Y(OTf)3 catalyzed substitution dependent oxidative C(sp 3)-C(sp3) cleavage and regioselective dehydration of β-allyl-β-hydroxydithioesters: Alternate route to α,β- unsaturated ketones and functionalized dienes

Article abstract of DOI:10.1016/j.tet.2013.07.092

β-Allyl-β-hydroxydithioesters have been generated by the regioselective Grignard addition to the β-oxodithioesters. They have been successfully employed in selective C(sp³)-C(sp³) bond cleavage to construct α,β-unsaturated ketone res

Full text of DOI:10.1016/j.tet.2013.07.092

Tetrahedron 69 (2013) 8899e8903
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Y(OTf)3 catalyzed substitution dependent oxidative C(sp3)eC(sp3)
cleavage and regioselective dehydration of
-hydroxydithioesters: alternate route to
and functionalized dienes
b
-allyl-
b
a,b-unsaturated ketones
Sushobhan Chowdhury a, Tanmoy Chanda a, Ganesh Chandra Nandi b, Suvajit Koley a,
,
B. Janaki Ramulu a, S.K. Pandey c, Maya Shankar Singh a
*
a Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi 221005, India
b Department of Chemistry, University of North Florida, 1 UNF Drive, Jacksonville, FL 32224, USA
c School of Chemistry and Biochemistry, Thapar University, Patiala 147004, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 22 June 2013
Received in revised form 18 July 2013
Accepted 30 July 2013
Available online 5 August 2013
b
-Allyl-
oxodithioesters. They have been successfully employed in selective C(sp3)eC(sp3) bond cleavage to
construct -unsaturated ketone residues by the treatment of an emerging catalyst yttrium(III)triflate
for the first time. On the other hand, hetaryl substituted -allyl- -hydroxydithioesters led to the useful
diene precursors through selective dehydration under the similar conditions.
Ó 2013 Elsevier Ltd. All rights reserved.
b-hydroxydithioesters have been generated by the regioselective Grignard addition to the b-
a,b
b
b
Keywords:
Regioselective allylation
Yttrium(III)triflate
CeC activation and cleavage
Allylic isomerization
a,b-Unsaturated ketone
Selective dehydration
Functionalized diene
1. Introduction
unstrained tertiary alcohol analogues.1,2 Further, transition-metal
complexes have well been utilized for the purpose.3 Namely,
The synthesis of important molecular structures has always
been the primary motto of organic synthesis. The total synthesis of
a molecule primarily needs the construction of the parts of its
framework. The architectural strategy to achieve the frameworks
includes fusion of small fragments to a large one or vice versa, i.e.,
the cleavage of fragments from a large skeleton until the access of
the desired fragment residue becomes possible. Both ways are of
equal synthetic importance. Fragmentation methodologies, espe-
cially, which are achieved by selective CeC bond activation, will
certainly demand a prior significance due to the well-known in-
ertness of the CeC bond. Tertiary alcohols in several cases have
proven themselves suitable for CeC bond cleavage strategy. For this
Kondo et al. have achieved b-allyl cleavage in open chain un-
strained tertiary homoallyl alcohol employing Ru complexes as
catalyst.1a
Rare-earth metal triflates are new type of Lewis acid catalysts,
which are playing vital roles in various organic transformations.4 Of
them yttrium poses very specific coordination property by virtue of
which its complexes like Y(OTf)3 have become a well established
catalyst in polymer science where it is mainly used to increase the
stereoregularity of polymers.5 In spite of its tremendous use in
polymer, there exists only few examples of Y(OTf)3 to catalyze
traditional organic transformations.4def This time, we disclose the
maiden example of selective cleavage of C(sp3)eC(sp3) bond from
purpose, one established approach involves the
via an alkoxy-metal intermediate of various strained as well as
b
-alkyl elimination
b
-allyl-
we have unveiled the highly selective dehydration in case of 2-
thiophenyl and 2-furyl substituted -allyl- -hydroxydithioesters.
-Unsaturated carbonyl groups are important structural units
b-hydroxydithioesters catalyzed by Y(OTf)3. Furthermore,
b
b
a,b
in a number of biologically active compounds, as well as ubiquitous
structural motifs to various organic transformations. Some specific
* Corresponding author. Tel./fax: þ91 (0)542 6702502; e-mail addresses:
mssinghbhu@yahoo.co.in, mayashankarbhu@gmail.com (M.S. Singh).
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.07.092

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S. Chowdhury et al. / Tetrahedron 69 (2013) 8899e8903
protocols for the synthesis of
a
,
b
-unsaturated ketones have been
-unsaturated ketones are
generated after a sequence of chemical transformations within our
reported (Scheme 1).6,7 In our protocol
a,b
b
-allyl-
b
-hydroxydithioester precursor in a single stroke.
Scheme 2. Regioselective addition of allyl magnesium bromide to b-oxodithioesters.
Various b-oxodithioesters derived from aryl, hetaryl, and aliphatic
ketones were tolerated well under the reaction conditions to give
homoallylic tertiary alcohols in moderate to good yields (Table 1).
Adducts 1 have been characterized by spectral studies.
Table 1
Regioselective addition of allyl magnesium bromide to b-oxodithioesters to form 1
Entry
R1
R2
R3
Product 1
Time (h)
Yielda (%)
1
2
3
4
5
6
7
8
C6H5
C6H5
C6H5
H
CH3
H
H
H
H
H
H
H
CH3
CH3
PhCH2
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
1a
1b
1c
1d
1e
1f
1g
1h
1i
4.5
5
5
4
5
4.5
5
5
5
4.5
5
80
55
58
73
75
68
70
70
62
63
45
42
2-ClC6H4
4-ClC6H4
2-BrC6H4
4-CH3C6H4
2-Naphthyl
2-Thienyl
2-Furyl
CH3
9
10
11
12
H
H
H
1j
1k
1l
Isopropyl
5
a
Isolated pure yields.
To execute our motto of selective CeC cleavage we employed
various transition and rare earth metal catalysts, of them Y(OTf)3
ends up with satisfactory results in successful execution of our
project. When b-allyl-b-hydroxydithioesters 1 were treated with
Scheme 1. Parallel comparison of previous works to this work.
Y(OTf)3 in dry dichloroethane at reflux, Y(OTf)3 selectively activates
and cleaves the C(sp3)eC(sp3) bond eliminating dithioacetate
moiety with a subsequent conversion of the terminal double bond
to the non-terminal one, resulting the a,b-unsaturated ketones 2 in
50e70% yields (Scheme 3, Table 3).
2. Results and discussion
-Oxodithioesters are not commercially sourced, and were
b
synthesized by literature method8a in 70e80% yields, which are
attractive synthetic scaffolds. Thanks to their dense number of re-
active centers coupled with their ambident reactivity that can be
exploited in sequential reactions or in cascade transformations into
a range of useful products.8 Moreover, it is always prone to show
unorthodox behavior due to the presence of the dithioacetate
group. Recently, our group has developed a number of synthetic
strategies for the synthesis of various valuable heterocyclic scaf-
Scheme 3. Synthesis of a,b-unsaturated ketones 2.
folds utilizing
initial vision, we became intrigued in scouting the use of
thioesters to prepare our target precursor. Masson and Thuillier10
b
-oxodithioesters as a key substrate.9 Based on this
-oxodi-
b
Initially,
a solution of methyl-3-hydroxy-3-(p-tolyl)hex-5-
have prepared alkyl addition product from
treating them with organometallic reagents.
Thus, following the same procedure when
treated with allyl magnesium bromide, it led to selective addition
on carbonyl carbon due to the preferable hardehard interaction,
providing tert-homoallylic alcohol adducts 1 exclusively. The al-
ternative attack of allyl magnesium bromide could lead to 10, which
was not observed even in trace during our investigations, thus,
making the nucleophilic attack highly regioselective (Scheme 2).
b
-oxodithioesters by
enedithioate 1g (1.0 mmol) in dry 1,2-dichloroethane (DCE) was
treated with 5 mol % of Y(OTf)3 at reflux for 40 h, which provided
the expected product 2g in 70% yield. Being lured by the obtained
results, we went for the optimization of reaction conditions in-
cluding catalysts, solvents, and temperature, and the results are
summarized in Table 2. Ultimately, optimal condition was identified
as 5 mol % of Y(OTf)3 in refluxing DCE (Table 2, entry 6). Blank re-
action did not give the desired product and therefore proved the
catalytic efficacy of Y(OTf)3 (Table 2, entry 11).
b-oxodithioesters are

S. Chowdhury et al. / Tetrahedron 69 (2013) 8899e8903
8901
Table 2
Optimization of reaction conditionsa
Entry
Catalyst (mol %)
Solventb
Temp
Yieldc (%)
1
2
3
4
5
6
7
8
Sc(OTf)3 (5)
Zn(OTf)2 (5)
CuBr2 (5)
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
Toluene
THF
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
60
20
Trace
55
d
In(OTf)3 (5)
Pd(OAc)2 (5)
Y(OTf)3 (5)
Y(OTf)3 (2)
Y(OTf)3 (10)
Y(OTf)3 (5)
Y(OTf)3 (5)
None
Scheme 4. Selective dehydration of adducts 1iej.
70
61
63
60
64
d
selectivity and regioselectivity of Y(OTf)3. The products 3 were
characterized as dienes by their spectral studies (NMR and mass).
Further transformations by using the diene residue as precursor is
under the way and will be coming shortly.
To gain some insights into the mechanism of the reaction pro-
cess, we have accumulated some experimental results like (i)
methyl-3-hydroxy-2-methyl-3-phenylhex-5-enedithioate
9
10
11
DCE
a
Reaction of adduct 1g (1.0 mmol) with various catalysts.
10 mL of each solvents were used.
Isolated pure yields.
b
c
(R2¼CH3, Table 3, entry 2) and 3-hydroxy-3-phenyl-hex-5-
enedithioic acid benzyl ester (R3¼PhCH2, Table 3, entry 3) also
led to the formation of the desired products (50e55%), which
support the eliminating part to be dithioacetate. (ii) Methyl-3-
hydroxy-3-(naphthalen-2-yl)hex-5-enedithioate did not furnish
the desired compound (Table 3, entry 8), which accounts for the
formation of a congested intermediate that could not accommodate
the naphthyl group into the intermediate and the precursor
remained unconsumed even after 48 h. It also shows the specific
coordination property of Y(OTf)3 as Lewis acid to drive the reaction
in such a complicated catalytic pathway. (iii) Insertion of allyl group
and elimination of dithioacetate signifies that it also is not merely
a retro aldol reaction. (iv) Precursors with 2-thiophenyl and 2-furyl
substitution did not led to the product proving the channelizing of
the reaction through different intermediate. The available lone pair
of the heteroatom, which can coordinate with the yttrium drives
the reaction through different intermediate.
Table 3
Substrate scope for the synthesis of 2
Entry
R1
R2
R3
Product
Time (h)
Yielda (%)
1
2
3
4
5
6
7
8
9
C6H5
C6H5
C6H5
2-ClC6H4
4-ClC6H4
2-BrC6H4
4-CH3C6H4
2-Naphthyl
CH3
H
CH3
H
H
H
H
H
H
H
CH3
CH3
CH2Ph
CH3
CH3
CH3
CH3
CH3
CH3
CH3
2a
2a
2a
2d
2e
2f
2g
2h
2k
2l
48
48
48
48
48
48
40
48
36
40
65
50
55
60
62
58
70
db
dc
dc
Therefore, after a careful study of the open literature11 and
taking into consideration the entire outcome, a plausible mecha-
nism for the formation of 2 is outlined in Scheme 5. A cyclic
mechanism for the catalytic activity of Y(OTf)3 has been postulated
in accordance with Ru, Pd, and Rh catalysis. We believe that the first
step is the addition of Y(OTf)3 to adduct 1 to form an alkoxy-metal
complex A, which is stabilized due to delocalization of the allylic
double bond over three centers forming a metal-3-center-2-
electron bond [Y(h3eCH2eCHeCH2)].11b Complex A undergoes
10
Isopropyl
H
a
Isolated pure yields.
No reaction and 1h remained unconsumed.
Decomposition of starting material.
b
c
Under the optimized reaction conditions, the scope of 1 for the
synthesis of -unsaturated ketones 2 was investigated. Both
electron-rich and electron-deficient substituents attached to the
a,b
phenyl rings could be smoothly transformed into the desired
product 2 (Table 3). b-Allyl-b
-hydroxydithioesters with aliphatic R1
groups provided only trace amount of products 2kel with several
very close spots on the TLC plate, which could not be isolated (Table
3, entries 9 and 10). As the aliphatic dithioesters are not too heat
stable and so the case may be for their Grignard adducts also.
Therefore, it can be assumed that due to prolonged heating
-hydroxydithioesters with aliphatic R1 groups may undergo some
sort of decomposition to give complex TLC pattern.
Interestingly, when R1 groups became 2-thiophenyl and 2-furyl,
instead of -unsaturated ketones 2 selectively less favorable
b-allyl-
b
a,b
dehydrated diene products 3 were obtained in 92e95% yields
within 12 h under the similar reaction conditions (Scheme 4). This
is entirely different from the dehydrated product 4 obtained by
Masson and Thuillier where more favorable dehydration occurred
by the participation of active a-hydrogen from b-allyl-b-hydrox-
ydithioesters.10 A blank reaction in the absence of Y(OTf)3 was also
carried out, which did not give the trace of dehydrated product
even after 24 h of reflux, suggesting catalytic efficacy, excellent site
Scheme 5. Plausible mechanism for the formation of a,b-unsaturated ketones 2.

8902
S. Chowdhury et al. / Tetrahedron 69 (2013) 8899e8903
selective CeC cleavage releasing dithioacetate moiety D to give
complex B. Finally, complex B undergoes shift of the terminal
double bond to thermodynamically more stable non-terminal
double bond yielding the desired product 2 and releases the par-
ent catalyst Y(OTf)3 completing the catalytic cycle.
shifts (d) are given in parts per million (ppm) using the residue
solvent peaks as reference relative to TMS. Coupling constant (J)
values are given in Hertz. Mass spectra were recorded using elec-
trospray ionization (ESI) mass spectrometry. The melting points are
uncorrected.
In case of b-allyl-b
-hydroxydithioesters with hetaryl R1 groups
due to possible chelation of yttrium between available lone pair on
the heteroatom of the heteroaryl groups of 1iej and terminal car-
bon of its allyl group in complex E may play an important role in
preventing the formation of alkoxy-metal complex intermediate
responsible for dithioacetate elimination. However, complex E,
which is highly susceptible for dehydration undergoes selective C-1
hydrogen elimination rather than C-10 hydrogen to give complex F.
Finally, complex F takes up one molecule of TfOH to come back to
the parent catalyst with the formation of dehydrated product diene
3 completing the catalytic cycle. A mechanistic model is presented
to understand in detail the results obtained (Scheme 6).
4.2. General procedure for the synthesis of 3-hydroxy-hex-5-
enedithioic acid esters (Grignard adducts) (1ael)
To a solution of b-oxodithioester (1.0 mmol) in 6 mL of dry THF,
10 mL of allyl magnesium bromide (1 M ethereal solution) was
added dropwise at ꢀ78 ꢁC. The mixture was stirred for the stipu-
lated period of time. After completion of the reaction (monitored by
TLC), the reaction mixture was quenched by the addition of am-
monium chloride solution followed by extraction with ethyl acetate
(2ꢂ10 mL). The organic layer was dried over anhydrous Na2SO4 and
was then evaporated in vacuo. The crude residue was purified by
column chromatography over silica gel using increasing amounts of
SMe
S
ethyl acetate in n-hexane to afford pure Grignard adducts
hydroxydithioesters 1.
b-allyl-b-
4.2.1. 3-Hydroxy-3-phenyl-hex-5-enedithioic acid methyl ester
(1a). Yellow oil. 1H NMR (300 MHz, CDCl3,
ppm): 7.38e7.35 (m,
HO
SMe
d
X
..
TfO
TfO
3
2H, Ar), 7.30e7.11 (m, 3H, Ar), 5.79e5.65 (m, 1H, olefinic CH),
5.08e5.00 (m, 3H, OH and olefinic CH2), 3.72 (d, J¼15 Hz, 1H, CH2),
3.33 (d, J¼14.7 Hz, 1H, CH2), 2.68e2.48 (m, 2H, CH2), 2.38 (s, 3H,
S
Y
OTf
X
..
TfOH
X = O, S
SMe); 13C NMR (75 MHz, CDCl3,
d ppm): 235.6 (thiocarbonyl),143.9,
SMe
OH
TfO
TfO
S
S
132.8, 132.6, 127.3, 126.1, 126.0, 125.0, 124.7, 118.5, 117.9, 76.0, 60.1,
47.5, 19.6; IR (KBr, nmax, cmꢀ1): 3400, 3073, 2913, 1446, 1196, 1062,
917, 841, 701, 591.
Y
TfO
TfO
X
SMe
Y
F
OTf
..
X
..
4.2.2. 3-(2-Chlorophenyl)-3-hydroxy-hex-5-enedithioic acid methyl
TfO
TfO
ester (1d). Yellow oil. 1H NMR (300 MHz, CDCl3,
d ppm): 7.66 (d,
H2O
S
SMe
1
Y
J¼7.8 Hz, 1H, Ar), 7.24 (t, J¼6.4 Hz, 1H, Ar), 7.17e7.06 (m, 2H, Ar),
5.77e5.63 (m, 1H, olefinic CH), 5.07e4.94 (m, 3H, OH and olefinic
CH2), 4.44 (d, J¼14.7 Hz, 1H, CH2), 3.35 (d, J¼14.4 Hz, 1H, CH2),
3.07e3.00 (m, 1H, CH2), 2.80e2.73 (m, 1H, CH2), 2.37 (s, 3H, SMe);
1'
X
TfOH
OH
E
Scheme 6. Plausible mechanism for the selective dehydration of adducts 1iej.
13C NMR (75 MHz, CDCl3,
d ppm): 235.9 (thiocarbonyl), 140.2, 132.7,
130.4, 129.8, 129.6, 128.0, 126.1, 118.4, 117.6, 76.6, 57.3, 43.2, 19.7; IR
(KBr, nmax, cmꢀ1): 3378, 3073, 2914, 1430, 1187, 1035, 917, 842, 758,
595; HRMS: m/z¼286.0253 (Mþ). Found: 287.0185 (Mþþ1).
3. Conclusions
In summary, we have established a successful synthetic opera-
4.2.3. 3-Hydroxy-3-p-tolylhex-5-enedithioic acid methyl ester
tion on
thioesters. The described protocol is highly substitution dependent
to give
-unsaturated ketones through the selective C(sp3)e
b-allyl-b-hydroxydithioesters generated from b-oxodi-
(1g). Yellow oil. 1H NMR (300 MHz, CDCl3,
d ppm): 7.25 (s, 2H, Ar),
7.09 (d, J¼4.8 Hz, 2H, Ar), 5.80e5.66 (m, 1H, olefinic CH), 5.09e5.03
(m, 2H, olefinic CH2), 4.77 (s, 1H, OH), 3.73 (d, J¼15.3 Hz, 1H, CH2),
3.34 (d, J¼15 Hz, 1H, CH2), 2.66e2.48 (m, 5H, CH2 and SMe), 2.30 (s,
a,b
C(sp3) bond cleavage with allylic isomerization for the aromatic
substitutions and dienes via a selective dehydration in case of
hetaryl substitution, in the presence of Y(OTf)3. The detailed
mechanistic aspects of the discussed methodology and its tolerance
to substituted allyl groups or their higher analogues are currently
the subject matter of our further investigation.
3H, CH3); 13C NMR (75 MHz, CDCl3,
d ppm): 235.0 (thiocarbonyl),
141.8, 136.3, 133.8, 133.7, 128.8, 125.7, 118.6, 76.7, 60.8, 48.2, 21.2,
20.2; IR (KBr, nmax, cmꢀ1): 3423, 2920, 2851, 1412, 1261, 1020, 814,
463; MS: m/z (%)¼249 (25), 201 (55), 168 (90), 119 (100).
4.3. General procedure for the synthesis of but-2-en-1-ones
4. Experimental section
4.1. General method
(2ael)
A solution of b-allyl-b-hydroxydithioester 1 (1.0 mmol) in di-
chloroethane (10 mL) was degassed for 15 min by continuous
purging of ultrapure argon. To this solution 5 mol % of Y(OTf)3 was
added and the mixture was refluxed for the stipulated period of
time. After completion of the reaction (monitored by TLC), the re-
action mixture was diluted with EtOAc (10 mL) followed by addi-
tion of water (20 mL). The organic layer was dried over anhydrous
Na2SO4 and then was evaporated in vacuo. The crude residue was
purified by column chromatography over silica gel using increasing
amounts of ethyl acetate in n-hexane as eluent to afford pure but-2-
en-1-ones 2.
The commercially available allyl magnesium bromide (Grignard
reagent) and yttrium triflate were used as received without any
further purification. b-Oxodithioesters were prepared following the
literature procedure. Thin-layer chromatography (TLC) was per-
formed using silica gel 60 F254 precoated plates. Column chroma-
tography was performed with 100e200 mesh silica gel. Infrared
(IR) spectra are measured in KBr, and wavelengths (
in cmꢀ1 1H and 13C NMR spectra were recorded on NMR spec-
trometers operating at 300 and 75.5 MHz, respectively. Chemical
n) are reported
.

S. Chowdhury et al. / Tetrahedron 69 (2013) 8899e8903
8903
4.3.1. 1-Phenyl-but-2-en-1-one (2a). Beige oil. 1H NMR (300 MHz,
CDCl3,
ppm): 7.91 (d, J¼7.8 Hz, 2H, Ar), 7.55e7.43 (m, 3H, Ar),
CH), 4.21 (s, 2H, CH2), 2.58 (s, 3H, SMe); 13C NMR (75 MHz, CDCl3,
d
d ppm): 235.1 (thiocarbonyl), 142.3, 142.2, 133.9, 132.2, 127.7, 125.3,
7.11e7.03 (m, 1H, olefinic CH), 6.89 (d, J¼15.3 Hz, 1H, olefinic CH),
120.2, 111.5, 107.6, 50.1, 20.1 (SMe); IR (KBr, nmax, cmꢀ1): 2922, 1655,
1440, 1230, 1018; MS: m/z¼223 (Mþꢀ1).
2.00 (d, J¼6.6 Hz, 3H, Me); 13C NMR (75 MHz, CDCl3,
d ppm): 190.7
(carbonyl), 145.0, 137.8, 133.3, 132.5, 128.4, 127.4, 125.2, 119.1, 18.5;
IR (KBr, nmax, cmꢀ1): 2925, 1682, 1448, 1218, 755, 691.
Acknowledgements
4.3.2. 1-(2-Chlorophenyl)-but-2-en-1-one (2d). Dark oil. 1H NMR
We gratefully acknowledge the generous financial supports
from the Council of Scientific and Industrial Research (CSIR), the
Department of Science and Technology (DST), and University
Grants Commission (UGC), New Delhi.
(300 MHz, CDCl3,
olefinic CH), 6.47 (dd, J¼14.4,1.2 Hz,1H, olefinic CH),1.96 (dd, J¼5.4,
1.2 Hz, 3H, Me); 13C NMR (75 MHz, CDCl3,
ppm): 194.2 (carbonyl),
d ppm): 7.41e7.26 (m, 4H, Ar), 6.77e6.65 (m, 1H,
d
147.9, 138.9, 131.9, 130.9, 130.0, 128.9, 126.5, 18.5; HRMS: m/
z¼180.0342 (Mþ). Found: 181.0423 (Mþþ1).
Supplementary data
4.3.3. 1-(4-Chlorophenyl)-but-2-en-1-one (2e). Dark oil. 1H NMR
Supplementary data (IR, 1H and 13C NMR, and HRMS spectra) are
available. Supplementary data related to this article can be found at
http://dx.doi.org/10.1016/j.tet.2013.07.092.
(300 MHz, CDCl3,
d
ppm): 7.86 (d, J¼8.1 Hz, 2H, Ar), 7.42 (d,
J¼8.4 Hz, 2H, Ar), 7.12e7.04 (m, 1H, olefinic CH), 6.86 (dd, J¼14.1,
1.2 Hz, 1H, olefinic CH), 2.00 (dd, J¼5.7, 1.2 Hz, 3H, Me); 13C NMR
(75 MHz, CDCl3,
d ppm): 189.3 (carbonyl), 145.6, 138.9, 136.1, 129.8,
References and notes
128.7, 126.9, 18.6.
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Burger, B. J.; Bercaw, J. E. J. Am. Chem. Soc. 1988, 110, 976.
3. (a) Hegedus, L. S. In Comprehensive Organometallic Chemistry II; Abel, E. W.,
Stone, F. G. A., Wilkinson, G., Eds.; Pergamon: Oxford, UK, 1995; Vol. 12; (b)
Bishop, K. C. Chem. Rev. 1976, 76, 461; (c) Crabtree, R. H. Chem. Rev. 1985, 85,
245; (d) Jennings, P. W.; Johnson, L. L. Chem. Rev. 1994, 94, 2241.
4.3.4. 1-(2-Bromophenyl)-but-2-en-1-one (2f). Beige oil. 1H NMR
(300 MHz, CDCl3, ppm): 7.62e7.58 (m, 1H, Ar), 7.40e7.26 (m, 3H,
d
Ar), 6.74e6.64 (m, 1H, olefinic CH), 6.46 (d, J¼15.3 Hz, 1H, olefinic
CH), 1.97 (d, J¼6.6 Hz, 3H, Me); 13C NMR (75 MHz, CDCl3,
d ppm):
195.1 (carbonyl), 148.4, 140.9, 133.2, 131.8, 131.0, 128.7, 127.0, 119.2,
18.6; IR (KBr, nmax, cmꢀ1): 2932, 2858, 1660, 1293, 1024, 764; MS:
m/z (%)¼202 (80), 185 (90), 183 (100), 138 (30), 102 (67).
4.3.5. 1-p-Tolyl-but-2-en-1-one (2g). Beige oil. 1H NMR (300 MHz,
4. (a) Zhang, C. X.; Dong, J. C.; Cheng, T. M.; Li, T. T. Tetrahedron Lett. 2001, 42, 461; (b)
Kobayashi, S. Lanthanides: Chemistry and Use in Organic Synthesis; Springer:
Berlin, Germany, 1999; p 63; (c) Sun, L.; Gao, C.; Zhou, W.; Wei, Y. Indian J. Chem.,
Sect. B 2008, 47, 481; (d) De, S. K. Tetrahedron Lett. 2004, 45, 2339; (e) Wang, Y.;
Onozawa, S. Y.; Kunioka, M. Green Chem. 2003, 5, 571; (f) Jha, M.; Enaohwo, O.;
Guy, S. Tetrahedron Lett. 2011, 52, 684.
5. (a) Ray, B.; Isobe, Y.; Matsumoto, K.; Habaue, S.; Okamoto, Y.; Kamigaito, M.;
Sawamoto, M. Macromolecules 2004, 37, 1702; (b) Biswas, C. S.; Patel, V. K.;
Vishwakarma, N. K.; Mishra, A. K.; Saha, S.; Ray, B. Langmuir 2010, 26, 6775; (c)
Biswas, C. S.; Vishwakarma, N.; Patel, V. K.; Mishra, A. K.; Saha, S.; Ray, B.
Langmuir 2012, 28, 7014 and references therein.
CDCl3,
d
ppm): 7.83 (d, J¼8.1 Hz, 2H, Ar), 7.24 (d, J¼8.0 Hz, 2H, Ar),
7.10e7.00 (m, 1H, olefinic CH), 6.90 (d, J¼15.9 Hz, 1H, olefinic CH),
2.41 (s, 3H, benzylic CH3), 1.98 (s, 3H, Me); 13C NMR (75 MHz, CDCl3,
d
ppm): 190.2 (carbonyl), 144.4, 143.3, 135.2, 129.1, 128.6, 127.4, 21.6,
18.5; IR (KBr, nmax, cmꢀ1): 2924, 2854, 1722, 1458, 1097, 815; MS: m/
z¼161 (Mþþ1).
4.4. General procedure for the synthesis of dienes (3iej)
6. (a) Clayden, J.; Greeves, N.; Warren, S.; Wothers, P. Organic Chemistry; Oxford
University: Oxford, UK, 2001; (b) Stefanoni, M.; Luparia, M.; Porta, A.; Zanoni,
G.; Vidari, G. Chem.dEur. J. 2009, 15, 3940; (c) Egi, M.; Yamaguchi, Y.; Fujiwara,
N.; Akai, S. Org. Lett. 2008, 10, 1867 and references therein.
7. (a) Rodriguez, N.; Manjolinho, F.; Grunberg, M. F.; Gooßen, L. J. Chem.dEur. J.
2011, 17, 13688 and references therein; (b) Manjolinho, F.; Grunberg, M. F.;
Rodriguez, N.; Gooben, L. J. Eur. J. Org. Chem. 2012, 4680; (c) Tsuji, J.; Yamada, T.;
Minami, I.; Yuhara, M.; Nisar, M.; Shimizu, I. J. Org. Chem. 1987, 52, 2988 and
references therein; (d) Tsuda, T.; Chujo, Y.; Nishi, S.-I.; Tawara, K.; Saegusa, T. J.
Am. Chem. Soc. 1980, 102, 6381; (e) Waetzig, S. R.; Tunge, J. A. J. Am. Chem. Soc.
2007, 129, 14860; (f) Levine, S. R.; Krout, M. R.; Stoltz, B. M. Org. Lett. 2009, 11,
289 and references therein.
A solution of b-allyl-b-hydroxydithioesters 1i and 1j (1.0 mmol)
in dichloroethane (10 mL) was degassed for 15 min by continuous
purging of ultrapure argon. To this solution 5 mol % of Y(OTf)3 was
added and the mixture was refluxed for the stipulated period of
time. After completion of the reaction (monitored by TLC), the re-
action mixture was diluted with EtOAc (10 mL) followed by addi-
tion of water (20 mL). The organic layer was dried over anhydrous
Na2SO4 and then evaporated in vacuo. The crude residue was pu-
rified by column chromatography over silica gel using n-hexane as
eluent to afford dienes 3iej.
8. (a) Samuel, R.; Asokan, C. V.; Suma, S.; Chandran, P.; Retnamma, S.; Anabha, E.
R. Tetrahedron Lett. 2007, 48, 8376; (b) Peruncheralathan, S.; Khan, T. A.; Ila, H.;
Junjappa, H. J. Org. Chem. 2005, 70, 10030; (c) Roy, A.; Nandi, S.; Ila, H.; Junjappa,
H. Org. Lett. 2001, 3, 229.
4.4.1. 3-Thiophen-2-yl-hexa-3,5-dienedithioic acid methyl ester
9. Recent papers: (a) Nandi, G. C.; Samai, S.; Singh, M. S. J. Org. Chem. 2010, 75,
7785; (b) Nandi, G. C.; Samai, S.; Singh, M. S. J. Org. Chem. 2011, 76, 8009; (c)
Chowdhury, S.; Nandi, G. C.; Samai, S.; Singh, M. S. Org. Lett. 2011, 13, 3762; (d)
Nandi, G. C.; Singh, M. S.; Ila, H.; Junjappa, H. Eur. J. Org. Chem. 2012, 967; (e)
Verma, R. K.; Verma, G. K.; Raghuvanshi, K.; Singh, M. S. Tetrahedron 2011, 67,
584; (f) Verma, R. K.; Verma, G. K.; Shukla, G.; Nagaraju, A.; Singh, M. S. ACS
Comb. Sci. 2012, 14, 224; (g) Verma, G. K.; Verma, R. K.; Singh, M. S. RSC Adv.
2013, 3, 245; (h) Singh, M. S.; Nagaraju, A.; Verma, G. K.; Shukla, G.; Verma, R.
K.; Srivastava, A.; Raghuvanshi, K. Green Chem. 2013, 15, 954; (i) Janaki Ramulu,
B.; Chanda, T.; Chowdhury, S.; Nandi, G. C.; Singh, M. S. RSC Adv. 2013, 3, 5345.
10. Masson, S.; Thuillier, A. Tetrahedron Lett. 1982, 23, 4087.
(3i). Yellow oil. 1H NMR (300 MHz, CDCl3,
4.2 Hz, 2H, Ar), 6.95 (d, J¼5.2 Hz, 1H, Ar), 6.79e6.72 (m, 2H, olefinic
CH2), 5.45 (d, J¼14.4 Hz, 1H, olefinic CH), 5.30 (d, J¼7.8 Hz, 1H,
olefinic CH), 4.32 (s, 2H, CH2), 2.58 (s, 3H, SMe); 13C NMR (75 MHz,
d
ppm): 7.14 (dd, J¼9.9,
CDCl3, d ppm): 234.7 (thiocarbonyl), 145.1, 132.3, 129.8, 127.5, 126.7,
125.6, 124.5, 124.4, 120.1, 52.1, 20.1 (SMe); MS: m/z¼239 (Mþꢀ1).
4.4.2. 3-Furan-2-yl-hexa-3,5-dienedithioic
acid
methyl
ester
(3j). Yellow oil. 1H NMR (300 MHz, CDCl3,
d ppm): 7.37 (s, 1H, Ar),
11. (a) Stanlake, L. J. E.; Schafer, L. L. Organometallics 2009, 28, 3990; (b) Casey, C. P.;
Tunge, J. A.; Fagan, M. A. J. Organomet. Chem. 2002, 663, 91 and references
therein; (c) Duchateau, R.; van Wee, C. T.; Teuben, J. H. Organometallics 1996, 15,
2291.
6.92e6.75 (m, 2H, Ar), 6.40 (dd, J¼11.7, 2.4 Hz, 2H, olefinic CH2),
5.47 (d, J¼16.8 Hz, 1H, olefinic CH), 5.31 (d, J¼9.3 Hz, 1H, olefinic