Cobalt-catalysed selective synthesis of aldehydes and alcohols from esters

Article abstract of DOI:10.1039/d0cc03076g

Efficient and selective reduction of esters to aldehydes and alcohols is reported in which a simple cobalt pincer catalyst catalyses both transformations using diethylsilane as a reductant. Remarkably, the reaction selectivity is controlled by the stoichiometry of diethylsilane. This journal is

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Cobalt-catalysed selective synthesis of aldehydes
and alcohols from esters†
Cite this:DOI: 10.1039/d0cc03076g
Sandip Pattanaik and Chidambaram Gunanathan
*
Received 28th April 2020,
Accepted 21st May 2020
DOI: 10.1039/d0cc03076g
rsc.li/chemcomm
Efficient and selective reduction of esters to aldehydes and alcohols is abundant metal based catalysts have been developed for hydro-
reported in which a simple cobalt pincer catalyst catalyses both silylation of esters.8,18 Cobalt catalysed hydrosilylation of esters
transformations using diethylsilane as a reductant. Remarkably, the to alcohols and aldehydes is limited to one recent report, which
reaction selectivity is controlled by the stoichiometry of diethylsilane. used two cobalt salts and the reaction proceeded under hetero-
geneous conditions (Scheme 1b).19
Alcohols and aldehydes are important building blocks in chemical
We have reported the cobalt catalysed selective synthesis of
synthesis and bulk industrial feedstocks. They are widely used in disiloxanes, monohydrodisiloxanes and oxidation of alcohols
the preparation of agrochemicals, cosmetics, various bioactive to carboxylic acids in which the reactions proceeded with
molecules and pharmaceutics. Reduction of carboxylic acids liberation of molecular hydrogen.20 In continuation of our
using hydride reagents such as DIBAL-H and LiAlH4 is one of interest in hydroelementation reactions6c–e,21 herein we report
t
the main synthetic methods for the preparation of alcohols.1 Such the cobalt pincer complex [NNNH BuCoBr2] 1 catalysed selective
synthesis suffers from the sensitivity of pyrophoric reagents, non- synthesis of aldehydes and alcohols using hydrosilylation of
compatibility with other functional groups and poor selectivity.1 esters. Interestingly, the same catalyst catalyses both transfor-
Alcohols can also be obtained from the hydrogenation of esters, mations and the complete selectivity was attained by stoichio-
which often requires high temperature and pressure.2–4 In this metry of diethylsilane (Scheme 1c).
direction, eminent research groups have developed cobalt cata-
Using methyl benzoate as a benchmark substrate the reac-
lysed hydrogenation of esters (Scheme 1a).5 Alternatively, selective tion conditions for the catalytic hydrosilylation of esters to
hydroboration and hydrosilylation of aldehyde, ketone and car- aldehydes was optimized. Thus, reaction of methyl benzoate
boxylic acid functionalities and subsequent acidic or basic workup and diethylsilane in the presence of catalyst 1 (1 mol%) and
provided primary and secondary alcohols.6 Reduction of carbox- KOtBu (2 mol%) was performed at 50 1C, which resulted in 24%
ylate esters using silanes leads to the formation of silylacetal and conversion of methyl benzoate (Table 1). Increase of the base
silyl ether intermediates, which can be converted to aldehydes load to 4 mol% resulted in 99% conversion of methyl benzoate
and alcohols upon hydrolysis.7–14
and benzaldehyde was isolated in 89% yield upon acidic
Selective reduction of esters to aldehydes and alcohols using workup (entry 3, Table 1). While performing the reaction at
silanes is becoming a topic of interest and method of choice room temperature failed to occur, decreasing the catalyst load
over the hydrogenation of esters due to the operational resulted in diminished conversion and yields (entries 4 and 5,
simplicity.15–18 In particular, hydrosilylation of esters is attrac- Table 1). No reaction was observed in the absence of catalyst
tive to implement in synthetic transformations of targeted (entry 6, Table 1).
molecular synthesis as chemo and regioselectivities can be
Using the optimised reaction conditions various esters were
attained. Using transition metals and Lewis acids, controlled subjected to the cobalt catalysed hydrosilylation reactions,
synthesis of acetal intermediates from esters and their further which transformed the esters to their corresponding aldehydes
conversion to aldehydes have been reported.7–10 Notably, earth under mild conditions (Table 2). When butyl benzoate and
benzyl benzoate were reacted with diethylsilane, benzaldehyde
School of Chemical Sciences, National Institute of Science Education and Research
was obtained in good yields (entries 2 and 3, Table 2). Electron-
donating group substituted esters provided the aldehydes 2b
and 2c in 78% and 91% yields, respectively. The cobalt-
(NISER), HBNI, Bhubaneswar, Khurda-752050, India.
E-mail: gunanathan@niser.ac.in
† Electronic supplementary information (ESI) available: Experimental proce-
catalysed hydrosilylation reaction is chemoselective to the ester
functionality and the presence of a nitrile group on the aryl
dures, NMR spectra of the products and their spectral data. See DOI: 10.1039/
d0cc03076g
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Table 2 Cobalt-catalysed transformation of esters to aldehydesa
Conv.b (%)
Entry
1
Esters
Aldehydes
Yieldc (%)
89
2a
2a
2a
2b
2c
99
89
83
86
99
2
3
4
5
81
72
78
91
6
2d
2e
91
89
78
83
7d
8
9
2f
53
84
39
73
2g
10
11
2h
2i
63
96
89
51
81
76
12
2j
Scheme 1 Advances in cobalt catalysis for the conversion of esters to
aldehydes and alcohols.
a
Catalytic conditions: ester (1 mmol), diethylsilane (1.5 mmol), catalyst
1 (1 mol%) and KOtBu (4 mol%) were heated at 50 1C for 12 h.
b
Conversion was determined by GC using dodecane as an internal
c
standard. Isolated yield after column chromatography.
Table 1 Optimization for cobalt catalysed synthesis of aldehydes from estersa
ester was tolerated and the p-cyanobenzaldehyde 2d was isolated
in 78% yield. When p-hydroxymethyl benzoate was reacted with
excess diethylsilane, the product 2e was isolated in 83% yield
(silylation on hydroxyl group was deprotected on acidic workup).
p-Dimethylamino, p-fluoro and p-bromo aryl esters reacted under
the optimized conditions and the corresponding aldehydes 2f–2h
were obtained in moderate to good yields. When methylphenyl
acetate and methyl cinnamate were reacted, aldehydes 2i and 2j
were isolated in 81% and 76% yields, respectively. Notably, the
Entry
1 (mol%)
Base (mol%)
Conv.b (%)
Yieldc (%)
1
2
1
1
1
1
0.5
0
2
3
4
4
4
4
24
61
99
0
57
0
16
51
89
0
44
0
3
4d
5
6
a
Reaction conditions: methyl benzoate (1 mmol), diethylsilane a,b-unsaturated alkene functionality was also tolerated and did
(1.5 mmol), catalyst 1, base and toluene (1 mL) taken in a vial was
heated at 50 1C under closed conditions. Conversion was determined
by GC using dodecane as an internal standard. Isolated yield after
column chromatography. Reaction performed at room temperature.
not interfere in the reaction.
Further, we envisaged the hydrosilylation of esters to alcohols
using the same cobalt catalyst 1. Thus, reaction of ester with
b
c
d
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Table 3 Optimization for cobalt catalysed synthesis of alcohols from
estersa
Table 4 Cobalt catalysed transformation of esters to alcoholsa
Conv.b (%)
Entry
1
Esters
Alcohols
Yieldc (%)
96
Entry
1 (mol%)
Base (mol%)
Convb. (%)
Yieldc (%)
3a
99
1
2
3
4
5
6
7
2
2
1
1.5
1.5
1.5
0
8
99
99
99
99
99
99
0
82
96
42
65
71
77
0
10
10
10
12
14
10
2
3
4
3a
3a
3b
99
99
99
92
87
95
a
Reaction conditions: methyl benzoate (1 mmol), diethylsilane (3 mmol),
catalyst 1, base and toluene (1 mL) were taken in a vial and heated at
50 1C under closed conditions. Conversion was determined by GC
using dodecane as an internal standard. Isolated yield after column
b
c
chromatography.
5
6
7
3c
3d
3e
99
99
99
91
98
88
excess of silane was optimized to provide benzyl alcohol (Table 3).
The reaction of methyl benzoate with diethylsilane in the presence
of catalyst 1 (2 mol%) and KOtBu (8 mol%) selectively provided
benzyl alcohol in 82% yield (entry 1, Table 3) and a similar re-
action with increased base load of 10 mol % leads to 96% yield
(entry 2, Table 3). Lowering the catalyst load and higher loading of
base provided the benzyl alcohol in lower yields (entries 3–6,
Table 3). A control experiment performed in the absence of
catalyst confirmed the requirement of catalyst (entry 7, Table 3).
The scope of this cobalt catalysed selective conversion of esters
to alcohols was explored using various aliphatic and aromatic
esters (Table 4). Under the optimized conditions the butyl and
benzyl benzoate esters were selectively transformed to benzyl
alcohol in good yields (entries 2 and 3, Table 4). Electron donating
group substituted aryl esters provided the corresponding alcohols
3b, 3c and 3d in good yields. p-Fluoromethyl benzoate resulted in
p-fluorobenzyl alcohol (3e, 88%). Esters such as methylphenyl
acetate, methylphenyl propanoate and linear aliphatic esters
delivered the alcohols 3f–3i in excellent yields. Interestingly, upon
reaction of diesters such as dimethyl adipate, the corresponding
hexamethylene diol (3j) was isolated in 86% yield.
8
9
3f
99
99
93
89
3g
10
11
3h
3i
99
99
86
84
12d
3j
99
86
a
Catalytic conditions: ester (1 mmol), diethylsilane (3 mmol), catalyst 1
(2 mol%) and KOtBu (10 mol%) were heated at 50 1C for 20 minutes.
b
Conversion was determined by GC using dodecane as an internal
c
d
standard. Isolated yield after column chromatography. Reaction
carried out using 6 mmol of diethylsilane.
More studies are required to understand the mechanism of this
cobalt-catalysed hydrosilylation of esters to aldehydes and alcohols. acidic workup provided the aldehydes or alcohols. Good substrate
However, a plausible mechanistic pathway involving the dehydro- scope with many functional group tolerances was demonstrated
halogenation reaction on catalyst 1 by base,20 Si–H activation, for the synthesis of both aldehydes and alcohols from esters. The
perhaps involving amine-amide metal–ligand cooperation,22 sub- hydrosilylation of esters is proposed to proceed via SiÀH bond
sequent hydrosilylation of esters leading to the selective formation activation by cobalt, facilitated by amine-amide metal–ligand
of silyl acetal or silyl ether intermediates based on the stoichio- cooperation and may involve CoÀH intermediacy.
metry of diethylsilane and acidic workup delivering the aldehydes
and alcohols, respectively is proposed in Scheme S1 (ESI†).
We thank SERB New Delhi (EMR/2016/002517), the Depart-
ment of Atomic Energy and NISER for financial support. C. G.
In summary, we have developed an efficient and simple thanks Prof. Bhargava B. L., NISER for the kind help. S. P.
catalytic system for the selective reduction of esters to aldehydes thanks CSIR for a research fellowship.
and alcohols using diethylsilane as a reductant. Notably, a single
cobalt pincer complex catalyses both transformations with com-
plete selectivity without requiring any additives. Remarkably, the
stoichiometry of diethylsilane controlled the selective reduction of
Conflicts of interest
esters to silylacetal or silylether intermediates and the subsequent There are no conflicts to declare.
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10 J. Nakanishi, H. Tatamidani, Y. Fukumoto and N. A. Chatani,
Synlett, 2006, 869–872.
11 D. J. Parks, J. M. Blackwell and W. E. Piers, J. Org. Chem., 2000, 65,
3090–3098.
12 (a) S. Das, K. Mc¸ller, K. Junge and M. Beller, Chem. – Eur. J., 2011, 17,
7414–7417; (b) K. Junge, B. Wendt, S. Zhou and M. Beller, Eur. J. Org.
Notes and references
1 (a) L. I. Zakharkin and I. M. Khorlina, Tetrahedron Lett., 1962, 3,
619–620; (b) L. I. Zakharkin, V. V. Gavrilenko, D. N. Maslin and
I. M. Khorlina, Tetrahedron Lett., 1963, 4, 2087–2090; (c) P. M. Weissman
and H. C. Brown, J. Org. Chem., 1966, 31, 283–287; (d) T. Izawa and
T. Mukaiyama, Bull. Chem. Soc. Jpn., 1979, 52, 555–558.
´
Chem., 2013, 2061–2065; (c) D. Bezier, G. T. Venkanna, L. C. Misal
2 (a) J. Zhang, G. Letius, Y. Ben-David and D. Milstein, Angew. Chem.,
Int. Ed., 2006, 45, 1113–1115; (b) L. A. Saudan, C. M. Saudan,
C. Debieux and P. Wyss, Angew. Chem., Int. Ed., 2007, 46, 7473–7475.
3 (a) T. Zell, Y. Ben-David and D. Milstein, Angew. Chem., Int. Ed.,
2014, 53, 4685–4689; (b) S. Chakraborty, H. Dai, P. Bhatatacharya,
N. T. Fairweather, M. S. Gibson, J. A. Krause and H. Guan, J. Am.
Chem. Soc., 2014, 136, 7869–7872.
Castro, J. Zheng, T. Roisnel, J.-B. Sortais and C. Darcel, Adv. Synth.
Catal., 2012, 354, 1879–1884.
13 (a) S. C. Berk, K. A. Kreutzer and S. L. A. Buchwald, J. Am. Chem. Soc.,
1991, 113, 5093–5095; (b) M. T. Reding and S. L. Buchwald, J. Org.
Chem., 1995, 60, 7884–7890.
14 (a) K. Matsubara, T. Iura, T. Maki and H. A. Nagashima, J. Org.
˜
Chem., 2002, 67, 4985–4988; (b) A. C. Fernandes and C. C. Romao,
4 (a) S. Elongovan, M. Garbe, H. Jiao, A. Spannerberg, K. Junge and
M. Beller, Angew. Chem., Int. Ed., 2016, 55, 15364–15368;
(b) M. B. Widegren, G. J. Harkness, M. Z. Z. Salwin, D. B. Cordes
and M. L. A. Clarke, Angew. Chem., Int. Ed., 2017, 56, 5825–5828;
(c) N. A. Espinosa-Jalapa, A. Nerush, L. J. W. Shimon, G. Leitus,
L. Avram, Y. Ben-David and D. Milstein, Chem. – Eur. J., 2017, 23,
5934–5938; (d) R. Van Putten, E. Uslamin, M. Garbe, C. Liu,
A. Gonzaleg-de-castro, M. Lutz, K. Junge, E. J. M. Hensen and
M. Beller, Angew. Chem., Int. Ed., 2017, 56, 7531–7534.
5 (a) T. J. Korstanje, J. I. V. Vlugt, C. J. Elsevier and B. de Bruin, Science,
2015, 350, 298–302; (b) D. Srimani, A. Mukherjee, A. F. G. Goldberg,
G. Leitus, Y. D. Posner, L. J. W. Shimon, Y. Ben-David and
D. Milstein, Angew. Chem., Int. Ed., 2015, 54, 12357–12360;
(c) J. Yuwen, S. Chakraborty, W. W. Brennessel and W. D. Jones,
ACS Catal., 2017, 7, 3735–3740; (d) K. Junge, B. Wendt, A. Cingolani,
A. Spannenberg, Z. Wei, H. Jiao and M. Beller, Chem. – Eur. J., 2018,
24, 1046–1052; (e) Z. Shao, R. Zhong, R. Ferraccioli, Y. Li and Q. Liu,
Chin. J. Chem., 2019, 37, 1125–1130.
J. Mol. Catal. A: Chem., 2006, 253, 96–98.
15 T. Ohta, M. Kamiya, M. Nobutomo, K. Kusui and I. Furukawa, Bull.
Chem. Soc. Jpn., 2005, 78, 1856–1861.
´
16 L. Pehlivan, E. Metay, S. Laval, W. Dayoub, D. Delbrayelle,
G. Mignani and M. Lemaire, Eur. J. Org. Chem., 2011, 7400–7406.
17 O. O. Kovalenko and H. Adolfsson, Chem. – Eur. J., 2015, 21, 2785–2788.
18 (a) R. R. Behera, R. Ghosh, S. Panda, S. Khamari and B. Bagh, Org.
´
Lett., 2020, 22, 3642–3648; (b) O. Martınez-Ferrate, B. Chatterjee,
´
C. Werle and W. Leitner, Catal. Sci. Technol., 2019, 9, 6370–6378;
(c) T. K. Mukhopadhyay, C. L. Rock, M. Hong, D. C. Ashley,
T. L. Groy, M.-H. Baik and R. J. Trovitch, J. Am. Chem. Soc., 2017,
139, 4901–4915; (d) C. M. Kelly, R. McDonald, O. L. Sydora,
M. Stradiotto and L. A. Turculet, Angew. Chem., Int. Ed., 2017, 56,
15901–15904; (e) J. Zheng, S. Chevance, C. Darcel and J.-B. Sortais,
Chem. Commun., 2013, 49, 10010–10012.
19 V. Rysak, A. Descamps-Mandine, P. Simon, F. Blanchard, L. Burylo,
M. Trentesaux, M. Vandewall, V. Colliere, F. Agbossou-Niedercorn
and C. Michon, Catal. Sci. Technol., 2018, 8, 3504–3512.
20 (a) S. Pattanaik and C. Gunanathan, ACS Catal., 2019, 9, 5552–5561;
(b) D. R. Pradhan, S. Pattanaik, J. Kishore and C. Gunanathan, Org.
Lett., 2020, 22, 1852–1857.
21 (a) S. Kisan, V. Krishnakumar and C. Gunanathan, ACS Catal., 2017,
7, 5950–5954; (b) A. Kaithal, B. Chatterjee and C. Gunanathan, J. Org.
Chem., 2016, 81, 11153–11161; (c) A. Kaithal, B. Chatterjee and
C. Gunanathan, Org. Lett., 2016, 18, 3402–3405; (d) B. Chatterjee
and C. Gunanathan, Chem. Commun., 2017, 53, 2515–2518.
22 Reviews on metal-ligand cooperation: (a) J. R. Khusnutdinova and
D. Milstein, Angew. Chem., Int. Ed., 2015, 54, 12236–12273; (b) C.
Gunanathan and D. Milstein, Acc. Chem. Res., 2011, 44, 588–602.
6 (a) M. L. Shegavi and S. K. Bose, Catal. Sci. Technol., 2019, 9,
3307–3336; (b) C. Erken, A. Kaithal, S. Sen, T. Weyhermu¨ller,
¨
´
M. Holscher, C. Werle and W. Leitner, Nat. Commun., 2018,
9, 4521; (c) S. Kisan, V. Krishnakumar and C. Gunanathan, ACS
Catal., 2018, 8, 4772–4776; (d) A. Kaithal, B. Chatterjee and
C. Gunanathan, Org. Lett., 2015, 17, 4790–4793; (e) B. Chatterjee
and C. Gunanathan, Chem. Commun., 2014, 50, 888–890.
7 C. Cheng and M. Brookhart, Angew. Chem., 2012, 51, 9422–9424.
8 H. Li, L. C. M. Castro, J. Zheng, T. Roisnel, V. Dorcet, J. B. Sortais
and C. Darcel, Angew. Chem., Int. Ed., 2013, 52, 8045–8049.
9 M. Igarashi, R. Mizuno and T. Fuchikami, Tetrahedron Lett., 2001,
42, 2149–2151.
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