Tandem aldol condensation/platinacycle-catalyzed addition reactions of aldehydes, methyl ketones, and arylboronic acids

Article abstract of DOI:10.1002/ejoc.201200867

Aldol condensation of aldehydes with methyl ketones followed by anionic four-electron donor-based (type I) platinacycle-catalyzed addition reactions of arylboronic acids to form β-arylated ketones is described. Good to excellent yields of β-arylated ketones were obtained for the tandem reactions of aromatic/aliphatic aldehydes, methyl ketones, and arylboronic acids, and moderate yields were observed for the tandem reactions of α,β-unsaturated aldehydes. The aldol condensation of aldehydes with methyl ketones was successfully combined with the platinacycle-catalyzed addition reactions of arylboronic acids in a tandem fashion. A variety of β-arylated ketones was obtained in good to excellent yields.

Full text of DOI:10.1002/ejoc.201200867

Job/Unit: O20867
/KAP1
Date: 04-09-12 15:18:29
Pages: 6
SHORT COMMUNICATION
DOI: 10.1002/ejoc.201200867
Tandem Aldol Condensation/Platinacycle-Catalyzed Addition Reactions of
Aldehydes, Methyl Ketones, and Arylboronic Acids
Yuan-Xi Liao[a] and Qiao-Sheng Hu*[a]
Keywords: Tandem reactions / Aldol reactions / Addition reactions / Platinum / Metallacycles
Aldol condensation of aldehydes with methyl ketones fol-
lowed by anionic four-electron donor-based (type I) plati-
nacycle-catalyzed addition reactions of arylboronic acids to
form β-arylated ketones is described. Good to excellent
yields of β-arylated ketones were obtained for the tandem
reactions of aromatic/aliphatic aldehydes, methyl ketones,
and arylboronic acids, and moderate yields were observed
for the tandem reactions of α,β-unsaturated aldehydes.
methyl ketones, and arylboronic acids could be realized in
a sequential fashion,[10] but not in a tandem fashion due to
the fast 1- or RhI/diene-catalyzed 1,2-addition reaction of
arylboronic acids with aldehydes. Because tandem reac-
tions, in which reaction materials are loaded altogether, are
operationally more convenient than sequential reactions, it
was of interest to us to realize such reactions in a tandem
fashion. On the basis of our previous study that showed
that type I platinacycle 2-catalyzed[12] (Figure 1) 1,2-ad-
dition reactions of aldehydes with arylboronic acids oc-
curred slower than reactions performed with type I pallada-
cycles as catalysts,[3a] we surmised that it might be possible
to realize the reaction of aldehydes, methyl ketones, and
arylboronic acids in a tandem fashion by using platinacycle
2 as the 1,4-addition reaction catalyst.[3a,11c] Herein, we re-
port our successful realization of tandem aldol condensa-
tion/type I platinacycle 2 catalyzed addition reactions.
Introduction
Over the past decade, transition-metal-catalyzed addition
reactions of arylboronic acids with α,β-unsaturated ketones
have emerged as useful tools for organic synthesis.[1,2] Al-
though impressive success including high enantioselectivi-
ties has been achieved for this type of addition reaction,
purified α,β-unsaturated ketones were used. Although α,β-
unsaturated ketones can be “readily” obtained from the
aldol condensation of aldehydes and/or ketones, the use of
purified α,β-unsaturated ketones apparently poses some li-
mits: they are less available than aldehydes/ketones and re-
quire an extra purification/separation step from widely
available aldehydes/ketones. During our study of transition-
metal-catalyzed addition reactions of arylboronic acids with
carbonyl-containing compounds,[3,4] we became interested
in combining such transition-metal-catalyzed addition reac-
tions with the formation of α,β-unsaturated ketones in a
sequential or tandem fashion.[5–7] We reasoned that achiev-
ing such sequential/tandem reactions would minimize the
effort for the preparation of α,β-unsaturated ketones be-
cause purification of such ketones is eliminated and may
also expand the substrate scope of the α,β-unsaturated
ketones. In this context, we have recently documented the
sequential aldol condensation of aldehydes with methyl
ketones followed by RhI-catalyzed or anionic four-electron
donor-based (type I) palladacycle 1 catalyzed (Figure 1)[8,9]
addition reactions to access β-arylated ketones
(Scheme 1).[10,11] We found that with palladacycle 1 or a
RhI/diene complex as the catalyst, the reaction of aldehydes,
Figure 1. Anionic four-electron donor-based (type I) palladacycle
1 and platinacycle 2.
[a] Department of Chemistry, College of Staten Island and the
Graduate Center of the City University of New York,
Staten Island, New York 10314, USA
Fax: +1-718-982-3910
E-mail: qiaosheng.hu@csi.cuny.edu
Homepage: http://www.chem.csi.cuny.edu/hu.htm
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201200867.
Scheme 1. Sequential aldol condensation/transition-metal-cata-
lyzed addition of aldehydes, methyl ketones, and arylboronic acids.
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1

Job/Unit: O20867
/KAP1
Date: 04-09-12 15:18:29
Pages: 6
Y.-X. Liao, Q.-S. Hu
SHORT COMMUNICATION
Table 1. Tandem aldol condensation/transition-metal-catalyzed re-
action of benzaldehyde, acetone, and phenylboronic acid.[a]
Results and Discussion
Our study began with screening the reaction conditions
for the tandem aldol condensation reaction of benzaldehyde
with acetone followed by platinacycle 2 catalyzed additions
of p-tolylboronic acid. Toluene was chosen as the solvent
and K3PO4 as the base for our study because they were
identified as the best solvent and base in 2-catalyzed ad-
dition reactions of arylboronic acids with aldehydes.[3a] As
a temperature of 80 °C or higher was needed for 2-catalyzed
addition reactions of arylboronic acids with aldehydes to
occur efficiently,[3a] we reasoned that carrying out the tan-
dem reaction at a temperature of lower than 80 °C might
suppress the 1,2-addition reaction of arylboronic acids with
aldehydes. We thus began our study at 70 °C. The desired
tandem reaction product was found to be only 31% of the
reaction mixture, the moderate reaction conversion (31%)
suggested that the 2-catalyzed addition reaction of p-tolyl-
boronic acid with benzaldehyde indeed occurred very slowly
(Table 1, entry 1). We speculated that the moderate conver-
sion might be because the first step, the aldol condensation
reaction step, occurred slowly. As K3PO4 is insoluble in tol-
uene, we reasoned that the presence of water might facilitate
the aldol condensation reaction and the tandem reaction
process. We thus tested the use of water as an additive and
found that, indeed, the presence of a small amount of water
significantly facilitated the tandem reaction (Table 1, en-
tries 1–3). By using 7 equiv. of water as the additive, the
tandem aldol condensation followed by 2-catalyzed ad-
dition reaction occurred efficiently to afford the β-arylated
ketone as the major product (Table 1, entry 4). Further test-
ing of other bases revealed that K2CO3, Cs2CO3, and KOH
were more effective than K3PO4 for the tandem reaction.
By using these bases, excellent conversions were observed,
[a] Reaction conditions: aldehyde (0.25 mmol), p-tolylboronic acid
(0.5 mmol, 2.0 equiv.), solvent (0.7 mL), acetone (0.3 mL, 4 mmol),
base (0.75 mmol, 3.0 equiv.), 70 °C. [b] Based on GC–MS analysis.
[c] 1,5-Diphenyl-1,5-di(p-tolyl)-3-pentanone was obtained in 15%
yield. [d] 1,5-Diphenyl-1,5-di(p-tolyl)-3-pentanone was obtained in
5% yield. [e] Platinacycle 2 was not used. [f] 4-Phenylbut-3-en-2-
one was the product.
and the tandem aldol condensation/addition reaction prod- mainly because of the availability of their precursors, β-
uct was obtained as the predominant product (Table 1, en- alkyl α,β-unsaturated ketones. We found aliphatic aldehydes
tries 6, 8, 10).
were suitable starting materials, and the β-alkyl-β-aryl
After identifying the reaction conditions, the scope of the ketones were obtained in good yields (Table 3); the self-
tandem aldol condensation/2-catalyzed addition reaction aldol condensation reaction was negligible. Thus, although
was examined. Different aromatic aldehydes, methyl β-alkyl α,β-unsaturated ketones are less available due to the
ketones, and arylboronic acids were suitable starting materi- self-aldol condensation of aliphatic aldehydes, our study
als for the tandem reaction, and high yields were observed provided an efficient route to a variety of β-alkyl-β-aryl
for all cases tested (Table 2). The combination of aromatic ketones from readily available methyl ketones, aliphatic al-
aldehydes, methyl ketones, and arylboronic acids permitted dehydes, and arylboronic acids.
access to a variety of β-aryl ketones including β-aryl
α,β-Unsaturated aldehydes were also examined as the al-
ketones that had not been reported before, mainly because dehyde source in the tandem reaction (Table 4). We found
of the availability of such α,β-unsaturated ketones (Table 2). that by using KOH as the base, the tandem aldol condensa-
We next examined aliphatic aldehydes in the tandem re- tion/1,4-addition reaction occurred, but the reaction did
action, which could lead to the formation of β-alkyl-β-aryl not reach complete conversion for the aldol condensation
ketones. Aliphatic aldehydes are considered to be more reaction products. A significant amount of the aldol con-
problematic aldehydes than aromatic aldehydes for the tan- densation reaction product was observed even after length-
dem reaction because they may undergo a self-aldol con- ening the reaction time, increasing the amount of phenyl-
densation reaction under the reaction conditions. This self- boronic acid, or raising the reaction temperature. Such an
aldol condensation reaction renders β-alkyl α,β-unsaturated observation might suggest that the δ,γ-double bond of the
ketones much less available than β-aryl α,β-unsaturated dienone likely served as a ligand to stabilize the Pt species
ketones. We were particularly interested in accessing β- after the 1,4-addition reaction of the arylboronic acid with
alkyl-β-aryl ketones that had not been previously reported the dienone, which might hinder the regeneration of the Pt
by using transition-metal-catalyzed addition reactions, catalyst for the tandem reaction.
2
www.eurjoc.org
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 0000, 0–0

Job/Unit: O20867
/KAP1
Date: 04-09-12 15:18:29
Pages: 6
Tandem Aldol Condensation/Platinacycle-Catalyzed Addition Reactions
Table 2. Tandem aldol condensation/2-catalyzed reaction of aromatic aldehydes, methyl ketones, and arylboronic acids.[a]
[a] Reaction conditions: aldehyde (0.25 mmol), arylboronic acid (0.5 mmol, 2.0 equiv.), toluene (0.8 mL), ketone (0.2 mL, 1.7–2.7 mmol),
H2O (7 equiv.), base (0.75 mmol, 3.0 equiv.), 70 °C. [b] Isolated yield. [c] H2O (13 equiv.) was used.
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3

Job/Unit: O20867
/KAP1
Date: 04-09-12 15:18:29
Pages: 6
Y.-X. Liao, Q.-S. Hu
SHORT COMMUNICATION
Table 3. Tandem aldol condensation/2-catalyzed reaction of ali- sation reaction of aromatic and aliphatic aldehydes with
phatic aldehydes, methyl ketones, and arylboronic acids.[a]
methyl ketones in a tandem fashion. A variety of β-arylated
ketones can be obtained in good to high yields from readily
available aromatic/aliphatic aldehydes, methyl ketones, and
arylboronic acids. Our future work will be directed towards
the development of an asymmetric version of this tandem
reaction and other tandem/sequential reactions involving
the addition reactions of arylboronic acids with aldehydes
as part of the reaction sequence.
Experimental Section
General Procedure for Tandem Aldol Condensation/2-Catalyzed Ad-
dition Reactions of Aromatic Aldehydes, Methyl Ketones, and Aryl-
boronic Acids: To a vial containing the aldehyde (0.25 mmol), aryl-
boronic acid (0.5 mmol), base (K2CO3, KOH, or Cs2CO3;
0.75 mmol), and platinacycle 2 (0.00125 mmol, 1.1 mg) was added
ketone (0.2 mL), toluene (0.8 mL), and water (7–13 equiv.). After
the mixture was stirred at 70 °C for 6–8 h, the reaction was
quenched by adding 4 n HCl (2 mL). The mixture was extracted
with CH2Cl2 (3ϫ 15 mL). The organic layers were combined. After
evaporation of the organic solvent, the residue was subjected to
column chromatography (silica gel; ethyl acetate/hexane, 1:20) to
afford the products.
General Procedure for the Platinacycle 2 Catalyzed Tandem Reac-
tions of Aliphatic Aldehydes, Methyl Ketones, and Arylboronic
Acids: To a vial containing the aldehyde (0.25 mmol), arylboronic
[a] Reaction conditions: aldehyde (0.25 mmol), arylboronic acid
(0.5 mmol, 2.0 equiv.), ketone (0.2 mL, 1.9–2.7 mmol), toluene
(0.8 mL), H2O (0.1 mL), KOH (0.75 mmol, 3.0 equiv.), 70 °C.
[b] Isolated yield.
acid (0.5 mmol, 2 equiv.), KOH (0.75 mmol, 3 equiv.), and plati-
nacycle 2 (0.00125 mmol, 1.1 mg) was added the ketone (0.2 mL),
toluene (0.8 mL), and water (0.1 mL). After the mixture was stirred
at 70 °C for 6 h, the reaction was quenched by adding 4 n HCl
(2 mL). The mixture was extracted with CH2Cl2 (3ϫ 15 mL). The
organic layers were combined. After evaporation of the organic sol-
vent, the residue was subjected to column chromatography (silica
gel; ethyl acetate/hexane, 1:20) to afford the products.
Table 4. Tandem aldol condensation/2-catalyzed reaction of α,β-
unsaturated aldehydes, acetone, and phenylboronic acid.[a]
Supporting Information (see footnote on the first page of this arti-
cle): Characterization data and copies of the 1H NMR and 13C
NMR spectra of the tandem reaction products.
Acknowledgments
We gratefully thank the National Science Foundation (NSF)
(CHE0719311) and National Institutes of Health (NIH) (1R15
GM094709) for funding. Partial support from Professional Staff
Congress–City University of New York (PSC-CUNY) Research
Award Programs is also acknowledged. We thank Frontier Scien-
tific for their generous gift of the arylboronic acids.
[a] Reaction conditions: aldehyde (0.25 mmol), arylboronic acid
(0.5 mmol, 2.0 equiv.), toluene (0.8 mL), acetone (0.2 mL,
2.7 mmol), H2O (13 equiv.), KOH (0.75 mmol, 3.0 equiv.), 70 °C.
[b] Isolated yield of C. [c] PhB(OH)2 (4 equiv.) was used. [d] 2,4,7,9-
Undecatetraen-6-one was observed as the aldol condensation prod-
uct.
[1] For recent reviews, see: a) D. V. Partyka, Chem. Rev. 2011, 111,
1529–1595; b) N. Miyaura, Synlett 2009, 2039–2050; c) A. Gut-
nov, Eur. J. Org. Chem. 2008, 4547–4554; d) F. Glorius, Angew.
Chem. 2004, 116, 3444; Angew. Chem. Int. Ed. 2004, 43, 3364–
3366; e) T. Hayashi, K. Yamasaki, Chem. Rev. 2003, 103, 2829–
2844; f) K. Fagnou, M. Lautens, Chem. Rev. 2003, 103, 169–
196 and references cited therein.
[2] For recent examples, see: a) M. S. Jeletic, I. Ghiviriga, K. Ab-
boud, A. S. Veige, Dalton Trans. 2010, 39, 6392–6394; b) X.
Hu, Z. Cao, Z. Liu, Y. Wang, H. Du, Adv. Synth. Catal. 2010,
352, 651–655; c) E. Drinkel, A. Briceno, R. Dorta, Organome-
tallics 2010, 29, 2503–2514; d) T. Nishimura, Y. Yasuhara, T.
Sawano, T. Hayashi, J. Am. Chem. Soc. 2010, 132, 7872–7873;
Conclusions
We have demonstrated that platinacycle 2 catalyzed ad-
dition reactions of arylboronic acids with α,β-unsaturated
ketones can be efficiently combined with the aldol conden-
4
www.eurjoc.org
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 0000, 0–0

Job/Unit: O20867
/KAP1
Date: 04-09-12 15:18:29
Pages: 6
Tandem Aldol Condensation/Platinacycle-Catalyzed Addition Reactions
e) Q. Xu, R. Zhang, T. Zhang, M. Shi, J. Org. Chem. 2010, 75,
3935–3937; f) J. Chen, J.-M. Chen, F. Lang, X.-Y. Zhang, L.-
F. Cun, J. Zhu, J.-G. Deng, J. Liao, J. Am. Chem. Soc. 2010,
132, 4552–4553; g) B. T. Hahn, F. Tewes, R. Fröhlich, F. Glor-
ius, Angew. Chem. 2010, 122, 1161; Angew. Chem. Int. Ed. 2010,
49, 1143–1146; h) S. Lin, X. Lu, Org. Lett. 2010, 12, 2536–
2539; i) Q.-A. Chen, X. Dong, M.-W. Chen, D.-S. Wang, Y.-G.
Zhou, Y.-X. Li, Org. Lett. 2010, 12, 1928–1931; j) T. Gendri-
neau, J.-P. Genet, S. Darses, Org. Lett. 2010, 12, 308–310; k)
M. K. Brown, E. J. Corey, Org. Lett. 2010, 12, 172–175; l) X.
Hu, M. Zhuang, Z. Cao, H. Du, Org. Lett. 2009, 11, 4744–
4747; m) T. Minuth, M. K. Boysen, Org. Lett. 2009, 11, 4212–
4215; n) W.-C. Yuan, L.-F. Cun, A.-Q. Mi, Y.-Z. Jiang, L.-Z.
Gong, Tetrahedron 2009, 65, 4130–4141; o) G. A. Wallace,
T. D. Gordon, M. E. Hayes, D. B. Konopacki, S. R. Fix-Sten-
zel, X. Zhang, P. Grongsaard, K. P. Cusack, L. M. Schaffter,
R. F. Henry, R. H. Stoffel, J. Org. Chem. 2009, 74, 4886–4889;
p) S. B. Kim, C. Cai, M. D. Faust, W. C. Trenkle, D. A. Swei-
gart, Organometallics 2009, 28, 2625–2628; q) J. J. Buergi, R.
Mariz, M. Gatti, E. Drinkel, X. Luan, S. Blumentritt, A. Lin-
den, R. Dorta, Angew. Chem. 2009, 121, 2806; Angew. Chem.
Int. Ed. 2009, 48, 2768–2771; r) T. Korenaga, K. Osaki, R.
Maenishi, T. Sakai, Org. Lett. 2009, 11, 2325–2328; s) R. Jana,
J. A. Tunge, Org. Lett. 2009, 11, 971–974; t) S. Facchetti, I.
Cavallini, T. Funaioli, F. Marchetti, A. Iuliano, Organometal-
lics 2009, 28, 4150–4158; u) A. Iuliano, S. Facchetti, T. Funai-
oli, Chem. Commun. 2009, 457–459.
[6]
For recent reviews on sequential/tandem reactions, see: a) K. C.
Nicolaou, J. S. Chen, Chem. Soc. Rev. 2009, 38, 2993–3009; b)
S. F. Kirsch, Synthesis 2008, 3183–3204; c) K. C. Nicolaou,
D. J. Edmonds, P. G. Bulger, Angew. Chem. 2006, 118, 7292;
Angew. Chem. Int. Ed. 2006, 45, 7134–7186; d) J.-C. Wasilke,
S. J. Obrey, T. Baker, G. C. Bazan, Chem. Rev. 2005, 105, 1001–
1020.
For examples of intramolecular tandem reactions initialized by
RhI-catalyzed addition reactions of arylboronic acids with α,β-
unsaturated ketones or esters, see: a) C. Navarro, A. G. Csaky,
Synthesis 2009, 860–863; b) S. W. Youn, J.-H. Song, D.-I. Jung,
J. Org. Chem. 2008, 73, 5658–5661; c) C. Navarro, A. G.
Csakye, Org. Lett. 2008, 10, 217–219; d) B. M. Bocknack, L.-
C. Wang, M. J. Krische, Proc. Natl. Acad. Sci. USA 2004, 101,
5421–5424; e) D. F. Cauble, J. D. Gipson, M. J. Krische, J. Am.
Chem. Soc. 2003, 125, 1110–1111; f) T. Nishikata, Y. Kobaya-
shi, K. Kobayshi, Y. Yamamoto, N. Miyaura, Synlett 2007,
3055–3057.
Recent reviews of metallacycles: a) J. Dupont, C. S. Consorti,
J. Spencer, Chem. Rev. 2005, 105, 2527–2572; b) I. P. Belets-
kaya, A. V. Cheprakov, J. Organomet. Chem. 2004, 689, 4055–
4082; c) R. B. Bedford, Chem. Commun. 2003, 1787–1796.
Most type I metallacycles are known to exist as bridged dimers
and to dissociate into monomeric forms during reactions.
Type I metallacycles in this paper were drawn in monomeric
forms.
[7]
[8]
[9]
[10] Y.-X. Liao, C.-H. Xing, M. Israel, Q.-S. Hu, Org. Lett. 2011,
[3] a) P. He, Y. Lu, C.-G. Dong, Q.-S. Hu, Org. Lett. 2007, 9, 343–
346; b) P. He, Y. Lu, Q.-S. Hu, Tetrahedron Lett. 2007, 48,
5283–5288; c) Y.-X. Liao, C.-H. Xing, P. He, Q.-S. Hu, Org.
Lett. 2008, 10, 2509–2512; d) Y.-X. Liao, C.-H. Xing, M. Israel,
Q.-S. Hu, Tetrahedron Lett. 2011, 52, 3324–3328; e) T.-P. Liu,
Y.-X. Liao, C.-H. Xing, Q.-S. Hu, Org. Lett. 2011, 13, 2452–
2455.
[4] a) C.-H. Xing, T.-P. Liu, J. R. Zheng, J. Ng, M. Esposito, Q.-
S. Hu, Tetrahedron Lett. 2009, 50, 4953–4957; b) Y.-X. Liao,
C.-H. Xing, Q.-S. Hu, J. Org. Chem. 2010, 75, 6986–6989; c)
Y.-X. Liao, C.-H. Xing, Q.-S. Hu, Org. Lett. 2012, 14, 1544–
1547.
13, 2058–2061.
[11] For other examples, see: a) Y. Suzuma, S. Hayashi, T. Yamam-
oto, Y. Oe, T. Ohta, Y. Ito, Tetrahedron: Asymmetry 2009, 20,
2751–2758; b) A. Yu, B. Cheng, Y. Wu, J. Li, K. Wei, Tetrahe-
dron Lett. 2008, 49, 5405–5407; c) T. Hayashi, K. Sasaki, Chem.
Lett. 2008, 37, 842–843; d) R. B. Bedford, M. Betham, J. P. H.
Charmant, M. F. A. Haddow, G. Orpen, L. T. Pilarski, S. J.
Coles, M. B. Hursthouse, Organometallics 2007, 26, 6346–6353.
[12] R. B. Bedford, S. L. Hazelwood, D. A. Albisson, Organometal-
lics 2002, 21, 2599–2600.
Received: July 1, 2012
Published Online: ᭿
[5] L. F. Tietze, G. Brasche, K. Gericke, Domino Reactions in Or-
ganic Synthesis Wiley-VCH, Weinheim, Germany, 2006.
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
5

Job/Unit: O20867
/KAP1
Date: 04-09-12 15:18:29
Pages: 6
Y.-X. Liao, Q.-S. Hu
SHORT COMMUNICATION
Tandem Reactions
Y.-X. Liao, Q.-S. Hu* ....................... 1–6
Tandem Aldol Condensation/Platinacycle-
Catalyzed Addition Reactions of Alde-
hydes, Methyl Ketones, and Arylboronic
Acids
The aldol condensation of aldehydes with
methyl ketones was successfully combined
with the platinacycle-catalyzed addition re-
actions of arylboronic acids in a tandem
fashion. A variety of β-arylated ketones
was obtained in good to excellent yields.
Keywords: Tandem reactions / Aldol reac-
tions / Addition reactions / Platinum /
Metallacycles
6
www.eurjoc.org
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 0000, 0–0