Incvestigation of the possible role of arylamine formation in the ortho-substituted nitroarenes reductive cyclization reactions to afford heterocycles

Article abstract of DOI:10.1016/S0022-328X(98)01076-6

Reductive carbonylation of nitroarenes with an unsaturated group in the ortho position generally affords high yields of heterocyclic compounds, including indoles, chalcones, quinolines, benzimidazoles, benzotriazoles, and indazoles. There is, however, no direct information on the organic intermediates formed during the reaction. In this paper, we have examined the possible formation of anilines as intermediates in the synthesis of indoles, acylindoles, quinolines, and quinolones with several catalytic systems based on palladium, ruthenium and rhodium. It transpired that, independent of the metal complex used as a catalyst, the formation of aniline as an intermediate is essential in the intra-molecular condensation reactions of nitroarenes involving an aldehydic or a keto group (including Michael addition reactions), but plays at best a very limited role in the addition reactions involving a C=C double bond.

Full text of DOI:10.1016/S0022-328X(98)01076-6

Journal of Organometallic Chemistry 577 (1999) 283–291
Investigation of the possible role of arylamine formation in the
ortho-substituted nitroarenes reductive cyclization reactions to afford
heterocycles
Fabio Ragaini *, Paola Sportiello, Sergio Cenini
Dipartimento di Chimica Inorganica, Metallorganica e Analitica and CNR Center, 6ia G. Venezian 21, I-20133 Milan, Italy
Received 21 September 1998
Abstract
Reductive carbonylation of nitroarenes with an unsaturated group in the ortho position generally affords high yields of
heterocyclic compounds, including indoles, chalcones, quinolines, benzimidazoles, benzotriazoles, and indazoles. There is,
however, no direct information on the organic intermediates formed during the reaction. In this paper, we have examined the
possible formation of anilines as intermediates in the synthesis of indoles, acylindoles, quinolines, and quinolones with several
catalytic systems based on palladium, ruthenium and rhodium. It transpired that, independent of the metal complex used as a
catalyst, the formation of aniline as an intermediate is essential in the intra-molecular condensation reactions of nitroarenes
involving an aldehydic or a keto group (including Michael addition reactions), but plays at best a very limited role in the addition
reactions involving a CꢀC double bond. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Reductive carbonylation; Catalysis; Palladium; Ruthenium; Rhodium
1
. Introduction
intermediate (by reduction by CO and traces of mois-
ture) that later condenses with the aldehyde to afford
the Schiff base, regenerating the water necessary to
carry out the reaction (Scheme 1) [3].
Thus it appears likely that at least those syntheses of
heterocyclic compounds that imply the intramolecular
condensation of a nitro and a keto group should also
proceed through aniline formation. However, the prob-
lem may be more general. It is well known that palladi-
um(II) complexes promote the synthesis of indoles from
o-aminostyrenes and that the reaction can be made
Reductive carbonylation of nitroarenes with an un-
saturated group in the ortho position generally affords
high yields of heterocyclic compounds, including in-
doles, chalcones, quinolines, benzimidazoles, benzotria-
zoles, and indazoles [1,2]. The synthesis of many of
these products has been proposed to proceed through
the intermediate formation of an imido complex, which
should be able to attack the unsaturated group to
afford the heterocyclic product. However, no direct
evidence has been obtained for the involvement of
imido species in the catalytic cycle and as such there are
other alternatives which can be considered. In particu-
lar, we have recently shown that the synthesis of Schiff
bases from nitroarenes and aldehydes under CO pres-
sure proceeds through the formation of an aniline as an
*
Corresponding author. Fax: +39-2-2362748.
E-mail address: ragaini@csmtbo.mi.cnr.it (F. Ragaini)
Scheme 1.
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(98)01076-6

284
F. Ragaini et al. / Journal of Organometallic Chemistry 577 (1999) 283–291
Scheme 2.
catalytic by the addition of an oxidant able to convert
the palladium(0) complex formed at the end of the
reaction back to palladium(II) [4]. Palladium com-
plexes, especially those with phenanthroline ligands, are
well known catalysts for the reductive carbonylation of
nitroarenes. The available mechanistic information [5]
indicates that the species reacting with the nitroarene is
a palladium(0) complex, which is oxidized to a palladi-
um(II) species during the reaction. Remarkably, in at
least some of the catalytic systems, the nitroarene is
initially reduced to aniline, independent of the identity
of the final product of the catalytic reaction. Thus the
possibility that the syntheses of indoles from o-ni-
trostyrenes (at least those catalyzed by palladium com-
plexes) proceed through the intermediate reduction of
the nitroarene to aniline, with simultaneous oxidation
of palladium(0) to palladium(II), which is followed by a
classical cyclization of the amine to afford the indole
with the initial palladium(0) complex regenerated,
should be considered.
should be obtained, with a prevalence for the one
derived from the aniline. On the other hand, if anilines
were not intermediates, only the heterocycle derived
from the nitroarene should be obtained. The results
discussed here reveal a complex situation. To the best
of our knowledge, this is the first time that the possible
role of anilines in this class of reactions has been
investigated.
2. Results and discussion
2.1. Synthesis of indoles
Three different, previously reported catalytic systems
for the synthesis of indoles from o-nitrostyrenes were
tested for the possible involvement of anilines in the
reaction: one employing Pd(TMB) in the presence of
2
TMPhen (TMB=2,4,6-trimethylbenzoate, TMPhen=
3,4,7,8-tetramethyl-1,10-phenanthroline) [6], one em-
To clarify the possible role of the intermediate for-
mation of anilines in the synthesis of different heterocy-
cles, we have performed three different syntheses, with
a total of six different catalytic systems. We have
worked with equimolar amounts of a nitroarene and an
aniline which bear in the ortho position reactive groups
of the same class, but have different substituents, so
that the products derived from the possible reaction of
the aniline could be distinguished from the ones derived
from the nitroarene. If anilines were intermediates in
the reaction, a mixture of two related heterocycles
ploying [PPN][Rh(CO) ] in the presence of
4
+
+
2-hydroxypyridine (PPN =(PPh ) N ) [7], and one
3
2
employing Ru (CO) [8] as catalysts. The substrates
3
12
used were methyl-2-nitrocinnamate (1) and 2-aminostil-
bene (2) (Scheme 2). The results of the GC analysis of
the final reaction mixtures are reported in Table 1.
The results obtained clearly show that the indole
products almost completely derive from the nitroarene
both in the case of the palladium and the ruthenium
catalytic systems; however, a significant amount of
indole derived from the aniline is also obtained. In the

F. Ragaini et al. / Journal of Organometallic Chemistry 577 (1999) 283–291
285
Table 1
Synthesis of indoles
Catalytic system
1 conversion
3 selectivity
(%)
2 conversion
(%)
4 selectivity
(%)
4/3 mol ratio
5 select
(%)
d
e
f
g
e
(
%)
Pd(TMB) /TMPhena
100
99.0
100
76.4
11.5
36.3
36.8
76.9
67.3
10.2
4.7
2.1
0.055
0.343
0.063
10.1
27.3
2.8
2
b
[
PPN][Rh(CO) ]/2-OH-pyridine
4
c
Ru (CO)
3
12
a
Experimental conditions: Pd(TMB) =0.011 mmol, molar ratios Pd/TMPhen/1/2=1:2:20:20, 180°C, 40 bar CO, in toluene (10 ml) for 3 h.
2
b
Experimental conditions: [PPN][Rh(CO) ]=0.0266 mmol, molar ratios Rh/2-OH-pyridine/1/2=1:6:20:20, 170°C, 60 bar CO, in o-
4
dichlorobenzene (10 ml) for 5 h.
c
Experimental conditions: Ru (CO) =6.57×10−3 mmol, molar ratios Ru (CO)12/1/2=1:15:15, 220°C, 70 bar CO, in toluene (3 ml) for
3
12
3
1
.5 h.
d
Calculated with respect to initial 1.
Calculated with respect to converted 1.
Calculated with respect to initial 2.
Calculated with respect to converted 2.
e
f
g
case of the rhodium catalyzed system, a majority of the
indole is still derived from the nitroarene. However, the
molar amount of indole 4, derived from the aniline, is
depressed. Nevertheless, this is the first time that evi-
dence for the existence of such a pathway is provided.
The formation of the indole derived from the aniline
even when the rhodium and ruthenium catalysts are
employed imply that catalysts based on these metals
should also be able to catalyze the formation of indoles
from o-aminostyrenes in the presence of an oxidant. For
this reaction only palladium-based catalysts have been
studied in detail. However, it should be noted that the
amount of 4 formed corresponds in all cases (including
the palladium-promoted reaction) to a substoichiometric
reaction with respect to the metal. This fact strengthens
the idea that, at least under the experimental conditions
typically employed for the cyclization reactions of ni-
troarenes [1,6–8], the intermediate formation of aniline
plays a very limited role in the syntheses of indoles.
34.3% of the nitroarene-derived indole (3). This rela-
tively high amount of indole derived from the aniline is
not due to a higher selectivity in the aniline reaction, but
to the unusually low selectivity in the nitroarene reac-
tion, which only gave a 11% selectivity in indole. Appar-
ently, the presence of an amine in solution has a negative
effect on the reaction. A certain amount of 2-hydrox-
yquinoline was also observed among the products. This
compound had been previously obtained in similar
reactions starting from 1. It probably derives from an
intramolecular cyclization of the by-product aniline
derived from 1, to afford the cyclic amide, which is in
tautomeric equilibrium with 5 (Scheme 3). The necessary
trans–cis isomerization of the double bond may be
caused by both the presence of a metal and the high
temperature.
2.2. Synthesis of acylindoles and quinolines
In the course of normal reactions the amount of
aniline present is much lower than the one in the
reactions performed in this study, as this compound is
only formed as a by-product. Thus the contribution of
the pathway passing through the aniline will be further
A second case we examined was the reaction of
2-nitrochalcones to afford a mixture of 2-acylindoles and
2-substituted quinolines. The catalytic systems tested for
these reactions were the Pd(TMB) /TMPhen one previ-
2
ously used also in the synthesis of simple indoles [9] and
the one based on the combination Ru (CO) /Tol-BIAN
3
12
1
[
9], where Tol-BIAN is the ligand shown below :
1
Note that in previous papers we used the name DIAN-Me for this
ligand. However, since other groups are using the general name
Ar-BIAN for this class of ligands [10] and this last terminology is of
more general application, we have decided to adhere to this conven-
tion in order to avoid the use of different names in the literature for
the same compound.
Scheme 3.

286
F. Ragaini et al. / Journal of Organometallic Chemistry 577 (1999) 283–291
Scheme 4.
In this case (Scheme 4) the products could not be
analyzed by gas chromatography and the evidence for
the formation of the different compounds in the reac-
tions was provided by TLC with long (20 cm) alumina
plates. Although the method did not allow for a quanti-
tative estimation of the amounts of the various prod-
ucts, their identity could be easily established by
comparison with authentic samples as several of the
products have distinctive fluorescent behavior. The
presence of the products observed by TLC was further
confirmed by mass spectra of the solids obtained by
evaporation of the solvent from the solutions after the
reactions.
In the case of the ruthenium catalyst, the solution at
the end of the reaction clearly showed the presence of
the quinolines derived from both of the starting
reagents, however only the acylindole 8 derived from
the nitroarene could be detected. Trace amounts of
both of the possible amines could also be observed on
the TLC plates and in the mass spectra. From the data
obtained it is clear that, in accord with what we
expected based on our studies on the synthesis of
Schiff bases from nitroarenes and aldehydes [3], the
synthesis of quinolines proceeds via the aniline, while
the water formed in the condensation reaction reduces
more nitro compound to afford initially the second
aniline, which later condenses to the nitroarene-derived
quinoline (9). In the case of the palladium-catalyzed
reaction, this ‘water recycling’ is essential for the
reaction to be catalytic as only trace amounts of
moisture, mainly from the CO gas, are present initially.
In the case of the ruthenium-catalyzed reaction, a
more than stoichiometric amount of water is added
at the beginning in order to facilitate a faster reac-
tion. The water, however, still acts in a catalytic man-
ner.
It should be noted that in the previous literature,
nitrenes have been most often proposed as the species
responsible for quinoline formation from nitroarenes
[11], although it has been proposed that anilines play a
role in one case [12].
A different situation occurs in the case of the synthe-
sis of acylindoles. Given the results reported in the
previous section on the synthesis of simple indoles, it
may appear surprising that the acylindole derived from
7 was not formed at all. Although it must be acknowl-
edged that a very small amount (ca. 1–2%) may have
escaped detection by TLC and mass spectra, the best
explanation for the data obtained is that, in the present
reaction, condensation of an intermediately formed ani-
line with the keto group already present in the molecule
(to afford the quinoline) must be much easier than
attack at the CꢀC double bond.
The Pd(TMB) /TMPhen catalytic system had been
2
previously observed to yield higher selectivities in
acylindole than the one based on ruthenium [9]. Ac-
cordingly, when the reaction in Scheme 4 was per-
formed by using the palladium-based catalytic system,
only the acylindole 8 and the quinoline 10 were formed.
No acylindole derived from the amine or quinoline
derived from the nitroarene could be detected by TLC
or mass spectra, although a trace amount of the amine
derived from 6 was present. The conversion of both 6
and 7 was almost quantitative. These results are even
more clear cut than those from the previous reaction in
indicating that the amine is the intermediate responsible
for the quinoline formation, but is not involved in the
synthesis of the acylindole.

F. Ragaini et al. / Journal of Organometallic Chemistry 577 (1999) 283–291
287
2
2
.3. Synthesis of 4-quinolones and
,3-dihydro-4-quinolones
We have previously shown that 2%-nitrochalcones,
isomeric products with respect to the ones considered in
the previous paragraph, are reduced to a mixture of
4-quinolones and 2,3-dihydro-4-quinolones by CO in
the presence of the same Ru (CO) /Ar-BIAN catalytic
3
12
system mentioned above (Scheme 5) [13].
When the same reaction was performed by using the
Pd(OAc) /TMPhen catalytic system, the saturated
2
product was formed only in small amounts or not at
all, although some other unidentified by-products were
observed. In the course of that work, we also showed
that 2%-aminochalcones gave intramolecular Michael
addition to the conjugated double bond to afford the
Scheme 6.
2,3-dihydro-4-quinolone only and that this reaction was
accelerated by the Ru (CO) /Ar-BIAN catalytic system
3
12
reagent, and unreacted 12. Minor amounts of uniden-
tified by-products derived from the nitroarene were also
[
13]. We also showed that the saturated product could
be converted to the unsaturated one by oxidation with
,3-dichloro-5,6-dicyanobenzoquinone, but nitroben-
observed in the CDCl -soluble fraction, but no product
3
2
derived from 12 was observed. Thus the aniline is not
an intermediate in the synthesis of the quinolone with
this palladium catalyst, neither in a direct way, nor in a
possible pathway including the intermediate formation
of the dihydroquinolone followed by fast oxidation by
the remaining nitroarene mediated by the metal itself.
zene, at least in the absence of a metal, was ineffective
as an oxidant for this last reaction even at high temper-
atures. Since the presence of a metal complex may
profoundly modify the ability of a nitroarene to act as
an oxidant and may even allow for different reactions
of the amine, as found for the minor pathway in the
synthesis of indoles, we performed the cross reaction
shown in Scheme 6.
Since it was already clear that the dihydroquinolone
was derived from the amine, the palladium-based cata-
lytic system was tested (which does not afford this
product in significant amounts) to ascertain if even the
quinolone may in part derive from the amine. In this
way the competitive (and possibly faster) pathway lead-
ing to the dihydroquinolone is not present. The solu-
tion mixtures after the reactions were analyzed by
3. Conclusions
The work reported in this paper has clearly shown
that, in accord with our results on the synthesis of
Schiff bases from nitroarenes and aldehydes [3], the
intermediate formation of aniline is essential in the
intra-molecular condensation reactions of nitroarenes
also involving an aldehydic or a keto group (including
Michael addition reactions), but plays at best a very
limited role in the addition reactions involving a CꢀC
double bond. In relation to this last class of reactions,
we can only speculate on the identity of the intermedi-
ate responsible for cyclization. An imido complex, as
often proposed, is a possibility. However, when the
carbonylation of some organic nitro derivatives was
conducted in cis-cyclooctene as a solvent and with
Ru (CO) as a catalyst, nitrones were detected among
1
H-NMR, taking advantage of the almost complete
insolubility of the unsaturated quinolones in CDCl3,
which allows for their separation and separate analysis
in DMSO-d . The results clearly showed that the only
6
quinolone formed was 13, derived from the nitroarene,
accompanied by some amine 14, derived from the same
3
12
the products [14]. These products appear to derive from
a coupling of the intermediate nitrosoarene with the
olefin, a reaction for which many precedents exists [15].
Deoxygenation of the nitrone by coordinated CO
would then lead to the final product. We note only that
the analogous azoxy derivative, PhN(O)ꢀNPh, is read-
ily deoxygenated by CO in the presence of a zerovalent
ruthenium catalyst [16].
Other products commonly obtained by reaction of
nitrosoarenes with olefins are hydroxylamines [17]. It is
Scheme 5.

288
F. Ragaini et al. / Journal of Organometallic Chemistry 577 (1999) 283–291
Scheme 7.
noteworthy that N-hydroxyindoles and N-hydroxy-
quinolones have been very recently observed as by-
products in the cases of some cyclization reactions of
o-nitrostyrenes and o-nitrochalcones catalyzed by
Although nitrosoarenes appear to directly react with
the olefin moiety during the reaction, it must also be
noticed that anilines are always by-products of the
reactions investigated here and their formation requires
a further reduction of the nitrogen-containing group,
which may even involve the formation of an imido
complex. Whether this imido complex also takes part
into the cyclisation reaction to some extent cannot be
deduced from our data.
A likely reaction scheme for the amine-mediated
synthesis of indoles catalyzed by the same palladium
system is reported in Scheme 8. Here again the reaction
starts with a nitroarene deoxygenation by a zerovalent
palladium complex [5]. In this case, we have evidenced
that this reduction also produces two equivalents of
trimethylbenzoic acid. The same acid may become in-
volved in the reduction of the nitroarene by CO and the
metal, affording the aniline and a palladium(II) com-
plex. Exchange with external arylamine would occur at
this stage of the process. From this point onward, the
steps should be analogous to the ones proposed by
Hegedus for his system [4], although the other ligands
around the palladium atom are different in the two
cases. In the Hegedus system, the oxidizing agent is
benzoquinone. In the present system, it would be the
nitroarene itself to play the dual role of oxidizing agent
and source of the amine. For the other catalytic sys-
tems, proton sources other than trimethylbenzoic or
Pd(TMB) /TMPhen [18] and this kind of product can
2
even become the dominant one when the reaction is run
in THF. Hydroxylamines are also known to be deoxy-
genated by metal carbonyls [19]. Finally, nitrosoarenes
have been also shown to be responsible for at least part
of the product in the inter-molecular addition of ni-
troarenes to olefins catalyzed by Ru (CO) in the
3
12
presence of Ar-BIAN [20]. Thus it appears that the
reaction of the intermediate nitrosoarene with the olefin
moiety is involved at least in part in the formation of
the indoles and of the quinolones. A likely reaction
scheme for the formation of the indoles catalyzed by
Pd(TMB) /TMPhen which shows the formation of both
2
of the possible nitrosoarene-derived intermediates (the
nitrone and the hydroxyindole) is shown in Scheme 7.
Similar mechanisms should operate in the cases involv-
ing other catalytic systems.
Adventitious moisture must be responsible for the
initial reduction of the palladium catalyst. Note that all
of the ‘organic’ species have been drawn as bound to
the metal throughout the catalytic cycle, but it is also
possible that the organic molecule leaves the metal
coordination sphere at some stages of the reaction (this
is quite likely for the hydroxylamine).

F. Ragaini et al. / Journal of Organometallic Chemistry 577 (1999) 283–291
289
Scheme 8.
acetic acid must be present. The most likely candidate
for this role in the rhodium-catalyzed system is 2-hy-
droxypyridine, whereas the protons are probably pro-
vided by water (even adventitious moisture) or by the
other protic solvents in the case of ruthenium-catalyzed
reactions.
by comparison with commercial samples (Aldrich). Tol-
BIAN was synthesized as previously reported [10,20b].
All other compounds were commercial products and
were used as received. GC analyses were performed on
a Perkin-Elmer 8420 capillary GC equipped with a PS
255 column. R values (R =response factor, relative to
i
i
naphthalene as an internal standard) were determined
by the use of solutions of known concentrations of the
compounds. GC–MS analyses were performed on a
Hewlett-Packard 5890 Series II GC, equipped with a
4. Experimental
5
971A mass selective detector. NMR spectra were
4
.1. General procedures
recorded on a Bruker AC 200 FT spectrometer (200
MHz) at room temperature. Elemental analyses and
mass spectra were recorded in the analytical laborato-
ries of Milan University.
Unless otherwise specified, all reactions and manipu-
lations were performed under a N atmosphere using
2
standard Schlenk apparatus, cannula techniques, and
magnetic stirring, but the products of the catalytic
reactions had to be handled in the air for at least some
time. Solvents were dried and distilled by standard
4.2. Catalytic reactions
procedures
and
stored
under
dinitrogen.
In a typical reaction, the reagents were weighed in a
glass liner. The liner was placed inside a Schlenk tube
with a wide mouth under dinitrogen and was frozen at
−78°C with dry ice, evacuated and filled with dinitro-
gen, after which the solvent was added. After the
solvent was also frozen, the liner was closed with a
screw cap having a glass wool-filled open mouth which
allows for gaseous reagents exchange and rapidly trans-
[
[
PPN][Rh(CO) ] [21], Ru (CO) [22], Pd(TMB) [23], 1
24], 2 [25], 6 [26], 7 [27], 11 [28], and 12 [29] were
4
3
12
2
synthesized by methods reported in the literature. Prod-
ucts 3 [6], 4 [6], 8 [26b,30], 10 [31], 13 [32], and 14 [18]
are known compounds and were identified by compari-
son with authentic samples or with the spectroscopic
data reported in the literature. 5 and 9 were identified

290
F. Ragaini et al. / Journal of Organometallic Chemistry 577 (1999) 283–291
ferred to a 200 ml stainless steel autoclave with mag-
netic stirring. The autoclave was then evacuated and
filled with dinitrogen three times. CO was then charged
at room temperature at the required pressure and the
autoclave was immersed in an oil bath preheated at the
required temperature. In the case of the reactions cata-
4.5. Synthesis of 4-quinolones
The reactions were performed as described above
using the following conditions: 11 (34.0 mg, 0.12
mmol), 12 (32.0 mg, 0.12 mmol), Pd(OAc) (3.0 mg,
2
−
2
−2
1.34×10
mmol), TMPhen (5.4 mg, 2.28×10
lyzed by [PPN][Rh(CO) ], to avoid contact with air of
mmol), in toluene (10 ml), PCO=30 bar, T=170°C, for
3 h. At the end of the reaction, a precipitate was
present, which was filtered on a glass frit and washed
4
this sensitive compound, it was weighed under dinitro-
gen and added to the glass liner only after the liner had
already been frozen in the Schlenk tube under dinitro-
gen. At the end of the reaction the autoclave was
cooled with an ice bath, vented and the products were
analyzed as described in the following.
1
with CH Cl (2×3 ml) The H-NMR (DMSO-d ) of
2
2
6
the solid showed it to be a 7:3 mixture of 13 and of the
amine derived from 11, but no product derived from 12
was present. The solution after filtration and the
CH Cl washings were combined and dried in vacuo.
2
2
1
4.3. Synthesis of indoles
The H-NMR (CDCl ) of this solid showed the pres-
3
ence of a very small amount of 11, but three more
peaks of comparable intensity were also present around
3.9 ppm (–OMe) indicating the presence of unidentified
by-products. The saturated product 2,3-dihydro-2-(4-
methoxyphenyl)-4-quinolone corresponding to 13 was
not formed anyway, as shown by the absence of the
signal for the hydrogenated double bond between 4 and
5 ppm. Only one signal was observed at 6.0 ppm in the
The reactions were performed as described above.
Reagents amounts and experimental conditions are re-
ported in Table 1. At the end of the reaction, naphtal-
ene was added as an internal standard and the solutions
were analyzed by gaschromatography. In all cases, but
especially in the case of the reaction catalyzed by
[
PPN][Rh(CO) ], a by-product was observed in the
4
gaschromatograms, showing in the mass spectrum a
parent peak at M =253. This mass corresponds to
that of the methyl carbamate derived from 2. Indeed,
region of the –O–CH –O– protons, indicating that the
2
+
amine 12 had not reacted at all. The nitroarene conver-
sion was complete, as indicated by the TLC analysis of
the solution and the CH Cl washings. The formation
anilines are known to be intermediate in the
2
2
−
[
Rh(CO) ] -catalyzed carbonylation of nitroarenes to
of 13 and the absence of the quinolone derived from 12
have also been proved by the analysis of the EI mass
spectra of the products of the reaction.
4
carbamates in the presence of alcohols [33] and some
methanol is liberated during the formation of 5.
4.4. Synthesis of acylindoles and quinolines
Acknowledgements
The reactions were performed as described above
using the following conditions: (a) 6 (13.4 mg, 0.053
mmol), 7 (15.0 mg, 0.053 mmol), Ru (CO) (1.0 mg,
The authors would like to thank MURST (ex 40%)
for financial support and Dr S. Tollari for kindly
helping in the analysis and identification of the organic
products.
3
12
−
3
−3
1.56×10
mmol), Tol-BIAN (1.7 mg, 4.7×10
mmol), in EtOH (10 ml)+H O (2.5 ml), PCO=30 bar,
2
T=170°C, for 3 h. (b) 6 (12.9 mg, 0.051 mmol), 7 (14.4
−
3
mg, 0.051 mmol), Pd(TMB)2 (1.1 mg, 2.54×10
mmol), TMPhen (1.2 mg, 5.8×10
−
3
mmol), in toluene
References
(
20 ml), PCO=20 bar, T=100°C, for 2 h. Products
were analyzed by TLC (aluminum oxide 60 F254 (type
[
1] S. Cenini, F. Ragaini, Catalytic Reductive Carbonylation of
Organic Nitro Compounds, Kluwer, Dordrecht, 1997, Ch. 5 and
references therein.
E) Merck, 20 cm, eluant CH Cl /EtOH=99.5:0.5) by
2
2
comparison with authentic samples and by also taking
advantage of the distinctive fluorescence of the prod-
ucts when irradiated at 366 nm (violet for quinolines
and yellow–green for acylindoles). After the reaction
and TLC analysis, the solutions were dried in vacuo
and an EI mass spectrum of the resulting solids was
recorded, confirming in all cases the presence of all and
only the products observed by TLC (see Section 2). The
conversion of the nitroarene 6 was complete for the
reaction catalyzed by Ru (CO) , but not for the one
[2] For some more recent references, see: (a) B.C. S o¨ derberg, J.A.
Schriver, J. Org. Chem. 62 (1997) 5838. (b) E. Bolzacchini, R.
Lucini, S. Meinardi, M. Orlandi, B. Rindone, J. Mol. Catal. A
1
10 (1996) 227. (c) S. Tollari, S. Cenini, C. Crotti, E. Giannella,
J. Mol. Catal. 87 (1994) 203. (d) R. Annunziata, S. Cenini, G.
Palmisano, S. Tollari, Synth. Commun. 26 (1996) 495.
[3] F. Ragaini, S. Cenini, J. Mol. Catal. A, in press.
[
4] L.S. Hegedus, Angew. Chem. Int. Ed. Engl. 27 (1988) 1113 and
references therein.
5] (a) S. Cenini, F. Ragaini, Catalytic Reductive Carbonylation of
Organic Nitro Compounds, Kluwer, Dordrecht, 1997, Ch. 3 and
6 and references therein. (b) F. Ragaini, S. Cenini, J. Mol. Catal.
A 109 (1996) 1.
[
3
12
catalyzed by Pd(TMB) . Conversion of the amine 7 was
2
almost complete in both cases.

F. Ragaini et al. / Journal of Organometallic Chemistry 577 (1999) 283–291
291
[
[
[
6] S. Tollari, S. Cenini, C. Crotti, E. Giannella, J. Mol. Catal. 87
1994) 203.
7] F. Ragaini, S. Tollari, S. Cenini, E. Bettetini, J. Mol. Catal. A
11 (1996) 91.
8] (a) C. Crotti, S. Cenini, B. Rindone, S. Tollari, F. Demartin, J.
Chem. Soc. Chem. Commun. (1986) 784. (b) C. Crotti, S. Cenini,
R. Todeschini, S. Tollari, J. Chem. Soc. Faraday Trans. 87
[19] V.A. Maksakov, V.A. Ershova, J. Organomet. Chem. 485 (1995)
69.
(
[20] (a) S. Cenini, F. Ragaini, S. Tollari, D. Paone J. Am. Chem. Soc.
118 (1996) 11964. (b) F. Ragaini, S. Cenini, S. Tollari, G.
Tummolillo, R. Beltrami, Organometallics, in press.
[21] L. Garlaschelli, R. Della Pergola, S. Martinengo, Inorg. Synth.
28 (1990) 211.
1
(
1991) 2811.
9] S. Cenini, E. Bettetini, M. Fedele, S. Tollari, J. Mol. Catal. 111
1996) 37.
[22] C.R. Eady, P.F. Jackson, B.F.G. Johnson, J. Lewis, M.C.
Malatesta, M. McPartlin, W.J. Nelson, J. Chem. Soc. Dalton
Trans. (1980) 383.
[
(
[
[
10] For an example, see: R. van Asselt, C.J. Elsevier, W.J.J. Smeets,
A.L. Spek, R. Benedix, Recl. Trav. Pays Bas 113 (1994) 88.
11] (a) M. Akazome, T. Kondo, Y. Watanabe, Chem. Lett. (1992)
[23] S. Cenini, F. Ragaini, M. Pizzotti, F. Porta, G. Mestroni, E.
Alessio, J. Mol. Catal. 64 (1991) 179.
[24] D.H. Wadsworth, O.E. Schupp III, E.J. Seus, J.A. Ford Jr., J.
Org. Chem. 30 (1965) 680.
7
5
69. (b) M. Akazome, T. Kondo, Y. Watanabe, J. Org. Chem.
9 (1994) 3375. (c) M. Akazome, T. Kondo, Y. Watanabe, J.
[25] (a) D.F. DeTar, Y.-W. Chu, J. Am. Chem. Soc. 76 (1954) 1686.
(b) D.F. DeTar, L.A. Carpino, J. Am. Chem. Soc. 78 (1956) 475.
[26] (a) R.L. Augustine, A.J. Gustavsen, S.F. Wanat, I.C. Pattison,
K.S. Houghton, G. Koletar, J. Org. Chem. 38 (1973) 3004. (b) I.
Tanasescu, A. Baciu, Bull. Soc. Chim. Fr. 4 (1937) 1742.
[27] T.F. Dankova, T.N. Bokova, N.A. Preobrazhenskii, A.E.
Petrushchenko, I.A. Il’shtein, N.I. Shvetsov, Zhur. Obshchei
Khim. 21 (1951) 787 [Chem. Abstr. 45 (1951) 9518].
[28] H.S. Mertha, K.B.L. Mathur, J. Indian. Chem. Soc. 33 (1956)
618.
[29] J.A. Donnelly, D.F. Farrel, J. Org. Chem. 55 (1990) 1757.
[30] R.J. Sundberg, L.-S. Lin, D.E. Blackburn, J. Heteroc. Chem. 6
(1969) 441.
[31] Ng.Ph. Buu-Hoi, P. Cagniant, Recl. Trav. Chim. 64 (1945) 214.
[32] S. Torii, H. Okumoto, L.H. Xu, M. Sadakane, M.V.
Shostakovsky, A.B. Ponomaryov, V.N. Kalinin, Tetrahedron 49
(1993) 6773.
Org. Chem. 58 (1993) 310. (d) Y. Watanabe, J. Yamamoto, M.
Akazome, T. Kondo, T. Mitsudo, J. Org. Chem. 60 (1995) 8328.
(
e) A.F.M. Iqbal, Helv. Chim. Acta. 55 (1972) 798. (f) A.F.M.
Iqbal, J. Org. Chem. 37 (1972) 2791. (g) A.F.M. Iqbal, Chemtech
1974) 566.
(
[
[
12] Y. Watanabe, K. Takatsuki, S.C. Shim, T. Mitsudo, Y.
Takegami, Bull. Chem. Soc. Jpn. 51 (1978) 3397.
13] (a) S. Tollari, S. Cenini, F. Ragaini, L. Cassar, J. Chem. Soc.
Chem. Commun. (1994) 1741. (b) R. Annunziata, S. Cenini, G.
Palmisano, S. Tollari, Synth. Commun. 26 (1996) 495.
14] A. Bassoli, S. Cenini, F. Farina, M. Orlandi, B. Rindone, J. Mol.
Catal. 89 (1994) 121.
15] J.J. Tufariello, in: A. Padwa (Ed.), Nitrones, in 1,3-Dipolar
Cycloaddition Chemistry, vol. 2, Wiley, New York, 1984.
16] F. Porta, M. Pizzotti, S. Cenini, J. Organomet. Chem. 222 (1981)
[
[
[
2
79.
[
[
17] M. Johannsen, K.A. Jørgensen, Chem. Rev. 98 (1998) 1689.
18] A. Penoni, S. Tollari, S. Cenini, in preparation.
[33] F. Ragaini, S. Cenini, F. Demartin, Organometallics 13 (1994)
1178.
.