Reactions of o-iodohalobenzenes with carbanions of aromatic ketones. Synthesis of 1-aryl-2-(o-halophenyl)ethanones

Article abstract of DOI:10.1039/b201692c

o-Iodohalobenzenes (X = I, Br, Cl) react in DMSO with the enolate ions of acetophenone, propiophenone and 1-(2-naphthyl)ethanone to afford mainly monosubstitution with retention of one halogen. The monosubstituted dehalogenated compounds are formed in low overall yields in the reactions of o-diiodobenzene with the carbanions of 1-(2-naphthyl)ethanone and of acetophenone and in the reaction of o-bromoiodobenzene with the carbanion of propiophenone. The reactions can be performed in the dark, with usually increased yields of substitution under irradiation, as well as under FeBr₂ initiation. Treatment of 2-(2-bromophenyl)-1-phenylethanone with Cu bronze affords the ring closure benzofuran product. The degree of dehalogenation is discussed in terms of the energetics of the intramolecular electron transfer (ET) from the ArCO-π system to the C-halogen σ bond in the monosubstituted radical anions proposed as intermediates. The lack of ring closure of the radicals formed by dehalogenation of these radical anions is analyzed in terms of geometric factors.

Full text of DOI:10.1039/b201692c

View Article Online / Journal Homepage / Table of Contents for this issue
Reactions of o-iodohalobenzenes with carbanions of aromatic
ketones. Synthesis of 1-aryl-2-(o-halophenyl)ethanones
María T. Baumgartner, Liliana B. Jiménez, Adriana B. Pierini* and Roberto A. Rossi*
2
INFIQC, Departamento de Química Orgánica, Facultad de Ciencias Químicas,
Universidad Nacional de Córdoba, Ciudad Universitaria, 5000 – Córdoba, Argentina
Received (in Cambridge, UK) 18th February 2002, Accepted 2nd April 2002
First published as an Advance Article on the web 26th April 2002
o-Iodohalobenzenes (X = I, Br, Cl) react in DMSO with the enolate ions of acetophenone, propiophenone and
1-(2-naphthyl)ethanone to afford mainly monosubstitution with retention of one halogen. The monosubstituted
dehalogenated compounds are formed in low overall yields in the reactions of o-diiodobenzene with the carbanions
of 1-(2-naphthyl)ethanone and of acetophenone and in the reaction of o-bromoiodobenzene with the carbanion
of propiophenone. The reactions can be performed in the dark, with usually increased yields of substitution under
irradiation, as well as under FeBr2 initiation. Treatment of 2-(2-bromophenyl)-1-phenylethanone with Cu bronze
affords the ring closure benzofuran product. The degree of dehalogenation is discussed in terms of the energetics of
the intramolecular electron transfer (ET) from the ArCO-π system to the C–halogen σ bond in the monosubstituted
radical anions proposed as intermediates. The lack of ring closure of the radicals formed by dehalogenation of these
radical anions is analyzed in terms of geometric factors.
The aromatic radical nucleophilic substitution, or SRN1 reac-
tion, has been shown to be an excellent route to perform the
nucleophilic substitution of unactivated aromatic compounds
with suitable leaving groups.1 Although the carbanions of ali-
phatic ketones are efficient nucleophiles in these reactions, the
enolates of aromatic ketones as the anion of acetophenone2
and derivatives3 have a low reactivity toward halobenzenes or
halonaphthalenes under irradiation in liquid ammonia. The
heteroarylation of the enolate of acetophenone is possible in
this solvent under irradiation4,5 and even in the dark,6 but with
π-electron deficient heteroaromatic halides and with aryl diazo-
sulfides.7 However, phenylation by phenyl halides has succeeded
under photoinitiation in DMSO.8 The difference in reactivity
between enolate anions of aromatic and aliphatic ketones
toward phenyl halides in liquid ammonia has been attributed to
the lower efficiency of the former in the photoinitiated electron
transfer (ET) step of the proposed mechanism.8,9
In the reaction of o-dibromobenzene with the enolate ion of
pinacolone, mainly disubstitution (62%) is obtained.10 When
the reaction is performed with the anion of acetone, cyclic
compounds from an aldol condensation of the disubstitution
product are formed (≈64%).10 In this reaction, it is proposed
that the o-bromophenyl radical 1, formed by fragmentation of
the radical anion of o-dibromobenzene, couples with the nucleo-
phile to afford the monosubstituted radical anion 2 [eqn. (1)].
This intermediate can fragment at the second C–Br bond to
give radical 3, which is able to react with the nucleophile to
form the radical anion of the disubstitution product 4 [eqn. (2)].
The C–halogen fragmentation of radical anion 2 depends
mainly on the type of halide and nucleophilic moieties present
as well as on their relative position in the phenyl ring.1 We
consider the study of the preferred reaction path followed by
o-iodohaloarenes with enolate ions of aromatic ketones 5 to
be of interest. In this system intermediate 6 could be formed
[eqn. (3)].
(3)
Monosubstitution with retention of halide will be obtained if
the fragmentation reaction of the C–halogen bond of this
intermediate is not favoured. On the other hand, if the bond
does fragment, radical 7 will be formed [eqn. (4)]. This radical
can couple with the nucleophile to afford disubstitution (a
probably unfavourable reaction due to steric constraints in the
case of aromatic enolates). Another possibility for radical 7 is
to form the reduced product by hydrogen abstraction from the
solvent or, more interestingly, to be trapped by the aryl ring of
the nucleophilic moiety to afford finally the cyclized product 9
[eqn. (4)].
(1)
(2)
(4)
1092
J. Chem. Soc., Perkin Trans. 2, 2002, 1092–1097
This journal is © The Royal Society of Chemistry 2002
DOI: 10.1039/b201692c

View Article Online
The SRN1 mechanism offers the possibility to obtain ring
closure compounds by trapping of the radicals, formed along
the propagation cycle, with adequate reactive centers.1 For
example, in the reaction of the radical probe o-(but-3-enyl-
oxy)iodobenzene 10 with different nucleophiles, both the
cyclized and straightforward substitution products were formed
in yields that depend on the nucleophile used. For instance, the
reaction with PhSϪ ions gave 11 (Nu = SPh) and 12 (Nu = SPh)
in 76 and 6% yields, respectively [eqn. (5)].11
The substitution of 15b can be achieved in the dark (Table 1,
expt. 5); similar behavior has previously been reported for the
reaction of some ketone enolate ions with good electron
acceptors aromatic halides, either in DMSO or in liquid
ammonia.17 Both the photoinitiated and the dark reactions
are inhibited by p-dinitrobenzene (p-DNB), a well known
scavenger of the SRN1 mechanism (Table 1, expts. 4, 6).
The monosubstituted dehalogenated compound 18 is not
formed in the reaction with 15a,b but it is obtained in 17% yield
with 15c (Table 1, expt. 7). Fig. 1 shows the results afforded by
(5)
Formation of compound 11 is ascribed to the trapping of the
aryl radical by the double bond of the but-3-enyloxy chain to
afford a cyclic primary alkyl radical which by reaction with
PhSϪ finally yields 11 (Nu = PhS).
Another known process is the trapping of the radical centre
by the π-system of an aromatic ring.12 For example, o-dihalo-
benzenes react with naphthalene-2-thiolate ions 13 to give the
cyclic product 14 as indicated in eqn. (6).13,14
Fig. 1 Product and substrate relationship obtained by sampling the
reaction of 16 with 15c at different irradiation times. PhI (᭿); 15c (᭺);
17c (᭹); 18 (ꢀ).
(6)
sampling the reaction at different irradiation times. As can be
seen from Fig. 1 both compounds 17c and 18 are formed simul-
taneously, indicating that 17c is not an intermediate in the
formation of 18.
In order to determine the preferred path followed in our
system, mainly focused on the possibility of achieving the
synthesis of cyclic compounds of type 9, we studied the
reaction of the enolates of acetophenone, propiophenone and
1-(2-naphthyl)ethanone with o-iodohalobenzenes in DMSO.
Theoretical calculations to elucidate the reactivity of the radical
anions proposed as intermediates as well as the geometric prop-
erties of the monosubstituted dehalogenated radicals formed
under our experimental conditions are presented at the UHF/
AM1 level.
The product distribution of the latter reaction varies with the
nucleophile : substrate ratio (Table 1, expts. 7, 8). Under shorter
irradiation times and with a 5-fold excess of nucleophile, the
percentage of 18 increases to 31% accompanied by 47% of 17c
(Table 1, expt. 8). On the other hand, only traces of 18 are
formed when the reaction of 16 with 15c is initiated with FeBr2;
the main product being 17c (65% yield, Table 1, expt. 9).
Acetophenone and propiophenone enolate ions
In the photoinitiated reaction of the enolate ion of aceto-
phenone (19) with o-bromoiodobenzene (15b), the mono-
substituted compound with retention of bromine 20b is formed
uncontaminated by the monosubstituted dehalogenated prod-
uct 21 (Table 1, expt. 10) [eqn. (8)]. The percentage of 20b
increases when a 6-fold excess of 19 is employed (76–88%) but
not under FeBr2 initiation (Table 1, expts. 11–13).
Results
Enolate ions of 1-(2-naphthyl)ethanone (16)
It is known that the enolate ion 16 reacts with iodobenzene in
DMSO under irradiation15 (for the results obtained under
our experimental conditions see Table 1, expt. 1), or FeCl2
initiation16 to afford 1-(2-naphthyl)-2-phenylethanone. In the
photoinitiated reaction of 16 with 15a–c, the substitution
products with retention of halogen 17a–c were obtained (71, 86
and 50% yields respectively) [eqn. (7), Table 1, expts. 2, 3, 7].
(8)
On the other hand, 20c and 21 are formed in the reaction
of 19 with o-diiodobenzene (15c) after 60 min of irradiation
(Table 1, expt. 14). The ratio 20c : 21 remains constant as shown
by sampling the reaction at different irradiation times (Fig. 2).
It is known that 20b reacts in DME with Cu (activated
copper bronze)18 to give the cyclic product 2-phenylbenzofuran
22. In order to obtain this compound we performed the reac-
tion of 15b with 19 in DMSO. After 60 min of irradiation Cu
was added and after 24 h at 50 ЊC, 20b was the only product
obtained (Table 1, expt. 12). Even though this one-pot approach
(7)
J. Chem. Soc., Perkin Trans. 2, 2002, 1092–1097
1093

View Article Online
Table 1 Photostimulateda reaction of o-dihalobenzene with carbanions in DMSO
Expt.
Substrate (103 M)
NuϪ (103 M)
t-BuOK/103 M
Yb
ArXc
NuArc
80
NuArXc
1
2
C6H5I (36)
16 (145)
16 (143)
16 (156)
16 (66)
162
156
170
77
75
67
128
142
209
90
245
323
263
332
199
610
550
75
o-C6H4ClI (41)
o-C6H4BrI (39)
o-C6H4BrI (27)
o-C6H4BrI (21)
o-C6H4BrI (21)
o-C6H4I2 (26)
I = 90
I = 81
I = 65
I = 53
I < 10
155
Nq
X = Cl, 71
X = Br, 86
X = Br, 33
X = Br, 31
3
X = Br, <1
X = Br, 31
X = Br, 24
4d
5e
16 (58)
6e, f
7
16 (61)
16 (69)
X = I, 1
X = I, 1
17
31
1
X = I, 50
X = I, 47
X = I, 65
X = Br, 44
X = Br, 76
X = Br, 88
X = Br, 54
X = I, 19
X = Br, 59
X = Br, 48
X = Br, 35
8g
o-C6H4I2 (19)
o-C6H4I2 (26)
16 (96)
135
9h
16 (159)
19 (75)
10
11i
12j, k
13h
14j
15g
16l
17e
o-C6H4BrI (39)
o-C6H4BrI (39)
o-C6H4BrI (34)
o-C6H4BrI (34)
o-C6H4I2 (26)
1-Br-2-IC10H6 (20)
o-C6H4BrI (50.6)
o-C6H4BrI (50.6)
X = Br, 15
X = Br, 14
19 (217)
19 (202)
19 (202)
19 (230)
19 (173)
26 (500)
26 (500)
I = 89
181
25
20
10
9
X = Br, 2
X = Br, 25
X = Br, 11
—
I = 100
Br = 10
I = 86
Br = 5
I = 100
Br = 21
18m
19
o-C6H4BrI (52.0)
o-C6H4BrI (50.6)
26 (520)
26 (500)
572
600
X = Br, 34
X = Br, 44
4
X = Br, 46
X = Br, 2
28
a Irradiation time = 180 min, unless otherwise indicated. b Percentage of halogen quantified potentiometrically on the basis of the substrate
concentration. c Quantified by GLC using the internal standard method. d p-Dinitrobenzene (38 mol%). e Dark reaction. f p-Dinitrobenzene
(48 mol%). g Irradiation time = 120 min. h FeBr2 (80 mol%). Reaction time = 30 min. i Irradiation time = 90 min. j Irradiation time = 60 min.
k After irradiation Cu = 2.24 mmol (220 mol%) was added and the reaction heated at 50 ЊC for 24 h. l FeBr2 (90 mol%). Reaction time = 90 min.
m Irradiation time = 30 min.
The enolate ion of propiophenone (26) reacts with 15b under
FeBr2 initiation to afford PhBr (25%), 27b (48%) and 28 (10%)
[eqn. (11), Table 1, expt. 16]. A similar product distribution is
(11)
obtained when the dark reaction is performed in the absence of
FeBr2 as well as under short irradiation times (30 min) (Table 1,
expts. 17, 18).
Sampling of the irradiated reaction at different reaction
times shows that the concentration of 28 increases to 28% after
3 h. Moreover, when 27b is treated with excess t-BuOK under
irradiation (60 min) in the presence of the enolate ion 26,
compound 28 is formed (14%). Thus, the anion of the halo-
monosubstituted product, formed in the basic medium can
account for approximately 14% of the formation of 28 but only
after prolonged irradiation times. This pathway has been dis-
regarded on experimental grounds for the bromo derivative
20b.19
Fig. 2 Product and substrate relationship obtained by sampling the
reaction of 19 with 15c at different irradiation times. PhI (᭿); 15c (᭺);
20c (᭹); 21 (ꢀ).
failed, compound 22 was obtained in 62% yield after treatment
of 20b, an isolated sample, with copper bronze [eqn. (9)] in
(9)
Discussion
DME. Compound 22 is also obtained although in low yields
(10%) by irradiation of 20b in DMSO (λmax = 253 nm, 60 min).
The monosubstituted 24 and monosubstituted-dehalogen-
ated 25 are formed by reaction of 1-bromo-2-iodonaphthalene
(23) with 19 (59 and 20% yield respectively) [eqn. (10)], Table 1,
expt. 15).
The mechanism of formation of the monosubstituted com-
pounds 17, 20 and 27b is straightforward. Once 15 receives an
electron, the radical anion formed fragments at the C–I bond to
afford radicals 1 which can be reduced to the halobenzene
(5–15% by reaction with anions 16 or 19 and 25–34% with
anion 26) or can couple with the enolates of the aromatic
Ϫ
ketones to give the monosubstituted radical anions 17Ϫ , 20
ؒ
ؒ
or 27bϪ . It is known that the radical–nucleophile coupling
reaction competes with the radical–hydrogen atom abstraction
from enolate ions bearing β-hydrogens.20 This explains the high
yields of PhBr formed with anion 26. Similarly, PhBr (93%)
and traces of substitution product are formed in the irradiated
ؒ
(10)
1094
J. Chem. Soc., Perkin Trans. 2, 2002, 1092–1097

View Article Online
Ϫ
Ϫ
Ϫ
Table 2 AM1 calculated heats of formation and C–X bond lengths for radical anions 17Ϫ , 20 , 27b and 24
ؒ
ؒ
ؒ
ؒ
r(C–X)/Å
RAπ
∆fH/kcal molϪ1
Radical anion (RA)
X
RAσ
RAπ
RAσ
∆Eσ–π/kcal molϪ1
Cl
Br
I
1.710
1.883
2.030
1.989
2.077
2.167
Ϫ9.6
2.5
13.4
12.0
14.9
22.9
21.6
12.4
8.8
Br
I
1.883
2.029
2.078
2.169
Ϫ8.7
2.8
Ϫ1.4
6.1
7.3
3.6
Br
Br
1.886
1.888
2.078
2.065
Ϫ9.77
Ϫ4.0
5.8
3.6
9.1
12.7
reaction of the enolate ion of isobutyrophenone with o-bromo-
iodobenzene (15b) and in the reaction of the carbanion derived
from 21 with o-diiodobenzene (6% of 1,2,2-triphenylethanone
and ≅50% of PhI).
The radical anions formed in the coupling afford the mono-
substituted compounds 17, 20 or 27b by ET to the substrate
[eqn. (12)] or can fragment at the C–halogen bond to afford
radicals 29 [eqn. (13)].
system, for example Ar = 2-naphthyl, to the σ C–halogen bond
of the 2-halophenyl substituent is favoured in the order Cl < Br
< I. When X = I, the intra-ET is more favourable for 20cϪ
ؒ
(Ar = PhCO) than for 17cϪ (Ar = 2-naphthylCO) (Table 2), in
ؒ
agreement with the experimental findings. According to our
calculations, the intra-ET from the 2-naphthylCO to the
2-iodophenyl moieties in 17cϪ and the intra-ET from the
ؒ
PhCO to the 2-bromophenyl moieties in 20bϪ have similar
ؒ
thermodynamics but the reaction was experimentally observed
only for X = I.
In the case of the bromo derivatives formed by coupling with
the enolates of propiophenone and acetophenone, both the
experimental results and the theoretical thermodynamics show
Ϫ
a slightly favoured intra-ET for 27bϪ with respect to 20b The
ؒ
ؒ
(12)
(13)
studies also indicate that the intra-ET is possible in 24Ϫ , that is,
ؒ
from the PhCO moiety to the C–Br bond of the 2-bromo-
naphthyl system, as indicated by the formation of 25 in
the reaction of 19 with 23 [eqn. (14)]. In intermediate 24Ϫ the
ؒ
(14)
Based on our experimental results, the intermolecular ET
[eqn. (12)] is the main reaction of all the radical anions formed.
The fragmentation of the C–X bond [eqn. (13)] is only in play
Ϫ
Ϫ
for intermediates 17cϪ , 20c (X = I, R = H) and 27b (R =
ؒ
ؒ
ؒ
electron affinity of the bromoaryl acceptor moiety is increased
Me,
X = Br) as indicated by the formation of the
with respect to that of the bromophenyl system of 20bϪ due to
ؒ
monosubstituted-reduced products.
Table 2 lists the heats of formation and electronic properties
the presence of the naphthyl π-system.
of radical anions 17Ϫ , 20 , and 27b , determined theoretic-
ally with the semiempirical AM1/UHF method as implemented
in AMPAC.21,22 In agreement with previous reports, these
intermediates display π–σ electronic isomerism;23,24 the
unpaired spin distribution in the most stable radical anions is
localized in the π-system of the arylcarbonyl group, which is
separated from the o-haloaryl moiety by an sp3 carbon atom.
The energy difference between the π and the σ species, which
has an elongated C–halogen bond in which the unpaired elec-
tron is located,25 has been proposed as an indication of the
feasibility of the intra-ET reaction between both electronic
systems and thus of the relative order of their fragmentation
rates.23b,c
The main difference between the intermediates formed by
coupling of radical 1 with enolates of aromatic and aliphatic
ketones [eqn. (1)] is that while in the former the most stable
radical anions have the unpaired spin at the π ArCO system, in
Ϫ
Ϫ
ؒ
ؒ
ؒ
the latter, for example in the case of 2Ϫ [eqn. (1), R = C(Me)3],
ؒ
the unpaired spin is located at the phenyl ring of the 2-bromo-
phenyl moiety, which is more stable than the π-system of the
C᎐O group. This radical anion behaves more like a bromo-
᎐
benzene radical anion which has been determined to fragment
with a rate close to diffusion.26
Another result to point out is that the radicals 29 and 30
formed by fragmentation of the C–X bond [eqns. (13), (14)]
neither react further with the nucleophile to afford disubstitu-
tion nor are trapped by the aromatic ring or the oxyanion centre
to afford cyclic compounds.
As can be seen from the values of ∆fHσ–π presented in Table 2,
in these radical anions the intra-ET from a given π arylcarbonyl
J. Chem. Soc., Perkin Trans. 2, 2002, 1092–1097
1095

View Article Online
The conformational potential surface of these radicals was
determined as a function of the main dihedral angles C4–C3–
C2–C1 and C3–C2–C1–C5 as indicated in Fig. 3.
performed with a Kügelrohr apparatus. Irradiation was per-
formed in a reactor equipped with two 400 W lamps with
maximum emission at 350 nm (Philips Model HPT, air- and
water-cooled). Potentiometric titration of halide ions was per-
formed with a pH meter using an Ag/Agϩ electrode. Melting
points were not corrected.
Materials
Potassium tert-butoxide, o-diiodobenzene, o-bromoiodo-
benzene, o-bromochlorobenzene and propiophenone were
commercially available and used as received. DMSO was dis-
tilled under vacuum and stored under molecular sieves (4 Å).
1-Bromo-2-iodonaphthalene was prepared by reaction of
potassium iodide with 2-bromonaphthalene-l-diazonium salt as
described elsewhere.28 Acetone and acetophenone were distilled
and stored on molecular sieve (4 Å). 1-(2-Naphthyl)ethanone
was recrystallized from petroleum ether.29
Fig. 3 AM1/UHF most stable conformation of the radicals formed by
C–halogen cleavage of the radical anion intermediates.
Photostimulated reaction of enolate ions of 1-(2-naphthyl)-
ethanone (16) with o-diiodobenzene
Four conformers were located as minima on the potential
surface, the most stable being in all cases the conformer shown
in Fig. 3 and this is taken as representative. In this conformer
the radical centre is twisted from the π molecular plane of the
enolate system. Furthermore, the C4–C6 distance (3.6–3.7Å) is
slightly longer than the distance of 2.97 Å calculated between
the reacting centres that afford compound 14 [eqn. (6)]. This
geometrical disposition could be one of the factors that kinet-
ically disfavours the trapping of the radical centre by the aro-
matic ring of the ketone moiety and thus the ring closure
reaction.
The following procedure is representative. The reactions were
carried out in a 100 mL three-necked round-bottomed flask
equipped with a nitrogen inlet and magnetic stirrer. To 40 mL
of dry and degassed DMSO under nitrogen were added
8.0 mmol of potassium tert-butoxide and 4.8 mmol of 16. After
15 min o-diiodobenzene (1.5 mmol) was added and the reaction
mixture was irradiated for 180 min. The reaction was quenched
with an excess of ammonium nitrate and water (120 mL). The
mixture was extracted twice with methylene chloride (40 mL),
the organic extract was washed twice with water, dried, and
quantified by GLC. The iodide ions in the aqueous solution
were determined potentiometrically.
The solvent was removed under reduced pressure. The resi-
due after column chromatography on silica gel [petroleum
ether–diethyl ether (95 : 5)] gave 2-phenyl-1-(2-naphthyl)-
ethanone (18) [mp 98–99 ЊC (lit.30 mp. 99–99.5 ЊC). νmax/cmϪ1
1677 (CO). δH 2.35 (2H, s, CH2), 7.0–8.2 (12H, m)] and 2-(2-
iodophenyl)-1-(2-naphthyl)ethanone (17c) contaminated with
nucleophile. This mixture was distilled under reduced pressure
in the Kügelrohr.
Conclusions
We have determined experimentally that the main reaction
pathway followed by the enolates of the aromatic ketones aceto-
phenone, propiophenone and 1-(2-naphthyl)ethanone with
o-iodohalobenzenes in DMSO under ET conditions is mono-
substitution with halide retention. Even though the mono-
substituted dehalogenated radicals are formed mainly by
reaction with o-diiodobenzene, these radicals do not react with
the aromatic ring of the ketone to afford ring closure products.
The results reported present an unexpected behaviour for
o-dihalobenzenes for which the most common reaction under
SRN1 conditions is usually disubstitution or monosubstitution
with dehalogenation. The reactions here presented are thus an
interesting route to 1-aryl-2-(o-haloaryl)ethanones which can
be converted to 2-substituted benzofuran derivatives by treat-
ment with Cu bronze as shown for 20b or under catalysis by
other transition metals.27
2-(2-Iodophenyl)-1-(2-naphthyl)ethanone (17c). Found: Mϩ,
372.0020. C18H13IO requires 372.0011. νmax/cmϪ11683 (CO).
δH 4.6 (2H, s, CH2); 6.9–7.1 (1H, m); 7.2–7.7 (5H, m); 7.8–8.2
(4H, m); 8.6 (1H, s). m/z 372 (Mϩ, 2%), 332 (2), 331 (2), 247
(0.2), 246 (33), 245 (11), 157 (1), 156 (13), 155 (100), 128 (3), 127
(22).
2-(2-Bromophenyl)-1-(2-naphthyl)ethanone (17b). Mp 113–
114 ЊC. Found: Mϩ, 324.0153 and 326.0134. C18H13BrO
requires 324.0150. νmax/cmϪ11683 (CO). δH 4.6 (2H, s, CH2);
7.1–7.7 (6H, m); 7.8–8.2 (4H, m); 8.6 (1H, s). m/z 327 (0.4), 326
(Mϩ, 1.4%), 325 (0.4), 324 (Mϩ, 1.5), 246 (1), 245 (3), 157 (1),
156 (12), 155 (100), 128 (2), 127 (22).
Experimental
General
1H NMR and 13C NMR spectra were recorded on a Bruker
200 MHz nuclear magnetic resonance spectrometer with CDCl3
as solvent. Infrared spectra were recorded on a Nicolet FTIR
5-SXC spectrophotometer. Gas chromatographic analyses were
performed on a Hewlett Packard 5890 Series II with a flame-
ionization detector and the data system Hewlett Packard 3396
Series II integrator, on a HP-1 capillary column (methyl
silicone, 10 m × 0.53 mm × 2.65 µm film thickness). The
GC-MS analyses were carried out on a Shimadzu GC-MS QP
5050 spectrometer, employing a 30 m × 0.12 mm DB-5 MS
column. HRMS spectra were recorded at the Microanalysis
Service and the Mass Spectrometry Laboratory of the Centro
de Investigación y Desarrollo (C.I.D.), C.S.I.C., Barcelona,
Spain. Column chromatography was performed on silica gel
(70–270 mesh ASTM). The distillation at reduced pressure was
2-(2-Chlorophenyl)-1-(2-naphthyl)ethanone (17a). mp 109–
110 ЊC. Found: Mϩ, 280.0652 and 282.0637. C18H13ClO requires
280.0655. νmax/cmϪ1 1683 (CO). δH 4.6 (2H, s, CH2); 7.1–7.7
(6H, m); 7.8–8.2 (4H, m); 8.6 (1H, s). m/z 283 (0.3), 282 (Mϩ,
1.3%), 281 (0.8), 280 (Mϩ, 3.1), 247 (0.3), 246 (0.5), 245 (2), 157
(1), 156 (13), 155 (100), 128 (3), 127 (25).
2-(2-Bromophenyl)-1-phenylethanone (20b). Mp 68–69 ЊC
(lit.31 69.5–70 ЊC). νmax/cmϪ11683 (CO). δH 4.5 (2H, s, CH2); 7.0–
7.7 (7H, m); 7.95–8.15 (2H, m). m/z 196 (1), 195 (M Ϫ Br, 15%),
106 (8), 105 (100), 89 (8), 78 (3), 77 (51).
2-(2-Iodophenyl)-1-phenylethanone (20c). νmax/cmϪ11683
(CO). δH 4.5 (2H, s, CH2); 6.9–7.95 (7H, m); 8–8.15 (2H, m).
1096
J. Chem. Soc., Perkin Trans. 2, 2002, 1092–1097

View Article Online
7 (a) C. Dell’Erba, M. Novi, G. Petrillo and C. Tavani, Tetrahedron,
m/z 196 (4), 195 (M Ϫ I, 29%), 106 (8), 105 (100), 89 (8), 78 (3),
77 (51).
1993, 49, 235; (b) C. Dell’Erba, M. Novi, G. Petrillo and C. Tavani,
Tetrahedron, 1992, 48, 325; (c) C. Dell’Erba, M. Novi, G. Petrillo
and C. Tavani, Tetrahedron, 1994, 50, 11239.
8 G. L. Borosky, A. B. Pierini and R. A. Rossi, J. Org. Chem., 1992, 57,
247.
9 M. T. Baumgartner, M. H. Gallego and A. B. Pierini, J. Org. Chem.,
1998, 63, 6394.
2-Phenylbenzofuran (22).32 Prepared following the procedure
described elsewhere.18 δH 7.04 (1H, s); 7.22–7.61 (7H, m); 7.87
(2H, m).
2-(2-Naphthyl)-1-phenylethanone (25).33 Mp 117–118 ЊC.
νmax/cmϪ11689 (CO). δH 4.48 (2H, s, CH2); 7.35–7.60 (6H, m);
7.70–7.85 (4H, m); 8.02–8.10 (2H, m). m/z 247 (1.4), 246 (Mϩ,
8.8%), 141 (11), 139 (5), 116 (1), 115 (17), 106 (7), 105 (100), 78
(2), 77 (35). Compared with an authentic sample prepared by
photostimulated reaction of the anion of acetophenone with
2-iodonaphthalene in DMSO.
10 J. F. Bunnett and P. Singh, J. Org. Chem., 1981, 46, 5022.
11 A. L. J. Beckwith and S. M. Palacios, J. Phys. Org. Chem., 1991, 4,
404.
12 (a) M. Novi, C. Dell’Erba, G. Garbarino and F. Sancassan,
J. Org. Chem., 1982, 47, 2292; (b) M. Novi, G. Garbarino and
C. Dell’Erba, J. Org. Chem., 1984, 49, 2799; (c) M. Novi,
C. Dell’Erba and G. Garbarino, J. Chem. Soc., Perkin Trans. 2, 1984,
951; (d ) M. Novi, G. Garbarino, C. Dell’Erba and G. Petrillo,
J. Organomet. Chem., 1984, 1205; (e) A. Postigo and R. A. Rossi,
J. Chem. Soc., Perkin Trans. 2, 2000, 485.
13 M. T. Baumgartner, A. B. Pierini and R. A. Rossi, J. Org. Chem.,
1993, 58, 2593.
14 R. A. Rossi and M. T. Baumgartner, Synthesis of Heterocycles
by the SRN1 Mechanism, in Targets in Heterocyclic Systems,
eds. O. A. Attanasi and D. Spinelli, Rome, Soc. Chimica Italiana,
1999, Vol. 3, pp. 215–243.
15 R. Beugelmans, M. Bois-Choussy and Q. Tang, J. Org. Chem., 1987,
52, 3880.
16 C. Galli, P. Gentili and A. Guarnieri, Gazz. Chim. Ital., 1995, 125,
409.
17 (a) R. G. Scamehorn, J. M. Hardacre, J. M. Lukanich and L. R.
Sharpe, J. Org. Chem., 1984, 49, 4881; (b) R. G. Scamehorn and
J. F. Bunnett, J. Org. Chem., 1977, 42, 1449.
18 J. Grimshaw and N. Thompson, J. Chem. Soc., Chem. Commun.,
1987, 240.
2-(1-Bromo-2-naphthyl)-1-phenylethanone (24). Solid. Found:
Mϩ, 324.0137 and 326.0104. C18H13BrO requires 324.0150.
νmax/cmϪ1 1683 (CO). δH 4.71 (2H, s, CH2); 7.35 (1H, d); 7.45–
7.64 (6H, m); 7.77–7.85 (2H, m); 8.09 (2H, dd). m/z 246 (7.4),
245 (M Ϫ Br, 36.8%), 221 (2), 219 (3), 215 (3), 140 (16), 139
(24), 106 (7), 105 (100), 78 (4), 77 (44).
2-(2-Bromophenyl)-1-phenylpropanone (27b). Mp 49–50 ЊC.
δH 1.48 (3H, d, CH3); 5.11 (1H, q, CH); 7.1–7.6 (8H, m); 7.9
(1H, dd). δC 17.8 (Me), 47.0 (CH), 123.9 (C-Br), 128.1, 128.4,
128.5, 128.6, 132.9, 133.4 (q), 141.0 (q), 200.0 (CO). m/z 209 (M
Ϫ Br, 7%); 106 (8); 105 (100), 78 (4); 77 (37).
1,2-Diphenylpropanone (28). Mp 40–41 ЊC (lit. 50–52 ЊC).7a
δH 1.53 (3H, d, CH3); 4.68 (1H, q, CH); 7.1–7.6 (9H, m); 7.9
(1H, dd). δC 19.5 (Me), 47.9 (CH), 126.9, 127.8, 128.5, 128.8,
128.9, 132.7 (c), 141.5 (c), 200.3 (CO). m/z 210 (Mϩ, 2%), 106
(8), 105 (100), 78 (4), 77 (33).
19 The bromo derivative 20b is recovered unchanged after treatment
under the same experimental conditions.
20 (a) M. F. Semmelhack and T. M. Bargar, J. Org. Chem., 1977, 42,
1481; (b) J. F. Wolfe, M. P. Moon, M. C. Sleevi, J. F. Bunnett and
R. R. Bard, J. Org. Chem., 1978, 43, 1019; (c) A. E. Lukach, A. N.
Santiago and R. A. Rossi, J. Org. Chem., 1997, 62, 4262.
21 D. A. Liotard, E. F. Healy, J. M. Ruiz and M. J. S. Dewar, AMPAC
version 2.1, Quantum Chemistry Program Exchange, program 506,
QCPE Bull., 1989, 9, 123.
22 The geometries of stable species were calculated by minimizing the
energy with respect to all geometrical variables. All stationary points
were characterized by force constant calculations. See M. J. S. Dewar
and K. Narayanaswami, J. Am. Chem. Soc., 1964, 86, 2422.
23 (a) A. B. Pierini, J. S. Duca and M. T. Baumgartner, THEOCHEM,
1994, 311, 343; (b) A. B. Pierini and J. S. Duca, J. Chem. Soc., Perkin
Trans. 2, 1995, 1821; (c) A. B. Pierini, J. S. Duca and D. M. Vera,
J. Chem. Soc., Perkin Trans. 2, 1999, 1003.
Acknowledgements
This work was supported by the Agencia Córdoba Ciencia,
FONCYT, the Consejo Nacional de Investigaciones Científicas
y Técnicas (CONICET), Fundación Antorchas and SECYT,
Universidad Nacional de Córdoba, Argentina.
References
1 For reviews, see: (a) R. A. Rossi and R. H. de Rossi, Aromatic
24 M. J. S. Dewar, A. H. Pakiari and A. B. Pierini, J. Am. Chem. Soc.,
1982, 104, 3242.
Substitution by the SRN
1 Mechanism, ACS Monograph 178;
Washington, D.C., 1983; (b) R. K. Norris, Comp. Org. Synth., 1991,
4, 451; (c) R. A. Rossi, A. B. Pierini and A. B. Peñéñory, Recent
25 The charge and the unpaired spin distribution of the radical anions
follow the pattern previously informed. The procedure used to find π
and σ intermediates was that previously described (see refs. 23b and
24).
26 (a) C. Amatore, C. Combellas, J. Pinson, M. A. Oturan, S. Robveille,
J. M. Savéant and A. Thiebault, J. Am. Chem. Soc., 1985, 107, 4846;
(b) J. M. Savéant, Adv. Phys. Org. Chem., 1990, 26, 1.
27 Y. Terao, T. Satoh, M. Miura and M. Nomura, Bull. Chem. Soc.
Jpn., 1999, 72, 2345.
28 E. R. Ward and B. D. Pearson, J. Chem. Soc., 1959, 1678.
29 D. D. Perrín and W. L. Armarego, Purification of Laboratory
Chemicals, 3rd edn., Butterworth-Heinemann Ltd.; Oxford, 1994.
30 P. Ruggli and M. Reinert, Helv. Chim. Acta, 1926, 9, 67.
31 J. E. Mulvaney and L. J. Carr, J. Org. Chem., 1968, 33, 3286.
32 A. Füster and D. N. Jumbam, Tetrahedron, 1992, 48, 5991.
33 J. McEwen and K. Yates, J. Am. Chem. Soc., 1987, 109, 5800.
Advances in the SRN
1 Reaction of Organic Halides, in The
Chemistry of Functional Group, eds S. Patai and Z. Rappoport,
Wiley, Chichester, 1995, Suppl. D2, Ch. 24, 1395–1485; (d ) R. A.
Rossi, A. B. Pierini and A. N. Santiago, Aromatic Substitution by
the SRN1 Reaction, in Organic Reactions, eds. L. A. Paquette and
R. Bittman, Wiley, New York, 1999, Vol. 54, pp. 1–271.
2 J. F. Bunnett and J. E. Sundberg, J. Org. Chem., 1976, 41, 1702.
3 R. Beugelmans, M. Bois-Choussy and Q. Tang, Tetrahedron, 1989,
45, 4203.
4 E. A. Oostvee and H. C. V. Plas, Recl. Trav. Chim. Pays-Bas, 1979,
98, 441.
5 V. Nair and S. D. Chamberlain, J. Am. Chem. Soc., 1985, 107, 2183.
6 D. R. Carver, A. P. Komin, J. S. Hubbard and J. F. Wolfe, J. Org.
Chem., 1981, 46, 294.
J. Chem. Soc., Perkin Trans. 2, 2002, 1092–1097
1097