Silatrane as a Practical and Selective Reagent for the Reduction of Aryl Aldehydes to Benzylic Alcohols

Article abstract of DOI:10.1002/ejoc.201501599

Hydrosilanes are cheap, readily available substrates, yet they do not see as extensive use for simple carbonyl reductions as borohydrides. Hydrosilane reducing agents broadly fall into one of two general categories: either a) they are easy to handle and require expensive and/or hazardous additives, or b) they are difficult and/or dangerous to handle. This work details the discovery of mild and functional group compatible conditions utilizing hydrosilatrane for the selective reduction of aryl aldehydes to benzylic alcohols without unwanted formation of ethers or deoxygenated products. This method offers significant advances in silane reductions as silatrane is an air- and moisture-stable yet relatively reactive reducing agent that can be used in benchtop open air reactions.

Full text of DOI:10.1002/ejoc.201501599

DOI: 10.1002/ejoc.201501599
Full Paper
Silane Reduction
Silatrane as a Practical and Selective Reagent for the Reduction
of Aryl Aldehydes to Benzylic Alcohols
Vladislav Skrypai,[a] Joseph J. M. Hurley,[a] and Marc J. Adler*[a]
Abstract: Hydrosilanes are cheap, readily available substrates, tions utilizing hydrosilatrane for the selective reduction of aryl
yet they do not see as extensive use for simple carbonyl reduc-
tions as borohydrides. Hydrosilane reducing agents broadly fall
into one of two general categories: either a) they are easy to
handle and require expensive and/or hazardous additives, or b)
they are difficult and/or dangerous to handle. This work details
the discovery of mild and functional group compatible condi-
aldehydes to benzylic alcohols without unwanted formation of
ethers or deoxygenated products. This method offers significant
advances in silane reductions as silatrane is an air- and mois-
ture-stable yet relatively reactive reducing agent that can be
used in benchtop open air reactions.
Introduction
ously making them difficult – or at least inconvenient – to han-
dle.[10] For example, Nikinov and co-workers have recently de-
scribed a useful and economical method to reduce carbonyls
to alcohols using the readily available polymethylhydrosiloxane
(PMHS) with catalytic hydroxide in a sealed vial within a glove-
box; this method necessitates the use of carefully sealed reac-
tion vessel and moisture-free techniques as the active reducing
agent is the volatile and highly reactive SiH4.[11]
In 1976, Eaborn and co-workers reported the use of 1-hydro-
silatrane (1, Figure 1) as a reducing reagent.[12] Silatranes are a
well-explored class of molecules that are structurally confined
so as to render the silicon effectively pentavalent: the lone pair
of the nitrogen – fixed directly opposed to the axial substituent
– has been shown to donate into the σ* orbital of the axial
substituent.[13] It is presumably by this mechanism that the hy-
drosilatrane would be activated, with the intramolecular coordi-
nation of the nitrogen playing the role of a Lewis base additive.
Similar types of intramolecular activation of hydrosilanes have
been demonstrated.[14] Because of their structural rigidity, silat-
ranes exhibit remarkable stability when compared to both
other pentavalent silanes and other silyl orthoesters.
The reduction of organic compounds is a vital and ubiquitous
reaction. This process is synthetically important on a range of
levels, from research laboratories to the processing of wood
pulp for paper. The state-of-the-art general reducing agent for
organic compounds is sodium borohydride; this method is ef-
fective, and has been applied countless times since its develop-
ment.[1] Because of its prevalence, millions of kilograms of so-
dium borohydride are produced and used every year.
Hydrosilanes are also versatile reducing agents for a variety
of organic functionalities[2] including aldehydes[3] and ket-
ones.[4] Similar to the pervasive borohydrides, the Si–H bond is
polarized towards the hydrogen allowing silanes to serve as
mild sources of hydride. Silanes are readily and cheaply avail-
able, as silicon is the second most abundant element in the
earth's crust. Despite this significant advantage with respect
both to environmental friendliness and cost as compared to
borohydrides, the synthetic community has not yet developed
a widely applied, operationally simple, mild, cheap, benchtop
method for the reduction of aldehydes using silanes.
The main reason for this state of affairs is that silane reactiv-
ity is difficult to tune. While alkylsilanes (such as triethylsilane)
are generally easy to handle,[5] they require forceful activation
in the form of a Brønsted acid,[6] Lewis acid,[7] Lewis base,[8] or
transition metal[9] in the reaction mixture; the method by which
these additives catalyze the reaction varies, but their presence
is vital to enhance the hydridic nature of the hydrosilane. Si-
lanes bearing more electronegative substituents (such as alkoxy
or halide) or multiple hydrides are more reactive, allowing for
the development of many excellent methods, yet simultane-
Figure 1. 1-Hydrosilatrane (1).
Since Eaborn et al. disclosed this finding, the enhanced react-
ivity of hydrosilatrane has been discussed several times in the
literature;[2,15] however, we could find no record of it being ap-
plied or further explored. Hydrosilatrane is easy to access from
inexpensive commercially available substrates and is stable to
open air and ambient moisture: for this study, we prepared 1-
hydrosilatrane on a multi-gram scale and stored the reagent in
a snap-top vial that was frequently uncapped for use without
[a] Northern Illinois University, Department of Chemistry & Biochemistry,
1425 W Lincoln Hwy, DeKalb, IL 60115, USA,
mjadler@niu.edu
http://www.themjalab.com
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/ejoc.201501599.
Eur. J. Org. Chem. 2016, 2207–2211
2207
© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
any special handling, and under these conditions no detectable
degradation occurred over the several-month period of the
study. For these reasons, silatrane is an attractive option for a
mild and user-friendly reducing reagent and we desired to ex-
plore the scope for wider application.
Table 1. Solvent screening for the reduction of para-anisaldehyde (2b) with
hydrosilatrane (1).
Results and Discussion
Entry
Solvent
Yield[a] [%]
We were particularly interested in the potential for using hydro-
silatrane as a means to mildly and selectively reduce benzalde-
hydes to benzylic alcohols without the generation of deleteri-
ous side products. The singular example of such a reaction from
Eaborn et al. (the reduction of para-hydroxybenzaldehyde) was
reported to afford the corresponding alcohol in low yield (32 %)
but seemingly without the appearance of any other products.
This is in contrast to what is often found in the silane reduction
of aldehydes, as they are frequently accompanied by the forma-
tion of symmetric ethers or, particularly in the case of aryl alde-
hydes, deoxygenated products.[16] While methods have been
developed to control the product ratios in known systems, ap-
plication to novel molecules requires optimization on a case-
by-case basis. We were encouraged by the reported result how-
ever, as despite the poor yield and forcing conditions (refluxing
xylene, 72 h) the reaction was run under highly dilute condi-
1
2
3
4
5
6
7
DMF
THF
95
87
3
30
3
diethyl ether
acetonitrile
hexane
methanol
dichloromethane
35
81
[a] Yield determined by NMR spectroscopy.
We next focused on identifying the mildest possible base to
enable the activation of silatrane (Table 2). While both sodium
and potassium hydroxide efficiently enabled the conversion of
para-anisaldehyde to the corresponding alcohol, no reaction
occurred in the presence of other ionic bases. Additionally,
basic amines (primary, secondary, and tertiary) failed to spur
any reaction under the attempted conditions.
tions (0.002
M). Dishearteningly we were unable to reproduce
Table 2. Additive screening for the reduction of para-anisaldehyde (2b) with
hydrosilatrane (1) in DMF.
these results using either the original or slightly modified condi-
tions (Figure 2, see Supporting Information for details).
Entry Solvent
Additive
Equiv. of additive
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
THF
NaOH
NaOH
KOH
tBuOK
iPrNH2
HNEt2
NEt3
30
1
20
1
1.5
1.5
1.5
1.5
30
10
10
1.5
0.5
24
0.5
0.5
1
1
1
24
0.5
1
95
53
84
80
0
0
0
0
87
0
Figure 2. Reduction of 4-hydroxybenzaldehyde (2a).
Despite our lack of success in the reduction of aldehydes
with silatrane in the absence of additives, we still believed that
the silatrane would display enhanced reactivity when compared
to alkylsilanes. Recently the reduction of a variety of carbon-
heteroatom π bonds through the use of silanes and simple
bases has been reported. These reductions predictably were
efficient when reactive silanes were utilized, and thus we set
out to explore whether silatrane would be a functional reagent
in this method.
CaCl2
9
NaOH
NaHCO3
Na2CO3
HCO2Na
10
11
12
THF
THF
THF
1
1
0
0
To demonstrate the unique properties of the silatrane with
For optimization, we chose to examine the reduction of para-
anisaldehyde for several reasons: a) the resulting alcohol has a
high enough boiling point to be isolated from high boiling sol-
vents, b) we believed such electron-rich aryl aldehydes would
be more challenging to reduce, and c) we did not envision any
side reaction with aryl-alkyl ethers. This substrate indeed served
as a good model reaction.
regard to stability and reactivity, the reaction was attempted
with commonly used silane reducing reagents (Figure 3). The
first, triethoxysilane, is a highly reactive species that unsurpris-
ingly quickly degraded in the open-air (and hydroxide-contain-
ing) solution following partial reduction of the aldehyde. The
second, triethylsilane, is a mild and well-behaved reducing
agent, which as expected did not undergo any detectable reac-
Solvent screening (Table 1) showed that both DMF and THF tion with the aldehyde under the conditions for the observed
were viable solvents for the conversion of 2b to 3b. Solvents period of four hours. The reaction proceeded vigorously and
were taken directly from a bottle as acquired from the manufac- relatively well under the conditions using PMHS (85 %), but in
turer and the reaction was set up in an open vessel on the the open-air environment silatrane was a more effective reduc-
benchtop.
tant.
Eur. J. Org. Chem. 2016, 2207–2211
www.eurjoc.org
2208
© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
reduction of 2e. Reactions run with 2e, 2k, 2m, and 2o in the
absence of silatrane showed conversion to mixtures of alcohol
and carboxylic acid, with the acid being the predominant spe-
cies; these results indicate that both side reactions may be tak-
ing place. In order to minimize the contribution of aerobic oxid-
ation to the generation of unwanted benzoic acid, several sub-
strates were run under oxygen-free conditions; these trials pro-
vided clean reductions and no observable benzoic acid (Entries
4, 12, 15, 16, 18, and 20).
Under the investigated conditions, hydrosilatrane (1) exhib-
ited no reaction with other reducible functionalities examined,
including the nitriles (Entries 11, 12), nitro group (Entry 15),
benzyl (Entry 9) and allyl ethers (Entry 10), and halides (Entries
14–20).
Hydroxybenzaldehydes were unfortunately not reduced ef-
fectively: while 3-hydroxy- (2q, Entry 23) was partially reduced
using the described method, 4-hydroxybenzaldehyde (2a, Entry
21) remained unmoved. In these cases, bubbling is observed
initially, which is consistent with an acid/base reaction occur-
ring between the hydride of the silatrane and the proton of
the phenol.[18] Reduction may then occur, though the anionic
benzaldehyde substituent significantly decreases the electro-
philicity of the aldehyde; this results in decreased reactivity of
the meta variant (2q) and no reaction at all in the para deriva-
tive (2a). Yields in both cases were not affected by increasing
both the concentration of silatrane and reaction time (Entries
22, 24).
The method was also applied to heteroatom-containing (4a,
4b, and 4c) and polycyclic (4d, 4e, and 4f) aryl aldehydes. In
all cases, the reaction proceeded as expected with excellent
yields and no observation of side products (Figure 4). This
method was also proven to be effective on aliphatic aldehyde
6 (Figure 5).
Figure 3. Efficiency of reaction with common silanes.
Finally, the generality of the method was explored: the opti-
mized conditions were applied to a range of commercially avail-
able and/or readily synthesized aryl aldehydes (Table 3). Gratify-
ingly, unsubstituted benzaldehyde 2c was reduced in excellent
yield (Entry 1). Electron-rich aryl aldehydes (e.g. 2d and 2h) also
were efficiently reduced, even when the substituent was in the
meta (2f) or ortho position (2g).
Table 3. Reduction of substituted benzaldehydes 2 with hydrosilatrane (1).
Entry
R
Aldehyde/alcohol
Yield[a] [%]
1
2
3
H
4-tBu
4-Me
2c/3c
2d/3d
2e/3e
98[b]
95
66[c]
92[b,d]
95
4
5
6
7
8
4-OMe
3-OMe
2-OMe
4-OPh
4-OBn
4-OAll
4-CN
2b/3b
2f/3f
2g/3g
2h/3h
2i/3i
96
88
94
99
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
2j/3j
2k/3k
98
60[c]
93[b,d]
88[c]
76[c]
98[b,d]
98[b,d]
28[c]
99[b,d]
46[c]
96[b,d]
0
3-NO2
4-Cl
2l/3l
2m/3m
4-F
3-F
2n/3n
2o/3o
2-F
2p/3p
2a/3a
2q/3q
4-OH
3-OH
0[e]
44
36[e]
[a] Yield determined by NMR unless otherwise noted. [b] Yield determined
by GC-FID. [c] Product mixture contained significant amounts (> 5 %) of cor-
responding benzoic acid. [d] Reaction run under oxygen-free conditions. [e]
Reaction run with 2.5 equiv. of 1 for 24 h.
Figure 4. Reduction of non-phenyl aryl aldehydes using hydrosilatrane (1).
While aldehydes bearing electron-withdrawing groups (in-
cluding 2k, 2l, and 2m) were well tolerated, the alcohol product
was generally accompanied by significant amounts of the corre-
sponding benzoic acid in the crude product mixture. This obser-
vation suggested that either a) Cannizaro reaction[17] and/or b)
aerobic oxidation were concurrently taking place. The deleteri-
ous benzoic acid product was also formed in the attempted
Figure 5. Reduction of an aliphatic aldehyde 6 using hydrosilatrane (1).
2209 © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2016, 2207–2211
www.eurjoc.org

Full Paper
reduced pressure and used to determine yield without any further
purification. All of the alcohols synthesized are known compounds.
Conclusions
The reported findings are encouraging for exploration and fur-
ther development of silatrane reactivity. Cheap and easily acces-
sible hydrosilatrane has been shown to be an effective reduc-
tant of aryl aldehydes bearing a variety of functionalities in this
user-friendly method. Furthermore, hydrosilatrane demon-
strates excellent stability to air and ambient moisture rendering
it amenable to benchtop reactions and long-term storage. Fur-
ther work is currently underway to help elucidate the mecha-
nism of this reaction and also to expand this work to other
reducible functionalities.
Acknowledgments
The authors would like to thank Northern Illinois University for
financial support and Prof. Thomas Gilbert for assistance in su-
pervision.
Keywords: Reduction · Silanes · Silatrane · Lewis bases ·
Aldehydes
[1] a) H. I. Schlesinger, C. H. Brown, A. E. Finholt, R. J. Gilbreath, R. H. Hoek-
stra, K. E. Hyde, J. Am. Chem. Soc. 1953, 75, 215–219; b) H. I. Schlesinger,
C. H. Brown, B. Abraham, A. C. Bond, N. Davidson, A. E. Finholt, R. J.
Gilbreath, H. Hoekstra, L. Horvitz, K. E. Hyde, J. Am. Chem. Soc. 1953, 75,
186–190.
Experimental Section
General Considerations: All reactions were carried out under am-
bient conditions in an open vessel, with no special effort to exclude
water or air from reaction mixtures unless otherwise noted. Chemi-
cals and reagents were purchased from Sigma–Aldrich and/or
Fisher, and were used without further purification unless otherwise
[2] G. L. Larson, J. L. Fry, Org. React. 2008, 71, 1–737.
[3] a) Z. Jia, M. Liu, X. Li, A. S. C. Chan, C.-J. Li, Synlett 2013, 24, 2049–2056;
b) M. Fujita, T. Hiyama, J. Org. Chem. 1988, 53, 5405–5415; c) M. P. Doyle,
D. J. DeBruyn, S. J. Donnelly, D. A. Kooista, A. A. Odubeta, C. T. West,
S. M. Zonnedelt, J. Org. Chem. 1974, 39, 2740–2747.
1
noted. H NMR spectra were recorded at 500/300 MHz at ambient
[4] a) M. Fujita, T. Hiyama, J. Am. Chem. Soc. 1984, 106, 4629–4630; b) L.
Gan, M. A. Brook, Can. J. Chem. 2006, 84, 1416–1425; c) I. Ojima, M.
Nihonyanagi, Y. Nagai, Bull. Chem. Soc. Jpn. 1972, 45, 3722–3722; d) H.
Mimoun, J. V. de Saint Laumer, L. Giannini, R. Scopelliti, C. Floriani, J. Am.
Chem. Soc. 1999, 121, 6158–6166.
temperature using a Bruker Avance III spectrometer. The chemical
shifts in 1H NMR spectra are reported relative to residual CHCl3 in
CDCl3 (δ =7.27 ppm). The chemical shifts in 13C NMR spectra are
reported relative to residual CHCl3 in CDCl3 (δ =77.23 ppm). The
yields were determined using mesitylene as an internal standard in
CDCl3. The abbreviations used for the chemical shifts are as follows:
s (singlet), d (doublet), t (triplet), dd (doublet of doublets), dt (dou-
blet of triplets), td (triplet of doublets), dq (doublet of quartets), m
(unresolved multiplet).
[5] a) S. Bhattacharyya, J. Org. Chem. 1998, 63, 7101–7102; b) T. Mizuta, S.
Sakaguchi, Y. Ishii, J. Org. Chem. 2005, 70, 2195–2199.
[6] M. P. Doyle, C. T. West, J. Org. Chem. 1975, 40, 3835–3838.
[7] a) V. Gevorgyan, M. Rubin, J.-X. Liu, Y. Yamamoto, J. Org. Chem. 2001, 66,
1672–1675; b) N. Gandhamsetty, J. Jeong, J. Park, S. Park, S. Chang, J. Org.
Chem. 2015, 80, 7281–7287; c) S. Rendler, M. Oestreich, Angew. Chem.
Int. Ed. 2008, 47, 5997–6000; Angew. Chem. 2008, 120, 6086–6089.
[8] A. Fedorov, A. Toutov, N. Swisher, R. Grubbs, Chem. Sci. 2013, 4, 1640–
1645.
[9] a) M. Rubio, J. Campos, E. Carmona, Org. Lett. 2011, 13, 5236–5239; b) K.
Matsubara, T. Iura, T. Maki, H. Nagashima, J. Org. Chem. 2002, 67, 4985–
4988; c) S. E. Denmark, J. D. Baird, Chem. Eur. J. 2006, 12, 4954–4963; d)
T. T. Metsanen, M. Oestreich, Organometallics 2015, 34, 543–546; e) S.
Díez-Gonzaález, N. M. Scott, S. P. Nolan, Organometallics 2006, 25, 2355–
2358.
[10] a) H. Zhou, H. Sun, S. Zhang, X. Li, Organometallics 2015, 34, 1479–1486;
b) H. Reuther, Z. Anorg. Allg. Chem. 1953, 272, 122–125; c) J. M. Roth,
A. M. Brook, H. B. Penny, J. Organomet. Chem. 1996, 521, 65–74; d) S. A.
Wells, Org. Process Res. Dev. 2010, 14, 484–484; e) M. Zhao, W. Xie, C. Cui,
Chem. Eur. J. 2014, 20, 9259–9262; f) K. Junge, B. Wendt, D. Addis, S.
Zhou, S. Das, M. Beller, Chem. Eur. J. 2010, 16, 68–73.
[11] K. Revunova, I. G. Nikonov, Chem. Eur. J. 2014, 20, 839–845.
[12] M. T. Attar-Bashi, C. Eaborn, J. Vencl, R. D. Walton, J. Organomet. Chem.
1976, 117, C87–C89.
Synthesis of Silatrane via Boratrane: To a 25 mL flask was added
boric acid (50 mmol) and triethanolamine (50 mmol). Water (3 mL)
was added to facilitate solubility. The flask was equipped with a
short path distillation apparatus and heated to 120 °C until no more
water condensed. The isolated boratrane was recrystallized from
acetonitrile and used directly in the next step. The experimental
data collected are in agreement with those described in the litera-
ture.[1] 70 %. 1H NMR (500 MHz, CDCl3): δ = 3.65 (t, J = 5.5 Hz, 6 H),
3.04 (t, J = 5.5 Hz, 6 H). 13C NMR (125 MHz, CDCl3) 62.1, 59.3. IR
(ATR) 2988, 2853, 1469, 1370, 1258, 1160, 1115, 1063, 1026, 1001,
933, 889, 730, 621, 560.
To an oven-dried, argon-flushed 100 mL flask containing boratrane
(5 mmol) in mixed xylenes (40 mL), was added triethoxysilane
(6 mmol) and anhydrous AlCl3 (0.05 mmol). The reaction was re-
fluxed over 4 h and then cooled to room temperature. The resulting
solids were filtered and further recrystallized from xylene to give
silatrane as white fibrous crystals. The experimental data collected
are in agreement with those described in the literature.[19] 88 %. 1H
NMR (500 MHz, CDCl3): δ = 3.94 (s, 1 H), 3.83 (t, J = 6 Hz, 6 H), 2.89
(t, J = 6 Hz, 6 H). 13C NMR (125 MHz, CDCl3) 57.2, 51.2. IR (ATR)
2975, 2936, 2886, 2087, 1487, 1457, 1347, 1268, 1090, 1047, 1020,
926, 860, 748, 630, 591.
[13] a) J. K. Puri, R. Singh, V. K. Chahal, Chem. Soc. Rev. 2011, 40, 1791–1840;
b) C. L. Frye, G. A. Vincent, W. A. Finzel, J. Am. Chem. Soc. 1971, 93, 6805–
6811; c) V. Pestunovich, S. Kirpichenko, M. Voronkov, Silatranes. In The
Chemistry of Organic Silicon Compounds; Z. Rappoport, Y. Apeloig, Wiley,
Chishester, UK, 1998, vol. 2, p. 1447–1537; d) M. G. Voronkov, V. M. Dy-
akov, S. V. Kirpichenko, J. Organomet. Chem. 1982, 233, 1–147; e) G. J.
Verkade, Acc. Chem. Res. 1993, 26, 483–489.
[14] a) M. Kira, K. Sato, H. Sakurai, J. Org. Chem. 1987, 52, 948–949; b) C.
Breliere, F. Carre, R. J. P. Corriu, M. Poirier, G. Royo, Organometallics 1986,
5, 388–390; c) M. Deneux, I. C. Akhrem, D. V. Avetisyan, E. I. Mysof, M. E.
Vol′pin, Bull. Soc. Chim. Fr. 1973, 2638–2642; d) J. Boyer, C. Breliere, R. J. P.
Corriu, A. Kpoton, M. Poirier, G. J. Royo, J. Organomet. Chem. 1986, 311,
C39–C43.
[15] a) J. Pietruszka, Science Synthesis 2002, 4, 159–185; b) C. Chuit, R. J. P.
Corriu, C. Reye, in: Chemistry of Hypervalent Compounds, Wiley-VCH,
Weinheim, Germany, 1999, p. 81–146.
General Method for the Reduction of Aryl Aldehydes: To a 2
dram vial containing a stir bar was added silatrane (0.15 mmol), aryl
aldehyde (0.1 mmol), and DMF (1 mL). The solution was stirred for
5 min to allow for all the silatrane to dissolve, after which additive
(1 pellet of NaOH finely ground) was added. After 30 min of stirring
in ambient conditions the solution was washed once with 1
M HCl,
then extracted three times with dichloromethane and once with
diethyl ether. The resulting organic extract was concentrated under
Eur. J. Org. Chem. 2016, 2207–2211
www.eurjoc.org
2210
© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
[16]
Chem. 2000, 23, 761–764; d) V. A. Pestunovich, Dokl. Akad. Nauk 1982,
263, 904–906.
[19] G. I. Zelcans, M. G. Voronkov, Chem. Heterocycl. Compd. 1967, 3, 296–
a) J. M. Aizpurua, B. Lecea, C. Palomo, Can. J. Chem. 1986, 64, 2342–2347;
b) J. M. Aizpurua, C. Palomo, Tetrahedron Lett. 1984, 25, 1103–1104; c)
C. T. West, S. J. Donnelley, D. A. Kooistra, M. P. Doyle, J. Org. Chem. 1973,
38, 2675–2681.
298.
[17] The Cannizzaro Reaction. T. A. Geissman, Org. React. 2011, 2, 94–113.
[18] a) S. S. Karlov, Inorg. Chim. Acta 2007, 360, 563–578; b) A. C. Black, Bioorg.
Med. Chem. Lett. 2002, 12, 3521–3523; c) E. Lukevics, Main Group Met.
Received: January 31, 2016
Published Online: March 30, 2016
Eur. J. Org. Chem. 2016, 2207–2211
www.eurjoc.org
2211
© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim