Efficient synthesis of dihydrofurans and furans by rhodium(II)-catalyzed reactions of cyclic diazodicarbonyl compounds

Article abstract of DOI:10.1016/S0040-4020(02)00118-7

An efficient synthesis of dihydrofurans and furans is achieved by rhodium-catalyzed reactions of cyclic diazodicarbonyl compounds with allyl halides. This method provides a rapid entry toward naturally occurring furocoumarin and furophenalenone derivative

Full text of DOI:10.1016/S0040-4020(02)00118-7

TETRAHEDRON
Pergamon
Tetrahedron 58 (2002) 2359±2367
Ef®cient synthesis of dihydrofurans and furans by
rhodium(II)-catalyzed reactions of cyclic
diazodicarbonyl compounds
Yong Rok Leep and Jung Yup Suk
School of Chemical Engineering and Technology, College of Engineering, Yeungnam University, Kyongsan 712-749, South Korea
Received 14 November 2001; accepted 30 January 2002
AbstractÐAn ef®cient synthesis of dihydrofurans and furans is achieved by rhodium-catalyzed reactions of cyclic diazodicarbonyl
compounds with allyl halides. This method provides a rapid entry toward naturally occurring furocoumarin and furophenalenone derivatives.
q 2002 Elsevier Science Ltd. All rights reserved.
Dihydrofurans and furans are two of the most important
heterocycles with widespread occurrence in nature.1 They
are frequently found in many natural products arising from
plants and marine organisms.2 Possessing a variety ofbio-
logical activities, they are used as pharmaceutical, ¯avor,
insecticidal, and ®sh antifeedant agents.3 Their important
biological activities and usefulness as synthetic inter-
mediates ofnatural products have prompted a search ofr
better methods ofsynthesis ofdihydroufrans and ufrans.
Although a number ofsynthetic methods for the preparation
ofdihydrofurans and furans have been reported, simple and
ef®cient approaches still remain scarce.4
Figure 1.
compounds with mesyl azide according to Taber's method.9
The rhodium-mediated decomposition ofdiazocarbonyl
Reactions with allyl halides were ®rst examined. When
diazodicarbonyl compound 5 was treated with allyl chloride
as a solvent and a reactant at room temperature for 5 h in the
presence of1 mol% ofRh 2(OAc)4, the [2,3]-rearranged
product 11 and the cycloaddition product 12 were obtained
in 75 and 12% yields, respectively (Table 1, entry 1). The
two isomers were easily separated by column chromato-
compounds has become an important method in the
synthesis of heterocyclic frameworks such as furans5 and
oxazoles.6 We have been interested in rhodium-catalyzed
reactions ofdiazodicarbonyl compounds with several
substrates.7 In particular, we have tried developing a new
methodology utilizing rhodium catalyzed reactions of
diazodicarbonyl compounds with halides such as acid
halides and benzyl halides.8 While continuing our studies
in the development ofnew synthetic applications, we
investigated the rhodium-catalyzed reactions ofdiazo-
dicarbonyl compounds with allyl halides. We report here a
new and ef®cient synthesis of dihydrofurans withexo-ole®n
and furans starting from diazodicarbonyl compounds
(Fig. 1).
1
graphy and assigned by spectroscopic data. The H NMR
spectrum of 11 showed two peaks at d 5.69 (multiplet) and
d 5.15 (double-doublet) which is associated with the vinyl
group, whereas 12 showed peaks at d 5.01 (multiplet), 3.64
(mutiplet), 2.95 (double-doublet), and 2.70 (double-doublet)
associated with the dihydrofuran ring.
With allyl bromide, the [2,3]-rearranged product 13 and the
cycloadduct 14 were also produced in 60 and 15% yields,
respectively. However, reaction of 5 with allyl iodide only
afforded cycloaddition product 15, without the formation of
the [2,3]-rearranged product, in a 92% yield. Reaction of
another diazodicarbonyl compound 10 with allyl halides
afforded similar results (entries 4±6). The results are
summarized in Table 1.
Diazodicarbonyl compounds 1±10 were prepared by the
diazotransfer reaction of the corresponding 1,3-dicarbonyl
Keywords: dihydrofurans and furans; rhodium(II)-catalyzed reaction;
cyclic diazodicarbonyl.
p
Corresponding author. Tel.: 182-53-810-2529; fax: 182-53-814-8790;
e-mail: yrlee@ynucc.yeungnam.ac.kr
0040±4020/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(02)00118-7

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Y. R. Lee, J. Y. Suk / Tetrahedron 58 (2002) 2359±2367
Table 1. Rhodium(II)-catalyzed reactions ofdiazodicarbonyl compounds with ally halides
Entry
1
Diazodicarbonyl compound
Allyl halide
Product
2
3
4
5
6
7
8
Scheme 1.

Y. R. Lee, J. Y. Suk / Tetrahedron 58 (2002) 2359±2367
2361
Figure 2.
Next, rhodium(II)-catalyzed reactions with other allyl
halides such as crotyl bromide and 3-bromocyclohexene
were examined. Treatment of 5 with crotyl bromide in the
presence of1 mol% ofrhodium(II) acetate aoffrded the
[2,3]-rearranged product 21 in 70% yield (entry 7). In this
case, no cycloadducts were found. Interestingly, with
3-bromocyclohexene, cycloadduct 22 was obtained in
58% yield as a mixture ofdiastereomers ofunassigned
stereochemistry (entry 8). This reaction produces a dramatic
reversal in the formation of product.
chemical shifts associated with the exo-ole®n group ofthe
dihydrofuran ring. On the other hand, increasing the
temperature in¯uences the formation of products. Heating
the iodide 15 at re¯ux with 3 equiv. ofDBU in toluene for
2 h afforded furan 32 in 88% yield, possibly via both
elimination and direct isomerization (method B). The
structure of 32 is easily identi®ed by the chemical shift of
the vinylic proton in the furan ring. Similarly other results
are also summarized in Table 2 (entries 1±4). These
reactions are expected to be used as a rapid way of
constructing dihydrofurans with exo-ole®n and 2-methyl-
furans. On the other hand, treatment of 22 with 3 equiv. of
DBU at re¯ux for 2 h in toluene gave 41 in 93% yield
(entry 5) (Scheme 2).
In view ofour results, competition between ylide generation
and 1,3-dipolar cycloaddition could be manipulated by
varying the electronegativity ofthe halogen in allyl halides.
Reactions with allyl chloride and allyl bromide resulted in
[2,3]-rearranged products as a major component via ylide
generation (path a), whereas reactions with allyl iodide
afforded 1,3-dipolar cycloaddition products as a single
compound (path b) as shown in Scheme 1. The decreased
electronegativity ofthe halogen going rfom chlorine to
iodine almost exclusively afforded 1,3-dipolar cyclo-
addition relative to the ole®n. These results are in clear
contrast to those ofDoyle, who reported that the
rhodium(II)-catalyzed reactions ofethyl diazoacetate with
allyl iodide afforded the [2,3]-rearranged product as a single
compound, whereas the cyclopropanation adduct occurred
almost exclusively with allyl chloride and bromide.10
However, reaction ofiodides 27±30 with DBU in benzene
(method A) at room temperature for 20 h gave furo-
coumarins 42±45 in 80±98% yields (entries 6±9). In these
cases, no expected dihydrofurocoumarins with exo-ole®n
were obtained. These reactions also provide a rapid
synthetic route toward furocoumarin derivatives which are
known to have such biological activities as anticoagulant,
insecticide, anthelminthic, hypnotic, antifungal, and HIV
protease inhibition.11 Although there are currently several
methods available for the synthesis of furocoumarins, their
synthetic exploitation has been limited by the dif®culties in
controlling regiochemistry ofthe linear and angular
adduct.12 Our technique is experimentally simple and highly
regioselective. Similarly, treatment of 20 with DBU in
benzene (method A) afforded furophenalenone derivative
43 in 98% yield, which is reported to have important
biological activities such as antibiotic, antimicrobial, and
phytoalexin (entry 10).13 The data are collected in Table 2.
Additional reactions ofa variety ofcyclic diazodicarbonyl
compounds with allyl iodide were next investigated.
Treatment ofdiazodicarbonyl compounds 1±4 with allyl
iodide gave the expected iodomethyldihydrofurans 23±26
in 88±93% yields after column chromatography. Extension
to 3-diazo-2,4-chromenediones was also successful.
Reactions of 6±9 with allyl iodide gave biologically
interesting iodomethyldihydrofurocoumarin derivatives
27±30 in 58±78% yields. The results are collected in
Fig. 2. These results seemed ideal for the synthesis of
dihydrofurans with exo-ole®n and 2-methylfurans by the
reaction ofcyclic diazodicarbonyl compounds with ally
iodide in the presence of1 mol% ofRh 2(OAc)4.
In conclusion, the rhodium(II)-catalyzed reactions ofcyclic
diazodicarbonyl compounds with allyl halides are
described. These reactions provide a rapid entry to the
synthesis ofdihydroufrans with exo-ole®n and 2-methyl-
furans. This methodology is expected to be widely used in
the synthesis of furocoumarin and furophenalenone natural
products.
Next, conversion ofthe halides to dihydrofurans with exo-
ole®n or 2-methylfurans was examined by two methods.
Reaction ofiodide 15 with 3 equiv. ofDBU in benzene at
room temperature for 20 h gave dihydrofuran 31 with exo-
ole®n in 94% yield, without the contamination ofisomeric
furans (method A). The dihydrofuran 31 is assigned by the
1. Experimental
All experiments were carried out under nitrogen
atmosphere. Merck precoated silica gel plates (Art. 5554)
with ¯uorescent indicator were used for analytical TLC.

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Y. R. Lee, J. Y. Suk / Tetrahedron 58 (2002) 2359±2367
Table 2. Synthesis of dihydrofurans and furans
Entry
Iodomethyldihydrofuran
Dihydrofuran, method A
2-Methylfuran, method B
1
2
3
4
5
6
7
8
9
10
Flash column chromatography was performed using silica
gel 9385 (Merck). Melting points were determined with
microcover glasses on a Fisher±Johns apparatus and are
uncorrected. Proton nuclear magnetic resonance (1H
NMR) spectra were recorded on a Bruker Model ARX
(300 MHz) spectrometer. IR spectra were recorded on a
JASCO FTIR 5300 spectrophotometer. High resolution
mass (HRMS) spectra were obtained on VG-MICROMASS
Autospec at Yeungnam University and JEOL JMS-700
spectrometer at Korea Basic Science Institute.

Y. R. Lee, J. Y. Suk / Tetrahedron 58 (2002) 2359±2367
2363
Scheme 2.
1.1. General procedure for the reactions of
diazodicarbonyl compounds and allyl halides
(75 MHz, CDCl3) d 194.49, 175.60, 111.30, 83.06, 50.76,
37.44, 34.45, 34.01, 30.49, 28.69, 28.35; IR (neat) 2961,
2872, 1634, 1404, 1368, 1260, 1219, 1169, 1146, 1099,
1040, 961 cm21; HRMS m/z (M1) calcd for C11H15O2Br:
258.0256. Found: 258.0251.
To a solution ofdiazodicarbonyl compound (1.0 mmol)
and allyl halide (3 mL) was added rhodium acetate
(5 mg, 0.01 mmol) at room temperature. The mixture
was stirred for 5 h under nitrogen. Evaporation of
allyl halide and puri®cation by silica gel chromatography
with 33% ethyl acetate in hexane as eluent afforded
products.
1.1.3. 2-Iodomethyl-6,6-dimethyl-2,3,4,5,6,7-hexahydro-
benzofuran-4-one (15). Reaction of5,5-dimethyl-2-diazo-
cyclohexane-1,3-dione (166 mg, 1.0 mmol) with allyl
iodide (3 mL) using rhodium acetate (5 mg, 0.01 mmol) as
1
a catalyst afforded 15 (282 mg, 92%) as a liquid: H NMR
(300 MHz, CDCl3) d 4.76 (1H, m), 3.29 (2H, d, Jˆ5.3 Hz),
2.93 (1H, dd, Jˆ14.6, 10.1 Hz), 2.54 (1H, dd, Jˆ14.6,
6.7 Hz), 2.24 (2H, s), 2.16 (2H, s), 1.05 (6H, s); 13C NMR
(75 MHz, CDCl3) d 194.40, 175.40, 111.20, 83.19, 50.73,
37.46, 33.93, 32.25, 28.70, 28.37, 8.72; IR (neat) 2959,
2870, 1636, 1402, 1368, 1256, 1219, 1167, 1144, 1098,
1.1.1. 2-Ally-2-chloro-5,5-dimethylcyclohexane-1,3-dione
(11) and 2-chloromethyl-6,6-dimethyl-3,5,6,7-tetra-
hydro-2H-benzofuran-4-one (12). Reaction of5,5-
dimethyl-2-diazocyclohexane-1,3-dione (166 mg, 1.0 mmol)
with allyl chloride (3 mL) using rhodium acetate (5 mg,
0.01 mmol) as a catalyst afforded 11 (161 mg, 75%) and
;
1038, 947, 930 cm21 HRMS m/z (M1) calcd for
1
12 (26 mg, 12%). 11: mp 30±328C; H NMR (300 MHz,
C11H15O2I: 306.0117. Found: 306.0113.
CDCl3) d 5.69 (1H, m), 5.15 (2H, dd, Jˆ17.2, 11.0 Hz),
3.10 (2H, d, Jˆ14.0 Hz), 2.87 (2H, d, Jˆ7.1 Hz), 2.42
(2H, d, Jˆ14.5 Hz), 1.11 (3H, s), 0.84 (3H, s); 13C NMR
(75 MHz, CDCl3) d 200.40 (2CO), 132.06, 121.10, 70.76,
49.74, 37.09, 30.52, 29.65, 26.58 (2CH3); IR (KBr) 3084,
2961, 2932, 2874, 1714, 1446, 1425, 1323, 1250, 1199,
1074, 1001, 932 cm21; HRMS m/z (M1) calcd for
C11H15ClO2: 214.0757. Found: 214.0754. 12: 1H NMR
(300 MHz, CDCl3) d 5.01 (1H, m), 3.64 (2H, m), 2.95
(1H, dd, Jˆ16.0, 8.6 Hz), 2.70 (1H, dd, Jˆ16.0, 6.8 Hz),
2.29 (2H, s), 2.21 (2H, s), 1.08 (6H, s); 13C NMR (75 MHz,
CDCl3) d 194.46, 175.74, 111.27, 83.40, 50.68, 46.00,
37.36, 33.95, 29.19, 28.60, 28.27; IR (neat) 2959, 2872,
1636, 1404, 1369, 1260, 1221, 1168, 1145, 1099, 1044,
978 cm21; HRMS m/z (M1) calcd for C11H15ClO2:
214.0757. Found: 214.0756.
1.1.4. 2-Allyl-2-chlorophenalene-1,3-dione (16) and 9-
chloromethyl-8,9-dihydrophenaleno[1,2-b]furan-7-one
(17). Reaction of2-diazophenalene-1,3-dione (222 mg,
1.0 mmol) with allyl chloride (3 mL) using rhodium acetate
(5 mg, 0.01 mmol) as a catalyst afforded 16 (200 mg, 74%)
and 17 (57 mg, 21%). 16: mp 142±1448C; 1H NMR
(300 MHz, CDCl3) d 8.50 (2H, d, Jˆ7.2 Hz), 8.25 (2H, d,
Jˆ8.2 Hz), 7.77 (2H, dd, Jˆ8.2, 7.2 Hz), 5.73 (1H, m), 5.10
(2H, dd, Jˆ17.4, 9.4 Hz), 3.19 (2H, d, Jˆ6.9 Hz); IR (KBr)
3080, 2932, 2861, 1709, 1687, 1580, 1506, 1433, 1316,
1231, 1009, 930, 837 cm21; HRMS m/z (M1) calcd for
C16H11ClO2: 270.0445. Found: 270.0448. 17: mp 130±
1328C; 1H NMR (300 MHz, CDCl3) d 8.60 (1H, d,
Jˆ7.5 Hz), 8.11 (1H, d, Jˆ7.8 Hz), 8.05 (2H, m), 7.72
(1H, dd, Jˆ7.8, 7.5 Hz), 7.60 (1H, dd, Jˆ7.8, 7.5 Hz),
5.28 (1H, m), 3.81 (2H, d, Jˆ5.3 Hz), 3.39 (1H, dd,
Jˆ15.9, 10.0 Hz), 3.14 (1H, dd, Jˆ15.9, 6.5 Hz); IR
(KBr) 3016, 2918, 2851, 1626, 1584, 1510, 1437, 1381,
1.1.2. 2-Ally-2-bromo-5,5-dimethylcyclohexane-1,3-dione
(13) and 2-bromomethyl-6,6-dimethyl-3,5,6,7-tetra-
hydro-2H-benzofuran-4-one (14). Reaction of5,5-
dimethyl-2-diazocyclohexane-1,3-dione (166 mg, 1.0 mmol)
with allyl bromide (3 mL) using rhodium acetate (5 mg,
0.01 mmol) as a catalyst afforded 13 (155 mg, 60%) and
1267, 1219, 1192, 1151, 1103, 1039, 1020, 889 cm21
;
HRMS m/z (M1) calcd for C16H11ClO2: 270.0445. Found:
270.0447.
1
14 (39 mg, 15%). 13: H NMR (300 MHz, CDCl3) d 5.60
1.1.5. 2-Allyl-2-bromophenalene-1,3-dione (18) and 9-
bromomethyl-8,9-dihydrophenaleno[1,2-b]furan-7-one
(19). Reaction of2-diazo-phenalene-1,3-dione (222 mg,
1.0 mmol) with allyl bromide (3 mL) using rhodium acetate
(5 mg, 0.01 mmol) as a catalyst afforded 18 (188 mg, 60%)
and 19 (82 mg, 26%). 18: mp 53±558C; 1H NMR
(300 MHz, CDCl3) d 8.54 (2H, d, Jˆ7.3 Hz), 8.24 (2H, d,
Jˆ8.3 Hz), 7.76 (2H, dd, Jˆ8.3, 7.3 Hz), 5.74 (1H, m), 5.15
(2H, dd, Jˆ17.2, 10.2 Hz), 3.48 (2H, d, Jˆ7.0 Hz); IR
(KBr) 3082, 3018, 2982, 1697, 1672, 1578, 1507, 1431,
1311, 1232, 1201, 1167, 999, 929 cm21; HRMS m/z (M1)
(1H, m), 5.11 (2H, dd, Jˆ17.2, 10.1 Hz), 3.23 (2H, d,
Jˆ14.6 Hz), 2.97 (2H, d, Jˆ7.1 Hz), 2.34 (2H, d,
Jˆ14.6 Hz), 1.09 (3H, s), 0.74 (3H, s); 13C NMR
(75 MHz, CDCl3) d 200.40 (2CO), 132.06, 121.10, 60.08,
49.35, 36.42, 30.86, 30.30, 25.58 (2CH3); IR (neat) 3083,
2959, 2930, 2872, 1709, 1466, 1425, 1393, 1373, 1299,
1250, 1199, 1085, 1072, 1002, 931 cm21; HRMS m/z
(M1) calcd for C11H15O2 Br: 258.0256. Found: 258.0255.
14: 1H NMR (300 MHz, CDCl3) d 4.99 (1H, m), 3.50 (2H,
m), 2.95 (1H, dd, Jˆ14.2, 10.2 Hz), 2.69 (1H, dd, Jˆ14.2,
6.7 Hz), 2.28 (2H, s), 2.20 (2H, s), 1.07 (6H, s); 13C NMR

2364
Y. R. Lee, J. Y. Suk / Tetrahedron 58 (2002) 2359±2367
calcd for C16H11BrO2: 313.9939. Found: 313.9943. 19: mp
45±478C; 1H NMR (300 MHz, CDCl3) d 8.60 (1H, d,
Jˆ7.6 Hz), 8.11 (1H, d, Jˆ7.8 Hz), 8.05 (2H, m), 7.71
(1H, dd, Jˆ7.8, 7.6 Hz), 7.60 (1H, dd, Jˆ7.8, 7.6 Hz),
5.28 (1H, m), 3.67 (2H, m), 3.40 (1H, dd, Jˆ15.8,
10.0 Hz), 3.12 (1H, dd, Jˆ15.8, 6.8 Hz); IR (KBr) 2920,
1628, 1584, 1510, 1422, 1381, 1262, 1219, 1192, 1150,
1101, 1032, 885 cm21; HRMS m/z (M1) calcd for
C16H11BrO2: 313.9939. Found: 313.9944.
HRMS m/z (M1) calcd for C9H11O2I: 277.9804. Found:
277.9804.
1.1.10.
2-Iodomethyl-6-methyl-2,3,4,5,6,7-hexahydro-
benzofuran-4-one (24). Reaction of5-methyl-2-diazo-
cyclohexane-1,3-dione (152 mg, 1.0 mmol) with allyl
iodide (3 mL) using rhodium acetate (5 mg, 0.01 mmol) as
1
a catalyst afforded 24 (286 mg, 93%) as a liquid: H NMR
(300 MHz, CDCl3) d 4.78 (1H, m), 3.28 (2H, dd, Jˆ7.0,
6.8 Hz), 2.91 (1H, m), 2.54 (1H, m), 2.37 (2H, m), 2.24 (1H,
m), 2.05 (2H, m), 1.05 (3H, d, Jˆ6.4 Hz); IR (neat) 2955,
2870, 1636, 1454, 1402, 1335, 1252, 1209, 1140, 1119,
1046, 1026, 937 cm21; HRMS m/z (M1) calcd for
C10H13O2I: 291.9960. Found: 291.9961.
1.1.6. 9-Iodomethyl-8,9-dihydro-phenaleno[1,2-b]furan-
7-one (20). Reaction of2-diazophenalene-1,3-dione
(222 mg, 1.0 mmol) with allyl iodide (3 mL) using rhodium
acetate (5 mg, 0.01 mmol) as a catalyst afforded 20
(293 mg, 81%) as a solid: mp 112±1138C; 1H NMR
(300 MHz, CDCl3) d 8.60 (1H, d, Jˆ7.3 Hz), 8.11 (1H, d,
Jˆ7.8 Hz), 8.06 (1H, d, Jˆ7.6 Hz), 8.03 (1H, d, Jˆ7.6 Hz),
7.71 (1H, dd, Jˆ7.8, 7.6 Hz), 7.60 (1H, dd, Jˆ7.8, 7.6 Hz),
5.13 (1H, m), 3.48 (3H, m), 3.02 (1H, dd, Jˆ15.8, 6.7 Hz);
13C NMR (75 MHz, CDCl3) d 181.48, 166.00, 134.13,
133.00, 131.83, 129.89, 126.85, 126.48, 125.94, 120.68,
114.63, 83.96, 33.67, 8.22; IR (KBr) 3051, 2951, 2853,
1622, 1582, 1564, 1510, 1422, 1381, 1258, 1217, 1186,
1150, 1018, 956 cm21; HRMS m/z (M1) calcd for
C16H11IO2: 361.9801. Found: 361.9804.
1.1.11. 2-Iodomethyl-6-isopropyl-2,3,4,5,6,7-hexahydro-
benzofuran-4-one (25). Reaction of5-isopropyl-2-diazo-
cyclohexane-1,3-dione (180 mg, 1.0 mmol) with allyl
iodide (3 mL) using rhodium acetate (10 mg, 0.02 mmol)
1
as a catalyst afforded 25 (297 mg, 93%) as a liquid: H
NMR (300 MHz, CDCl3) d 4.79 (1H, m), 3.27 (2H, dd,
Jˆ10.2, 5.9 Hz), 2.90 (1H, m), 2.52 (1H, m), 2.38 (2H,
m), 2.06 (2H, m), 1.91 (1H, m), 1.56 (1H, m), 0.87 (6H,
d, Jˆ6.7 Hz); IR (neat) 2959, 2872, 1638, 1402, 1372, 1254,
1206, 1152, 1111, 1038, 939 cm21; HRMS m/z (M1) calcd
for C12H17O2I: 320.0273. Found: 320.0270.
1.1.7.
2-Bromo-5,5-dimethyl-2-(1-methyl-allyl)-cyclo-
hexane-1,3-dione (21). Reaction of5,5-dimethyl-2-diazo-
cyclohexane-1,3-dione (166 mg, 1.0 mmol) with crotyl
bromide (3 mL) using rhodium acetate (5 mg, 0.01 mmol)
as a catalyst afforded 21 (191 mg, 70%); 1H NMR
(300 MHz, CDCl3) d 5.96 (1H, m), 5.08 (2H, dd, Jˆ16.7,
11.0 Hz), 3.21 (3H, m), 2.45 (2H, d, Jˆ14.7 Hz), 1.23 (3H,
d, Jˆ6.9 Hz), 1.06 (3H, s), 0.88 (3H, s); IR (neat) 3080,
2959, 2874, 1707, 1640, 1464, 1418, 1395, 1373, 1325,
1298, 1242, 1217, 1080, 925 cm21; HRMS m/z (M1)
calcd for C12H17 BrO2: 272.0407. Found: 272.0411.
1.1.12. 2-Iodomethyl-5,5-dimethyl-2,3,4,5,6,7-hexahydro-
benzofuran-4-one (26). Reaction of4,4-dimethyl-2-diazo-
cyclohexane-1,3-dione (166 mg, 1.0 mmol) with allyl
iodide (3 mL) using rhodium acetate (5 mg, 0.01 mmol) as
a catalyst afforded 26 (269 mg, 88%) as a solid: mp 59±
1
618C; H NMR (300 MHz, CDCl3) d 4.70 (1H, m), 3.27
(2H, d, Jˆ4.9 Hz), 2.90 (1H, dd, Jˆ14.9, 10.1 Hz), 2.53
(1H, dd, Jˆ14.9, 6.4 Hz), 2.34 (2H, t, Jˆ6.0 Hz), 1.78
(2H, t, Jˆ6.0 Hz), 1.19 (3H, s), 1.16 (3H, s); IR (KBr)
2965, 2930, 2865, 1651, 1628, 1472, 1400, 1341, 1292,
1248, 1198, 1157, 1119, 1065, 1005, 937 cm21; HRMS
m/z (M1) calcd for C11H15O2I: 306.0117. Found: 306.0114.
1.1.8. 6-Bromo-3,4,5a,6,7,9,9a-octahydro-2H-dibenzo-
furan-1-one (22). Reaction of2-diazocyclohexane-1,3-
dione (138 mg, 1.0 mmol) with 3-bromocyclohexene
(3 mL) using rhodium acetate (5 mg, 0.01 mmol) as a
catalyst afforded 22 (157 mg, 58%) as a mixture ofdia-
1.1.13. 2-Iodomethyl-2,3-dihydrofuro[3,2-c]chromen-4-
one (27). Reaction of3-diazo-chroman-2,4-dione (188 mg,
1.0 mmol) with allyl iodide (3 mL) using rhodium acetate
(5 mg, 0.01 mmol) as a catalyst afforded 27 (256 mg, 78%)
1
stereomers. Major isomer: H NMR (300 MHz, CDCl3) d
1
4.78 (1H, dd, Jˆ8.3, 7.1 Hz), 4.21 (1H, m), 3.28 (1H, m),
2.39 (2H, m), 2.30 (2H, m), 2.04±1.50 (8H, m); IR (neat)
2946, 2868, 1626, 1454, 1421, 1399, 1179, 1136, 1059, 997,
972, 922 cm21; HRMS m/z (M1) calcd for C12H15BrO2:
270.0251. Found: 270.0254. Minor isomer: 1H NMR
(300 MHz, CDCl3) d 4.91 (1H, m), 4.72 (1H, d, Jˆ7.1,
3.5 Hz), 3.63 (1H, m), 2.39 (2H, m), 2.30 (2H, m), 2.04±
1.50 (8H, m).
as a solid: mp 144±1458C; H NMR (300 MHz, CDCl3) d
7.64 (1H, d, Jˆ7.8 Hz), 7.55 (1H, dd, Jˆ8.4, 7.8 Hz), 7.36
(1H, d, Jˆ8.4 Hz), 7.27 (1H, dd, Jˆ8.4, 7.8 Hz), 5.14 (1H,
m), 3.48 (2H, m), 3.34 (1H, dd, Jˆ15.6, 9.9 Hz), 2.97 (1H,
dd, Jˆ15.6, 6.8 Hz); IR (KBr) 3061, 3019, 2959, 1724,
1644, 1603, 1566, 1495, 1443, 1414, 1343, 1300, 1273,
1252, 1211, 1150, 1094, 1030, 910 cm21; HRMS m/z
(M1) calcd for C12H9O3I: 327.9597. Found: 327.9596.
1.1.9. 2-Iodomethyl-2,3,4,5,6,7-hexahydrobenzofuran-4-
one (23). Reaction ofof2-diazocyclohexane-1,3-dione
(138 mg, 1.0 mmol) with allyl iodide (3 mL) using rhodium
acetate (5 mg, 0.01 mmol) as a catalyst afforded 23
(252 mg, 91%) as a solid: mp 72±748C; 1H NMR
(300 MHz, CDCl3) d 4.78 (1H, m), 3.28 (2H, d,
Jˆ5.6 Hz), 2.92 (1H, m), 2.92 (1H, dd, Jˆ14.5, 10.7 Hz),
2.52 (1H, dd, Jˆ14.5, 6.5 Hz), 2.38 (2H, m), 2.28 (2H, t,
Jˆ6.2 Hz), 1.98 (2H, m); IR (KBr) 2946, 2866, 1634, 1453,
1.1.14. 2-Iodomethyl-9-methyl-2,3-dihydro-furo[3,2-c]-
chromen-4-one (28). Reaction of3-diazo-5-methyl-
chroman-2,4-dione (202 mg, 1.0 mmol) with allyl iodide
(3 mL) using rhodium acetate (5 mg, 0.01 mmol) as a
catalyst afforded 28 (215 mg, 63%) as a solid: mp 130±
1318C; 1H NMR (300 MHz, CDCl3) d 7.40 (1H, dd,
Jˆ8.0, 7.8 Hz), 7.19 (1H, d, Jˆ8.0 Hz), 7.03 (1H, d,
Jˆ7.8 Hz), 5.14 (1H, m), 3.46 (2H, m), 3.30 (1H, dd,
Jˆ15.6, 10.1 Hz), 2.91 (1H, dd, Jˆ15.6, 6.7 Hz), 2.67
(3H, s); IR (KBr) 3057, 2961, 2856, 1709, 1632, 1601,
1402, 1339, 1231, 1181, 1140, 1109, 1059, 1011, 976 cm21
;

Y. R. Lee, J. Y. Suk / Tetrahedron 58 (2002) 2359±2367
2365
1483, 1447, 1418, 1393, 1254, 1223, 1142, 1049, 1026,
914 cm21 HRMS m/z (M1) calcd for C13H11IO3:
341.9750. Found: 341.9752.
3.48 (2H, m), 2.36 (2H, s), 2.25 (2H, s), 1.12 (6H, s); 13C
NMR (75 MHz, CDCl3) d 193.25, 173.88, 160.69, 112.63,
87.87, 50.63, 36.71, 33.83, 29.05, 28.41, 28.33; IR (KBr)
2959, 2924, 2886, 1640, 1466, 1402, 1372, 1346, 1402,
1372, 1346, 1296, 1231, 1204, 1165, 1148, 1092, 1032,
;
1.1.15. 2-Iodomethyl-8-methyl-2,3-dihydrofuro[3,2-c]-
chromen-4-one (29). Reaction of3-diazo-6-methyl-
chroman-2,4-dione (202 mg, 1.0 mmol) with allyl iodide
(3 mL) using rhodium acetate (5 mg, 0.01 mmol) as a
catalyst afforded 29 (198 mg, 58%) as a solid: mp 142±
;
1019, 974, 926 cm21 HRMS m/z (M1) calcd for
C11H14O2: 178.0994. Found: 178.0996.
1.3.2. 2,6,6-Trimethyl-4,5,6,7-tetrahydrobenzofuran-4-
one (32). Reaction ofthe iodide 15 (141 mg, 0.5 mmol)
with DBU (228 mg, 1.5 mmol) in toluene (method B)
1
1438C; H NMR (300 MHz, CDCl3) d 7.43 (1H, s), 7.36
(1H, d, Jˆ8.2 Hz), 7.25 (1H, d, Jˆ8.2 Hz), 5.15 (1H, m),
3.48 (2H, m), 3.34 (1H, dd, Jˆ15.6, 10.0 Hz), 2.96 (1H, dd,
Jˆ15.6, 6.8 Hz), 2.40 (3H, s); IR (KBr) 2961, 1720, 1649,
1612, 1578, 1500, 1441, 1400, 1346, 1298, 1273, 1252,
1206, 1100, 1042, 1009, 936 cm21; HRMS m/z (M1)
calcd for C13H11IO3: 341.9750. Found: 341.9754.
1
afforded 32 (72 mg, 88%) as a liquid: H NMR (300 MHz,
CDCl3) d 6.16 (1H, s), 2.62 (2H, s), 2.27 (2H, s), 2.22 (3H,
s), 1.06 (6H, s); 13C NMR (75 MHz, CDCl3) d 193.76,
164.97, 152.73, 120.64, 101.69, 51.84, 37.20, 35.10,
28.51, 28.43, 13.29; IR (neat) 2961, 2874, 1680, 1605,
1584, 1433, 1387, 1346, 1302, 1248, 1227, 1184, 1115,
1933, 930 cm21; HRMS m/z (M1) calcd for C11H14O2:
178.0994. Found: 178.0991.
1.1.16. 2-(Iodomethyl)-7-methyl-2,3-dihydro-4H-furo-
[3,2-c]chromen-4-one (30). Reaction of3-diazo-7-methyl-
chroman-2,4-dione (202 mg, 1.0 mmol) with allyl iodide
(3 mL) using rhodium acetate (5 mg, 0.01 mmol) as a
catalyst afforded 30 (212 mg, 62%) as a solid: mp 105±
1068C; 1H NMR (300 MHz, CDCl3) d 7.50 (1H, d,
Jˆ8.0 Hz), 7.15 (1H, s), 7.08 (1H, d, Jˆ8.0 Hz), 5.15
(1H, m), 3.46 (2H, m), 3.32 (1H, dd, Jˆ15.5, 9.9 Hz),
2.94 (1H, dd, Jˆ15.5, 7.0 Hz), 2.43 (3H, s); IR (KBr)
3061, 2926, 1719, 1647, 1620, 1516, 1424, 1358, 1163,
1036, 912 cm21; HRMS m/z (M1) calcd for C13H11IO3:
341.9750. Found: 341.9751.
1.3.3. 2-Methylene-2,3,4,5,6,7-hexahydrobenzofuran-4-
one (33). Reaction ofthe iodide 23 (355 mg, 1.3 mmol)
with DBU (594 mg, 3.9 mmol) in benzene (method A)
1
afforded 33 (156 mg, 81%) as a solid: mp 33±348C; H
NMR (300 MHz, CDCl3) d 4.76 (1H, dd, Jˆ5.6, 2.7 Hz),
4.42 (1H, dd, Jˆ5.3, 2.7 Hz), 3.47 (2H, m), 2.51 (2H, m),
2.38 (2H, t, Jˆ6.6 Hz), 2.09 (2H, m); IR (KBr) 2943, 1653,
1456, 1402, 1362, 1256, 1235, 1206, 1181, 1144, 1101,
1057, 997, 922 cm21; HRMS m/z (M1) calcd for C9H10O2:
150.0681. Found: 150.0685.
1.2. General procedure for the preparation of
dihydrofurans with exo-ole®n (method A)
1.3.4. 2-Methyl-4,5,6,7-tetrahydrobenzofuran-4-one (34).
Reaction ofthe iodide 23 (210 mg, 0.8 mmol) with DBU
(365 mg, 2.4 mmol) in toluene (method B) afforded 34
(94 mg, 83%) as a solid: mp 36±378C; 1H NMR
(300 MHz, CDCl3) d 6.23 (1H, s), 2.82 (2H, t, Jˆ6.3 Hz),
2.48 (2H, t, Jˆ6.5 Hz), 2.29 (3H, s), 2.15 (2H, m); IR (KBr)
2951, 1674, 1582, 1458, 1433, 1383, 1358, 1433, 1383,
1358, 1316, 1238, 1192, 1163, 1123, 1057, 1011, 988,
938 cm21; HRMS m/z (M1) calcd for C9H10O2: 150.0681.
Found: 150.0683.
DBU (0.9±3.9 mmol) was added to a stirred solution ofthe
iodide (0.3±1.3 mmol) in benzene (5 mL). The solution was
stirred at room temperature for 20 h. To the mixture, water
(20 mL) was added and the solution was extracted with
ethyl acetate (3£20 mL). The combined organic extracts
were washed with saturated ammonium chloride solution
and evaporated under reduced pressure to give the residue.
The residue was puri®ed by ¯ash chromatography on silica
gel with 33% ethyl acetate in hexane as eluent to give the
product.
1.3.5. 6-Methyl-2-methylene-2,3,4,5,6,7-hexahydroben-
zofuran-4-one (35). Reaction ofthe iodide 24 (215 mg,
0.74 mmol) with DBU (338 mg, 2.2 mmol) in benzene
(method A) afforded 35 (107 mg, 88%) as a solid: mp 42±
1.3. General procedure for the preparation of 2-methyl-
furans (method B)
1
448C; H NMR (300 MHz, CDCl3) d 4.69 (1H, dd, Jˆ5.7,
2.7 Hz), 4.35 (1H, dd, Jˆ5.3, 2.7 Hz), 3.40 (2H, m), 2.54
(1H, dd, Jˆ16.8, 3.0 Hz), 2.42 (1H, dd, Jˆ16.8, 3.0 Hz),
2.33 (1H, m), 2.20 (1H, m), 2.10 (2H, Jˆ16.1, 10.0 Hz),
1.12 (3H, d, Jˆ6.4 Hz); IR (KBr) 2955, 2874, 1640, 1456,
DBU (1.2±3.0 mmol) was added to a stirred solution ofthe
iodide (0.4±1.0 mmol) in toluene (5 mL). The solution was
re¯uxed for 2 h. To the cold mixture, water (20 mL) was
added and the solution was extracted with ethyl acetate
(3£20 mL). The combined organic extracts were washed
with saturated ammonium chloride solution and evaporated
under reduced pressure to give residue. The residue was
puri®ed by ¯ash chromatography on silica gel with 33%
ethyl acetate in hexane as eluent to give the product.
1399, 1323, 1226, 1196, 1140, 1109, 1040, 1019, 931 cm21
;
HRMS m/z (M1) calcd for C10H12O2: 164.0838. Found:
164.0839.
1.3.6. 2,6-Dimethyl-4,5,6,7-tetrahydrobenzofuran-4-one
(36). Reaction ofthe iodide 24 (200 mg, 0.7 mmol) with
DBU (320 mg, 2.1 mmol) in toluene (method B) afforded
36 (95 mg, 85%) as a solid: mp 58±608C; 1H NMR
(300 MHz, CDCl3) d 6.21 (1H, s), 2.89 (1H, dd, Jˆ15.7,
4.0 Hz), 2.86±2.38 (3H, m), 2.27 (3H, s), 2.20 (1H, dd,
Jˆ15.2, 9.9 Hz), 1.13 (3H, d, Jˆ6.3 Hz); 13C NMR
(75 MHz, CDCl3) d 194.14, 165.61, 152.61, 121.48,
1.3.1. 6,6-Dimethyl-2-methylene-2,3,4,5,6,7-hexahydro-
benzofuran-4-one (31). Reaction ofthe iodide 15
(245 mg, 0.8 mmol) with DBU (365 mg, 2.4 mmol) in
benzene (method A) afforded 31 (134 mg, 94%) as a
solid: mp 61±628C; H NMR (300 MHz, CDCl3) d 4.75
1
(1H, dd, Jˆ5.8, 2.7 Hz), 4.41 (1H, dd, Jˆ5.3, 2.7 Hz),

2366
Y. R. Lee, J. Y. Suk / Tetrahedron 58 (2002) 2359±2367
101.71, 45.92, 31.26, 30.74, 20.94, 13.29; IR (KBr) 2951,
1674, 1582, 1458, 1433, 1358, 1238, 1123, 1057, 1011,
938 cm21; HRMS m/z (M1) calcd for C10H12O2: 164.0838.
Found: 164.0840.
1.3.12. 2-Methylfuro[3,2-c]chromen-4-one (42). Reaction
ofthe iodide 27 (328 mg, 1.0 mmol) with DBU (457 mg,
3.0 mmol) in benzene (method A) afforded 42 (160 mg,
80%) as a solid: mp 166±1688C; 1H NMR (300 MHz,
CDCl3) d 7.82 (1H, d, Jˆ7.4 Hz), 7.44 (2H, m), 7.33
(1H, d, Jˆ7.2 Hz), 6.56 (1H, s), 2.49 (3H, s); 13C NMR
(75 MHz, CDCl3) d 158.40, 156.70, 155.66, 152.23,
130.10, 124.37, 120.50, 117.22, 112.87, 111.58, 104.06,
13.76; IR (KBr) 3106, 2919, 1728, 1632, 1589, 1502,
1451, 1360, 1319, 1283, 1250, 1203, 1101, 1061, 1030,
974 cm21; HRMS m/z (M1) calcd for C12H8O3: 200.0471.
Found: 200.0470.
1.3.7. 6-Isopropyl-2-methylene-2,3,4,5,6,7-hexahydro-
benzofuran-4-one (37). Reaction ofthe iodide
25
(270 mg, 0.84 mmol) with DBU (365 mg, 2.4 mmol) in
benzene (method A) afforded 37 (143 mg, 88%) as a liquid:
1H NMR (300 MHz, CDCl3) d 4.73 (1H, dd, Jˆ5.9, 2.7 Hz),
4.38 (1H, Jˆ5.5, 2.7 Hz), 3.43 (2H, br s), 2.50 (1H, dd,
Jˆ16.9, 3.0 Hz), 2.44 (1H, Jˆ16.9, 3.0 Hz), 2.24 (1H,
Jˆ17.0, 11.0 Hz), 2.13 (1H, Jˆ17.0, 11.5 Hz), 1.99 (1H,
m), 1.63 (1H, m), 0.93 (6H, d, Jˆ6.8 Hz); IR (neat) 2961,
2876, 1659, 1468, 1400, 1372, 1339, 1302, 1227, 1198,
1152, 1103, 1028, 920 cm21; HRMS m/z (M1) calcd for
C12H16O2: 192.1150. Found: 192.1149.
1.3.13. 2,9-Dimethylfuro[3,2-c]chromen-4-one (43).
Reaction ofthe iodide 28 (342 mg, 1.0 mmol) with DBU
(457 mg, 3.0 mmol) in benzene (method A) afforded 43
(199 mg, 93%) as a solid: mp 175±1778C; 1H NMR
(300 MHz, CDCl3) d 7.36±7.22 (2H, m), 7.10 (1H, d,
Jˆ7.2 Hz), 6.58 (1H, s), 2.75 (3H, s), 2.49 (3H, s); 13C
NMR (75 MHz, CDCl3) d 158.46, 157.60, 155.42, 152.83,
133.56, 129.37, 126.36, 126.30, 114.88, 111.77, 103.74,
20.86, 13.89; IR (KBr) 3128, 3057, 2922, 1732, 1615,
1595, 1451, 1385, 1352, 1312, 1229, 1161, 1057, 1036,
956 cm21; HRMS m/z (M1) calcd for C13H10O3: 214.0627.
Found: 214.0632.
1.3.8.
6-Isopropyl-2-methyl-4,5,6,7-tetrahydrobenzo-
furan-4-one (38). Reaction ofthe iodide 25 (119 mg,
0.37 mmol) with DBU (183 mg, 1.2 mmol) in toluene
(method B) afforded 38 (58 mg, 81%) as a liquid: 1H
NMR (300 MHz, CDCl3) d 6.15 (1H, s), 2.80 (1H, dd,
Jˆ17.0, 4.9 Hz), 2.49 (1H, dd, Jˆ17.0, 4.9 Hz), 2.47 (1H,
d, Jˆ16.3 Hz), 2.22 (3H, s), 2.16 (1H, d, Jˆ15.9 Hz), 2.03
(1H, m), 1.63 (1H, m), 0.91 (6H, d, Jˆ6.8 Hz); 13C NMR
(75 MHz, CDCl3) d 194.48, 166.23, 152.73, 121.59, 101.68,
42.12, 41.76, 31.91, 26.85, 19.76, 19.50, 13.32; IR (neat)
2961, 2876, 1678, 1586, 1460, 1433, 1389, 1370, 1337,
1244, 1217, 1179, 1127, 1042, 1003, 934 cm21; HRMS
m/z (M1) calcd for C12H16O2: 192.1150. Found: 192.1152.
1.3.14. 2,8-Dimethylfuro[3,2-c]chromen-4-one (44).
Reaction ofthe iodide 29 (172 mg, 0.5 mmol) with DBU
(229 mg, 1.5 mmol) in benzene (method A) afforded 44
(105 mg, 98%) as a solid: mp 157±1598C; 1H NMR
(300 MHz, CDCl3) d 7.61 (1H, s), 7.28 (2H, Jˆ8.2 Hz),
6.55 (1H, s), 2.47 (s, 3H), 2.43 (s, 3H); IR (KBr) 2926,
1728, 1634, 1589, 1572, 1437, 1377, 1352, 1314, 1281,
1200, 1155, 1117, 1059, 1007, 908 cm21; HRMS m/z
(M1) calcd for C13H10O3: 214.0627. Found: 214.0630.
1.3.9. 5,5-Dimethyl-2-methylene-2,3,4,5,6,7-hexahydro-
benzofuran-4-one (39). Reaction ofthe iodide
26
(100 mg, 0.3 mmol) with DBU (137 mg, 0.9 mmol) in
benzene (method A) afforded 39 (50 mg, 86%) as a solid:
mp 58±618C; 1H NMR (300 MHz, CDCl3) d 4.70 (1H, dd,
Jˆ5.7, 2.7 Hz), 4.34 (1H, dd, Jˆ5.2, 2.7 Hz), 3.40 (2H, m),
2.37 (2H, t, Jˆ6.6 Hz), 1.82 (2H, t, Jˆ6.6 Hz), 1.2 (6H, s);
IR (KBr) 2968, 2932, 1661, 1634, 1474, 1401, 1329, 1306,
1231, 1202, 1148, 1119, 1065, 993 cm21; HRMS m/z (M1)
calcd for C11H14O2: 178.0994. Found: 178.0993.
1.3.15. 2,7-Dimethylfuro[3,2-c]chromen-4-one (45).
Reaction ofthe iodide 30 (212 mg, 1.0 mmol) with DBU
(457 mg, 3.0 mmol) in benzene (method A) afforded 45
(171 mg, 80%) as a solid: mp 168±1708C; 1H NMR
(300 MHz, CDCl3) d 7.69 (1H, d, Jˆ8.0 Hz), 7.22 (1H,
s), 7.13 (1H, d, Jˆ8.0 Hz), 6.54 (s, 1H), 2.47 (3H, s), 2.44
(3H, s); 13C NMR (75 MHz, CDCl3) d 158.62, 156.97,
155.13, 152.47, 141.12, 125.53, 120.17, 117.38, 110.67,
110.36, 103.90, 21.73, 13.72; IR (KBr) 3130, 3057, 2924,
1749, 1632, 1595, 1512, 1439, 1360, 1321, 1260, 1163,
1142, 1115, 1065, 976, 949 cm21; HRMS m/z (M1) calcd
for C13H10O3: 214.0627. Found: 214.0632.
1.3.10. 2,5,5-Trimethyl-4,5,6,7-tetrahydrobenzofuran-4-
one (40). Reaction ofthe iodide 26 (260 mg, 0.9 mmol)
with DBU (411 mg, 2.7 mmol) in toluene (method B)
afforded 40 (138 mg, 91%) as a liquid: 1H NMR
(300 MHz, CDCl3) d 6.19 (1H, s), 2.53 (2H, t, Jˆ6.6 Hz),
2.28 (3H, s), 1.96 (2H, t, Jˆ6.6 Hz), 1.35 (6H, s); IR (neat)
2967, 1680, 1578, 1472, 1433, 1383, 1364, 1327, 1304,
1258, 1227, 1202, 1150, 1227, 1150, 1088, 1038, 1005,
934 cm21; HRMS m/z (M1) calcd for C11H14O2: 178.0994.
Found: 178.0991.
1.3.16.
9-Methylphenaleno[1,2-b]furan-7-one
(46).
Reaction ofthe iodide 20 (293 mg, 1.0 mmol) with DBU
(457 mg, 3.0 mmol) in benzene (method A) afforded 46
(229 mg, 98%) as a solid: mp 129±1328C; 1H NMR
(300 MHz, CDCl3) d 8.69 (1H, d, Jˆ7.3 Hz), 8.12 (1H,
dd, Jˆ8.2, 7.8 Hz), 7.95 (1H, d, Jˆ8.3 Hz), 7.73 (1H, dd,
Jˆ7.8, 7.6 Hz), 7.60 (1H, dd, Jˆ7.9, 7.5 Hz), 6.62 (1H, s),
2.48 (3H, s); 13C NMR (75 MHz, CDCl3) d 180.06, 157.60,
154.32, 134.55, 131.94, 130.26, 130.30, 129.47, 126.30,
125.94, 124.96, 122.66, 120.47, 103.60, 13.63; IR (KBr)
3124, 2916, 1644, 1580, 1549, 1507, 1506, 1466, 1435,
1.3.11. 3,4,5a,8,9,9a-Hexahydro-2H-dibenzofuran-1-one
(41). Reaction ofthe iodide 22 (270 mg, 1.0 mmol) with
DBU (457 mg, 3.0 mmol) in toluene (method B) afforded
41 (177 mg, 93%) as a liquid: 1H NMR (300 MHz, CDCl3)
d 6.18 (1H, m), 5.94 (1H, dd, Jˆ7.8, 1.5 Hz), 4.86 (1H, dd,
Jˆ8.8, 1.5 Hz), 3.14 (1H, m), 2.42±2.30 (4H, m), 2.04±1.99
(6H, m); IR (neat) 2946, 1615, 1452, 1404, 1238, 1181,
1134, 1061, 1007, 959 cm21; HRMS m/z (M1) calcd for
C12H14O2: 190.0990. Found: 190.0995.
1377, 1323, 1273, 1197, 1151, 1101, 1024, 939 cm21
;
HRMS m/z (M1) calcd for C16H10O2: 234.0678. Found:
234.0682.

Y. R. Lee, J. Y. Suk / Tetrahedron 58 (2002) 2359±2367
2367
5. (a) Ye, T.; McKervey, M. A. Chem. Rev. 1994, 94, 1091.
(b) Padwa, A.; Kinder, F. R. J. Org. Chem. 1993, 58, 21.
(c) Davies, H. M. L.; Romines, K. R. Tetrahedron 1988, 44,
3343.
Acknowledgements
This work was supported by Grant (R02-2000-00070) from
the Basic Research Program ofthe Korea Science and
Engineering Foundation. Dr Ronald Tepper in discussion
ofthis work is greatly appreciated.
6. (a) Connell, R.; Scavo, F.; Helquist, P.; Akermark, B.
Tetrahedron Lett. 1986, 27, 5559. (b) Shi, G.; Xu, Y.
J. Chem. Soc., Chem. Commun. 1989, 607.
7. (a) Lee, Y. R.; Suk, J. Y.; Kim, B. S. Tetrahedron Lett. 1999,
40, 6603. (b) Lee, Y. R.; Suk, J. Y.; Kim, B. S. Tetrahedron
Lett. 1999, 40, 8219. (c) Lee, Y. R.; Suk, J. Y. Tetrahedron
Lett. 2000, 41, 4795.
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