Table 3 Selective reduction of carboxylic acids into aldehydes with
TMDS using Fe(CO)3(t-PBO) catalyst Ba
2 For a book: G. Tojo and M. Ferna
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ndez, Oxidation of Alcohols to
Aldehydes and Ketones: a Guide to Current Common Practice,
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RCHO/
RCH2OHb [%]
Yieldc
4 P. Four and F. Guibe, J. Org. Chem., 1981, 46, 4439; D. V. Gutsulyak
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Entry Carboxylic acid
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1e
2
3
4
5
6
7
8
R = o-Me-C6H4 96/4
77c
95c
83c
80c
87c
71c
45d
48c
72c
81c
85c
72d
74c
9c
R = m-Me-C6H4 98/2
R = p-Me-C6H4 97/3
R = p-OH-C6H4 88/12
R = p-Br-C6H4 98/2
R = p-F-C6H4 94/6
R = 1-naphthyl 96/4
R = 2-thiophenyl 98/2
3-Phenylpropanoic acid 90/10
9
10
11f
Hexadecanoic acid
Dodecane-1-12-dioic
acid
87/13
87/13
12e Oleic acid
94/6
—
97/3
13
2-Phenylpropanoic acid
14g 2-Phenylpropanoic acid
92c
10 K. Miyamoto, Y. Motoyama and H. Nagashima, Chem. Lett.,
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(i) RCO2H (1 mmol), B (5 mol%), TMDS (2 mmol, 2 equiv.), toluene
b
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(2 mL) at 50 1C for 24 h. (ii) Acidic work up. Ratio (%) determined
by GC. Yields of 3 determined by 1H-NMR of the crude mixture using
c
d
e
f
DMF as an internal standard. Isolated yields. 48 h. 10 mol% of B
g
and 4 equiv. of TMDS. 4 equiv. of TMDS at 70 1C for 30 h.
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Scheme 1 Plausible silyl-acetal intermediates leading to aldehydes.
In order to rationalize the formation of the aldehyde, we have
tried to isolate silylated intermediates that might lead to the
formation of the carbonyl moieties after the hydrolysis step. Based
on the recent work of Nagashima with ruthenium,24 we have
initially postulated a cyclic disilylacetal intermediate such as 4a
(Scheme 1). However, the analysis of the crude reaction mixture
using MS allows us to identify the open disilyl intermediate 4b
(M+Na+ C16H33O479BrNaSi4 calc. 503.0537, found 503.0545).
The NMR data of the crude reaction mixture also indicate the
presence of the disilyl acetal unit CH(OSi)2 characterized by the
chemical shift of 5.35 and 92.2 ppm, respectively, in 1H and
13C NMR.24 Moreover, the signal of Si–H was also identified at
4.68 ppm.25 The structure of 4b is in agreement with the require-
ment of 2 equiv. of TMDS to get a full conversion, as with
1 equiv., even at 70 1C after 48 h, the conversion could reach only
50%. The stability of the disilylacetal intermediates derived from
TMDS is the key to obtain aldehydes chemoselectively.
2011, 47, 6581; D. Be
C. Darcel, ChemCatChem, 2011, 3, 1747.
14 D. Bezier, G. T. Venkanna, L. C. Misal Castro, J. Zheng,
´
zier, G. T. Venkanna, J.-B. Sortais and
´
T. Roisnel, J.-B. Sortais and C. Darcel, Adv. Synth. Catal., 2012,
354, 1879.
15 F. Jiang, D. Be
2011, 353, 239; D. Be
Eur. J. Inorg. Chem., 2012, 1333.
16 L. C. Misal Castro, D. Bezier, J.-B. Sortais and C. Darcel, Adv.
´
zier, J.-B. Sortais and C. Darcel, Adv. Synth. Catal.,
´
zier, F. Jiang, J.-B. Sortais and C. Darcel,
´
Synth. Catal., 2011, 353, 1279; J. Zheng, L. C. Misal Castro,
T. Roisnel, C. Darcel and J.-B. Sortais, Inorg. Chim. Acta, 2012,
380, 301; H. Jaafar, H. Li, L. C. Misal Castro, J. Zheng,
T. Roisnel, V. Dorcet, J.-B. Sortais and C. Darcel, Eur. J. Inorg.
Chem., 2012, 3546.
17 L. C. Misal Castro, J.-B. Sortais and C. Darcel, Chem. Commun.,
2012, 48, 151.
¨
18 H.-J. Knolker, Chem. Rev., 2000, 100, 2941.
19 A. J. Deeming, S. S. Ullah, A. J. P. Domingos, B. F. G. Johnson
and J. Lewis, J. Chem. Soc., Dalton Trans., 1974, 2093.
20 N. W. Alcock, C. J. Richards and S. E. Thomas, Organometallics,
1991, 10, 231.
21 Example of (CO)3Fe(COD) catalyzed alkene isomerisation:
H. Fleckner, F.-W. Grevels and D. Hess, J. Am. Chem. Soc.,
1984, 106, 2027.
22 Examples of Fe(CO)5-catalyzed alkene isomerisation: E. Frankel,
E. Emken and V. Davison, J. Am. Oil Chem. Soc., 1966, 43, 30;
H. Fleckner, F. W. Grevels and D. Hess, J. Am. Chem. Soc., 1984,
106, 2027; R. Jennerjahn, R. Jackstell, I. Piras, R. Franke, H. Jiao,
M. Bauer and M. Beller, ChemSusChem, 2012, 5, 734.
23 Over-reduction products were already observed for the iron-
catalyzed hydrosilylation of benzoate derivatives, see ref. 14.
24 Disilylacetal intermediates derived from 1-adamantanoic acid and
1,2-bis(dimethylsilyl)benzene have been characterized. See ref. 10.
25 In the crude mixture, the disilylacetal derivative 4b was character-
ized by 1H NMR, 13C NMR, COSY, HMBC and HMQC, see
ESIw.
In summary, we have developed the first iron-catalyzed
efficient and selective switchable hydrosilylation of carboxylic
acids either to alcohols or aldehydes depending on the silanes.
We are grateful to CNRS, UR1, and Ministere de l’Enseigne-
ment Supe
´
rieur et de la Recherche for support, the ministere des
n Gran Mariscal de Ayacucho
affaires etrangeres and the fundacio
´ ´
(grant to L.C.M.C.) and the foundation Rennes1 (grant to H.L).
Notes and references
1 J. Seyden-Penne, Reductions by the Alumino- and Borohydrides in
Organic Synthesis, Wiley, New York, 2nd edn, 1997.
c
10516 Chem. Commun., 2012, 48, 10514–10516
This journal is The Royal Society of Chemistry 2012