Synthesis and some transformations of 5-(N-tosylaminomethyl)furfuryl alcohols

Article abstract of DOI:10.1007/s10593-009-0302-y

Preparative methods were developed for the synthesis of 5-(N-tosylaminomethyl)furfuryl alcohols, and their behavior during the action of acidic catalysts was studied. It was established that the furan ring of these compounds is stable in the presence of o

Full text of DOI:10.1007/s10593-009-0302-y

Chemistry of Heterocyclic Compounds, Vol. 45, No. 5, 2009
SYNTHESIS AND SOME TRANSFORMATIONS
OF 5-(N-TOSYLAMINOMETHYL)FURFURYL
ALCOHOLS
T. A. Stroganova1* and A. V. Butin1
Preparative methods were developed for the synthesis of 5-(N-tosylaminomethyl)furfuryl alcohols, and
their behavior during the action of acidic catalysts was studied. It was established that the furan ring of
these compounds is stable in the presence of orthophosphoric acid in glacial acetic acid and that their
hydroxyl and N-tosylaminomethyl groups are involved in the transformations.
Keywords: N-tosylaminomethylfuran, furylmethanols, furfurylamine, acylation, acid catalysis,
formylation.
Among the various furan derivatives furan alcohols (furylmethanols), which are widely used in fine
organic synthesis, are of great interest. There are two main transformation paths for these compounds, i.e., with
retention of and with opening of the furan ring.
One transformation of the first type often encountered in the literature is the self-condensation of
furylmethanols, leading to the formation of symmetrical difurylmethane structures [1-4].
The reactions of furan alcohols taking place with opening of the heterocycle have found considerably
wider application. Numerous papers have been devoted to intramolecular Diels–Alder reactions in which the
furan acts as 1,3-diene [5, 6]. Such approaches have been used actively for the construction of the carbocyclic
frameworks of natural compounds and their synthetic analogs [7, 8] and also for the formation of condensed
heterocyclic systems [9].
The oxidative opening of the furan ring in 2-furylmethanols (the Akhmatovich reaction) has been used
successfully in the synthesis of heterocycles [10-13]. The reaction products are derivatives of pyranone –
convenient precursors for the production of sugars [14] and various biologically active compounds [15-19].
Examples of the protolytic opening of the furan ring are not so numerous, and this is probably explained
by the well-known acidophobic nature of furan compounds and also by the possibility of self-condensation of
furfuryl alcohols and the formation of difurylmethane structures [1, 3, 5]. With the fortuitous choice of
conditions, however, the transformation provides a convenient method for the synthesis of heterocyclic systems
[20].
_______
* To whom correspondence should be addressed, e-mail: strog@kubstu.ru.
1Department of Organic Chemistry, Kuban State University of Technology, Krasnodar 350072, Russia.
__________________________________________________________________________________________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 671-679, May, 2009. Original
article submitted June 24, 2007. Revision submitted February 23, 2008.
524
0009-3122/09/4505-0524©2009 Springer Science+Business Media, Inc.

In the present work we present the results from a study of the transformations of 5-(N-tosyl-
aminomethyl)furfuryl alcohols 1-3 in acetic acid in the presence of orthophosphoric acid. Since furfurylamines,
like furylmethanols, are widely used for the production of various nitrogen-containing heterocycles [21-24], it
was of undoubted interest to investigate the mutual effect and possible competition of two nucleophilic
substituents present in one furan ring.
The alcohols 1-3 were synthesized on the basis of N-tosylaminomethylfuran 4, which was obtained by
the tosylation of furfurylamine.
The formylation of compound 4 and reduction of the obtained aldehyde 5 with NaBH4 led to the alcohol 1.
NaBH4
EtOH
HCONMe2
POCl3
O
O
O
O
NH–Ts
NH–Ts
HO
NH–Ts
4
5
1
The secondary alcohol 2 was synthesized by the acylation of compound 4 with acetic anhydride
followed by reduction of the acetyl derivative 6 with NaBH4.
NaBH4
EtOH
Me
Me
HO
Ac2O
4
O
O
Mg(ClO4)2
O
NH–Ts
NH–Ts
6
2
The secondary alcohol 3 was obtained from the corresponding aryl furyl ketone 7, which was synthesized
by acylation of the tosylate 4 with p-toluoyl chloride in the presence of aluminium chloride (yield 57%).
Me
Me
Cl
NaBH4
AlCl3
4
Me
+
EtOH/THF
O
O
O
O
NH–Ts
HO
NH–Ts
7
3
The composition and structure of compounds 1-3 and 5-7 agree with the results from elemental analysis
and 1H NMR spectra (Tables 1 and 2).
Preliminary investigation of the behavior of the alcohols 1-3 in various solvent–catalyst systems
(AcOH–H3PO4, AcOH–HCl, dioxane–HClO4) showed that each of the compounds 1-3 under various conditions
gave a mixture of identical products and that appreciable resinification of the reaction mixture was always
observed. For subsequent investigations we chose the AcOH–H3PO4 system, in which resin formation was
lowest.
The treatment of furfuryl alcohol 1 with phosphoric acid in glacial acetic acid gave a mixture of
products, from which compounds 8-11 were isolated by column chromatography (Tables 1 and 2).
The main products of this transformation were difurylmethane 8 and the ester 9. The formation of the
difurylmethane 8 (yield 33%) is explained by the already mentioned tendency of furfuryl alcohols to undergo
self-condensation during the action of a mineral acid. The fairly high yield of the ester 9 (25%) demonstrates the
ease of esterification of the primary alcohol under the selected conditions.
525

TABLE 1. The Physicochemical Characteristics of the Synthesized
Compounds
Found, %
——————
Calculated, %
Com-
pound
Empirical
formula
mp, °C
Yield, %
С
Н
N
1
C13H15NO4S
C14H17NO4S
C20H21NO4S
C13H13NO4S
C14H15NO4S
C20H19NO4S
C25H26N2O6S2
C15H17NO5S
C13H13NO3S
C14H15NO3S
C20H19NO3S
55.47
55.50
56.89
56.93
64.64
64.67
55.92
55.90
57.31
57.32
65.05
65.02
58.42
58.35
55.67
55.72
5.40
5.37
5.76
5.80
5.76
5.70
4.71
4.69
5.17
5.15
5.17
5.18
5.02
5.09
5.32
5.30
5.00
4.98
4.78
4.74
3.75
3.77
4.97
5.01
4.73
4.77
3.81
3.79
5.46
5.44
4.29
4.33
100-102
113-114
159-161
84-86
83
84
74
84
81
57
33
25
22
39
42
2
3
5
6
91-92
7
137-138
96-98
8
9
115-116
120-122
148-149
193-195
11
12
15
59.33
59.30
60.65
60.63
68.02
67.97
5.00
4.98
5.40
5.45
5.55
5.42
5.28
5.32
5.10
5.05
3.93
3.96
AcOH / H3PO4
1
+
NH–Ts
+
+
Me
Me
O
O
O
O
O
O
Ts–NH
O
NH–Ts
O
N–Ts
8
10
11
9
Me
The formation of 5-methylfurfural (10) is obviously due to protonation at the nitrogen atom of the amide
group and removal of the tosylamide molecule. Redistribution of electron density in the obtained cation leads to
the ejection of a proton and rearrangement of the produced enol with restoration of the furan aromatic system.
Evidence for such a mechanism is provided by the discovery of tosylamide in the reaction mixture (TLC, in
comparison with an authentic sample).
H+
H
H
1
CH2
+
10
O
O
+
O
–H
–TsNH2
HO
NH–Ts
+
HO
HO
H
Analogous transformations probably provide the basis for the formation of the imine 11. In this case the
reaction begins with protonation of the hydroxyl group of the alcohol 1.
H+
H
11
1
H2C
+
H
O
O
O
+
–H
– H2O
O
+
NH–Ts
N–Ts
H
N–Ts
H
H
H
526

TABLE 2. The 1H NMR Spectra of the Synthesized Compounds
Com-
pound
Chemical, δ, ppm (J, Hz)
1
2
3
5
6
2.43 (3Н, s, CH3*); 4.16 (2Н, d, J = 5.5; CH2N); 4.56 (2Н, s, CH2O);
4.92 (2H, br. s, NH, OH); 6.06 (1H, d, J = 3.2, H Het); 6.11 (1H, d, J = 3.2, H Het);
7.29 (2H, d, J = 7.8, H Ts); 7.73 (2H, d, J = 7.8, H Ts)
2.22 (3Н, d, J = 6.2, CH3); 2.43 (3Н, s, CH3*); 4.30 (1Н, br. s, CHO); 4.55 (2Н, s, CH2N);
4.86 (2H, br. s, NH, OH); 6.32 (1H, d, J = 3.2, H Het); 6.44 (1H, d, J = 3.2, H Het);
7.24 (2H, d, J = 7.8, H Ts); 7.60 (2H, d, J = 7.8, H Ts)
2.42 (3Н, s, CH3*); 2.47 (3Н, s, CH3); 4.26 (1Н, br. s, CHO); 4.53 (2Н, s, CH2N);
4.92 (2H, br. s, NH, OH); 6.22 (1H, d, J = 3.2, H Het); 6.41 (1H, d, J = 3.2, H Het);
7.17 (4Н, m, H Tol); 7.26 (2H, d, J = 7.8, H Ts); 7.63 (2H, d, J = 7.8, H Ts)
2.40 (3Н, s, CH3*); 4.46 (2Н, s, CH2N); 4.92 (1H, br. s, NH); 6.16 (1H, d, J = 3.2, H Het);
6.25 (1H, d, J = 3.2, H Het); 7.26 (2H, d, J = 7.8, H Ts); 7.66 (2H, d, J = 7.8, H Ts);
9.24 (1H, s, CH=O)
2.41 (3Н, s, CH3*); 2.49 (3Н, s, CH3); 4.47 (2Н, s, CH2N); 4.96 (1H, br. s, NH);
6.13 (1H, d, J = 3.2, H Het); 6.29 (1H, d, J = 3.2, H Het); 7.26 (2H, d, J = 7.8, H Ts);
7.63 (2H, d, J = 7.8, H Ts)
7
8
2.40 (3Н, s, CH3*); 2.53 (3Н, s, CH3); 4.51 (2Н, s, CH2N); 4.96 (1H, br. s, NH);
6.12 (1H, d, J = 3.2, H Het); 6.38 (1H, d, J = 3.2, H Het); 7.26−7.57 (8H, m, H Ar)
2.42 (6Н, s, CH3*); 3.71 (2Н, s, CH2); 4.12 (4Н, d, J = 5.7; CH2N); 4.82 (2H, br. s, NH);
5.86 (2H, d, J = 3.2, H Het); 6.23 (2H, d, J = 3.2, H Het); 7.26 (4H, d, J = 7.8, H Ts);
7.71 (4H, d, J = 7.8, H Ts)
9
2.07 (3Н, s, CH3); 2.43 (3Н, s, CH3*); 4.18 (2Н, d, J = 6.0, CH2N); 4.79 (1H, br. s, NH);
4.90 (2H, s, CH2O); 6.08 (1H, d, J = 3.2, H Het); 6.23 (1H, d, J = 3.2, H Het);
7.28 (2H, d, J = 7.8, H Ts); 7.73 (2H, d, J = 7.8, H Ts)
11
12
2.43 (6Н, s, CH3, CH3*); 6.29 (1H, d, J = 3.2, H Het); 7.24 (1H, d, J = 3.2, H Het);
7.32 (2H, d, J = 8.0, H Ts); 7.87 (2H, d, J = 8.0, H Ts); 8.71 (1H, s, CH=N)
2.18 (3Н, t, J = 7.6, CH3); 2.43 (3Н, s, CH3*); 2.51 (2Н, q, J = 7.6, СН3CH2);
6.39 (1H, d, J = 3.2, H Het); 6.95 (1H, d, J = 3.2, H Het); 7.33 (2H, d, J = 8.0, H Ts);
7.67 (2H, d, J = 8.0, H Ts); 8.79 (1H, s, CH=N)
15
2.20 (3Н, s, CH3); 2.42 (3Н, s, CH3*); 3.60 (2Н, s, CH2); 6.49 (1H, d, J = 3.2, H Het);
6.90 (1H, d, J = 3.2, H Het); 7.08 (2H, d, J = 8.1, H Tol); 7.21 (2H, d, J = 8.1, H Tol);
7.33 (2H, d, J = 8.0, H Ts); 7.67 (2H, d, J = 8.0, H Ts); 8.93 (1H, s, CH=N)
_______
*CH3 in Ts.
A similar mechanism was considered earlier to explain the formation of methylfurfural during the
treatment of 2,5-dihydroxymethylfuran with an alcohol solution of HCl under the conditions of the Marckwald
reaction [25].
Two products, i.e., the imine 12 and acetylsilvan 13, were obtained with yields of 39 and 46%
respectively as a result of treatment of the alcohol 2 with H3PO4 in acetic acid.
It is clear that the mechanisms of formation of compounds 12 and 13 are similar to those examined
above for compounds 10 and 11.
H3PO4
Me
Me
2
Me
+
O
O
AcOH
N–Ts
O
12
13
The presence of trace quantities of a product with a difurylmethane structure in the reaction mixture was
also detected by TLC (a characteristic color with bromine vapor), but it was not possible to isolate it by column
chromatography.
527

We supposed that the reaction of the alcohol 3 with orthophosphoric acid would not lead to a derivative
of difurylmethane since it had previously been established [26] that arylfurylmethanols do not form
difurylmethane structures under acidic conditions. Actually, two products were obtained as a result of the
reaction of the alcohol with an acidic catalyst – the ketone 14 and the imine 5 – with yields of 41 and 42%
respectively. The structure of the ketone was confirmed by an alternative synthesis by the acylation of toluene
with 5-methylpyromucic chloride in the presence of aluminium chloride.
Me
Me
H3PO4
AcOH
3
Me
+
O
O
N–Ts
O
15
14
The composition and structure of the products from the transformations of compounds 1-3 agree with
the results from elemental analysis and the 1H NMR spectra (Table 2).
Thus, our results from study of the behavior of 5-(N-tosylaminomethyl)furfuryl alcohols indicate that
the furan ring does not undergo any transformations under the selected conditions while all the transformations
of the alcohols take place with the participation of the hydroxymethyl and N-tosylaminomethyl groups.
EXPERIMENTAL
The 1H NMR spectra were recorded on a Brucker AMX-400 instrument (400 MHz) in CDCl3 with TMS
as internal standard. Thin-layer chromatography was performed on Silufol UV-254 plates and Sorbfil (OOO
"Sorbpolimer") with iodine and bromine vapor and 2,4-dinitrophenylhydrazine as developer. For column
chromatography we used silica gel KSK ("Sorbpolimer") (50-100 µ).
2-(N-Tosylaminomethyl)furan (4). To a mixture of furfurylamine (9.7 g, 100 mmol) and pyridine
(12 ml, 150 mmol) we added p-toluenesulfonyl chloride (28.5 g, 150 mmol). The reaction mass was kept at
30-35°C until the initial furfurylamine had disappeared (TLC, 1:2 acetone–petroleum ether) and was then
poured into water. The precipitate was filtered off, dried in air, and recrystallized from 3:1 mixture of methylene
chloride and hexane. We obtained 22.3 g (89%) of the product 4 in the form of colorless crystals melting at
111-112°C.
5-(N-Tosylaminomethyl)furfural (5). To a mixture of compound 4 (2.51 g, 10 mmol) and DMF
(10 ml) with stirring and cooling in iced water we added dropwise over 30 min POCl3 (2.8 ml, 30 mmol). The
mixture was stirred at 40-45°C until the initial compound 4 had completely disappeared (TLC, 1:2 acetone–
petroleum ether). The reaction mass was poured into iced water and neutralized carefully by the addition of dry
sodium carbonate, after which it was extracted with ethyl acetate (3×20 ml). The extract was washed with
sodium carbonate solution and with water and dried with sodium sulfate. Activated carbon was then added, and
the suspension was filtered through a thin layer of silica gel. The filtrate was evaporated on a rotary evaporator
to a quarter of its initial volume, and after crystallization (2.34 g) of the furfural 5 was obtained in the form of
fine colorless needles.
5-Acetyl-2-(N-tosylaminomethyl)furan (6). A mixture of compound 4 (5 g, 20 mmol), acetic
anhydride (15 ml), and Mg(ClO4)2 (anhydrone) (2.23 g, 10 mmol) was boiled with a reflux condenser until the
initial compound 4 had disappeared. The cooled reaction mixture was then poured into iced water (200 ml) and
neutralized with NaHCO3. The crystalline precipitate was filtered off, washed with sodium carbonate solution
and with water, dried in air, and recrystallized from a 3:1 mixture of methylene chloride and petroleum ether,
and 2.37 g of the product 6 was obtained in the form of colorless crystals.
528

5-(4-Methylbenzoyl)-2-(N-tosylaminomethyl)furan (7). To a suspension of anhydrous aluminium
chloride (2.0 g, 15 mmol) in dry methylene chloride (20 ml) with stirring and cooling with ice we slowly added
dropwise 4-methylbenzoyl chloride (1.7 ml, 13 mmol). We then added in portions compound 4 (3.14 g,
12.5 mmol) at such a rate that the temperature of the reaction mixture did not exceed 25°C. The reaction mixture
was stirred at room temperature for 4 h, after which it was carefully poured onto 50 g of crushed ice, 5-7 ml of
concentrated hydrochloric acid was added, and the product was extracted with methylene chloride (5×20 ml).
The extracts were washed with water, 2% sodium hydroxide solution, and again with water, and dried over
sodium sulfate, and the solvent was distilled. The solid residue was dissolved in a 7:2 mixture of methylene
chloride and petroleum ether, and the hot solution was passed through a layer of silica gel. The white crystals
that separated after cooling were filtered off, and 2.36 g of the product 7 was obtained.
Reduction of Compounds 5 and 6 (General Method). To a solution of compound 5 or 6 (5 mmol) in
ethanol (40 ml) we added in small portions finely divided NaBH4 (0.1 g, 2.5 mmol). The reaction mass was
heated to boiling. The heating was then stopped, and after 10 min 150 ml of water was added. The obtained
mixture was carefully acidified to pH ~6-7 with dilute hydrochloric acid and extracted with methylene chloride
(3×20 ml). The extract was dried over sodium sulfate, the solvent was evaporated on a rotary evaporator, the
residue was crystallized from a 3:1 mixture of methylene chloride and petroleum ether, and 5-hydroxymethyl-
2-(N-tosylaminomethyl)furan (1) (1.16 g) or 5-(1-hydroxyethyl)-2-(N-tosylaminomethyl)furan (2) (1.24 g)
was obtained in the form of a fluffy white cotton.
5-[Hydroxy-(4-methylphenyl)methyl]-2-(N-tosylaminomethyl)furan (3). A mixture of compound 7
(1.85 g, 5 mmol), ethanol (5 ml), THF (20 ml), and finely divided NaBH4 (0.3 g, 7.5 mmol) was boiled with a
reflux condenser for 1 h and cooled, and 100 ml of water was added. The mixture was carefully acidified to pH
~6-7 with dilute hydrochloric acid and extracted with methylene chloride (3×25 ml). The extract was dried over
sodium sulfate, the solvent was evaporated on a rotary evaporator, the residue was crystallized from a 4:1 mixture
of methylene chloride and petroleum ether, and alcohol 3 (1.37 g) was obtained in the form of a white powder.
Reaction of Compounds 1-3 with Orthophosphoric Acid in Glacial Acetic Acid. A mixture of
compound 1, 2, or 3 (0.5 g), glacial acetic acid (8 ml), and orthophosphoric acid (0.6 ml) was boiled with a
reflux condenser until the initial alcohol had disappeared (TLC, 1.5:7:16 acetone–methylene chloride–petroleum
ether). The cooled reaction mixture was poured into 100 ml of cold water, sodium bicarbonate was added to
pH~7, and the product was extracted with methylene chloride (3×10 ml). The extract was dried with anhydrous
sodium sulfate, and the solvent was evaporated to 3-4 ml on a rotary evaporator. The obtained solution was
applied to a column of silica gel. Chromatographic separation of the reaction products from the transformation
of the alcohol 1 (eluant 1.5:7:16 acetone–methylene chloride–petroleum ether) gave the following compounds:
2-(N-tosylaminomethyl)-5-[5-(N-tosylaminomethyl)-2-furylmethyl]furan (8) (0.15 g). IR spectrum, ν, cm−1:
3300 (NH–Ts). 5-(N-Tosylaminomethyl)-2-furylmethyl acetate (9) (0.145 g). IR spectrum, ν, cm−1: 1737
(C=O), 3296 (NH–Ts). 5-Methyl-2-(N-tosylaminomethyl)furan (11) (0.104 g). IR spectrum, ν, cm−1: 1646
(C=N–Ts). 5-Methylfurfural (10) (0.027 g, 13%). Compound 10 was identified by comparison with an
authentic sample (TLC, 1.5:7:16 acetone–methylene chloride–petroleum ether).
Chromatography of the products obtained from the alcohol 2 (4:7:30 acetone–methylene chloride–
petroleum ether) gave the following compounds: 5-ethyl-2-(N-tosyliminomethyl)furan (12) (0.184 g). IR
spectrum, ν, cm−1: 1643 (C=N–Ts). 2-Acetyl-5-methylfuran (13) (0.100 g) identical with an authentic sample
(TLC, 14:7:30 acetone–methylene chloride–petroleum ether).
Chromatography of the products from the transformations of compound 3 (2:5 ethyl acetate–petroleum
ether) gave the following: 5-(4-methylbenzyl)-2-(N-tosyliminomethyl)furan (15) (0.205 g). IR spectrum, ν,
cm−1: 1642 (C=N–Ts). 4-Methylphenyl-5-methylfuran-2-yl-methanone (14) (0.103 g), identical (TLC, 2:5
ethyl acetate–petroleum ether) with a sample synthesized by the acylation of toluene (20 ml) with
5-methylpyromucic chloride (13 mmol) in the presence of aluminium chloride (15 mmol) at 20-25°C. The
1H NMR spectrum of this sample was identical with that described in the literature for the ketone 14 [27].
529

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