Photochemical generation and reactivity of naphthyl cations: cine substitution

Article abstract of DOI:10.1002/ejoc.200700338

The photochemical solvolyses of naphthalen-1-yl(phenyl)-iodonium tetrafluoroborate and naphthalen-2-yl(phenyl)-iodonium tetrafluoroborate in methanol regiospecifically yield the naphthalen-1- and -2-yl ethers but afford scrambled 1- and 2-phenylnaphthalene Friedel-Crafts products. It is demonstrated that singlet naphthyl cations account for the formation of the naphthyl ethers, but that the cine substitution is most likely to be due to the intermediacy of triplet naphthyl cations. According to the experiments reported here, the singlet naphthyl cations are lower in energy than their triplet isomers. High-level MO calculations for the cations in methanol support this finding. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejoc.200700338

FULL PAPER
DOI: 10.1002/ejoc.200700338
Photochemical Generation and Reactivity of Naphthyl Cations:
cine Substitution
Micha Slegt,[a] Floor Minne,[a] Han Zuilhof,[b] Hermen S. Overkleeft,[a] and
Gerrit Lodder*[a]
Keywords: Photochemistry / Naphthyl cations / Spin multiplicity / cine substitution / Ab initio calculations
The photochemical solvolyses of naphthalen-1-yl(phenyl)-
iodonium tetrafluoroborate and naphthalen-2-yl(phenyl)-
iodonium tetrafluoroborate in methanol regiospecifically
yield the naphthalen-1- and -2-yl ethers but afford scrambled
1- and 2-phenylnaphthalene Friedel–Crafts products. It is
demonstrated that singlet naphthyl cations account for the
formation of the naphthyl ethers, but that the cine substitu-
tion is most likely to be due to the intermediacy of triplet
naphthyl cations. According to the experiments reported
here, the singlet naphthyl cations are lower in energy than
their triplet isomers. High-level MO calculations for the cat-
ions in methanol support this finding.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
NH3 and – especially – H2 and D2 is the subject of many
reports.[5]
Introduction
Research on aryl cation intermediates in organic (photo)-
chemistry has focussed mainly on phenyl cations.[1] Theo-
retical and experimental studies have shown that substitu-
ents have pronounced effects on the natures (singlet or trip-
let), and thus on the reactivities, of phenyl cations.[2] Re-
cently, density functional theory (DFT) calculations on the
singlet–triplet energy gaps in the naphthalen-1- and -2-yl
cations and in the anthracen-9-yl cation examined the influ-
ence of a larger electronic framework on spin multiplicity.[3]
The unsubstituted phenyl cation possesses a singlet,
closed-shell π6σ0 structure. Phenyl cations substituted with
electron-donating substituents in their para positions prefer
open-shell π5σ1 structures, with triplet multiplicity.[2a]
The naphthalen-1-yl and naphthalen-2-yl cations can be
regarded as phenyl cations bearing electron-donating sub-
stituents. Also, their rigidities hamper the cations’ abilities
to adopt the distorted structures normally encountered for
singlet, closed-shell species. Both factors lower the singlet–
triplet energy gaps. In fact, the MO calculations in ref.[3]
indicate that the singlet and triplet forms of the naphthyl
cations have about the same energies.
Upon irradiation, vinyl iodonium salts efficiently yield
vinyl cations.[6] Likewise, diphenyliodonium salts, com-
monly used as photo-acid generators in lithography, release
phenyl cations upon photolysis.[7] It was therefore antici-
pated that photolysis of iodonium salts of polynuclear aro-
matic systems should provide the corresponding cations.
The photochemical generation of the naphthalen-1-yl cat-
ion (I1) and the naphthalen-2-yl cation (I2), from naph-
thalen-1-yl(phenyl)iodonium tetrafluoroborate (1) and
naphthalen-2-yl(phenyl)iodonium tetrafluoroborate (2),
respectively, and a study of their reactivities are presented
(Scheme 1). For reasons of comparison, naphthalen-1-
+
+
and -2-yldiazonium tetrafluoroborates (1-N2 and 2-N2
)
and 1-iodonaphthalene (3) were also photolysed. The sing-
let/triplet natures of the photogenerated naphthyl cations
were investigated by the fingerprint method reported in the
accompanying paper.[8]
Results and Discussion
Naphthyl cations, and other cationic polyaromatic hydro-
carbons, are not only of fundamental chemical interest.
They also play relevant roles in combustion processes and
are present in the interstellar medium.[4] The chemistry of
aryl cations and derivatives in the presence of H2O, CO,
Synthesis
Compounds 1 and 2 were synthesised by treatment of 1-
and 2-(4,4,5,5-tetramethyl-1,3,2-dioxoborolanyl)naphtha-
lene with equimolar amounts of (diacetoxy)iodobenzene in
the presence of two mol equivalents of hydrogen tetrafluo-
roborate (in diethyl ether) at –30 °C in dichloromethane.
After the reaction mixtures had been stirred for 90 min, n-
hexane was added, which causes the products to crystallise.
Repetitive crystallisation at 0 °C from tetrahydrofuran and
n-hexane gives the pure salts 1 and 2 in 21% and 28%
[a] Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden
University,
P. O. Box 9502, 2300 RA Leiden, The Netherlands
E-mail: lodder@chem.leidenuniv.nl
[b] Laboratory of Organic Chemistry, Wageningen University,
Dreijenplein 8, 6703 HG Wageningen, The Netherlands
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M. Slegt, F. Minne, H. Zuilhof, H. S. Overkleeft, G. Lodder
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Scheme 1.
+
+
yields, respectively. Diazonium salts 1-N2 and 2-N2 were centrations as a function of time of irradiation revealed that
synthesized by a literature procedure.[9]
all products are primary photoproducts. The products are
grouped along the various C–I bond cleavage modes. Next
to the two leaving groups, 1-iodonaphthalene (3) and iodo-
benzene (6), and the reductive dehalogenation products,
benzene (4) and naphthalene (7), two nucleophilic aromatic
substitution products, anisole (5) and 1-methoxynaphtha-
lene (8), are produced. Furthermore, the Friedel–Crafts-
type products 1-phenylnaphthalene (9a) and 1-(2-, 3- and
Photoproducts
Irradiation of naphthalen-1-yl(phenyl)iodonium tetra-
fluoroborate (1) in methanol at λexc = 254 nm yielded the
mixture of products depicted in Scheme 2,[10] in the compo-
sition recorded in Table 1. Examination of the product con-
Scheme 2. Products of the photolysis of 1 in methanol.
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Generation and Reactivity of Naphthyl Cations: cine Substitution
4-iodophenyl)naphthalene (9b–d) are also formed. Intrigu- ethanol as solvent (vide infra). In methanol, unlike in tri-
ingly, 2-phenylnaphthalene (10a) and 2-(2-, 3- and 4-iodo- fluoroethanol, trapping of I5 by the leaving group appar-
phenyl)naphthalene (10b–d) are produced as well. To the ently cannot compete with its trapping by the nucleophilic
best of our knowledge, this pattern of reactivity, commonly solvent.
referred to as cine substitution, has only been observed in
Homolytic cleavage of the B bond gives two intermedi-
the aryl(phenyl)iodonium salt chemistry of ortho-unsubsti- ates: iodobenzene radical cation (I6) and naphthyl radical
tuted precursors if a strong base is present.[11]
I7. These, in turn, produce 6 and 7 through abstraction of
an electron and a hydrogen atom, respectively, from the
methanol solvent. Upon heterolytic cleavage of bond B, the
naphthalen-1-yl cation (I1) is produced together with the
leaving group 6. I1 is trapped by methanol to form 8 or by
the leaving group iodobenzene (6) to form 9a and 9b–d. The
mode of formation of the cine-substitution products 10a
Table 1. Product composition upon photolysis of 1 in methanol at
λexc = 254 nm[a,b] (ca. 4% conversion[c]).
3
8[d]
4
5
6
7
8
9a
9b–d 10a 10b–d
traces
5
3
19
20
19
12
4
2
[a] Percentages of total yield (GC). [b] Product composition after
45 min of irradiation. [c] 1.2% 3 and 2.4% 6 (GC yields relative to and 10b–d is discussed later (see Scheme 8).
internal standard). [d] Estimated yield; the signal of 1-iodonaph-
thalene overlaps with the internal standard.
Prompted by the formation of both 9 and 10 from the
naphthalen-1-yl(phenyl)iodonium salt 1, we subjected the
naphthalen-2-yl(phenyl)iodonium salt 2 to photolysis under
the same conditions (methanol, λexc = 254 nm; Scheme 4,
Table 2). In analogy with the results obtained in the photol-
ysis of 1, the mixture of primary products consists of the
two leaving groups 2-iodonaphthalene (11) and iodo-
benzene (6), the reductive dehalogenation products benzene
(4) and naphthalene (7), anisole (5), 2-methoxynaphthalene
(12), the 2-arylnaphthalenes 10a–d and the cine-substitution
products 9a–d.
It is proposed that all products were formed through
photolytic cleavage of either the phenyliodonium (A) or the
naphthalen-1-yliodonium (B) bond of 1 (Scheme 3). Both
cleavages can occur through homolysis (A1 and B1) or het-
erolysis (A2 and B2). Homolytic fission of the A bond pro-
duces the 1-iodonaphthyl radical cation (I3) and the phenyl
radical (I4). Radical cation I3 can acquire an electron from
the solvent and form 3. Phenyl radical (I4) will produce 4 by
hydrogen atom abstraction. The parent phenyl cation (I5),
formed after heterolytic fission of bond A, is trapped by
methanol and forms 5. Alongside I5, 3 is formed. In prin-
ciple, the phenyl cation (I5) may also be trapped by the leav-
ing group 1-iodonaphthalene (3), and form 9a via ipso sub-
stitution. In that case, however, a non-ipso substitution
product, a phenylated iodonaphthalene, should also be
formed, but such a product is only formed in trifluoro-
Table 2. Product composition upon photolysis of 2 in methanol at
λexc = 254 nm[a,b] (ca. 10% conversion[c]).
11
4
5
6
7
12
10a
10b–d 9a
9b–d
8[d]
5
2
19
17
16
3
1
7
traces
[a] Percentages of total yield (GC). [b] Product composition after
45 min of irradiation. [c] 3.0% 11 and 6.8% 6 (GC yields relative
to internal standard). [d] Estimated yield; the signal of 2-iodonaph-
thalene overlaps with the internal standard.
Scheme 3. Mechanism of product formation upon photolysis of 1 in methanol.
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FULL PAPER
Both 9 and 10 were also observed in the photoproduct and adventitious water (Ritter reaction), yielding the acet-
mixtures of 1 or 2 when the effect of the solvent was studied anilido products 8-NHAc and 12-NHAc. The nucleophilic
and the irradiation was carried out in acetonitrile and tri- additions of trifluoroethanol to I1 and I2 yield the trifluoro-
fluoroethanol. The leaving groups 3, 6 and 11 and the re- ethoxy ethers 8-OCH2CF3 and 12-OCH2CF3, respectively.
ductive dehalogenation products 4 and 7 are formed as be- The Friedel–Crafts-type products 9 and 10 are found in all
fore, as are the products C6H5NHAc and C6H5OCH2CF3 irradiation mixtures. No cine substitution is found in the
resulting from trapping of the phenyl cation (I5) by the sol- production of 8 and 12.
vent. As shown in Scheme 5, in acetonitrile the naphthyl
Only in trifluoroethanol does the photolysis of 1 yield
cation intermediates I1, and I2 are trapped by that solvent a phenylated iodonaphthalene as one of the products. The
Scheme 4. Products of the photolysis of 2 in methanol.
Scheme 5. Products of the photolysis of 1 and 2 in acetonitrile and trifluoroethanol (only the products of Route B2 are depicted).
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Generation and Reactivity of Naphthyl Cations: cine Substitution
irradiation of 2 produces another phenylated iodonaph- Table 5. Ratios of 9b/9c/9d and 10b/10c/10d produced upon irradia-
tion of 1 or 2 in various solvents.
thalene. The identities of these products could not be estab-
lished rigorously, but it is speculated that they are 1-iodo-
2- or -4-phenyl-naphthalene in the photoproduct mixture of
1 and 1-phenyl-2-iodonaphthalene in that of 2. They are the
Solvent
Ratio 9b/9c/9d
(precursor 1)
Ratio 10b/10c/10d
(precursor 2)
Methanol
56:21:23
35:22:44
52:19:30
59:17:24
43:25:30
54:21:25
products of the trapping of the phenyl cation (I5) by the Acetonitrile
Trifluoroethanol
leaving groups 3 or 11 (cf. Scheme 3, Route A2), which is
only competitive with trapping by the solvent in the nonnu-
cleophilic trifluoroethanol.
To study the effects of the natures of the leaving groups
on the substitution patterns of the photoproducts, the
The ratios in which the nucleophilic substitution prod-
ucts 8 and 12 and the Friedel–Crafts products 9 and 10
are formed depend on the solvent (Table 3). The ratios of
formation of 9 to 10, starting from 1 or 2, also vary with
the solvent (Table 4), as do the o/m/p ratios of the iodobi-
aryls 9b–d produced in the photolysis of 1 and of 10b–d
produced in the photolysis of 2 (Table 5).[12] The last of
these ratios could not be determined for the products 10b–
d in the irradiation of 1 and 9b–d in the irradiation of 2.
These products appear in minute amounts and can only be
detected by GC-MS.
+
naphthalen-1- and -2-yldiazonium tetrafluoroborates 1-N2
+
and 2-N2 were photolysed in methanol and in trifluoro-
ethanol, in the presence of benzene (Scheme 6).[10] In meth-
+
anol, the photolysis of 1-N2 yields 8-OR and 9a in a ratio
of 1.6:1, while in trifluoroethanol the ratio of 8-OR to 9a
is 1:1.7. Similar ratios are obtained in the photolysis of 2-
N2+: in methanol 12-OR/10a = 1.5:1 and in trifluoro-
ethanol 12-OR/10a = 1:1.6. The formation of the reduction
product 7 and the Schiemann products 8-F and 12-F was
confirmed by GC-MS. Solely naphthalen-1- or -2-yl prod-
ucts are formed. No cine substitution was observed.
Table 3. Ratios of 8/9a–d and 12/10a–d produced upon irradiation
of 1 or 2 in various solvents.
The formation of 8-F and 12-F from I1 and I2 occurs
–
through abstraction of fluoride from the BF4 counter-
ion[13,14] and in the case of trifluoroethanol as solvent poss-
ibly also partly through abstraction of fluoride from the
solvent.[15] Although the amounts of 8-F and 12-F in the
reaction mixtures could not be quantified, because their GC
peaks overlap with that of naphthalene, in trifluoroethanol
not significantly more F product was produced than in
methanol. This indicates that fluoride abstraction from tri-
fluoroethanol is not a significant reaction pathway for
naphthyl cations I1 and I2. β-Silicon-stabilized phenyl cat-
ions, generated from their triflate in trifluoroethanol, do
not yield products derived from fluoride abstraction.[16]
Remarkably, the iodonium tetrafluoroborate salts 1 and
2 do not yield the naphthyl fluorides 8-F and 12-F, whereas
Solvent
Ratio 8/9a–d
(precursor 1)
Ratio 12/10a–d
(precursor 2)
Methanol
Acetonitrile
Trifluoroethanol
1:1
1:3.3
1:4.3
1.5:1
1:1.1
1:2.3
Table 4. Ratios of 9/10 produced upon irradiation of 1 or 2 in vari-
ous solvents.
Solvent
Ratio 9/10
(precursor 1)
Ratio 9/10
(precursor 2)
Methanol
Acetonitrile
Trifluoroethanol
8:1
5:1
28:1
1.8:1
1:2
1:11
+
+
the diazonium tetrafluoroborate salts 1-N2 and 2-N2 do
+
+
Scheme 6. Products of the photolysis of 1-N2 and 2-N2 in methanol or trifluoroethanol and benzene.
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FULL PAPER
(see Schemes 2 and 4 vs. Scheme 6). We suggest that in the those of the solvent-optimised structures (columns 4 vs. 6).
(polar) nucleophilic solvents used, the iodonium salts form According to the calculations in vacuo, the triplet cations
3
diaryl-λ3-iodane complexes with the solvent: [Ar-I- 3I1 and I2 are slightly lower in energy than the singlet cat-
– [17,18]
Ph·solvent]+BF4 .
Excitation of these solvent-coordi- ions. This situation is reversed when the cations are placed
nated complexes results in the formation of the naphthyl in methanol. The differences are small: the energies of the
cations (I1 or I2), iodobenzene, and a solvent molecule singlet and triplet species are all within a few kcalmol–1 of
–
within a solvent cage: [I1 or I2 PhI solvent]BF4 . The un- each other. Most earlier reports on the calculated stabilities
stable and short-lived naphthyl cations react with the of I1 and I2 in vacuo place the triplets energetically below
nearby solvent and iodobenzene in the cage, yielding 8- and the singlet structures, whereas in contrast one report finds
12-OMe, -OCH2CF3, -NHAc and 9 and 10, and not with the singlet cations to be more stable, albeit also only with
–
the further removed BF4 anion, thus not yielding 8-F and small differences.[3,4b,21] The near-equal energies demon-
12-F. This interpretation is supported by results of the strate that isomerization of the singlet to the triplet cations,
photolysis of phenanthren-9-yl(phenyl)iodonium tetra- or vice versa, is energetically feasible.
3
fluoroborate.[19] This salt does not give the Schiemann
The triplet naphthyne I8 is calculated to be significantly
product 9-fluorophenanthrene in methanol, but does so in less stable than the singlet naphthyne 1I8 in vacuo, in agree-
trifluoroethanol. In the less nucleophilic TFE, λ3-iodane ment with earlier calculations.[22] This is also the case in
–
formation is less important and the BF4 can now compete methanol.
with other nucleophiles for the photogenerated phen-
Three of the four I1 and I2 structures are calculated to
anthren-9-yl cation, which is more stable and thus longer- be minima with Cs symmetry (Figure 1). The exception is
lived than the naphthyl cations I1 and I2.
the singlet naphthalen-2-yl cation (1I2). Within the con-
straints of Cs symmetry, the structure has one large imagi-
Quantum Chemical Calculations
The singlet and triplet naphthyl cations I1 and I2 and the
corresponding 1,2-naphthynes I8 (vide infra, Scheme 8)
were studied by density functional theory methods. To
study the role of solvent effects, the structures were opti-
mized at the B3LYP/6-311G(d,p) level of theory both in
vacuo and in a dielectric medium resembling methanol.[20]
Subsequently, single-point calculations were performed at
the B3LYP/6-311++G(2d,2p) level of theory, in vacuo on
the “in vacuo” structures (Table 6, column 2), in the dielec-
tric medium on the “in vacuo” structures (Table 6, column
4), and in the dielectric medium on the “in solvent” struc-
tures (Table 6, column 6), respectively. This approach allows
a separate evaluation of the solvent effects on both the geo-
metries and the energies of the resulting structures. For the
first time, optimisation in a solvent worked at this level of
calculation.
Table 6. B3LYP/6-311++G(2d,2p)-calculated energies[a,b] of the sin-
glet and triplet naphthalen-1- and -2-yl cations I1 and I2 and 1,2-
naphthyne I8, optimised in vacuo and in methanol.
Vacuum
Rel. VacuumǞMeOH Rel. MeOH
Rel.
1I1
3I1
1I2
3I2
–385.02153
–385.02330 –1.1 –385.10255
–385.01968
–385.02103
0
–385.10433 –385.10417
0
0
1.1 –385.10257
0.9 –385.10335
1.8 –385.10144
1.0
0.5
1.7
1.2 –385.10290
0.3 –385.10140
1I8
3I8
–384.66696
–384.61188
0
–384.67488
0
–384.67483
0
35
35 –384.60333
45 –384.61932
[a] Absolute values (Hartrees) and values relative to 1I1 (kcalmol–1)
for the cations. [b] Absolute values (Hartrees) and values relative to
1I8 (kcalmol–1) for the naphthynes (1 Hartree = 627.51 kcalmol–1).
Comparison of the data in column 2 with those in col-
umns 4 and 6 shows a significant effect of stabilisation of
the solvent on the cations. Vacuum-optimised structures
that are placed in methanol have energies largely similar to Figure 1. Calculated structures (top and side view) of I1 and I2.
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Generation and Reactivity of Naphthyl Cations: cine Substitution
nary frequency, and this structure is therefore not a mini- 1,4-ditritiobenzene in anisole (65:13:22).[23] The product-
mum. The real minimum is a distinctly nonplanar structure forming intermediate in the last three reactions is a phenyl
with C1 symmetry (e.g., the H atom at C-1 adjacent to the cation of singlet nature. The results of the photolyses of
formally positively charged carbon atom is pointing slightly naphthalen-1-yldiazonium tetrafluoroborate (1-N2+) and 1-
upwards, as can be seen in the side view of 1I2 in Figure 1). iodonaphthalene (3)[10] in acetonitrile/anisole (1:1) at λexc
=
254 nm further clarify the picture. The first reaction, which,
like those of other aryl diazonium salts,[24] presumably oc-
curs through the singlet naphthyl cation intermediate I1,
yields 13 in an o/m/p ratio of 61:15:25. The second reaction,
Singlet/Triplet Natures of the Product-Forming
Intermediates
1
The formation of the nucleophilic substitution products
8 and 12 and the Friedel–Crafts-type products 9 and 10
upon irradiation of 1 and 2 indicate the intermediacy of the
naphthyl cations I1 and I2, which are trapped by the solvent
or by the iodobenzene leaving group (Scheme 3, Route B2).
It is of interest to know whether these intermediates are of
singlet or triplet natures. Irradiation of diphenyliodonium
salts may yield triplet phenyl cations from the triplet excited
state, together with singlet phenyl cations from the singlet
excited state.[8] Here, singlet excited 1 might give cleavage of
which occurs through the naphthyl radical intermediate
· [25]
I1 ,
produces 13 in an o/m/p ratio of 67:17:16. The ratio
+
obtained with 1-N2 is similar to that obtained with 1 and
to that seen in singlet phenyl cation reactions.[8,23] The ratio
+
obtained with 3 is unlike that observed with 1 and 1-N2
,
but is reminiscent of the ratio obtained upon irradiation
of iodobenzene, which generates the phenyl radical as an
intermediate, in acetonitrile/anisole (1:1; o/m/p ratio
75:13:12).[8] The regioselectivities in the reaction of 1 thus
show that both the naphthyl and the phenyl cation interme-
diates in their singlet states are the product-forming inter-
mediates in the formation of 13 and of 2-, 3- and 4-meth-
oxybiphenyl, respectively.
1
the naphthyl-I bond and yield singlet I1 (Scheme 7, singlet
route). Alternatively, because of the heavy atom effect of
iodine, it can undergo efficient intersystem crossing to give
triplet excited 1, which upon cleavage of the naphthyl-I
1
That the singlet naphthyl cation I1 is the (major) prod-
3
1
3
bond yields triplet I1 (Scheme 7, triplet route). I1 and I1
may interconvert, provided that their spin inversion is ener-
getically feasible and fast enough to compete with their re-
actions with nucleophiles.
uct-forming intermediate does not necessarily mean that a
singlet cation is generated upon photolysis of 1. The triplet
3
1
naphthyl cation I1, if formed, may convert into I1 before
being trapped by the solvent, provided that trapping is
slower than spin inversion (see Scheme 7), and also pro-
A fingerprint of the singlet/triplet nature of the product-
forming naphthyl cation I1 was made by irradiating 1 in
acetonitrile/anisole (1:1) at λexc = 254 nm (Scheme 7) by the
method described in the accompanying paper.[8] 1-(2-, 3-
and 4-Methoxyphenyl)naphthalenes 13 were formed in an
o/m/p ratio of 66:12:22. This ratio is quite similar to the
ratio (71:11:17) observed for 2-, 3- and 4-methoxybiphenyl
produced through trapping by anisole of the phenyl cation
I5, formed after heterolytic phenyl–I bond cleavage of 1
(Route A2 in Scheme 3). Moreover, the o/m/p ratio in 13 is
practically the same as the ratios obtained for the photoly-
ses of benzenediazonium tetrafluoroborate (68:13:19) and
diphenyliodonium tetrafluoroborate (68:12:19) under the
same reaction conditions[8] and also for the radiolysis of
1
3
vided that I1 is of lower energy than I1. The calculated
stabilities of the naphthyl cations in methanol assembled
in Table 6 indicate that this process is thermodynamically
feasible.
The o/m/p ratios of the iodobiaryls 9b/9c/9d produced in
the irradiation of 1 and of 10b/10c/10d produced in the irra-
diation of 2 (Table 5) are also fingerprints of the naphthyl
cations I1 and I2, reacting with the leaving group iodo-
benzene in the solvent cage. Photolysis of diphenyliodon-
ium hexafluorophosphate in acetonitrile produces iodobiar-
yls in a 73:13:15 ratio, whereas the bromonium and the
chloronium salts produce halobiaryls in 53:30:19 and
48:31:21 ratios, respectively, under these reaction condi-
Scheme 7. Formation of singlet or triplet I1 and their fingerprinting by photolysis of 1 in acetonitrile/anisole.
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tions.[7b] The o/m/p ratios of the biaryls 9b–d in the irradia- shift (Scheme 8, Route C). Such a shift has been reported
tion of 1 and of 10b–d in the irradiation of 2 (Table 5) in for 1I1, generated by β-decay of 1,4-ditritionaphthalene:
methanol and trifluoroethanol more closely correspond to with benzene both in solution and in the gas phase a mix-
the regioselectivities of the diphenylbromonium and -chlo- ture of 1- and 2-phenylnaphthalene is produced.[27,28] This
ronium salts, which supposedly react through a singlet shift is feasible because the energy of the vibrationally ex-
phenyl cation, than to that of the -iodonium salt, which cited naphthyl cation, left after expulsion of helium, is suf-
reacts both through a singlet and through a triplet phenyl ficient to allow isomerisation. Photolysis of 1 and 2 would
cation. They are therefore attributed to substantial forma- not be expected to yield vibrationally excited naphthyl cat-
1
1
3
1
tion of singlet I1 and I2, through initially formed I1 and ions. Anyhow, if interconversion of 1I1 and I2 were to have
3I2 and the subsequent reaction with iodobenzene. It is not taken place, not only 1- and 2-phenylnaphthalene but also
clear why little or no regioselectivity is found in acetonitrile. 1- and 2-alkoxynaphthalene and the corresponding Ritter
The nucleophilic trapping of I1 and I2 by the solvent products should have been formed. This is not the case and
(methanol, acetonitrile or trifluoroethanol), producing 8 therefore singlet cation isomerisation is not the operative
and 12, relative to trapping by the leaving group iodo- mechanism.
3
3
benzene, producing 9 and 10 (Scheme 5, Table 3), shows
Isomerisation of the triplet naphthyl cations I1 and I2,
that the order of the efficiency of the solvents in trapping formed directly or via the singlet cations, through 1,2 hy-
the intermediates is: methanol, acetonitrile, trifluoro- drogen atom shifts, opens another route for isomerisation
ethanol. In trifluoroethanol the alkylation of the leaving (Scheme 8, Route D). These triplet cations react with the π-
group outperforms the alkylation of the solvent. The order nucleophile iodobenzene and not with the n-nucleophiles
parallels the nucleophilicities of the solvents.[26]
R-OH and acetonitrile. This would explain why only
scrambled phenylnaphthalenes and no scrambled alkoxy-
naphthalenes are observed. It would also explain why no
+
scrambling occurs with 1-N2 and 2-N2+: photolysis of un-
cine Substitution
substituted diazonium salts only yields singlet cations. It is
A number of pathways that may explain the observed not clear whether or not 1,2 hydrogen atom shifts in 3I1 and
cine substitution can be envisioned. The singlet naphthalen- 3I2 are kinetically feasible (in other words, what their ener-
1-yl cation (1I1), formed either directly or via the triplet gies of activation are). A 1,2 hydrogen shift has recently
cation, may undergo isomerisation to the singlet naph- been observed in high-temperature gas-phase chemistry of
thalen-2-yl cation (1I2), and vice versa through a 1,2 hydride naphthyl radicals.[29] In the phenyl radical the shift occurs
Scheme 8. Interconversion of singlet and triplet naphthyl cations and corresponding naphthynes.
5360
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 5353–5363

Generation and Reactivity of Naphthyl Cations: cine Substitution
with an activation energy of 58 kcalmol–1.[29] The barrier is affinities. Currently we can offer no explanation for this ob-
3
probably lower in naphthyl radicals, and even lower in I1 servation.
and 3I2 (for which naphthyl radicals may not be a good
To substantiate the possible occurrence of cine substitu-
model), but may still be too high to overcome.
tion via naphthyne I8 as intermediate we tried to trap it in
cine substitution is typically found in alkyne[30] or [4 + 2] or [2 + 2] cycloaddition reactions with benzene. The
aryne[11,31] chemistry. If a 1,2-naphthyne intermediate is re- efforts were in vain. The products of those reactions would
sponsible for the formation of the cine products in the pho- be 1,2-naphthobarrelene or dihydrobenzo[a]naphthalene,[40]
tolysis of 1 and 2, the singlet or triplet naphthyl cations I1 each with molecular mass 204. The photoreaction of 1 in
and I2 must be prone to losing β-protons to their environ- methanol in the presence of benzene (1:benzene = 1:20)
ments, yielding singlet or triplet naphthynes 1I8 and 3I8, produced, together with 1-methoxynaphthalene (8), 1- and
respectively (Scheme 8, Route E). Aryne formation through 2-phenylnaphthalene (9a, 10a), by in-cage reactions be-
an aryl cation intermediate has been reported previously in tween I1 and iodobenzene and by reaction with benzene.
the thermolysis of 2,5-di-tert-butylbenzenediazonium ace- No products of molecular mass 204 other than 9a and 10a
tate in dichloromethane.[32] The acetate counterion not only were detected by GC-MS. An “ene” reaction may also pro-
traps the aryl cation intermediate, forming the acetate prod- duce 9a and 10a from I8 and benzene.[41] However, there is
uct, but also abstracts a proton to form 2,5-di-tert-butyl- no reason why I8 should favour the “ene” reaction totally
benzyne. 1,2-Naphthyne has been prepared as an intermedi- over [4 + 2] cycloaddition.
ate by 1,2 HX elimination from halonaphthalenes by a
strong base[33] and in matrix photodecarboxylation experi-
ments.[34] All naphthynes found in matrix trapping experi-
Conclusions
ments possess singlet multiplicities. The singlet structure 1I8
The naphthalen-1- and -2-yl cations I1 and I2 were gener-
ated by photolysis of their iodonium and diazonium salt
is calculated to be far lower in energy than its triplet spin
3
isomer I8, not only in the gas phase (in agreement with
earlier calculations[22]) but also in methanol (Table 6). Still,
precursors and their reactivities were studied. The naphthyl
cations react (predominantly) through their singlet, closed-
shell isomers. With the iodonium salt precursors, which also
fragment from the triplet excited state, a contribution of
the triplet naphthyl cations to the patterns of reactivity was
found. Presumably, under the circumstances investigated,
the singlet closed-shell naphthyl cations are lower in energy
than their triplet isomers.
It appears that, with use of the naphthyliodonium pre-
cursors, the triplet naphthyl cations formed isomerise
through 1,2 hydrogen atom shifts or lose protons to the
solvent, producing triplet 1,2-naphthyne. These processes
lead to the cine-substitution patterns found in the pho-
toproduct mixtures. No cine substitution occurs upon irra-
diation of naphthalen-1- and -2-yldiazonium tetrafluorobo-
rates, which generates only the singlet naphthalen-1- and
-2-yl cations.
1
singlet naphthyne I8 cannot be the cine product-forming
intermediate. This species would be expected to react with
methanol to yield predominantly 2-methoxynaphthalene,[35]
a product not found in the photolysis of 1. Also, no cine
+
+
substitution occurs with diazonium salts 1-N2 and 2-N2
,
which fragment in the singlet excited state to produce 1I1 or
1I2, which upon proton loss would yield singlet naphthyne
1I8. On the other hand, the iodonium salts 1 and 2, which
do give cine substitution, fragment not only in the singlet
but also in the triplet excited states.[7] The latter process
3
3
would yield triplet cations I1 or I2 and after proton loss
3
triplet naphthyne I8. Proton abstraction from the triplet
cations 3I1 and 3I2, yielding 1,2-naphthyne 3I8, is thought to
be feasible because these species are formally also radical
cations, which are known to lose protons easily, especially
from their benzylic positions.[36–38]
An argument in favour of naphthyne as a cine product-
forming intermediate is the variation in the 9:10 ratio as a
function of the solvent (Table 4). Under the photolysis reac-
tion conditions, the proton abstraction can only be effected
by the solvent. Acetonitrile (779.2 kJmol–1), methanol
(754.3 kJmol–1) and trifluoroethanol (700 kJmol–1) differ
markedly in their proton affinities.[39] It is reasonable to ex-
Experimental Section
Materials: Iodonium salts 1 and 2 were synthesised by a modified
literature procedure.[42,43] HBF4 (0.50 mL) in diethyl ether (54 wt.-
%) was added at –30 °C to (diacetoxyiodo)benzene (0.5 g) in dry
dichloromethane (25 mL). The temperature was allowed to rise to
pect more aryne-derived product in the better proton-ab- 0 °C, after which the clear yellow solution was cooled back to
–30 °C. Stepwise, over a few min. commercially available 1- or 2-
(4,4,5,5-tetramethyl-1,3,2-dioxoborolanyl)naphthalene (0.39 g) was
added. The reaction mixtures turned dark. After the reaction mix-
tures had been stirred for 90 min at –30 °C, the temperature was
allowed to rise to 0 °C. n-Hexane (40 mL) was added, causing crys-
tallisation. Filtration of the crude products and repeated crystalli-
sations from dichloromethane and n-hexane yielded off-white, pow-
stracting solvent. Indeed, in the photolyses with 1 in the
three solvents, the relative abundances of the cine substitu-
tion products increase with the proton affinities of the sol-
vents. In the photolysis of 2, scrambling is more prevalent
than for 1 (Table 4). The triplet naphthalen-2-yl cation (3I2),
which is a benzylic-type radical cation, must be a stronger
acid than the naphthalen-1-yl cation; already in the less ba-
sic solvent trifluoroethanol significant scrambling occurs.
The photolysis of 2 in methanol yields more scrambled
1
dery crystals in 21% and 28% yields, respectively. {1: H NMR[44]
(200 MHz, [D6]DMSO): δ = 7.3–7.7 (m, 3 H), 7.7–8.1 (m, 6 H),
8.1–8.4 (d, 2 H), 8.9 (s, 1 H) ppm. IR[45] (neat): ν=1000–1100 cm–1,
˜
–
1
product than expected on the basis of the relative proton strong (BF4 )}. {2: H NMR (200 MHz, [D6]DMSO): δ = 7.4–7.8
Eur. J. Org. Chem. 2007, 5353–5363
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
5361

M. Slegt, F. Minne, H. Zuilhof, H. S. Overkleeft, G. Lodder
FULL PAPER
(m, 6 H), 7.9–8.1 (d, 2 H), 8.1–8.4 (t, 3 H); 8.9 (s, 1 H) ppm. IR
(neat): ν=1000–1100 cm–1, strong (BF )}. Diazonium salts 1-N
–
+
˜
[1]
[2]
4
2
a) P. J. Stang, in Dicoordinated Carbocations (Eds.: Z. Rappo-
port, P. J. Stang), Wiley, Chichester, UK, 1997, p. 451; b) M.
Hanack, L. R. Subramanian, in Methoden Org. Chemie (Ed.:
M. Hanack), Thieme, Stuttgart, Germany, 1990, vol. E19C,
p. 249; c) M. Winkler, W. Sander, J. Org. Chem. 2006, 71, 6357–
6367.
a) J. N. Harvey, M. Aschi, H. Schwarz, W. Kock, Theor. Chem.
Acc. 1998, 99, 95–99; b) M. Aschi, J. N. Harvey, J. Chem. Soc.
Perkin Trans. 2 1999, 1059–1062; c) B. Guizzardi, M. Mella,
M. Fagnoni, A. Albini, J. Org. Chem. 2001, 66, 6353–6563; d)
S. Milanesi, M. Fagnoni, A. Albini, Chem. Commun. 2003,
216–217; e) S. Protti, M. Fagnoni, M. Mella, A. Albini, J. Org.
Chem. 2004, 69, 3465–3467.
K. K. Laali, G. Rasul, G. K. Prakash, G. A. Olah, J. Org.
Chem. 2002, 67, 2913–2918.
a) V. Le Page, Y. Keheyan, T. P. Snow, V. M. Bierbaum, J. Am.
Chem. Soc. 1999, 121, 9435–9446; b) D. Ascenzi, P. Bassi, P.
Francheschi, O. Hadjar, P. Tosi, M. Di Stefano, M. Rosi, A.
Sgamellotti, J. Chem. Phys. 2004, 121, 6728–6737.
a) T. P. Snow, V. Le Page, Y. Keheyan, V. M. Bierbaum, Nature
1998, 259–260; b) V. Le Page, Y. Keheyan, V. M. Bierbaum,
T. P. Snow, J. Am. Chem. Soc. 1997, 119, 8373–8374; c) V.
Le Page, Y. Keheyan, T. P. Snow, V. M. Bierbaum, Int. J. Mass
Spectrom. 1999, 185/186/187, 949–959; d) Y. Keheyan, Chem.
Phys. Lett. 2001, 340, 405–412; e) S. Petrie, D. K. Bohme, Top.
Curr. Chem. 2003, 225, 37–75; f) M. Di Stefano, M. Rosi, A.
Sgamellotti, Future Gener. Comput. Syst. 2004, 20, 807–819.
a) R. Gronheid, G. Lodder, M. Ochiai, T. Sueda, T. Okuyama,
J. Am. Chem. Soc. 2001, 123, 8760–8765; b) R. Gronheid, G.
Lodder, T. Okuyama, J. Org. Chem. 2002, 67, 693–702; c) T.
Okuyama, G. Lodder, Nucleophilic Vinylic Substitution and
Vinyl Cation Intermediates in the Reactions of Vinyl Iodonium
Salts, Advances in Physical Organic Chemistry, vol. 37 (Eds.:
T. Tidwell, J. P. Richard), Elsevier Science Ltd., Amsterdam,
2002.
+
and 2-N2 were prepared from commercially available starting ma-
terials by a literature procedure.[9] 1-Iodonaphthalene (3) is com-
mercially available. Anisole was distilled under argon to obtain GC
purity. Methanol, acetonitrile, trifluoroethanol and anisole were ar-
gon-purged prior to their use in the photolysis experiments.
Photochemistry: The photochemical reactions were carried out un-
der argon in quartz tubes fitted with rubber seals. The starting
materials were dissolved at 0.02  in the solvent (10 mL). n-Decane
was used as internal standard. For the experiments in which prod-
uct formation was followed as a function of irradiation time, the
tubes were placed in a merry-go-round apparatus. A Hanau TNN-
15/32 low-pressure mercury lamp placed in a water-cooled quartz
tube was used to supply light with a main emission at λ = 254 nm.
For product studies, the tubes were placed in a Rayonet Reactor
(RPR200) fitted with seven 254 nm lamps. The photolyses of the
salts 1, 2, 1-N2 and 2-N2 in methanol and acetonitrile were fol-
lowed as a function of time by taking aliquots (0.050 mL sample)
and adding them to water (0.5 mL) and diethyl ether (0.050 mL).
Aliquots from the irradiation mixtures in trifluoroethanol were
added to water (0.5 mL) and dichloromethane (0.050 mL). The or-
ganic layers were analysed by GC and GC-MS and the assignments
of the structures were confirmed by coinjection of commercially
available or independently prepared products. After completion of
the irradiations, the reaction mixtures were poured into water
(10 mL) and extracted twice with diethyl ether (5 mL). The com-
bined ether fractions were analysed by GC and GC-MS. The pho-
tolysis of 3 in acetonitrile/anisole (1:1) was followed as a function
of time by taking samples (0.050 mL). The samples were analysed
by GC and GC-MS. After completion of the irradiation the reac-
tion mixture was analysed by GC and GC-MS.
[3]
[4]
+
+
[5]
[6]
[7]
Photoproducts: The products 3, 4, 5, 6, 7, 8, 8-OCH2CF3, 8-NHAc,
8-F, 9a, 10a, 12, 12-NHAc and 12-F were identified by GC, GC-
MS and coinjection with the aid of commercially obtained refer-
ence samples. Products 11[46] and 12-OCH2CF3[47] were synthesised
by literature procedures. The o/m/p biaryl mixtures 9b–d, 10b–d and
a) J. L. Dektar, N. P. Hacker, J. Org. Chem. 1990, 55, 639–647;
b) J. L. Dektar, D. V. Leff, N. P. Hacker, J. Org. Chem. 1991,
56, 2280–2282; c) T. Kitamura, in CRC Handbook of Organic
Photochemistry and Photobiology, 2nd ed. (Eds.: W. M. Hor-
spool, F. Lenci), CRC Press LLC, Boca Raton, Fl: 2004, Chap-
ter 110.
M. Slegt, H. S. Overkleeft, G. Lodder, Eur. J. Org. Chem. 2007,
5364–5375; following paper.
a) T. Kuokkanen, J. Palokangas, M. Talvensaari, J. Phys. Org.
Chem. 2000, 13, 452–460; b) T. Kuokkanen, J. Palokangas, M.
Talvensaari, J. Phys. Org. Chem. 2001, 14, 618–624.
+
+
13 were prepared by allowing the diazonium salts 1-N2 or 2-N2
to react with neat iodobenzene or anisole at 80 °C for 6 h.[12]
[8]
[9]
Quantum Chemical Calculations: The computations were per-
formed with the Gaussian 03 program, version B3.[20] DFT calcula-
tions for the compounds under study were performed with the
B3LYP functional[48] as implemented in G03. The total energies
were corrected with zero-point energies, obtained at the level of
optimisation.
[10]
[11]
Under the same reaction conditions as used for the photolysis
+
experiments, upon exclusion of light, 1, 2, 1-N2+, 2-N2 and 3
are inert.
Equipment: UV spectra were recorded at room temperature with a
a) T. Akiyama, Y. Imasaki, M. Kawanisi, Chem. Lett. 1974,
229–230; b) T. Kitamura, M. Yamane, K. Inoue, M. Todaka,
N. Fukatsu, Z. Meng, Y. Fujiwara, J. Am. Chem. Soc. 1999,
121, 11674–11679.
The assignments of the o/m/p isomers are based on the assump-
tion that the products elute from the GC column in the usual
order: 1 = ortho, 2 = meta, 3 = para.
S. M. Gasper, C. Devadoss, G. B. Schuster, J. Am. Chem. Soc.
1995, 117, 5206–5211.
H. Eustathopoulos, J. Court, J. M. Bonnier, J. Chem. Soc. Per-
kin Trans. 2 1983, 803–807.
P. S. J. Canning, K. McCrudden, H. Maskill, B. Sexton, Chem.
Commun. 1998, 1971–1972.
Y. Himeshima, H. Kobayashi, T. Sonada, J. Am. Chem. Soc.
1985, 107, 5286–5288.
a) T. Okuyama, T. Takino, K. Sato, M. Ochiai, J. Am. Chem.
Soc. 1998, 120, 2275–2282 and references cited therein; b) G. F.
Koser, Aldrichimica Acta 2001, 34, 89–102.
double beam Varian DMS 200 spectrophotometer, if applicable
1
with pure solvent in the reference cell. H NMR spectra were re-
corded on a JEOL 200 instrument, in CDCl3 as solvent. As analyti-
cal GC a Hewlett–Packard 6890 model was used, equipped with a
automatic injector, fitted with a CP-Sil5-CB column (25 m, ø =
0.25 mm, 1.2 µm) with hydrogen as carrier gas. The Flame-Ionis-
ation Detector (FID) was calibrated with commercially available
reference chemicals. HP Chemstation was used for the analysis of
the analytical data.
[12]
[13]
[14]
[15]
[16]
[17]
Mass spectra were measured on a GC-MS set-up consisting of a
Hewlett–Packard 5890 series 2 model GC, equipped with a auto-
matic injector, fitted with a AT-5MS column (30 m, ø = 0.25 mm,
0.25 µm) with helium as carrier gas. The GC was coupled to a
Finnigan Mat SSQ 710 mass spectrometer, with electron impact as
the ionisation method. The GC-MS data were analysed with Xcal-
iber.
5362
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 5353–5363

Generation and Reactivity of Naphthyl Cations: cine Substitution
[18] λ3-Iodanes are also the reactive species in the photolysis of
[30]
a) T. Okuyama, M. Fujita, Acc. Chem. Res. 2005, 38, 679–
686; b) M. Fujita, W. H. Kim, Y. Sakanishi, S. Fujiwara, T.
Okuyama, Y. Ohki, K. Tatasumi, Y. Yoshioka, J. Am. Chem.
Soc. 2004, 126, 7548–7558.
H. H. Wenk, M. Winkler, W. Sander, Angew. Chem. Int. Ed.
2003, 42, 502–528.
R. W. Franck, K. Yanaga, Tetrahedron Lett. 1966, 25, 2905–
2909.
H. Gilman, N. N. Crounce, S. P. Massie, R. A. Benkeser, S. M.
Spatz, J. Am. Chem. Soc. 1945, 67, 2106–2108.
a) J. Lohmann, J. Chem. Soc. Faraday Trans. 1 1972, 814–824;
b) T. Sato, A. Niino, A. Yabe, J. Phys. Chem. A 2001, 105,
7790–7798.
a) Studies in Modern Chemistry: Carbenes, Nitrenes and Arynes,
T. L. Gilchrist, C. W. Rees, Nelson Press, London, 1969, chap-
ter 8, pp. 103–119; b) Reactive Intermediates in Organic Chem-
istry, N. S. Isaacs, John Wiley & Sons Ltd., London, 1973,
chapter 7, pp. 408–419.
vinyl iodonium tetrafluoroborates in methanol and (to a lesser
extent) in TFE; see ref.[6a–6b]
.
[19] M. Plugge, Leiden University, unpublished results.
[20] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman Jr, Montgomery, T. Vreven,
K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar, J. Tom-
asi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega,
G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota,
R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda,
O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratch-
ian, J. B. Cross, C. Adamo, J. Jaramillo, R. Gomperts, R. E.
Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli,
J. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P. Sal-
vador, J. J. Dannenberg, V. G. Zakrzewski, S. Dapprich, A. D.
Daniels, M. C. Strain, O. Farkas, D. K. Malick, A. D, Rabuck,
K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Ba-
boul, S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A. Lia-
shenko, P. Piskorz, L. Komaromi, R. L. Martin, D. J. Fox, T.
Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, M.
Challa-Combe, P. M. W. Gill, B. Johnson, W. Chen, M. W.
Wong, C. Gonzalez, J. A. Pople, Gaussian 03, Revision B.3,
Gaussian, Inc., Pittsburgh, PA, 2003.
[31]
[32]
[33]
[34]
[35]
[36]
[37]
L. A. Deardurff, M. S. Alnajjar, D. M. Camaioni, J. Org.
Chem. 1986, 51, 3686–3693.
Loss of the other β proton, the non-benzylic 3-H proton, from
3
I2 , yielding 2,3-naphthyne, is unlikely.
[21] a) P. Du, F. Salama, G. H. Loew, Chem. Phys. 1993, 173, 421–
437; b) K. Fujiwara, A. Harada, J. Aihara, J. Mass Spectrom.
1996, 31, 1216–1220.
[38]
[39]
L. A. Huck, P. Wan, Org. Lett. 2004, 6, 1797–1799.
NIST Chemistry Webbook, NIST Standard Reference Database
Number 69 (Eds.: W. G. Mallard, P. J. Linstrom), National In-
stitute Of Standards and Technology, Gaitherburg, MD, 20899,
March 2003 (http://webbook.nist.gov).
[22] a) R. R. Squires, C. J. Cramer, J. Phys. Chem. A 1998, 102,
9072–9081; b) J. Cioslowski, A. Szarecka, D. Moncrieff, Mol.
Phys. 2003, 101, 1221–1225.
[23] G. Angelini, Y. Keheyan, M. Speranza, Helv. Chim. Acta 1988,
[40] a) H. E. Zimmerman, C. O. Bender, J. Am. Chem. Soc. 1970,
92, 4366–4376; b) M. Jones, R. H. Levin, J. Am. Chem. Soc.
1969, 91, 6411–6415.
[41] E. K. Fields, in Organic Reactive Intermediates (Ed.: S. P.
McManus), Academic Press, New York, 1973, p. 486.
[42] M. Ochiai, M. Toyonari, T. Nagaoka, D.-W. Chen, M. Kida,
Tetrahedron Lett. 1997, 38, 6709–6712.
[43] M. Caroll, V. W. Pike, D. A. Widdowson, Tetrahedron Lett.
2000, 41, 5393–5396.
[44] B. R. Kaafarani, H. Gu, A. A. Pinkerton, D. C. Neckers, J.
Chem. Soc. Dalton Trans. 2002, 2318–2321.
[45] P. J. Stang, Angew. Chem. Int. Ed. Engl. 1992, 31, 274–285.
[46] J. Schmidlin, M. Huber, Ber. Dtsch. Chem. Ges. 1910, 43, 2834.
[47] H. Suzuki, T. Matuoka, I. Ohtsuka, A. Osula, Synthesis 1985,
499–500.
[48] P. J. Stephens, F. J. Devlin, C. F. Chabalowski, M. J. Frisch, J.
Phys. Chem. 1994, 98, 11623–11627.
71, 107–119.
[24] S. M. Gasper, C. Devadoss, G. B. Schuster, J. Am. Chem. Soc.
1995, 117, 5206–5211.
[25] a) D. R. Augood, J. I. G. Cadogan, D. H. Hey, G. H. Williams,
J. Chem. Soc. 1953, 3412–3417; b) R. L. Dannley, E. C. Gregg,
R. E. Phelps, C. B. Coleman, J. Am. Chem. Soc. 1954, 76, 445–
448.
[26] a) S. Minegishi, S. Kobayashi, H. Mayr, J. Am. Chem. Soc.
2004, 126, 5174–5181; b) Advances in Chemistry: Nucleophilic-
ity, J. M. Harris, S. P. MacManus, American Chemical Society,
Washington, 1987.
[27] G. Angelini, Y. Keheyan, E. Lilla, G. Perez, Radiochim. Acta
1990, 51, 173–176.
[28] Y. Keheyan, R. Bassanelli, Radiat. Phys. Chem. 1996, 47, 465–
468.
[29] a) M. A. Brooks, L. T. Scott, J. Am. Chem. Soc. 1999, 121,
5444–5449; b) R. F. C. Brown, Eur. J. Org. Chem. 1999, 3211–
3222.
Received: April 17, 2007
Published Online: September 14, 2007
Eur. J. Org. Chem. 2007, 5353–5363
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
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