α-Oxothiones, IV: Electrophilic substitution of phenols with α,α′-dioxothiones and ortho-thioquinones

Article abstract of DOI:10.1002/1099-0690(200011)2000:21<3653::aid-ejoc3653>3.0.co;2-0

α,α′-Dioxothione 1a and ortho-thioquinones 2a and 2b are able to react with several phenols and N,N-dimethylaniline to give the corresponding alkyl aryl or diaryl sulfides. The mechanism of this reaction was proved to be an electrophilic aromatic substitu

Full text of DOI:10.1002/1099-0690(200011)2000:21<3653::aid-ejoc3653>3.0.co;2-0

FULL PAPER
α-Oxothiones, IV[‡]
Electrophilic Substitution of Phenols with α,αЈ-Dioxothiones and
ortho-Thioquinones
Giuseppe Capozzi,*[a] Stefano Menichetti,*[b] and Cristina Nativi[a]
Keywords: Electrophilic aromatic substitution / Thioketones / Thioquinones / Regioselectivity / Sulfides / Sulfur
α,αЈ-Dioxothione 1a and ortho-thioquinones 2a and 2b are
able to react with several phenols and N,N-dimethylaniline
to give the corresponding alkyl aryl or diaryl sulfides. The
mechanism of this reaction was proved to be an electrophilic
aromatic substitution undergone by the highly polarised
carbon−sulfur double bond. Following this procedure, the
atropoisomeric biphenyl compound 26 was also prepared.
Over recent years we have demonstrated the utility in or-
ganic synthesis of α,αЈ-dioxothiones 1 and ortho-thioqui-
nones 2, thanks to their ability to act as enophiles,[1] elec-
tron-poor dienophiles[2] and heterodienes[3] in electrocyclic
reactions. Derivatives 1 and 2 can be generated and trapped
in situ by treating the corresponding N-thiophthalimides 3
and 4 with tertiary amines. Compounds 3 and 4 are, in turn,
obtained by treating β-dicarbonyls[2] and phenols[4] with
phthalimidesulfenyl chloride (5) (PhthNSCl, Phth
ϭ
phthaloyl): the key reagent of this simple and efficient
methodology for the generation of α-oxothiocarbonyl com-
pounds (Scheme 1).
Scheme 2. Reaction of thione 1a with o-allyl phenol 6 and o-cre-
sol 9
of sulfide 8, isolated in 12% yield (Scheme 2). Compound 8
can be considered as the product of the SEAr of thione 1a
on the para position of phenol 6. Indeed, when we repeated
the reaction using o-cresol 9, we were able to isolate sulfide
10 in 31% yield (Scheme 2) after 72 h at room temperature.
Several examples of thiophilic attack by carbon nucleo-
philes are reported in the chemistry of thiocarbonyl com-
pounds,[5] but to the best of our knowledge, no example of
electrophilic thiones involved in SEAr has been described.
The formation of sulfide 10 could also be explained by in-
voking a direct attack of the para carbon of phenol 9, or
the corresponding phenolate, onto the sulfenamidic sulfur[6]
of 3a (Scheme 3, path a), without the effective intermediacy
of thione 1a (Scheme 3, path b).
To test these hypotheses, we carried out two different ex-
periments. Firstly, o-cresol 9 was treated under the same
conditions (i.e., chloroform, pyridine, room temperature)
with sulfenamide 11. No evidence was found for the forma-
tion of sulfide 12, thus indicating that 9 is unable to attack
the sulfur atom of similar N-thiophthalimido derivatives
(Scheme 4, Equation 1).
Scheme 1. Generation of α, αЈ-dioxothiones and ortho-thioqui-
nones
In this paper we report that, in addition to their utility
in cycloaddition reactions, thiones 1 and 2 also react with
activated arenes, through an electrophilic aromatic substitu-
tion (SEAr), affording alkyl aryl or diaryl sulfides.
During our study into the ene reaction[1] of thione 1a
(R ϭ Y ϭ Me) with o-allyl phenol 6, we observed, together
with the expected ene-adduct 7, the unforeseen formation
[‡]
Part III: Ref.[1]
[a]
Centro C.N.R. ‘‘Chimica dei Composti Eterociclici’’.
`
Dipartimento di Chimica Organica, Universita di Firenze
Via G. Capponi 9, 50121, Firenze, Italy
E-mail: capozzi@chimorg.unifi.it
[b]
Dipartimento di Chimica Organica e Biologica,
`
Universita di Messina,
Salita Sperone 31, 98166, Messina, Italy
E-mail: menichet@isengard.unime.it
Eur. J. Org. Chem. 2000, 3653Ϫ3657
WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000
1434Ϫ193X/00/1121Ϫ3653 $ 17.50ϩ.50/0
3653

G. Capozzi, S. Menichetti, C. Nativi
FULL PAPER
Scheme 3. Possible mechanisms for the formation of sulfide 10
Figure 1. Aryl alkyl sulfides 14؊19 obtained by treating thione 1a
with phenols and with N,N-dimethylaniline
Scheme 4. Evidence for the actual mechanism operative in the
formation of 10
In the second experiment, we took advantage of the par-
ticular behaviour of thione 1a, which, when generated in
the absence of trapping reagents, dimerizes to give the 1,3-
dithiacyclobutane 13, which in turn undergoes a slow, base-
catalysed retro-dimerization.[2] Thus, after treating 3a with
pyridine and filtering off the phthalimide formed, we had
in solution mainly dimer 13 and pyridine. Addition of o-
cresol (9) to this mixture resulted in the isolation of sulfide
10, clearly formed through an electrophilic aromatic substi-
tution process undergone by thione 1a (Scheme 4, Equa-
tion 2).
Scheme 5. Diarylsulfides obtained from SEAr of thioquinone 2a
We verified that this unusual reactivity of thione 1a oc-
curs with highly activated arenes, such as EDG-substituted
phenols and N,N-dimethylaniline,[7] affording the corre-
sponding alkyl aryl sulfides 14؊19 as reported in Figure 1.
The next step was to verify whether such reactions could
Compounds 16؊18 were obtained as mixtures of two re- also take place with ortho-thioquinones. Thus, thioquinone
gioisomers: tentative attribution[8] of the regiochemistry 2a was generated from thiophthalimide 4a and pyridine in
was carried out by examination of the spectroscopic data chloroform at 60 °C and treated with several activated ar-
of minor and major isomers (see Experimental).
enes. As reported in Scheme 5, the SEAr reaction also oc-
The long reaction time required for the synthesis of sul- curred with thioquinone 2a, allowing us to isolate diaryl
fides 14؊19 is among the reasons for the moderate yields sulfides 20؊24 in moderate to good yields (Scheme 5).
obtained. As a matter of fact, under these conditions the
Structure assignment for regioisomers 23 and 24, ob-
irreversible polymerization of thione 1a becomes a compet- tained by treatment of 2a with m-methoxyphenol,[11] was
itive side reaction.[2] On the other hand, no improvement unequivocally confirmed by comparison of derivative 23
was achieved by using higher temperatures (60 and 80 °C), with an authentic sample obtained by treating thioquinone
different solvents[9] or stronger bases.[10]
2b, generated from the corresponding thiophthalimide 4b,
3654
Eur. J. Org. Chem. 2000, 3653Ϫ3657

α-Oxothiones, IV
FULL PAPER
Experimental Section
1
NMR: Varian Gemini-200 (200 and 50 MHz, for H and 13C, re-
spectively). For 1H and 13C NMR, CDCl3 as solvent δH ϭ 7.26;
δC ϭ 77.0 respectively. Ϫ MS: Carlo Erba QMD100 (70 eV). Ϫ IR:
PerkinϪElmer 4800. Ϫ Melting points are uncorrected. Ϫ CHCl3,
CH2Cl2 and pyridine were dried following standard procedures; all
commercial reagents were used without further purification as ob-
tained from freshly opened containers. Thiophthalimides 3a,[2]
4a,[4] 4b,[4] 4c,[14] and phthalimidesulfenyl chloride 5[15] were pre-
pared as described elsewhere.
Scheme 6. Reaction of thioquinone 2b with β-naphthol
with β-naphthol (Scheme 6). As expected, in this case the
electrophilic aromatic substitution afforded sulfide 23 in
67% yield, as the sole product (Scheme 6).
The generality of this approach to the synthesis of sym-
metrical and unsymmetrical polyhydroxylated diaryl sul-
fides[12] was further demonstrated by treating sulfenamide
4c[14] with β-naphthol, which resulted in the isolation of
biphenyl derivative 26 in 69% yield, as reported in
Scheme 7.
General Procedure for the Synthesis of Sulfides 10, 14؊25: Pyridine
(2 mmol) was added to a solution of the phthalimide derivatives
(1 mmol) and the required arene (1 mmol) in ethanol-free chloro-
form (3 mL), and the mixtures were kept at room temperature (or
60 °C for ortho-thioquinones) until the complete disappearance of
1
the thiophthalimide, monitored by H NMR and/or tlc. Evapora-
tion of the solvent, followed by silica gel flash chromatography,
gave the sulfides as pure compounds. Regioisomer ratios of deriva-
tives 16؊18 and 23 and 24 were obtained by 1H NMR on the crude
reaction mixtures. Yields, reaction times, and regioisomer ratios are
as reported in the General Section.
3-(4-Hydroxy-3-methylphenylthio)pentane-2,4-dione (10): Colour-
1
less oil (hexane/ethyl acetate, 6:1). Ϫ H NMR: δ ϭ 17.13 (s, 1 H,
enolic OH), 6.89Ϫ6.68 (m, 3 H, arom), 5.19 (br. s, 1 H, phenolic
OH), 2.37 (s, 6 H, CH3ϪCϭO), 2.22 (s, 3 H, CH3). Ϫ 13C NMR:
δ ϭ 198.2 (s, CϭO), 152.3 (s, CϪOH), 128.3 (d), 127.9 (s), 125.3
(s), 124.3 (d), 115.8 (d), 103.3 (s), 24.5 (q, CH3ϪCϭO), 15.9 (q).
Ϫ MS; m/z (%): 238 (72) [Mϩ], 196 (10) [Mϩ Ϫ 42], 162 (13), 138
(100). Ϫ C12H14O3S (238.3): calcd. C 60.48, H 5.92; found C 60.73,
H 5.76.
3-(4-Hydroxy-3,5-dimethylphenylthio)pentane-2,4-dione (14): Pale
yellow solid, m.p. 117Ϫ119 °C (hexane/ethyl acetate, 6:1) Ϫ 1H
NMR: δ ϭ 17.17 (s, 1 H, enolic OH), 6.71 (s, 2 H, arom), 4.53 (s,
1 H, phenolic OH), 2.36 (s, 6 H, CH3ϪCϭO), 2.20 (s, 6 H, CH3).
Scheme 7. Synthesis of atropoisomeric biphenyl sulfide 26
Ϫ
13C NMR: δ ϭ 198.0 (s, CϭO), 150.5 (s, CϪOH), 134.8 (s),
In conclusion, we have shown that dioxothiones and thio-
quinones are able to react with phenols to give polyhyd-
roxylated alkyl aryl or diaryl sulfides, by an SEAr mechan-
ism, as a further demonstration of the synthetic versatility
of these species. Incidentally, on treating di-p-tolylthioke-
tone with β-naphthol in the presence of pyridine, we did
not observe the formation of any product deriving from an
SEAr process, even after prolonged reaction time. Thus, this
work represents the first example of such a reaction for thio-
carbonyl compounds and strongly supports the conjecture
of an unusually high polarizability in α-oxothiones (Fig-
ure 2).
128.1 (s), 125.6 (d), 103.3 (s), 24.4 (q, CH3ϪCϭO), 15.9 (q). Ϫ
MS; m/z (%): 252 (40) [Mϩ], 154 (36), 122 (100). Ϫ C13H16O3S
(252.3): calcd. C 61.88, H 6.39; found C 61.97, H 6.60.
3-(2-Hydroxynaphthylthio)pentane-2,4-dione (15): Colourless oil
1
(hexane/ethyl acetate, 5:1). Ϫ H NMR: δ ϭ 17.96 (s, 1 H, enolic
OH), 8.04 (d, J ϭ 8.0 Hz, 1 H arom), 7.80Ϫ7.73 (m, 2 H arom.),
7.60Ϫ7.44 (m, 1 H arom), 7.41Ϫ7.32 (m, 1 H arom), 7.18 (d, J ϭ
8.8 Hz, 1 H arom), 6.78 (br. s, 1 H, phenolic OH), 2.40 (s, 6 H, 2
CH3ϪCϭO). Ϫ MS; m/z (%): 274 (9) [Mϩ], 144 (100). Ϫ
C15H14O3S (274.3): calcd. C 65.67, H 5.14; found C 65.51, H 5.03.
3-(4-Hydroxy-3-methoxyphenylthio)pentane-2,4-dione (16 major):
1
Colourless oil (hexane/ethyl acetate, 6:1). Ϫ H NMR: δ ϭ 17.19
(s, 1 H, enolic OH), 6.85 (d, J ϭ 8.4 Hz, 1 H arom), 6.65 (d, J ϭ
2.2 Hz, 1 H arom), 6.57 (dd, J ϭ 2.2, 8.4 Hz, 1 H arom), 5.48 (br.
s, 1 H, phenolic OH), 3.86 (s, 3 H, CH3ϪO), 2.36 (s, 6 H, CH3ϪCϭ
O). Ϫ MS; m/z (%): 254 (7) [Mϩ], 51 (100). Ϫ C12H14O4S (254.3):
calcd. C 56.68, H 5.55; found C 56.50, H 5.48.
Figure 2. Polarizability of α-oxothiones
3-(3-Hydroxy-4-methoxyphenylthio)pentane-2,4-dione (16 minor):
Colourless oil (hexane/ethyl acetate, 6:1). Ϫ H NMR: δ ϭ 17.28
1
Further aspects of the chemistry of oxothiones 1 and 2,
including the extension of the SEAr reaction to the prepara-
tion of synthetically valuable sulfides,[12] are currently under
investigation in these groups.
(s, 1 H, enolic OH), 6.78 (d, J ϭ 7.6 Hz, 1 H arom), 6.72 (d, J ϭ
1.4 Hz, 1 H arom), 6.50 (dd, J ϭ 1.4, 7.6 Hz, 1 H arom), 5.92 (br.
s, 1 H, phenolic OH), 3.90 (s, 3 H, CH3ϪO), 2.35 (s, 6 H, CH3ϪCϭ
O).3-(2-Hydroxy-4-methoxyphenylthio)pentane-2,4-dione (17 ma-
jor): Colourless oil (hexane/ethyl acetate, 5:1). Ϫ 1H NMR: δ ϭ
Eur. J. Org. Chem. 2000, 3653Ϫ3657
3655

G. Capozzi, S. Menichetti, C. Nativi
FULL PAPER
17.05 (s, 1 H, enolic OH), 7.03 (d, J ϭ 12.0 Hz, 1 H arom),
arom), 6.26 (br. s, 1 H, OH), 3.68 (s, 3 H, CH3ϪO). Ϫ 13C NMR:
6.49Ϫ6.40 (m, 2 H arom), 5.96 (br. s, 1 H, phenolic OH), 3.78 (s, δ ϭ 161.2 (s), 156.2 (s, 2 C), 135.0 (s), 133.8 (d), 132.1 (d), 129.6
3 H, CH3ϪO), 2.41 (s, 6 H, CH3ϪCϭO). Ϫ MS; m/z (%): 254 (46)
[Mϩ], 124 (100). Ϫ C12H14O4S (254.3): calcd. C 56.68, H 5.55;
found C 56.99, H 5.49.
(s), 128.7 (d), 127.9 (d), 124.3 (d), 123.8 (d), 117.0 (d), 110.9 (s),
110.6 (s), 108.0 (d), 101.4 (d), 55.3 (q). Ϫ MS; m/z (%): 298 (26)
[Mϩ], 124 (100). Ϫ C17H14O3S (298.4): calcd. C 68.44, H 4.73
found C 68.29, H 4.67.
3-(4-Hydroxy-2-methoxyphenylthio)pentane-2,4-dione (17 minor):
1
Pale yellow oil, (hexane/ethyl acetate, 5:1). Ϫ H NMR: δ ϭ 17.22
1-(4-Hydroxy-2-methoxyphenylthio)naphthalen-2-ol (24): White
(s, 1 H, enolic OH), 6.72 (d, J ϭ 8.4 Hz, 1 H arom), 6.45 (d, J ϭ
2.2 Hz, 1 H arom), 6.38 (dd, J ϭ 2.2, 8.4 Hz, 1 H arom), 5.27
(br. s, 1 H, phenolic OH), 3.86 (s, 3 H, CH3ϪO), 2.34 (s, 6 H,
CH3ϪCϭO).
1
solid, m.p. 149Ϫ151 °C (hexane/ethyl acetate, 10:1). Ϫ H NMR:
δ ϭ 8.44 (d, J ϭ 8.4 Hz, 1 H arom), 7.90Ϫ7.84 (m, 2 H, 1 H arom
ϩ 1 OH), 7.55Ϫ7.48 (m, 1 H arom), 7.38Ϫ7.30 (m, 2 H arom),
7.27 (d, J ϭ 11.4 Hz, 1 H arom), 6.86 (d, J ϭ 8.4 Hz, 1 H arom),
6.41 (d, J ϭ 2.6 Hz, 1 H arom), 6.21 (dd, J ϭ 2.6, 8.4 Hz, 1 H
arom), 5.10 (s, 1 H, OH), 3.90 (s, 3 H, CH3ϪO) Ϫ 13C NMR: δ ϭ
158.7 (s), 156.9 (s), 156.5 (s), 135.7 (s), 132.1 (d), 132.0 (d), 129.4
(s), 128.5 (d), 127.5 (d), 124.8 (d), 123.5 (d), 117.0 (d), 113.9 (s),
110.0 (s), 108.1 (d), 99.5 (d), 56.0 (q)
3-[4-(Dimethylamino)-2-hydroxyphenylthio]pentane-2,4-dione
(18
major) and 3-[2-(dimethylamino)-4-hydroxyphenylthio]pentane-2,4-
dione (18 minor): In this case separation of the two isomers by flash
chromatography was not possible. Data for the mixture of major
(M) and minor (m) isomer are as follows: Colourless oil (CH2Cl2/
1
methanol, 50:1). Ϫ H NMR: δ ϭ 17.00 (s, 1 H, enolic OH), 7.18
(d, J ϭ 8.8 Hz, 1 H arom, m), 7.04 (s, 1 H, phenolic OH, m), 7.03
(d, J ϭ 9.2 Hz, 1 H arom, M), 6.33Ϫ6.23 (m, 3 H arom, M ϩ m),
6.19 (dd, J ϭ 3.0, 8.8 Hz, 1 H arom, m), 6.10 (br. s, 1 H, phenolic
OH, M), 2.93 (s, 12 H, CH3ϪN, M ϩ m), 2.44 (s, 6 H, CH3ϪCϭ
O, M), 2.32 (s, 6 H, CH3ϪCϭO, m). Ϫ MS; m/z (%): 267 (40)
[Mϩ], 168 (73), 137 (100). Ϫ C13H17NO3S (267.3): calcd. C 58.40,
H 6.41, N 5.24; found C 58.24, H 6.58, N 5.17.
1-[4-Hydroxy-5-(2-hydroxynaphthylthio)-2-methoxyphenylthio]-
naphthalen-2-ol (25): Glassy solid, (hexane/ethyl acetate, 10:1). Ϫ
1H NMR: δ ϭ 8.12Ϫ8.00 (m, 4 H arom), 7.82Ϫ7.45 (m, 6 H arom),
7.42 (s, 1 H, OH), 7.16 (d, J ϭ 8.0 Hz, 1 H arom), 7.11 (s, 1 H,
OH), 7.07 (d, J ϭ 8.0 Hz, 1 H arom), 6.82 (s, 1 H arom), 6.56 (br.
s, 1 H, OH), 6.38 (s, 1 H arom), 3.75 (s, 3 H, CH3ϪO). Ϫ MS; m/z
(%): 472 (6) [Mϩ], 298 (34), 144 (100).
3-[4-(Dimethylamino)phenylthio]pentane-2,4-dione (19): Yellow oil
1
(hexane/ethyl acetate, 15:1). Ϫ H NMR: δ ϭ 17.05 (s, 1 H, enolic
2,2Ј-Dihydroxy-3,3Ј-bis(α-thio-β-naphthyl)-6,6Ј-dimethoxy-1,1Ј-
biphenyl (26): White solid, m.p. 195Ϫ196 °C (hexane/ethyl acetate/
CH2Cl2, 4:1:1). Ϫ H NMR (DMSO d6): δ ϭ 8.59 (d, J ϭ 8.4 Hz,
OH), 7.08Ϫ6.98 (m, 2 H arom), 6.72Ϫ6.62 (m, 2 H arom), 2.91 (s,
6 H, CH3ϪN), 2.37 (s, 6 H, CH3ϪCϭO). Ϫ MS; m/z (%): 251 (37)
[Mϩ], 121 (100). Ϫ C13H17NO2S (251.3): calcd. C 62.12, H 6.82, N
5.57; found C 61.93, H 6.74, N 5.82.
1
2 H), 7.91 (d, J ϭ 8.8 Hz, 2 H), 7.87 (d, J ϭ 8.2 Hz, 2 H), 7.59 (t,
J ϭ 7.4 Hz, 2 H), 7.38 (t, J ϭ 7.4 Hz, 2 H), 7.30 (d, J ϭ 8.8 Hz, 2
H), 7.10 (d, J ϭ 8.8 Hz, 2 H), 6.40 (d, J ϭ 8.8 Hz, 2 H), 3.50 (s, 6
H, CH3ϪO). Ϫ 13C NMR (DMSO d6): δ ϭ 158.2 (s, CϪOH),
157.1 (s, CϪOCH3), 154.7 (s, CϪOH b), 136.0 (d), 131.7 (d), 131.5
(s, CHϪCϪCS), 128.9 (d), 128.6 (s), 127.6 (d), 124.6 (d), 123.4 (d),
118.2 (s), 113.4 (d), 110.7 (s, CϪS), 110.5 (s, CϪS), 103.4 (s), 55.4
(q). Ϫ MS (ESI-Finnigan LCQ ion trap); m/z 595 [MHϩ].
1-(4-Hydroxy-3,5-dimethylphenylthio)naphthalen-2-ol (20): Colour-
less oil (hexane/ethyl acetate, 4:1). Ϫ H NMR: δ ϭ 8.28 (d, J ϭ
1
8.4 Hz, 1 H arom), 7.87 (d, J ϭ 8.8 Hz, 1 H arom), 7.80 (s, 1 H,
phenolic OH), 7.54Ϫ7.29 (m, 4 H arom), 6.76 (s, 2 H arom), 4.48
(s, 1 H, phenolic OH), 2.10 (s, 6 H, CH3). Ϫ MS; m/z (%): 296 (27)
[Mϩ], 122 (100). Ϫ C18H16O2S (296.4): calcd. C 72.94, H 5.44;
found C 73.11, H 5.82.
1-(2-Hydroxynaphthylthio)naphthalen-2-ol (21): White solid; m.p.
217Ϫ219 °C (CH2Cl2); ref.[13a] m.p. 215 °C. Ϫ 1H NMR: δ ϭ
8.46Ϫ8.38 (m, 2H arom), 7.75 (br. d, J ϭ 8.4 Hz, 4 H arom),
7.56Ϫ7.47 (m, 2 H arom), 7.38Ϫ7.30 (m, 2 H arom), 7.17 (d, J ϭ
9.2 Hz, 2 H arom), 6.83 (s, 2 H, phenolic OH). Ϫ 13C NMR: δ ϭ
155.8 (s), 134.7 (s), 131.7 (d), 129.6 (s), 128.7 (s), 128.9 (d), 128.0
(d), 123.9 (d), 123.7 (d), 117.4 (d). Ϫ MS; m/z (%): 318 (16) [Mϩ],
145 (100). Ϫ C20H14O2S (318.1): calcd. C 75.45, H 4.43; found C
75.62, H 4.31.
Acknowledgments
This work was carried out under the auspices of the National Pro-
ject ‘‘Stereoselezione in Sintesi Organica. Metodologie ed Applica-
zioni’’ supported by the Ministero dellЈUniversita e della Ricerca
`
Scientifica e Tecnologica, Rome, and by the University of Florence.
[1]
G. Capozzi, M. Fragai, S. Menichetti, C. Nativi, Eur. J. Org.
1-[4-(Dimethylamino)phenylthio]naphthalen-2-ol (22): Yellow oil. Ϫ
1H NMR: δ ϭ 8.36 (d, J ϭ 8.0 Hz, 1 H arom), 7.87Ϫ7.76 (m, 2 H
arom), 7.55Ϫ7.47 (m, 1 H arom), 7.42 (s, 1 H, phenolic OH),
7.38Ϫ7.29 (m, 2 H arom), 7.13Ϫ7.04 (m, 2 H arom), 6.60Ϫ6.51
(m, 2 H arom), 2.86 (s, 6 H, CH3ϪN). Ϫ MS; m/z (%): 295 (34)
[Mϩ], 121 (100). Ϫ C18H17NOS (295.4): calcd. C 73.19, H 5.80, N
4.74; found C 73.02, H 5.68, N 4.73.
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δ ϭ 8.39 (d, J ϭ 8.4 Hz, 1 H arom), 7.83Ϫ7.73 (m, 2 H, 1 H arom
ϩ 1 OH), 7.60Ϫ7.52 (m, 2 H arom), 7.40Ϫ7.33 (m, 2 H arom),
7.25 (d, J ϭ 8.8 Hz, 1 H arom), 7.17 (d, J ϭ 8.8 Hz, 1 H arom),
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Ϫ
M. Dagonneau, J. Vialle, Tetrahedron 1974, 30,
3656
Eur. J. Org. Chem. 2000, 3653Ϫ3657

α-Oxothiones, IV
3119Ϫ3126. Ϫ
FULL PAPER
[5c]
P. Beak, J. Yamamoto, C. J. Upton, J. Org.
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Chem 1975, 40, 3052Ϫ3062. Ϫ
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A. Degl’Innocenti, A. Capperucci, Sulf. Rep. 1998, 20,
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S. J. Grossert, K. P. Dubey, J. Chem. Soc., Chem. Commun.
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[7]
[8]
Several other electron-rich arenes tested Ϫ such as, among
others, 1,3-dimethoxybenzene, anthracene, and aniline Ϫ were
unreactive towards thione 1a.
In the case of sulfide 17, the attribution of the relative regio-
chemistry was also achieved by comparison with the result ob-
served in the same reaction with ortho-thioquinone 2a (vide
infra).
Chloroform and dichloromethane are the best solvents for
these reactions. Benzene, THF, acetone, acetonitrile, and
DMSO cause a remarkable decrease in the reaction rate, while
with DMF we observed only polymerization of the thione 1a.
Generation of thione 1a with TEA or DBU in the presence of
phenol 9, resulted in a drastic decrease in the reaction yield.
[12]
Polyhydroxylated diaryl sulfides have found several applica-
tions as stabilisers against oxidation (see ref.[13]).
[13] [13a] K. Daimler, Ger. 831.729 Feb. 18, 1952, Chem. Abstr. 1952,
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E. G.
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Abstr. 1966, 64, 3782d. Ϫ
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[15]
G. Capozzi, G. Delogu, M. A. Dettori, D. Fabbri, S. Meni-
chetti, C. Nativi, R. Nuti, Tetrahedron Lett. 1999, 40,
4421Ϫ4424.
[10]
[11]
G. Boccardo, G. Capozzi, M. Giuntini, S. Menichetti, C. Na-
tivi, Tetrahedron 1997, 53, 17383Ϫ17394.
Received April 10, 2000
In the reaction of 2a with m-methoxyphenol, we also isolated
the corresponding bis-substituted derivative 25 (6%).
[O00177]
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