23
(184 mg, 0.50 mmol) in MeCN (5 mL) at 908C (oil-bath
temperature) for 25 h gave, after air-oxidation (16 h)
and chromatography (hexanes–EtOAc, 4:1), 23c (36 mg,
0.21 mmol, 42%) followed by 23b (17 mg, 0.10 mmol,
29%) as faint yellow oils.
4.1.45. 2,4-Dimethylquinoline (4)64 and 2,4-dimethyl-1,2,
3,4-tetrahydroquinoline (5).79 Thermolysis of a solution of
3 (863 mg, 2.46 mmol) in toluene (30 mL, 1208C, 16 h), as
described above, gave after air-oxidation (24 h) and
Thermolysis of 23 (184 mg, 0.50 mmol) in hexanes (5 mL)
at 908C (oil-bath temperature) for 25 h gave, after air-
oxidation (16 h) and chromatography (hexanes–EtOAc,
4:1), 23c (49 mg, 0.28 mmol, 57%) followed by 23b
(17 mg, 0.10 mmol, 29%) as faint yellow oils.
chromatography (hexanes–EtOAc, 8:2),
0.55 mmol, 22%) followed by 4 (133 mg, 0.85 mmol,
5
(88 mg,
34%) both as faint yellow oils.
4.1.39. 2-Ethenyl-5-methoxybenzenamine (17). Thermo-
lysis of 24 (130 mg, 0.35 mmol) in MeCN (5 mL) at 908C
(oil-bath temperature) for 3 h gave, after air-oxidation
(14 h) and chromatography (hexanes–EtOAc, 9:1), 17
(42 mg, 0.28 mmol, 80%).
4.1.46. 2,4-Dimethylquinoline (4) and 2-(1-methylethenyl)-
benzenamine. Thermolysis of 3 (351 mg, 1.00 mmol) in
MeCN (10 mL) at 908C (oil-bath temperature) for 14.5 h
gave in order of elution, after air-oxidation (12H) and

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B. C. G. Soderberg et al. / Tetrahedron 59 (2003) 8775–8791
8789
chromatography (hexanes–EtOAc, 9:1), 2-(1-methyl-
ethenyl)benzenamine (55 mg, 0.41 mmol, 41%), and 4
(35 mg, 0.22 mmol, 22%), both as yellow oils.
13C NMR d 152.1 (þ), 146.2 (þ), 142.9 (þ), 129.2 (2),
128.1 (þ), 126.2 (2), 123.5 (þ), 122.8 (2), 12.1 (2), 10.4
(2), 7.1 (þ); MS (EI) m/z 199 (Mþ), 198 (100%), 184;
HRMS (EI) calcd for C13H13NO 199.0957 (Mþ), obsd
199.0960.
4.1.47. 4-Methyl-2-phenylquinoline (27c),80 1,2,3,4-tetra-
hydro-4-methyl-2-phenylquinoline (27d),81,82 and
3-hydroxy-4-methyl-2-phenylquinoline (27e). Thermoly-
sis of a solution of 27 (423 mg, 1.02 mmol) in toluene
(20 mL, 1108C, 24 h), as described above, gave after air-
oxidation (2H) and chromatography (hexanes–EtOAc, 9:1
then 8:2), a 26:9 mixture of 27c and 27d (79 mg, ca 26 and
9% respectively) followed by 27e (46 mg, 0.22 mmol, 22%)
as faint yellow crystals.
4.1.51. 2-(2-Furyl)-4-methylquinoline (29c).80 Thermoly-
sis of 29 (352 mg, 1.00 mmol) in MeCN (10 mL) at 908C
(oil-bath temperature) for 23.5 h gave, after air-oxidation
(12H) and chromatography (hexanes–EtOAc, 19:1), 29c
(54 mg, 0.26 mmol, 26%) as a yellow oil.
Thermolysis of 29 (352 mg, 1.00 mmol) in hexanes (10 mL)
at 908C (oil-bath temperature) for 23.5 h gave, after air-
oxidation (12H) and chromatography (hexanes–EtOAc,
19:1), 29c (44 mg, 0.21 mmol, 21%).
1
Analytical data for 27e. H NMR d 8.08–8.04 (m, 1H),
7.91–7.87 (m, 1H), 7.74–7.68 (m, 2H), 7.59–7.35 (m, 5H),
6.95 (br s, 1H), 2.57 (s, 3H); 13C NMR d 150.0 (þ), 144.8
(þ), 143.0 (þ), 136.8 (þ), 129.7 (2), 129.2 (2), 129.1 (2),
128.9 (þ), 128.8 (2), 126.6 (2), 126.5 (2), 126.3 (þ),
123.0 (2), 10.7 (2); IR (neat) 3060 cm21; GC-MS (EI) m/z
(Mþ) 235, 234 (100%), 206, 128; HRMS (EI) calcd for
C16H13NO (Mþ21), 234.0919. Found: 234.0921.
4.1.52. Dubamine86 and piperonal. Reaction of tetra-
methylammonium
pentacarbonyl(1-(1,3-benzodioxol-5-
yl)methylidene)chromium (1-) (200 mg, 0.45 mmol) in
CH2Cl2 (20 mL) with acetyl chloride (34 mL, 0.48 mmol)
and 2-ethenylbenzenamine (57 mg, 0.48 mmol), as
described above, gave after chromatography (hexanes–
EtOAc, 6:4) and solvent removal on a rotary evaporator, 30
(186 mg, ,0.42 mmol, ,87%)87 as brown-red crystals. The
resulting solid was immediately dissolved in acetonitrile
(5 mL) and heated as described above (908C, 45 min).
Evaporation of the solvent and purification by column
chromatography (hexanes–EtOAc, 9:1) gave 30c (10 mg,
0.04 mmol, 9%) followed by piperonal (32 mg, 0.21 mmol,
51%).
4.1.48. 4-Methyl-2-phenylquinoline (27c). Thermolysis of
27 (422 mg, 1.02 mmol) in hexanes (20 mL) at 908C (oil-
bath temperature) for 3 h gave, after air-oxidation (3 days)
and chromatography (hexanes–EtOAc, 19:1), 27c (120 mg,
0.55 mmol, 55%) as white crystals.
Thermolysis of 27 (265 mg, 0.64 mmol) in MeCN (20 mL)
at 908C (oil-bath temperature) for 3 h gave, after air-
oxidation (3 days) and chromatography (hexanes–EtOAc,
19:1), 27c (86 mg, 0.39 mmol, 61%) as white crystals.
4.1.53. 4-Carbomethoxy-1,2-dimethylindole (35) and
N-methyl-N-(2-ethenyl)phenyl acetamide (35). Thermo-
lysis of 33 (421 mg, 1.03 mmol) in benzene (30 mL) at 908C
for 28 h as described above gave, after air oxidation (24 h)
and chromatography (hexanes–EtOAc, 8:2 followed by
hexanes–EtOAc, 1:1), 34 (44 mg, 0.22 mmol, 21%) as faint
yellow crystals followed by 35 (73 mg, 0.31 mmol, 30%) as
faint yellow oil.
4.1.49. 4-Methyl-2-phenylquinoline (27c) and 2-(1-methyl-
ethenyl)-N-phenylmethylenebenzenamine (32).83 Ther-
molysis of 27 (200 mg, 0.50 mmol) in MeCN (5 mL) at
908C (oil-bath temperature) under CO (3 atm) for 6 h gave
in order of elution (hexanes–EtOAc, 9:1), 27c (22 mg,
0.10 mmol, 20%) and 32 (23 mg, 0.11 mmol, 22%), the
latter as yellow crystals.84
1
Spectral data for 34. Mp ,258C. H NMR (300 MHz) d
4.1.50. 3-Hydroxy-4-methyl-2-cyclopropylquinoline
(28e) and 4-methyl-2-cyclopropylquinoline (28c).85 Ther-
molysis of 28 (335 mg, 1.00 mmol) in MeCN (10 mL) at
908C (oil-bath temperature) for 20 h gave in order of
elution, after air-oxidation (17 h) and chromatography
(hexanes–EtOAc, 19:1), 28c (25 mg, 0.14 mmol, 14%) as
faint yellow oil and 28e (39 mg, 0.23 mmol, 23%) as faint
yellow crystals.
7.84 (d, J¼7.6 Hz, 1H), 7.41 (d, J¼8.1 Hz, 1H), 7.15 (t,
J¼7.8 Hz, 1H), 6.86 (s, 1H), 3.96 (s, 3H), 3.64 (s, 3H), 2.44
(s, 3H); 13C NMR (75 MHz) d 168.2, 139.5, 138.2, 127.6,
122.7, 120.1, 119.4, 113.3, 51.5, 29.5, 12.8; IR (neat) 2960,
1705, 1260 cm21; HRMS (EI) exact mass calcd for
C12H13NO2 m/z 203.0946, obsd 203.0974.
1
Spectral data for 35. H NMR d 7.74 (dd, J¼7.7, 2.6 Hz,
1H), 7.49–7.29 (m, 3H), 6.89 (dd, J¼17.8, 11.6 Hz, 1H),
5.49 (d, J¼11.9 Hz, 1H), 5.31 (d, J¼18.4 Hz, 1H), 3.88 (s,
3H), 3.16 (s, 3H), 1.80 (s, 3H); 13C NMR d 170.3 (s), 168.1
(s), 142.8 (s), 136.7 (s), 132.9 (s), 131.4 (d), 131.2 (d), 129.4
(d), 128.5 (d), 120.2 (t), 52.4 (q), 36.4 (q), 22.2 (q); IR (neat)
1715, 1640 cm21. Anal. calcd for C13H15NO3: C, 66.93; H,
6.48. Found: C, 66.94; H, 7.02.
Thermolysis of 28 (335 mg, 1.00 mmol) in hexanes (10 mL)
at 908C (oil-bath temperature) for 20 h gave in order of
elution, after air-oxidation (17 h) and chromatography
(hexanes–EtOAc, 19:1), 28c (56 mg, 0.31 mmol, 31%) as
faint yellow oil and 28e (42 mg, 0.25 mmol, 25%) as faint
yellow crystals.
Spectral data for 28e. Mp 93–948C; IR (neat) 3406, 1594,
1389, 1192 cm21. 1H NMR d 7.94 (dd, J¼7.6, 1.7 Hz, 1H),
7.84 (dd, J¼7.2, 2.0 Hz, 1H), 7.51 (td, J¼6.9, 1.7 Hz, 1H),
5.71 (br s, 1H), 2.56 (s, 3H), 2.29 (tt, J¼8.2, 4.9 Hz, 2H),
1.18 (dt, J¼5.2, 2.2 Hz, 2H), 1.09 (dt, J¼8.4, 2.5 Hz, 2H);
Acknowledgements
This research was supported by grants from the National
Science Foundation (CHE-9203146) and, in part, from the

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B. C. G. Soderberg et al. / Tetrahedron 59 (2003) 8775–8791
8790
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University of South Alabama Research Council. Copy
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