Unexpected novel rearrangement reaction: Synthesis of benzo-medium-ring anhydride

Article abstract of DOI:10.1080/00397910701866338

When we attempted to synthesize (E)-3-(benzo[d][1,3]dioxol-5-ylmethylene)- 4-(propan-2-ylidene)-dihydrofuran-2,5-dione, we found a novel rearrangement and obtained the unexpected compound that is assigned as benzo-medium-ring anhydride instead of the expected compound. We described the novel rearrangement and a potential method for the synthesis of benzo-medium-ring anhydride derivatives. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910701866338

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Unexpected Novel Rearrangement Reaction:
Synthesis of Benzo‐Medium‐Ring Anhydride
Wen‐Liang Dong a b , Bao‐Xiang Zhao a , Fang Wei a , Hua Zuo c & Dong‐Soo
Shin c
a Institute of Organic Chemistry, School of Chemistry and Chemical
Engineering , Shandong University , Jinan, China
b School of Pharmacy , Shandong University of Traditional Chinese Medicine ,
Jinan, China
c Department of Chemistry , Changwon National University , Changwon,
South Korea
Published online: 17 Apr 2008.
To cite this article: Wen‐Liang Dong , Bao‐Xiang Zhao , Fang Wei , Hua Zuo & Dong‐Soo Shin (2008)
Unexpected Novel Rearrangement Reaction: Synthesis of Benzo‐Medium‐Ring Anhydride, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 38:8,
1224-1235, DOI: 10.1080/00397910701866338
To link to this article: http://dx.doi.org/10.1080/00397910701866338
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Synthetic Communicationsw, 38: 1224–1235, 2008
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910701866338
Unexpected Novel Rearrangement
Reaction: Synthesis of Benzo-Medium-Ring
Anhydride
Wen-Liang Dong,1,2 Bao-Xiang Zhao,1 Fang Wei,1 Hua Zuo,3
and Dong-Soo Shin3
1Institute of Organic Chemistry, School of Chemistry and Chemical
Engineering, Shandong University, Jinan, China
2School of Pharmacy, Shandong University of Traditional Chinese
Medicine, Jinan, China
3Department of Chemistry, Changwon National University, Changwon,
South Korea
Abstract: When we attempted to synthesize (E)-3-(benzo[d][1,3]dioxol-5-ylmethy-
lene)-4-(propan-2-ylidene)-dihydrofuran-2,5-dione, we found a novel rearrangement
and obtained the unexpected compound that is assigned as benzo-medium-ring
anhydride instead of the expected compound. We described the novel rearrangement
and a potential method for the synthesis of benzo-medium-ring anhydride derivatives.
Keywords: Cleavage, condensation, fragmentation, rearrangements
Photochromic compounds have attracted considerable attention because of
their potential application to photonic devices, such as optical memories
and switches.[1] Considerable efforts have been devoted to the development
of photochromic compounds such as diarylethenes,[2,3] fulgides,[4] spiropyr-
ans and spirooxazines,[5] and chromenes.[6] Among them, fulgides are the
most promising candidates for the application because of their thermally irre-
versible and fatigue-resistant photochromic performance.
Received June 8, 2007
Address correspondence to Bao-Xiang Zhao, Institute of Organic Chemistry,
School of Chemistry and Chemical Engineering, Shandong University, Jinan, China.
E-mail: bxzhao@sdu.edu.cn
1224

Benzo-Medium-Ring Anhydride
1225
Photochromic fulgides are derivatives of dimethylene succinic anhydrides,
containing a hexatriene frame. The photochromic reaction is based on revers-
ible light-induced hexatriene/cyclohexadiene interconversion, a concerted
reaction in accordance with Woodward–Hoffmann selection rules. Usually
for aromatic heterocyclic fulgides, both the open-ring and closed-ring forms
are thermally stable and their absorption spectra are well separated from
each other. These properties make fulgides potentially attractive photochromic
systems for application in optical memory devices and optical switches.[7] To
achieve certain properties, such as absorption of the colored form at longer
wavelengths and higher fatigue resistance to coloration–bleaching cycles,
improvement has been made by modifying the fulgide frame.[8]
In continuation of our ongoing interest in the preparation of photochromic
fulgides,[9] we devote our effort to the synthesis of compounds with new struc-
tures. Interestingly, when we attempted to synthesize (E)-3-(benzo[d][1,3]-
dioxol-5-ylmethylene)-4-(propan-2-ylidene)-dihydrofuran-2,5-dione (Fig. 1),
we found a novel rearrangement and obtained the unexpected compound
that is assigned as benzo-medium-ring anhydride (Fig. 2) instead of the
expected compound.
The development of new methods for the construction of hetero- and
carbo-cyclic medium-ring systems has been a long-standing goal for
organic chemists. Among the targeted structures, medium-ring lactones
are of interest as backbones of many bioactive compounds, such as antibiotics.
Thus, the synthesis of ring lactone has attracted considerable attention.[10–13]
One facile synthetic method for ring lactone is reduction of anhydride.[14] On
the other hand, benzo-ring anhydride should be useful in the synthesis of sub-
stituted benzene derivatives, such as half-esters, which are versatile synthons
for the synthesis of various natural products:[15] esters, acids, and amides via
the reaction with alcohols, water, and amines respectively. However, to the
Figure 1. Fulgide
Figure 2. Benzo-medium-ring anhydride.

1226
W.-L. Dong et al.
best of our knowledge, access to ring aromatic anhydride is difficult despite a
number of synthetic methods, and the anhydride reported has been very
limited.[16,17]
Herein, we would like to report this first finding.
As shown in Scheme 1, the diacid 6, precursor of anhydride, was prepared
in good overall yields (36–62%) from commercially available diethyl
Scheme 1. Synthesis of fulgide and benzo-medium-ring anhydride.

Benzo-Medium-Ring Anhydride
1227
succinate 1, ketone 2, and piperonal in four steps. Thus, the Stobbe
condensation reaction of diethyl succinate 1 and ketone 2 in the presence of
potassium tert-butoxide and tert-butanol at refluxing temperature afforded
acid ester 3 in 86–98% yields, which can be easily converted to diester 4 in
the conventional esterafication by acid catalyst in 51–76% yields. Then, the
Stobbe condensation reaction of diester 4 with piperonal in the presence of
sodium hydride and toluene at room temperature gave 5 in 65–90% yields.
The diacid 6 was prepared by alkaline saponification of 5 with alcoholic
potassium hydroxide in 97–100% yield.
The diacid with a similar structure can be easily dehydrated to give
fulgide.[18] Indeed, in the present research, when R1 and R2 were ethyl
groups, fulgide 7d was obtained as an exclusive product that was determined
by X-ray diffraction as shown in Fig. 3.[19] Similarly, fulgide 7e, in which R1
and R2 were methyl and phenyl groups, respectively, was synthesized in a
good yield (76%). However, when R1 was methyl and R2 was alkyl, such as
methyl, ethyl, propyl, surprisingly, unexpected products 8 were obtained.
When R1 and R2 were methyl, interestingly, fulgide 7a and unexpected
product 8a were obtained in 56% and 13% yield, respectively.
The structures of (1E,7E)-6H-30,40-methelenedioxybenzo[e]oxecine-3,5-
diones (8a–c), benzo-medium-ring anhydride, were determined by IR, 1H
NMR, 13C NMR, and MS spectroscopy. For example, 8a, obtained as a yellow
crystal, gave a peak at m/z 271 in the ESI-MS, in accordance with the
molecular formula C15H11O5 (M-H), which was confirmed by the 13C-NMR
spectra exhibiting signals for 15 C-atoms. The carbonyl group absorptions in
Figure 3. X-ray crystal structures of 7d. Displacement ellipsoids are drawn at 50%
probability level.

1228
W.-L. Dong et al.
1
the anhydride moiety were observed in the IR spectra. The H NMR spectra
indicated the presence of two double bonds, and the chemical shift of the
double bond protons appeared at d ¼ 8.29 and 7.03 ppm in the form of doublet
peaks respectively. The coupling constant (J ¼ 16 Hz) is consistent with trans
vinylic protons. Another vinylic proton is shown in the 1H NMR spectrum as a
characteristic singlet at d ¼ 7.15 ppm. Two ortho- aromatic proton signals
appeared in the range of d ¼ 6.81 and 7.04 ppm as doublet peaks (J ¼ 8 Hz).
Three singlet signals appeared at d ¼ 6.02, 3.63, and 2.14 ppm, consistent with
methylene protons in methylenedioxy moiety, methylene attached carbonyl,
and methyl group respectively. Furthermore, the structure of 8a was determined
by H-H COSY and H-C COSY spectrum, as shown in Figs. 4 and 5.
A proposed mechanism is shown in Scheme 2. First, diacid (6) reacts with
acetyl chloride to afford protonated anhydride (9). After the proton transfer in 9
and intramolecular nucleophilic addition reaction of 10 take place, the inter-
mediate 11 is formed. After the proton transfer in 11 and leaving of the
acetic acid moiety in 12, the intermediate 13 is obtained. Intermediate 15 is
obtained by the proton transfer of 13 and deprotonation of 14. The intermediate
15 reacts with acetyl chloride to produce 16 in which a tandem reaction similar
to Friedel–Crafts reaction mechanism and fragmentation take place to afford
17. The intermediate 17 was unstable, and an intramolecular nucleophilic
Figure 4. H-H COSY (DMSO-6d) for compound 8a.

Benzo-Medium-Ring Anhydride
1229
Figure 5. H-C COSY (CDCl3/DMSO-6d) for compound 8a.
reaction and a cleave proceed to give 18. The protonation of 18 gives 19 in
which the enol isomarization proceeds to give 20. The hydrogen shift in inter-
mediate 20 takes place to afford 8. As described previously, the structure 8 can
1
be distinguished from structure 20 by H NMR spectrum because the vinylic
proton in structure 8 appeared as a characteristic singlet at d ¼ 7.15 ppm, due
to the conjugation effect with aryl ring. However, the chemical shift of the
vinylic proton in structure 20 should be upfield. The plausible reason why the
unexpected reaction did not proceed when R2 was phenyl is double bond con-
jugation with phenyl in intermediate 16. In another case, when R1 was ethyl, an
unexpected reaction did not proceed because of the steric effect.
In conclusion, we described a novel rearrangement and a method that has
potential for synthesis of benzo-medium-ring anhydride derivatives after
optimization.
EXPERIMENTAL
Thin-layer chromatography (TLC) was conducted on silica-gel 60 F254 plates
1
(Merck KGaA). H NMR spectra were recorded on a Bruker Avance 400

1230
W.-L. Dong et al.
Scheme 2. Proposed mechanism of the rearrangement.

Benzo-Medium-Ring Anhydride
1231
(400-MHz) spectrometer, using CDCl3 or the mixture of CDCl3 and DMSO as
solvents and tetramethylsilane (TMS) as internal standard. Melting points
were determined on an XD-4 digital micromelting-point apparatus. IR
spectra were recorded with an IR spectrophotometer Avtar 370 FT-IR
(Termo Nicolet). Elemental analyses were performed on a Vario EL III
(Elementar Analysensysteme GMbH) spectrometer. MS spectra were
recorded on a Trace DSQ mass spectrograph.
General Procedure
Preparation of 3
Potassium (4.68 g, 120 mmol) and t-BuOH (100 mL) were added to a 250-mL
flask, and the mixture was heated to refluxing. Then a mixture of ketone
(100 mmol) and ethyl succinate (25 mL, 150 mmol) was added dropwise,
followed by refluxing for 8 h. Solvent was removed in vacuo, and the
residue was dissolved in 40 mL of water and then washed completely with
ether. The aqueous layer was made strongly acidic with 6 mol/L hydrochloric
acid. The organic layer was separated, and the aqueous layer was extracted
with ethyl ether (30 mL ꢀ 3). The organic phase was washed with water
and dried over anhydrous magnesium sulfate. Concentration in vacuo gave
half-acid (3), yield 86–98%.
Preparation of 4
The half-acid 3 (98 mmol) and anhydrous alcohol (57 mL, 980 mmol) were
added to a flask (100 mL), and concentrated H2SO4 (1 mL) was added.
After refluxing for 8 h, the alcohol was removed in vacuo. The residue was
poured into ice water (30 mL), and the ester layer was taken up in ethyl
ether. The aqueous layer was extracted with ether (20 mL ꢀ 3), and the
extracts were neutralized by washing with aqueous sodium carbonate and
water, then dried over anhydrous magnesium sulfate. Concentration in
vacuo afforded diester product 4, yield 51–76%.
Preparation of 5
The mixture of diester 4 (50 mmol) and piperonal (6.00 g, 40 mmol) in
toluene (50 mL) was added dropwise to a suspension of NaH (1.25 g,
50 mmol) in toluene (100 mL) with stirring at room temperature. After the
addition was completed, the stirring was continued overnight at room temp-
erature. The mixture was extracted with water (50 mL ꢀ 3), and the
aqueous phase was acidified with hydrochloric acid (10%). The organic
layer was separated, and the aqueous layer was extracted with ethyl acetate
(30 mL ꢀ 3). The organic phase was washed with water and dried over

1232
W.-L. Dong et al.
anhydrous magnesium sulfate. Concentration in vacuo gave half-acid 5, yield
65–90%.
Preparation of 6
The half-acid 5 (4 mmol) was dissolved in alcoholic KOH (50 mL, 10%) and
heated at reflux for 6 h; then the solvent was removed in vacuo. The residue
was dissolved in water and acidified with hydrochloric acid (10%). The pre-
cipitate was filtered and dried to give diacid 6, yield 97–100%.
Preparation of 7 and 8
The diacid (35 mmol) was dissolved in dichloromethane (100 mL), and acetyl
chloride (50 mL) was added dropwise to this mixture with stirring at 0–5 8C.
Then the mixture was stirred for 5 h at room temperature. The excess acetyl
chloride and dichloromethane were removed in vacuo, and the residue was
recrystallized with ethyl acetate to give a yellowish solid, yield 56–76% for
7 and 13–79% for 8.
Data
Compound 7a
Yield 56%, mp 109–112 8C. IR (KBr) v: 1756, 1816 (O55C-O-C55O) cm21
.
1H NMR (400 MHz, CDCl3) d ¼ 1.71 (s, 3H, CH3), 2.43 (s, 3H, CH3), 6.05
(s, 2H, CH2), 6.80 (s, 1H, ArH), 6.85 (d, 1H, J ¼ 8 Hz, ArH), 6.92 (d, 1H,
J ¼ 8 Hz, ArH), 7.57(s, 1H, CH). Anal. calcd. for C15H12O5: C, 66.17; H,
4.44. Found: C, 66.20; H, 4.39. HRMS (EI) calcd. for C15H12O5 272.0685;
found 272.0693.
Compound 7d
Yield 60%, mp 114–116 8C. IR (KBr) v: 1768, 1818 (O55C-O-C55O) cm21
.
1H NMR (300 MHz, CDCl3) d ¼ 0.94 (t, 3H, J ¼ 7.2 Hz, CH3), 1.21 (t, 3H,
J ¼ 7.2 Hz, CH3), 2.04 (q, 2H, J ¼ 7.2 Hz, CH2), 2.87 (q, 2H, J ¼ 7.2 Hz,
CH2), 6.06 (s, 2H, CH2), 6.84–6.87 (m, 2H, ArH), 6.96 (dd, 1H, J ¼ 1.8,
8.1 Hz, ArH), 7.52 (s, 1H, CH). Anal. calcd. for C17H16O5: C, 67.99; H,
5.37. Found: C, 68.06; H, 5.33. HRMS (EI) calcd. for C17H16O5 300.0998;
found 300.0989.
Compound 7e
Yield 76%, mp 200–202 8C. IR (KBr) v: 1760, 1805 (O55C-O-C55O) cm21
.
1H NMR (400 MHz, CDCl3) d ¼ 2.82 (s, 3H, CH3), 5.89 (s, 2H, CH2), 6.09

Benzo-Medium-Ring Anhydride
1233
(s, 1H, ArH), 6.46 (d, 1H, J ¼ 8 Hz, ArH), 6.56 (d, 1H, J ¼ 8 Hz, ArH), 6.96
(t, 2H, J ¼ 7.2 Hz, ArH), 7.06 (t, 1H, J ¼ 7.2 Hz, ArH), 7.14 (d, 2H,
J ¼ 7.2 Hz, ArH), 7.48 (s, 1H, CH). Anal. calcd. for C20H14O5: C, 71.85;
H, 4.22. Found: C, 71.91; H, 4.19. HRMS (EI) calcd. for C20H14O5
334.0841, found 334.0836.
Compound 8a
Yield 13%, mp 225 8C (decomposition). IR (KBr) v: 1743, 1817 (O55C-O-
C55O) cm21
.
1H NMR (400 MHz, CDCl3) d ¼ 2.14 (s, 3H, CH3), 3.63
(s, 2H, CH2), 6.01 (s, 2H, CH2), 6.82 (d, 1H, J ¼ 8 Hz, ArH), 7.01
(d, 1H, J ¼ 8 Hz, ArH), 7.03 (d, 1H, J ¼ 16 Hz, CH), 7.15 (s, 1H, CH),
8.29 (d, 1H, J ¼ 16 Hz, CH). 13C NMR (100 MHz, CDCl3) d ¼ 17.2,
34.4, 101.1, 106.0, 108.1, 114.8, 122.6, 123.5, 129.9, 137.6, 148.0, 148.7,
150.9, 163.2, 168.2. Anal. calcd. for C15H12O5: C, 66.17; H, 4.44.
Found: C, 66.23; H, 4.36. ESI-MS (negative) 271.2 (M-H)2, 259.1,
227.2, 199.1. HRMS (ESI-negative) calcd. for C25H11O5 271.0606; found
271.0607.
Compound 8b
Yield 65%, mp 177–181 8C. IR (KBr) v: 1752, 1816 (O55C-O-C55O) cm21
.
1HNMR (400 MHz, CDCl3) d ¼ 1.20 (t, 3H, J ¼ 8 Hz, CH3), 2.49 (q, 2H,
J ¼ 8 Hz, CH2), 3.60 (s, 2H, CH2), 6.00 (s, 2H, CH2), 6.81 (d, 1H,
J ¼ 8 Hz, ArH), 7.02 (d, 1H, J ¼ 8 Hz, ArH), 7.04 (d, 1H, J ¼ 16 Hz, CH),
7.15 (d, 1H, J ¼ 1.6 Hz, CH), 8.21 (d, 1H, J ¼ 16 Hz, CH). 13C NMR
(100 MHz, CDCl3) d ¼ 12.7, 24.2, 33.6, 101.1, 106.0, 108.1, 113.9, 121.2,
123.5, 130.0, 137.3, 148.0, 148.8, 156.8, 163.5, 168.3. Anal. calcd. for
C16H14O5: C, 67.13; H, 4.93. Found: C, 67.19; H, 4.89. ESI-MS 287.3
(M þ H)þ, 269.4, 259.3, 241.4, 213.3, 187.3, 137.3. HRMS (ESI) calcd. for
C16H15O5 (M þ H)þ 287.0919; found 287.0913.
Compound 8c
Yield 79%, mp 184–187 8C. IR (KBr) v: 1760, 1823 (O55C-O-C55O) cm21
.
1H NMR (400 MHz, CDCl3) d ¼ 1.06 (t, 3H, J ¼ 8 Hz, CH3), 1.60 (q, 2H,
J ¼ 8 Hz, CH2), 2.45 (t, 2H, J ¼ 8 Hz, CH2), 3.62 (s, 2H, CH2), 6.01
(s, 2H, CH2), 6.81 (d, 1H, J ¼ 8, ArH), 7.01 (d, 1H, J ¼ 8 Hz, ArH), 7.03
(d, 1H, J ¼ 16 Hz, CH), 7.15 (s, 1H, CH), 8.23 (d, 1H, J ¼ 16 Hz, CH). 13C
NMR (100 MHz, CDCl3) d ¼ 13.9, 21.9, 33.0, 33.9, 101.1, 106.0, 108.1,
114.4, 121.7, 123.5, 130.0, 137.4, 148.0, 148.7, 155.5, 163.4, 168.3. Anal.
calcd. for C17H16O5: C, 67.99; H, 5.37. Found: C, 68.05; H, 5.42. HRMS
(EI) calcd. for C17H16O5 300.0998; found 300.0992.

1234
W.-L. Dong et al.
ACKNOWLEDGMENT
This study was supported by the Foundation of the Ministry of Education
(Grant No. 104112) and the Natural Science Foundation of Shandong
Province (Grant No. Y2005B12).
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