Microwave-accelerated coupling-isomerization reaction (MACIR) - A general coupling-isomerization synthesis of 1,3-diarylprop-2-en-1-ones

Article abstract of DOI:10.1002/adsc.200600280

The microwave-accelerated coupling-isomerization reaction (MACIR) of (hetero)aryl halides and propargyl alcohols represents a general Pd/Cu and base-catalyzed process for the synthesis of 3-arylprop-2-en-1-ones in good yields.

Full text of DOI:10.1002/adsc.200600280

COMMUNICATIONS
DOI: 10.1002/adsc.200600280
Microwave-Accelerated Coupling-Isomerization Reaction
(MACIR) – A General Coupling-Isomerization Synthesis of 1,3-
Diarylprop-2-en-1-ones
Oana G. Schramm (nØe Dediu)a and Thomas J. J. Müllera,b,*
a
Organisch-Chemisches Institut der Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg,
Germany
Fax : (+49)-6221-546-579; e-mail: Thomas.J.J.Mueller@oci.uni-heidelberg.de
Present address: Institut für Organische Chemie und Makromolekulare Chemie der Heinrich-Heine-Universität
b
Düsseldorf, Universitätsstr. 1, 40225 Düsseldorf, Germany
Fax : (+49)-211-84-14324; e-mail: ThomasJJ.Mueller@uni-duesseldorf.de
Received: June 14, 2006; Accepted: September 22, 2006
Supporting information for this article is available on the WWW under http://asc.wiley-vch.de/home/.
Abstract: The microwave-accelerated coupling-iso-
merization reaction (MACIR) of (hetero)aryl hal-
ides and propargyl alcohols represents a general
Pd/Cu and base-catalyzed process for the synthesis
of 3-arylprop-2-en-1-ones in good yields.
Although the CIR is a mild and versatile synthesis
of chalcones it has some inherent scope limitations
and shortcomings under the conditions of conductive
heating. Besides a limited choice of the reaction
media, a relatively large excess of base, and long reac-
tion times (16–24 h), most strikingly, the demand for
an activating electron-deficient (hetero)aryl halide as
a coupling partner is less advantageous. However, the
advent of microwave acceleration of organic reactions
has drastically reduced reaction times and has consid-
erably improved and facilitated transformations clas-
sically performed by conductive heating.[6] Since So-
Keywords: alkynes; copper; cross-coupling; isomer-
ization; palladium
The coupling-isomerization reaction[1] (CIR) of elec- nogashira alkynylations can be significantly accelerat-
tron-deficient (hetero)aryl halides and (hetero)aryl ed by dielectric heating, i.e., under microwave irradia-
propargyl alcohols under the conditions of the Sono- tion,[6a,e,7] the inevitable of probing microwave-acceler-
gashira coupling[2] is a domino process[3] and furnishes ated CIR (MACIR) should lead to an improved
1,3-di
A
in
good
yields process. Here, we communicate the optimization and
(Scheme 1). In recent years, this new chalcone synthe- generalization of the CIR under microwave irradia-
tion leading to the general MACIR synthesis of 3-ar-
ylprop-2-en-1-ones.
A suitable model reaction to optimize the MACIR
is the reaction of p-bromobenzonitrile (1a) and 1-phe-
nylpropyn-1-ol (2a) that has been thoroughly studied
under conductive heating (Scheme 2).[5] After Sonoga-
shira alkynylation, the intermediate propargyl alcohol
3a is isomerized by triethylamine to furnish the chal-
Scheme 1. Synthesis of electron-deficient chalcones by CIR.
cone 4a. Therefore, parameters such as solvent, effec-
sis has been elaborated into an entry to novel consec- tive temperature in the reaction vessel, irradiation
utive one-pot syntheses of pharmaceutically relevant time, triphenylphosphane, triethylamine and sub-
heterocycles.[1,4] Mechanistically, the CIR proceeds as strates concentrations were varied and optimized
a rapid palladium/copper-catalyzed alkyne coupling (Table 1).
followed by a rate-determining base-catalyzed prop-
Kinetics of the model reaction under conventional
argyl alcohol to enone isomerization. Kinetic studies heating revealed that, for the rate-limiting isomeriza-
of the isomerization step show that the reaction pro- tion step, dipolar aprotic solvents such as acetonitrile
ceeds fastest at a more than five-fold excess of amine and DMF give rise to fastest conversions and almost
base and in a dipolar aprotic medium.[5]
quantitative yields.[5] However, under dielectric heat-
Adv. Synth. Catal. 2006, 348, 2565 – 2571
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2565

Oana G. Schramm (nØe Dediu) and Thomas J. J. Müller
COMMUNICATIONS
Scheme 2. MACIR of p-bromobenzonitrile (1a) and 1-phenylpropyn-1-ol (2a).
Table 1. MACIR optimization experiments for the reaction of 1a and 2a with NEt3 as a base.
Entry
Solvent
PPh3
c0(1a) [mol/L][a]
c
(NEt3) [mol/L][a]
T [8C]
t [min]
Yield of 4a[b]
1
2
3
4
5
6
7
8
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
DMF
DMF
DMF
DMF
THF
THF
THF
THF
THF
THF
THF
none
none
none
none
none
none
none
none
none
none
0.2 equivs.
0.2 equivs.
none
0.5
1.4
0.5
0.77
0.5
0.5
0.33
0.33
2.0
2.0
1.0
0.5
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.5
4.3
2.5
3.8
2.5
2.5
1.7
3.3
20.0
20.0
2.6
2.6
2.5
5.0
2.5
2.5
2.5
2.5
1.05[c]
120
120
150
150
150
120
120
120
120
120
150
150
150
150
150
150
150
150
150
60
60
60
60
20
40
60
60
10
20
10
5
30
30
15
20
30
45
5
63%
61%
52%
44%
58%
52%
66%
67%
70%
73%
87%
87%
62%
84%
96%
92%
88%
79%
85%
9
10
11
12
13
14
15
16
17
18
19
none
0.2 equivs.
0.2 equivs.
0.2 equivs.
0.2 equivs.
0.2 equivs.
[a]
Concentration in THF.
Based upon isolated yields after standardized chromatography on silica gel.
DBU as a base.
[b]
[c]
ing the yields in acetonitrile never exceeded 67% (en- only reduced the base concentration and the reaction
tries 1–8). Increasing the effective temperature inside times but also complete conversion and almost quan-
the reaction vessel from 120 to 1508C led to de- titative yields of 4a were obtained (entry 15). En-
creased yields of 4a (entries 3 and 4), whereas, a tries 15 to 18 also clearly show that prolonged reac-
shorter reaction time at higher temperature gave tion times at an effective temperature of 1508C led to
comparable yields (entry 5). Interestingly, switching a decrease in the yields of 4a. Further increases in the
from acetonitrile to DMF and increasing the triethyl- rate were achieved by increasing the base strength
amine concentration caused a considerable reduction from triethylamine (pKb =3.35) to DBU (pKb =1.1)
of the reaction times to obtain slightly higher yields where not only the base concentration could be re-
(entries 9 and 10). Upon adding 20 mol% of triphe- duced to the stoichiometrically necessary amount of
nylphosphane for stabilizing the palladium and 1.05 equivs., but also a reaction time of 5 min for full
copper species at the higher effective temperature[8] conversion with 85% yield of 4a was obtained
not only the triethylamine concentration was lowered (entry 19).
by one order of magnitude but also the reaction times
Although increased substrate concentration (by re-
for complete conversion were reduced to 5 and duction of the solvent volume) generally enhance the
10 min resulting in significantly higher yields of 4a reaction rates, it should be noted that, at higher con-
(entries 11 and 12). Changing the solvent from a dipo- centrations, the chance for explosion of the reaction
lar aprotic one to the weak microwave absorber THF mixture rises. Since Pd and Cu catalysts are very
gave rise to higher yields at 1508C and 5.0M triethyl- strong microwave absorbers, higher catalyst concen-
amine concentration (entry 14). However, as before trations might be critical.
the addition of 20 mol% of triphenylphosphane not
2566
www.asc.wiley-vch.de
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2006, 348, 2565 – 2571

A General Coupling-Isomerization Synthesis of 1,3-Diarylprop-2-en-1-ones
COMMUNICATIONS
In comparison to conductive heating, MACIR the significant difference of the isolated yields can be
shortens the reaction time for full conversion from attributed to the entirely thermal microwave effect[10]
14 h to 15 min. The question arises of whether the re- as a consequence of more efficient gradient-less
action might have been affected by any kind of pecu- energy transfer to the medium and the reactants, the
liar rate enhancing microwave effect. Such non-ther- so-called “molecular heating”.
mal effects were for a long time discussed in the liter-
Based upon these findings the MACIR for elec-
ature.[9] Therefore, CIR were conducted for the model tron-deficient (hetero)aryl halides 1 was probed for
reaction (Scheme 3) under exactly similar conditions some representative examples (Scheme 4, Table 2).[11]
(15 min, THF/NEt3 =2:1, substrate concentrations of For comparison, the results of CIR under conductive
1.0M) using both conventional (reflux temperature at heating were included in Table 2.
Scheme 3. Conductive vs. dielectric heating for the reaction
of 1a and 2a.
808C and 1508C oil bath temperature) and microwave
heating (effective temperature inside the vessel of
Scheme 4. MACIR of (hetero)aryl halides 1 and propargyl
alcohols 2.
1508C). As expected, the classical conventional CIR
at 808C gives the predominant formation of the prop-
argyl alcohol 3a with only a minor amount of the
chalcone 4a. The direct comparison at 1508C between
conductive heating CIR and MACIR furnishes in the
With the combination of high effective internal
former case only 61% of 4a along with 12% of 3a, temperatures and short reaction times good to excel-
yet with incomplete conversion of 1a and 2a, whereas lent yields (62–96%) were obtained in 15 min. The
the latter microwave-accelerated process furnishes ex- yields of MACIR are comparable to those of conduc-
clusively the chalcone 4a in excellent yield. Therefore, tive heating for 16–24 h in the most cases. Interesting-
Table 2. MACIR of (hetero)aryl halides 1 and propargyl alcohols 2 (at an effective internal temperature of 1508C, 15 min, 5
equivs. of NEt3).
Entry
C
Propargyl alcohol 2
R=Ph (2a)
T [8C]
Product
Yield of 4[a,b]
1
150
4a
96% (95%)
2
3
4
2a
2a
2a
120
150
150
4b
4c
4d
84% (91%)
78% (79%)
62% (31%)
5
1a
R=3-thienyl (2b)
R=n-propyl (2c)
150
150
4e
4f
70% (À)
6[c]
p-NCC6H4I (1e)
62% (0%)
[a]
Based upon isolated yields after chromatography on silica gel.
The yields for conductive heating CIR (808C, 16-24 h) are given in parentheses.
DBU as a base.
[b]
[c]
Adv. Synth. Catal. 2006, 348, 2565 – 2571
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.asc.wiley-vch.de
2567

Oana G. Schramm (nØe Dediu) and Thomas J. J. Müller
COMMUNICATIONS
ly, the results are significantly better for sulfonamides creasing the amount of DBU to 2 equivs. gave rise to
under microwave irradiation (entry 5). An alkyl prop- complete conversion of 1f and 2a to give a yield of
argyl alcohol like 1-hexyn-3-ol (2c) is transformed to 92% of the chalcone 4g in 30 min at an effective in-
the enone in reasonable yield (entry 6). It is notewor- ternal temperature of 1008C (entry 6). Applying the
thy that under conventional heating 2c only gives rise same parameters, however, under conductive heating
to the formation of the coupling product but the iso- in an oil bath, only 71% of 4g were obtained
merization does not occur.
(entry 7). As before, the difference in the isolated
Encouraged by the general acceleration of CIR by yields can be accounted to heating by gradient-less,
dielectric heating we next scouted the possibility of efficient energy transfer to the reactants and the reac-
applying electroneutral aryl halides such as iodoben- tion medium.
zene (1f) under MACIR conditions (Scheme 5,
Finally, we wanted to probe the generality of
Table 3). It is interesting to mention in advance that, MACIR for even electron-rich aryl iodides. In three
under prolonged conventional heating at 808C, the re- examples, iodobenzenes 5 bearing electron-releasing
action of 1f and 2a exclusively gives rise to the forma- substituents were reacted with 2a under MACIR con-
tion of the coupling product 3g without any trace of ditions giving rise to the formation of the correspond-
the isomerization product 4g.[1]
ing chalcones
(Scheme 6).
6
in good to excellent yields
Scheme 6. MACIR of electron-rich iodobenzenes 5 and 2a.
Scheme 5. CIR of iodobenzene (1f) and 2a under dielectric
and conductive heating.
In conclusion, we have developed a general, rapid
Since the isomerization step is a base-catalyzed pro- and efficient synthesis of enones based upon the mi-
cess, several amine bases of various pKb were tested. crowave-assisted coupling-isomerization reaction
For triethylamine as a base (pKb =3.35) the isolated (MACIR) of (hetero)aryl halides and propargyl alco-
yields were poor both for the coupling product 3g and hols. The enones were generally obtained in good to
for the enone 4g (entries 1 and 2). In the case of pi- excellent yields and within 8–30 min. For electron-rich
peridine, a slightly stronger base (pKb =3.2) than tri- aryl iodides DBU is the most favorable base both for
ethylamine, the coupling product 3g was formed at the coupling and the isomerization steps. This proto-
1008C in higher yield (entry 3). However, increasing col under dielectric heating overcomes the limitation
the temperature led to extensive side reactions and of CIR under conductive heating to use only electron-
only 9% of coupling product 3g was obtained deficient (hetero)aryl halides. Further studies address-
(entry 4). Using only 1.05 equivs. of DBU as a much ing the development of MACIR-based sequential and
stronger amine base (pKb =1.1), the reaction furnish- consecutive processes and the scope and limitations in
ed 70% of 3g and 8% of 4g (entry 5). Therefore, in- the propargyl substrates are currently underway.
Table 3. MACIR and conductive CIR of iodobenzene (1f) and 2a.
Entry
Base
Conditions
T [8C]
t [min]
Yield of 3g[b]
Yield of 4g[b]
1
2
3
4
5
6
7
NEt3 (5 equivs.)
NEt3 (5 equivs.)
microwave
microwave
microwave
microwave
microwave
microwave
oil bath
100
120
100
150
100
100
120
30
20
30
30
60
30
30
0%
35%
0%
0%
0%
8%
30%
80%
9%
70%
0%
piperidine (5 equivs.)
piperidine (5 equivs.)
DBU (1.05 equivs.)
DBU (2 equivs.)
DBU (2 equivs.)
92%
71%
0%
[a]
Based upon isolated yields after standardized chromatography on silica gel.
2568
www.asc.wiley-vch.de
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2006, 348, 2565 – 2571

A General Coupling-Isomerization Synthesis of 1,3-Diarylprop-2-en-1-ones
COMMUNICATIONS
Experimental Section
Acknowledgements
Financial support of the Deutsche Forschungsgemeinschaft
and the Fonds der Chemischen Industrie is gratefully ac-
knowledged. We also cordially thank Mrs. Birgit Thaler for
experimental assistance and BASF AG for the generous dona-
tion of chemicals.
General Considerations
All reactions involving palladium-copper catalysis were per-
formed in degassed oxygen-free solvents under a nitrogen
atmosphere in sealed reaction vessels. All reactions involv-
ing microwave irradiation were conducted under nitrogen in
heavy-walled glass Smith process vials sealed with alumini-
um crimp caps fitted with a silicon septum. The inner diame-
ter of the vial filled to the height of 2 cm was 1.3 cm. The
microwave heating was performed in a Smith Synthesizer
single-mode microwave cavity producing continuous irradia-
tion at 2450 MHz (Personal Chemistry AB, Uppsala,
Sweden). Reaction mixtures were stirred with a magnetic
stir bar during the irradiation. The temperature, pressure
and irradiation power were monitored during the course of
the reaction. The average pressure during the reaction was
3–4 bar. After completed irradiation, the reaction tube was
cooled with high pressure air until the temperature had
fallen below 398C (ca. 2 min). Halogen compounds 1,
(Ph3P)2PdCl2, and CuIwere purchased as reagent grade
from ACROS, Aldrich, Fluka or Merck and used without
further purification. Triethylamine, acetonitrile, DMF, and
THF were dried and distilled according to standard proce-
dures.[12] Propargyl alcohols 2 were prepared in analogy to
literature procedures[13] by addition of ethynylmagnesium
bromide to the corresponding aldehydes.
References
[1] T. J. J. Müller, M. Ansorge, D. Aktah, Angew. Chem.
Int. Ed. 2000, 39, 1253–1256.
[2] For lead reviews on Sonogashira couplings, see for ex-
ample, a) S. Takahashi, Y. Kuroyama, K. Sonogashira,
N. Hagihara, Synthesis 1980, 627–630; b) K. Sonoga-
shira, in: Metal catalyzed Cross-coupling Reactions,
Wiley-VCH, Weinheim, 1998, pp 203–229; c) K. Sono-
gashira, J. Organomet. Chem. 2002, 653, 46–49; d) E.-I.
Negishi, L. Anastasia, Chem. Rev. 2003, 103, 1979–
2018.
[3] For excellent reviews and classifications of domino re-
actions, see for example, a) L. F. Tietze, J. Heterocycl.
Chem. 1990, 27, 47–69; b) L. F. Tietze, U. Beifuss,
Angew. Chem. Int. Ed. Engl. 1993, 32, 131–163; c) L. F.
Tietze, Chem. Rev. 1996, 96, 115–136.
[4] a) T. J. J. Müller, R. Braun, M. Ansorge, Org. Lett.
2000, 2, 1967–1970; b) R. U. Braun, K. Zeitler, T. J. J.
Müller, Org. Lett. 2000, 2, 4181–4184; c) R. U. Braun,
K. Zeitler, T. J. J. Müller, Org. Lett. 2001, 3, 3297–
3300; d) N. A. M. Yehia, K. Polborn, T. J. J. Müller, Tet-
rahedron Lett. 2002, 43, 6907–6910; e) O. G. Dediu,
N. A. M. Yehia, Z. Naturforsch. 2004, 59b, 443–450;
f) O. G. Dediu, N. A. M. Yehia, T. Oeser, K. Polborn,
T. J. J. Müller, Eur. J. Org. Chem. 2005, 1834–1858;
g) O. G. Schramm, nØe Dediu, T. Oeser, T. J. J. Müller,
J. Org. Chem. 2006, 71, 3494–3500.
Column chromatography: silica gel 60 (Merck, Darm-
stadt), mesh 70–230. TLC: silica gel plates (60 F254 Merck,
Darmstadt). Melting points (uncorrected values): Büchi
Melting Point B-540. 1H and 13C NMR spectra: Bruker
ARX 300, Varian VXR 400S CDCl3, C2D6O and DMSO-d6.
The assignments of quaternary C, CH, CH2 and CH3 have
been made by using DEPT spectra. IR: Perkin–Elmer
Lambda 3. UV/vis: Perkin–Elmer Model Lambda 16. Fluo-
rescence: Perkin–Elmer LS-55. MS: Finnigan MAT 90 and
MAT 95 Q. Elemental analyses were carried out in the Mi-
croanalytical Laboratories of the Organisch-Chemisches In-
stitut, Ruprecht-Karls-Universität Heidelberg.
[5] R. U. Braun, M. Ansorge, T. J. J. Müller, Chem. Eur. J.
2006, 12, DOI: 10.1002/chem.200600530.
[6] For recent reviews and monographs on microwave ac-
celerated syntheses, see for example, a) C. O. Kappe,
Angew. Chem. Int. Ed. 2004, 43, 6250–6284; b) M.
Nüchter, B. Ondruschka, W. Bonrath, A. Gum, Green
Chem. 2004, 6, 128–141; c) M. Nüchter, U. Müller, B.
Ondruschka, A. Tied, W. Lautenschläger, Chem. Eng.
Technol. 2003, 26, 1207–1216; d) A. de La Hoz, A.
D’Waz-Ortis, A. Moreno, F. Langa, Eur. J. Org. Chem.
2000, 3659–3673; e) Y. Xu, Q.-X. Guo, Heterocycles
2004, 63, 903–974; f) Microwaves in Organic Synthesis,
(Ed.: A. Loupy), Wiley-VCH, Weinheim, 2002; g) B. L.
Hayes, Microwave Synthesis: Chemistry at the Speed of
Light, CEM Publishing, Matthews NC, 2002; h) Micro-
wave-Assisted Organic Synthesis (P. Lidstrçm, J. P. Tier-
ney, eds.), Blackwell, Oxford, 2004; i) C. O. Kappe, A.
Stadler, Microwaves in Organic and Medicinal Chemis-
try, Wiley-VCH, Weinheim, 2005.
General Procedure for the CIR of Aryl Halides 1
with Propargyl Alcohols 2
A solution of 1.00 mmol of halogen compound 1 (or 5),
1.05 mmol of propargyl alcohol 2, 20 mg (0.02 mmol) of
(PPh3)2PdCl2, and 2 mg (0.01 mmol) of CuIin 2–5 equivs. of
degassed base and 1.5 mL of THF under nitrogen was mag-
netically stirred in a heavy-walled SmithCreator process vial
at the microwave generated temperature and for the time
indicated (for experimental details see Table 3) in the micro-
wave cavity. After cooling to room, aqueous work-up and
extraction with ethyl acetate (4”15 mL), the combined or-
ganic phases were dried with magnesium sulfate. After fil-
tration the solvents were removed under vacuum and the
residue was chromatographed on silica gel (hexane/ethyl
acetate, 4:1 or 1:1) and crystallized from ethanol or pentane/
chloroform (1:1) to give the analytically pure enones 4 or 6,
respectively.
[7] For microwave-accelerated Sonogashira coupling in ho-
mogenous media, see e.g. a) E. Petricci, M. Radi, F.
Corelli, M. Botta, Tetrahedron Lett. 2003, 44, 9181–
9184; b) N. Kaval, K. Bisztray, W. Dehaen, C. O.
Kappe, E. Van der Eycken, Mol. Diversity 2003, 7,
Characterization data of the isolated compounds are
given in the Supporting Information.
Adv. Synth. Catal. 2006, 348, 2565 – 2571
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.asc.wiley-vch.de
2569

Oana G. Schramm (nØe Dediu) and Thomas J. J. Müller
COMMUNICATIONS
125–133; c) M. Erdelyi, A. Gogoll, J. Org. Chem. 2001,
66, 4165–4169.
[8] S. Thorand, N. Krause, J. Org. Chem. 1998, 63, 8551–
8553.
[9] a) K. C. Westaway, R. Gedye, J. Microwave Power
1995, 30, 219–230; b) F. Langa, P. de La Cruz, A. de
La Hoz, A. Diaz-Ortiz, E. Diez-Barra, Contemp. Org.
Synth. 1997, 4, 373–386; c) L. Perreux, A. Loupy, Tetra-
hedron 2001, 57, 9199–9223; d) N. Kuhnert, Angew.
Chem. Int. Ed. 2002, 41, 1863–1866; e) C. R. Strauss,
Angew. Chem. Int. Ed. 2002, 41, 3589–3590.
[10] D. A. Stuerga, P. Gaillard, Tetrahedron 1996, 52, 5505–
5510.
[11] All new compounds have been fully characterized spec-
troscopically and by correct elemental analysis or
HRMS, respectively.
[12] Organikum, 21st edn., (Eds.: H. G. O. Becker, R. Beck-
ert, G. Domschke, E. Fanghänel, W. D. Habicher, P.
Metz, D. Pavel, K. Schwetlick), Wiley-VCH, Weinheim,
New York, Chichester, Brisbane, Singapore, Toronto,
2001.
[13] a) L. Brandsma, Preparative Acetylenic Chemistry,
Elsevier, Amsterdam, Oxford, New York, Tokyo, 1988;
b) N. Krause, D. Seebach, Chem. Ber. 1987, 120, 1845–
1851.
2570
www.asc.wiley-vch.de
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2006, 348, 2565 – 2571

A General Coupling-Isomerization Synthesis of 1,3-Diarylprop-2-en-1-ones
COMMUNICATIONS
Adv. Synth. Catal. 2006, 348, 2565 – 2571
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.asc.wiley-vch.de
2571