A facile synthesis of dihydrobenzofuranols by photocyclization of (2-alkoxy-5-methyl-phenyl)(aryl) methanone and Ethyl 2-aroyl-4- methylphenyloxyacetates

Article abstract of DOI:10.1002/hc.20111

Irradiation of 2-alkoxy substituted benzophenones 2a-f and ethyl 2-aroyl-4-methylphenyl-oxyacetates 2g-i in benzene and in acetonitrile underwent photocyclization to substituted dihydrobenzofuranols 3a-i with 3a-c in very less yield being racemate and 3d-

Full text of DOI:10.1002/hc.20111

Heteroatom Chemistry
Volume 16, Number 3, 2005
A Facile Synthesis of Dihydrobenzofuranols
by Photocyclization of (2-Alkoxy-5-methyl-
phenyl)(aryl) methanone and Ethyl
2-aroyl-4-methylphenyloxyacetates
S. Shashikanth,1 B. S. Sudha,2 and S. A. Khanum2
1Department of Studies in Chemistry, Manasagangotri, University of Mysore, Mysore 570006, India
2Yuvaraja’s College, University of Mysore, Mysore 570005, India
Received 17 November 2003; revised 27 September 2004
the solvents used in the reaction [7,8]. In the liter-
ABSTRACT: Irradiation of 2-alkoxy substituted ben-
ature, there are few examples that discuss in detail
zophenones 2a–f and ethyl 2-aroyl-4-methylphenyl-
solvent and substituent effects on cyclization of 1,5-
oxyacetates 2g–i in benzene and in acetonitrile un-
biradicals [9,10]. In fact, Wagner et al. have studied
derwent photocyclization to substituted dihydroben-
that photocyclization of 2-benzyloxybenzophenone
zofuranols 3a–i with 3a–c in very less yield being
and 2-benzyloxy acetophenone derivatives in nonpo-
racemate and 3d–i in good yield being mixture of
lar solvent like benzene, and revealed high stereose-
cis-trans isomers showing high stereoselectivity in
lectivity of cis isomer [5,6]. However, in the presence
benzene and decreased stereoselectivity in acetoni-
of Lewis base solvents stereoselectivity decreased
ꢀ
C
trile.
2005 Wiley Periodicals, Inc. Heteroatom Chem
markedly [4,6].
In this paper, we report the synthesis of sub-
16:212–217, 2005; Published online in Wiley InterScience
(www.interscience.wiley.com). DOI 10.1002/hc.20111
stituted dihydrobenzofuranols (3a–c) (racemate,
R = H) and 3d–i (cis-trans isomers with regard to
R and OH), using photocyclization of 2-alkoxy sub-
stituted benzophenones (2a–f) and ethyl-2-benzoyl
phenyloxyacetates (2g–i, Scheme 1).
INTRODUCTION
Photocyclization reactions of o-alkoxy aromatic car-
bonyl compounds have been used for synthesis
of benzofuran derivatives [1–3]. Among the com-
pounds, benzophenones have been extensively stud-
ied from a viewpoint of reaction mechanisms and
synthetic applications [4–6]. Photocyclization reac-
tions of ortho alkoxy benzophenones and its deriva-
tives proceed via 1,5-biradical intermediates formed
through δ-hydrogen abstraction by the excited car-
bonyl group. The isomer ratios vary according to
RESULTS AND DISCUSSION
Compounds 2a–i were synthesized by the benzoy-
lation of p-cresol with the corresponding acid chlo-
rides followed by Fries rearrangement and etherifi-
cation [11–13]. Their structural elucidation was con-
firmed by IR and 1H NMR data.
Photocyclization reactions of compounds 2a–i
were conducted with a 400 W high-pressure mercury
lamp (pyrex filter) in two solvents of different polar-
ity (benzene and acetonitrile) under nitrogen atmo-
sphere. From the results of irradiation of 2a–i, the
Correspondence to: S. Shashikanth; e-mail: skanth1@rediffmail.
com.
c
ꢀ
2005 Wiley Periodicals, Inc.
212

A Facile Synthesis of Dihydrobenzofuranols by Photocyclization 213
possible reaction pathway of photocyclization is as
shown in Scheme 1 . During the process (n, π∗)
excited triplet state is produced after intersystem
crossing process (ISC) [4]. At this stage the carbonyl
group abstracts δ-hydrogen to give 1,5-biradicals
(2a–i)∗. When 2-methoxy substituted benzophe-
nones (R = H in Scheme 1) 2a–c were irradiated
in benzene as well as in acetonitrile solution, 3-aryl-
2,3-dihydro-3-benzofuranols 3a–c were obtained as
a racemic mixture in 28–32% yield (Scheme 1 and
Table 1).
Compounds 2a–c generated less stable primary
radical at the carbon atom adjacent to phenoxy
group as in (2a–c)∗. The products 3a–c were formed
only on long exposure of 2a–c to UV light (13–20 h).
After 10 h of exposure, only 15% of the product
formed (observed by TLC). Irradiation was contin-
ued up to 20 h and gave only 28–32% of 3a–c. In
contrast, 2d–i afforded the corresponding compara-
tively stable secondary radical as in (2d–i)∗ [14]. For-
mation of relatively stable secondary radical from
2d–i made intramolecular ꢀ-hydrogen abstraction
favorable compared with the ꢀ-hydrogen abstraction
forming primary radical which was proved by irra-
diation period of 2d–i (4–10 h), giving 76–90% of
cis-trans 3d–i. In addition to the stability of the radi-
cals, the presence of CH3 or bulkier group on alkoxy
radical favors the stereoselective formation of cis iso-
mer in benzene whereas in acetonitrile a mixture of
cis-trans isomers was obtained.
Irradiation of 2-ethoxy substituted benzophe-
nones 2d–f (R = CH3 in Scheme 1) and ethyl 2-
aroyl-4-methylphenyloxyacetates 2g–i (R = CO2Et
SCHEME 1
TABLE 1 Time Required (h) and Yield (%) of All Compounds Prepared
Product 3a–i
Starting Material
R
H
R1
H
R 2
H
R 3
CH3
Br
Solvent
Irradiation Time
(cis:trans)
Yield
2a
2b
2c
2d
2e
2f
C6H6
CH3CN
C6H6
CH3CN
C6H6
CH3CN
C6H6
CH3CN
C6H6
CH3CN
C6H6
CH3CN
C6H6
CH3CN
C6H6
CH3CN
C6H6
13
14
18
20
19
18
4
4
8
9
8
8
4
4
9
10
9
10
3a
3b
3c
30
32
32
30
28
31
88
82
80
76
86
81
90
86
85
79
83
80
H
H
H
H
Cl
H
Cl
H
H
CH3
CH3
CH3
CO2Et
CO2Et
CO2Et
CH3
Br
3d (7.8:1)
(1.56:1)
3e (5.6:1)
1.71:1
3f (8.5:1)
1.25:1
3g (14:1)
1.26:1
3h (16:1)
1.14:1
H
H
Cl
H
Cl
H
H
2g
2h
2i
CH3
Br
H
H
Cl
Cl
H
3i (9.4:1)
1.5:1
CH3CN

214 Shashikanth, Sudha, and Khanum
in Scheme 1) in benzene solution under the same
conditions gave cis isomer of benzofuranols 3d–i as a
predominant product selectively. In the experiment a
small amount of trans-isomer 3d–i was also isolated.
The total yield was in the range 80–90%, and cis and
trans ratio was varied from 5.6:1 to 16:1. The selec-
tivity of cis product is attributed to little hydrogen
bonding between the hydroxyl group of 1,5-biradical
(2d–i)∗ and the nonpolar solvent benzene resulting in
thermodynamically more stable product and hence
cis ratio increases.
On the other hand, photo reactions of 2d–i in
acetonitrile solution furnished a mixture of cis and
trans benzofuranols 3d–i in 76–86% yield with cis-
trans ratio ranging from 1.14:1 to 1.71:1 showing
decrease in stereoselectivity. Since in polar solvent
acetonitrile, intermolecular hydrogen bonding is es-
tablished between hydroxyl group of 1,5-biradical
and solvent molecule, which restricts the free ro-
tation between hydroxyl group and o-alkoxy phenyl
ring, thereby decreasing the stereoselectivity. Stere-
ochemistry of cis and trans isomers of 3d–i was de-
termined by considering an anisotropic effect of C3-
phenyl group on C2-H in the 1H NMR spectra [5,9]. In
substituted dihydrobenzofuranols, C3-phenyl group
shields C2-H at the cis position, that is C2-H chem-
ical shift appears at a higher magnetic field than
that of trans position. In a typical example, for com-
pound 3d, signals for C2-H in cis isomer appeared at δ
3.9–4.2 and in trans isomer signals appeared at δ 4.3–
4.5. Small difference in steric bulkiness between the
substituted phenyl group and the hydrogen bonded
hydroxyl group would make both counterclockwise
and clockwise rotations possible resulting in de-
creased stereoselectivity in polar solvent acetonitrile.
The large difference in cis and trans ratios from reac-
tion in benzene and acetonitrile is attributed to the
solvent effect.
EXPERIMENTAL
The melting points are uncorrected. Column chro-
matography was performed on silica gel (60–120
mesh). Unless otherwise stated anhydrous sodium
sulfate was employed as a drying agent. Benzene for
photoreactions was dried by distilling over sodium
metal, and acetonitrile was dried by distilling over
phosphorus pentoxide then over potassium carbon-
ate. Photoreactions were carried out with 400 W
high pressure mercury lamp (Riko UVL-400HA) with
pyrex filter. The IR spectra in Nujol were deter-
mined on a Shimadzu 8300 FT-IR spectrophotome-
1
ter. H NMR and 13C NMR were recorded on 300
and 75 MHz respectively, in deuterated chloroform
(CDCl3) using tetramethylsilane (TMS) as an internal
standard.
The substituted benzophenone 1a–c was pre-
pared by Fries rearrangement according to the pro-
cedure described by Vogel [11] and Olah et al. [12].
These compounds have been thoroughly character-
ized by IR and 1H NMR spectral data and were puri-
fied by column chromatography prior to use.
General Procedure for 2a–i
A
mixture of (2-hydroxy-5-methylphenyl)(aryl)-
methanone 1 (10 mmol), alkyl bromide/ethyl bromo
acetate (10 mmol), potassium carbonate (20 mmol),
and acetone (25 mL) was refluxed for 4 h [13].
After the removal of insoluble material by filtration,
water (25 mL) was added and extracted with ether
(3 × 30 mL). Ether layer was washed with 5%
sodium hydroxide (3 × 15 mL) and then with water
(2 × 15 mL). Ether layer was dried with anhydrous
sodium sulfate and evaporated. The residue was
chromatographed and eluted with benzene-afforded
product 2.
2a: Yield 83% (1.99 g), mp 160–62◦C; IR (Nu-
Intramolecular cyclization of (2a–i)∗ afforded
racemate-substituted dihydrobenzofuranols 3a–c
and cis-trans isomers of substituted dihydrobenzo-
furanols 3d–i. But the presence of methyl group
in 1,5-biradical (2d–f)∗, which is electron releasing,
stabilizes the 1,5-biradical intermediate and gives
good yield of substituted dihydrobenzofuranols in
a short time irradiation compare to irradiation pe-
riod of 2a–c. Irradiation period of 2a, 2d, and 2g
is less than that of 2b–c, 2e–f and 2h–i respec-
tively. This is due to the presence of CH3 group on
phenyl ring which is also electron releasing that fa-
vors the cyclization of 1,5-biradical. Under similar
conditions, electron withdrawing group bromo in
2b, 2e, 2h and also chloro group in 2c, 2f, 2i destabi-
lizes the 1,5-biradical there by decrease in the rate of
cyclization.
jol): 1658 cm−1 (C O); H NMR (CDCl3): δ 2.25 (s,
1
3H, Ar-CH3), 2.32 (s, 3H, Ar-CH3), 3.6 (s, 3H, OCH3),
6.7–7.7 (bm, 7H, Ar-H); 13C NMR (CDCl3): δ 20.9 (q),
56.0 (q), 113.7 (d), 123.3 (s), 128.9 (d), 129.9 (s), 130
(d), 131.8 (d), 133.9 (d), 134.8 (s), 141.4 (s), 160.6 (s)
187.0 (s). Anal. Calcd for C16H16O2(240):C, 80.0; H,
6.67%. Found: C, 80.12; H, 6.63%.
2b: Yield 75% (2.29 g), mp 55–58◦C; IR (Nujol):
1660 cm−1 (C O); 1H NMR (CDCl3): δ 2.23 (s, 3H, Ar-
CH3), 3.55 (s, 3H, OCH3), 6.65–7.5 (bm, 7H, Ar-H);
13C NMR (CDCl3): δ 20.9 (q), 56.0 (q), 113.7 (d), 123.3
(s), 126.8 (s), 129.7 (s), 131.5 (d), 131.8 (d), 132.3 (d),
133.9 (d), 136.8 (s), 160.6 (s), 187.0 (s). Anal. Calcd
for C15H13BrO2(305): C, 59.02; H, 4.26; Br, 26.23%.
Found: C, 58.95; H, 4.25; Br, 26.21%.
2c: Yield 71% (2.09 g), mp 150–52◦C; IR (Nujol):
1659 cm−1 (C O); H NMR (CDCl3): δ 2.22 (s, 3H,
1

A Facile Synthesis of Dihydrobenzofuranols by Photocyclization 215
Ar-CH3), 3.5 (s, 3H, OCH3), 6.6–7.8 (bm, 6H, Ar-H);
13C NMR (CDCl3): δ 20.9 (q), 56.0 (q), 113.7 (d), 123.3
(s), 127.7 (d), 129.6 (d), 129.7 (s), 131.8 (d), 133.9
(s), 133.9 (d), 134.0 (d), 135.8 (s), 139.6 (s), 160.6
(s), 187.0 (s). Anal. Calcd for C15H12Cl2O2 (295): C,
61.02; H, 4.07; Cl, 24.07%. Found: C, 60.89; H, 4.02;
Cl, 24.05%.
57.29; H, 4.51; Br, 21.22%. Found: C, 57.30; H, 4.50;
Br, 21.28%.
2i: yield 74% (2.71 g), liquid; IR (neat): 1762 (es-
ter, C O); 1661 cm−1 (C O); 1H NMR (CDCl3): δ 1.2
(t, J = 7 Hz, 3H, ester CH3), 2.2 (s, 3H, Ar-CH3), 4.15
(q, J = 7 Hz, 2H, ester O-CH2), 4.45 (s, 2H, OCH2),
6.65–7.7 (bm, 6H, Ar-H); 13C NMR (CDCl3): δ 13.6 (q),
20.9 (q), 59.5 (t), 75.6 (t), 113.7 (d), 123.3 (s), 127.7
(d), 129.6 (d), 129.7 (s), 131.8 (d), 133.9 (d), 134.0 (d),
139.6 (s), 160.6 (s), 171.0 (s), 187.0 (s). Anal. Calcd
for C18H16Cl2O4(367): C, 58.86; H, 4.36; Cl, 19.35%.
Found: C, 58.78; H, 4.32; Cl, 19.31%.
2d: Yield 77% (1.96 g), liquid; IR (neat): 1650
1
cm−1 (C O); H NMR (CDCl3): δ 1.3 (t, J = 7 Hz,
3H, CH3), 2.2 (s, 3H, Ar-CH3), 2.4 (s, 3H, Ar-CH3),
4.1 (q, J = 7 Hz, 2H, OCH2), 6.7–7.7 (bm, 7H, Ar-H)
;13C NMR (CDCl3): δ 14.3 (q), 20.9 (q), 65.1 (t), 113.8
(d), 123.4 (s), 128.9 (d), 129.0 (s), 130.0 (d), 131.4
(d), 133.5 (d), 134.8 (s), 141.4 (s), 157.7 (s), 187.0 (s).
Anal. Calcd for C17H18O2(254): C, 80.31; H, 7.09%.
Found: C, 80.5; H, 7.1%.
General Procedure for 3a–i
In benzene or in acetonitrile solvent (50 mL), the
starting material 2 (15 mmol) was dissolved and de-
oxygenated by bubbling nitrogen gas for 1 h and then
irradiated for 4–20 h. After the completion of the re-
action (monitored by TLC), the solvent was evap-
orated under reduced pressure at 40◦, the residue
chromatographed and eluted with hexane : chloro-
form : acetone mixture (7:3:1) to give 3.
2e: Yield 82% (2.62 g), pale yellow liquid; IR
1
(neat): 1660 cm−1(C O); H NMR (CDCl3): δ 1.3 (t,
J = 7 Hz, 3H, CH3), 2.23 (s, 3H, Ar-CH3), 4.1 (q,
J = 7 Hz, 2H, OCH2), 6.65–7.5 (bm, 7H, Ar-H);13C
NMR (CDCl3): δ 14.3 (q), 20.9 (q), 65.1 (t), 113.8 (d),
123.4 (s), 126.8 (s), 129.0 (s), 131.4 (d), 131.5 (d),
132.3 (d), 133.5 (d), 136.8 (s), 157.4 (s), 187.0 (s).
Anal. Calcd for C16H15BrO2(319): C, 60.19; H, 4.70;
Br, 24.6%. Found: C, 60.09; H, 4.65; Br, 24.4%.
2f: Yield 75% (2.42 g), pale yellow liquid; IR
3a: mp 156–157◦C; IR (Nujol): 3410 cm−1 (OH);
1H NMR (CDCl3): δ 2.4 (s, 3H, Ar-CH3), 2.5 (s, 3H, Ar-
CH3), 3.9 (s, 1H, C2-H), 4.3 (s, 1H, C2-H), 6.0–6.2 (bs,
1H, OH), 7.2–8.0 (bm, 7H, Ar-H); 13C NMR (CDCl3):
δ 20.9 (q), 21.2 (q), 80.5 (t), 88.3 (s), 114.6 (d), 127.3
(d), 128.3 (d), 128.6 (s), 129.7 (d), 129.8 (s), 135.2 (s),
140.0 (s), 155.7 (s). Anal. Calcd for C16H16O2(240): C,
80.0; H, 6.67%. Found: C, 79.60; H, 6.62%.
1
(neat): 1659 cm−1(C O); H NMR (CDCl3): δ 1.3 (t,
J = 7 Hz, 3H, CH3), 2.22 (s, 3H, Ar-CH3), 4.1 (q,
J = 7 Hz, 2H, OCH2), 6.6–7.5 (bm, 6H, Ar-H); 13C
NMR (CDCl3): δ 14.3 (q), 20.9 (q), 61.1 (t), 113.8 (d),
123.4 (s), 127.7 (d), 129.0 (s), 129.6 (d), 131.4 (d),
133.5 (d) 133.9 (s), 134.0 (d), 135.8 (s), 139.6 (s),
157.4 (s), 187.0 (s). Anal. Calcd for C16H14Cl2O2(323):
C, 62.14; H, 4.53; Cl, 22.72%. Found: C, 62.11; H,
4.51; Cl, 22.68%.
3b: mp 155–157◦C; IR (Nujol): 3420 cm−1(OH);
1H NMR (CDCl3); δ 2.4 (s, 3H, Ar-CH3), 3.8 (s, 1H,
C2-H), 4.4 (s, 1H, C2-H), 6.0–6.2 (bs, 1H, OH), 7.2–
8.0 (bm, 7H, Ar-H); 13C NMR (CDCl3): δ 21.2 (q), 80.5
(t), 88.3 (s), 114.6 (d), 120.6 (s), 127.3 (d), 128.3 (d),
128.6 (s), 129.7 (d), 129.8 (s), 155.7 (s). Anal. Calcd
for C15H13BrO2(305): C, 59.02; H, 4.26; Br, 26.23%.
Found: C, 59.0; H, 4.21; Br 26.18%.
2g: Yield 90% (2.81 g), liquid; IR(neat): 1760 (es-
1
ter, C O); 1664 cm−1(C O); H NMR (CDCl3): δ 1.2
(t, J = 7 Hz, 3H, ester CH3), 2.4 (s, 3H, Ar-CH3),
2.45 (s, 3H, Ar-CH3), 4.2 (q, J = 7 Hz, 2H, ester O-
CH2), 4.5 (s, 2H, OCH2), 6.5–7.8 (bm, 7H, Ar-H);
13C NMR (CDCl3): δ 13.6 (q), 20.9 (q), 20.9 (q), 59.5
(t), 75.6 (t), 113.7 (d), 123.0 (d), 128.9 (d), 129.9
(s), 130.6 (d), 131.8 (d), 133.9 (d), 134.8 (s), 141.4
(s), 160.6 (s) 171.0 (s), 187.0 (s). Anal. Calcd for
C19H20O4(312): C, 73.08; H, 6.41%. Found: C, 7310;
H, 6.38%.
2h: Yield 88% (3.32 g), brown liquid; IR (neat):
1763 (ester, C O); 1660 cm−1 (C O); 1H NMR
(CDCl3): δ 1.2 (t, J = 7 Hz, 3H, ester CH3), 2.3 (s,
3H, Ar-CH3), 4.2 (q, J = 7 Hz, 2H, ester O-CH2),
4.5 (s, 2H, OCH2), 6.5–7.8 (bm, 7H, Ar-H); 13C NMR
(CDCl3): δ 13.6 (q), 20.9 (q), 59.5 (t), 75.6 (t), 113.7
(d), 123.3 (s), 126.8 (s), 129.7 (s), 131.5 (d), 131.8
(d), 132.3 (d), 133.9 (d), 136.8 (s), 160.6 (s), 171.0
(s), 187.0 (s). Anal. Calcd for C18H17BrO4(377): C,
3c: mp 158–159◦C; IR (Nujol): 3415 (OH) cm−1;
1H NMR (CDCl3): 2.4 (s, 3H, Ar-CH3), 3.9 (s, 1H, C2-
H), 4.4 (s, 1H, C2-H), 6.0–6.3 (bs, 1H, OH), 7.2–8.0
(bm, 6H, Ar-H); 13C NMR (CDCl3): δ 21.2 (q), 78.7 (s),
80.0 (t), 114.6 (d), 127.3 (d), 127.8 (d), 127.9 (d), 128.5
(d), 128.6 (s), 129.7 (d), 129.8 (s), 134.1 (s), 134.7 (s),
144.8 (s), 155.7 (s). Anal. Calcd for C15H12Cl2O2(295):
C, 61.02; H, 4.07; Cl, 24.07%. Found: C, 61.0; H, 4.08;
Cl, 23.04%.
Cis-3d: mp 158–159◦C; IR (Nujol): 3410
1
cm−1(OH); H NMR (CDCl3): δ 1.22 (d, J = 7 Hz,
3H, C2-CH3), 2.4 (s, 3H, Ar-CH3), 2.6 (s, 3H, Ar-CH3),
3.9–4.2 (q, J = 7 Hz ,1H, C2-H), 6.1–6.2 (bs, 1H,
OH), 7.3–8.1 (bm, 7H, Ar-H); 13C NMR (CDCl3): δ
13.8(q), 20.9 (q), 21.2 (q), 83.9 (d), 94.7 (s), 114.6
(d), 127.3 (d), 128.3 (d), 128.6 (s), 129.7 (d), 129.8

216 Shashikanth, Sudha, and Khanum
(s), 135.2 (s), 140.0 (s), 155.7 (s). Anal. Calcd for
C17H18O2(254): C, 80.31; H, 7.09%. Found: C, 80.11;
H, 7.05%.
CH2), 3.9 (s, 1H, C2-H), 5.1–5.3 (bs, 1H, OH), 7.3–
7.8 (bm, 7H, Ar-H);13C NMR (CDCl3): δ 13.6 (q), 20.9
(q), 21.2 (q), 59.8 (t), 87.6 (s), 93.6 (d), 114.6 (d),
127.3 (d), 128.3 (d), 128.6 (s), 129.7 (d), 129.8 (s),
135.2 (s), 140.0 (s), 155.7 (s), 172 (s). Anal. Calcd for
C19H20O4(312): C, 73.08; H, 6.41%. Found: C, 73.05;
H, 6.38%.
Trans-3d: mp 146–148◦C; IR (Nujol): 3400 cm−1
(OH); 1H NMR (CDCl3): δ 1.15–1.56 (d, J = 7 Hz, 3H,
C2-CH3), 2.2 (s, 3H, Ar-CH3), 2.4 (s, 3H, Ar-CH3), 4.3–
4.5 (q, J = 7 Hz, 1H, C2-H), 6.0–6.2 (bs, 1H, OH),
7.2–7.8 (bm, 7H, Ar-H);13C NMR (CDCl3): δ 13.8 (q),
20.9 (q), 21.2 (q), 82.9 (d), 93.7 (s), 114.6 (d), 127.3
(d), 128.3 (d), 128.6 (s), 129.7 (d), 129.8 (s), 135.2 (s),
140.0 (s), 155.7 (s). Anal. Calcd for C17H18O2(254): C,
80.31; H, 7.09%. Found: C, 80.10; H, 7.04%.
Trans-3g: mp 90–95◦C; IR (Nujol): 3420–3480
1
(OH), 1745 cm−1 (ester C O); H NMR (CDCl3): δ
1.2–1.4 (t, J = 7 Hz, 3H, ester CH3), 2.4 (s, 3H, Ar-
CH3), 2.6 (s, 3H, Ar-CH3), 4.0–4.2 (q, J = 7 Hz, 2H,
ester CH2), 4.3 (s, 1H, C2-H), 5.2–5.4 (bs, 1H, OH),
7.3-7.8 (bm, 7H, Ar-H); 13C NMR (CDCl3): δ 13.6 (q),
20.9 (q), 21.2 (q), 59.8 (t), 86.6 (s), 92.6 (d), 114.6 (d),
127.3 (d), 128.3 (d), 128.6 (s), 129.7 (d), 129.8 (s),
135.2 (s), 140.0 (s), 155.7 (s), 172 (s). Anal. Calcd for
C19H20O4(312): C, 73.08; H, 6.41%. Found: C, 73.06;
H, 6.37%.
Cis-3e: mp 160–162◦C; IR (Nujol): 3410 cm−1
(OH); 1H NMR (CDCl3): δ 1.09–1.10 (d, J = 7 Hz, 3H,
C2-CH3), 2.4 (s, 3H, Ar-CH3), 3.7–4.0 (q, J = 7 Hz,
1H, C2-H), 6.1–6.2 (bs, 1H, OH), 7.3–8.1 (bm, 7H,
Ar-H); 13C NMR (CDCl3): δ 13.8 (q), 21.2 (q), 83.9
(d), 88.3 (s) 114.6 (d), 120.6 (s), 127.3(d), 128.6
(s), 129.7 (d), 129.8 (s), 130.6 (d), 132.3 (d), 142.0
(s), 155.7 (s). Anal. Calcd for C16H15BrO2(319): C,
60.19; H, 4.70; Br, 24.6%. Found: C, 60.15; H, 4.71;
Br, 24.4%.
Cis-3h: mp 130–132◦C; IR (Nujol): 3340–3380
1
(OH), 1763 cm−1 (ester C O); H NMR (CDCl3): δ
1.2–1.4 (t, J = 7 Hz, 3H, ester CH3), 2.3 (s, 3H, Ar-
CH3), 3.4–3.7 (q, J = 7 Hz, 2H, ester CH2), 4.0 (s, 1H,
C2-H), 5.2–5.4 (bs, 1H, OH), 6.5–7.8 (bm, 7H, Ar-H);
13C NMR (CDCl3): δ 13.6 (q), 21.2 (q), 59.8 (t), 87.6
(s), 93.6 (d), 114.6 (d), 120.6 (s), 127.3 (d), 128.6
(s), 129.7 (d), 130.6 (d), 132.3 (d), 142.0 (s), 155.7
(s), 172.0 (s). Anal. Calcd for C18H17BrO4(377): C,
57.24; H, 4.51; Br, 21.22%. Found: C, 57.23; H, 4.50;
Br, 21.20%.
Trans-3e: mp 118–119◦C; IR (Nujol): 3400 cm−1
(OH); 1H NMR (CDCl3): δ 1.15–1.6 (d, J = 7 Hz , 3H,
C2-CH3), 2.2 (s, 3H, Ar-CH3), 4.0–4.3 (q, J = 7 Hz ,
1H, C2-H), 6.0–6.2 (bs, 1H, OH), 7.2–7.8 (bm, 7H,
Ar-H); 13C NMR (CDCl3): δ 13.8 (q), 21.2 (q), 82.9 (d),
87.3 (s), 114.6 (d), 120.6 (s), 127.3(d), 128.6 (s), 129.7
(d), 129.8 (s), 130.6 (d), 132.3 (d), 142.0 (s), 155.7 (s).
Anal. Calcd for C16H15BrO2(319): C, 60.19, H, 4.70,
Br, 24.6%. Found: C, 60.15, H, 4.68, Br, 24.3%.
Cis-3f: mp 162–164◦C; IR (Nujol): 3410 cm−1
(OH); 1H NMR (CDCl3): δ 1.1–1.2 (d, J = 7 Hz , 3H,
C2-CH3), 2.4 (s, 3H, Ar-CH3), 3.8–4.0 (q, J = 7 Hz ,
1H, C2-H), 6.1–6.2 (bs, 1H, OH), 7.3–8.1 (bm, 6H,
Ar-H); 13C NMR (CDCl3): δ 13.8 (q), 21.2 (q), 83.9
(d), 94.7 (s), 114.6 (d), 127.3 (d), 127.8 (d), 128.5 (d),
128.6 (s), 129.7 (d), 129.8 (s), 129.9 (d), 134.1 (s),
144.8 (s), 155.7 (s). Anal. Calcd for C16H16Cl2O2(323):
C, 62.14; H, 4.53; Cl, 22.98%. Found: C, 62.11; H,
4.48; Cl, 22.95%.
Trans-3h: mp 85–88◦C; IR (Nujol): 3460–3500
(OH), 1763 cm−1(ester C O); 1H NMR (CDCl3): δ 1.2–
1.4 (t, J = 7 Hz, 3H, ester CH3), 2.3 (s, 3H, Ar-CH3),
4.2–4.4 (q, J = 7 Hz, 2H, ester CH2), 4.45 (s, 1H, C2-
H), 5.2–5.3 (bs, 1H, OH), 7.1–7.8 (bm, 7H, Ar-H); 13
C
NMR (CDCl3): δ 13.6 (q), 21.2 (q), 59.8 (t), 86.6 (s),
92.6 (d), 114.6 (d), 120.6 (s), 127.3 (d), 128.6 (s), 129.7
(d), 130.6 (d), 132.3 (d), 142.0 (s), 155.7 (s), 172.0 (s).
Anal. Calcd for C18H17O4Br (377): C, 57.29; H, 4.51;
Br, 21.22%. Found: C, 57.25; H, 4.49; Br, 21.21%.
Cis-3i: mp 128–130◦C; IR (Nujol): 3460–3500
(OH), 1762 cm−1(ester C O);1H NMR (CDCl3): δ 1.2–
1.4 (t, J = 7 Hz, 3H, ester CH3), 2.2 (s, 3H, Ar-CH3),
3.7–4.0 (q, J = 7 Hz, 2H, ester CH2), 4.1 (s, 1H,
C2-H), 5.0–5.2 (bs, 1H, OH), 7.0–7.7 (bm, 6H, Ar-
H); 13C NMR (CDCl3): δ 13.6 (q), 21.2 (q), 78.0 (s),
93.1 (d), 114.6 (d), 127.3 (d), 127.6 (d), 127.9 (d),
128.5 (d), 128.6 (s), 129.7 (d), 129.8 (s), 134.1 (s),
134.7 (s), 144.8 (s), 155.7 (s), 172.0 (s). Anal. Calcd
for C18H16Cl2O4(367): C, 58.86, H, 4.36, Cl, 19.35%.
Found: C, 58.85; H, 4.4; Cl, 19.32%.
Trans-3f: mp 112–113◦C; IR (Nujol): 3400 cm−1
(OH); 1H NMR (CDCl3): δ 1.15–1.17 (d, J = 7 Hz , 3H,
C2-CH3), 2.2 (s, 3H, Ar-CH3), 4.1–4.4 (q, J = 7 Hz ,
1H, C2-H), 6.0–6.2 (bs, 1H, OH), 7.2–7.8 (bm, 6H, Ar-
H);13C NMR (CDCl3): δ 13.8 (q), 21.2 (q), 82.9 (d), 93.7
(s), 114.6 (d), 127.3 (d), 127.8 (d), 128.5 (d), 128.6
(s), 129.7 (d), 129.8 (s), 129.9 (d), 134.1 (s), 144.8
(s), 155.7 (s). Anal. Calcd for C16H16Cl2O2(323): C,
62.14; H, 4.53; Cl, 22.98%. Found: C, 62.11; H, 4.51;
Cl, 22.95%.
Trans-3i: mp 80–82◦C; IR (Nujol): 3460–3500
(OH), 1762 cm−1(ester C O);1H NMR (CDCl3): δ 1.3–
1.5 (t, J = 7 Hz, 3H, ester CH3), 2.2 (s, 3H, Ar-CH3),
4.15–4.4 (q, J = 7 Hz, 2H, ester CH2), 4.5 (s, 1H, C2-
H), 4.6–4.9 (bs, 1H, OH), 6.65–7.7 (bm, 6H, Ar-H);
Cis-3g: mp 120–122◦C; IR (Nujol): 3420–3480
(OH), 1745 cm−1 (ester C O);1H NMR (CDCl3): δ 1.1–
1.3 (t, J = 7 Hz, 3H, ester CH3), 2.1 (s, 3H, Ar-CH3),
2.3 (s, 3H, Ar-CH3), 3.6–3.8 (q, J = 7 Hz , 2H, ester

A Facile Synthesis of Dihydrobenzofuranols by Photocyclization 217
13C NMR (CDCl3): δ 13.6 (q), 21.2 (q), 77.0 (s),
92.1 (d), 114.6 (d), 127.3 (d), 127.6 (d), 127.9 (d),
128.5 (d), 128.6 (s), 129.7 (d), 129.8 (s), 134.1 (s),
134.7 (s), 144.8 (s), 155.7 (s), 172.0 (s). Anal. Calcd
for C18H16Cl2O4(367): C, 58.86; H, 4.36; Cl, 19.35%.
Found: C, 58.83; H, 4.33; Cl, 19.31%.
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CONCLUSION
In conclusion, we have synthesized a new series of
dihydrobenzofuranols using photocyclization reac-
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meta, para positions on intramolecular cyclization
of 1,5-biradicals. From the above results, photocy-
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AKNOWLEDGMENTS
The authors express their sincere gratitude to Uni-
versity of Mysore, Mysore., for the laboratory facil-
ity. Two of the authors (BSS and SAK) are indebted
to the UGC for the award of teacher’s fellowship.
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