Zinc perchlorate hexahydrate catalysed conjugate addition of thiols to α,β-unsaturated ketones

Article abstract of DOI:10.1055/s-2005-868480

Zn(II) perchlorate hexahydrate has been found to be a new and efficient catalyst for conjugate addition of thiols to α,β-unsaturated ketones under solvent-free conditions at room temperature. The reaction of aryl, arylalkyl and alkyl thiols with cyclic an

Full text of DOI:10.1055/s-2005-868480

1370
LETTER
Zinc Perchlorate Hexahydrate Catalysed Conjugate Addition of Thiols
to a,b-Unsaturated Ketones
Conjugate
A
dd
a
ition of
T
h
n
iols to ,-Uns
j
aturated
e
Ketones ev K. Garg, Raj Kumar, Asit K. Chakraborti*
National Institute of Pharmaceutical Education and Research (NIPER), Sector 67, S. A. S. Nagar, Punjab 160062, India
Fax +91(172)2214692; E-mail: akchakraborti@niper.ac.in
Received 24 February 2005
We felt that the use of a metal catalyst that can form a
strong coordinate bond with the carbonyl oxygen of the
a,b-unsaturated ketones should increase the electrophilic-
ity of the b-carbon and assist the conjugate addition to be
Abstract: Zn(II) perchlorate hexahydrate has been found to be a
new and efficient catalyst for conjugate addition of thiols to a,b-un-
saturated ketones under solvent-free conditions at room tempera-
ture. The reaction of aryl, arylalkyl and alkyl thiols with cyclic and
acyclic a,b-unsaturated ketones takes place affording excellent carried out under milder conditions and in short reaction
yields after five minutes to six hours. The compatibility of
times (Scheme 1).
Zn(ClO4)2·6H2O with different solvents provides a means to carry
out the reaction under versatile experimental conditions. The rate of
–
MXn
+
MXn
thiol addition was dependent on the electronic and steric factors of
the enones and the thiols. The substituent at the b-carbon of the a,b-
unsaturated ketone substrate caused steric hindrance during conju-
gate addition and required longer reaction times. The rate of reac-
tion for alkane thiols e.g. ethanethiol was sluggish compared to that
of aryl thiols.
O
O
R1
R1
RSH
R2
R2
MXn
–
MXn
O
O
R1
R1
Keywords: conjugate addition, thiol, a,b-unsaturated ketone,
zinc(II) perchlorate, catalyst
H
H
+
S
O
O
R2
R2
R1
R1
R
R2
S
R
R2
S
R
MXn
Thia-Michael addition is an important transformation due
its important role in biosynthesis1 as well as in the synthe-
sis of bioactive compounds.2 The reaction has versatile
applications in synthetic organic chemistry. The ease of
generation of the double bond by removal of the sulfur
moiety either by copper(I)-induced elimination3 or by ox-
idative elimination,2b offers an elegant strategy for
chemoselective protection of the olefinic double bond of
conjugated enones.2b It is known that b-sulfido carbonyl
compounds, derived from thia-Michael addition to a,b-
unsaturated carbonyl compounds, serve as starting mate-
rials for the generation of b-acylvinyl cation equivalents4
and homoenolate equivalents.5 These are of interest to or-
ganic/medicinal chemists for the development of new
methodologies for thia-Michael additions. Various cata-
lysts have been used for the conjugate addition of thiols to
a,b-unsaturated carbonyl compounds. These include met-
al halides,6 nitrate,7 phosphates,8 triflates,9 solid acids,10
and ionic liquids.11 The various disadvantages (e.g. long
reaction times,6a,b,9a use of halogenated solvents,6b,7,9a dif-
ficulty in recovery of high boiling solvents,10b high tem-
peratures,10b,11c special efforts required for preparation of
catalysts,8,9b use of costly catalysts,6b,9,11a moderate
yields,6b,7 use of toxic chemicals,6a etc.) encountered in the
reported methodologies necessitate the development of a
better method.
Scheme 1 Role of metal salts in catalyzing thia-Michael addition.
While designing a cheap and effective catalyst, we con-
sidered the following aspects: (i) the catalyst should be
derived from group I/II metals so as to reduce its cost, (ii)
the central metal ion of the metal salt should have strong
oxophilic property for more effective coordinate bond for-
mation with the carbonyl oxygen, and (iii) the counter
anion should be highly electron-withdrawing in nature to
make the central metal ion more oxophilic. While select-
ing suitable group I/II metal salts, we thought that the
metal ion of salts of strong protic acids should have a more
pronounced oxophilic property. Triflic acid is the
strongest protic acid due to the large negative H0 value
(–14.1)12 and perchloric acid is the second strongest protic
acid. Recently it has been demonstrated that the per-
chlorate counter anion increased the oxophilicity of the
central metal ion of metal perchlorates and made them
highly efficient catalysts for electrophilic activation dur-
ing acetylation.13 Thus, we planned to evaluate the cata-
lytic efficiency of various commercially available group I
and II metal triflates and perchlorates and report that zinc
perchlorate hexahydrate is a new and efficient catalyst for
the thia-Michael addition.
SYNLETT 2005, No. 9, pp 1370–1374
0
1.
0
6.
2
0
0
5
Advanced online publication: 21.04.2005
DOI: 10.1055/s-2005-868480; Art ID: D05205ST
© Georg Thieme Verlag Stuttgart · New York

LETTER
Conjugate Addition of Thiols to a,b-Unsaturated Ketones
1371
and 3) indicated the sensitivity of Mg2+ derived catalysts
to non-anhydrous conditions. Surprisingly, magnesium
and zinc triflates were found to be inferior to the corre-
sponding perchlorates (Table 1, compare the result of en-
try 6 with those of entries 2 and 3 and the result of entry 7
with that of entry 5). A similar observation was made dur-
ing the acetylation reaction.13c
SH
O
O
S
cat. (1 mol%)
+
neat, r.t.,
1.5 h
1a
2a
3aa
Scheme 2 Conjugate addition of 1a with 2a under the catalytic
influence of various group I and II metal perchlorates and triflates.
We next planned to determine the influence of solvents on
the catalytic property of Zn(ClO4)2·6H2O during the reac-
tion of 1a with 2a (Table 2). The catalyst was compatible
with non-polar (entry 5), weakly polar (Table 2, entries 1,
6 and 8), aprotic polar (Table 2, entries 3, 7, 9 and 10) and
protic polar (Table 2, entry 11) solvents affording moder-
ate to high yields. The results revealed that
Zn(ClO4)2·6H2O retained its catalytic activity in solvents
with poor (Table 2, entry 5) and weak (Table 2, entries 1,
3, 6, 8, 9 and 10) coordinating properties. The poor cata-
lytic activity in MeCN (Table 2, entry 4) is probably due
to competitive coordination of the solvent with the cata-
lyst. The inferior results obtained in DMF are probably
due to its specific affinity towards cations, which inter-
feres with the formation of a coordinate bond between the
carbonyl oxygen atom and Zn2+ ion. Although a similar
interference of coordination between the carbonyl sub-
strate and the Zn2+ ion is expected to take place in MeOH,
the hydrogen bonding effect of MeOH probably compen-
sates for this. The poor result obtained in water is due to
the poor solubility of 1a and 2a in water.
In a model reaction, trans-4-phenyl-3-butene-2-one (1a)
(2.5 mmol) was taken as a representative a,b-unsaturated
carbonyl compound; this was treated with thiophenol (2a)
(1.1 equiv) in the presence of various group I and II metal
triflates and perchlorates under neat conditions at room
temperature (Scheme 2).
The reactions were monitored by IR and GCMS and the
optimum results are provided in Table 1.
Table 1 Reaction of 1a with 2a in the Presence of Various
Perchlorates and Triflatesa
Entry
Catalyst (1 mol%)
LiClO4
Yield (%)b
1
2
3
4
5
6
7
48
51
45
31
92
32
83
Mg(ClO4)2
Mg(ClO4)2·6H2O
Ba(ClO4)2
Zn(ClO4)2·6H2O
Mg(OTf)2
Table 2 Reaction of 1a with 2a in Various Solvents under the Cat-
alytic Influence of Zn(ClO4)2·6H2Oa
Zn(OTf)2
Entry
Solvent
(CH2)4O
H2O
Yield (%)b,c
a The substrate (1 equiv) was treated with thiophenol (1.1 equiv) in the
presence of catalyst (1 mol%) at r.t. (ca. 25–30 °C) in the absence of
solvent for 1.5 h.
1
2
63
17
66
54
75
77
60
81
70
75
84
b GCMS yield of the corresponding conjugate addition product 3aa.
3
EtOAc
The best result was obtained in the presence of
Zn(ClO4)2·6H2O (1 mol%) affording 92% conversion to
the desired conjugate addition product 3aa after 1.5 hours
(Table 1, entry 5). The poor catalytic activity of LiClO4
and Ba(ClO4)2 is probably due to the lower charge to size
4
MeCN
5
C6H14
6
Et2O
(Z2/r) value of Li+ (1.35 e2m–10) and Ba2+ (2.94 e2m–10
)
7
Me2NCHO
(CH2CH2)2O2
CH2Cl2
MeNO2
MeOH
ions compared to that of Zn2+ ion (15.33 e2m–10).14 The ox-
ophilicity of Li+ and Ba2+ ions became significantly lower
compared to that of Zn2+ ion as a result of lower Z2/r val-
ues of the former ions. The parallels between the catalytic
activity and charge-size function of metal perchlorates
was also observed during the metal perchlorate-catalysed
acetylation13c and Diels–Alder reaction.15 However, the
inferior results obtained for Mg(ClO4)2 (Table 1, entry 2)
and Mg(ClO4)2·6H2O (Table 1, entry 3) are probably due
to the higher hydrolysis constant (pKh value) of 11.42 for
the Mg2+ ion compared to a value of 9.6 for the Zn2+ ion.16
Thus, the magnesium salts became susceptible to hydro-
lytic decomposition in the presence of trace amounts of
moisture and lost their catalytic property.13d The decrease
in catalytic activity of Mg(ClO4)2·6H2O compared to that
of Mg(ClO4)2 (Table 1, compare the results of entries 2
8
9
10
11
a Conditions: 1a (2.5 mmol) was treated with 2a (1.1 equiv) in the
presence of Zn(ClO4)2·6H2O (1 mol%) at r.t. (~25–30 °C) for 1.5 h.
b GCMS yield of the corresponding conjugate addition product 3aa.
c GCMS revealed the presence of unreacted 1a and 2a.
To establish the generality of this process, various enones
such as 1a, 2-cyclohexen-1-one (1b), 3-buten-2-one (1c)
and trans-1,3-diphenylpropenone (1d) were treated with a
range of aryl thiols e.g., 2a, 4-methylthiophenol (2b),
Synlett 2005, No. 9, 1370–1374 © Thieme Stuttgart · New York

1372
S. K. Garg et al.
LETTER
Table 3 Zn(ClO4)2·6H2O-Catalysed Conjugate Addition of Thiols
to a,b-Unsaturated Ketonesa
arylalkyl thiols e.g., benzyl thiol (2c), 2-furfuryl thiol (2d)
and alkyl thiols e.g. ethane thiol (2e) under the above-de-
scribed optimum conditions (Scheme 3). Excellent results
were obtained in each case. The reactions were completed
within five minutes to six hours (TLC, IR, GCMS)
(Table 3). After the addition of the catalyst to the magnet-
ically stirred mixture of the enone and the thiol, an exo-
thermic reaction took place indicating product formation.
Entry Enone Thiol
Product Time Yield
(min) (%)b,c
O
Ph
1
2
3
4
5
1a
1a
1a
1a
1a
Thiophenol (2a)
3aa
90
120
120
120
360
89d
80
82
78
83
O
O
Zn(ClO4)2·6H2O
(1 mol%)
4-Methylthiophenol (2b) 3ab
R1
R1
+RSH
R2
Benzyl thiol (2c)
2-Furfuryl thiol (2d)
Ethane thiol (2e)
3ac
3ad
3ae
R2
SR
1
2
3
Scheme 3 Conjugate addition of various thiols to cyclic and acyclic
enones under the catalytic influence of Zn(ClO4)2·6H2O.
O
The conjugate addition reaction of thiols, catalysed by
Zn(ClO4)2.6H2O, was found to be dependent on steric and
electronic factors of the a,b-unsaturated ketones and thi-
ols. The comparison of the results of 1b and 1c with those
of 1a and 1d reveal that the substituent at the b-position of
the enone exhibited steric and electronic effects. The reac-
tion of 1a with certain thiols took longer compared to the
corresponding reaction with 1c carried out under similar
conditions (Table 3, compare the results of entries 1–5
with those of entries 11–15). This may be due to the steric
hindrance exhibited by the 2-phenyl group of 1a towards
the approaching thiol. Furthermore, the p-resonance ef-
fect of the 2-phenyl substituent in 1a and 1d makes these
enones less electrophilic compared to 1b and 1c. The
combined steric and resonance effects of the 2-phenyl
substituent make the conjugate addition reactions of 1a
and 1d, with particular thiols, sluggish compared to those
of 1b and 1c (Table 3, compare the results of entries 6–10
and 11–15 with those of entries 1–5 and 16–20). The com-
parison of the results of 1a with those of 1d suggested that
the R1 group of the a,b-unsaturated ketone exhibited elec-
tronic effects in controlling the conjugate addition. The
resonance (hyperconjugative) effect of the methyl group
in 1a (R1 = Me) increased the electron density at the car-
bonyl oxygen and enhanced the coordinating ability with
the Zn2+. Contrary to this, the phenyl group in 1d
(R1 = Ph), decreased the electron density at the carbonyl
oxygen by inductive and resonance effects and resulted in
weak coordination between the carbonyl oxygen and the
Zn2+. Therefore, the reaction of 1d with thiols required a
longer time and higher temperature compared to the cor-
responding reaction of 1a (Table 3, compare the results of
entries 1–5 with those of entries 16–20). The longer times
required for the conjugate addition of 2e, an aliphatic thi-
ol, represented the generalised steric effect of the thiol
(Table 3, compare entry 5 with entries 1–4, entry 10 with
entries 5–9, entry 15 with entries 11–14 and entry 20 with
entries 16–19). The reaction rates of a six-membered cy-
clic enone without a b-substituent, exhibited parallels
with those of an analogous acyclic enone having an
unsubstituted b-carbon (Table 3, compare the results of
entries 11–15 with those of entries 6–10).
6
7
1b
1b
1b
1b
1b
2a
2b
2c
2d
2e
3ba
3bb
3bc
3bd
3be
5
15
10
20
20
90
85
91
88
82
8
9
10
O
11
12
13
14
15
1c
1c
1c
1c
1c
2a
2b
2c
2d
2e
3ca
3cb
3cc
3cd
3ce
5
10
10
15
20
84
81
83
80
81
O
Ph
Ph
16
17
18
19
20
1d
1d
1d
1d
1d
2a
3da
3db
3dc
3dd
3de
90
150
150
140
240
87e
85e
91e
92e
88e
2b
2c
2d
2e
a The enone (1 equiv) was treated with the thiol (1.1 equiv) in the
presence of Zn(ClO4)2·6H2O (1 mol%) at r.t. (ca. 25–30 °C except for
entries 16–20) in the absence of solvent (except for entries 16–20).
b Isolated yield of the corresponding conjugate addition product
obtained after chromatographic purification.
c The products were characterized by IR spectroscopy, NMR
spectroscopy and MS.
d A 85% yield was obtained in carrying out the reaction in MeOH at
r.t. for 1.5 h.
e The reaction was carried out in MeOH under reflux.
Synlett 2005, No. 9, 1370–1374 © Thieme Stuttgart · New York

LETTER
Conjugate Addition of Thiols to a,b-Unsaturated Ketones
1373
To compare the catalytic efficiency of Zn(ClO4)2·6H2O A recent report suggested that the InCl3-catalysed (10
with that of reported catalysts, we chose a few representa- mol%) conjugate addition reaction of chalcones requires
tive examples involving the same reactants and the results anhydrous MeOH.6c The feasibility of carrying out the re-
are summarized in Table 4. The results established that action of trans-1,3-diphenylpropenone (1d) with various
Zn(ClO4)2·6H2O is a better suited for conjugate addition thiols in non-anhydrous MeOH using Zn(ClO4)2·6H2O as
of thiols to a,b-unsaturated ketones with respect to (i) catalyst (Table 3, entries 16–20) established that the
amount of catalyst, (ii) range of solvents, (iii) reaction present methodology is advantageous over the reported
times, (iv) reaction temperatures and (v) product yields.
procedure.
We have described herein a highly efficient catalyst for
thia-Michael addition under solvent-free conditions at
room temperature. The advantages include, (i) the use of
a cheap, easy to handle and commercially available cata-
lyst, room temperature and non-anhydrous reaction condi-
tions, (ii) short reaction times and (iii) high yields. With
increasing environmental concerns17 the solvent-free re-
action conditions should make this methodology environ-
mentally friendly and applicable for large scale
operations.
Table 4 Comparison of the Results of Zn(ClO4)2·6H2O-Catalysed
Conjugate Addition of Thiols to a,b-Unsaturated Ketones with those
of Reported Catalysts
Entry Product Cat. (mol%)
Solvent Temp Time
(°C)
Yield
(%)b
a
1
2
3ba
3ba
3ba
3ba
3bb
3bb
3bc
3bc
3be
3be
3ca
3ca
3ca
3ca
3ab
3ab
InBr3
(10)
CH2Cl2 r.t.
16–24 h 746b
a
Bi(NO3)3
(15)
CH2Cl2 r.t.
2–4 h
1.5 h
5 min
12 h
657
729b
90
3
Bi(OTf)3
(5)
MeCNa r.t.
4-Phenylthio-4-phenylbutan-2-one; Typical Procedure
To a magnetically stirred mixture of trans-4-phenyl-3-buten-2-one
(0.36g, 2.5 mmol) and thiophenol (0.30g, 2.75 mmol, 1.1 equiv)
was added Zn(ClO4)2·6H2O (9.3 mg, 0.025 mmol, 1 mol%). The re-
action mixture was stirred at 25–30 °C for 1.5 h. After the comple-
tion of the reaction (TLC, IR), the reaction mixture was diluted with
EtOAc (2 mL), adsorbed onto silica gel, charged onto a column of
silica gel (60–120 mesh, 5 g), and eluted with hexane (to eliminate
any disulfide formed), followed by EtOAc–hexane (1:10) to afford
4-phenylthio-4-phenyl-butan-2-one (570 mg, 89%, Table 3, entry
1) as a colourless oil.
IR (neat): 1708 cm–1.
1H NMR (300 MHz, CDCl3): d = 2.04 (s, 3 H), 3.04 (dd, 2 H,
J = 2.7, 7.8 Hz), 4.70 (t, 1 H, J = 7.2 Hz), 7.20–7.25 (m, 10 H).
13C NMR (300 MHz, CDCl3): d = 30.63, 47.98, 49.44, 127.38,
127.57, 127.65, 128.43, 128.79, 132.83, 140.98, 205.46.
4
Zn(ClO4)2
(1)
neat
r.t.
r.t.
r.t.
r.t.
r.t.
a,b
5
CdI2
(1)
PhCH3
neat
746a
6
Zn(ClO4)2
(1)
15 min 85
a,b
7
CdI2
(1)
PhCH3
neat
12 h
486a
8
Zn(ClO4)2
(1)
10 min 91
9
TBAB
(excess)
neatc
neat
105 45 min 9011b
MS (EI): m/z = 256.
10
11
12
13
14
15
16
Zn(ClO4)2
(1)
r.t.
20 min 82
709b
7211b
105 45 min 7511c
Anal. Calcd for C16H16OS: C, 74.96; H, 6.29; S, 12.51. Found: C,
74.94; H, 6.30; S, 12.49.
Bi(OTf)3
(5)
CH3CN r.t.
1 h
The remaining reactions were carried out following this general
procedure. In each occasion, the spectral data (IR, NMR and MS) of
known compounds were found to be identical with those reported in
the literature. New spectral data are given below for representative
adducts.
TBAB
(excess)
neatc
neatd
neat
105 2 h
[pmim]Br
(300 mg/mmol)
4-Benzylthio-4-phenylbutan-2-one (3ac)
Colourless oil.
IR (neat): 1716 cm–1.
1H NMR (300 MHz, CDCl3): d = 1.98 (s, 3 H), 2.91 (d, 2 H, J = 7.0
Hz), 3.47 (q, 2 H, JAB = 13.3 Hz), 4.19 (t, 1 H, J = 7.2 Hz), 7.17–
7.31 (m, 10 H).
13C NMR (300 MHz, CDCl3): d = 30.39, 35.63, 43.81, 49.89,
126.93, 127.30, 127.86, 128.36, 128.49, 128.83, 137.73, 141.43,
205.18.
Zn(ClO4)2
(1)
r.t.
5 min
84
a
InBr3
(10)
CH2Cl2 r.t.
16–24 h 786b
Zn(ClO4)2
(1)
neat
r.t.
2 h
80
a Anhydrous solvent was used.
b Two equivalents of thiol were used.
c The molten catalyst was used as solvent.
d Ionic liquid was used as solvent.
MS (EI): m/z = 270.
Anal. Calcd for C17H18OS: C, 75.51; H, 6.71; S, 11.86. Found: C,
75.48; H, 6.73; S, 11.89.
Synlett 2005, No. 9, 1370–1374 © Thieme Stuttgart · New York

1374
S. K. Garg et al.
LETTER
3-(4-Methylphenylthio)cyclohexan-1-one (3bb)
Colourless oil.
References
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1H NMR (300 MHz, CDCl3): d = 1.62–1.75 (m, 2 H), 2.06–2.13 (m,
2 H), 2.20–2.37 (m, 6 H), 2.60–2.67 (m, 1 H), 3.30–3.34 (m, 1 H),
7.10 (d, 2 H, J = 7.8 Hz), 7.31 (d, 2 H, J = 7.8 Hz).
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47.53, 128.95, 129.62, 133.69, 137.84, 208.58.
MS (EI): m/z = 220.
Anal. Calcd for C13H16OS: C, 70.87; H, 7.32; S, 14.55. Found C,
70.84; H, 7.33; S, 14.57.
4-(2-Furfurylthio)butan-2-one (3cd)
Colourless oil.
IR (neat): 1715 cm–1.
1H NMR (300 MHz, CDCl3): d = 2.12 (s, 3 H), 2.65–2.73 (m, 4 H),
3.71 (s, 2 H), 6.18 (s, 1 H), 6.30 (s, 1 H), 7.35 (s, 1 H).
13C NMR (300 MHz, CDCl3): d = 25.28, 28.39, 29.74, 43.09,
107.29, 110.26, 141.87, 151.33, 206.46.
MS (EI): m/z = 184.
Anal. Calcd for C9H12O2S: C, 58.67; H, 6.56; S, 17.40. Found: C,
58.64; H, 6.58; S, 17.43.
3-Benzylthio-1,3-diphenylpropan-1-one (3dc)
White solid; mp 67–69 °C
(11) (a) Yadav, J. S.; Reddy, B. V. S.; Baishya, G. J. Org. Chem.
2003, 68, 7098. (b) Ranu, B. C.; Dey, S. S.; Hajra, A.
Tetrahedron 2003, 59, 2417. (c) Ranu, B. C.; Dey, S. S.
Tetrahedron 2004, 60, 4183.
(12) Olah, G. A.; Prakash, G. K. S. Superacids; Wiley: New
York, 1985.
(13) (a) BiOClO4: Chakraborti, A. K.; Gulhane, R.; Shivani,
Synthesis 2003, 1805. (b) Zn(ClO4)2: Bartoli, G.; Bosco, M.;
Dalpozzo, R.; Marcantoni, E.; Massaccesi, M.; Sambri, L.
Eur. J. Org. Chem. 2003, 4611. (c) Mg(ClO4)2:
IR (KBr): 1682 cm–1.
1H NMR (300 MHz, CDCl3): d = 3.40–3.57 (m, 4 H), 4.45 (t, 1 H,
J = 7.1 Hz), 7.18–7.31 (m, 8 H), 7.34–7.39 (m, 4 H), 7.46–7.51 (m,
1 H), 7.82 (d, 2 H, J = 7.4 Hz).
13C NMR (300 MHz, CDCl3): d = 35.78, 44.05, 45.15, 126.90,
127.23, 127.98, 128.36, 128.46, 128.85, 133.09, 136.59, 137.78,
141.67, 196.64.
MS (EI): m/z = 332.
Chakraborti, A. K.; Sharma, L.; Gulhane, R.; Shivani,
Tetrahedron 2003, 59, 7661. (d) Mg(ClO4)2: Bartoli, G.;
Bosco, M.; Dalpozzo, R.; Marcantoni, E.; Massaccesi, M.;
Rinaldi, S.; Sambri, L. Synlett 2003, 39. (e) LiClO4: Nakae,
Y.; Kusaki, I.; Sato, T. Synlett 2001, 1584.
Anal. Calcd for C22H20OS: C, 79.48; H, 6.06; S, 9.65. Found: C,
79.50; H, 6.09; S, 9.67.
3-Ethylthio-1,3-diphenylpropan-1-one (3de)
White solid; mp 59–61 °C
(14) Huhey, J. E. Inorganic Chemistry: Principles of Structure
and Reactivity, 3rd ed.; Harper & Row: Singapore, 1990,
Chap. 7.
(15) Casachi, A.; Desimoni, G.; Faita, G.; Invernizzi, A. G.;
Lanati, S.; Righetti, P. J. Am. Chem. Soc. 1993, 115, 8002.
(16) Yatsimirskii, K. B.; Vasil’ev, V. P. Instability Constants of
Complex Compounds; Pergamon: Elmsford N. Y., 1960.
(17) Garrett, R. L. In Designing Safer Chemicals, In American
Chemical Society Symposium Series 640, Chap. 1; Garrett,
R. L.; De Vito, S. C., Eds.; ACS: Washington DC, 1996.
IR (KBr): 1678 cm–1.
1H NMR (300 MHz, CDCl3): d = 1.16 (t, 3 H, J = 7.3 Hz), 2.29–
2.41 (m, 2 H), 3.53 (d, 2 H, J = 7.1 Hz), 4.58 (t, 1 H, J = 7.1 Hz),
7.18–7.23 (m, 1 H), 7.25–7.32 (m, 2 H), 7.40–7.45 (m, 4 H), 7.51–
7.56 (m, 1 H), 7.91 (d, 2 H, J = 7.5 Hz).
13C NMR (300 MHz, CDCl3): d = 14.13, 25.43, 43.98, 45.35,
127.17, 127.80, 128.08, 128.49, 128.58, 133.18, 136.81, 142.22,
196.93.
MS (EI): m/z = 270.
Anal. Calcd for C17H18OS: C, 75.51; H, 6.71; S, 11.86. Found: C,
75.54; H, 6.72; S, 11.85.
Synlett 2005, No. 9, 1370–1374 © Thieme Stuttgart · New York