Light-driven organocatalysis using inexpensive, nontoxic Bi 2O3 as the photocatalyst

Article abstract of DOI:10.1002/anie.201405118

The development of enantioselective catalytic processes that make use of sunlight as the energy source and nontoxic, affordable materials as catalysts represents one of the new and rapidly evolving areas in chemical research. The direct asymmetric α-alkylation of aldehydes with α-bromocarbonyl compounds can be successfully achieved by combining bismuth-based materials as low-band-gap photocatalysts with the second-generation MacMillan imidazolidinone as the chiral catalyst and simulated sunlight as a low-cost and clean energy source. This reaction also proceeded with high efficiency when the reaction vial was exposed to the morning sunlight on a clear September day in Tarragona, Spain. Now it's bismuth time! The asymmetric intermolecular α-alkylation of aldehydes with α-bromocarbonyl compounds can be achieved under visible-light irradiation by combining the second-generation MacMillan catalyst and an inexpensive, nontoxic, and commercially available Bi₂O ₃ powder. This reaction also proceeded with high efficiency when the reaction vial was exposed to the morning sunlight in Tarragona, Spain.

Full text of DOI:10.1002/anie.201405118

Angewandte
Chemie
DOI: 10.1002/anie.201405118
Organo-Photocatalysis Hot Paper
Light-Driven Organocatalysis Using Inexpensive, Nontoxic Bi O as
2
3
the Photocatalyst**
Paola Riente, Alba Matas Adams, Josep Albero, Emilio Palomares,* and Miquel A. Pericꢀs*
Abstract: The development of enantioselective catalytic pro-
cesses that make use of sunlight as the energy source and
nontoxic, affordable materials as catalysts represents one of the
new and rapidly evolving areas in chemical research. The direct
asymmetric a-alkylation of aldehydes with a-bromocarbonyl
compounds can be successfully achieved by combining
bismuth-based materials as low-band-gap photocatalysts with
the second-generation MacMillan imidazolidinone as the
chiral catalyst and simulated sunlight as a low-cost and clean
energy source. This reaction also proceeded with high effi-
ciency when the reaction vial was exposed to the morning
sunlight on a clear September day in Tarragona, Spain.
research. As a result of these efforts, several reports have
+
2
appeared where the commonly used [Ru(bpy)3] catalyst is
[
7]
avoided. In this regard, heterogeneous semiconductors as
[
8]
well as organic dyes have been applied to the asymmetric a-
alkylation of aldehydes to avoid the use of expensive
ruthenium and the presence of traces of ruthenium in the
final products.
In a complementary approach, Melchiorre and co-work-
ers have recently shown that for some combinations of
aldehyde and alkylating agent, a photocatalyst is not required
for the light-driven alkylation to proceed, and that diaryl-
prolinol organocatalysts alone suffice to promote the photo-
chemical activation of the substrates through the transient
[9]
C
hemical transformations that are promoted by sunlight are
formation of electron donor–acceptor (EDA) complexes.
Photocatalysts that are based on heterogeneous semi-
[1]
currently the subject of intense research. Photocatalytic
methods have shown promising potential for bulk production
and are widely accepted and popular as convenient strategies
[
10]
conductors have found some applications in the catalysis of
[
7,11]
organic reactions.
Among them, TiO is by far the most
2
[
2]
in the area of asymmetric catalysis. In a pioneering effort,
MacMillan and co-workers merged organo- and photoredox
catalysis to promote the direct asymmetric a-alkylation of
used because of its low toxicity, low cost, and high reactiv-
[
12]
ity. However, its wide band gap (> 3 eV) makes the use of
UV light for its photoexcitation necessary, which should limit
its use in visible-light-driven photocatalysis. In spite of this,
several carbon–carbon, carbon–hydrogen, or carbon–hetero-
[3]
2+ [4]
aldehydes through a process catalyzed by [Ru(bpy) ] .
3
Since then, much effort has been devoted to the development
of more convenient reaction conditions and to the extension
of this combined approach to other key asymmetric organic
[
13]
atom bond formation reactions
and even asymmetric
a-alkylation reactions of aldehydes that are promoted by
[
5]
transformations. In view of the future, substantial use of
such reactions, the “Achillesꢀ heel” of these methods is their
dependence on ruthenium. This is a scarce and expensive
metal with rather low production (ca. twelve tons of
ruthenium are mined every year) and very limited estimated
world reserves (5000 tons). Furthermore, ruthenium com-
pounds are highly toxic and suspected carcinogens. For these
reasons, the identification of more convenient visible-light
photocatalysts that are suitable for singly occupied molecular
visible light in the presence of TiO have been reported, but
2
[
7]
they proceed with low efficiency. In turn, low-band-gap
semiconductors such as PbBiO Br have been revealed to be
2
efficient visible-light photocatalysts for the asymmetric
a-alkylation of aldehydes when they were employed either
[
7]
as a bulk material or in nanocrystalline form. In any case,
the toxicity of this material, associated with the presence of
lead, severely limits its practical use.
Inspired by these results, we have focused our research on
the identification of photocatalytic materials that fulfill
a series of basic requirements in view of large-scale applica-
tions: They should be characterized by a low band gap
(< 1.5 eV) to ensure successful photoexcitation by visible
light, and they should be abundant and nontoxic. Among the
possible candidates, we identified bismuth sulfide (Bi S ) and
[
6]
orbital (SOMO) activation has become an area of intense
[*] Dr. P. Riente, A. Matas Adams, Dr. J. Albero, Prof. E. Palomares,
Prof. M. A. Pericꢀs
Institute of Chemical Research of Catalonia (ICIQ)
Avda.Paꢁsos Catalans 16, 43007 Tarragona (Spain)
E-mail: epalomares@iciq.es
2
3
bismuth oxide (Bi O ) as the most promising. These com-
2
3
mapericas@iciq.es
pounds are semiconductors with a low band gap (ca. 1.3 eV).
Although Bi is ranked as the 69th most abundant element in
the earth’s crust (Ru is ranked 74th), a large amount of
bismuth is obtained each year as a side product in the refining
Prof. E. Palomares
Catalan Institution for Research and Advanced Studies (ICREA)
Avda. Lluis Companys 23, 08010 Barcelona (Spain)
Prof. M. A. Pericꢀs
Department de Quꢂmica Orgꢀnica, Universitat de Barcelona
c/Martꢂ i Franquꢃs 1-11, 08028 Barcelona (Spain)
[14]
of different metals, such as copper, lead, tin, and tungsten,
and the estimated world reserves exceed 320000 tons. There-
fore, bismuth and its compounds are rather inexpensive.
Moreover, bismuth and most of its derivatives are nontoxic,
noncarcinogenic, and non-bioaccumulative, with low solubil-
[**] This work was funded by MINECO (CTQ2012-38594-C02-01), DEC
(
2009SGR623), and the ICIQ Foundation.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201405118.
[
15]
ity in blood and water.
Binary bismuth(III) compounds
Angew. Chem. Int. Ed. 2014, 53, 1 – 5
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1
These are not the final page numbers!

.
Angewandte
Communications
[
16]
have found applications in organic synthesis, but they have
never been used in the context of dual organo-photocatalysis.
We accordingly decided to study the photocatalytic
activity of Bi S and Bi O . In particular, we herein report
We next explored the use of commercial Bi O powder in
2 3
the reaction (entries 5–8). Under the previously optimized
reaction conditions (entry 2), complete conversion was
recorded after one hour (entry 5), and the alkylated aldehyde
4 was obtained with excellent yield (86%) and enantioselec-
tivity (93% ee). Control experiments showed that the reac-
tion did not proceed in the dark (entry 6), and that the
presence of dissolved oxygen had a negative effect on the
process (entry 7). Most gratifyingly, the reaction proceeded to
completion in one hour with high efficiency when the reaction
vial was exposed to the morning sunlight on a clear Septem-
ber day in Tarragona, Spain (entry 8).
2
3
2
3
the successful application of these materials, in combination
with a second-generation MacMillan catalyst, to promote the
asymmetric alkylation of aldehydes with a-bromocarbonyl
derivatives. Furthermore, we wanted to evaluate the influence
of the physical state of these materials (nanostructured or
bulk) on its catalytic behavior.
As the test reaction for process optimization, we selected
the a-alkylation of hydrocinnamaldehyde with diethyl bro-
momalonate in the presence of MacMillan catalyst 3
[
7]
For comparison, titanium dioxide was tested under the
optimized conditions, which are given in entry 5 (entry 9). As
anticipated from band-gap considerations, a rather low
conversion was recorded (12%). The even cheaper semi-
conductor Fe O was also tested as a photoredox catalyst of
(
Table 1). The use of Bi S was studied first (entries 1–4),
2 3
and a nanostructured material (15 nm long and 5 nm wide)
was our initial catalyst of choice (entry 1). Quite gratifyingly,
full conversion was achieved in only one hour (entry 1) by
irradiating with a 15 W fluorescent-bulb lamp, and the
alkylated product 4 was obtained with excellent enantiose-
lectivity (93% ee). Product 4 could be isolated in a slightly
improved yield (80%) with the use of a 23 W lamp (entry 2),
which was thus used for the rest of the study. As anticipated,
the reaction did not proceed in the dark (entry 3). With
respect to the effect of the particle size on the performance of
the photoredox catalyst, it was found that a reaction per-
formed with commercial bulk Bi S (entry 4) showed only
2
3
this transformation (entry 10). In this case, a much longer
reaction time (72 h) was required for complete conversion,
and the alkylated product was obtained with lower yield
(45%) and moderate enantioselectivity (78% ee). Finally, we
wanted to test the viability of the reaction in the absence of
[9]
a photocatalyst. When the reaction mixture was irradiated
for one hour in the absence of a semiconductor (entry 11),
only 8% conversion was observed. These last results
(entries 9–11) clearly show that the bismuth derivatives
employed in this study are real photocatalysts under irradi-
ation with visible light, with efficiencies that are in accordance
with their low band gaps.
2
3
minor erosion in catalytic activity and enantioselectivity.
Table 1: a-Alkylation of hydrocinnamaldehyde with diethyl bromomalo-
nate using a second-generation MacMillan catalyst and semiconduc-
tors.
To establish the scope of the asymmetric a-alkylation of
aldehydes enabled by bismuth-based semiconductors as
photocatalysts, we selected a representative family of alde-
hyde substrates and reacted them with dialkyl (methyl or
ethyl) bromomalonates and with some a-bromocarbonyl
compounds in the presence of either Bi S nanoparticles or
[
a]
2
3
bulk Bi O and the second-generation MacMillan catalyst 3
2
3
under the previously optimized reaction conditions. The
results are summarized in Figure 1. Although not explicitly
shown, the results obtained with Bi O showed much higher
[
b]
[c]
[d]
Entry
Semiconductor
t [h]
Conv. [%]
Yield [%]
ee [%]
2
3
[
e]
reproducibility than those obtained with Bi S nanoparticles.
2 3
1
2
3
4
5
6
7
8
9
Bi2S3
Bi2S3
Bi2S3
Bi2S3
1
1
12
3
1
48
3
1
1
72
1
100
100
2
98
100
–
99
100
12
96
8
71
80
nd
54
86
–
81
80
nd
45
nd
93
93
nd
85
93
–
72
93
nd
78
nd
This is most probably due to the fact that nanostructured Bi2S
3
[
[
f]
is almost completely insoluble in the reaction medium, and
changes in aggregation between different batches of this
material lead to substantial differences in catalytic behavior.
Bismuth oxide, in turn, dissolves in the reaction media as the
reaction proceeds. Thus, reactions mediated by Bi O are
g]
[
[
[
[
g]
2
Bi O3
f]
h]
i]
Bi O3
Bi O3
2
2
2
3
Bi O
2
3
j]
[
essentially homogeneous and hence are not influenced by the
physical state of the photoredox catalyst.
TiO2
[
g]
1
1
0
1
Fe O3
2
–
By comparison with the seminal contribution of Nicewicz
and MacMillan, which illustrated the potential of
[
(
(
a] Hydrocinnmaldehyde (0.90 mmol), diethyl bromomalonate
0.45 mmol), 2,6-lutidine (0.90 mmol), 3 (0.09 mmol), semiconductor
0.011 mmol), DMF (1 mL), 23 W fluorescent-bulb lamp as the light
source. The reactions were performed in Pyrex glassware, and the
reaction mixture was degassed before irradiation. [b] Determined by
H NMR spectroscopy. [c] Yield of isolated product. [d] Determined by
H NMR analysis of the diastereomeric acetals obtained by derivatiza-
tion with (2S,4S)-2,4-pentanediol. [e] A 15 W fluorescent-bulb lamp was
used. [f] Reaction carried out in the dark. [g] Commercially available
powder. [h] The reaction mixture was not degassed. [i] Reaction pro-
moted by sunlight. [j] P25 Degussa, a mixture of rutile and anatase.
2
+
[
Ru(bpy)3] in this transformation, some important advan-
tages (as well as some limitations) that are associated with the
use of bismuth-based semiconductors as photocatalysts
became evident. First, the reactions with bromomalonate
alkylating agents (products 4–9) are much faster (1–3 h vs. 5–
1
1
7
h) and slightly more enantioselective with the bismuth-
2
+
based photoredox catalysts than with [Ru(bpy) ] . In con-
3
trast, for processes that involve a-bromocarbonyl alkylating
agents (products 10–14), the reactions mediated by Bi X
2
3
2
www.angewandte.org
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2014, 53, 1 – 5
These are not the final page numbers!

Angewandte
Chemie
enantiodiscriminating step to afford an
a-amino radical that delivers an electron
to the semiconductor, which closes the
catalytic cycle.
In any case, after the findings by
Melchiorre and co-workers, a back-
ground
photoreaction
proceeding
through
a secondary photocatalytic
cycle that involves the formation of an
EDA complex and does not require the
participation of an external photocata-
[9]
lyst should be considered. Although
kinetic considerations tend to indicate
that the semiconductor cycle should be
much faster than the EDA cycle (the
latter involves the coupling of two low-
abundance radical species), which was
clearly confirmed by our results on the
alkylation of 3-phenylpropanal in the
presence of Bi S and Bi O (compare
2
3
2
3
entries 2, 5, and 11 in Table 1), this
situation could be reverted when alky-
lating agents that are prone to the
formation of EDA complexes are used
in the reaction. To assess the relative
importance of the two considered reac-
tion modes under these circumstances,
the a-alkylation of butanal with 2,4-
dinitrobenzyl bromide leading to 15
was studied under Melchiorreꢀs condi-
[9]
tions and in the presence of Bi O .
2
3
Very interestingly, even in this case, the
semiconductor cycle appears to predom-
inate over the EDA cycle (Scheme 1; see
the Supporting Information for the com-
plete reaction profile).
In summary, the feasibility of using
Bi O and Bi S semiconductors as pho-
tocatalysts for the direct asymmetric a-
alkylation of aldehydes with a-bromo-
carbonyl compounds under organo-pho-
Figure 1. a-Alkylation of aldehydes with a-bromocarbonyl compounds. Conversion determined
1
by H NMR spectroscopy. Yields of isolated products are given in parentheses. Enantiomeric
2
3
2 3
1
excess (ee) values were determined by H NMR analysis of the diastereomeric acetals obtained
by derivatization with (2S,4S)-2,4-pentanediol or by HPLC analysis on a chiral stationary phase.
required substantially more time to reach completion,
although the enantioselectivities remained high (ca. 90% ee,
with the exception of 12). Furthermore, for these substrates,
both aryl (products 10–13) and heteroaryl substituents
tocatalytic conditions has been established. Aside from the
advantages of bismuth compounds in terms of their low cost
and nontoxicity, we have found that bulk, commercial Bi O is
2
3
an even more active catalyst of this process than nano-
structured Bi S , which appears to be due to the solubility of
(
product 14) were tolerated in the a-bromocarbonyl compo-
2
3
nent. Unfortunately, both Bi O and Bi S failed to mediate
the formation of quaternary centers.
From a mechanistic perspective, a catalytic cycle that
involves the promotion of electrons from the valence band
the oxide in the reaction medium. Both bismuth compounds
are catalytically active at low concentrations under irradiation
with white light from a standard-illumination fluorescent bulb
or under simple exposure to sunlight. The findings reported in
this communication pave the way for future applications of
these environmentally friendly materials in photocatalyzed
organic reactions.
2
3
2 3
(
VB) to the conduction band (CB) as a key photochemical
step should be considered (Figure 2). This type of mechanism,
[7]
which has already been proposed by different groups,
involves the generation of radicals derived from the alkylating
2
agent (R ·) by semiconductor-mediated single electron trans-
fer (SET) with electrons that have previously been photo-
promoted to the CB. These radicals in turn react with the
rather abundant enantiopure enamine (its concentration is
dictated by the amount of organocatalyst used) in the
Experimental Section
General procedure for the a-alkylation of aldehydes: A sealed vial
containing 3 (0.09 mmol, 0.2 equiv), the corresponding bromocar-
bonyl compound (0.45 mmol, 1 equiv), and the photocatalyst
Angew. Chem. Int. Ed. 2014, 53, 1 – 5
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
3
These are not the final page numbers!

.
Angewandte
Communications
Hopkinson, B. Sahoo, J.-L. Li, F. Glorius,
Chem. Eur. J. 2014, 20, 3874 – 3886.
[
2] For reviews, see: a) J. Xuan, L.-Q. Lu, J.-R.
Chen, W.-J. Xiao, Eur. J. Org. Chem. 2013,
6
755 – 6770; b) M. Reckenthꢂler, A. G.
Griesbeck, Adv. Synth. Catal. 2013, 355,
727 – 2744; c) D. Ravelli, M. Fagnoni, A.
2
Albini, Chem. Soc. Rev. 2013, 42, 97 – 113;
for selected examples, see: d) G. Bergon-
zini, C. S. Schindler, C. J. Wallentin, E. N.
Jacobsen, C. R. J. Stephenson, Chem. Sci.
2014, 5, 112 – 116; e) T. M. Nguyen, N.
Manohar, D. A. Nicewicz, Angew. Chem.
Int. Ed. 2014, 53, 6198 – 6201; Angew.
Chem. 2014, 126, 6312 – 6315.
[
[
[
3] N. Vignola, B. List, J. Am. Chem. Soc. 2004,
126, 450 – 451.
4] D. A. Nicewicz, D. W. C. MacMillan, Sci-
ence 2008, 322, 77 – 80.
5] a) H.-W. Shih, M. N. Vander Wal, R. L.
Grange, D. W. C. MacMillan, J. Am.
Chem. Soc. 2010, 132, 13600 – 13603;
b) M. T. Pirnot, D. A. Rankic, D. B. C.
Martin, D. W. C. MacMillan, Science
Figure 2. Proposed reaction mechanism for the organo-photocatalyzed a-alkylation of alde-
hydes in the presence of low-gap semiconductors.
2
013, 339, 1593 – 1596; c) F. R. Petroni-
jevi c´ , M. Nappi, D. W. C. MacMillan, J.
Am. Chem. Soc. 2013, 135, 18323 – 18326.
[
[
[
[
6] a) T. D. Beeson, A. Mastracchio, J.-B. Hong, K. Ashton, D. W. C.
MacMillan, Science 2007, 316, 582 – 585; b) A. Mastracchio,
A. A. Warkentin, A. M. Walji, D. W. C. MacMillan, Proc. Natl.
Acad. Sci. USA 2010, 107, 20648 – 20651.
7] M. Cherevatskaya, M. Neumann, S. Fꢃldner, C. Harlander, S.
Kꢃmmel, S. Dankesreiter, A. Pfitzner, K. Zeitler, B. Kçnig,
Angew. Chem. Int. Ed. 2012, 51, 4062 – 4066; Angew. Chem.
2012, 124, 4138 – 4142.
Scheme 1. Photocatalytic a-alkylation of butanal catalyzed by 3 in the
8] a) M. Neumann, S. Fꢃldner, B. Kçnig, K. Zeitler, Angew. Chem.
Int. Ed. 2011, 50, 951 – 954; Angew. Chem. 2011, 123, 981 – 985;
b) K. Fidaly, C. Ceballos, A. Falguiꢄres, M. S.-I. Veitia, A. Guy,
C. Ferroud, Green Chem. 2012, 14, 1293 – 1297.
9] E. Arceo, I. D. Jurberg, A. ꢅlvarez-Fernꢆndez, P. Melchiorre,
Nat. Chem. 2013, 5, 750 – 756.
presence or in the absence of Bi O .
2
3
(
0.01 mmol or 5 mg for Bi S nanoparticles) was purged with argon,
2 3
and anhydrous DMF (1 mL) was added through a septum. The
aldehyde (0.9 mmol, 2 equiv) and 2,6-lutidine (0.9 mmol, 2 equiv)
were added to this suspension via syringe, and the mixture was
degassed for 10 minutes by bubbling argon through the reaction
medium. Then, the inlet and outlet needles were removed; the vial
was sealed (parafilm) and placed at a distance of 10 cm from
a household bulb lamp. When the reaction was complete according to
[
10] a) M. R. Hoffmann, S. T. Martin, W. Choi, D. W. Bahnemann,
Chem. Rev. 1995, 95, 69 – 96; b) K. Rajeshwar, N. R. de Tacconi,
C. R. Chenthamarakshan, Chem. Mater. 2001, 13, 2765 – 2782;
c) N. Serpone, A. V. Emeline, J. Phys. Chem. Lett. 2012, 3, 673 –
77; d) H. Kisch, Angew. Chem. Int. Ed. 2013, 52, 812 – 847;
Angew. Chem. 2013, 125, 842 – 872.
[11] a) N. Zeug, J. Buecheler, H. Kisch, J. Am. Chem. Soc. 1985, 107,
459 – 1465; b) B. Ohtani, S. Kusakabe, S.-i. Nishimoto, M.
6
1
TLC analysis or H NMR spectroscopy, the crude reaction mixture
was poured into a funnel containing diethyl ether (5 mL) and H O
2
(5 mL). The layers were separated; the aqueous phase was extracted
1
with diethyl ether (3 ꢁ 5 mL), and the combined organic phases were
dried over MgSO4 and concentrated. The resulting residue was
purified by column chromatography on silica gel (hexane/EtOAc,
Matsumura, Y. Nakato, Chem. Lett. 1995, 24, 803 – 804; c) S.
Marinkovi c´ , N. Hoffmann, Eur. J. Org. Chem. 2004, 3102 – 3107;
d) T. Mitkina, C. Stanglmair, W. Setzer, M. Gruber, H. Kisch, B.
Kçnig, Org. Biomol. Chem. 2012, 10, 3556 – 3561; e) X. Lang, X.
Chen, J. Zhao, Chem. Soc. Rev. 2014, 43, 473 – 486.
9
0:10) to afford the corresponding product.
Received: May 8, 2014
Published online: && &&, &&&&
[12] X. Chen, S. S. Mao, Chem. Rev. 2007, 107, 2891 – 2959.
[13] a) X.-H. Ho, M.-J. Kang, S.-J. Kim, E. D. Park, H.-Y. Jang, Catal.
Sci. Technol. 2011, 1, 923 – 926; b) M. Rueping, J. Zoller, D. C.
Fabry, K. Poscharny, R. M. Koenigs, T. E. Weirich, J. Mayer,
Chem. Eur. J. 2012, 18, 3478 – 3481; c) C. Vila, M. Rueping,
Green Chem. 2013, 15, 2056 – 2059.
14] U.S. Geological Survey, Mineral Commodity Summaries, Jan-
uary 2012.
15] G. G. Briand, N. Burford, Chem. Rev. 1999, 99, 2601 – 2658.
16] a) N. M. Leonard, L. C. Wieland, R. S. Mohan, Tetrahedron
Keywords: alkylation · bismuth oxide · organocatalysis ·
.
photocatalysis · visible light
[
[
1] For reviews, see: a) T. P. Yoon, M. A. Ischay, J. Du, Nat. Chem.
010, 2, 527 – 532; b) J. M. R. Narayanam, C. R. J. Stephenson,
[
[
2
Chem. Soc. Rev. 2011, 40, 102 – 113; c) C. K. Prier, D. A. Rankic,
D. W. C. MacMillan, Chem. Rev. 2013, 113, 5322 – 5363; d) D. M.
Schultz, T. P. Yoon, Science 2014, 343, 1239176; e) M. N.
2002, 58, 8373 – 8397; b) D. H. Aggen, J. N. Arnold, P. D. Hayes,
N. J. Smoter, R. S. Mohan, Tetrahedron 2004, 60, 3675 – 3679.
4
www.angewandte.org
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2014, 53, 1 – 5
These are not the final page numbers!

Angewandte
Chemie
Communications
Organo-Photocatalysis
P. Riente, A. Matas Adams, J. Albero,
E. Palomares,*
M. A. Pericꢁs*
&&&& — &&&&
Light-Driven Organocatalysis Using
Inexpensive, Nontoxic Bi O as the
2
3
Photocatalyst
Now it’s bismuth time! The asymmetric
intermolecular a-alkylation of aldehydes
with a-bromocarbonyl compounds can
be achieved under visible-light irradiation
by combining the second-generation
MacMillan catalyst and an inexpensive,
nontoxic, and commercially available
Bi O powder. This reaction also pro-
ceeded with high efficiency when the
reaction vial was exposed to the morning
sunlight in Tarragona, Spain.
2
3
Angew. Chem. Int. Ed. 2014, 53, 1 – 5
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
5
These are not the final page numbers!