A simple synthesis of 2-{(Arylmethylidene)hydrazinylidene]-3-hydroxy-4H- furo[3,2-c]pyran-4(3H)-ones

Article abstract of DOI:10.1002/hlca.201200419

A simple synthesis of 2-hydrazinylidene-3-hydroxy-4H-furo[3,2-c]pyran-4- ones is described. A mixture of (isocyanoimino)(triphenyl)phosphorane, an aromatic aldehyde, and dehydroacetic acid (=3-acetyl-2-hydroxy-6-methyl-4H- pyran-4-one) undergo a 1: 1: 1 addition reaction under mild conditions to afford the title compounds in excellent yields. Copyright

Full text of DOI:10.1002/hlca.201200419

Helvetica Chimica Acta – Vol. 96 (2013)
675
A Simple Synthesis of 2-{(Arylmethylidene)hydrazinylidene]-3-hydroxy-4H-
furo[3,2-c]pyran-4(3H)-ones
by Mehdi Adib*a), Samira Ansaria), Long-Guan Zhub), and Mehdi Rahimi-Nasrabadic)
a) School of Chemistry, University College of Science, University of Tehran, P.O. Box 14155 – 6455,
Tehran, Iran (phone/fax: þ 98-21-66495291; e-mail: madib@khayam.ut.ac.ir)
b) Chemistry Department, Zhejiang University, Hangzhou 310027, P. R. China
c) Department of Chemistry, Imam Hossein University, Tehran, Iran
A simple synthesis of 2-hydrazinylidene-3-hydroxy-4H-furo[3,2-c]pyran-4-ones is described. A
mixture of (isocyanoimino)(triphenyl)phosphorane, an aromatic aldehyde, and dehydroacetic acid (¼ 3-
acetyl-2-hydroxy-6-methyl-4H-pyran-4-one) undergo a 1:1:1 addition reaction under mild conditions to
afford the title compounds in excellent yields.
Introduction. – Furo[3,2-c]pyrans, fused five/six-membered heterocyclic com-
pounds with two O-atoms (in positions 1 and 5), are of interest because of the
occurrence of their saturated and partially saturated derivatives in biologically active
compounds and natural products. For example, patulin, 4-hydroxy-4H-furo[3,2-
c]pyran-2(6H)-one (Fig. 1), is a mycotoxin produced by several species of Penicillium,
Aspergillus, and Byssochlamys fungi, with the most commonly encountered species
being Penicillium expansum [1]. It occurs in unfermented apple juice, grape juice, and
field crops [2]. It has antibiotic properties and has been shown to be carcinogenic and
mutagenic, and it causes chromosome damage in biological systems [3].
Fig. 1. Structure of Patulin
The most common synthetic approaches reported for the preparation of furo[3,2-
c]pyran ring systems involve: intramolecular Claisen condensation of 2-ketomethyl-
furan-3-carboxylates [4], anhydropyranose annulation [5], CAN (ceric ammonium
nitrate; (NH4)2Ce(NO3)6)-mediated reaction of 4-hydroxy-2H-pyran-2-ones with
alkenes or alkynes [6], reaction between tetrahydro-2-oxofuran-3-yl propanoate and
benzaldehyde in the presence of a base via a modified benzilic acid rearrangement [7],
cyclization of 3-[3-(dimethylamino)prop-2-enoyl]-4-hydroxy-2H-pyran-2-ones in the
presence of SOCl2 [8], and reaction of 3,4-dihydro-2H-pyran-4-ol with 1,2-dibro-
moethyl ether, followed by radical cyclization of the intermediate [9].
ꢀ 2013 Verlag Helvetica Chimica Acta AG, Zꢁrich

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There are several reports on the use of (isocyanoimino)(triphenyl)phosphorane
(Ph3PNNC; 1; Scheme 1) in syntheses of metal complexes [10][11]. Recently, syntheses
of 1,3,4-oxadiazepines [12a], 2-aryl-1,3,4-oxadiazoles [12b], a-keto-1,3,4-oxadiazoles
[12c], 3-(5-aryl-1,3,4-oxadiazol-2-yl)-3-hydroxybutan-2-ones [12d], N2,N2-dicyclohex-
yl-5-aryl-1,3,4-oxadiazole-2-carboximidamides [12e], 1-chloro-2-(5-aryl-1,3,4-oxadi-
azol-2-yl)propan-2-amines [12f], 2-(arylamino)-2-(5-aryl-1,3,4-oxadiazol-2-yl)propyl
benzoates (and acetates) [12g], and N-benzyl-N-[1-(5-aryl-1,3,4-oxadiazol-2-yl)cyclo-
butyl]amines [12h] by using 1 in multicomponent reactions (MCRs) were reported.
Scheme 1. One-Pot Three-Component Synthesis of 2-[(Arylmethylidene)hydrazinylidene]-3-hydroxy-
4H-furo[3,2-c]pyran-4(3H)-ones 4
As part of our current studies on new routes for the preparation of biologically
active heterocyclic compounds from readily available building blocks [13], we have
described the syntheses of 2-aryl-5-(hydroxyalkyl)-1,3,4-oxadiazoles [14a], 3-(1-
hydroxyalkyl)[1,2,4]triazolo[4,3-c]quinazolines [14b], 3-(5-aryl/alkyl-1,3,4-oxadiazol-
2-yl)-3-hydroxy-1,3-dihydro-2H-indol-2-ones [14c], 3-aryl-1-(arylmethylideneamino)-
pyrrolidine-2,5-diones [14d], and 3,4-disubstituted N-aminopyrrolidine-2,5-diones
[14e] by using 1 in MCRs.
Results and Discussion. – We report herein an efficient synthesis of functionalized
4H-furo[3,2-c]pyranes. Thus, a mixture of 1, an aldehyde 2, and 3-acetyl-6-methyl-2H-
pyran-2,4(3H)-dione (dehydroacetic acid, 3) underwent a 1:1:1 addition reaction in
CH2Cl2 at room temperature to afford the corresponding 2-(arylmethylidenehydrazi-
nylidene)-3-hydroxy-4H-furo[3,2-c]pyran-4(3H)-ones 4a – 4l in 85 – 94% yields
1
(Scheme 1 and Table). All the reactions went to completion within 4 h. H-NMR
Analysis of the reaction mixtures clearly indicated formation of the corresponding 4H-
furo[3,2-c]pyran-4-ones 4 in excellent yields.
Table. Synthesis of 4H-Furo[3,2-c]pyran-4-ones 4a – 4l
Product
Ar
Yield [%]a)
Product
Ar
Yield [%]a)
4a
4b
4c
4d
4e
4f
4-O2NꢀC6H4
4-FꢀC6H4
94
91
93
90
88
86
4g
4h
4i
4j
4k
4l
Pyridin-4-yl
4-ClꢀC6H4
4-BrꢀC6H4
Thiophen-2-yl
Ph
89
95
92
85
89
90
3-ClꢀC6H4
3-MeOꢀC6H4
Furan-2-yl
3,4-(MeO)2C6H3
4-MeꢀC6H4
a) Yields of the isolated products.

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1
The structures of the isolated products were deduced on the basis of their IR, H-
and 13C-NMR, and mass spectra, and elemental analysis. The mass spectrum of 4i
displayed the molecular ion (Mþ) peaks at m/z 378 and 376, consistent with a 1:1:1
product of 1, 3, and 4-bromobenzaldehyde after losing Ph3P¼O. The IR spectrum of 4i
showed absorptions at 3293, 1729, 1712, and 1636 cmꢀ1 indicating the presence of OH,
1
C¼O, and C¼N functionalities. The H-NMR spectrum of 4i exhibited four sharp
singlets at 1.82 and 2.33 ppm due to the Me groups, 6.43 ppm arising from OC¼CH
moiety, and 8.35 ppm for the aldimine H-atom. A fairly sharp signal appeared at
5.25 ppm (exchangeable by D2O addition) for the OH group along with the
characteristic signals with appropriate chemical shifts and coupling constants for the
four aromatic H-atoms of the 4-bromophenyl substituent. The 1H-decoupled 13C-NMR
spectrum of 4i showed 14 distinct resonances in agreement with the proposed structure
(see Exper. Part).
Single-crystal X-ray analysis of 4i conclusively confirmed its structure and, by
analogy, those of other isolated products. An ORTEP diagram of 4i is shown in
Fig. 21).
Fig. 2. ORTEP Diagram of the molecular structure of 4i
A plausible mechanism for the reaction is provided in Scheme 2. On the basis of the
well-established chemistry of isocyanides [15 – 19], it is reasonable to assume that the
first step may involve conjugate addition of the isocyanide 1 on the enol form of
dehydroacetic acid 3b and formation of the enolate intermediate 5, followed by
intramolecular nucleophilic addition of the enolate to the nitrilium moiety and
cyclization to give the iminolactone intermediate 6. Aza-Wittig reaction of this
1
)
Selected X-ray crystallographic data for compound 4i: C16H13O4N2Br, monoclinic, space group P21/
c, a ¼ 11.319(3) ꢂ, b ¼ 7.9512(19) ꢂ, c ¼ 17.502(4) ꢂ, b ¼ 92.264(4)8, V¼ 1573.9(7) ꢂ3, T¼ 295(2) K,
Z ¼ 4, Dcalc. ¼ 1.583 g cmꢀ3, m ¼ 2.629 mmꢀ1, 1368 observed reflections, final R1 ¼ 0.055, wR2 ¼ 0.139,
and for all data R1 ¼ 0.143, wR2 ¼ 0.200. CCDC-755586 contains the supplementary crystallographic
data for this article. These data can be obtained free of charge from the Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data request/cif.

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Scheme 2. Proposed Mechanism
intermediate with the aldehyde 2 would afford the 4H-furo[3,2-c]pyran-4(3H)-ones 4
by removal of Ph3P¼O.
In conclusion, we have developed a simple reaction between (isocyanoimino)-
(triphenyl)phosphorane, aromatic aldehydes and dehydracetic acid for the efficient
synthesis of 4H-furo[3,2-c]pyran-4-ones, which are of potential synthetic and
pharmacological interest. The reactions have been performed under neutral conditions,
and the substances have been mixed without any activation or modification.
This work was supported by the Research Council of the University of Tehran as research project
(6102036/1/03).
Experimental Part
General. All the chemicals were obtained from Merck (Germany), and were used without further
purification. (Isocyanoimino)(triphenyl)phosphorane (1) was prepared according to [10]. Column
chromatography (CC): silica gel 60 (Merck). M.p.: Electrothermal 9100 apparatus; uncorrected. IR
Spectra: Shimadzu IR-460 spectrometer; ˜n in cmꢀ1. 1H- and 13C-NMR spectra: Bruker DRX-500 Avance
(at 500.1 and 125.8 MHz, resp.) and Bruker DPX-250 (at 250.1 and 62.9 MHz, resp.) instruments; in
(D6)DMSO or (D6)acetone soln. ; d in ppm rel. to Me4Si as internal standard, J in Hz. EI-MS (20 eV):
Agilent Technologies (HP) 5973 mass spectrometer; in m/z (rel. %). Elemental analyses: Heraeus CHN-
O-Rapid analyzer. X-Ray crystallography: Bruker SMART diffractometer; CCD area detector; graphite
monochromatized MoKa radiation.
General Procedure for the Preparation of Compounds 4. A soln. of the appropriate aldehyde 2
(1 mmol), 1 (0.302 g, 1 mmol), and 3-acetyl-6-methyl-2H-pyran-2,4(3H)-dione (¼dehydroacetic acid, 3;
0.168 g, 1 mmol) in CH2Cl2 (4 ml) was stirred at 258 for 4 h. After complete conversion to the
corresponding 4H-furo[3,2-c]pyran-4-one (TLC monitoring), the precipitated product (in the case of
compounds 4a – 4h) was filtered and washed with CH2Cl2 (2 ꢁ 2 ml). For the other compounds, 4i – 4l, the
solvent was removed, and the residue was purified by CC (SiO2; hexane/AcOEt 4 :1). The solvent was
removed to afford the product.
(2Z)-2,3-Dihydro-3-hydroxy-3,6-dimethyl-2-[(2E)-(4-nitrobenzylidene)hydrazinylidene]-4H-fu-
ro[3,2-c]pyran-4-one (4a). Pale-yellow powder. Yield: 0.32 g (94%). M.p. 179 – 1808. IR (KBr): 3529
(OH), 1732 (C¼O), 1682, 1639, 1587, 1512, 1447, 1404, 1337, 1248, 1221, 1144, 1123, 1010, 1057, 982, 922,
1
856, 821, 779, 752. H-NMR (500.1 MHz, (D6)DMSO): 1.68, 2.30 (2s, 6 H); 6.34 (s, 1 H); 6.66 (s, 1 H);
8.07 (d, J ¼ 7.2, 2 H); 8.32 (d, J ¼ 7.2, 2 H); 8.57 (s, 1 H). 13C-NMR (125.8 MHz, (D6)DMSO): 20.2; 23.5;
72.8; 94.9; 105.4; 124.0; 129.2; 139.4; 148.8; 157.8; 158.1; 162.4; 166.0; 168.4. EI-MS: 343 (6, Mþ), 328

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679
(83), 277 (6), 194 (17), 180 (34), 168 (27), 153 (96), 149 (24), 125 (13), 103 (17), 85 (30), 76 (13), 69 (23),
43 (100). Anal. calc. for C16H13N3O6 (343.30): C 55.98, H 3.82, N 12.24; found: C 55.82, H 3.98, N 12.11.
(2Z)-2-[(2E)-(4-Fluorobenzylidene)hydrazinylidene]-2,3-dihydro-3-hydroxy-3,6-dimethyl-4H-fu-
ro[3,2-c]pyran-4-one (4b). Cream powder. Yield: 0.28 g (91%). M.p. 1668. IR (KBr): 3402 (OH), 1744
(C¼O), 1715, 1693, 1641, 1603, 1578, 1512, 1447, 1425, 1400, 1229, 1198, 1144, 1069, 1040, 978, 926, 839.
1H-NMR (250.1 MHz, (D6)DMSO): 1.67, 2.31 (2s, 6 H); 6.30 (s, 1 H); 6.67 (s, 1 H); 7.35 (dd, 3J(H,H) ¼
8.6, 3J(F,H) ¼ 8.9, 2 H); 7.91 (dd, 3J(H,H) ¼ 8.6, 4J(F,H) ¼ 5.8, 2 H); 8.47 (s, 1 H). 13C-NMR (62.9 MHz,
2
4
(D6)DMSO): 20.2; 23.5; 72.5; 94.8; 105.3; 116.0 (d, J(C,F) ¼ 22.0); 130.1 (d, J(C,F) ¼ 3.0); 130.5 (d,
3J(C,F) ¼ 8.9); 158.7; 160.0 (d, 1J(C,F) ¼ 240.0); 161.8; 165.8; 166.1; 168.2. EI-MS: 316 (9, Mþ), 301 (78),
194 (30), 180 (41), 168 (17), 153 (76), 122 (74), 108 (19), 95 (48), 85 (28), 69 (27), 55 (13), 43 (100).
Anal. calc. for C16H13FN2O4 (316.29): C 60.76, H 4.14, N 8.86; found: C 60.73, H 4.24, N 8.66.
(2Z)-2-[(2E)-(3-Chlorobenzylidene)hydrazinylidene]-2,3-dihydro-3-hydroxy-3,6-dimethyl-4H-fu-
ro[3,2-c]pyran-4-one (4c). Cream powder. Yield: 0.31 g (93%). M.p. 1738. IR (KBr): 3310 (OH), 1742
1
(C¼O), 1693, 1643, 1580, 1441, 1402, 1225, 1140, 1061, 980, 910, 883, 795, 682. H-NMR (500.1 MHz,
(D6)DMSO): 1.67, 2.30 (2s, 6 H); 6.30 (s, 1 H); 6.66 (s, 1 H); 7.50 – 7.58 (m, 2 H); 7.79 (d, J ¼ 6.8, 1 H); 7.86
(s, 1 H); 8.44 (s, 1 H). 13C-NMR (125.8 MHz, (D6)DMSO): 20.2; 23.6; 72.7; 94.9; 105.4; 126.7; 127.5;
130.8; 131.0; 133.7; 135.7; 158.1; 158.3; 162.1; 166.1; 168.3. EI-MS: 334 (2, Mþ(37Cl)), 332 (5, Mþ(35Cl)),
319 (21), 317 (57), 194 (24), 180 (37), 168 (24), 153 (71), 138 (37), 125 (13), 111 (31), 85 (25), 75 (24), 69
(23), 43 (100). Anal. calc. for C16H13ClN2O4 (332.74): C 57.76, H 3.94, N 8.42; found: C 57.80, H 4.07, N
8.15.
(2Z)-2,3-Dihydro-3-hydroxy-2-[(2E)-(3-methoxybenzylidene)hydrazinylidene]-3,6-dimethyl-4H-fu-
ro[3,2-c]pyran-4-one (4d). Pale-yellow powder. Yield: 0.29 g (90%). M.p. 1728. IR (KBr): 3356 (OH),
1722 (C¼O), 1681, 1604, 1479, 1454, 1353, 1269, 1213, 1161, 1083, 1045, 969, 928, 875, 812, 783, 690.
1H-NMR (250.1 MHz, (D6)DMSO): 1.67, 2.31 (2s, 6 H); 3.82 (s, 3 H); 6.30 (s, 1 H); 6.66 (d, J ¼ 7.5, 1 H);
7.11 (s, 1 H); 7.41 – 7.45 (m, 3 H); 8.41 (s, 1 H). 13C-NMR (62.9 MHz, (D6)DMSO): 20.7; 24.1; 55.7; 73.1;
95.4; 105.8; 113.3; 117.6; 121.3; 130.5; 135.4; 158.7; 160.1; 161.0; 162.2; 166.7; 168.8. EI-MS: 328 (34, Mþ),
313 (100), 268 (12), 253 (9), 194 (17), 180 (33), 153 (60), 134 (73), 120 (16), 107 (36), 92 (24), 77 (32), 43
(35). Anal. calc. for C17H16N2O5 (328.32): C 62.19, H 4.91, N 8.53; found: C 62.11, H 5.13, N 8.40.
(2Z)-2-{[(2E)-(Furan-2-yl)methylidene]hydrazinylidene}-2,3-dihydro-3-hydroxy-3,6-dimethyl-4H-
furo[3,2-c]pyran-4-one (4e). Cream powder. Yield: 0.25 g (88%). M.p. 2188. IR (KBr): 3296 (OH), 1740
(C¼O), 1682, 1601, 1585, 1475, 1408, 1384, 1235, 1148, 1126, 1065, 1042, 1018, 980, 935, 908, 823, 768.
1H-NMR (500.1 MHz, (D6)DMSO): 1.64, 2.30 (2s, 6 H); 6.26 (s, 1 H); 6.67 (s, 1 H); 6.69 (dd, J ¼ 3.3, 1.7,
1 H); 7.10 (d, J ¼ 3.3, 1 H); 7.93 (d, J ¼ 1.7, 1 H); 8.29 (s, 1 H). 13C-NMR (125.8 MHz, (D6)DMSO): 20.2;
23.6; 72.6; 94.9; 105.3; 112.5; 117.6; 146.7; 148.8; 149.2; 158.1; 162.5; 166.1; 168.3. EI-MS: 288 (29, Mþ),
273 (100), 194 (20), 180 (69), 168 (15), 153 (70), 121 (39), 108 (31), 94 (94), 80 (29), 69 (17), 55 (18), 43
(73). Anal. calc. for C14H12N2O5 (288.26): C 58.33, H 4.20, N 9.72; found: C 58.33, H 4.16, N 9.68.
(2Z)-2-[(2E)-(3,4-Dimethoxybenzylidene)hydrazinylidene]-2,3-dihydro-3-hydroxy-3,6-dimethyl-
4H-furo[3,2-c]pyran-4-one (4f). Cream powder. Yield: 0.30 g (86%). M.p. 1638. IR (KBr): 3202 (OH),
1755 (C¼O), 1697, 1649, 1599, 1576, 1512, 1461, 1463, 1425, 1381, 1273, 1236, 1213, 1150, 1167, 1065, 1034,
969, 916, 862, 808, 748. 1H-NMR (250.1 MHz, (D6)DMSO): 1.66, 2.31 (2s, 6 H); 3.82, 3.83 (2s, 6 H); 6.25
(s, 1 H); 6.67 (s, 1 H); 7.07 (d, J ¼ 8.5, 1 H); 7.38 (d, J ¼ 8.5, 1 H); 7.42 (s, 1 H); 8.36 (s, 1 H). 13C-NMR
(62.9 MHz, (D6)DMSO): 20.7; 24.2; 56.0; 56.1; 73.0; 95.5; 105.8; 110.0; 112.0; 123.8; 126.7; 149.4; 152.2;
158.7; 160.4; 161.9; 166.7; 168.7. EI-MS: 358 (100, Mþ), 343 (49), 328 (61), 301 (10), 206 (13), 191 (27),
179 (20), 163 (73), 150 (55), 137 (23), 120 (32), 107 (20), 92 (40), 77 (51), 65 (31), 43 (66). Anal. calc. for
C18H18N2O6 (358.35): C 60.33, H 5.06, N 7.82; found: C 60.38, H 5.21, N 7.57.
(2Z)-2,3-Dihydro-3-hydroxy-3,6-dimethyl-2-{[(2E)-(pyridin-4-yl)methylidene]hydrazinylidene}-
4H-furo[3,2-c]pyran-4-one (4g). Pale-brown powder. Yield: 0.26 g (89%). M.p. 1858. IR (KBr): 3297
(OH), 1735 (C¼O), 1680, 1641, 1605, 1584, 1452, 1406, 1249, 1142, 1130, 1067, 1042, 976, 914. 1H-NMR
(250.1 MHz, (D6)DMSO): 1.69, 2.31 (2 s, 6 H); 6.36 (s, 1 H); 6.68 (s, 1 H); 7.76 (d, J ¼ 5.6, 2 H); 8.46 (s,
1 H); 8.73 (d, J ¼ 5.6, 2 H). 13C-NMR (62.9 MHz, (D6)DMSO): 20.2; 23.4; 72.7; 94.8; 105.3; 121.7; 140.3;
150.4; 157.6; 158.0; 162.0; 166.0; 168.4. EI-MS: 299 (3, Mþ), 284 (51), 256 (7), 194 (7), 180 (17), 168 (15),
153 (74), 132 (20), 105 (25), 85 (24), 78 (29), 69 (24), 43 (100). Anal. calc. for C15H13N3O4 (299.29): C
60.20, H 4.38, N 14.04; found: C 60.14, H 4.42, N 13.88.

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(2Z)-2-[(2E)-(4-Chlorobenzylidene)hydrazinylidene]-2,3-dihydro-3-hydroxy-3,6-dimethyl-4H-fu-
ro[3,2-c]pyran-4-one (4h). Cream powder. Yield: 0.31 g (95%). M.p. 183 – 1848. IR (KBr): 3299 (OH),
1739 (C¼O), 1687, 1605, 1582, 1438, 1400, 1230, 1144, 1040, 980, 928, 880, 810, 780, 691. 1H-NMR
(500.1 MHz, (D6)acetone): 1.90, 2.32 (2s, 6 H); 3.82 (s, 1 H); 6.18 (s, 1 H); 7.41 (d, J ¼ 8.5, 2 H); 7.74 (d,
J ¼ 8.5, 2 H); 8.38 (s, 1 H). 13C-NMR (125.8 MHz, (D6)acetone): 21.0; 24.9; 74.0; 95.1; 105.4; 129.2;
129.9; 131.9; 137.8; 159.0; 160.7; 161.9; 166.9; 168.6. EI-MS: 334 (7, Mþ(37Cl)), 332 (18, Mþ(35Cl)), 319
(30), 317 (76), 274 (10), 221 (15), 194 (33), 180 (51), 153 (100), 138 (63), 125 (20), 111 (25), 89 (19), 69
(15). Anal. calc. for C16H13ClN2O4 (332.74): C 57.76, H 3.94, N 8.42; found: C 57.57, H 4.10, N 8.23.
(2Z)-2-[(2E)-(3-Bromobenzylidene)hydrazinylidene]-2,3-dihydro-3-hydroxy-3,6-dimethyl-4H-fu-
ro[3,2-c]pyran-4-one (4i). Pale-pink crystals. Yield: 0.34 g (92%). M.p. 1658. IR (KBr): 3293 (OH), 1729
(C¼O), 1712, 1636, 1580, 1485, 1454, 1408, 1344, 1246, 1138, 1069, 1034, 984, 953, 922, 829, 802, 779, 678.
1H-NMR (500.1 MHz, (D6)acetone): 1.82, 2.33 (2s, 6 H); 5.25 (s, 1 H); 6.43 (s, 1 H); 7.68 (d, J ¼ 8.5, 2 H);
7.81 (d, J ¼ 8.5, 2 H); 8.35 (s, 1 H). 13C-NMR (125.8 MHz, (D6)acetone): 20.7; 24.2; 74.3; 95.3; 106.3;
125.9; 130.8; 132.9; 134.2; 158.8; 159.2; 162.7; 167.4; 169.5. EI-MS: 378 (10, Mþ(81Br)), 376 (10,
Mþ(79Br)), 363 (92), 361 (87), 209 (12), 194 (55), 180 (77), 168 (46), 157 (25), 153 (100), 140 (8), 125
(15), 109 (11), 89 (22), 85 (26), 76 (14), 43 (33). Anal. calc. for C16H13BrN2O4 (377.19): C 50.95, H 3.47, N
7.43; found: C 50.89, H 3.51, N 7.38.
(2Z)-2,3-Dihydro-3-hydroxy-3,6-dimethyl-2-{[(2E)-(thiophen-2-yl)methylidene]hydrazinylidene}-
4H-furo[3,2-c]pyran-4-one (4j). Pale-yellow powder. Yield: 0.25 g (85%). M.p. 1578. IR (KBr): 3395
(OH), 1738 (C¼O), 1709, 1686, 1641, 1589, 1443, 1420, 1407, 1381, 1248, 1223, 1144, 1063, 1038, 982, 935,
910, 746. 1H-NMR (250.1 MHz, (D6)DMSO): 1.66, 2.31 (2 s, 6 H); 6.27 (s, 1 H); 6.71 (s, 1 H); 7.21 (dd,
J ¼ 4.7, 3.5, 1 H); 7.64 (d, J ¼ 3.5, 1 H); 7.80 (d, J ¼ 4.7, 1 H); 8.67 (s, 1 H). 13C-NMR (62.9 MHz,
(D6)DMSO): 20.8; 24.1; 73.1; 95.5; 105.8; 128.7; 131.7; 134.6; 138.5; 155.7; 158.7; 162.9; 166.7; 168.8. EI-
MS: 304 (22, Mþ), 289 (86), 253 (24), 225 (13), 194 (20), 180 (60), 168 (16), 153 (72), 137 (36), 125 (24),
110 (100), 96 (39), 85 (28), 69 (24). Anal. calc. for C14H12N2O4S (304.33): C 55.25, H 3.97, N 9.21; found:
C 55.19, H 4.14, N 9.07.
(2Z)-2-[(2E)-Benzylidenehydrazinylidene]-2,3-dihydro-3-hydroxy-3,6-dimethyl-4H-furo[3,2-c]py-
ran-4-one (4k). Pale yellow crystals. Yield: 0.26 g (89%). M.p. 1498. IR (KBr): 3269 (OH), 1742 (C¼O),
1693, 1639, 1603, 1580, 1450, 1412, 1402, 1317, 1248, 1227, 1144, 1069, 1036, 978, 912, 818, 734, 692.
1H-NMR (250.1 MHz, (D6)DMSO): 1.70, 2.32 (2s, 6 H); 6.32 (s, 1 H); 6.67 (s, 1 H); 7.50 – 7.54 (m, 3 H);
7.83 – 7.91 (m, 2 H); 8.46 (s, 1 H). 13C-NMR (62.9 MHz, (D6)DMSO): 20.2; 23.5; 72.5; 94.8; 105.3; 128.2;
128.8; 131.3; 133.4; 158.1; 159.8; 161.8; 166.1; 168.2. EI-MS: 298 (9, Mþ), 283 (82), 194 (44), 180 (32), 168
(22), 153 (69), 131 (12), 104 (83), 90 (20), 77 (70), 51 (31), 43 (100). Anal. calc. for C16H14N2O4 (298.30):
C 64.42, H 4.73, N 9.39; found: C 64.42, H 4.79, N 9.40.
(2Z)-2,3-Dihydro-3-hydroxy-3,6-dimethyl-2-[(2E)-(4-methylbenzylidene)hydrazinylidene]-4H-fu-
ro[3,2-c]pyran-4-one (4l). Cream powder. Yield: 0.28 g (90%). M.p. 1598. IR (KBr): 3307 (OH), 1728
(C¼O), 1690, 1634, 1574, 1445, 1412, 1381, 1240, 1177, 1138, 1109, 1026, 978, 951, 924, 833, 783, 760.
1H-NMR (250.1 MHz, (D6)DMSO): 1.67, 2.31, 2.37 (3s, 9 H); 6.27 (s, 1 H); 6.68 (s, 1 H); 7.32 (d, J ¼ 8.0,
2 H); 7.74 (d, J ¼ 8.0, 2 H); 8.42 (s, 1 H). 13C-NMR (62.9 MHz, (D6)DMSO): 20.2; 21.1; 23.5; 72.5; 94.9;
105.2; 128.2; 129.4; 130.8; 141.4; 156.5; 160.0; 161.7; 166.1; 168.2. EI-MS: 312 (11, Mþ), 297 (72), 274 (4),
237 (4), 194 (34), 180 (20), 168 (15), 153 (51), 118 (100), 104 (32), 91 (65), 65 (33). Anal. calc. for
C17H16N2O4 (312.33): C 65.38, H 5.16, N 8.97; found: C 65.43, H 5.22, N 8.94.
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Received August 6, 2012