Iron(III) chloride-catalysed direct nucleophilic α-substitution of Morita-Baylis-Hillman alcohols with alcohols, arenes, 1,3-dicarbonyl compounds, and thiols

Article abstract of DOI:10.1039/b908447a

A general and efficient direct method for the α-substitution of Morita-Baylis-Hillman alcohols with carbon- and heteroatom-centred nucleophiles such as alcohols, arenes, 1,3-dicarbonyl compounds, and thiols in the presence of FeCl₃·6H₂

Full text of DOI:10.1039/b908447a

www.rsc.org/obc
Volume 7 | Number 20 | 21 October 2009 | Pages 4133–4320
ISSN 1477-0520
FULL PAPER
hilip Wai Hong Chan et al.
P
PERSPECTIVE
FeCl -catalysed direct nucleophilic
D. A. Engel and G. B. Dudley
The Meyer–Schuster rearrangement
for the synthesis of α,β-unsaturated
carbonyl compounds
α-su3bstitution of Morita–Baylis–
Hillman alcohols with alcohols, arenes,
1,3-dicarbonyl compounds, and thiols

PAPER
www.rsc.org/obc | Organic & Biomolecular Chemistry
Iron(III) chloride-catalysed direct nucleophilic a-substitution of
Morita-Baylis-Hillman alcohols with alcohols, arenes, 1,3-dicarbonyl
compounds, and thiols†
Xiaoxiang Zhang, Weidong Rao, Sally and Philip Wai Hong Chan*
Received 29th April 2009, Accepted 30th June 2009
First published as an Advance Article on the web 31st July 2009
DOI: 10.1039/b908447a
A general and efficient direct method for the a-substitution of Morita-Baylis-Hillman alcohols with
carbon- and heteroatom-centred nucleophiles such as alcohols, arenes, 1,3-dicarbonyl compounds, and
thiols in the presence of FeCl3·6H2O as catalyst has been developed. The reaction is operationally
straightforward, accomplished in good to excellent product yields (40–99%) and with exclusive
a-regioselectivity under mild conditions that did not need an inert and moisture-free environment.
that gave the corresponding g -allylic chlorides in good yields.9
Following this work, Jia and co-workers reported a similar
iron-mediated approach for the g -alkoxylation of acyclic MBH
Introduction
Nucleophilic substitution of Morita-Baylis-Hillman (MBH)
alcohols.10 At about the same time, Kim and co-workers also
showed nucleophilic substitution of cyclic MBH alcohols with
sulfonamides that proceeded with complete a-regioselectivity in
excellent yields.11 To our knowledge, however, the analogous iron-
catalysed a-substitution reactions of cyclic MBH alcohols with
C-, O- and S-centered nucleophiles are not known. Herein, we
report the use of FeCl3·6H2O for the a-substitution of cyclic
MBH alcohols with a wide variety of carbon- and heteroatom-
centered nucleophiles that include alcohols, arenes, 1,3-dicarbonyl
compounds, and thiols (Scheme 1). The substituted cyclic MBH
products were afforded in good to excellent yields with exclusive
a-regioselectivity and without the need for inert and moisture-free
conditions.
adducts has received an increasing amount of attention in
recent years due to their versatility as building blocks in organic
synthesis.1–3 Generally, the MBH acetate is used as the substrate
in this type of reaction presumably due to the perceived poor
leaving group ability and low reactivity of the hydroxyl group in
the alcohol precursor.1,2 Although shown to be highly efficient, a
drawback of this approach is the need to perform the acylation
step. Added to this is the possibility of competitive side reactions
mediated by the acetic acid byproduct formed during the course
of the reaction. For this reason, the establishing of strategies for
the direct nucleophilic substitution of MBH alcohols has been
actively pursued since the only potential byproduct produced
in such reactions would be H2O.3–11 As part of an ongoing
program examining the utility of alcohols as pro-electrophiles,8
we recently reported that the direct a-arylation of a cyclic MBH
alcohol with 2,6-dimethylphenol could be accomplished in near
quantitative yield using gold catalysis.8d The efficiency of the
catalysis led us to explore the scope of these substitutions due
to their frequent use as intermediates in numerous synthetic
routes to heterocycles and compounds of biological interest.1–3
We envisioned the method would also greatly benefit from the
use of cheaper and commercially available catalysts, such as iron
complexes. Recently, iron-mediated substitutions of alcohol pro-
electrophiles with a variety of nucleophiles as the basis for efficient
and selective C–X (X = C, N, O, S, halide) have been reported.5,12
While the majority of these works have focused on the reactions
of allylic, benzylic and propargylic alcohols, this has also hitherto
included three reports on regioselective substitutions of acyclic
and cyclic MBH alcohols. Das and co-workers described an
efficient iron-catalyzed g -chlorination of acyclic MBH alcohols
Scheme 1 FeCl3·6H2O-catalysed direct nucleophilic a-substitution of
MBH alcohols.
Results and discussion
At the outset of this study, we chose 2-(hydroxy(phenyl)-
methyl)cyclohex-2-enone 1a and 1,3-diphenylpropane-1,3-dione
2a as the model substrates to establish the reaction conditions
(Table 1). This revealed that treating an open round flask
containing 1a and 2a in CH2Cl2 with 10 mol% of FeCl3·6H2O at
40 ◦C for 4 h gave the best result (entry 1). Under these conditions,
2-((6-oxocyclohex-1-enyl)(phenyl)methyl)-1,3-diphenylpropane-
1,3-dione 3a was afforded as the sole product in 90% yield. No
side-products that could be attributed to competitive substitution
at the g -carbon or elimination of the hydroxyl group of 1a could be
Division of Chemistry and Biological Chemistry, School of Physical and
Mathematical Sciences, Nanyang Technological University, Singapore,
637371, Singapore. E-mail: waihong@ntu.edu.sg
† Electronic supplementary information (ESI) available: 1H and 13C
NMR spectra for all compounds and HPLC measurements for the
reaction of 1a. CCDC reference numbers 711037 and 729201. For ESI
and crystallographic data in CIF or other electronic format see DOI:
10.1039/b908447a
4186 | Org. Biomol. Chem., 2009, 7, 4186–4193
This journal is
The Royal Society of Chemistry 2009
©

Table 1 Optimisation of reaction conditionsa
2a was the only example where a low product yield of 27% was
obtained under the standard conditions but could be increased
to 80% yield on repeating with a catalyst loading of 50 mol%
(entry 4). On the other hand, moderate to good product yields
were afforded for reactions of 1f and 1g bearing an electron-
donating aryl group on the carbinol carbon centre (entries 8–9).
Mixtures of side-products were also afforded in both reactions
that could not be identified by 1H NMR analysis. Stereoelectronic
effects of the cyclic MBH alcohol may also play a role since
a substrate containing the strongly coordinating o-nitrophenyl
group on the carbinol carbon resulted in no reaction (entry 10).
A similar outcome was found on repeating this reaction with a
stoichiometric amount of catalyst. In contrast, a-substitution of
1i, which contains a bulky o-chlorophenyl group on the carbinol
carbon, with 2a was found to give 3l in 88% yield (entry 11).
Reactions of starting alcohols containing an a,b-unsaturated
cyclopentanone or 2,3-dihydropyran-4-one ring moiety with 2a
were also shown to provide 3m and 3n in good to excellent yields
(entries 12–13).
Entry
Catalyst
Solvent
Yield (%)
1b
2
FeCl3·6H2O
FeCl3·6H2O
FeCl3·6H2O
FeCl3·6H2O
FeCl3·6H2O
FeCl3·6H2O
FeCl3·6H2O
FeCl3·6H2O
Yb(OTf)3
CH2Cl2
CH2Cl2
CH2ClCH2Cl
CH2ClCH2Cl
PhMe
MeCN
MeNO2
THF
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
90
92
89
77
37
26
40
3
4c
5
6
7
8
9
10
11
12
d
—
—
d
d
AgOTf
CuOTf
InCl3
—
29
25
a All reactions were performed at room temperature for 23 h with a
catalyst:1a:2a ratio of 1:10:20. b Reaction conducted at 40 ◦C for 4 h.
c Reaction conducted with a catalyst loading of 5 mol%. d No reaction
detected based on TLC and 1H NMR analysis.
In this work, the FeCl3·6H2O-catalysed direct a-substitution of
1a with a variety of different carbon, oxygen and sulfur-centered
nucleophiles was also examined (Table 3). Under the standard
conditions, Friedel-Crafts arylation of 1a with arenes 2e and
2f afforded the a-substituted MBH products 3o and 3p in 62
and 88% yield (entries 1–2). Inspection of entries 3–8 revealed
that the present procedure also proceeds well on switching C-
centered nucleophiles to O- and S-centered nucleophiles. When
EtOH 2g was employed as the nucleophile, the reaction was
found to give 3q in 94% yield (entry 3). We were also pleased
to find comparable high product yields of 95 and 85% could be
furnished for the analogous FeCl3·6H2O-catalysed a-substitutions
of 1a with 2h and 2i, respectively (entries 4–5). Similarly, when 1a
was treated with ethanethiol 2j under the standard conditions,
the corresponding MBH thioether adduct 3t was afforded in
96% yield (entry 6). In our hands, the arylthiols 2k and 2l,
which contain either a para-substituted electron-withdrawing or
electron-donating aryl group, respectively, were also found to
be good sulfur sources (entries 7–8). In these reactions, the
corresponding a-substituted cyclic MBH thioethers 3u and 3v
were furnished in yields of 83–87%. Consistent with our earlier
findings for the substitution of 1a with 2a, in all the above reactions
no side-products resulting from competitive g -substitution or
elimination of the hydroxyl group of the MBH alcohol could be
detected by 1H NMR analysis of the crude reaction mixture.13 The
a-substituted MBH product was confirmed by 1H NMR analysis
and X-ray crystal structure determination of two closely related
products (see later). At room temperature, a longer reaction time
of 23 h was required to obtain a comparable product yield (entry
2). Under these latter conditions at room temperature, repeating
the reaction with a catalyst loading of 5 or 10 mol% and 1,2-
dichloroethane as the solvent was also found to give 3a in similar
yields of 89 and 77%, respectively (entries 3–4). In contrast,
performing the reaction in other solvents at room temperature
was found to be markedly less effective (entries 5–8). When either
toluene, MeCN or MeNO2 were employed as the solvent, low
product yields of 26–40% were obtained (entries 5–7). On the
1
other hand, TLC and H NMR analysis of the crude mixture of
the reaction conducted in THF detected only the starting alcohol
and 1,3-dicarbonyl compound (entry 8). Inspection of entries 9–12
in Table 1 also revealed the reaction proceeded less well with
other common and commercially available Lewis acid catalysts.
In these latter reactions, the use of either CuOTf or InCl3 resulted
in the formation of 3a in markedly lower yields of 29 and 25%,
respectively (entries 11–12). However, switching the catalyst to
Yb(OTf)3 or AgOTf was found to lead to no reaction on the basis
of TLC and 1H NMR analysis (entries 9–10).
Applying the conditions shown in entry 1 of Table 1, a variety of
substituted cyclic MBH alcohols and 1,3-dicarbonyl compounds
were examined to determine the substrate scope of the present
procedure (Table 2). As shown in entries 1–3, substitution of
1a with a variety of substituted 1,3-dicarbonyl compounds gave
the corresponding a-substituted cyclic MBH products 3b–d in
excellent yields. Notably, this included a-substitution of 1a with
the less acidic b-ketoester 2d, which gave 3d as a separable 5:1
mixture of diastereomers in near quantitative yield (entry 3). The
present procedure was also shown to work well for reactions of 2a
with cyclic MBH alcohols with a pendant electron-withdrawing
aryl group on the carbinol carbon centre, affording 3e–h in
excellent yields (entries 4–7). In our hands, reaction of 1b with
1
detected by H NMR and TLC analysis. Without exception, the
a-substituted MBH adduct was obtained as the sole product in
every case. This was further confirmed by X-ray crystal structure
determination of 3m and 3p, as shown in Fig. 1.14
Although a mechanistic discussion would be highly speculative
at this juncture, we tentatively propose one possible pathway in
Scheme 2 for the present FeCl3·6H2O-catalysed a-substitution
reaction. This could involve activation of the alcohol substrate
through coordination of the iron catalyst with the hydroxyl
and carbonyl groups. This delivers an iron(III)-coordinated
intermediate 6 which can undergo elimination to give a putative
carbocation species 7. It is possible that the newly formed
cationic species subsequently undergoes nucleophilic attack by 2
and protodemetallation of [Fe]-OH to deliver the a-substituted
cyclic MBH product 3 and metal catalyst. The role of the
iron catalyst in facilitating dehydroxylation of the cyclic MBH
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Org. Biomol. Chem., 2009, 7, 4186–4193 | 4187
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Table 2 FeCl3·6H2O-catalysed a-substitution of 1a-k with 2a-da
Entry
Substrates
Time (h)
Product
Yield (%)
1
2
3
1a + 2b
1a + 2c
1a + 2d
4
4
1.5
3b, R1 = R2 = Me
90
92
97b
3c, R1 = Ph, R2 = Me
3d, R1 = Ph, R2 = OEt
4c
5
6
7
8
9
1b + 2a
1c + 2a
1d + 2a
1e + 2a
1f + 2a
1g + 2a
1
1
1.5
2
4
3e, R = NO2
3f, R = F
80
99
95
91
66
40
3g, R = Cl
3h, R = Br
3i, R = Me
3j, R = OEt
3.5
d
10
11
1h + 2a
1i + 2a
3
48
3k, R = NO2
3l, R = Cl
—
88
12
1j + 2a
1
3m
84
13
1k + 2a
72
3n
61
a All reactions were performed at 40 ◦C with a catalyst:1:2 ratio of 1:10:20. b Obtained as a 5:1 mixture of diastereomers separable by flash column
chromatography. c Reaction conducted with 50 mol% of FeCl3·6H2O. d No reaction based on TLC and 1H NMR analysis.
alcohol would account for our earlier findings showing the need
for a catalyst loading of 50 mol% and no product formation
for the respective reactions of 1b and 1h with 2a (entries 4
and 10 in Table 2). It would not be inconceivable that such
interactions are weakened due to the introduction of a strongly
coordinating nitro moiety on the alcohol substrate. It is possible
that the a-regioselectivities obtained could also be attributed
to such interactions since coordination of the metal catalyst
to the carbonyl oxygen would give a stable six-membered ring
coordinate in 6, as shown in Scheme 2. The gradual decrease
in product yields with increasing electron-donating ability of
the substituent on the carbinol on going from 1a → 1f → 1g
shown in entry 1 in Table 1 and entries 8–9 in Table 2 would
Scheme 2 Tentative mechanism for FeCl3·6H2O-catalysed direct nucle-
be consistent with the formation of the resultant carbocation
ophilic a-substitution of MBH alcohols.
4188 | Org. Biomol. Chem., 2009, 7, 4186–4193
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©

Table 3 FeCl3·6H2O-catalysed a-substitution of 1a with 2e–la
Entry
Nuc
Product
Yield (%)
1b
2b
2e
2f
3o, R = H
62
88
3p, R = Me
3c
4c
2g
2h
3q, R = Et
3r, R = Bn
94
95
5b
6d
2i
2j
3s
3t
85
96
7d
8d
2k
2l
3u, R = Cl
3v, R = Me
87
83
Fig. 1 ORTEP drawings of (a) 3m and (b) 3p with thermal ellipsoids at
50% probability levels.14
a-regioselectivity and provide the corresponding a-substituted
MBH products in good to excellent yields. The reaction was also
demonstrated to be practical and operationally straightforward
since inert and moisture-free conditions were not required.
Moreover, the present method offers a highly atom economical
synthetic route to important building blocks from simple alcohol
substrates that can be accessed in one step from low cost starting
materials and an iron catalyst that is also inexpensive. Efforts to
apply the method to the preparation of heterocycles and natural
products synthesis are currently underway and will be reported in
due course.
a All reactions were performed at 40 ◦C with a catalyst:1:2 ratio of 1:10:20.
b Reaction time = 2 h. c Reaction time = 3 h. d Reaction time = 4 h.
species. It might be expected that this is a result of decreasing
reactivity as inductive and resonance stabilization of the cation
species increases with increasing electron-donating ability of the
substituent. The involvement of a carbocation intermediate would
also account for our results on the reaction of enantioenriched
1a with 2a. Under our experimental conditions, the a-substituted
cyclic MBH product 3a was obtained as a racemic mixture in 80%
yield, as shown in Scheme 3.
Experimental section
General details
All reactions were performed open to the atmosphere. Unless
specified, all reagents and starting materials were purchased from
commercial sources and used as received. All cyclic MBH alcohol
substrates reported in this work were prepared following literature
procedures.15 Solvents were purified following standard literature
procedures; CH2Cl2 was purified prior to use by passing through
a PURESOLV(tm) Solvent Purification System. Analytical thin
layer chromatography (TLC) was performed using Merck 60
F254 pre-coated silica gel plate. Visualization was achieved by
UV light (254 nm). Flash chromatography was performed using
Merck silica gel 60 with freshly distilled solvents. Unless otherwise
stated, 1H and 13C NMR spectra were measured on Bruker Avance
400 MHz spectrometer. Unless otherwise stated, chemical shifts
(ppm) were recorded with respect to TMS in CDCl3. Multiplicities
were given as: s (singlet), bs (broad singlet), d (doublet), t (triplet),
Scheme 3 FeCl3·6H2O-catalysed direct nucleophilic a-substitution of
enantioriched 1a with 2a.
Conclusions
In summary, a general and efficient iron-catalysed method for
the direct nucleophilic a-substitution of MBH alcohols with
a structurally diverse set of nucleophiles that include alcohols,
1,3-dicarbonyl compounds, sulfamates and thiols, has been re-
ported. These results show the reaction to proceed with complete
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The Royal Society of Chemistry 2009
Org. Biomol. Chem., 2009, 7, 4186–4193 | 4189
©

dd (doublet, doublet) or m (multiplet). The number of protons (n)
for a given resonance is indicated by nH. Coupling constants are
reported as a J value in Hz. Infrared spectra were recorded on
Shimadzu IR Prestige-21 FTIR Spectrometer. High Resolution
Mass (HRMS) spectra were obtained using Finnigan MAT95XP
LC/HRMS. Mass spectral data were reported in units of mass
to charge (m/z). Enantioselectivities were determined by high
performance liquid chromatography (HPLC) analysis employing
a Daicel Chirapak AD-H or OJ-H column.
J = 12.1 Hz, 1H), 5.78 (d, J = 12.0 Hz, 1H), 6.84 (t, J = 4.0 Hz,
1H), 7.02–7.89 (m, 17H), 7.88 (d, J = 7.6, 2H), 8.05 (d, J = 7.6,
2H); 13C NMR (CDCl3, 100 MHz): d 22.3, 22.5, 26.1, 26.3, 27.5,
28.6, 38.7, 38.8, 45.1, 46.9, 66.3, 67.2, 126.7, 127.0, 128.1, 128.4,
128.4, 128.6, 128.7, 128.7, 128.9, 128.9, 133.6, 133.7, 136.9, 137.0,
139.5, 139.7, 140.1, 140.4, 146.6, 147.8, 194.5, 194.7, 198.2, 198.4,
202.9, 203.5; IR (neat): 3024, 2926, 1722, 1676, 1595, 1236, 756,
665 cm-1; MS (ESI) m/z 347 [M + H]+; HRMS (ESI) calcd for
C23H23O3: 347.1647, found: 347.1648.
Ethyl 2-benzoyl-3-(6-oxocyclohex-1-enyl)-3-phenylpropanoate
(3d). Yield: 97%; Major isomer: white solid; m.p. 166–167 ◦C;
1H NMR (CDCl3, 400 MHz): d 0.91 (t, J = 7.1 Hz, 3H),
1.72–1.79 (m, 2H), 2.15–2.28 (m, 4H), 3.86–3.89 (m, 2H), 4.76 (d,
J = 11.8 Hz, 1H), 5.57 (d, J = 11.8 Hz, 1H), 6.84 (t, J = 4.0 Hz,
1H), 7.18–7.58 (m, 8H), 8.07 (d, J = 7.4 Hz, 2H); 13C NMR
(CDCl3, 100 MHz): d 13.7, 22.3, 26.1, 38.8, 47.1, 57.4, 61.4,
126.8, 128.3, 128.5, 128.7, 128.9, 133.6, 136.6, 139.6, 140.4,
146.5, 168.0, 193.7, 198.3; IR (neat): 3019, 1733, 1682, 1215,
756, 667 cm-1; MS (ESI) m/z 377 [M + H]+; HRMS (ESI) calcd
for C24H25O4: 377.1753, found: 377.1735. Minor isomer: white
solid; m.p. 120–121 C; H NMR (CDCl3, 400 MHz): d 1.14 (t,
J = 7.0 Hz, 3H), 1.90–1.94 (m, 2H), 2.36–2.40 (m, 4H), 4.02–4.13
(m, 2H), 4.82 (d, J = 11.8 Hz, 1H), 5.58 (d, J = 11.8 Hz, 1H),
7.02–7.54 (m, 9H), 7.95 (d, J = 7.5 Hz, 2H); 13C NMR (CDCl3,
100 MHz): d 14.1, 22.6, 26.3, 38.9, 46.7, 56.8, 61.5, 126.5, 128.2,
128.2, 128.6, 128.7, 133.4, 136.7, 140.0, 140.3, 147.0, 168.3, 193.2,
198.1; IR (neat): 3019, 1734, 1682, 1215, 754, 665 cm-1; MS (ESI)
m/z 377 [M + H]+; HRMS (ESI) calcd for C24H25O4: 377.1753,
found: 377.1744.
General procedure for optimising the Lewis acid-catalysed
a-substitution of 1a with 2a
To a solution of CH2Cl2 (3 mL) contained in a round bottom
flask open to air at room temperature was successively added
1a (0.25 mmol), 2a (0.5 mmol) and 10 mol% of the Lewis ac◦id.
The reaction mixture was stirred at room temperature or 40 C
and monitored by TLC analysis. On completion, the solvent
was removed under reduced pressure and the resultant residue
obtained was directly purified by flash column chromatography
(EtOAc/n-hexane) to afford the product 3a.
◦
1
General procedure for iron(III) chloride-catalysed a-substitution of
cyclic MBH alcohols 1a–k with 2a–l
To a solution of CH2Cl2 (3 mL) contained in a round bottom
flask open to air at room temperature was successively added 1
(0.25 mmol), 2 (0.5 mmol) and FeCl3·6H2O (0.025 mmol). The
reaction mixture was stirred at 40 ◦C and monitored by TLC
analysis. On cooling to room temperature, the solvent was re-
moved under reduced pressure and the resultant residue obtained
was directly purified by flash column chromatography (EtOAc/
n-hexane) to afford the product 3.
2-((4-Nitrophenyl)(6-oxocyclohex-1-enyl)methyl)-1,3-diphenyl-
prop◦ane-1,3-dione (3e). Pale yellow solid; yield: 80% m.p. 174–
175 C; 1H NMR (CDCl3, 400 MHz): d 1.53–1.56 (m, 1H), 1.73–
1.76 (m, 1H), 2.00–2.27 (m, 4 H), 4.89 (d, J = 11.3 Hz, 1H), 6.77
(d, J = 11.3 Hz, 1 H), 7.00 (t, J = 4.1 Hz, 1 H), 7.34–7.60 (m, 8 H),
7.89 (d, J = 7.2 Hz, 2H), 8.00–8.03 (m, 4H); 13C NMR (CDCl3,
100 MHz): d 22.1, 26.2, 38.8, 50.3, 58.0, 123.4, 128.6, 128.8, 129.0,
129.0, 129.3, 133.7, 133.9, 136.5, 138.1, 146.5, 148.2, 150.3, 193.5,
194.7, 199.2; IR (neat): 3019, 1694, 1668, 1215, 756, 667 cm-1;
MS (ESI) m/z 454 [M + H]+; HRMS (ESI) calcd for C28H24NO5:
454.1654, found: 454.1646.
2-((6-Oxocyclohex-1-enyl)(phenyl)methyl)-1,3-diphenylpropane-
◦
1
1,3-dione (3a). White solid; yield: 92%; m.p. 177–178 C; H
NMR (CDCl3, 400 MHz): d 1.56–1.65 (m, 1H), 1.72–1.79 (m,
1H), 2.05–2.25 (m, 4H), 4.87 (d, J = 11.4 Hz, 1H), 6.73 (d,
J = 11.4 Hz, 1H), 6.95 (t, J = 4.1 Hz, 1H), 7.03–7.54 (m, 11H),
7.86 (d, J = 7.4 Hz, 2H), 8.00 (d, J = 7.4 Hz, 2H); 13C NMR
(CDCl3, 100 MHz): d 22.3, 26.2, 39.0, 50.0, 59.2, 126.6, 128.2,
128.5, 128.6, 128.7, 128.8, 129.0, 133.2, 133.5, 136.8, 137.0, 139.4,
140.4, 148.7, 194.4, 195.1, 199.2; IR (neat): 3019, 1697, 1670,
1215, 756, 667, 513 cm-1; MS (ESI) m/z 409 [M + H]+; HRMS
(ESI) calcd for C28H25O3: 409.1804, found: 409.1811.
2-((4-Fluorophenyl)(6-oxocyclohex-1-enyl)methyl)-1,3-diphenyl-
propane-1,3-dione (3f). White solid; yield: 99%; m.p. 160–162 ◦C;
1H NMR (CDCl3, 400 MHz): d 1.61–1.77 (m, 2H), 2.05–2.12
(m, 1H), 2.19–2.26 (m, 3H), 4.85 (d, J = 11.4 Hz, 1H), 6.69 (d,
J = 11.4 Hz, 1H), 6.79–6.83 (m, 2H), 6.94 (t, J = 8.3 Hz 1H), 7.27–
7.54 (m, 8H), 7.86 (d, J = 7.6 Hz, 2H), 8.00 (d, J = 7.2 Hz, 2H);
13C NMR (CDCl3, 100 MHz): d 22.3, 26.2, 39.0, 49.4, 59.2, 114.9,
115.1, 128.6, 128.8, 128.9, 130.0, 130.1, 133.3, 133.5, 136.1, 136.8,
136.9, 139.2, 148.8, 160.2, 162.7, 194.2, 194.9, 199.3; IR (neat):
3017, 2928, 1694, 1670, 1595, 1223, 754, 687 cm-1; MS (ESI) m/z
427 [M + H]+; HRMS (ESI) calcd for C28H24FO4: 427.1709, found:
427.1703.
3-((6-Oxocyclohex-1-enyl)(phenyl)methyl)pentane-2,4-dione
(3b). White solid; yield: 90%; m.p. 110–111 ◦C; 1H NMR
(CDCl3, 400 MHz): d 1.89–1.90 (m, 5H), 2.14 (s, 3H), 2.33–2.38
(m, 4H), 4.68 (d, J = 12.5 Hz, 1H), 4.78 (d, J = 12.5 Hz, 1H),
6.90 (t, J = 3.8 Hz, 1H), 7.17–7.27 (m, 5H); 13C NMR (CDCl3, 100
MHz): d 22.5, 26.2, 28.5, 30.7, 38.6, 44.5, 72.8, 127.0, 128.1, 128.6,
139.5, 140.0, 146.3, 197.9, 202.9, 203.1; IR (neat): 3019, 1730, 1697,
1674, 1215, 756, 667 cm-1; MS (ESI) m/z 285 [M + H]+; HRMS
(ESI) calcd for C18H21O3: 285.1491, found: 285.1490.
2-((6-Oxocyclohex-1-enyl)(phenyl)methyl)-1-phenylbutane-1,3-
2-((4-Chlorophenyl)(6-oxocyclohex-1-enyl)methyl)-1,3-diphenyl-
propane-1,3-dione (3g). White solid; yield: 95%; m.p. 178–179 ◦C;
1H NMR (CDCl3, 400 MHz): d 1.62–1.63 (m, 1H), 1.74–1.79 (m,
1H), 2.03–2.10 (m, 1H), 2.17–2.27 (m, 3H), 4.82 (d, J = 11.4 Hz,
1H), 6.70 (d, J = 11.4 Hz, 1H), 6.94 (t, J = 8.1 Hz 1H), 7.09–7.56
◦
1
dione (3c). Pale yellow solid; yield: 92%; m.p. 120–121 C; H
NMR (CDCl3, 400 MHz): d 1.68–1.77 (m, 2H), 1.91–1.94 (m,
2H), 1.99 (s, 3H), 2.12 (s, 3H), 2.21–2.22 (m, 4H), 2.38–2.41 (m,
4H), 4.86 (d, J = 12.0 Hz, 1H), 5.05 (d, J = 12.1 Hz, 1H), 5.58 (d,
4190 | Org. Biomol. Chem., 2009, 7, 4186–4193
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The Royal Society of Chemistry 2009
©

(m, 10H), 7.87 (d, J = 7.6 Hz, 2H), 7.99 (d, J = 8.0 Hz, 2H); 13
C
7.08–7.10 (m, 2 H), 7.31–7.52 (m, 9H), 7.81 (d, J = 7.6 Hz, 2H),
7.97 (d, J = 7.2 Hz, 2H); 13C NMR (CDCl3, 100 MHz): d 26.7,
35.3, 45.1, 58.9, 128.6, 128.6, 128.7, 128.8, 128.9, 130.1, 132.8,
133.4, 133.6, 136.6, 136.7, 138.3, 145.3, 161.7, 194.2, 194.3, 209.4;
IR (neat): 3393, 1686, 1659, 756 cm-1; MS (ESI) m/z 429 [M + H]+;
HRMS (ESI) calcd for C27H22ClO3: 429.1257, found: 429.1260.
NMR (CDCl3, 100 MHz): d 22.2, 26.2, 39.0, 49.7, 58.9, 128.3,
128.3, 128.6, 128.7, 128.8, 129.0, 129.9, 132.3, 133.4, 133.6, 136.7,
136.9, 139.0, 149.1, 194.0, 194.9, 199.2; IR (neat): 3019, 1695,
1653, 1215, 756, 667 cm-1; MS (ESI) m/z 443 [M + H]+; HRMS
(ESI) calcd for C28H24ClO3: 443.1414, found: 443.1416.
2-((4-Chlorophenyl)(4-oxo-4H-chromen-3-yl)methyl)-1,3-di-
phenylpropane-1,3-dione (3n). Pale yellow solid; yield: 61%; m.p.
213–214 ◦C; 1H NMR (CDCl3, 400 MHz): d 4.93 (d, J = 10.9 Hz,
1H), 7.09–7.12 (m, 2H), 7.31–7.60 (m, 12H), 7.93–8.12 (m, 6H);
13C NMR (CDCl3, 100 MHz): d 47.4, 57.4, 118.1, 123.6, 124.3,
125.2, 125.7, 128.5, 128.7, 128.7, 128.9, 128.9, 130.2, 132.8, 133.5,
133.7, 136.7, 136.7, 138.5, 155.1, 155.9, 178.0, 194.2, 194.7; IR
(neat): 3019, 1690, 1634, 1466, 1263, 1215, 756, 667 cm-1; MS
(ESI) m/z 493 [M + H]+; HRMS (ESI) calcd for C31H22ClO4:
493.1207, found: 493.1214.
2-((4-Bromophenyl)(6-oxocyclohex-1-enyl)methyl)-1,3-diphenyl-
propane-1,3-dione (3h). White solid; yield: 91%; m.p. 190–191 ◦C;
1H NMR (CDCl3, 400 MHz): d 1.57–1.60 (m, 1H), 1.62–1.78 (m,
1H), 2.05–2.09 (m, 1H), 2.16–2.26 (m, 3H), 4.81 (d, J = 11.4 Hz,
1H), 6.70 (d, J = 11.4 Hz, 1H), 6.94 (t, J = 4.2 Hz 1H), 7.20–
8.00 (m, 14H); 13C NMR (CDCl3, 100 MHz): d 22.2, 26.2, 38.9,
49.7, 58.8, 120.5, 128.6, 128.7, 128.8, 129.0, 130.2, 131.3, 133.4,
133.6, 136.7, 136.8, 138.9, 139.5, 149.2, 194.0, 194.9, 199.2; IR
(neat): 3019, 1695, 1653, 1215, 756, 667 cm-1; MS (ESI) m/z 487
[M + H]+; HRMS (ESI) calcd for C28H24BrO3: 487.0909, found:
487.0912.
2-((4-Hydroxy-3-methylphenyl)(phenyl)methyl)cyclohex-2-
1
enone (3o). Colourless oil; yield: 62%; H NMR (CDCl3, 400
2-((6-Oxocyclohex-1-enyl)(p-tolyl)methyl)-1,3-diphenylpropane-
1,3-dione (3i). Pale brown solid; yield: 66%; m.p. 204–205 ◦C;
1H NMR (CDCl3, 400 MHz): d 1.58–1.61 (m, 1H), 1.70–1.75
(m, 1H), 2.04–2.09 (m, 2H), 2.18 (s, 3H), 2.21–2.22 (m, 2H),
4.86 (d, J = 11.4 Hz, 1H), 6.72 (d, J = 11.4 Hz, 1H), 7.20–7.22
(m, 3H), 7.26–7.52 (m, 8H), 7.87 (d, J = 7.6 Hz, 2H), 8.01 (d,
J = 7.6 Hz, 2H); 13C NMR (CDCl3, 100 MHz): d 20.9, 22.3, 26.2,
39.0, 49.6, 59.4, 128.3, 128.5, 128.7, 128.7, 129.0, 129.0, 133.1,
133.4, 136.0, 136.9, 137.1, 137.4, 139.5, 148.5, 194.3, 195.2, 199.2;
IR (neat): 3019, 1690, 1667, 1215, 756, 667 cm-1; MS (ESI) m/z
445 [M + Na]+; HRMS (ESI) calcd for C29H26O3Na: 445.1780,
found: 445.1768.
MHz): d 1.99–2.02 (m, 2H), 2.15 (s, 1H), 2.37–2.38 (m, 2H), 2.44–
2.47 (m, 2 H), 5.36 (s, 1 H), 5.39 (s, 1 H), 6.42 (s, 1 H), 6.58–6.60
(m, 2H), 6.71–6.74 (m, 1H), 6.83 (s, 1H), 7.06–7.08 (m, 2H), 7.15–
7.18 (m, 1H), 7.23–7.27 (m, 1H); 13C NMR (CDCl3, 100 MHz):
d 16.0, 22.9, 26.2, 38.7, 48.6, 114.7, 123.8, 126.2, 127.4, 128.3,
129.0, 131.6, 134.1, 142.8, 143.0, 148.2, 152.5, 198.7; IR (neat)
1662, 1505, 1269, 910, 730 cm-1; MS (ESI) m/z 293 [M + H]+;
HRMS (ESI) calcd. for C20H21O2: 293.1542, found: 293.1542.
2-({4-Hydroxy-3,5-dimethylphenyl}(phenyl)methyl)cyclohex-2-
enone (3p). White solid; yield: 88%; m.p. 174–176 ◦C; 1H NMR
(CDCl3, 400 MHz) d 1.98–2.04 (m, 2H), 2.17 (s, 6H), 2.37–2.47
(m, 4H), 4.60 (s, 1H), 5.36 (s, 1H), 6.41 (t, 1H, J = 4.0 Hz),
6.68 (s, 2H), 7.07–7.27 (m, 5H); 13C NMR (CDCl3, 100 MHz) d
16.1, 22.9, 26.2, 38.7, 48.6, 122.8, 126.1, 128.2, 129.0, 129.1, 133.8,
142.8, 143.1, 147.8, 150.7, 198.2; IR (neat) 1670, 1489, 1263, 908,
738 cm-1; HRMS (ESI) calcd. for C21H22O2Na: 329.1517, found:
329.1977.
2 - ( ( 4 - Ethoxyphenyl ) ( 6 - oxocyclohex - 1 - enyl ) methyl ) - 1 , 3 -
diphenylpropane-1,3-dione (3j). White solid; yield: 40%; m.p.
215–216 ◦C; 1H NMR (CDCl3, 400 MHz): d 1.31 (t, J = 7.0 Hz,
3H), 1.63–1.79 (m, 2H), 2.04–2.26 (m, 4H), 3.88 (q, J = 7.2 Hz,
2H), 4.83 (d, J = 11.4 Hz, 1H), 6.64–6.69 (m, 3H), 6.92 (t,
J = 3.9 Hz, 1H), 7.21–7.53 (m, 8H), 7.86 (d, J = 8.0 Hz, 2H),
7.99 (d, J = 8.0 Hz, 2H); 13C NMR (CDCl3, 100 MHz): d 14.8,
22.3, 26.2, 39.0, 49.2, 59.7, 63.2, 114.2, 128.5, 128.7, 128.7, 129.0,
129.5, 132.3, 133.1, 133.4, 136.9, 137.1, 139.6, 148.3, 157.5, 194.5,
195.1, 199.3; IR (neat): 3019, 1692, 1674, 1661, 1215, 756, 667 cm-1;
MS (ESI) m/z 475 [M + Na]+; HRMS (ESI) calcd for C30H28O4Na:
475.1885, found: 475.1881.
2-(Ethoxy(phenyl)methyl)cyclohex-2-enone (3q). Colourless
oil; yield: 94%; 1H NMR (CDCl3, 400 MHz): d 1.20 (t, J = 7.0 Hz,
3H), 1.92–2.00 (m, 2H), 2.32–2.45 (m, 4H), 3.44 (q, J = 7.2 Hz,
2H), 5.38 (s, 1H), 7.02 (t, J = 4.8 Hz, 1H), 7.20–7.36 (m, 5H);
13C NMR (CDCl3, 100 MHz): d 15.3, 22.6, 25.8, 38.4, 64.6,
76.3, 127.1, 127.3, 128.2, 140.9, 142.2, 145.7, 197.9; IR (neat):
2926, 1672, 1454, 1377, 1169, 1086, 698 cm-1; MS (ESI) m/z 185
[M - OC2H5]+; HRMS (ESI) calcd for C13H13O: 185.0966, found:
185.0958.
2-((2-Chlorophenyl)(6-oxocyclohex-1-enyl)methyl)-1,3-diphenyl-
propane-1,3-dione (3l). White solid; yield: 88%; m.p. 169–170 ◦C;
1H NMR (CDCl3, 400 MHz): d 1.43–1.48 (m, 1H), 1.68–1.70
(m, 1H), 1.96–2.24 (m, 4H), 5.20 (d, J = 11.2 Hz, 1H), 6.92 (d,
J = 11.2 Hz, 1H), 6.99–7.08 (m, 3H), 7.22–7.68 (m, 8H), 7.89 (d,
J = 7.2 Hz, 2H), 8.04 (d, J = 7.6 Hz, 2H); 13C NMR (CDCl3, 100
MHz): d 22.1, 26.2, 39.1, 47.2, 57.7, 126.3, 127.7, 128.5, 128.6,
128.8, 129.0, 129.9, 133.3, 133.6, 133.6, 134.5, 136.3, 136.9, 136.9,
137.2, 152.1, 193.5, 195.5, 199.7; IR (neat): 3019, 1697, 1670, 1215,
756, 667 cm-1; MS (ESI) m/z 443 [M + H]+; HRMS (ESI) calcd
for C28H24ClO3: 443.1414, found: 443.1408.
2-(Benzyloxy(phenyl)methyl)cyclohex-2-enone (3r). Pale yel-
1
low oil; yield: 95%; H NMR (CDCl3, 400 MHz): d 1.90–2.00
(m, 2H), 2.34–2.43 (m, 4H), 4.42–4.48 (m, 2H), 5.48 (s, 1H), 7.10
(t, J = 4.0 Hz 1H), 7.23–7.40 (m, 10H); 13C NMR (CDCl3, 100
MHz): d 22.6, 25.8, 38.5, 71.0, 76.4, 127.3, 127.5, 127.6, 127.8,
128.3, 128.3, 138.4, 140.7, 140.8, 145.9, 197.8; IR (neat): 3391,
2922, 1663, 1452, 1375, 1169, 734, 696 cm-1; MS (ESI) m/z 293
[M + H]+; HRMS (ESI) calcd for C20H21O2: 293.1542, found:
293.1536.
2-((4-Chlorophenyl)(5-oxocyclopent-1-enyl)methyl)-1,3-di-
phenylpropane-1,3-dione (3m). White solid; yield: 84%; m.p. 195–
196 ◦C; 1H NMR (CDCl3, 400 MHz): d 2.17–2.33 (m, 2H), 2.46–
2.47 (m, 2H), 4.97 (d, J = 11.2, 1H), 6.75 (d, J = 11.2 Hz, 1H),
2-((But-3-enyloxy)(phenyl)methyl)cyclohex-2-enone (3s). Pale
yellow oil; yield: 85%; 1H NMR (CDCl3, 400 MHz): d 1.90–2.00
(m, 2H), 2.31–2.43 (m, 6H), 3.41–3.46 (m, 2H), 4.99–5.07 (m, 2H),
This journal is
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Org. Biomol. Chem., 2009, 7, 4186–4193 | 4191
©

5.36 (s, 1H), 5.74–5.85 (m, 1H), 7.23 (t, J = 7.2 Hz, 1H), 7.25–7.35
(m, 5 H); 13C NMR (CDCl3, 100 MHz): d 22.6, 25.8, 34.3, 38.4,
68.5, 76.5, 116.3, 127.1, 127.4, 128.2, 135.3, 140.8, 141.1, 145.8,
197.9; IR (neat): 2926, 1674, 1641, 1454, 1375, 1086, 1074, 914,
700, 525 cm-1; MS (ESI) m/z 185 [M - OC4H6]+; HRMS (ESI)
calcd for C13H13O: 185.0966, found: 185.0961.
8798; (k) S. Madapa, V. Singh and S. Batra, Tetrahedron, 2006, 62,
8740; (l) S. C. Kim, H. S. Lee, Y. J. Lee and J. N. Kim, Tetrahedron
Lett., 2006, 47, 5681; (m) G. W. Kabalka, G. Dong, B. Venkataiah and
C. Chen, J. Org. Chem., 2005, 70, 9207; (n) K. Y. Lee, S. Gowrisankar,
Y. J. Lee and J. N. Kim, Tetrahedron Lett., 2005, 46, 5387; (o) J. Li,
X. Wang and Y. Zhang, Tetrahedron Lett., 2005, 46, 5233; (p) S. Ma,
S. Yu and Z. Peng, Org. Biomol. Chem., 2005, 3, 1933; (q) J. S. Yadav,
B. V. S. Reddy, A. K. Basak, A. V. Narsaiah, A. Prabhakar and B.
Jagadeesh, Tetrahedron Lett., 2005, 46, 639; (r) C.-W. Cho and M. J.
Krische, Angew. Chem., Int. Ed., 2004, 43, 6689; (s) Y. Du, X. Han and
X. Lu, Tetrahedron Lett., 2004, 45, 4967; (t) C.-W. Cho, J.-R. Kong
and M. J. Krische, Org. Lett., 2004, 6, 1337; (u) G. W. Kabalka, B.
Venkataiah and G. Dong, Org. Lett., 2003, 5, 3803; (v) Y. M. Chung,
J. H. Gong, T. H. Kim and J. N. Kim, Tetrahedron Lett., 2001, 42, 9023;
(w) D. Basavaiah and T. Satyanarayana, Org. Lett., 2001, 3, 3619; (x) O.
Roy, A. Riahi, F. He´nin and J. Muzart, Tetrahedron, 2000, 56, 8133;
(y) B. M. Trost, H. C. Tsui and F. D. Toste, J. Am. Chem. Soc., 2000,
122, 3534.
2-((Ethylthio)(phenyl)methyl)cyclohex-2-enone
(3t). White
solid; yield: 96%; m.p. 41–42 ◦C; 1H NMR (CDCl3, 400 MHz): d
1.17–1.21 (m, 3H), 1.92–2.00 (m, 2H), 2.35–2.5 (m, 6H), 5.25 (s,
1H), 7.12 (t, J = 3.8, 1H), 7.18–7.40 (m, 5H); 13C NMR (CDCl3,
100 MHz): d 14.2, 22.7, 26.2, 26.4, 38.4, 45.2, 127.0, 128.3, 128.4,
140.0, 141.0, 147.3, 197.2; IR (neat): 3017, 1670, 1454, 1373, 1215,
756, 667 cm-1; MS (ESI) m/z 185 [M - SC2H5]+; HRMS (ESI)
calcd for C13H13O: 185.0966, found: 185.0959.
3 For selected examples using MBH alcohols, see: (a) J. S. Yadav, B. V. S.
Reddy, S. S. Mandal, A. P. Singh and A. K. Basak, Synthesis, 2008,
1943; (b) L. D. S. Yadav, R. Patel and V. P. Srivastava, Synlett, 2008,
1789; (c) M. L. Kantam, K. B. S. Kumar and B. Sreedhar, J. Org.
Chem., 2008, 73, 320; (d) J. Li, X. Liu, P. Zhao and X. Jia, J. Chem.
Res., 2008, 159; (e) B. Das, H. Holla, Y. Srinivas, N. Chowdhury and
B. P. Bandgar, Tetrahedron Lett., 2007, 48, 3201; (f) M. J. Lee, D. Y.
Park, K. Y. Lee and J. N. Kim, Tetrahedron Lett., 2006, 47, 1833;
(g) B. Das and P. Thirupathi, J. Mol. Catal. A: Chem., 2007, 269, 12;
(h) B. Das, A. Majhi and J. Banerjee, Tetrahedron Lett., 2006, 47, 7619;
(i) S. Chandrasekhar, B. Saritha, V. Jagadeshwar, C. Narsihmulu, D.
Vijay, G. D. Sarma and B. Jagadeesh, Tetrahedron Lett., 2006, 47, 2981;
(j) B. Das, A. Majhi, J. Banerjee and N. Chowdhury, J. Mol. Catal. A:
Chem., 2006, 260, 32; (k) B. Das, A. Majhi, J. Banerjee, N. Chowdhury
and K. Venkateswarlu, Tetrahedron Lett., 2005, 46, 7913; (l) B. Das,
J. S. Rao and R. J. Reddy, J. Org. Chem., 2004, 69, 7379; (m) A. B.
Charette, M. K. Janes and A. A. Boezio, J. Org. Chem., 2001, 66, 2178;
(n) J. S. Yadav, B. V. S. Reddy and C. Madan, New J. Chem., 2001, 25,
1114; (o) J. N. Kim, K. Y. Lee, H. S. Kim and T. Y. Kim, Org. Lett.,
2000, 2, 343; (p) D. Basavaiah, R. S. Hyma, K. Muthukumaran and N.
Kumaragurubaran, Synthesis, 2000, 217.
2-((4-Chlorophenylthio)(phenyl)methyl)cyclohex-2-enone (3u).
Colourless oil; yield: 87%; 1H NMR (CDCl3, 400 MHz): d
1.94–1.97 (m, 2H), 2.39–2.46 (m, 4H), 5.63 (s, 1H), 7.12–7.35
(m, 10H); 13C NMR (CDCl3, 100 MHz): d 22.6, 26.2, 38.3, 49.0,
127.4, 128.3, 128.5, 128.9, 131.5, 132.6, 134.5, 139.0, 139.7, 148.2,
197.1; IR (neat): 2947, 2926, 1672, 1476, 1452, 1371, 1246, 1167,
1094, 1011, 812, 723, 696, 507 cm-1; MS (ESI) m/z 185 [M -
SClC6H4]+; HRMS (ESI) calcd for C13H13O: 185.0966, found:
185.0961.
2-(Phenyl(p-tolylthio)methyl)cyclohex-2-enone (3v). Colour-
1
less oil; yield: 83%; H NMR (CDCl3, 400 MHz): d 1.92–1.97
(m, 2H), 2.26 (s, 3H), 2.38–2.47 (m, 4H), 5.60 (s, 1H), 6.98–7.00
(m, 2H), 7.13–7.27 (m, 4H), 7.35–7.37 (m, 2H), 7.97 (d, J = 7.2 Hz,
2H); 13C NMR (CDCl3, 100 MHz): d 21.1, 22.6, 26.2, 38.4, 49.4,
127.1, 128.3, 128.4, 129.6, 130.9, 132.2, 136.7, 139.3, 140.3, 148.0,
197.2; IR (neat): 3026, 2945, 2866, 1672, 1634, 1597, 1492, 1452,
1371, 1246, 1167, 1130, 1090, 979, 802, 721, 698, 525 cm-1; MS
(ESI) m/z 185 [M - SC7H7]+; HRMS (ESI) calcd for C13H13O:
185.0966, found: 185.0960.
4 For reviews on the use of alcohols as pro-electrophiles, see: (a) M
Bandini and M. Tragni, Org. Biomol. Chem., 2009, 7, 1501; (b) J.
Muzart, Tetrahedron, 2008, 64, 5815; (c) J. Muzart, Eur. J. Org. Chem.,
2007, 3077; (d) J. Muzart, Tetrahedron, 2005, 61, 4179; (e) Y. Tamaru,
Eur. J. Org. Chem., 2005, 2647.
5 For selected recent examples on iron-catalysed reactions of alcohols,
see: (a) W. Huang, P. Zheng, Z. Zhang, R. Liu, Z. Chen and X. Zhou,
J. Org. Chem., 2008, 73, 6845; (b) S. Babu, M. Yasuda, Y. Tsukahara, T.
Yamauchi, Y. Wada and A. Baba, Synthesis, 2008, 1717; (c) W. Huang,
Q. Shen, J. Wang and X. Zhou, J. Org. Chem., 2008, 73, 1586; (d) U.
Jana, S. Biswas and S. Maiti, Tetrahedron Lett., 2008, 49, 858; (e) W.-H.
Ji, Y.-M. Pan, S.-Y. Zhao and Z.-P. Zhan, Synlett, 2008, 3046; (f) U.
Jana, S. Maiti and S. Biswas, Tetrahedron Lett., 2007, 48, 7160; (g) U.
Jana, S. Biswas and S. Maiti, Tetrahedron Lett., 2007, 48, 4065; (h) J.
Kischel, K. Mertins, D. Michalik, A. Zapf and M. Beller, Adv. Synth.
Catal., 2007, 349, 865; (i) Z.-P. Zhan, J.-L. Yu, H.-J. Liu, Y.-Y. Cui,
R.-F. Yang, W.-Z. Yang and J.-P. Li, J. Org. Chem., 2006, 71, 8298; (j) I.
Iovel, K. Mertins, J. Kischel, A. Zapf and M. Beller, Angew. Chem., Int.
Ed., 2005, 44, 3913; (k) P. Salehi, N. Iranpoor and F. K. Behbahani,
Tetrahedron, 1998, 54, 943.
6 For recent examples using other Lewis acid catalysts, see: (a) M.
Georgy, V. Boucard, O. Debleds, C. Dal Zotto and J.-M. Campagne,
Tetrahedron, 2009, 65, 1758; (b) X. Du, F. Song, Y. Lu, H. Chen and
Y. L i u , Tetrahedron, 2009, 65, 1839; (c) M. Bandini, A. Eichholzer,
P. Kotrusz, M. Tragni, S. Troisi and A. Umani-Ronchi, Adv. Synth.
Catal., 2009, 351, 319; (d) Y. Lu, X. Fu, H. Chen, X. Du, X. Jia and Y.
Liu, Adv. Synth. Catal., 2009, 351, 129; (e) K. Namba, H. Yamamoto,
I. Sasaki, K. Mori, H. Imagawa and M. Nishizawa, Org. Lett., 2008,
10, 1767; (f) A. Aponick, C.-Y. Li and B. Biannic, Org. Lett., 2008, 10,
669; (g) X.-Z. Shu, X.-Y. Liu, H.-Q. Xiao, K.-G. Ji, L.-N. Guo and
Y.-M. Liang, Adv. Synth. Catal., 2008, 350, 243; (h) M. Noji, Y. Konno
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Acknowledgements
This work was supported by a College of Science Start-Up Grant
and Supplementary Equipment Purchase Grant (RG134/06) from
Nanyang Technological University.
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