A new simple method for the preparation of aryl formates from phenols

Article abstract of DOI:10.1515/znb-2008-0414

Aryl formates are prepared in a two step one-pot procedure from phenols. Firstly the formylating reagent triformamide (1b) is generated from sodium diformamide (2) and methane-sulfonyl chloride in situ, which reacts with phenols 4a-f to give aryl formates 5a-f in good yields. Triformamide, prepared in situ, transforms anisole in the presence of aluminum chloride to the N-(diarylmethyl)formamide 7.

Full text of DOI:10.1515/znb-2008-0414

478
Note
chemists. Despite the importance of the Fries reac-
tion in synthetic organic chemistry, the details of its
mechanism are still unclear. A few investigations deal-
ing with the mechanism of the Fries rearrangement of
aryl formates have appeared [4]. In the course of this
work, it turned out that aryl formates can formylate
phenols [4c]. If these observations can be generalized
and confirmed on a preparative scale very likely aryl
formates will attain significance as stable and easy to
handle formylating reagents for aromatic compounds.
A New Simple Method for the Prepara-
tion of Aryl Formates from Phenols
Imran Ali Hashmia, Willi Kantlehnera,
and Ivo C. Ivanovb
a Fakulta¨t Chemie/Organische Chemie, Hochschule Aalen,
Beethovenstraße 1, D-73430 Aalen, Germany
b
Department of Organic Chemistry, Faculty of Pharmacy,
Medical University of Sofia, Dunav 2, BG-1000 Sofia,
Bulgaria
Reprint requests to Prof. Dr. Willi Kantlehner.
Fax: +49(0)7361-576-2250.
E-mail: willi.kantlehner@htw-aalen.de
R−CON(CHO)2 1a R = CH3
1b R = H
Z. Naturforsch. 2008, 63b, 478 – 480;
received January 8, 2008
Results and Discussion
Dedicated to Professor George A. Olah on the occasion of
his 80th birthday
The O-formylation of hydroxyaromatic compounds
has been performed with various formic acid deriva-
tives [1]. In the present note we wish to report a new,
even simpler method for the synthesis of aryl for-
mates from phenols without isolating the formylating
agent triformamide (1b) which could be prepared in
situ (Scheme 1) starting from the very stable and eas-
ily obtainable sodium diformamide (2) and methane-
sulfonylchloride (3) in anhydrous acetonitrile at am-
bient temperature. Then, the corresponding hydroxy-
arene (4a – f) was added to the mixture and refluxed
for 2 h to afford the known aryl formates 5a – f in good
yields (62 – 78 %). The substituents, yields, physical
properties and some IR and NMR spectral data of prod-
ucts 5a – f are summarized in Table 1.
In a series of papers [2, 5a – d], novel formylat-
ing agents and their formylating potential for aro-
matic compounds in electrophilic aromatic substitu-
tions have been evaluated. A review article on new
methods for direct aromatic formylation was published
recently [3]. For example, triformamide (1b) in the
presence of aluminum chloride was used for the prepa-
ration of numerous aromatic aldehydes [5a, b, d]. That
is why we decided to explore whether the above de-
scribed one-pot approach could also be applied to
the direct formylation of aromatic compounds. Trifor-
mamide 1b (Scheme 1) was prepared in situ, but in 1,2-
dichloroethane instead of acetonitrile. Then, equimolar
amounts of anisole (6) and anhydrous aluminum chlo-
Aryl formates are prepared in a two step one-pot procedure
from phenols. Firstly the formylating reagent triformamide
(1b) is generated from sodium diformamide (2) and methane-
sulfonyl chloride in situ, which reacts with phenols 4a – f to
give aryl formates 5a – f in good yields. Triformamide, pre-
pared in situ, transforms anisole in the presence of aluminum
chloride to the N-(diarylmethyl)formamide 7.
Key words: Aryl Formates, Formylation, Hydroxyarenes
Introduction
Aryl formates are of significance in various fields of
organic chemistry [1]. In recent papers [2, 3] a conve-
nient method for the preparation of aromatic aldehydes
from aryl formates by means of the Fries rearrange-
ment has been described. Lewis acids, such as boron
tribromide, boron trichloride and trifluoromethanesulf-
onic acid, were shown to be the most effective cata-
lysts for this rearrangement. As starting compounds,
several aryl formates of wide structural diversity were
prepared in good yields [1] using a new method for
O-formylation of hydroxyarenes by means of N,N-di-
formylacetamide (1a) or of triformamide (1b). The re-
action can be catalyzed by sodium diformamide or by
trifluoromethanesulfonic acid salts of some rare earth
elements.
Actually aryl formates have attracted the attention ride were added, and the mixture was refluxed for 2 h
of mechanistically and theoretically interested organic (Scheme 2). The colorless crystalline diarylmethane
c
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Note
479
Table 1. Synthesis of aryl formates 5a – f from phenols 4a – f. IR and NMR spectral data for 5a – fa.
Lit. data
IR
Starting
n2D0
Product name
(5a – f)
Yield
(%)
n2D0
(ATR)
νC=O
(cm−1
phenol R1
(4a – f)
R2
(b. p., ◦C /
hPa)
NMR (CDCl3)a, δ (ppm)
(b. p., ◦C /
hPa)
)
1H NMR: δ = 7.12 (dd, 3J = 7.8, 4J = 2.1 Hz,
2H, 2-H, 6-H), 7.26 (t, J = 7.8 Hz, 1H, 4-H), 7.39
(t, J = 7.8 Hz, 2H, 3-H, 5-H), 8.28 (s, 1H, CHO).
Phenyl
formate
5a
1.5088
(30/0.1
approx.)
1.5072
(35/0.1) [6]
4a
4b
H
H
62
78
1734
–
13C NMR: δ = 121.1 (C-4), 126.4 (C-3, C-5),
129.7 (C-2, C-6), 149.9 (C-1), 159.4 (C=O).
1H NMR: δ = 2.36 (s, 3H, CH3), 6.92 (d, J =
7.5 Hz, 1H, 4-H), 6.93 (s, 1H, 2-H), 7.08 (d, J =
7.5 Hz, 1H, 6-H), 7.30 (t, J = 7.5 Hz, 1H, 5-H),
8.28 (s, 1H, CHO). – 13C NMR: δ = 21.3 (CH3),
118.0 (C-3), 121.7 (C-4), 127.2 (C-5), 129.4 (C-6),
140.1 (C-2), 149.9 (C-1), 159.5 (CHO).
3-Tolyl
3-CH3 formate
1.5008
(35/0.1
approx.) 20.5 torr) [1]
1.508
(95.5 – 98.5 / 1744
3-CH3
5b
1H NMR: δ = 7.01 (d, J = 2.1 Hz, 1H, 2-H), 7.08
(td, 3J = 7.4 Hz, 4J = 2.1 Hz, 1H, 4-H, 6-H), 7.41
(dd, J = 7.4 Hz, 1H, 5-H), 8.26 (s, 1H, CHO). –
13C NMR: δ = 114.8 (C-2), 119.2 (2C, C-4, C-6),
130.3 (C-5), 150.4 (2C, C-1, C-3), 158.7 (2 ×
C=O).
1,3-Phenylene
diformate
5c
1.5189
1.5175
4c
3-OH
4-OH
3-OCHO 72
4-OCHO 78
(66/0.1
1747
1724
(70/0.1) [1]
approx.)
1H NMR: δ = 7.17 (s, 4Harom.), 8.28 (s, 2H,
2 × CHO). – 13C NMR: δ = 122.4 (4 × Carom.),
147.6 (2C, C-1, C-4), 158.9 (2 × C=O). (1H NMR
(CCl4): δ = 8.60 (formyl H) [7]).
1,4-Phenylene
diformate
5d
1.5185
(m. p. 68 –
(55/0.1
4d
70) [7]
approx.)
1H NMR: δ = 3.78 (s, 3H, OCH3), 6.68 (d, J =
2.3 Hz, 1H, 2-H), 6.68 (dd, 3J = 8.2, 4J = 2.3 Hz,
2H, 4-H), 6.73 (dd, 3J = 8.2, 4J = 2.3 Hz, 1H,
6-H), 7.28 (dd, J = 8.2 Hz, 1H, 5-H), 8.27 (s, 1H,
CHO). – 13C NMR: δ = 55.5 (OCH3), 107.2 (C-3),
112.1 (C-4), 113.2 (C-5), 130.1 (C-6), 150.9 (C-2),
159.3 (C=O), 160.7 (C-1).
3-Methoxy-
phenyl
formate
5e
1.5188
1.5190
4e
3-OCH3
3-OCH3 77
(55/0.1
1736
1741
(57/0.1) [1]
approx.)
1H NMR: δ = 7.07 (dd, 3J = 8.0 Hz, 4J = 2.2 Hz,
2H, 2-H, 6-H), 7.35 (dd, 3J = 8.0 Hz, 4J = 2.2 Hz,
2H, 3-H, 5-H), 8.25 (s, 1H, CHO). – 13C NMR:
δ = 122.6 (2C, C-3, C-5), 129.7 (2C, C-2, C-6),
131.8 (C-4), 148.3 (C-1), 158.8 (C=O).
4-Chloro-
phenyl formate 3-Cl
5f
1.5301
1.5277
4f
3-Cl
68
(42/0.1
(45/0.1) [1]
approx.)
a 1H NMR at 250.1 MHz; 13C NMR at 62.9 MHz.
Scheme 1. (substituents are given in Table 1).
derivative 7 was isolated after hydrolysis as main prod- for the methine proton. The 13C NMR spectrum of 7
1
uct (yield: 40 %). Its H NMR spectrum shows a sin- also confirms this structure. The product 7 has been
glet for the two methoxy groups at δ = 3.78 ppm, a sin- prepared earlier [5a] from anisole and diformamide in
glet at δ = 8.23 for the formyl proton and at δ = 6.33 the presence of aluminum chloride.
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480
Note
tonitrile is evaporated in vacuum. Finally, the crude product
is distilled to give the corresponding pure aryl formates 5a – f
as colorless liquids (Table 1).
N-[Bis(4-methoxyphenyl)methyl]-formamide (7)
Sodium diformamide (2) (38.0 g, 0.4 mol) is dissolved
in 100 mL of 1,2-dichloroethane, and 22.9 g (0.2 mol) of
methanesulfonyl chloride (3) is added at 0 ◦C under stir-
ring. After completion of the addition, the reaction mixture
is stirred at r. t. for 2 h. Afterwards, 42.5 g (0.39 mol) of
anisole (6) and 51.9 g (0.39 mol) of AlCl3 are added, and
the mixture is refluxed for further 2 h. Completion of the re-
action is monitored by TLC. The reaction mixture is then
filtered to remove insoluble salts, and the filtrate is evapo-
rated under reduced pressure to afford the crude formamide 7
which is then recrystallized from ethanol. Yield 26.0 g
(40 %), colorless crystals with m. p. 148 – 149 ◦C (149 –
150 ◦C [4a]). – 1H NMR (CDCl3, 500.16 MHz): δ = 3.78 (s,
6H, 2 × OCH3), 6.21 (d, 1H, J = 8.17 Hz, CH–N), 6.33 (br, d,
1H, NH), 6.84 (d, 4H, J = 8.7 Hz, 2 × 2Harom.), 7.13 (d, 4H,
J = 8.7 Hz, 2 × 2Harom.), 8.23 (br, 1H, CHO). – 13C NMR
(CDCl3, 125.78 MHz): δ = 54.5 (CH–N), 55.3 (2 × OCH3),
114.0 (2 × 3-Carom. and 5-Carom.), 128.4 (2 × 2-Carom. and
6-Carom.), 133.4 (2 × 1-Carom.), 158.9 (2 × 4-Carom.), 160.1
(CHO).
Scheme 2.
Experimental Section
General procedure for the O-formylation of phenols
Sodium diformamide (2) (38.0 g, 0.4 mol) is dissolved
in 100 mL of anhydrous acetonitrile and 22.9 g (0.2 mol) of
methanesulfonyl chloride (3) is added at 0 ◦C. After comple-
tion of the addition the reaction mixture is stirred at room
temperature for 2 h. Afterwards, 0.1 mol of the correspond-
ing phenol is added, and the mixture is refluxed under stirring
for further 2 h. Completion of reaction is monitored by means
of TLC (silica gel pre-coated plastic sheets Polygram SIL
G/UV254, Macherey-Nagel GmbH; solvent system : toluene-
acetone (8 : 2); detection by UV irradiation at 254 nm). The
mixture is then filtered to remove the insoluble salts, and ace-
[5] a) W. Kantlehner, M. Vettel, A. Gissel, E. Haug,
G. Ziegler, M. Ciesielski, O. Scherr, R. Haas, J. Prakt.
Chem. 2000, 342, 297 – 310; b) W. Kantlehner,
G. Ziegler, M. Ciesielski, O. Scherr, M. Vettel,
Z. Naturforsch. 2001, 56b, 105 – 107; c) W. Frey,
W. Kantlehner, G. Ziegler, O. Scherr, Z. Kristallogr.
2001, 216, 97; d) A. Bagno, W. Kantlehner, O. Scherr,
J. Vetter, G. Ziegler, Eur. J. Org. Chem. 2001, 2947 –
2954.
[6] S. Sofuku, I. Muramatsu, A. Hagitani, Bull. Chem. Soc.
Japan 1967, 40, 2942 – 2945.
[7] D. H. Holsboer, J. W. Scheeren, A. P. M. Van der Veek,
Recl. Trav. Chim. Pays-Bas 1971, 90, 556 – 561.
[1] A compilation of methods for the preparation of aryl
formates and some of their synthetic applications can
be found in G. Ziegler, W. Kantlehner, Z. Naturforsch.
2001, 56b, 1172 – 1177.
[2] G. Ziegler, E. Haug, W. Frey, W. Kantlehner, Z. Natur-
forsch. 2001, 56b, 1178 – 1187.
[3] W. Kantlehner, Eur. J. Org. Chem. 2003, 2530 – 2546.
[4] a) A. Bagno, W. Kantlehner, R. Kreß, G. Saielli,
Z. Naturforsch. 2004, 59b, 386 – 397; b) A. Bagno,
W. Kantlehner, R. Kreß, G. Saielli, E. V. Stoyanov,
J. Org. Chem. 2006, 71, 9331 – 9340; c) A. Bagno,
W. Kantlehner, G. Saielli, J. Phys. Org. Chem. 2008,
accepted for publication.
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