Photochemical arylation reactions by 4-chlorothioanisole

Article abstract of DOI:10.1002/ejoc.200700290

The photochemistry of 4-chlorothioanisole (1) was investigated in various solvents, and it was found to involve the reduction to thioanisole as the main process. This occurs by heterolytic fragmentation of the triplet state of 1 and formation of the triplet 4-thiomethoxyphenylium ion, as supported by DFT calculations. The cation is trapped by alkenes and, less efficiently, by benzene, resulting in new examples of the recently emerging arylation reactions by S_N1 substitution of phenyl halides. The products from alkenes involve the phenonium ion as a further intermediate. The product distribution differs from the analogous reactions via 4-methoxyphenylium for including a larger proportion of 4-(β-substituted alkyl)- rather than 4-allylthioanisoles derivatives in alcohols, for the lower fraction of rearranged α-substituted 4-alkyl-thioanisoles and for the formation of some 4-cyclopropylthioanisole with allyltrimethylsilane. The difference is accounted for by the more developed dipolar character of the C-C cyclopropane bonds in the intermediate phenonium, as indicated by DFT calculations. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejoc.200700290

FULL PAPER
DOI: 10.1002/ejoc.200700290
Photochemical Arylation Reactions by 4-Chlorothioanisole
[a]
[a,b]
[a]
[a]
Simone Lazzaroni, Daniele Dondi,
Maurizio Fagnoni, and Angelo Albini*
Keywords: Arylation / Cations / Photochemistry / Nucleophilic substitution / Sulfur
The photochemistry of 4-chlorothioanisole (1) was investi-
gated in various solvents, and it was found to involve the
reduction to thioanisole as the main process. This occurs by
ylium for including a larger proportion of 4-(β-substituted
alkyl)- rather than 4-allylthioanisoles derivatives in alcohols,
for the lower fraction of rearranged α-substituted 4-alkyl-
heterolytic fragmentation of the triplet state of 1 and forma- thioanisoles and for the formation of some 4-cyclopro-
tion of the triplet 4-thiomethoxyphenylium ion, as supported
by DFT calculations. The cation is trapped by alkenes and,
less efficiently, by benzene, resulting in new examples of the
pylthioanisole with allyltrimethylsilane. The difference is ac-
counted for by the more developed dipolar character of the
C–C cyclopropane bonds in the intermediate phenonium, as
indicated by DFT calculations.
recently emerging arylation reactions by S
phenyl halides. The products from alkenes involve the phe-
nonium ion as a further intermediate. The product distribu- (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
N
1 substitution of
tion differs from the analogous reactions via 4-methoxyphen-
Germany, 2007)
Introduction
was a change in the electron-donating substituent, and to
the previously investigated –OR and–NR groups, a –SR
2
In recent years, we have been involved in the photochem-
istry of electron-donating (usually para) substituted phenyl
halides and of some of the corresponding esters, viz. phenyl
mesylates, triflates, and phosphates.[ In polar media, these
compounds, for example 4-chlorophenol, -anisole, and -ani-
line, underwent photoheterolysis of the carbon–halogen
bond (of the carbon–oxygen bond for the esters). The cleav-
age occurred in the triplet state and generated the corre-
group was added for study. Accordingly, we explored the
photochemistry of 4-chlorothioanisole (1) in neat solvents
and in the presence of various π-nucleophiles and we were
gratified to find that functionalized thioanisoles could be
conveniently obtained in this way.
1]
Results
sponding phenyl cations, likewise as the triplet en-
tity.[
1b,1c,1e,2]
The cations demonstrated to be quite useful in
Irradiation in Neat Solvents
synthesis because in the triplet multiplicity these did not
add to n-nucleophiles, but only to π-nucleophiles. This al-
The photoreactivity of 1 was examined in 0.05 m solu-
lowed the irradiation to be carried out in a polar solvent as tions in four solvents, viz., acetonitrile, methanol, 2,2,2-tri-
required for efficient heterolysis, for example in an alcohol, fluoroethanol (TFE), as well as in MeCN/H O (5:1). The
2
yet avoiding addition of the phenyl cation to the solvent irradiation was carried out in the presence of triethylamine
and obtaining selective addition to alkenes and aromatics.
(0.05 m) to buffer the acid that is liberated during the course
In some cases mixtures are obtained, but in other cases of the reaction (though this had only a marginal effect on
the yields and selectivity are high. The synthetic potential the results). Compound 1 was consumed, and the only
of this arylation process appears to be remarkable and practically product formed was anisole 2 (Scheme 1a). To
seems to be competitive with palladium-catalyzed meth- facilitate the comparison of the results, the experiments
[
1a]
ods. This encouraged us to explore the scope of the reac- were carried out by irradiating for a fixed time (16 h), as
tion. An obvious issue for the development of this method shown in Table 1. The progress of the reaction was some-
what hampered by the formation of a film sticking to the
walls of the irradiation vessel during the irradiation, which
was a result of the separation of a small amount of a non-
identified, sulfur-containing product. This made it difficult
to arrive at 100% conversion, particularly with alcohol as
[
[
a] Department of Organic Chemistry, University of Pavia,
Via Taramelli 10, 27100 Pavia, Italy
Fax: +39-0382-987323
E-mail: angelo.albini@unipv.it
b] Interuniversity Consortium INCA, Research Unit at the Uni- the solvent.
versity of Pavia,
Via Taramelli 10, 27100 Pavia, Italy
Supporting information for this article is available on the
WWW under http://www.eurjoc.org or from the author.
The quantum yield of the reaction was then determined
through separate, low (Ͻ20%) conversion experiments by
comparison with potassium ferrioxalate actinometer and
4360
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 4360–4365

Photochemical Arylation Reactions by 4-Chlorothioanisole
FULL PAPER
Allyltrimethylsilane (ATMS), 2,3-dimethyl-2-butene
DMB), and benzene were chosen for this purpose. The
(
products formed are shown in Scheme 1 and the yields ob-
tained (again by irradiation for the fixed time of 16 h) are
reported in Table 2. In the presence of the traps, the forma-
tion of a film on the walls of the vessel was much reduced,
and in general the reactions could be carried out to comple-
tion.
Table 2. Products from the irradiation of 1 in the presence of π-
nucleophiles.
Additive
Solvent
Consumed Yield of products
[a]
[a]
1
m
1
[%]
formed [%]
DMB
MeOH
TFE
MeCN/H
100
100
100
2 (11), 3 (5), 4 (6), 5 (30)
2 (8), 3 (26), 6(5), 7(27)
2 (16), 3 (5), 4 (6), 8 (40)
2
O
2
O
2
O
ATMS
Benzene
MeOH
TFE
MeCN/H
92
100
100
2 (14), 9 (24)
9 (31), 10 (7), 11 (8)
2 (14), 9 (29)
MeOH
TFE
MeCN/H
62
57
72
2 (29), 12 (6)
2 (7), 12 (22)
2 (26), 12 (33)
[
a] The consumption and the product yields (referred to the initial
amount of reagent after 16 h irradiation) were determined by GC.
With 1 m DMB (Scheme 1b), compound 1 was in part
reduced to thioanisole (2), but in part converted into alkyl-
ated thioanisoles with a distribution that depended on the
solvent. Thus, in MeOH, an alkene 2,3-dimethyl-3-[4-(thio-
methoxy)phenyl]-1-butene (3) and the corresponding al-
kane, 2,3-dimethyl-2-[4-(thiomethoxy)phenyl]butane (4),
were formed in low yield, but the main single product was
an ether resulting from a three-component combination:
Scheme 1. Products from the irradiation of 1: a) in neat solvent; b)
in the presence of DMB; c) in the presence of ATMS; d) in the
presence of benzene.
2,3-dimethyl-2-[4-(thiomethoxy)phenyl]-3-methoxybutane
(
5, 30%).
Table 1. Products from the irradiation of 1 in neat solvents and the
In TFE, alkene 3 (26%) and two solvent incorporating
quantum yield of the reaction (Φ
r
).
products viz. 2,2-dimethyl-3-[4-(thiomethoxy)phenyl]-3-
Solvent
Consumed 1 [%][a] Product yield [%][a]
Φ
r
(2,2,2-trifluoroethoxy)butane (6, 5%) and isomeric 2,3-di-
MeOH
TFE
MeCN/H
MeCN
85
86
100
44
2 (63)
2 (37)
2 (50)
2 (14)
0.38
0.13
0.29
methyl-2-[4-(thiomethoxy)phenyl]-3-(2,2,2-trifluoroethoxy)-
butane (7, 27%) were formed along with a little amount of
2
O
2
(8%). In MeCN/H O, the main product was an alcohol,
[
b]
2
2,3-dimethyl-3-[4-(thiomethoxy)phenyl]butan-2-ol
(8),
[
a] The consumption and the product yields (referred to the initial
formed in 40% yield along with a small amount of alkyl-
ated products 3 and 4 and 16% of reduced 2.
In the presence of 1 m ATMS (Scheme 1c), compound 1
gave 4-allylthioanisole (9) as the main product along with
amount of reagent after 16 h of irradiation) were determined by
GC. [b] Difficult to measure owing to some filming on the walls,
see text.
some thioanisole (2) both in methanol and in MeCN/H O
2
was found to attain the maximum value (0.38) in methanol
(5:1). In TFE, the results were somewhat different in that
(Table 1). Compound 1 showed a modest fluorescence in
reduced 2 was no longer formed and main product 9 was
accompanied by small amounts of two additional products
viz. 4-cyclopropylthioanisole (10, 7%) and 4-(2-chloropro-
pyl)thioanisole (11, 8%).
solution and phosphorescence at 77 K in glass, both of
them similar in shape and somewhat less intensive than that
of thioanisole 2.
The photochemical reaction in the presence of 1 m ben-
zene (Scheme 1d) was less efficient and starting compound
Irradiation in the Presence of π-Nucleophiles
1
was not fully converted in 16 h. The products were thioan-
We next explored the irradiation of compound 1 in the isole (2) and 4-phenylthioanisole (12), with the former more
presence of representative π-nucleophiles (again with equi- abundant in methanol, the latter in TFE, and the two form-
molar triethylamine).
ing in about the same yield in mixed MeCN/H O solvent.
2
Eur. J. Org. Chem. 2007, 4360–4365
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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S. Lazzaroni, D. Dondi, M. Fagnoni, A. Albini
FULL PAPER
3
+
Finally, we notice that during systematic studies of the oxyphenylium ion, 13 formed a triplet, diradical cation
[3]
reaction of phenylium ions with alkynes, nonconjugated adduct with propene, then leading to a more stabilized cat-
[
4]
[5]
+
unsaturated acids and cyanide, the corresponding thio- ion adduct, viz. phenonium ion 15 (stabilized by 86.8 kcal/
3
+
methoxyaryl derivatives were obtained by irradiation of mol with respect to 13 + propene). This was necessarily
compound 1 (Scheme 2).
a singlet, and intersystem crossing must intervene in be-
tween. The geometry in this adduct, and in particular the
C–C distances in the three-membered ring, were similar to
+
those in oxa analogue 16 (Table 3), but the (Mulliken)
charge distribution was somewhat different. In the sulfur
derivative, the positive charge was localized to a greater ex-
tent on the heteroatom and on the neighboring carbon
atoms and to a lesser extent at C with respect to the oxa
1
analogue. This gave the C –C and C –C bonds a marked
1
2
1
3
+
dipolar character in 15 when in solution. In particular, the
C –C bond was more polarized by 28% in 15 with respect
to 16 (as calculated from the Mulliken charges at the car-
bon atom, with the hydrogen summed in, see Table 3; Fig-
ure 2).
Scheme 2. Products from the irradiation of 1 in the presence of
various nucleophiles.
+
1
3
+
Computational Studies
Table 3. C–C distances and Mulliken charges for the adduct be-
tween 4-thiomethoxy and 4-methoxyphenylium and propene (phe-
nonium ions). Data refer to the optimized (UB3LYP/6-
The experimental work was complemented by DFT cal-
culations. These were carried out at the UB3LYP/6-
3
11G++ (2d,p) level, known to be suitable for sulfur-con- 311G++(2d,p) structures.
taining compounds. The structure and energy of the pro-
posed intermediate, 4-thiomethoxyphenylium ion (1 13 )
,3
+
were examined in both spin states. It resulted that the triplet
was the ground state in the gas phase, with a gap ΔES–T
.1 kcal/mol. Solvation effects calculated with the CPCM
method (acetonitrile as solvent) on the optimized geome-
=
8
1
+
tries showed that singlet state 13 was somewhat more sta-
3
+
bilized than triplet 13 , decreasing the gap to 7.1 kcal/mol,
but leaving the order unchanged. The optimized geometry
of both states was essentially the same as that of the respec-
tive nonsubstituted cations,[
1c,2a–2c]
with the triplet state
characterized by a planar, hexagonal structure, and the sin-
glet state differing by a puckering inwards of C-1 (Figure 1).
In particular, there was a close likeness to corresponding 4-
+
methoxyphenylium ions 14 .
Figure 2. Optimized geometry and Mulliken charges (with the hy-
drogens summed in) for phenonium ions 16+ (left) and 15 (right).
+
Figure 1. Optimized geometry of singlet and triplet 4-thiomethoxy-
phenylium ion (1 13 ) and of triplet 4-chlorothioanisole ( 1).
,3
+
3
Discussion
The exploration was extended to the energy and geome-
try of the putative precursor of the cation, triplet chloro-
Comparison with previous work suggests that the thio-
3
thioanisole 1 and to the ensuing chemistry of such an in- ether functionality can be added to previously studied O-
3
[1]
termediate. As for 1, this was characterized by a conspicu- and N-bonded functionalities that facilitate unimolecular
ous out-of-plane deformation of the C–Cl bond (Figure 1). fragmentation of the corresponding aryl chlorides from the
To calculate the C–Cl bond dissociation energy in this ex- triplet state. DFT calculations support that heterolytic
cited state, the bond was stretched up to 4 Å in increments cleavage of the C–Cl bond confronts a modest barrier
3
of 0.1 Å (in MeCN bulk, CPCM method as above). The (6.4 kcal/mol) in triplet 4-chlorothioanisole 1 (triplet en-
cleavage was endothermic by 6.4 kcal/mol and no maximum ergy 74.0 kcal/mol from the phosphorescence spectrum)
was encountered along the path.
and the experiments show that the quantum yield of de-
As for the chemistry of the triplet phenylium ion, this chlorination ranges from ca. 0.1 to 0.4, that is more efficient
was explored for the case of propene as the nucleophile. It than with 4-chloroanisole and less than with 4-chloro-N,N-
was found that, similar to the previously studied 4-meth- dimethylaniline.
4362
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Eur. J. Org. Chem. 2007, 4360–4365

Photochemical Arylation Reactions by 4-Chlorothioanisole
FULL PAPER
Therefore, it seems safe to assume that in polar solvents latter solvent favors ion separation, and the free ion clearly
4
-chlorothioanisole undergoes heterolytic cleavage from the is a better electrophile under these conditions.
+
triplet state and the first-formed intermediate is triplet thio-
methoxyphenylium ion 13 . Indeed, no 4-thiomethoxy- (Scheme 3, path c) as a further intermediate. Also in this
The arylation of alkenes proceeds via phenonium ion 15
3
+
+
phenyl ethers, the products expected from singlet cation case, it is instructive to compare the reactivity of ion 15
1
+
+
1
3 , are formed in alcohol solvents. Previous studies with with that of oxa analogue 16 . Thus, in the reaction with
the corresponding chloroanisole and aniline showed that DMB (X = H) deprotonation (Scheme 3, path e) is the pre-
+
the main processes form triplet phenylium ions in neat sol- ferred process from methoxyphenonium 16 and allylben-
vents (at concentrations in the range of those presently zene (3) is the main product in MeOH (not in less basic
+
used) was reduction (Scheme 3, path a). This may involve MeCN). On the other hand, with thio analogue 15 nucleo-
either direct hydrogen transfer from the solvent to cation philic addition of the solvent to give a β-alkoxy(hydroxy)-
+
Ar or previous reduction to the aryl radical (electron alkylbenzene (Scheme 3, path f) predominates in all of the
+
·
·+
transfer from the halide Ar + ArClǞAr + ArCl ) and solvents tested (MeOH, TFE, MeCN/H O), although its
2
ensuing H transfer from the solvent.[
1c,6]
Reduction to 2 is proportion decreases in TFE (ratio ether/allylbenzene 0.5 in
in fact a major process (Table 1), whereas the other often MeOH and 1.8 in TFE for 4-MeOC H Cl, 6 in MeOH, and
6
4
observed process involving the cation and the starting ha- 1.2 in TFE for 1). In the case of ATMS, the main process
+
+
lide, viz. formation of a biphenyl, does not take place here. via both cations 15 and 16 is solvent-assisted desilylation,
However, the formation of films on the walls suggests that giving again an allylbenzene (Scheme 3, path e, X = Me Si).
3
+
some polymerization occurs (Scheme 3, path b).
Indeed, this is the only process, except for the case of 15
in TFE, where a different reaction leading to a cyclopropyl
derivative is observed as a minor process. This can be envis-
aged as an alternative elimination path (Scheme 3, path g)
and has analogy in the known formation of cyclopropane
[
7,8]
from 3-chloropropylsilanes by an S 1 process.
A third
N
difference has to do with the role of the Wagner–Meerwein
rearrangement (Scheme 3, path h). The rearranged/nonre-
+
arranged ratio is 1.6 for methoxy-substituted ion 16 and
+
0
.2 for sulfur analogue 15 .
In other words, 4-methoxy- and thiomethoxyphenylium
3
+
3
+
ions 14 , 13 are similar electrophiles. In the alkene ad-
+
duct (phenonium) ions, however, methoxy derivative 16 is
more prone to base-induced proton (or silyl cation) transfer
+
to the solvent, and thiomethoxy analogue 15 is prone to
inter- and intramolecular nucleophilic addition. These
pieces of evidence suggest that anchimeric assistance by the
thiomethoxyphenyl group is less effective, or, as it can be
also expressed, the phenylium–alkene interaction maintains
more of a dipolar character, making nucleophile attack at
the three-membered ring easier. This view is supported by
the calculated geometry of the phenonium ion where it ap-
pears that, although the bond lengths in the spirocyclopro-
pane ring change little, the C –C bond is more polarized
1
+
3
Scheme 3. Main paths in the photochemistry of 1.
+
in 15 than in oxa analogue 16 . This facilitates both attack
by an external nucleophile (Scheme 3, path f), and the sec-
+
Calculations predict that analogous to what was ob- ond mode of elimination of the electrofugal group X ,
served with other phenylium ions[ 13 adds to π-nucleo- characterized by formation of a C–C σ bond with the distal
philes such as alkenes. Indeed, arylation both of alkenes carbon of the spirocyclopropane ring (Scheme 3, path g)
and of benzene occurred satisfactorily. Comparison of the rather than of a π bond with the vicinal carbon (Scheme 3,
1] 3
+
+
results from 1 with those previously obtained with 4-chloro- path e; the only elimination path from 16 , whereas both
[
6]
3
+
+
anisole via triplet 4-methoxyphenylium ion ( 14 ) shows compete from 15 ). On the other hand, the greater stabiliza-
several common characteristics and some differences. Trap- tion imparted to the phenonium ion by the methoxy group
ping by alkenes is efficient with both cations (Scheme 3, arguably lengthens the lifetime of this intermediate (or gives
path c). As an example, the ratio addition/reduction is 3.7 a greater role to the free cation in comparison to the ion
3
+
3
+
for 13 and 2.7 for 14 with 1 m DMB in MeOH. The less pair). This makes it possible to undergo Wagner–Meerwein
nucleophilic benzene (Scheme 3, path d) is a poorer trap, rearrangement for a larger fraction of ions.
at least when competing with reducing methanol, with an
In conclusion, the thioanisolium ion is conveniently gen-
arylation/reduction ratio 0.2 and 0.4 for 1 m benzene in erated by photolysis of 4-chlorothioanisole and adds to al-
MeOH, but the ratio increased to 3.1 and 20 in TFE. The kenes and benzene, widening the scope of the photochemi-
Eur. J. Org. Chem. 2007, 4360–4365
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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4363

S. Lazzaroni, D. Dondi, M. Fagnoni, A. Albini
FULL PAPER
cal arylation by a photo-S 1 reaction of aryl halides, which 4 H) ppm. 13C NMR (75 MHz, CDCl
): δ = 16.0 (CH
), 38.1 (CH), 40.1, 126.4 (CH), 126.6 (CH),
27.8, 128.8 ppm. GC–MS: m/z = 208.
N
3
3
), 17.8 (2
3 3
CH ), 24.6 (2 CH
has been recently emerging. The products formed are the
analogues of those isolated from 4-chloroanisole, as ex-
1
pected from the similar DFT calculated structure. However, 2,3-Dimethyl-2-[4-(thiomethoxy)phenyl]-3-methoxybutane (5): 1H
3
with alkenes in alcohols, β-alkoxyalkylbenzenes are formed NMR (300 MHz, CDCl ): δ = 1.1 (s, 6 H), 1.4 (s, 6 H), 2.4 (s, 3
1
3
H), 3.2 (s, 3 H), 7.1–7.5 (AAЈ-BBЈ, 4 H) ppm. C NMR (75 MHz,
CDCl ): δ = 15.9 (CH ), 19.8 (CH ), 20.0 (CH ), 24.3 (CH ), 24.9
CH ), 45.0, 49.4 (CH ), 78.4, 125.4 (CH), 128.8 (CH), 129.0 (CH),
29.2 (CH), 134.8, 144.5 ppm. IR (neat): ν˜ = 2964, 1492, 1373,
to a larger extent than with the oxa analogue and with allyl-
trimethylsilane a previously unobserved cyclization to a cy-
clopropylbenzene occurs. These are indications of the lower
stabilization of the intermediate phenonium ion by the sul-
fur versus the oxygen atom in the 4-position.
3
3
3
3
3
(
3
3
1
1
9
–
1
152, 1113, 1068, 812 cm . C14
.30; found C 70.2, H 9.1.
H22OS (238.28): calcd. C 70.54, H,
In Trifluoroethanol: After 16 h of irradiation, evaporation and chro-
matographic separation (cyclohexane/ethyl acetate, 99:1) of the res-
idue afforded 39 mg of 3 (26% yield), 11 mg of 6 (5% yield), 57 mg
of 7 (27% yield).
Experimental Section
General Remarks: The photochemical reactions were performed by
using nitrogen-purged solutions in quartz tubes by using a
multilamp reactor fitted with six 15-W phosphor-coated lamps
2,2-Dimethyl-3-[4-(thiomethoxy)phenyl]-3-(2,2,2-trifluoroethoxy)bu-
1
tane (6): H NMR (300 MHz, CDCl ): δ = 0.9 (s, 9 H), 1.6 (s, 3
3
1
3
(maximum emission is 310 nm) for the irradiation. The reaction
H), 2.5 (s, 3 H), 3.7 (m, 2 H), 7.1–7.3 (AAЈ-BBЈ, 4 H) ppm.
C
course was followed by thin-layer chromatography (TLC, cyclohex-
ane/ethyl acetate) and gas chromatography (GC). Workup of the
photolytes involved concentration in vacuo and chromatographic
separation on silica gel. Allyltrimethylsilane, 2,3-dimethyl-2-butene,
benzene, and 4-chlorothioanisole were freshly distilled before use.
The solvents were used as received. No previous anhydrification
was carried out as it was found that this did not affect the results.
NMR spectra were recorded with a 300 MHz spectrometer. The
structure attributions were made on the basis of analytical and
NMR (75 MHz, CDCl ): δ = 15.5 (CH ), 19.2 (CH ), 25.4 (CH ),
3
3
3
3
38.6, 61.0 (q, J = 34 Hz, CH ), 84.3, 125.2 (CH), 125.8 (q, J =
2
276 Hz, CF ), 128.6 (CH), 136.9, 137.4 ppm. IR (neat): ν˜ = 2962,
3
–
1
1597, 1492, 1281, 1163, 1133, 1103, 971, 824, 676 cm .
C H F OS (306.27): calcd. C 58.80, H, 6.91; found C 58.4, H,
1
5
21 3
7.0.
2
,3-Dimethyl-2-[4-(thiomethoxy)phenyl]-3-(2,2,2-trifluoroethoxy)bu-
1
tane (7): H NMR (300 MHz, CDCl
3
): δ = 1.1 (s, 6 H), 1.45 (s, 6
H), 2.5 (s, 3 H), 3.65 (q, J = 8.6 Hz, 2 H), 7.15–7.5 (AAЈ-BBЈ, 4
1
13
spectroscopic data, in particular H and C NMR spectra, sup-
ported by DEPT-135 experiments.
1
3
H) ppm. C NMR (75 MHz, CDCl
4.1 (CH ), 44.9 (CH ), 60.3(q, J = 34 Hz, CH
= 276 Hz, CF ), 129.0 (CH), 135.2, 143.4 ppm. IR (neat): ν˜ = 2976,
3
): δ = 15.7 (CH
3 3
), 20.4 (CH ),
2
3
3
2
), 80.3, 125.8 (q, J
Irradiation of 1 in Neat Solvent: A solution of 1 (0.05 m) was irradi-
3
–
1
ated in the solvent chosen (MeOH; TFE; or MeCN/H
2
O, 5:1) in
1494, 1377, 1280, 1152, 972, 820 cm . C15
C 58.80, H, 6.91; found C 58.6, H, 7.0.
21 3
H F OS (306.27): calcd.
the presence of triethylamine (0.05 m) for 16 h. The product distri-
bution was analyzed by GC. Thioanisole was determined on the
basis of calibration curves. A precipitate formed (Յ3% of the initial
weight) and was filtered and washed with methanol. This material
contained sulfur and gave signals compatible with a sulfonium salt
In MeCN/H
ane/ethyl acetate, 99:1) of the raw photolyte afforded 67 mg of 8
40%) and a mixture containing 9 mg of 4 (6% yield) and 7 mg of
(5% yield) all as a slightly yellow viscous oils.
2
O: After 16 h of irradiation, purification (cyclohex-
(
3
[9]
in accordance with a polymer from 1. IR: ν˜ = 1630, 1500, 1235,
2,3-Dimethyl-3-[4-(thiomethoxy)phenyl]butan-2-ol (8): 1H NMR
300 MHz, CDCl ): δ = 1.2 (s, 6 CH ), 1.4 (s, 6 CH ), 2.5 (s, CH ),
.2–7.4 (AAЈ-BBЈ, 4 H) ppm. 13C NMR (75 MHz, CDCl
): δ =
), 44.3, 74.0, 125.5 (CH), 128.2
–1 1
7
65 cm . H NMR large signals at δ = 2.4, 3.7, 7.0–7.4.
(
3
3
3
3
General Procedure for the Irradiation of 1 in the Presence of π Nu-
cleophiles: Experiments were carried out as described above starting
from 1 (100 μL, 0.75 mmol, 0.05 m) in the chosen solvent (15 mL)
after adding the π-nucleophile (1 m of 2,3-dimethyl-2-butene, allyl-
trimethylsilane, or benzene) again in the presence of triethylamine
7
1
3
3 3 3
5.4 (CH ), 23.9 (CH ), 25.2 (CH
(
1
CH), 135.3, 142.8 ppm. IR (neat): ν˜ = 3468, 2976, 1494, 1375,
–1
112, 822 cm . C13
H20OS (224.26): calcd. C 69.59, H, 8.98; found
C 69.2, H, 9.0.
(0.05 m).
Photochemical Reactions of 1 in the Presence of ATMS
Photochemical Reactions of 1 in the Presence of DMB
In TFE: After 16 h of irradiation, evaporation, and chromato-
In Methanol: After 16 h of irradiation, evaporation and chromato-
graphic separation (cyclohexane/ethyl acetate, 99:1) of the residue
afforded 61 mg of compound 5 (30% yield) and a mixture contain-
ing 9 mg of 4 (6% yield) and 7 mg of 3 (5% yield) all of these
slightly yellow viscous oils.
graphic separation (cyclohexane/ethyl acetate, 99:1) of the residue,
38 mg of 9 (31% yield) as a yellow liquid and 9 mg of 10 (7% yield,
admixed with some 9), and a pure fraction containing 12 mg of 11
(
8% yield) as a yellowish oil were obtained.
1
4
-Allylthioanisole (9): H NMR (300 MHz, CDCl
3
, from the mix-
2
(
(
,3-Dimethyl-3-[4-(thiomethoxy)phenyl]-1-butene (3): 1H NMR
300 MHz, CDCl , from the mixture with 4): δ = 1.5 (s, 6 H), 1.6
s, 3 H), 2.5 (s, 3 H), 4.9 (br. s, 1 H), 5.0 (br. s, 1 H), 7.2–7.4 (AAЈ-
ture): δ = 2.5 (s, 3 H), 3.4 (d, J = 6.6 Hz, 2 H), 5.2 (m, 2 H), 5.9
1
3
3
(m, 1 H), 7.15–7.3 (AAЈ-BBЈ, 4 H) ppm. C NMR (75 MHz,
CDCl ): δ = 16.2 (CH ), 39.6 (CH ), 115.8 (CH ), 127.1 (CH),
3
3
2
2
1
3
BBЈ, 4 H) ppm. C NMR (75 MHz, CDCl
CH ), 28.2 (2 CH ), 40.1, 109.5 (CH ), 126.4 (CH), 126.7 (CH),
28.5, 129.4, 130.3 ppm. IR (for the mixture): ν˜ = 2968, 1476, 1110,
3
): δ = 16.1 (CH
3
), 20.0
129.0 (CH), 137.2 (CH, allyl), 135.6, 137.0 ppm. GC–MS: m/z =
164. The product was previously reported, but not spectroscopi-
cally characterized.[
(
1
8
3
3
2
10]
–
1
21 cm .
4
-Cyclopropylthioanisole (10): 1H NMR (300 MHz, CDCl
3
, from
2
,3-Dimethyl-2-[4-(thiomethoxy)phenyl]butane (4): 1H NMR the mixture): δ = 0.7 (m, 2 H), 1.0 (m, 2 H), 1.9 (m, 1 H), 2.5 (s, 3
1
3
(300 MHz, CDCl
3
, from the mixture with 3): δ = 0.8 (d, J = 6.8 Hz,
H), 7.1–7.3 (AAЈ-BBЈ, 4 H) ppm. C NMR (75 MHz, CDCl
= 9.0 (2 CH ), 14.9 (CH), 16.5 (CH ), 126.2 (CH), 127.3 (CH),
3
): δ
6
H), 1.25 (s, 6 H), 1.9 (m, 1 H), 2.45 (s, 3 H), 7.2–7.4 (AAЈ-BBЈ,
2
3
4364
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 4360–4365

Photochemical Arylation Reactions by 4-Chlorothioanisole
FULL PAPER
1
8
34.6, 141.2 ppm. IR (for the mixture): ν˜ = 2921, 1493, 1091, 915,
00, 797 cm . GC/MS: m/z = 164.
S. Protti, M. Fagnoni, A. Albini, Angew. Chem. Int. Ed. 2005,
44, 1232; e) I. Manet, S. Monti, M. Fagnoni, S. Protti, A. Al-
bini, Chem. Eur. J. 2005, 11, 140.
–1
1
4
=
-(2-Chloropropyl)thioanisole (11): H NMR (300 MHz, CDCl
3
): δ
[
2] For other references to phenylium ions, see: a) K. K. Laali, G.
Rasul, G. K. S. Prakash, G. A. Olah, J. Org. Chem. 2002, 67,
2913; b) A. Filippi, G. Lilla, G. Occhiucci, C. Sparapani, O.
Ursini, M. Speranza, J. Org. Chem. 1995, 60, 1250; c) M. As-
chi, J. N. Harvey, J. Chem. Soc. Perkin Trans. 2 1999, 1059; d)
S. M. Gasper, C. Devadoss, G. Schuster, J. Am. Chem. Soc.
1.5 (d, J = 6.5 Hz, 3 H), 2.5 (s, 3 H), 3.0 (ABX, 2 H), 4.2 (X, 1
13
H), 7.1–7.3 (AAЈ-BBЈ, 4 H) ppm. C NMR (75 MHz, CDCl
15.9 (CH ), 24.5 (CH ), 46.0 (CH ), 58.3 (CH), 126.7 (CH), 129.7
CH), 134.7, 136.6 ppm. IR (neat): ν˜ = 2923, 1495, 1092, 798 cm .
13ClS (200.70): calcd. C 59.84, H, 6.53; found C 60.0, H, 6.7.
3
): δ
=
(
3
3
2
–
1
10
C H
1
995, 117, 5206.
[3] S. Protti, M. Fagnoni, A. Albini, Angew. Chem. Int. Ed. 2005,
4, 5675.
4] S. Protti, M. Fagnoni, A. Albini, J. Am. Chem. Soc. 2006, 128,
0670.
Photochemical Reactions of 1 in the Presence of Benzene
4
In Trifluoroethanol: A solution of 1 (100 μL, 0.75 mmol, 0.05 m),
benzene (1.4 mL, 15 mmol, 1 m), and TEA (100 μL, 0.75 mmol) in
TFE (15 mL) was irradiated for 16 h. Separation of the residue
by column chromatography (cyclohexane/ethyl acetate, 99:1) gave
[
[
1
5] V. Dichiarante, M. Fagnoni, A. Albini, Chem. Commun. 2006,
3001.
2
3 mg of 2 (16% yield) and 33 mg of the known compound 12
[6] S. Protti, M. Fagnoni, M. Mella, A. Albini, J. Org. Chem. 2004,
(22% yield) as a white solid, m.p. 98–100 °C.
69, 3465.
[
7] L. H. Sommer, R. E. Van Strien, F. C. Whitmore, J. Am. Chem.
1
4
-Phenylthioanisole (12): H NMR (300 MHz, CDCl
3
): δ = 2.5 (s,
Soc. 1949, 71, 3056.
3
H), 7.3–7.4 (m, 4 H), 7.5–7.6 (m, 2 H), 7.7–7.8 (m, 3 H) ppm.
[8] In turn, literature precedent suggest that 2-chloropropyl deriva-
tive 11 may be a secondary product from 9, see J. Yoshida,
Synlett 2006, 515.
[9] S. Imazeki, M. Sumino, K. Fukasawa, M. Ishihara, T. Aki-
yama, Synthesis 2004, 1648.
13
C NMR (75 MHz, CDCl
3 3
): δ = 15.8 (CH ), 126.7 (CH), 126.8
(CH), 127.1 (CH), 127.4 (CH), 128.7 (CH), 137.4, 137.9,
–1 [11]
1
40.4 ppm. IR (neat): ν˜ = 2917, 1265, 824, 753, 685 cm .
Quantum Yield Measurement: Quantum yields were measured on
-mL samples of solutions as above in 1-cm optical path cuvettes
[
10] a) M. Tiecco, L. Testaferri, M. Tingoli, D. Chianelli, E. Wenk-
ert, Tetrahedron Lett. 1982, 44, 4629; b) R. S. Varma, K. P.
Naicker, Green Chem. 1999, 1, 247.
2
by irradiating by means of a focalized high pressure mercury arc
through an interference filter. The extent of the reaction was as-
sessed by GC, the light absorbed by ferrioxalate actinomety.
[11] G. Y. Li, J. Org. Chem. 2002, 67, 3643.
[
12] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, J. A. Montgomery Jr, 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-
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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, I. Komaromi, R. L. Martin, D. J. Fox, T.
Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, M.
Challacombe, P. M. W. Gill, B. Johnson, W. Chen, M. W.
Wong, C. Gonzalez, J. A. Pople, Gaussian 03, Revision B.02,
Gaussian, Inc., Pittsburgh, PA, 2003.
Computational Study: Structure and energy were optimized at the
UB3LYP/6-311G++(2d,p) level by using the Gaussian 03W pack-
age (see Supporting Information).[
12]
Supporting Information (see footnote on the first page of this arti-
cle): Coordinates and energies of the investigated intermediates are
available.
Acknowledgments
Partial support of this work by MIUR (Ministero dellЈIstruzione,
Università e Ricerca), Rome is gratefully acknowledged.
[1] a) M. Fagnoni, A. Albini, Acc. Chem. Res. 2005, 38, 713; b)
M. Freccero, M. Fagnoni, A. Albini, J. Am. Chem. Soc. 2003,
125, 13182; c) B. Guizzardi, M. Mella, M. Fagnoni, M. Frec-
Received: April 2, 2007
cero, A. Albini, J. Org. Chem. 2001, 66, 6353; d) M. De Carolis,
Published Online: July 6, 2007
Eur. J. Org. Chem. 2007, 4360–4365
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
4365