Synthesis of 2-amino-4-(2-hydroxynaphthyl)-4H-chromene-3-carbonitriles by Michael addition and their transformaion into new pentacyclic compounds

Article abstract of DOI:10.1080/00397911.2014.924142

2-Amino-4-(2-hydroxynaphthyl)-4H-chromene-3-carbonitriles were synthesized by Michael addition of various 3-cyanoiminocoumarins and β-naphthol in good yield. The heterocyclization of these materials in an acidic medium leads new heterocyclic compounds, which have not previously been described, in moderate to good yields and good selectivity. The synthesized compounds were characterized by infrared, ¹H NMR, ¹³C NMR, two-dimensional NMR, and elemental analysis.

Full text of DOI:10.1080/00397911.2014.924142

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Synthesis of 2-Amino-4-(2-
hydroxynaphthyl)-4H-chromene-3-
carbonitriles by Michael Addition
and Their Transformation into New
Pentacyclic Compounds
Lamia Dammak a , Myriam Kammoun a , Houcine Ammar a , Souhir
Abid a & Rachid El Gharbi a
a Laboratoire de Chimie Appliquée: Hétérocycles, Corps Gras et
Polymères, Faculté des Sciences de Sfax , Université de Sfax , Sfax ,
Tunisia
Accepted author version posted online: 29 May 2014.Published
online: 06 Aug 2014.
To cite this article: Lamia Dammak , Myriam Kammoun , Houcine Ammar , Souhir Abid & Rachid El
Gharbi (2014) Synthesis of 2-Amino-4-(2-hydroxynaphthyl)-4H-chromene-3-carbonitriles by Michael
Addition and Their Transformation into New Pentacyclic Compounds, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 44:19, 2870-2878,
DOI: 10.1080/00397911.2014.924142
To link to this article: http://dx.doi.org/10.1080/00397911.2014.924142
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Synthetic Communications1, 44: 2870–2878, 2014
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2014.924142
SYNTHESIS OF 2-AMINO-4-(2-HYDROXYNAPHTHYL)-
4H-CHROMENE-3-CARBONITRILES BY MICHAEL
ADDITION AND THEIR TRANSFORMATION INTO NEW
PENTACYCLIC COMPOUNDS
Lamia Dammak, Myriam Kammoun, Houcine Ammar,
Souhir Abid, and Rachid El Gharbi
´
Laboratoire de Chimie Appliquee: Heterocycles, Corps Gras et Polymeres,
Faculte des Sciences de Sfax, Universite de Sfax, Sfax, Tunisia
´ ´
`
´
´
GRAPHICAL ABSTRACT
Abstract 2-Amino-4-(2-hydroxynaphthyl)-4H-chromene-3-carbonitriles were synthesized
by Michael addition of various 3-cyanoiminocoumarins and b-naphthol in good yield.
The heterocyclization of these materials in an acidic medium leads new heterocyclic
compounds, which have not previously been described, in moderate to good yields and good
selectivity. The synthesized compounds were characterized by infrared, 1H NMR, 13C
NMR, two-dimensional NMR, and elemental analysis.
Keywords 2-Amino-4H-chromene; heterocyclization; iminocoumarin; Michael addition;
b-naphthol
INTRODUCTION
In the past decades, the synthesis of heterocyclic compounds has been a subject
of great interest because of their wide applicability.[1–3] Heterocyclic compounds
occur very widely in nature and are essential to life.[4–6] Among the various hetero-
cyclic systems, the pyran ring is one of the most interesting and has been a widely
exploited skeleton for various synthetic transformations.[7–10] The benzopyran moi-
ety is a building block for a wide variety of natural products, bioactive molecules,
and dye compounds. They showed antitumor, antibiotic, anti-oxidant, antibacterial,
antiallergic, hypolipidemic, and immunomodulating activities.[11–14] A considerable
Received April 16, 2014.
Address correspondence to Houcine Ammar, Laboratoire de Chimie Appliquee: Heterocycles,
´ ´ ´
Corps Gras et Polymeres, Faculte des Sciences de Sfax, Universite de Sfax, Route Soukra, BP1170,
`
3000 Sfax, Tunisia. E-mail: houcine_fss@yahoo.fr
´
´
2870

SYNTHESIS OF PENTACYCLIC COMPOUNDS
2871
number of benzopyran derivatives have shown potent relaxant activity on blood
vessels, cardiac muscle, and other smooth muscles.[15–18] Recently, it was shown that
some natural products with a tricyclic benzopyran core structure belong to a new
class of inhibitors for bacterial metallo-b lactams.[19] This skeleton also exists in
the fungal metabolite fulvic acid.[20] Therefore, the development of efficient methods
for the synthesis of benzopyran tethered polyheterocycles is one of the most attract-
ive fields in organic chemistry.[21,22]
As a part of our research interest in the development of polycyclic compounds
consisting of a benzopyran fragment, we have focused on the reactivity of 3-cyano-2-
iminocoumarins and their derivatives toward (i) N-nucleophilic reagents such as
hydrazine, hydrazide, amine, and hydroxylamine to obtain benzopyranopyrimidines,
benzopyranopyrazoles, benzopyranoisoxazoles, and 3-triazolonyl iminocoumarins,
which could exhibit interesting biological activities[23–28] and (ii) C-electrophilic
reagents such as ethylchloroformate, acylchlorides, isocyanates, and thioisocyanates
to lead corresponding N-substituted iminicoumarins with proven optical
properties.[27,29–30]
As part of our program aimed at developing new methods for the preparation
of heterocyclic compounds, we report herein an efficient and simple process for
the synthesis of novel pentacyclic compounds in good yields by the condensation
reaction of b-naphthol and 3-cyanoiminocoumarins via a Michael addition followed
by an intramolecular cyclization in acid acetic. The choice of b-naphthol was based
on its well-documented role in pharmaceutical intermediate because of its wide use as
a disinfectant, a rubber auxiliary, and a dye auxiliary.[31]
RESULTS AND DISCUSSION
Our synthesis began with the condensation of salicylic aldehydes with malono-
nitrile in ethanol containing a catalytic amount of piperidine at room temperature to
give 3-cyanoiminocoumarins (1–7).[25] The obtained compounds were converted with
b-naphthol by Michael addition to 2-amino-4H-chromenes (8–14) and then some of
these derivatives (8–12) were transformed into the corresponding pentacyclic com-
pounds (15–19) by heterocyclization reaction with formic acid=toluene=methanol
under reflux (Scheme 1).
To determine the appropriate conditions for the maximum conversion
efficiency of 2-amino-4H-chromenes (8–14), several parameters such as reaction
time, temperature, basic catalysts, and organic solvent have been thoroughly studied
and analyzed. 3-Cyano-8-methoxyiminocoumarin (1) and b-naphthol were chosen as
a model system for this study. The best yield for 2-amino-4-(2-hydroxynaphthyl)-8-
methoxy-4H-chromene-3-carbonitriles 8 was obtained when the reaction was carried
out in chloroform at room temperature, using piperidine as catalyst reagent. The
crude product, which resulted after stirring the reaction mixture for one day, was iso-
lated by simple filtration with high selectivity and excellent yield (90%). Under the
optimized reaction conditions, derivatives 9–14 were obtained in isolated yields of
65–85% as described in Table 1.
To explain the formation of 2-amino-4-(2-hydroxynaphthyl)-8-methoxy-4H-
chromene-3-carbonitriles (8), we suggest in Scheme 2 a possible mechanism involving
in three steps: (i) The formation of enolate ion can be explained by acido-basic

2872
L. DAMMAK ET AL.
Scheme 1. Synthesis route to polycyclic compounds. Reagents and conditions: (a) EtOH, piperidine, rt;
(b) CHCl3, piperidine, rt; and (c) MeOH, toluene, formic acid, reflux, 12 h.
reaction between piperidine and b-naphthol, (ii) this nucleophile reacts with the elec-
trophilic pyranic cycle of iminocoumarin by Michael reaction, and (iii) proton
abstraction from protonated base by the enolate is the final step.
The important diagnostic bands in the infrared (IR) spectra of compound 8
were assigned and the band positions are compiled in the experimental section. This
compound gave medium-strength bands in the 2186 cmꢀ1 range, which can be attrib-
uted to the stretching vibration of the original CꢁN group excluding the cyclocon-
densation. The compound also showed the disappearance of original peak at
3289 cmꢀ1 corresponding to NH function,[25] as well as the appearance of an absorp-
tion bands at 3341 and 3517 cmꢀ1 related to NH2 and OH groups respectively. In the
1H NMR spectrum the disappearance of peaks at 8.34 ppm (H4) and 8.92 ppm (NH)
and the appearance of peaks at 5.61 and 6.42 attributed to the H4 and NH2 protons
respectively confirmed that the 1,4-addition have be observed.
In the second part these compounds were subsequently investigated for their
ability to transform into new heterocyclic products. Thus to optimize the reaction
conditions, we examined a series of preliminary runs on compound 8 modified oper-
ating conditions (solvent and acid). The best result was obtained when the
2-amino-4H-chromene 8 was refluxed in mixture of formic acid=methanol=toluene
medium. The desired product (15) was obtained in good yield after the imine

SYNTHESIS OF PENTACYCLIC COMPOUNDS
2873
Table 1. Synthesis of 2-amino-4H-chromene (8–14)
Compound Iminocoumarins[25] R5
R6
R7
R8
Time (days) Yielda (%) Mp (ꢂC)
8
9
1
2
3
4
5
6
7
H
H
H
H
H
H
H
H
H
OCH3
H
OCH3
H
1
2
90
80
85
65
70
60
80
>260
142
240
10
11
12
13
14
OCH3
Cl
H
8
H
H
10
2
>260
>260
>260
>260
H
N(Et)2
OH
H
H
H
H
2
H
8
aIsolated yield.
hydrolysis reaction (Scheme 3). The progress of the reaction was followed by the
changes in the IR spectra of samples, withdrawn at regular intervals from the reac-
tion media, which showed a decreasing of the absorption band characteristic of the
cyano function in the 3 position and the appearance of an intense absorption band at
1702 cmꢀ1 assigned to C O group resulting from the hydrolysis reaction.
=
The 1H NMR spectrum showed the disappearance of H4 and NH2 protons and
the appearance of the NH proton at 9.46 ppm corresponding to the imine function.
These spectroscopic data provide adequate evidence for the formation and structure
of the desired compound. However, the nonhydrolysis pyrane imine function
obtained from amino group is an unexplainable result. Hence, keeping these results
Scheme 2. Proposed mechanism of the 2-amino-4H-chromene (8).

2874
L. DAMMAK ET AL.
Scheme 3. Proposed mechanism of transformation 2-amino-4H-chromene into pentacyclic compounds
15–19.
in hand a tentative mechanism is proposed for the formation of the pentacyclic
compound (Scheme 3).
This initial success prompted us to investigate the transformation of other
2-amino-4H-chromenes (9–12) into corresponding heterocyclic compounds in the
same operating protocol. We obtained a series of new heterocyclic compounds
15–19 in moderate to good yields (30–70%) as described in Table 2.
Table 2. Synthesis of polycyclic compounds 15–19
Compound
R5
R6
R7
R8
Time (h)
Yielda (%)
Mp (ꢂC)
15
16
17
18
19
H
H
H
H
H
H
H
H
OCH3
H
OCH3
H
12
12
12
12
12
70
65
45
55
50
216
240
OCH3
Cl
H
260
>260
174
H
N(Et)2
H
H
H
aIsolated yield.

SYNTHESIS OF PENTACYCLIC COMPOUNDS
2875
In developing a one-pot method, the reactants such as 3-methoxy hydroxy-
benzaldehyde, malononitrile, and b-naphthol are mixed together in the presence of
piperidine as basic catalyst at room temperature using ethanol as an efficient solvent.
This method undergoes spontaneous cyclization, and 2-amino-4-(2-hydroxy-
naphthyl)-8-methoxy-4H-chromene-3-carbonitriles (8) was not isolated. This new
process was shown to have some advantages but the yields of heterocyclic compound
(15) thus obtained were relatively poor (30%).
CONCLUSION
We have presented a facile route for the formation of novel 2-amino-4-(2-
hydroxynaphthyl)-4H-chromene-3-carbonitriles via Michael addition. The obtained
products were transformed into pentacyclic compounds. The method developed in
this work is particularly interesting for the simplicity of providing this family of com-
pounds in good yield with high selectivity. Work is in progress to assess the biologi-
cal activities and the optical properties of these dyes.
EXPERIMENTAL
b-Naphthol was commercially available from Aldrich. 3-Cyano-iminocou-
marin 1–7 was prepared as previously described.[25] Ethanol and dichloromethane
(analytical grade) used for spectroscopic measurements were from VWR Prolabo
and SDS, respectively. The melting points were determined on an Electrothermal
9100 apparatus. Infrared spectra were registered on a Jasco FT-IR 420 spectrophot-
ometer apparatus using Perkin Elmer 100. 1H spectra were recorded on a Bruker WP
200 spectrometer operating at 300 and 75 MHz, respectively, in dimethylsulfoxide
(DMSO-d6) with tetramethylsilane (TMS) as internal standard (chemical shifts in
ppm). Elemental microanalysis were performed on a EA 1112 analyzer from CE
Instruments.
General Procedure for the Synthesis of 2-Aminobenzopyrans 8–14
A solution of b-naphthol (5 mmol) in 30 ml of chloroform with a catalytic
amount of piperidine was stirred with equipped a magnetic stirrer. After 5 min,
3-cyano-iminocoumarin 1–7 (5 mmol) was added and the reaction mixture was
stirred at room temperature during the time indicated in Table 1. After complete
reaction, the simple 2-amino-4H-chromene obtained was separated by filtration
and washed with chloroform.
2-Amino-4H-chromene (8)
1
White solid. IR (cmꢀ1): n ¼ 2186 (CꢁN), 3341–3450 (NH2), 3517 (OH). H
NMR (DMSO-d6): d ¼ 3.77 (s, 3H, OCH3), 5.61 (s, 1H, H4), 6.42 (d, J ¼ 7.20 Hz,
1H, H5), 6.59 (t, J ¼ 7.80 Hz, 1H, H6), 6.71 (d, J ¼ 7.20 Hz, 1H, H7), 6.88 (s, 2H,
NH2), 7.30 (d, J ¼ 9 Hz, 1H, HAr), 7.40–7.45 (m, 2H, HAr), 7.87–7.95 (m, 3H,
H
Ar), 9.03 (s, 1H, OH). 13C NMR (DMSO-d6): d ¼ 31.24, 55.68, 57.59, 109.59,
116.63, 116.71, 119.26, 120.33, 120.51, 123.13, 124.77, 126.97, 128.34, 128.89,

2876
L. DAMMAK ET AL.
130.53, 130.63, 132.21, 142.51, 146.90, 147.28, 160.10. Calculated for C21H16N2O3:
C, 73.24%; H, 4.68%; N, 8.13%. Found: C, 73.29%; H, 4.63%; N, 8.10%.
General Procedure for the Synthesis of Polycyclic Compounds 15–19
A mixture of 2-amino-4H-chromene 8–12 (5 mmol), methanol (6 ml), and tolu-
ene (15 ml) in the presence of formic acid (20 ml) was heated at 65 ꢂC for 12 h. The
mixture was cooled, and the precipitate filtered off and then washed with methanol.
Compound 15
White solid. IR (cmꢀ1): n ¼ 1592 (C C), 1616 (C N), 1752 (C O), 3394 (NH).
1H NMR (DMSO-d6): d ¼ 3.78 (s, 1H, OCH3), 5.50 (d, J ¼ 7.2 Hz, 1H, HAr), 5.75 (d,
J ¼ 7.2 Hz, 1H, HAr), 6. 55 (d, J ¼ 7.3 Hz, 1H, H5), 6.69 (t, J ¼ 7.8, 1H, H6), 6.87 (d,
J ¼ 7.8, 1H, H7), 7.42–7.57 (m, 2H, HAr), 7.90–8.02 (m, 2H, HAr), 9.46 (s, 1H, NH).
Calculated for C21H13NO4: C, 73.46%; H, 3.82%; N, 4.08%. Found: C, 73.40%; H,
3.90%; N, 4.04%.
=
=
=
FUNDING
The authors acknowledge the Ministry of Higher Education, Scientific
Research, and Technology in Tunisia for its financial support.
SUPPORTING INFORMATION
Supplemental data for this article can be accessed on the publisher’s website.
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