The DDQ mediated cyclization products of some 2-hydroxy-3(1′-alkenyl)-1,4-naphthoquinones

Article abstract of DOI:10.1081/SCC-120002120

The DDQ mediated cyclisation products derived from 2-hydroxy-3-(1′-alkenyl)-1,4-napthoquinones viz. 17 were found to be temperature dependent. At 60°C the naphthofuranquinone 19 was the predominant isomer whereas at 8°C the naphthopyranquinone 18 was exclusively formed.

Full text of DOI:10.1081/SCC-120002120

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THE DDQ MEDIATED CYCLIZATION PRODUCTS
OF SOME 2-HYDROXY-3-(1′-ALKENYL)-1,4-
NAPHTHOQUINONES
Farouk Ameer a , Robin G. F. Giles b , Ivan R. Green a & Kyatanahalli S. Nagabhushana a
a Department of Chemistry , University of the Western Cape , Private Bag X17, Bellville,
7530, Republic of South Africa
b Department of Chemistry , Murdoch University , Murdoch, WA, 6150, U.S.A.
Published online: 16 Aug 2006.
To cite this article: Farouk Ameer , Robin G. F. Giles , Ivan R. Green & Kyatanahalli S. Nagabhushana (2002) THE
DDQ MEDIATED CYCLIZATION PRODUCTS OF SOME 2-HYDROXY-3-(1′-ALKENYL)-1,4-NAPHTHOQUINONES, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 32:3, 369-380
To link to this article: http://dx.doi.org/10.1081/SCC-120002120
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SYNTHETIC COMMUNICATIONS, 32(3), 369–380 (2002)
THE DDQ MEDIATED CYCLIZATION
PRODUCTS OF SOME 2-HYDROXY-3-
(10-ALKENYL)-1,4-NAPHTHOQUINONES
Farouk Ameer,1 Robin G. F. Giles,2
Ivan R. Green,1, and Kyatanahalli S. Nagabhushana1
*
1Department of Chemistry, University of the
Western Cape, Private Bag X17, Bellville, 7530,
Republic of South Africa
2Department of Chemistry, Murdoch University,
Murdoch, WA 6150, Australia
ABSTRACT
The DDQ mediated cyclisation products derived from
2-hydroxy-3-(10-alkenyl)-1,4-napthoquinones viz. 17 were
found to be temperature dependent. At 60ꢀC the naphthofur-
anquinone 19 was the predominant isomer whereas at 8ꢀC,
the naphthopyranquinone 18 was exclusively formed.
The synthesis of alkenylnaphthoquinones has been undertaken to
study both their medicinal properties1 as well as their potential as starting
materials for naturally occurring biologically active compounds.2,3 In our
previous preparation of the 10-hexenyl-1,4-naphthoquinone 17 we estab-
lished the best conditions for its synthesis.4 The prime aim of the exercise
*Corresponding author.
369
Copyright & 2002 by Marcel Dekker, Inc.
www.dekker.com

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AMEER ET AL.
was to develop a methodology in which an aliphatic aldehyde can be
condensed with 2-hydroxy-1,4-naphthoquinone 1 under basic conditions
to form molecules that could be transformed into naphthopyrans having
similar structural features to the biologically active erythrostominone 2.5,9
In this paper, the condensation between acid labile aldehydes and
lawsone 1 as well as the consequent cyclisation products formed upon treat-
ment of these products with dichlorodicyanobenzoquinone (DDQ) will be
presented.
Transformation of the six-carbon ketoester 3 into the corresponding
dioxolan 4 was accomplished in 91% yield by heating in benzene under
reflux in the presence of ethylene glycol and para-toluenesulphonic acid.6
Reduction of ester 4 to the corresponding alcohol 5 was effected with
lithium aluminium hydride in ether at 0ꢀC in a yield of 97%. Finally, oxida-
tion of alcohol 5 to the desired aldehyde 6 was achieved by the use
of pyridinium chlorochromate in a yield of 61%. In the same way the
five-carbon keto-ester 7 was transformed into the dioxolane 8 (89%), then
into the alcohol 9 and finally into the odoriferous aldehyde 10 (65%)
(Scheme 1).
Condensation between lawsone 1 and aldehyde 6 in acetonitrile at
75ꢀC in the presence of triethylamine lead to the isolation of the desired
alkenyl condensation product 11 in 56% yield after flash chromatography.
It was found that prolonged exposure of the reaction mixture to column
chromatography lead to a lower yield and the recovery of 2–3% of the
deprotected ketone 12. The trans configuration of the double bond in
quinone 11 is clearly evident from the 1H-n.m.r. spectrum. Evidence
supporting the assignment of structure 12 to the fraction isolated after
longer column exposure is also found in the 1H-n.m.r. spectrum which
shows a deshielding effect for the CH3 from 1.36 ppm in 11 to 2.19 ppm
for 12 as well as the disappearance of the O-CH2-CH2-O signal at
3.97 ppm in 11. Similar condensation between lawsone 1 and aldehyde 10
afforded, after flash chromatography, the desired quinone 14 in 60% yield.

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371
Scheme 1.
1
Again the H-n.m.r. spectrum clearly demonstrated the trans nature of the
double bond.
Previously, it has been shown that base catalysed condensations
between lawsone 1 and aldehydes lead to 2-hydroxy-3-(10-alkenyl)-1,4-
naphthoquinones but in addition on array of naphthopyran products
were also isolated.4,7 The effectiveness of using DDQ to catalyse the cyclisa-
tion of 2-hydroxy-3-(10-alkenyl)-1,4-naphthoquinones had been demon-
strated earlier8 and this prompted us to apply similar reaction conditions
to the systems we had in hand.
A mixture of quinone 174 and 1.2 mol equivalents of DDQ in benzene
was heated at 60ꢀC for 2 h to afford two products. The major isomer
(70%) was assigned the naphthofuranquinone structure 19 whilst the desired
minor product (5%) was assigned the dehydronaphthopyranquinone struc-
ture 18. Assignment of structure 19 to the major isomer is based on the
1H-n.m.r. spectrum which showed a singlet at 6.61 ppm for 3-H as the only
olefinic proton, a triplet at 2.81 ppm with J 7.0 Hz, for 10-H of the butano
side chain and for aliphatic C signals at 13.7, 22.2, 28.1 and 29.5 ppm in the
13C-n.m.r. spectrum. On the other hand assignment of structure 18 to the

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AMEER ET AL.
minor isomer is also based on the 1H-n.m.r. spectrum which shows a
multiplet at 5.19 ppm for 2-H. A COSY spectrum clearly demonstrated
coupling between 2-H and 3-, 4- and the 10-H. A doublet of a doublet at
5.80 ppm with J 10.2 and 3.8 Hz is assigned to 3-H while a doublet of
a doublet at 6.71 ppm with J 10.2 and 1.4 Hz is assigned to 4-H. In
the 13C-n.m.r. spectrum only three aliphatic signals are observed at 13.8,
17.4 and 37.7 ppm.
Repeating the reaction at 25ꢀC lead to the formation of the naphtho-
furanquinone 19 in 43% yield and the dehydronaphthopyranquinone 18 in
42% yield but with a time period of 18 h. By lowering the temperature to
7–8ꢀC and extending the stirring period to 36 h, the sole product isolated
was the desired naphthopyranquinone 18 in 78% yield. It may be speculated
that thermodynamic factors are of greater significance than kinetic ones at
this temperature.
Treatment of the alkenyl quinone 14 with 1.2 mol equivalent of DDQ
in benzene at 60ꢀC for 2.5 h followed by very careful chromatographic
separation afforded two products. The major product has been assigned
the naphthofuranquinone structure 15 (54%) and the minor product has
been assigned the dehydronaphthopyranquinone structure 16 (24%). The
1H-n.m.r. spectrum of quinone 15 exhibited three well defined single peaks
viz., a 3-proton peak at 1.43 ppm, a 2-proton peak at 3.16 and a 1-proton
peak at 6.80 ppm assigned to 30-, 10- and the olefinic 3-H respectively.
1
On the other hand the H-n.m.r. spectrum of quinone 16 showed a doublet
of a doublet at 5.08 ppm with J 3.6 and 1.8 Hz assigned to 2-H, a doublet of
a doublet at 5.87 ppm with J 10.4 and 3.6 Hz, assigned to 3-H and a doublet
of a doublet at 6.82 ppm with J 10.4 and 1.8 Hz, assigned to 4-H of the
dehydropyran ring.
Repeating the reaction at lower temperatures viz., 25 and 8ꢀC and
stirring for longer times resulted in an improved relative yield of the
dehydronaphthopyranquinone 16. However, the best relative yields were
obtained at 8ꢀC where the isolated ratio of quinones 15 : 16 was 38 : 32.
The near proximity of the dioxolane ring to the tricyclic ring system may
have an effect on the relative ratio.
Finally, treatment of the alkenylquinone 11 with 1.2 mol equivalents
of DDQ in benzene at 25ꢀC for 12 h yielded a single product in 68%
1
yield to which structure 13 has been assigned. In the H-n.m.r. spectrum a
multiplet at 5.37 ppm is assigned to 2-H on the basis that a COSY spectrum
shows coupling to 3-, 4- and 10-H. In addition a doublet of a doublet
at 5.90 ppm with J 10.0 and 3.8 Hz is assigned to 3-H while a doublet of
a doublet at 6.69 ppm with J 10.0 and 1.6 Hz is assigned to 4-H of
the dehydropyran ring. An interesting observation was made in that
the signals of the two enantiotopic 10-hydrogens appear as a doublet of a

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373
Scheme 2.
doublet at 2.05 ppm with J 14.80 and 6.0 Hz and 2.37 ppm with J 14.80
and 6.8 Hz.
Repeating the reaction at 60ꢀC for 2 h in benzene afforded the same
dehydronaphthopyranquinone 13 in 60% yield. In this case t.l.c did show
a very minor fraction running just ahead of the product. However, the
quantity was so insignificant that it was not pursued further.
The ease with which the double bond of the dehydropyran ring can be
reduced was demonstrated by the quantitative catalytic hydrogenation of

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AMEER ET AL.
dehydronaphthopyranquinone 18 into the corresponding naphthopyranqui-
none 20.
Thus a new strategy has been developed for the synthesis of intermedi-
ates viz., 13, 16, and 20 which can be transformed into trideoxyerythrosto-
minone analogues9 to be used for biological evaluations currently being
investigated in our laboratories.
EXPERIMENTAL
1H- and 13C-n.m.r. spectra were recorded using a Varian 200 MHz
instrument at 20ꢀC in deutereochloroform. Infrared spectra were measured
as Nujol mulls unless otherwise stated and recorded on a Perkin Elmer
FT-IR 1000 pc spectrometer. Melting points were recorded on a Fischer-
John apparatus and are uncorrected. C and H analyses were performed
on a Carlo Erba NA 1500 Nitrogen analyser and GC-MS were performed
on a Finnigan-Matt GCQ instrument. Column chromatography was carried
out using Merck Kielselgel 60 (35–230 mesh) as dry columns. Hexane refers
to that fraction boiling between 60–75ꢀC. Residue obtained upon workup
refers to the material obtained from the dried (MgSO4) organic extract after
filtration and removal of solvent.
Ethyl 5-Dioxolan Hexanoate 46
As solution of benzene (400 mL), ethylene glycol (29.8 g; 0.480 mol)
and p-toluene sulphonic acid (1.03 g; 5.4 mmol) were stirred and
heated under reflux in a Dean-Stark apparatus to ensure all reagents were
dry. To this mixture was added ethyl 4-acetyl butyrate 3 (50 g; 0.316 mol)
and the resulting solution was stirred under reflux with water being
removed via the Dean-Stark separator for 18 h. The cooled benzene
layer was washed with saturated aqueous sodium hydrogen carbonate
(150 ml) and then water (100 mL). The residue obtained upon workup
was distilled to afford the ester 4 (58 g; 91%) as a light olive-coloured oil,
b.p. 98–102ꢀC (1 mmHg); nmax 1744 cmÀ1; dH 1.25 (t, 3H, J 7.2 Hz,
OCH2CH3), (1.32 (s, 3H, 6-H), 1.73–1.68 (m, 4H, 3- and 4-H), 2.32 (t,
2H, J 7.2 Hz, 2-H), 3.93 (sharp m, 4H, OCH2CH2O), 4.12 (q, J 7.2 Hz,
OCH2CH3), dC 14.2 (OCH2CH3), 19.6 (6-C), 23.7 (3-C), 34.3 (4-C), 38.3
(2-C), 60.3 (OCH2CH3), 64.6 (OCH2CH2O), 109.9 (5-C) and 173.7 (C¼O).
(Found: C, 59.2; H, 8.7%; M+, 202. Calc. for C10H18O4: C, 59.4; H. 8.9%;
M, 202).

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5-Dioxolane Hexan-1-ol 5
375
To a slurry of lithium aluminium hydride (3.98 g; 0.105 mol) in dry
ether (100 mL) at 0ꢀC was added dropwise a solution of ester 4 (20.14 g;
0.099 mol) in dry ether (50 mL) over a period of 30 min. The resulting slurry
was stirred at 25ꢀC for a further 2 h after which time the reaction was
quenched by the careful addition of saturated aqueous ammonium chloride.
The residue obtained upon workup afforded the alcohol 5 as an oil (15.48 g;
97%); nmax 3412 cmÀ1; dH 1.31 (3H, s, 6-H), 1.60 (7H, m, 2-, 3-, 4-H and C-1
OH), 3.64 (2H, t, J 6.2 Hz, 1-H), and 3.93 (4H, sharp m, OCH2CH2O); dC
20.2 (6-C), 23.8 (3-C), 32.8 (4-C), 38.8 (2-C), 62.8 (1-C), 64.7 (OCH2CH2O),
and 110.2 (5-C). (Found: C, 59.9; H, 10.1%; M+, 160. Calc. for C8H16O3:
C, 60.0; H, 10.0%; M, 160).
5-Dioxolan Hexanol 6
To a stirred suspension of pyridinium chlorochromate (10.13 g;
47 mmol) in dichloromethane (50 mL) was added dropwise a solution of
alcohol 5 (5.0 g; 31 mmol) in dichloromethane (20 mL) at 25ꢀC and stirring
was maintained at this temperature for an additional 3 h. Ether (100 mL)
and magnesium sulphate (5 g) were added and the resultant slurry was
vigorously stirred and then filtered through celite using additional ether as
the wash solvent. The residue obtained was further purified by flash chro-
matography using hexane-ether (4 : 1) as eluent to afford hexanal 6 (3.0 g;
61%) as a mobile liquid, nmax 1735 cmÀ1; dH 1.32 (3H, s, 6-H), 1.72 (4H, m,
3- and 4-H), 2.47 (2H, dt, J 6.3 and 1.8 Hz, 2-H), and 3.94 (4H, sharp m,
OCH2CH2O) and 9.77 (1H, t, J 1.8 Hz, 1-H); dC 16.7 (6-C), 23.8 (3-C), 38.3
(4-C), 43.9 (2-C), 64.8 (OCH2CH2O), 109.9 (5-C) and 202.7 (C¼O). (Found:
C, 60.6; H, 8.7%; M+, 158. Calc. for C8H14O3: C, 60.8; H, 8.9%; M, 158).
Ethyl 4-Dioxolan Pentanoate 8
By a similar methodology employed for the synthesis of dioxolane 4
the dioxolane 8 was obtained from ketoester 7 as an oil (89%), b.p. 87–91ꢀC
at 1 mmHg; nmax 1744 cmÀ1; dH 1.24 (3H, t, J 7.2 Hz, OCH2CH3), 1.21 (3H,
s, 5-H), 2.01 (2H, t, J 8.0 Hz, 3-H), 2.38 (2H, t, J 8.0 Hz, 2-H), 3.93 (4H,
sharp m, OCH2CH2O), and 4.12 (2H, q, J 7.2 Hz, OCH2CH3), dC 14.3
(OCH2CH3), 19.8 (5-C), 34.2 (3-C), 38.5 (2-C), 59.4 (OCH2CH3), 64.6
(OCH2CH2O), 109.4 (4-C) and 174.2 (C¼O). (Found: C, 58.1; H, 8.8%;
Mþ, 188. Calc. for C9H16O4: C, 57.45; H, 8.5%; M, 188).

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4-Dioxolan Pentan-1-ol 9
By a similar methodology employed for the synthesis of dioxolane 5
the alcohol 9 was obtained as an oil in 90% yield; nmax 3420 cmÀ1; dH 1.33
(3H, s, 5-H), 1.74 (4H, m, 2- and 3-H), 1.95 (1H, brs, 1-OH), D2O exchange-
able) 3.64 (2H, t, J 6.2 Hz, 1-H), and 3.96 (4H, sharp m, OCH2CH2O), dC
23.7 (5-C), 27.2 (3-C), 35.9 (2-C), 63.1 (1-C), 64.7 (OCH2CH2O) and 110.1
(4-C). (Found: C, 57.4; H, 9.5%; M+, 146. Calc. for C7H14O3: C, 57.5; H,
9.6%; M, 146).
4-Dioxolan Pentanal 10
By similar methodology employed for the synthesis of aldehyde 6 the
pentanal 10 was obtained as an odoriferous oil in 65% yield; nmax
1738 cmÀ1; dH 1.33 (3H, s, 5-H), 2.07 (2H, t, J 7.0 Hz, 3-H), 2.47 (2H, dt,
J 7.0 and 2.0 Hz, 2-H), 3.91 (4H, sharp m, OCH2CH2O), and 9.72 (1H, t,
J 2.0 Hz, 1-H), dC 24.2 (5-C), 31.8 (3-C), 38.5 (2-C), 64.8 (OCH2CH2O),
109.2 (4-C) and 202.4 (1-C). Found: C, 58.4; H, 8.2%; M+, 144. Calc. for
C7H12O3: C, 58.3; H, 8.3%; M, 144).
2-Hydroxy-3-(E-50-dioxolano-10-hexenyl)-1,4-naphthoquinone 11
and 2-Hydroxy-3-(E-50-oxo-10-hexenyl)-1,4-naphthoquinone 12
To solution of lawsone 1 (655 mg; 3.76 mmol) and aldehyde 6 (850 mg;
5.38 mmol) in acetonitrile (20 mL) was added triethylamine (1.51 g;
15 mmol) and the resulting ruby red solution was stirred at 75ꢀC (oil
bath) under nitrogen for 6 h. The cooled solution was diluted with ether
(100 mL) and briefly washed with sulphuric acid (40 mL of a 1 M solution)
and water (2 ꢁ 40 mL). The residue obtained upon workup was flash chro-
matographed using hexane–ethyl acetate (7 : 3) as eluent to yield the quinone
11 (662 mg; 56%) as yellow crystals, m.p. 114–116ꢀC (from hexane), nmax
3350 and 1646 cmÀ1; dH 1.36 (3H, s, 60-H), 1.86 (2H, m, 40-H), 2.40 (2H, m,
30-H), 6.64 (1H, dt, J 16.2 and 1.6 Hz, 10-H), 7.08 (1H, dt, J 16.2 and 7.0 Hz,
20-H), 7.70 (2H, m, 6- and 7-H), 7.77 (1H, s, D2O exchangeable, 2-OH), and
8.30 (2H, m, 5- and 8-H). dC 24.1, 29.7, 38.3, 64.8 (x2), 109.9, 118.7, 118.8,
126.1, 127.2, 129.6, 133.2, 135.1, 143.5, 181.6 and 184.5. (Found: C, 68.9; H,
5.6%; Mþ, 314. Calc. for C18H18O5: C, 68.8; H, 5.7%; M, 314). Further
slow elution of the column with the same solvent afforded the ketone 12
(24 mg; 24%) as dark brown crystals, m.p. 125–126ꢀC (from hexane), nmax
3344, 1723 and 1659 cmÀ1; dH 2.19 (3H, s, 60-H), 2.58–2.65 (4H, m, 40- and

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30-H), 6.60 (1H, dt, J 16.3 and 1.6 Hz, 10-H), 7.04 (1H, dt, J 16.3 and 7.1 Hz,
20-H), 7.75 (2H, m, 6- and 7-H), 7.80 (1H, s, D2O exchangeable, 2-OH), and
8.10 (2H, m, 5- and 8-H). dC 28.9, 30.1, 42.8, 118.3, 119.6, 126.2, 127.2,
129.5, 132.8, 133.3, 135.2, 141.5, 151.7, 181.6, 184.4 and 208.1. (Found: C,
71.0; H, 5.3%; Mþ, 270. Calc. for C16H14O4: C, 71.1; H, 5.2%; M, 270).
2-Hydroxy-3-(E-40-dioxolano-10-pentenyl)-1,4-naphthoquinone 14
To a solution of lawsone 1 (2.03 g; 11.7 mmol) and aldehyde 10 (2.4 g;
16.7 mmol) in acetonitrile (25 mL) was added triethylamine (4.72 g;
46.7 mmol) and the resulting ruby red solution was stirred at 75ꢀC (oil
bath) for 6 h under nitrogen. After similar workup as for quinone 11 and
flash chromatography using hexane–ethyl acetate (7 : 3) as eluent the
quinone 14 was isolated (2.11 g; 60%) as yellow crystals, m.p. 115–116ꢀC
(from hexane), nmax 3471, 1672 and 1640 cmÀ1; dH 1.39 (3H, s, 50-H), 2.64
(2H, dd, J 7.4 and 1.4 Hz, 30-H), 3.99 (4H, s, OCH2CH2O), 6.68 (1H, dt, J
16.4 and 1.4 Hz, 10-H), 7.06 (1H, dt, J 16.4 and 7.4 Hz, 20-H) 7.72 (2H, m,
6- and 7-H), 7.81 (1H, s, D2O exchangeable, 2-OH), and 8.10 (2H, m, 5- and
8-H). dC 24.3, 45.0, 65.0 (ꢁ 2C), 109.7, 118.4, 121.9, 126.1, 127.2, 129.6,
132.8, 133.3, 135.2, 138.0, 151.7, 181.6 and 184.3. (Found: C, 67.8; H,
5.5%; Mþ, 300. Calc. for C17H16O5: C, 68.0; H, 5.3%; M, 300).
2-Propyl-3,4-dehydronaphtho[2,3-b]pyran-5,10-dione 18 and
2-Butylnaphtho[2,3-b]furan-4,9-dione 19
To a solution of quinone 174 (786 mg; 3.0 mmol) in benzene (40 mL)
was added a solution of DDQ (820 mg; 3.6 mmol) in benzene (40 mL) and
the resulting solution was stirred at 25ꢀC for 18 h. The precipitated quinol
was filtered and the filtrate evaporated and the residue obtained was chro-
matographed and eluted with hexane–ethyl acetate (7 : 3) to afford firstly the
furanquinone 19 (327 mg; 43%) as yellow crystals, m.p. 102–103ꢀC (from
hexane), nmax 1684 cmÀ1; dH 0.95 (3H, t, J 7.0 Hz, 40-H), 1.42 (2H, hextet,
J 7.0 Hz, 30-H), 1.75 (2H, pentet, J 7.0 Hz, 20-H), 2.81 (2H, t, J 7.0 Hz, 10-H),
6.61 (1H, s, 3-H), 7.74 (2H, m, 6- and 7-H), and 8.17 (2H, m, 5- and 8-H). dC
13.7, 22.2, 28.1, 29.5, 77.7, 104.3, 126.9, 127.0, 128.4, 132.0, 132.8, 133.7,
134.0, 165.1, 181.2 and 183.1. (Found: C, 75.4; H, 6.4%; Mþ, 254. Calc. for
C16H14O3: C, 75.6; H, 6.3%; M, 254). Further very careful elution with the
same solvent afforded the pyranquinone 18 (320 mg; 42%) as yellow crys-
tals, m.p. 70–72ꢀC (from hexane); nmax 1672 and 1640 cmÀ1; dH 0.96 (3H, t,
J 7.2 Hz, 30-H), 1.70 (4H, m, 10- and 20-H), 5.19 (1H, m, 2-H), 5.80 (1H, dd,

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J 10.2 and 3.8 Hz, 3-H), 6.71 (1H, dd, J 10.2 and 1.4 Hz, 4-H), 7.70 (2H, m,
7- and 8-H), and 8.09 (2H, m, 6- and 8-H). dC 13.8, 17.4, 37.7, 77.7, 117.0,
118.6, 126.2 (ꢁ 2), 126.3, 128.4, 131.5, 133.5, 134.0, 153.0, 179.7 and 181.8.
(Found: C, 75.3; H, 6.4%; Mþ, 254. Calc. for C16H14O3: C, 75.6; H, 6.3%;
M, 254).
2-Propylnaphtho[2,3-b]pyran-5,10-dione 20
The quinone 18 (30 mg; 0.12 mmol) in ethyl acetate (10 mL) containing
Pd-C (10%) catalyst (5 mg) was hydrogenated for 2 h and the resulting sol-
ution passed through a short column to give the pyran 20 (30 mg; 100%) as
yellow crystals, m.p. 61–63ꢀC (from hexane); nmax 1678 cmÀ1; dH 0.99 (3H, t,
J 6.8 Hz, 30-H), 1.70 (6H, m, 10-, 20- and 3-H), 2.60 (2H, m, 4-H), 4.18 (1H,
m, 2-H), 7.68 (2H, m, 7- and 8-H), and 8.07 (2H, m, 6- and 9-H). dC 14.1,
18.4, 18.6, 25.5, 29.8, 36.5, 78.0, 117.1, 121.4, 126.1, 126.4, 132.2, 133.6,
134.0, 155.6, 179.9 and 184.5. (Found: C, 75.3; H, 6.3%; Mþ, 256. Calc.
for C16H16O3: C, 75.0; H, 6.25%; M, 256).
2-(20-Dioxolanopropyl)-naphtho[2,3-b]furan-4,9-dione 15
and 2-(10-Dioxolano-ethyl)-3,4-dehydronaphtho[2,3-b]pyran-5,10-
dione 16
To solution of quinone 14 (1.06 g; 3.53 mmol) in benzene (40 mL) was
added a solution of dichlorodicyanoquinone (962 mg; 4.24 mmol) in benzene
(40 mL) and the mixture was stirred and heated at 60ꢀC (oil bath) under
nitrogen for 2.5 h. The cooled reaction mixture was filtered and the residue
obtained after removal of the solvent was chromatographed and eluted with
hexane–ethyl acetate (3 : 7) as eluent to afford the naphthofuranquinone 15
(568 mg; 54%) as orange crystals, m.p. 142–143ꢀC (from hexane–ethyl
acetate); nmax 1666 and 1634 cmÀ1; dH 1.43 (3H, s, 30-H), 3.16 (2H, s,
10-H), 3.97 (4H, m, OCH2CH2O), 6.80 (1H, s, 3-H), 7.73 (2H, m, 6- and
7-H), and 8.19 (2H, m, 5- and 8-H). dC 24.5, 38.4, 65.1 (x2), 107.0, 108.4,
126.4, 127.0, 127.1, 131.9, 132.7, 133.3, 133.7, 133.9, 159.7, 173.2 and 181.0.
(Found: C, 68.6; H, 4.5%; Mþ, 298. Calc. for C17H14O5: C, 68.5; H, 4.7%;
M, 298). Further elution with the same solvent afforded the naphthopyran-
quinone 16 (252 mg; 24%) as orange crystals, m.p. 124–126ꢀC (from
hexane–ethyl acetate); nmax 1670 and 1640 cmÀ1; dH 1.44 (3H, d, J 1.8 Hz,
20-H), 4.00 (4H, m, OCH2CH2O), 5.08 (1H, dd, J 3.6 and 1.8 Hz), 2-H), 5.87
(1H, dd, J 10.4 and 3.6 Hz, 3-H), 6.82 (1H, dd, J 10.4 and 1.8 Hz), 4-H), 7.70
(2H, m, 7- and 8-H), 8.09 (1H, m, 6-H) and 8.19 (1H, m, 8-H). dC 20.6, 24.4,

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DDQ MEDIATED CYCLIZATION PRODUCTS
379
65.8, 66.3, 80.5, 109.9, 118.7, 122.7, 126.4, 127.1, 131.6, 131.9, 133.4, 134.2,
159, 179.3 and 181.9. (Found: C, 68.6; H, 4.6%; Mþ, 298. Calc. for
C17H14O5: C, 68.5; H, 4.7%; M, 298).
2-(20-Dioxolanopropyl)-3,4-dehydronaphtho[2,3-b]pyran-5,10-dione 13
To a solution of quinone 11 (1.12 g; 3.57 mmol) in benzene (40 mL)
was added a solution of dichlorodicyanoquinone (972 mg; 4.28 mmol) in
benzene (40 mL) and the resulting mixture was stirred under nitrogen at
25ꢀC for 12 h and then filtered. Evaporation of the filtrate afforded a residue
that was chromatographed using hexane–ethyl acetate (7 : 3) as eluent to
given the naphthopyranquinone 13 (757 mg; 68%) as bright orange crystals,
m.p. 115–116ꢀC (from hexane); nmax 1700 cmÀ1; dH 1.42 (3H, s, 30-H), 2.05
(1H, dd, J 14.8 and 6.0 Hz, 10-H), 2.37 (1H, dd, J 14.8 and 6.8 Hz, 10-H), 3.99
(4H, sharp m, OCH2CH2O), 5.37 (1H, m, 2-H), 5.90 (1H, dd, J 10.0 and
3.8 Hz, 3-H), 6.69 (1H, dd, J 10.0 and 1.6 Hz, 4-H), 7.70 (2H, m, 7- and 8-H)
and 8.09 (2H, m, 6- and 8-H). dC 25.1, 44.3, 64.7, 64.8, 74.2, 108.2, 116.8,
119.2, 126.4, 126.5, 126.9, 131.6, 131.7, 133.4, 134.2, 152.8, 179.7 and 182.0.
(Found: C, 69.3; H, 5.0%; Mþ, 312. Calc. for C18H16O5: C, 69.2; H, 5.1%;
M, 312).
ACKNOWLEDGMENTS
We wish to thank the Council of the University of the Western Cape
and the National Research Foundation for financial support and Mr. James
Beukes for laboratory assistance.
REFERENCES
1. Papageoriou, V.P.; Assimopoulou, A.N.; Couladouros, E.A.;
Hepworth, D.; Nicolaou, K.C. Angew. Chem. Int. Ed. 1999, 38,
270–300.
2. Aso, M.; Kanematsu, K. Chem. Pharm. Bull. 1993, 41(9), 1549–1556.
3. Ferreira, V.F.; Coutada, L.C.; Pinto, M.C.F.R.; Pinto, A.V. Synth.
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4. Ameer, F.; Green, I.R.; Nagabhushana, K.S. Synth. Commun. 2001,
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5. Cross, B.E.; Edinberry, M.N.; Turner, W.B. J. Chem. Soc. Perkin
Trans. 1 1973, 380–390.

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AMEER ET AL.
6. Benchikh-Le-Hocine, M.; Do Khac. D.; Fetizon, M. Synth. Commun.
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Received in the USA March 19, 2001

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