Preparation of isobenzofurandiones by flash vacuum pyrolysis involving retro-Diels-Alder expulsion of ethylene and concomitant C-O cleavage of methoxy or ethylenedioxy groups

Article abstract of DOI:10.1016/j.tet.2007.10.020

Flash vacuum pyrolysis (fvp) of a number of substrates, prepared by hydrogenating adducts derived from dimethoxy- or ethylenedioxy-substituted benzynes and furan, affords isobenzofurandiones through retro-Diels-Alder expulsion of ethylene and C-O bond cleavage of the methoxy or ethylenedioxy groups. The parent isobenzofuran-4,5-dione is reactive and undergoes two-fold conjugate addition of water to afford 3,4-dihydroxybenzene-1,2-dicarboxaldehyde.

Full text of DOI:10.1016/j.tet.2007.10.020

Tetrahedron 63 (2007) 12621–12628
Preparation of isobenzofurandiones by flash vacuum
pyrolysis involving retro-Diels–Alder expulsion of ethylene and
concomitant C–O cleavage of methoxy or ethylenedioxy groups
*
Riskiono Slamet and Dieter Wege
Chemistry M313, School of Biomedical, Biomolecular and Chemical Sciences, University of Western Australia,
5 Stirling Highway, Crawley, WA 6009, Australia
3
Received 11 April 2007; revised 18 September 2007; accepted 4 October 2007
Available online 6 October 2007
Abstract—Flash vacuum pyrolysis (fvp) of a number of substrates, prepared by hydrogenating adducts derived from dimethoxy- or ethyl-
enedioxy-substituted benzynes and furan, affords isobenzofurandiones through retro-Diels–Alder expulsion of ethylene and C–O bond cleav-
age of the methoxy or ethylenedioxy groups. The parent isobenzofuran-4,5-dione is reactive and undergoes two-fold conjugate addition of
water to afford 3,4-dihydroxybenzene-1,2-dicarboxaldehyde.
Ó 2007 Elsevier Ltd. All rights reserved.
1
. Introduction
structural moiety, which makes the system prone to 1,3-ad-
dition. The driving force for this is the generation of a benz-
enoid aromatic ring. Various strategies, including the
introduction of bulky substituents, and the annulation
of benzene rings to the e- and f-bonds of the six-membered
3
,4
The chemistry of isobenzofuran 1 (Fig. 1) and its derivatives
continues to attract considerable attention. The parent com-
pound 1 is highly reactive as it incorporates an o-xylylene
1
,2
1c,2h
ring, have been used to attenuate this reactivity; benzo-fusion
to the f-bond increases the reactivity.
3
–5
Isobenzofuran-4,7-dione 2 and isobenzofuran-4,5-dione 4
can be viewed as simple quinonoid derivatives of 1. The
6
,7
p-quinone 2 has been known for some time, and the re-
lated naphtho[2,3-c]furan-4,9-dione ring system 3 is present
in a number of natural products. The parent o-quinone 4 is
8
currently unknown, but the derivative 5 (albidin, a mould
metabolite) and the sterically stabilised 7-tert-butylisoben-
zofuran-4,5-dione 6 have been synthesised.
9
1
0
In an effort to extend the range of o-quinones related to iso-
benzofuran, we wondered if a difuran derivative such as 7
might be accessible through epoxidation and hydrolysis of
the double enol ether 8. This compound in turn should be
available by the two-fold retro-Diels–Alder extrusion of eth-
ylene from bridged diepoxide 9 induced by flash vacuum py-
1
1–14
rolysis (fvp).
a study.
In this paper we report the results of such
2. Results and discussion
Figure 1. Some isobenzofurandiones and a possible route to 7.
The precursor 9 was prepared as shown in Scheme 1. Treat-
ment of the dibromide 10 with sodium tert-butoxide and so-
dium amide (Caub ꢀe re’s base) in the presence of furan gave
*
Corresponding author. Tel.: +61 8 6488 3151; fax: +61 8 6488 1005;
e-mail: dw@chem.uwa.edu.au
1
5
0
040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.10.020

12622
R. Slamet, D. Wege / Tetrahedron 63 (2007) 12621–12628
ꢁ
1
a mixture of syn- and anti-9,10-dimethoxy-1,4:5,8-tetra-
hydro-1,4:5,8-diepoxyphenanthrene (11) in 25% yield.
Although the dehydrobromination of 10 and subsequent
trapping by furan is undoubtedly a step-wise process, the di-
bromide 10 can be considered to have acted as a ‘bisbenzyne’
equivalent. Hydrogenation of the diepoxytetrahydro-
phenanthrene 11 over palladium on charcoal then gave 9
in 97% yield.
bond dissociation energy by about 16 kJ mol due to addi-
tional resonance stabilisation of the phenoxy radical.
1
9,20
In
our system for radical 13 such stabilisation can occur in con-
tributing structures 13b and 13c due to electron-donation
from the adjacent oxygen atoms. This additional stabilisa-
tion will lower the activation energy for Me–O bond cleav-
age and hence the isolation of 7 rather than 8 in the fvp of
9 under our conditions is not surprising.
1
3,16
Scheme 1. Preparation of the dione 7.
ꢀ
benzo[1,2-c:3,4-c ]difuran-4,5-dione 7 in 36% yield instead
Fvp of 9 at 550 C/0.01 Torr directly gave yellow crystalline
0
of the expected 4,5-dimethoxybenzo[1,2-c:3,4-c ]difuran 8
0
Scheme 1). The H NMR spectrum of the dione 7 showed
1
(
two doublets at 7.74 and 8.26 ppm with J¼1.2 Hz. The sig-
nal at 8.26 ppm arises from the ‘outer’ furyl protons since
these possess some of the character of the b proton of an
a,b-unsaturated carbonyl system, as well as experiencing
peri-deshielding from the carbonyl groups (Fig. 2). For com-
parison, the chemical shifts of the furyl protons of
Scheme 2. Pathway for the formation of 7 and some products from the ther-
molysis of anisole 14.
1
7
If the proposal that the formation of the o-quinone 7 involves
step-wise Me–O homolysis is correct, then the pyrolytic
procedure should also be applicable to the generation of
p-quinones incorporating an isobenzofuran moiety. This
was confirmed by the synthesis of 2 and 21 by fvp of the ap-
propriate precursors 17 and 20 (Scheme 3). We note that
0
13
benzo[1,2-c:3,4-c ]difuran 12 are also shown.
The formation of the o-quinone 7 can be rationalised as
shown in Scheme 2. Two-fold retro-Diels–Alder extrusion
of ethylene from 9 gives compound 8, which undergoes ho-
molytic C–O cleavage of the methoxy groups to ultimately
deliver 7. The pyrolysis of aromatic methyl ethers in both
the liquid and vapour phase is known to give some products
7
a previous approach to the difuran 21 was unsuccessful.
Wiersum has reported that fvp of 22, the ethylenedioxy
derivative of catechol, yields o-benzoquinone by loss of eth-
ylene (Scheme 4), although the ultimate product of the reac-
1
7–21
derived from initial Me–O bond cleavage.
For example,
1
2,22,23
tion is the dimer of cyclopentadienone.
The expulsion
the thermolysis of anisole 14 in a flow-system at atmospheric
pressure yields phenol 15 (52%) as well as other products
of ethylene could be viewed as a concerted retro-Diels–Al-
der reaction, although Mulder and co-workers have pro-
posed on the basis of kinetic and product studies that the
1
7
(
Scheme 2). It should be noted that in this case the reaction
temperature is higher and the contact time within the hot
zone is considerably greater than in our flash vacuum pyro-
lysis. However, in the thermolysis of o-dimethoxybenzene
the ortho-methoxy group is known to lower the O–Me
2
0
reaction occurs via a step-wise pathway. For example,
thermolysis of 22 in the gas phase above 750 K in the pres-
ence of propene as a radical trap at atmospheric pressure
gave, amongst other products, the dioxole 27, apparently
arising from diradical 25. Irrespective of the mechanistic
details, this led us to examine whether such a reaction would
be advantageous for the preparation of isobenzofuran
o-quinones.
The ethylenedioxy derivative 30 was prepared as shown in
Scheme 4. Fvp of 30 afforded the quinone 7 in 63% yield.
Although this is better than that observed (36%) in the ther-
molysis of the dimethoxy derivative 9 under similar
1
Figure 2. H NMR (CDCl
3
) chemical shifts of dione 7 and difuran 12.

R. Slamet, D. Wege / Tetrahedron 63 (2007) 12621–12628
12623
Finally, we examined the pyrolytic approach to the synthesis
of the parent isobenzofuran-4,5-dione 4 (Scheme 5). Fvp of
both the dimethyl ether 35 and the ethylenedioxy derivative
3
6 provided 4 as a relatively unstable solid. Immediate mea-
1
surement of the H NMR spectrum revealed the chemical
shifts and coupling constants shown in Figure 3. In particu-
lar, a long-range coupling constant through five bonds of
0.7 Hz was observed between H3 and H7. For comparison,
the H NMR data for the other known isobenzofuran-4,5-di-
ones 5 and 6 are also shown.
1
Scheme 3. Preparation of the p-quinones 2 and 21 by fvp.
conditions, we do not attach particular significance to this
finding as in our experience yields can be variable due to
pressure fluctuations or difficulties in vapourising substrates
during fvp runs. A systematic study has shown that rigorous
control of experimental conditions is often necessary to
Scheme 5. Formation of the parent isobenzofuran-4,5-dione 4 by fvp of 35
and 36.
On brief standing, a solution of 4 in CDCl developed new
3
2
4
signals ascribable to the dihydroxy-dialdehyde 39 and the
conversion of 4 into 39 was complete by the time the
maximise yields in fvp reactions.
1
3
C
NMR spectrum was acquired. This conversion arises from
a two-fold conjugate addition of water to the furanoid double
bonds of 4, presumably catalysed by traces of acid in the sol-
vent (Scheme 6). This transformation also could be effected
by stirring a solution of 4 with dilute hydrochloric acid. Thus
the o-quinone 4 shows the properties characteristic of o- and
p-quinonemethides (nucleophilic attack at C3 and C1, re-
spectively). In the derivative 6 the bulky tert-butyl group
provides steric protection against attack at C1, while in the
natural product albidin 5 the methyl group hinders approach
to C3, and the conjugative effect of the methoxy group
reduces the electrophilicity of C1. The latter effect results
in a 0.32 ppm upfield shift of the H1 resonance in albidin
(7.33 ppm) compared to that within the parent quinone 4
(7.65 ppm).
In summary, we have provided a concise route to the isoben-
zofurandiones 2, 4, 7 and 21 by fvp of the appropriate pre-
cursors. There appears to be no significant advantage to
the use of ethylenedioxy- over methoxy-substituted deriva-
tives since the loss of ethylene from the former probably is
2
0
not concerted. Because of the relatively high temperature
1
2,20,22,23
1
Figure 3. H NMR chemical shifts (CDCl
4–6.
Scheme 4. Some products of the thermolysis of 22
ration of dione 7 by fvp of ethylenedioxy derivative 30.
and the prepa-
3
) of the isobenzofuran-4,5-diones

12624
R. Slamet, D. Wege / Tetrahedron 63 (2007) 12621–12628
were dried over anhydrous magnesium sulfate. Flash vac-
uum pyrolysis were carried out by loading the substrate at
the sealed end of a silica tube (500ꢂ10 mm) and placing
the tube horizontally in a Thermolyne 21100 tube having
a heating zone of 400 mm. The open end of the tube was con-
nected to the vacuum system and the tube was cooled with
solid dry ice near the exit. The substrate was heated slowly
using a Kugelrohr oven to effect passage into the hot zone.
The time required to vapourise each substrate is given for
each fvp experiment.
3
.1.1. 9,10-Dimethoxy-1,2,3,4,5,6,7,8-octahydro-1,4:5,8-
diepoxyphenanthrene (9). A solution of tert-butyl alcohol
5.50 g, 0.074 mmol) in anhydrous tetrahydrofuran (10 mL)
was added dropwise to a stirred suspension of sodium amide
7.87 g, 202 mmol) in anhydrous tetrahydrofuran (10 mL)
(
Scheme 6. Conversion of dione 4 into the dialdehyde 39.
(
under an argon atmosphere and was then used directly in
the dehydrobromination. To the stirred complex base was
added a solution of 1,2-dibromo-4,5-dimethoxybenzene
(10) (2.00 g, 6.76 mmol) in dry furan (20 mL) and stirring
was continued for 1.5 h. The reaction mixture was poured
into ice-water and extracted with ether. The ether extract
was washed successively with water, brine, dried and evap-
orated. The residue was submitted to rapid silica filtration.
Elution with 5–30% ethyl acetate/light petroleum gave
required, the pyrolytic route may well be limited to com-
pounds possessing thermally robust substituents. Thus an
attempt to prepare 7-tert-butylisobenzofuran-4,5-dione 6
(
Fig. 1) by fvp of the appropriately tert-butyl-substituted di-
methoxy derivative yielded a complex mixture, possibly as
a result of competing benzylic C–C homolysis within the
tert-butyl group.
9,10-dimethoxy-1,4,5,8-tetrahydro-1,4:5,8-diepoxyphenan-
threne (11) (1.38 g, 75%) as a white crystalline solid, which
3. Experimental
crystallised from dichloromethane/petrol as prisms, mp
150–153 C, consisting of one diastereomer on the basis of
ꢀ
NMR spectroscopy. MS: m/z 270 (M, 15%), 269 (93), 244
3
.1. General
Melting points were determined on a Kofler hot stage appa-
ratus and are uncorrected. Microanalyses were performed by
M.H.W. Laboratories (Phoenix, Arizona). NMR spectra
(28), 227 (22), 213 (49), 199 (100), 183 (48), 171 (25),
153 (34), 139 (29), 127 (30), 115 (17), 102 (17). H NMR
1
(300 MHz, CDCl ): d 3.86 (s, 6H, OCH ), 5.72 (narrow m,
3
3
1
were measured at 200 MHz ( H) on a Varian Gemini,
300 MHz ( H), 75.5 MHz ( C) on a Bruker AM 300 spec-
trometer, and at 500 MHz ( H), 126 MHz ( C) on a Bruker
2H, bridgehead), 6.85 (narrow m, 2H, vinyl), 6.97 (narrow
m, 2H, vinyl). C NMR (75.5 MHz, CDCl ): d 60.7
1
13
13
3
1
13
(OCH ), 80.2 (CH), 80.6 (CH), 141.9 (CH), 141.6 (CH),
3
1
3
ARX 500 spectrometer. C assignments were made with the
aid of DEPT experiments. Mass spectra were measured on
a VG Autospec. mass spectrometer in the EI mode unless
stated otherwise. Only molecular ion peaks, and peaks reg-
istering above 10% relative abundance in terms are reported.
Infrared spectra were recorded using KBr discs with a Bio-
Rad FTS45 FTIR spectrophotometer. Electronic spectra
were recorded using a Milton Roy Array 3000 Spectropho-
tometer. Analytical thin layer chromatography (TLC) was
carried out using Merck (Art. 554) silica gel 60 F254 pre-
coated on aluminium sheets. The spots were first visualised
using UV light (254 nm) and then spraying with 6% ceric
sulfate in 2 M H SO solution and heating for 30 s. Prepar-
132.7 (C), 134.2 (C), 143.7 (C). The diepoxy compound
11 (700 mg, 2.59 mmol) in ethyl acetate (50 mL) was stirred
with 10% palladium on charcoal (300 mg) under hydrogen
until 2 equiv of gas were absorbed. The mixture was filtered
through Celite, evaporated and the residue recrystallised
from ethyl acetate/light petroleum to give the title compound
ꢀ
9 as colourless crystals (690 mg, 97%) mp 158–159 C. MS:
m/z 274 (M, 2%), 246 (10), 238 (100), 223 (77), 217 (12),
1
195 (61), 180 (43), 167 (14), 151 (30), 104 (15). H NMR
(300 MHz, CDCl ): d 1.40–1.47 (m, 4H, CH CH ), 1.98–
3
2
2
2.05 (m, 4H, CH CH ), 3.86 (s, 6H, OCH ), 5.32–5.35
2
2
3
(narrow m, 2H, bridgehead), 5.57–5.59 (narrow m, 2H,
bridgehead). C NMR (75.5 MHz, CDCl ): d 26.7 (CH ),
1
3
2
4
3
2
ative radial chromatography was carried out using a Chroma-
totron Model 7924T (Harrison Research, Palo Alto,
California) with Kieselgel 60 PF254 gipshaltig (Merk Art.
26.9 (CH ), 60.7 (OCH ), 77.0 (CH), 77.2 (CH), 131.9
2 3
(C), 135.2 (C), 143.3 (C). Anal. Calcd for C H O : C,
1
6 18 4
70.06; H, 6.61. Found: C, 70.31, H, 6.43.
7
749). Silica gel filtrations were performed using Fluka Kie-
0
selgel 60 as adsorbent packed dry under water aspirator vac-
uum on a sintered glass funnel. In both chromatographic
techniques, increasing proportions of ethyl acetate in light
petroleum were used as eluting solvents, unless stated other-
wise. Fractions were monitored by TLC, and appropriate
fractions were combined. Anhydrous tetrahydrofuran was
obtained by distillation from benzophenone potassium ketyl.
All reactions requiring anhydrous reagents were carried out
under an inert atmosphere of nitrogen or argon. Light petro-
3.1.2. Benzo[1,2-c:3,4-c ] difuran-4,5-dione (7). The di-
epoxy compound 9 (50 mg, 0.182 mmol) was subjected to
ꢀ
flash vacuum pyrolysis (fvp) over 2 h at 550 C/0.01 Torr.
The product was washed from the pyrolysis tube with chlo-
roform and evaporated to give a yellow solid residue. Rapid
silica filtration using ethyl acetate/light petroleum (5–30%)
0
gave benzo[1,2-c:3,4-c ]difuran-4,5-dione (7) (14.3 mg,
36%), which was recrystallised from chloroform/light petro-
ꢀ
100), 160 (31), 132 (47), 104 (25). H NMR (500 MHz,
leum, mp>230 C (dec). MS: m/z 189 (M+1, 10%), 188 (M,
ꢀ
1
leum refers to the fraction bp 65–70 C and organic extracts

R. Slamet, D. Wege / Tetrahedron 63 (2007) 12621–12628
12625
CDCl ): d 7.74 (d, J 1.2 Hz, 2H, H1, H8), 8.26 (d, J 1.2 Hz,
3
H3, H6). C NMR (125.7 MHz, CDCl ): d 114.3 (C), 123.0
3
a crystalline residue, which was recrystallised from di-
chloromethane/light petroleum to give the title compound
20 as colourless plates (983 mg, 85%), mp 145–147 C.
1
3
ꢀ
MS: m/z 274 (M, 28%), 247 (14), 246 (100), 219 (10), 218
(
nm/(log 3) 246 (3.88), 390 (3.31). IR (KBr) nmax/cm 3154
C), 138.3 (CH), 149.9 (CH), 176.9 (CO). UV (CHCl ) l
3
max
ꢁ
1
1
m, 3132 m, 2385 w, 2371 w, 1671 s, 1548 s, 1122 s, 1029 s,
8
(78), 204 (10), 203 (89). H NMR (500 MHz, CDCl ):
3
67 m, 842 m, 595 m. Anal. Calcd for C H O : C, 63.83; H,
4
d 1.37–1.40 (m, 4H, CH CH ), 2.03–2.04 (m, 4H,
2
1
0
4
2
2
.14. Found: C, 64.03; H, 2.14.
CH CH ), 3.88 (s, 6H, OCH ), 5.57–5.58 (m, 4H, bridge-
2 2 3
1
3
head). C NMR (125.7 MHz, CDCl ): d 26.4 (CH ), 26.5
2
3
3
.1.3. 5,8-Dimethoxy-1,2,3,4-tetrahydro-1,4-epoxynaph-
thalene (17). A solution of 5,8-dimethoxy-1,4-dihydro-
(CH ), 60.0 (CH), 60.1 (CH), 77.0 (OCH ), 77.2 (OCH ),
2 3 3
135.5 (C), 135.6 (C), 140.2 (C), 140.3 (C). Anal. Calcd for
C H O : C, 70.06; H, 6.61. Found: C, 69.99; H, 6.63.
7
1
,4-epoxynaphthalene (16) (250 mg, 1.22 mol) in ethyl
1
6 18 4
acetate (20 mL) was hydrogenated over palladium on char-
coal (100 mg) at room temperature. The required volume
of hydrogen (28 mL) was absorbed. The catalyst was re-
moved by filtration through Celite and the solution was eva-
porated to give a colourless oil, which crystallised on
cooling. Recrystallisation from dichloromethane/light
petroleum gave 17 as colourless prisms (238 mg, 92%),
0
3.1.6. Benzo[1,2-c:4,5-c ]difuran-4,8-dione (21). 5,10-Di-
methoxy-1,2,3,4,5,6,7,8,9-octahydro-1,4:5,8-diepoxyanthra-
cene (20) (50 mg, 0.182 mmol) was subjected to fvp over 2 h
ꢀ
at 550 C/0.01 Torr. The product was washed out with chlo-
roform. Evaporation and recrystallisation from chloroform
ꢀ
m/z 189 (M+1, 11%), 188 (M, 100), 160 (25), 132 (13),
gave 20 as needles (20 mg, 58%), mp 212 C (dec). MS:
ꢀ
mp 78–79 C. MS (FAB): m/z 208 (M+2, 8%), 207 (M+1,
1
5
1
2
1), 206 (M, 100), 190 (13), 189 (58), 179 (12), 178 (86),
63 (11.5). H NMR (300 MHz, CDCl ): d 1.36–1.41 (m,
123 (15). H NMR (300 MHz, CDCl ): d 8.17 (s, furyl).
3
C NMR (75.5 MHz, CDCl ): d 125.3 (C), 145.9 (CH),
3
175.9 (CO). UV (CHCl ): l
3
(2.76). IR (KBr): nmax/cm 3495 s, 3414 s, 2924 w, 2379
w, 2374 w, 1678 s, 1536 m, 1412 w, 1385 m, 1129 m, 1020
w, 557 m, 742 m. Anal. Calcd for C H O : C, 63.83;
H, 2.14. M 188.0113. Found: C, 64.03; H, 2.20. M
88.0109.
1
13
3
H, CH CH ), 2.01–2.06 (m, 2H, CH CH ), 3.79 (s, 6H,
2
nm/(log 3) 233 (2.93), 306
max
2
2
2
ꢁ
1
OCH ), 5.56–5.58 (m, 2H, bridgehead), 6.63 (s, 2H, aryl).
3
1
3
C NMR (75.5 MHz, CDCl ): d 26.0 (CH ), 56.1 (OCH ),
3
2
3
77.4 (CH), 110.9 (CH), 134.7 (C), 146.4 (C). Anal. Calcd
for C H O : C, 69.89; H, 6.84. Found: C, 69.96; H, 6.86.
1
0 4 4
+
+
12 14 3
1
3
1
0
0
.1.4. Isobenzofuran-4,7-dione (2). 5,8-Dimethoxy-
,2,3,4-tetrahydro-1,4-epoxynaphthalene (17) (85 mg,
.41 mmol) was subjected to fvp over 20 min at 550 C/
3.1.7. 6,7-Dibromo-2,3-dihydro-1,4-benzodioxin (28). To
a solution of 2,3-dihydro-1,4-benzodioxin (12.8 g,
ꢀ
.01 Torr. The product was washed from the pyrolysis tube
0.094 mol) in acetic acid (100 mL) was added dropwise a so-
lution of bromine (9.7 mL, 0.198 mol) in acetic acid
(100 mL) with stirring under a nitrogen atmosphere. The
with chloroform. Radial chromatography using ethyl ace-
tate/light petroleum 5–30% afforded the quinone 2 (21 mg,
ꢀ
7
ꢀ
3
1
4%) as brown prisms mp 141–142 C (lit. mp 140–
ꢀ
mixture was then heated for 4 h at 40–45 C, poured into wa-
1
42 C). H NMR (200 MHz, CDCl ): d 6.84 (s, 2H, H5,
3
ter and extracted with ether. The ether extract was washed
with sodium hydroxide, water, brine and dried. Evaporation
under reduced pressure gave a crystalline residue, which was
recrystallised from ethanol to give 6,7-dibromo-2,3-dihy-
dro-1,4-benzodioxin (28) (18.9 g, 68%) as colourless
H6), 8.09 (s, 2H, H1, H3), identical with the reported spec-
trum.
7
3
1
.1.5. 5,10-Dimethoxy-1,2,3,4,5,6,7,8,9-octahydro-
,4:5,8-diepoxyanthracene (20). A solution of tert-butyl
ꢀ
25
ꢀ
1
needles mp 139–140 C (lit. mp 138 C). H NMR
(200 MHz, CDCl ): d 4.24 (s, 4H, OCH CH O), 7.13
(s, 2H, aryl).
alcohol (22 g, 0.074 mol) in anhydrous tetrahydrofuran
50 mL) was added dropwise to a stirred suspension of
3
2
2
(
sodium amide (31.4 g, 0.806 mol) in anhydrous tetrahydro-
furan (50 mL) at room temperature under argon. The com-
plex base mixture was heated at 40–45 C for 1.5 h and
3.1.8. 2,3,5,8,9,12-Hexahydro-5,8:9,12-diepoxyphenan-
thro[9,10-b]-1,4-dioxin (29). A solution of tert-butyl alco-
hol (7.7 mL, 82 mmol) in anhydrous tetrahydrofuran
(30 mL) was added dropwise a stirred suspension of sodium
amide (9.57 g, 245 mmol) in anhydrous tetrahydrofuran
(30 mL) at room temperature under argon. The mixture
ꢀ
then allowed to cool to room temperature. To the stirred
complex base was added a solution of 1,4-dibromo-2,5-di-
methoxybenzene (8.0 g, 0.029 mol) in dry furan (80 mL).
The stirring was continued overnight and the mixture was
poured into ice-water and extracted with ether. The organic
layers were washed with water, brine and dried. Evaporation
under reduced pressure followed by rapid silica filtration of
the residue using 5–40% ethyl acetate/light petroleum gave
ꢀ
was heated at 40–45 C for 1.5 h and then allowed to cool
to room temperature. To the stirred complex base was added
a solution of 6,7-dibromo-2,3-dihydro-1,4-benzodioxin (28)
(2.4 g, 8.16 mmol) in dry furan (50 mL). Stirring was contin-
ued for 4 h and then the reaction mixture was poured into
ice-water and extracted with ether. The ether layers were
washed with water, brine and dried. Evaporation of the sol-
vent under reduced pressure gave a solid product, which was
recrystallised from dichloromethane/light petroleum to give
the title compound 29 as a mixture of diastereomers (1.1 g,
48%) as colourless plates. Anal. Calcd for C H O : C,
9,10-dimethoxy-1,4,5,8-tetrahydro-1,4:5,8-diepoxyanthra-
cene (19) as a crystalline solid, which recrystallised from di-
chloromethane/light petroleum as colourless plates (5.9 g,
ꢀ
7
ꢀ
1
5
(
4%), mp 209–211 C (lit. mp 203–223 C). H NMR
200 MHz, CDCl ): d 3.84 (s, 6H, OCH ), 5.84 (s, 4H,
3
3
bridgehead), 7.04 (s, 4H, vinyl). A solution of 19 (1.00 g,
.70 mmol) in ethyl acetate (150 mL) was hydrogenated
3
1
6 12 4
over 10% palladium on charcoal (400 mg) until 2 equiv of
gas were absorbed (165 mL). The solution was filtered
through Celite. Evaporation under reduced pressure gave
71.64; H, 4.51. Found: C, 71.42; H, 4.70. Radial chromato-
graphy of 270 mg of this mixture using dichloromethane/
light petroleum 30–90% gave diastereomer A (159 mg,

12626
R. Slamet, D. Wege / Tetrahedron 63 (2007) 12621–12628
5
(
8%) as the more polar component and diastereomer B
107 mg, 40%) as the less polar component.
3.1.12. 5,6-Dimethoxy-1,4-dihydro-1,4-epoxynaphtha-
lene (33). A solution of tert-butyl alcohol (6.5 mL,
0
.069 mol) in anhydrous tetrahydrofuran (15 mL) was added
ꢀ
1
Diastereomer A: mp 170–173 C. H NMR (300 MHz,
CDCl ): d 4.19 (s, 4H, OCH CH O), 5.70 (dd, J 1.8,
dropwise to a stirred suspension of sodium amide (8.1 g,
0.21 mol) in anhydrous tetrahydrofuran (15 mL) under an
argon atmosphere. To the complex base was added a solution
of 4-bromo-1,2-dimethoxybenzene (31) (3.0 g, 0.016 mol)
in dry furan (30 mL). Stirring was continued overnight, after
which the reaction mixture was poured into ice-water and
extracted with ether. The ether extracts were washed succes-
sively with water and brine. Evaporation of the dried extract
under reduced pressure followed by rapid silica filtration
using 3–25% ethyl acetate/light petroleum gave the adduct
3
2
2
0.8 Hz, 2H, bridgehead), 5.75 (dd, J 1.8, 0.8 Hz, 2H, bridge-
head), 6.84 (dd, J 5.6, 1.8 Hz, 2H, vinyl), 6.96 (dd, J 5.6,
.8 Hz, 2H, vinyl). C NMR (75.5 MHz, CDCl ): d 64.4
3
CH ), 79.3 (CH), 80.6 (CH), 130.3 (C), 133.3 (C), 136.4
2
1
3
1
(
(
C), 142.0 (CH), 142.3 (CH).
ꢀ
42 (42), 239 (14), 216 (48), 214 (42), 212 (88), 211 (60),
88 (14), 158 (50), 156 (43), 155 (54), 128 (50). H NMR
Diastereomer B: mp 139–141 C. MS m/z 268 (M, 100%),
2
1
1
ꢀ
33 as colourless prisms (1.08 g, 33%) mp 92–93 C.
(
(
300 MHz, CDCl ): d 4.22 (s, 4H, OCH CH O), 5.65–5.66
3 2 2
narrow m, 2H, bridgehead), 5.77–5.79 (narrow m, 2H,
MS: m/z 205 (M+1, 14%), 204 (M, 100), 189 (62), 172 (13),
161 (30), 146 (12), 143 (17), 133 (12), 118 (13), 115 (23),
102 (13). H NMR (300 MHz, CDCl ): d 3.79 (s, 3H,
3
1
3
bridgehead), 6.93–6.98 (narrow m, 4H, vinyl). C NMR
(
1
75.5 MHz, CDCl ): d 64.4 (CH ), 79.5 (CH), 80.5 (CH),
3
2
1
30.0 (C), 133.7 (C), 136.5 (C), 141.7 (CH), 141.9 (CH).
OCH ), 3.92 (s, 3H, OCH ), 5.62 (m, 1H, bridgehead),
3
3
6
6.83 (d, J 7.6 Hz, 1H, aryl), 6.98 (narrow, m, 2H, vinyl).
C NMR (75.5 MHz, CDCl ): d 56.2 (OCH ), 60.4
3 3
.02 (m, 1H, bridgehead), 6.40 (d, J 7.6 Hz, 1H, aryl),
3.1.9. 2,3,5,6,7,8,9,10,11,12-Decahydro-5,8:9,12-diepoxy-
phenanthro[9,10-b]-1,4-dioxin (30). A mixture of diastereo-
mers of 2,3,5,8,9,12-hexahydro-5,8:9,12-diepoxyphenanthro-
1
3
(OCH ), 81.2 (CH), 81.9 (CH), 107.2 (CH), 114.4 (CH),
3
[
(
(
9,10-b]-1,4-dioxin (29) (377 mg, 1.41 mmol) in ethyl acetate
100 mL) was stirred with 10% palladium on charcoal
150 mg) under hydrogen until 2 equiv of gas (63 mL) were
136.6 (C), 141.4 (C), 141.7 (CH), 143.0 (CH), 143.8 (C),
149.7 (C). Anal. Calcd for C H O : C, 70.58; H, 5.92.
Found: C, 70.71; H, 6.05.
1
2 12 3
absorbed. The mixture was filtered through the Celite, evapo-
rated and the residue was recrystallised from dichlorome-
thane/light petroleum to give the title compound 30 as
3.1.13. 5,6-Dimethoxy-1,2,3,4-tetrahydro-1,4-epoxy-
naphthalene (35). A solution of 33 (300 mg, 1.47 mmol)
in ethyl acetate (50 mL) was hydrogenated over 10% palla-
dium on charcoal (100 mg) at room temperature and pres-
sure until the required volume of hydrogen (33 mL) had
been absorbed. The catalyst was removed by filtration
through Celite and the solution was evaporated under re-
duced pressure to give a colourless crystalline solid, which
recrystallised from dichloromethane/light petroleum to
ꢀ
colourless plates (367 mg, 96%), mp 200–203 C. MS: m/z
2
72 (M, 13%), 244 (39), 217 (14), 216 (100), 188 (20), 160
1
(
CH CH ), 1.95–2.03 (m, 4H, CH CH ), 4.23 and 4.24
13). H NMR (300 MHz, CDCl ): d 1.35–1.46 (m, 4H,
3
2
2
2
2
(
2ꢂs, 4H, OCH CH O), 5.33–5.36 (m, 2H, bridgehead),
2
2
1
3
5
CDCl ): d 26.3 (CH ), 26.8 (CH ), 64.5 (CH ), 76.1 (CH),
.46–5.49 (m, 2H, bridgehead). C NMR (75.5 MHz,
3
2
2
2
ꢀ
7
1
6.4 (CH), 77.4 (CH), 77.5 (CH), 129.7 (C), 129.9 (C),
31.2 (C), 131.4 (C), 135.4 (C), 175.5 (C). Anal. Calcd for
give 35 (291 mg, 96%), mp 52–53 C. MS: m/z 206 (M,
16%), 188 (20), 179 (11), 178 (100), 173 (14), 167 (13),
1
C H O : C, 70.58; H, 5.92. Found: C, 70.37; H, 5.86.
16 16 4
163 (53), 149 (51), 145 (11), 127 (11). H NMR
(300 MHz, CDCl ): d 1.38–1.47 (m, 2H, CH CH ), 2.03–
3 2 2
0
,3,5,6,7,8,9,10,11,12-Decahydro-5,8:9,12-diepoxyphenan-
3
.1.10. Benzo[1,2-c:3,4-c ]difuran-4,5-dione (7).
2.06 (m, 2H, CH CH ), 3.83 (s, 3H, OCH ), 3.95 (s, 3H,
2 2 3
OCH ), 5.32–5.33 (br d, J 4.3 Hz, 1H, bridgehead), 5.69–
3
2
thro[9,10-b]-1,4-dioxin (30) (57 mg, 0.21 mmol) was sub-
5.70 (br d, J 4.3 Hz, 1H, bridgehead), 6.65 (d, J 7.8 Hz,
1H aryl), 6.83 (d, J 7.8 Hz, 1H, aryl).
ꢀ
13
jected to fvp over 2 h at 550 C/0.01 Torr. The product
C NMR
(75.5 MHz, CDCl ): d 27.0 (CH ), 27.2 (CH ), 56.3
3 2 2
was washed out with chloroform. Evaporation and rapid sil-
ica filtration using ethyl acetate/light petroleum (5–30%)
gave the quinone 7 (25 mg, 63%), spectroscopically identi-
cal to the material prepared earlier.
(OCH ), 60.3 (OCH ), 77.6 (CH), 78.7 (CH), 110.1 (CH),
3
3
112.8 (CH), 135.3 (C), 139.8 (C), 141.9 (C), 150.5 (C).
Anal. Calcd for C H O : C, 69.89; H, 6.84. Found: C,
1
2 14 3
6
9.96; H, 6.86.
3
(
.1.11. 4-Bromo-1,2-dimethoxybenzene (31). Bromine
3.3 mL, 0.065 mmol) in acetic acid (50 mL) was added
dropwise with stirring over 2 h to 1,2-dimethoxybenzene
3.1.14. 6-Bromo-2,3-dihydro-1,4-benzodioxin (32).
To a solution of 2,3-dihydro-1,4-benzodioxin (33.5 g,
0.246 mol) in acetic acid (100 mL) was added dropwise a
solution of bromine (13 mL, 0.246 mol) in acetic acid
(100 mL) with stirring under a nitrogen atmosphere. The
(
9.0 g, 0.065 mmol) in acetic acid (20 mL) under nitrogen
ꢀ
atmosphere at 5–10 C. The mixture was kept at this temper-
ature for 30 min and then overnight at room temperature,
poured into water and extracted with light petroleum. The
extract was washed with aqueous sodium hydroxide and
then successively with water and brine. The dried solution
ꢀ
mixture was then heated for 1.5 days at 40–45 C and then
poured into water and extracted with ether. The ether extract
was washed with 5% sodium hydroxide, water, brine and
dried. Evaporation under reduced pressure followed by dis-
tillation gave 32 as colourless oil (44.3 g, 87%), bp 115–
was evaporated and distilled under reduced pressure to give
3
ꢀ
.8 Torr (lit. bp 69–70 C/0.04 Torr). H NMR (200 MHz,
1 as a colourless oil (5.28 g, 63.8%), bp 100–104 C/
2
6
ꢀ
CDCl ): d 3.81 (s, 3H, OCH ), 3.82 (s, 3H, OCH ), 6.69
1
ꢀ
25
ꢀ
1
0
120 C/0.5 Torr (lit. bp 275–276 C/754 Torr). H NMR
(200 MHz, CDCl ): d 4.23 (s, 4H, OCH CH O), 6.71–7.02
(m, 3H, aryl).
3
3
3
3
2
2
(
d, J 8.8 Hz, 1H, H6), 6.93–7.01 (m, 2H, H3 and H5).

R. Slamet, D. Wege / Tetrahedron 63 (2007) 12621–12628
12627
1
3
.1.15. 2,3,5,8-Tetrahydro-5,8-epoxynaphtho[1,2-b]-1,4-
dioxin (34). A solution of tert-butyl alcohol (20 mL,
.21 mol) in anhydrous tetrahydrofuran (50 mL) was added
dropwise to a stirred suspension of sodium amide (24.5 g,
.63 mol) in anhydrous tetrahydrofuran (50 mL) under an
temperature the sample was shown by H NMR analysis
to consist of 4 (33%) and 3,4-dihydroxybenzene-1,2-di-
1
3
0
carboxaldehyde (39) (67%). After 5 h the C NMR
spectrum was identical to that of dialdehyde 39 (see
below).
0
argon atmosphere. The complex base was heated at 40–
4
(b) 2,3,5,6,7,8-Hexahydro-5,8-epoxynaphtho[1,2-b]-1,4-
dioxin (36) (103 mg, 0.50 mmol) was subjected to fvp at
ꢀ
the stirred mixture was added a solution of 6-bromo-2,3-di-
hydro-1,4-benzodioxin (32) (9.0 g, 0.04 mol) in dry furan
5 C for 1.5 h and then cooled to room temperature. To
ꢀ
550 C/0.01 Torr over 2 h. The yellow product was dis-
solved in dichloromethane. Evaporation under reduced
pressure gave the crude product, which was subjected
to rapid radial chromatography using 3–10% ethyl ace-
tate/light petroleum to give 4 (54 mg, 72%).
(100 mL). Stirring was continued for 0.5 h (TLC monitor-
ing) and then the reaction mixture was poured into ice-water
(
400 mL) and extracted with dichloromethane (3ꢂ150 mL).
The combined extracts were washed with water, brine and
dried. The solvent was evaporated under reduced pressure
and the residue was submitted to rapid silica filtration using
3.1.18. 3,4-Dihydroxybenzene-1,2-dicarboxaldehyde (39)
by acid-catalysed hydrolysis of isobenzofuran-4,5-dione
(4). To a solution of freshly prepared isobenzofuran-4,5-di-
one (4) (37 mg, 0.25 mmol) in dichloromethane (5 mL)
was added 3 drops aqueous 2 M hydrochloric acid and the
mixture was stirred under argon for 2 days, during which
the solution changed from yellow to colourless. The mixture
was diluted with dichloromethane (10 mL), washed with
water, brine and dried. Evaporation gave 3,4-dihydroxyben-
zene-1,2-dicarboxaldehyde (39) (39 mg, 94%) as colourless
3
pound 34 as a colourless oil (6.25 g, 74%), bp 150–
–10% ethyl acetate/light petroleum to give the title com-
ꢀ
00%), 202 (80), 201 (14), 192 (13). H NMR (300 MHz,
1
1
60 C/0.7 Torr (Kugelrohr). MS (FAB): m/z 203 (M+1,
1
CDCl ): d 4.22–4.27 (m, 4H, OCH CH O), 5.64–5.65 (nar-
3
2
2
row m, 2H, bridgehead), 6.45 (d, J 7.5 Hz, 1H, aryl), 6.74
dd, J 7.5, 0.6 Hz, 1H, aryl), 7.03–7.04 (narrow m, 2H, vi-
nyl). C NMR (75.5 MHz, CDCl ): d 64.3 (CH ), 64.5
(
1
3
3
2
ꢀ
(
CH ), 79.8 (CH), 82.4 (CH), 112.7 (CH), 113.4 (CH),
2
prisms, mp 152 C (dec) after recrystallised from ether/light
petroleum. MS: m/z 166 (M, 72%), 138 (31), 137 (100), 109
1
1
35.7 (C), 138.4 (C), 142.3 (CH), 142.4 (C), 142.7 (C),
43.4 (CH). Anal. Calcd for C H O : C, 71.28; H, 4.98.
Found: C, 71.11; H, 5.00.
1
(27), 92 (11), 81 (23). H NMR (300 MHz, CDCl ): d 6.41
3
1
2
10
3
(br s, 1H, OH), 7.27 (d, J 8.1 Hz, 1H, aryl), 7.40 (d, J
8.1 Hz, 1H, aryl), 9.94 (s, 1H, CHO), 11.03 (s, 1H, CHO),
1
3
3
1
.1.16. 2,3,5,6,7,8-Hexahydro-5,8-epoxynaphtho[1,2-b]-
,4-dioxin (36). A solution of 2,3,5,8-tetrahydro-5,8-epoxy-
12.75 (br s, 1H, OH). C NMR (75.5 MHz, CDCl3):
d 117.4 (C), 118.7 (CH), 128.5 (C), 130.3 (CH), 150.4 (C),
151.0 (C), 192.0 (CHO), 198.3 (CHO). IR (KBr): nmax/
naphtho[1,2-b]-1,4-dioxin (34) (306 mg, 1.57 mol) in meth-
anol (100 mL) was flushed with argon and 10% palladium on
charcoal (100 mg) was added. The mixture was stirred under
hydrogen until 1 molar equivalent was absorbed. The solu-
tion was filtered through Celite and evaporated under re-
duced pressure to give a crystalline residue, which was
recrystallised from ether/light petroleum to give 36 as col-
ꢁ1
cm 3999 br, 2373 w, 2341 w, 1664 s, 1642 m, 1574 m,
1446 m, 1392 m, 1302 m, 1214 m, 1012 m, 1001 m.
HRMS Calcd for C H O M : 166.0266. Found M :
+
+
8
6 4
166.0265.
ꢀ
ourless plates (298 mg, 96%), mp 84–86 C. MS: m/z 204
References and notes
(
(
M, 5%), 186 (70), 131 (15), 130 (100), 120 (16), 102
39). H NMR (300 MHz, CDCl ): d 1.32–1.47 (2H,
1
1. (a) For selected reviews see: Steel, P. G. Science of Synthesis;
Thomas, J., Ed.; Thieme: Stuttgart, 2001; Vol. 10, p 87; (b)
Friedrichsen, W. Adv. Heterocycl. Chem. 1999, 73, 1; (c)
Wege, D. Advances in Theoretically Interesting Molecules;
Thummel, R. P., Ed.; JAI: Greenwich and London, 1998;
Vol. 4, p 1; (d) Friedrichsen, W. Methoden der Organischen
Chemie; Kreher, R., Ed.; Thieme: Stuttgart, 1994; Vol. E6b,
p 163; (e) Rickborn, B. Advances in Theoretically Interesting
Molecules; Thummel, R. P., Ed.; JAI: Greenwich and London,
3
CH CH ), 1.96–2.20 (m, 2H, CH CH ), 4.20–4.29 (m, 4H,
2
OCH CH O), 5.31–5.32 (m, 1H, bridgehead), 5.52–5.54
2
2
2
2
2
1
3
(
(
m, 1H, bridgehead), 6.62–6.74 (m, 2H, aryl). C NMR
75.5 MHz, CDCl ): d 26.1 (CH ), 26.8 (CH ), 64.2 (CH ),
3
2
2
2
6
4.5 (CH ), 76.4 (CH), 78.9 (CH), 111.4 (CH), 115.1
2
(CH), 132.9 (C), 136.6 (C), 139.8 (C), 142.6 (C). Anal.
Calcd for C H O : C, 70.58; H, 5.92. Found: C, 70.72;
H, 6.10.
1
2 12 3
1989; Vol. 1, p 1; (f) Rodrigo, R. Tetrahedron 1988, 44, 2093.
3
.1.17. Isobenzofuran-4,5-dione (4)
2. Some recent studies: (a) Rainbolt, J. E.; Miller, G. P. J. Org.
Chem. 2007, 72, 3020; (b) Sander, M.; Jarrosson, T.; Chuang,
S.-C.; Khan, S. I.; Ruben, Y. J. Org. Chem. 2007, 72, 2724;
(c) Kuninobu, Y.; Nishina, Y.; Nakagawa, C.; Takai, K.
J. Am. Chem. Soc. 2006, 128, 12376; (d) Sygula, A.; Sygula,
R.; Rabideau, P. W. Org. Lett. 2006, 8, 5909; (e) Chen, Y.-L.;
Hau, C.-K.; Wang, H.; He, H.; Wong, M.-S.; Lee, A. W. M.
J. Org. Chem. 2006, 71, 3512; (f) Nair, V.; Abhilash, K. G.
Synthesis 2005, 1967; (g) Payne, A. D.; Wege, D. Org.
Biomol. Chem. 2003, 1, 383; (h) Siu-Hin, C.; Chung-Yan, Y.;
Wong, H. N. C. Tetrahedron 2002, 58, 9413.
(
a) The epoxy compound 35 (99.3 mg, 0.481 mmol) was
ꢀ
subjected to fvp at 550 C/0.01 Torr over 2 h. The yel-
low product was dissolved in dichloromethane, filtered
through a small plug of cotton wool and the solution
concentrated by bubbling argon through it. Addition of
light petroleum gave 4 as a yellow solid (62 mg, 87%),
ꢀ
mp>300 C due to decomposition during heating. The
compound decomposed on standing. HRMS Calcd for
+
+
1
C H O M : 148.0160. Found M : 148.0158. H NMR
8
4 3
(
(
8
500 MHz, CDCl ): d 6.34 (d, J 9.9 Hz, 1H, H6), 7.47
3
dd, J 9.9, 0.7 Hz, 1H, H7), 7.65 (d, J 1.1 Hz, 1H, H1),
.17 (dd, J 1.1, 0.7 Hz, 1H, H3). After ca. 3 h at room
3. Moursounidis, J.; Wege, D. Aust. J. Chem. 1988, 41, 235.
4. Margetic, D.; Warrener, R. N.; Dibble, P. W. J. Mol. Model.
2004, 10, 87.

12628
R. Slamet, D. Wege / Tetrahedron 63 (2007) 12621–12628
5
6
7
. Tu, N. P. W.; Yip, J. C.; Dibble, P. W. Synthesis 1996, 77. 17. Freidlin, L. Kh.; Balandin, A. A.; Nazarova, N. M. Izvest. Akad.
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. Cragg, G. L.; Giles, R. G. F.; Roos, G. H. P. J. Chem. Soc.,
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Nauk. SSSR, Otdel. Khim. Nauk. 1949, 1, 102; Chem. Abstr.
1949, 43, 5758i.
18. Harrison, A. G.; Honnen, L. A.; Dauben, H. J., Jr.; Lossing, F. P.
J. Am. Chem. Soc. 1960, 82, 5593.
8
9
. Review: Piggott, M. J. Tetrahedron 2005, 61, 9929.
. Structural elucidation: Grove, J. F.; Hitchcock, P. B. J. Chem.
Soc., Perkin Trans. 1 1986, 1145; synthesis: Tennant, S.;
Wege, D. J. Chem. Soc., Perkin Trans. 1 1989, 2089.
19. Suryan, M. M.; Kafafi, S. A.; Stein, S. E. J. Am. Chem. Soc.
1989, 111, 1423.
20. Schraa, G.-J.; Arends, I. W. C.; Mulder, P. J. Chem. Soc., Perkin
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1
1
0. Sims, C. G.; Wege, D. Aust. J. Chem. 1992, 45, 1983.
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21. Britt, P. F.; Buchanan, A. C., III; Cooney, M. J.; Martineau,
D. R. J. Org. Chem. 2000, 65, 1376.
1
1
1
1
1
2. Wiersum, U. E. Aldrichimica Acta 1981, 14, 53.
22. Wiersum, U. E. Recl. Trav. Chim. Pays-Bas 1982, 101, 317.
23. Hageman, H. J.; Wiersum, U. E. Chem. Ber. 1973, 9, 206.
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Biomol. Chem. 2004, 2, 2677.
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(
b) Caub ꢀe re, P. Acc. Chem. Res. 1974, 7, 301.
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1