Novel stereoselective synthesis of densely functionalized 2H-indeno[2,1-b]furans

Article abstract of DOI:10.1080/00397910801929374

An easy access to densely functionalized 2H-indeno[2,1-b]furans is presented starting from triphenylphosphine, dialkyl acetylenedicarboxylates, alcohols (propargyl alcohol, 2,2,2-trichloroethanol, and methanol), and ninhydrin. The stereochemistry of dimethyl 8-oxo-8a-(2,2,2-trichloroethoxy)-8, 8a-dihydro-2H-indeno[2,1-b]furan-2,3-dicarboxylate was established by single-crystal X-ray structure determination. The reaction is completely stereoselective. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910801929374

Synthetic Communicationsw, 38: 1560–1568, 2008
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910801929374
Novel Stereoselective Synthesis of Densely
Functionalized 2H-Indeno[2,1-b]furans
Nader Noshiranzadeh,1 Ali Ramazani,1
2
Katarzyna Slepokura, and Tadeusz Lis
2
´
1Department of Chemistry, University of Zanjan, Zanjan, Iran
2Faculty of Chemistry, University of Wrocław, Wrocław, Poland
Abstract: An easy access to densely functionalized 2H-indeno[2,1-b]furans is presented
starting from triphenylphosphine, dialkyl acetylenedicarboxylates, alcohols (propargyl
alcohol, 2,2,2-trichloroethanol, and methanol), and ninhydrin. The stereochemistry
of dimethyl 8-oxo-8a-(2,2,2-trichloroethoxy)-8,8a-dihydro-2H-indeno[2,1-b]furan-2,3-
dicarboxylate was established by single-crystal X-ray structure determination. The
reaction is completely stereoselective.
Keywords: 2H-Indeno[2,1-b]furan, ninhydrin, stereoselective synthesis, triphenyl-
phosphine, Wittig reaction
1
INTRODUCTION
Compounds containing the [2,1-b]furan skeleton have attracted interest in bio-
organics, natural products, and medicinal chemistry. They are an important
class of heterocyclic compounds that has pharmaceutical and biological
activities including antimicrobial and anti-fungal activities.[1–4]
For several years, acetylenic esters have attracted the attention of organic
chemists and are reactive systems that can take part in many chemical
syntheses, almost like a Michael acceptor in the organic reactions.[5] In
recent years, there has been increasing interest in the applications of acetylenic
esters in multicomponent synthesis,[5,6] especially for preparing stabilized
Received in the U.K. September 18, 2007
Address correspondence to Ali Ramazani, Department of Chemistry, University of
Zanjan, P. O. Box 45195-313, Zanjan, Iran. E-mail: aliramazani@yahoo.com
1560

2H-Indeno[2,1-b]furans
1561
phosphorus ylides.[7–13] Because of the atom economy, convergent character,
and simplicity of one-pot procedures, multicomponent condensation reactions
(MCRs) have an advantageous position among other reactions. The develop-
ment of novel MCRs is receiving growing interest from industrial chemistry
research groups and represents a challenge for organic chemists.[5,6]
Few methods have been reported in the literature for the synthesis of
indeno[2,1-b]furan heterocycles.[2,3] These protocols are multistep in nature.
Based on our literature survey, reports on the synthesis of 2H-indeno[2,1-b]
furan heterocycles are fairly rare.[2,3]
In the past, we have established a convenient, one-pot method for
preparing stabilized phosphorus ylides utilizing in situ generation of the phos-
phonium salts.[8–13] As part of our ongoing program to develop efficient and
robust methods for the preparation of heterocyclic compounds,[14–18] we
sought to develop a convenient preparation of densely functionalized 2H-
indeno[2,1-b]furans (11). In this article, we describe the one-pot stereo-
selective synthesis of densely functionalized 2H-indeno[2,1-b]furans (11)
from the reaction of triphenylphosphine (1), dialkyl acetylenedicarboxylates
(2), alcohols (3), and ninhydrin (6) in fairly good yields (Scheme 1 and
Table 1).
2
RESULTS AND DISCUSSION
Reactions are known in which an a,b-unsaturated carbonyl compound is
produced from a phosphorane and a carbonyl compound such as an
aldehyde or ketone.[7,16] Thus, compounds 11 may be regarded as the
product of an intramolecular Wittig reaction. Such addition–olefination
products may result from an initial addition of triphenylphosphine 1 to
the acetylenic ester 2 and concomitant protonation of the 1:1 adduct,
followed by attack of the anion of alcohol 3 on the vinylphosphonium
cation to form stabilized phosphorane 5. It seems that the compounds 4
and 5 are in equilibrium in dichloromethane solvent at room temperature.
Attack of the anion of alcohol 3 (4) on the highly electron-deficient
carbonyl group of indane-1,2,3-trione 7 leads to formation of vinyltriphe-
nylphosphonium salt 9, which converts to phosphorus ylide 10. Intramole-
cular Wittig reaction of the phosphorus ylide 10 would lead to the
formation of corresponding densely functionalized 2H-indeno[2,1-b]
furans (11) and triphenylphosphine oxide (12) (Scheme 1 and Table 1).
Thin-layer chromatogrphy (TLC) indicated that the reaction was
completed after 24 h in CH2Cl2 at room temperature. The reaction
proceeds smoothly and cleanly under mild conditions, and no side
reactions were observed. The mechanism of the reaction has not been estab-
lished experimentally. However, a possible explanation is proposed in
Scheme 1. We have also used EtOH, i-PrOH, and n-BuOH in this
reaction instead of the alcohols 3, but yields of corresponding products

1562
N. Noshiranzadeh et al.
Scheme 1. Synthesis of densely functionalized 2H-indeno[2,1-b]furans 11a–e (see
Table 1).
11 were low (6–9%). The weak acidity of these alcohols may be the factor
in the reduction of yields. We have also used less reactive aldehydes (ben-
zaldehyde and 4-nitrobenzaldehyde) and ketones (acetone and acetophe-
none) in this reaction, but no products were observed even at reflux
Table 1. Synthesis of densely functionalized 2H-indeno[2,1-b]furans
11a–e (see Scheme 1)
Entry
Product
R
R0
Isolated yield (%)
1
2
3
4
5
11a
11b
11c
11d
11e
Me
Et
CH2CCl3
CH2CCl3
60
74
61
68
70
;;
Me
Me
t-Bu
CH2C CH
Me
Me

2H-Indeno[2,1-b]furans
1563
temperature (toluene as solvent) after 24 h. TLC indicated that the solution
contained ylide 5 and the starting aldehyde or ketone. The structures of the
final products 11a–e were confirmed by IR, 1H and 13C NMR spectroscopy,
and mass spectrometry (see the Experimental section). Because compound
11 possesses two stereogenic centers, four stereoisomers (2R, 8aR; 2S, 8aS;
2R, 8aS; and 2S, 8aR) are possible. We have proved the stereochemistry of
Figure 1. ORTEP diagram of single-crystal X-ray structure of 11a. Selected intera-
˚
tomic distances [A]: O(1)–C(1) ¼ 1.454(2), O(1)–C(4) ¼ 1.392(2), O(4)–C(14) ¼
1.204(2), O(5)–C(14) ¼ 1.328(2), O(5)–C(15) ¼ 1.450(2), O(6)–C(16) ¼ 1.210(2),
O(7)–C(16) ¼ 1.336(2), O(7)–C(17) ¼ 1.450(2), C(1)–C(2) ¼ 1.515(2), C(2)–
C(3) ¼ 1.340(2), C(3)–C(4) ¼ 1.499(2), and C(3)–C(7) ¼ 1.463(2). Selected valence
angles [8]: C(1)–O(1)–C(4) ¼ 108.02(8), C(4)–O(3)–C(12) ¼ 114.65(8), C(1)–C(2)–
C(3) ¼ 108.88(9), C(1)–C(2)–C(16) ¼ 120.67(9), C(3)–C(2)–C(16) ¼ 130.11(10),
C(2)–C(3)–C(4) ¼ 108.17(9), C(2)–C(3)–C(7) ¼ 140.88(10), and C(4)–C(3)–
C(7) ¼ 108.10(9). Selected torsion angles [8]: C(12)–O(3)–C(4)–O(1) ¼ 50.9(1),
C(12)–O(3)–C(4)–C(3) ¼ 168.3(1), C(4)–O(3)–C(12)–C(13) ¼ 2139.4(1), C(15)–
O(5)–C(14)–O(4) ¼ 0.9(2), C(15)–O(5)–C(14)–C(1) ¼ 178.6(1), C(17)–O(7)–
C(16)–O(6) ¼ 45.0(2), C(17)–O(7)–C(16)–C(2) ¼ 2173.4(1), O(1)–C(1)–C(2)–
C(16) ¼ 170.1(1), C(14)–C(1)–C(2)–C(16) ¼ 55.2(2), O(1)–C(1)–C(14)–O(5) ¼266.0
(1), C(16)–C(2)–C(3)–C(4) ¼ 2179.8(1), C(16)–C(2)–C(3)–C(7) ¼ 2 22.6(2),
C(1)–C(2)–C(16)–O(7) ¼ 164.4(1), C(2)–C(3)–C(4)–O(3) ¼ 2105.2(1), C(7)–
C(3)–C(4)–O(3) ¼ 89.7(1), C(3)–C(4)–C(5)–O(2) ¼ 2162.9(1), C(4)–C(5)–C(6)–
C(11) ¼ 171.2(1), C(4)–O(1)–C(1)–C(2) ¼ 13.6(1), C(1)–O(1)–C(4)–C(3) ¼ 217.7
(1), O(1)–C(4)–C(5)–C(6) ¼ 138.4(1), C(1)–O(1)–C(4)–C(5) ¼2134.6(1), and
O(1)–C(1)–C(2)–C(3) ¼ 23.9(1).

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N. Noshiranzadeh et al.
dimethyl 8-oxo-8a-(2,2,2-trichloroethoxy)-8,8a-dihydro-2H-indeno[2,1-
b]furan-2,3-dicarboxylate 11a (2S, 8aR and its mirror image 2R, 8aS) via
single-crystal X-ray diffraction method (see the Experimental section and
Fig. 1). The reaction is completely stereoselective.
3
CONCLUSIONS
In conclusion, we believe that the reported method offers a mild, simple, and
efficient route for the completely stereoselective synthesis of densely func-
tionalized 2H-indeno[2,1-b]furans (11). Its ease of workup, good yields,
and fairly mild reaction conditions make it a useful addition to modern
synthetic methodologies. Other aspects of this process are under
investigation.
4
EXPERIMENTAL
Freshly distilled solvents were used throughout, and anhydrous solvents were
dried according to Perrin and Armarego.[19] Elemental analyses were
1
performed using a Heraeus CHN-O-Rapid analyzer. H (250-MHz) and 13C
(62.5-MHz) NMR measurements were recorded on a Brucker 250 spec-
trometer in CDCl3 with tetramethylsilane as internal standard. UV spectra
were recorded on a Shimadzu UV-160 spectrophothometer. IR spectra were
recorded on a Mattson-1000 FTIR spectrophotometer. Mass spectra were
recorded on a Finnigan-Matt 8430 mass spectrometer operating at an ioniz-
ation potential of 20 eV. Melting points were measured on an Electrothermal
9100 apparatus and are uncorrected.
4.1 General Procedure for the Preparation of Densely
Functionalized 2H-indeno[2,1-b]furans (11)
To a magnetically stirred solution of triphenylphosphine 1 (0.262 g, 1 mmol)
and alcohol 3 (1 mmol) in CH2Cl2 (4 ml), a mixture of 2 (1 mmol) in CH2Cl2
(4 ml) was added dropwise at 210 8C over 15 min. The mixture was allowed
to warm up to room temperature, powdered ninhydrin 6 (0.18 g, 1 mmol) was
added, and the mixture was stirred for 24 h. The solvent was removed under
reduced pressure, and the viscous residue was purified by flash column chrom-
atography (silica gel; petroleum ether–ethyl acetate). The solvent was
removed under reduced pressure, and the products were obtained.
4.1.1 Dimethyl 8-oxo-8a-(2,2,2-Trichloroethoxy)-8,8a-dihydro-2H-
indeno[2,1-b]furan-2,3-dicarboxylate (11a)
Yield: 261 mg (60%); white solids; mp 134–138 8C. IR (KBr): v ¼ 2984,
2924, 2862, 1751, 1727, 1597, 1443, 1280, 1241, 1157, 1080, 1025 and

2H-Indeno[2,1-b]furans
1565
783 cm21. 1H NMR (CDCl3, 250 MHz): d ¼ 3.79 and 3.89 (2 s, 6H, 2 OCH3);
2
4.31 and 4.54 (2 d, 2H, J ¼ 211.1 Hz, OCHAHBCCl3); 6.08 (s, 1H, OCH);
7.66 (t, 1H, 3J ¼ 7.6 Hz, arom.); 7.81 (t, 1H, 3J ¼ 7.6 Hz, arom.); 7.88
3
3
(d, 1H, J ¼ 7.6 Hz, arom.); 8.33 (d, 1 H, J ¼ 7.6 Hz, arom.). 13C NMR
(CDCl3, 62.5 MHz): d ¼ 52.45 and 52.98 (2 OCH3); 76.31 (OCH2); 90.09
(OCH); 95.92 (CCl3); 112.90 (C8a); 125.58, 128.53, 132.64 and 136.45 (4
CH, arom.); 123.50, 138.28, 139.89 and 148.35 (4 C); 161.92 and 167.76 (2
C55O of 2 esters); 189.01 (C55O of ketone). C17H13Cl3O7 (435.64): calcd.
C, 46.87; H, 3.01; found C, 46.74; H, 3.07.
4.1.1.1 Preparation of Single Crystals of Dimethyl 8-oxo-8a-(2,2,2-
Trichloroethoxy)-8,8a-dihydro-2H-indeno[2,1-b]furan-2,3-
dicarboxylate (11a)
Colorless single crystals of 11a were obtained from its dichloromethane/light
petroleum ether/diethyl ether (1:1:1) solution (20–25 8C). The colorless
single crystals were filtered off, washed with a cold mixture of dichloro-
methane/light petroleum ether/diethyl ether (1:1:1), and dried at room temp-
erature (mp 135–136 8C).
Crystal data for 11a C17H13Cl3O7 (CCDC 637830): MW ¼ 435.62,
˚
˚
orthorhombic, space group Pbca, a ¼ 7.602(2) A, b ¼ 16.609(3) A,
c ¼ 28.471(4) A, V ¼ 3594.8(13) A , Z ¼ 8, Dc ¼ 1.610 mg/mm3,
3
˚
˚
F(000) ¼ 1776, crystal dimension 0.68 ꢀ 0.60 ꢀ 0.38 mm, radiation, Mo
˚
Ka (l ¼ 0.71073 A), 6.52 ꢁ 2u ꢁ 75.08. Intensity data were collected at
100(2) K with a Kuma KM4CCD diffractometer employing the v scanning
technique, in the range of 212 ꢁ h ꢁ 13, 225 ꢁ k ꢁ 25, 246 ꢁ l ꢁ 48.
The structure was solved by direct methods; all nonhydrogen atoms were posi-
tioned and anisotropic thermal parameters refined from 6696 observed reflec-
tions with R(int) ¼ 0.0353 by a full matrix least-squares technique converged
to R1 ¼ 0.0600, wR2 ¼ 0.1104. The Cambridge crystallographic data
(excluding structure factors) for the structure in this article have been
deposited with the Cambridge Crystallographic Data Centre as supplementary
publication number CCDC-637830. Copies of the data can be obtained, free of
charge, on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK
[fax: þ44(0)-1223-336033, e-mail: deposit@ccdc.cam.ac.uk, and Web:
www.ccdc.cam.ac.uk/data_request/cif].
4.1.2 Diethyl 8-oxo-8a-(2,2,2-Trichloroethoxy)-8,8a-dihydro-2H-
indeno[2,1-b]furan-2,3-dicarboxylate (11b)
Yield: 343 mg (74%); white solids; mp 109–111 8C. IR (KBr): v ¼ 2985,
1
2939, 1743, 1596, 1450, 1296, 1095, 1034, 995 and 733 cm21. H NMR
(CDCl3, 250 MHz): d ¼ 1.28 and 1.36 (2 t, 6H, 3J ¼ 7.1 Hz, 2 CH3 of 2 Et);
4.10–4.40 (m, 4H, 2 OCH2 of 2 Et); 4.32 and 4.54 (2 d, 2H, 2J ¼ 211.1 Hz,
3
OCHAHBCCl3); 6.05 (s, 1H, OCH); 7.65 (t, 1H, J ¼ 7.7 Hz, arom.); 7.81

1566
N. Noshiranzadeh et al.
3
3
(t, 1H, J ¼ 7.7 Hz, arom.); 7.87 (d, 1H, J ¼ 7.7 Hz, arom.); 8.34 (d, 1H,
3J ¼ 7.7 Hz, arom.). 13C NMR (CDCl3, 62.5 MHz): d ¼ 13.99 and 14.16 (2
CH3); 61.70 and 62.14 (2 OCH2 of 2 Et); 76.31 (OCH2CCl3); 90.35 (OCH);
95.96 (CCl3); 112.97 (C8a); 125.52, 128.62, 132.50, and 136.34 (4 CH,
arom.); 124.04, 138.40, 139.85, and 148.11 (4 C); 161.51 and 167.37 (2
C55O of 2 esters); 189.14 (C55O of ketone). C19H17Cl3O7 (463.70): calcd.
C, 49.22; H, 3.70; found C, 49.31; H, 3.63.
4.1.3 Dimethyl 8-oxo-8a-(Propargyloxy)-8,8a-dihydro-2H-
indeno[2,1-b]furan-2,3-dicarboxylate (11c)
Yield: 209 mg (61%); white solids; mp 130–132 8C. UV (ethanol 95%):
lmax/nm (log 1) ¼ 208 (3.97); 246 (4.25); 280 (4.14). IR (KBr): v ¼ 3300,
3000, 2150, 1757, 1727, 1600, 1400, 1126, and 778 cm21
.
1H NMR
4
(CDCl3, 250 MHz): d ¼ 2.43 (t, 1H, J ¼ 22.5 Hz, ;C–H); 3.75 and 3.84
2
4
(2 s, 6H, 2 OCH3); 4.36 and 4.53 (2 dd, 2H, J ¼ 215.5 Hz, J ¼ 22.5 Hz,
3
;;
OCHAHBC ); 6.01 (s, 1H, OCH); 7.62 (t, 1H, J ¼ 7.5 Hz, arom.); 7.77
3
4
3
(td, 1H, J ¼ 7.5, J ¼ 1.0 Hz, arom.); 7.84 (d, 1H, J ¼ 7.5 Hz, arom.);
8.25 (d, 1H, J ¼ 7.5 Hz, arom.). 13C NMR (CDCl3, 62.5 MHz): d ¼ 52.36
3
and 52.89 (2 OCH3); 53.19 (OCH2); 75.01 and 78.88 (2 C, C ; C); 89.89
(OCH); 113.24 (C8a); 125.44, 128.30, 132.47, and 136.16 (4 CH, arom.);
122.88, 138.15, 139.96, and 148.76 (4 C); 161.89 and 168.94 (2 C55O of 2
esters); 189.28 (C55O of ketone). C18H14O7 (342.28): calcd. C, 63.10; H,
4.09; found C, 62.87; H, 3.95.
4.1.4 Dimethyl 8-oxo-8a-(Methoxy)-8,8a-dihydro-2H-indeno[2,1-b]
furan-2,3-dicarboxylate (11d)
Yield: 216 mg (68%); white solids; mp 115–117 8C. IR (KBr): v ¼ 3069,
2960, 1749, 1718, 1803, 1449, 1363, 1225, 1186, 1040, 993, 901, and
1
778 cm21. H NMR (CDCl3, 250 MHz): d ¼ 3.15, 3.76, and 3.86 (3 s, 9H,
3
3 OCH3); 5.97 (s, 1H, OCH); 7.67 (t, 1H, J ¼ 7.5 Hz, arom.); 7.79 (t, 1H,
3J ¼ 7.5 Hz, arom.); 7.86 (d, 1H, 3J ¼ 7.6 Hz, arom.); 8.28 (d, 1H,
3J ¼ 7.7 Hz, arom.). 13C NMR (CDCl3, 62.5 MHz): d ¼ 52.64, 52.80, and
53.27 (3 OCH3); 90.10 (OCH); 114.26 (C8a); 125.73, 128.52, 132.80, and
136.36 (4 CH, arom.); 122.88, 138.55, 140.63, and 149.41 (4 C); 162.43,
and 168.60 (2 C55O of 2 esters); 190.03 (C55O of ketone). MS (EI): m/z
(%): 318 (Mþ, 30), 290 (32), 274 (60), 259 (54), 243 (100), 231 (90), 187
(20), 157 (38), 129 (30), 75 (17), and 59 (73). C16H14O7 (318.28): calcd. C,
60.38; H, 4.43; found C, 60.32; H, 4.68.
4.1.5 Di-tert-Butyl-8-oxo-8a-(methoxy)-8,8a-dihydro-2H-
indeno[2,1-b]furan-2,3-dicarboxylate (11e)
Yield: 282 mg (70%); white solids; mp 131–133 8C. IR (KBr): v ¼ 2978, 2930,
1738, 1700, 1462, 1369, 1162, 1054, and 777 cm21 1H NMR (CDCl3,
.

2H-Indeno[2,1-b]furans
1567
250 MHz): d ¼ 1.43 and 1.55 [2 s, 18 H, 2 OC(CH3)3]; 3.49 (s, 3H, OCH3); 5.77
(s, 1H, OCH); 7.59 (t, 1H, 3J ¼ 7.6 Hz, arom.); 7.75 (t, 1H, 3J ¼ 7.6 Hz, arom.);
7.83 (d, 1H, 3J ¼ 7.6 Hz, arom.); 8.29 (d, 1H, 3J ¼ 7.7 Hz, arom.). 13C NMR
(CDCl3, 62.5 MHz): d ¼ 28.18 and 28.50 [2 OC(CH3)3]; 52.52 (OCH3);
82.87 and 83.39 (2 OCMe3); 91.95 (OCH); 114.59 (C8a); 125.51, 128.70,
132.20, and 136.05 (4 CH, arom.); 125.20, 139.04, 140.32, and 147.36 (4 C);
161.48 and 167.56 (2 C55O of 2 esters); 190.71 (C55O of ketone). MS (EI):
m/z (%); 402 (Mþ, 6), 371 (28), 347 (42), 315 (45), 291 (55), 271 (16), 258
(14), 245 (30), 228 (42), 57 (100), and 41 (32). C22H26O7 (402.44): calcd. C,
65.66; H, 6.51; found C, 65.23; H, 6.55.
ACKNOWLEDGMENTS
The Iranian authors are thankful to the Zanjan University for partial support of
this work.
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