Synthesis of fused bromofurans via mg-mediated dibromocyclopropanation of cycloalkanone-derived chalcones and Cloke-Wilson rearrangement

Article abstract of DOI:10.1021/jo3022988

A convenient two-step sequence for the conversion of alkylidenecycloalkanones to bromofurans is reported. The steps involve Mg-mediated diastereoselective dibromocyclopropanation of alkylidenecycloalkanone followed by acidic alumina-mediated regioselective ring expansion of the cyclopropyl ketone. The scope of the reaction was investigated using alkylidenecycloalkanones derived from tetralone, indanone, and benzosuberone to afford 2-aryl-3-bromofurans fused to various benzocycloalkanes. Representative examples of stereoconvergent dibromocyclopropanation and total aromatization of the furobenzocycloalkane are also reported.

Full text of DOI:10.1021/jo3022988

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Article
Synthesis of Fused Bromofurans via Mg Mediated Dibromocyclopropanation
of Cycloalkanone Derived Chalcones and Cloke-Wilson Rearrangement
Elumalai Gopi, and Irishi N. N. Namboothiri
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/jo3022988 • Publication Date (Web): 28 Dec 2012
Downloaded from http://pubs.acs.org on December 28, 2012
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Page 1 of 32
The Journal of Organic Chemistry
Synthesis of Fused Bromofurans via Mg Mediated Dibromocyclopropanation of Cycloalkanone
Derived Chalcones and Cloke-Wilson Rearrangement
Elumalai Gopi and Irishi N. N. Namboothiri*
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Department of Chemistry Indian Institute of Technology, Bombay, Mumbai 400 076, India,
irishi@iitb.ac.in
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Abstract. A convenient two step sequence for the conversion of alkylidenecycloalkanones to
bromofurans is reported. The steps involve Mg mediated diastereoselective dibromocyclopropanation of
alkylidenecycloalkanone followed by acidic alumina mediated regioselective ring expansion of the
cyclopropyl ketone. The scope of the reaction was investigated using alkylidenecycloalkanones derived
from tetralone, indanone and benzosuberone to afford 2-aryl-3-bromofurans fused to various
benzocycloalkanes. Representative examples of stereoconvergent dibromocyclopropanation and total
aromatization of the furobenzocycloalkane are also reported.
Introduction
Cyclopropane ring is an integral part of many natural products and drug molecules such as plant
hormone precursor 1-aminocyclopropane-1-carboxylic acid (ACC), anticancer agent (+)-ptaquiloside,
insecticide (+)-trans-chrysanthemic acid and renal dehydropeptidase inhibitor Cilastatin, to name a few.1
Methods involving dihalocarbenes, diazoalkanes or sulfonium ylides are frequently used for the
synthesis of cyclopropanes.2 Cyclopropane derivatives have been employed as key scaffolds in the
synthesis of complex heterocycles, for instance, pyrrolidine alkaloids.3 Ring expansion of
vinylcyclopropane to cyclopentene and cyclopropyl ketone to furan (Cloke-Wilson rearrangement)
emerged as some of the elegant applications of the cyclopropane scaffold in natural product synthesis.4
However, spirocyclopropanes, to which illudin class of anticancer natural products belong, have
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received less attention presumably due to inherent strain and poor stereoselectivity in the ring
formation.5
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Among the cyclopropanation methods, gem-dihalocyclopropanation, normally using haloform and a
base, often under PTC conditions, has found applications in total synthesis and in a multitude of
synthetic transformations such as chain elongation, ring cleavage, ring expansion etc.6-7 However, ring
expansion of dihalocyclopropyl ketones to (halo)furans has received only limited attention.8 These
include Banwell’s base mediated conversion of alkoxydichlorocyclopropane to furan, Chen’s Bronsted
acid catalyzed transformation of difluorocyclopropyl ketone and carboxaldehyde to 3-fluorofuran, and
Tanabe’s and Dolbier’s Lewis acid catalyzed ring expansion of dihalocyclopropyl ketones to 3-
halofurans.8 Furthermore, ring expansion of spirodihalocyclopropyl ketones to 3-halofurans remains
unreported, to our knowledge. Owing to the synthetic and biological significance of furans,9 such a
regioselective ring expansion appeared an attractive approach to access functionalized and fused 3-
halofurans.10
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Recently, we reported the Mg mediated conjugate addition of bromoform to electron deficient alkenes
such as nitroalkenes 2 and chalcones 5 (Scheme 1).11-12 The Michael adducts 1 were transformed via
HBr elimination to dibromomethylenated nitroalkanes which in turn were excellent partners in Suzuki
coupling.11 The Michael adducts 6, on the other hand, were valuable precursors to
dialkoxydihydrofurans and ꢀ-ketoesters.12 Herein, we report an efficient dibromocyclopropanation of ꢁ-
substituted enones of type 7 under the above conditions to generate novel spirodibromocyclopropanes of
type 8 and subsequent rearrangement of 8 to fused 3-bromofurans 9.
Scheme 1
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Results and Discussion
The optimized conditions for the conjugate addition of bromoform to nitroalkenes 2 and enones 5, viz
22 equiv bromoform and 8 equiv Mg in THF, appeared suitable for the addition of bromoform to ꢀ-
substituted enones of type 7 as well. Interestingly, when tetralone derivative 10a was treated with
bromoform in the presence of Mg in THF, we isolated dibromocyclopropane 11a in 62% yield as the
only product (Table 1, entry 1). We were pleased by this new product profile that emerged because
although unactivated alkenes, e.g. 4, were reported to give dibromocyclopropanes, e.g. 3,13 conjugated
electron deficient alkenes such as 2 and 5, including ꢀ-substituted nitroalkenes 2 (R2ꢁ H) afforded
exclusively the Michael adducts 1 and 6, respectively (see Scheme 1).11-12, 14
In light of the above, we desired to investigate this Mg mediated dibromocyclopropanation in detail
by screening different tetralone derivatives 10b-p (Table 1, entries 2-17). In general, the
cyclopropanation was complete in less than 5 h and the products were isolated in moderate to good yield
(52-75%). Substrates with single and multiple electron donating groups on the aromatic ring ꢀ to
carbonyl reacted with bromoform to afford cyclopropanes 11b-h and 11p in 60-73% yield (entries 2-8
and 17). Similarly, cyclopropanes were isolated in good yield when substrates with electron
withdrawing ꢀ-aryl groups were reacted with bromoform (69-75%, entries 9-10). The products were
isolated in good yield in the presence of unsubstituted ꢀ-aryl groups as well (Ph and naphthyl, 62-71%,
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entries 1 and 11). However, the reaction of bromoform with a ꢀ-heteroaryl enone 10l (entries 12-13) and
ꢀ-styrenyl enones 10m-o (entries 14-16), could not be generalized. But nevertheless, these reactions
gave us valuable insights into the mechanism of the dibromocyclopropanation as well as the potential of
the dibromocyclopropyl ketones of type 8 to undergo ring expansion to afford synthetically and
biologically relevant furans of type 9 (see Scheme 1).
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First of all, when enone 10l was treated with bromoform for a limited time (1.5 h) under our
optimized conditions, the product isolated was not cyclopropane, but 1,4-adduct 12l in 65% yield (Table
1, entry 12 and Figure 1). However, when the reaction was prolonged for 12 h in another experiment,
we were pleased to isolate the cyclopropane 11l in 60% yield (entry 13). This observation confirmed
that dibromocyclopropanation of enones of type 7 took place via initial Michael addition followed by
intramolecular cyclization.
Table 1. Mg Mediated Dibromocyclopropanation of Tetralonesa
entry 10
X
Ar
11
time (h) % yieldb
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2
10a
H
H
H
H
H
H
H
H
H
H
Ph
11a 1.5
11b 1.5
11c 1.5
11d 1.5
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10b
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10d
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10f
10g
10h
10i
4-MePh
3
4-MeOPh
3-MeOPh
2,4-(MeO)2Ph
3,4-(MeO)2Ph
2,3,4-(MeO)3Ph
3,4,5-(MeO)3Ph
4-CF3Ph
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5
11e
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6
11f 1.5
11g 1.5
11h 1.5
11i 1.5
11j 1.5
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10j
4-FPh
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The Journal of Organic Chemistry
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10k
10l
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H
1-Naphthyl
2-furyl
11k 3.5
11l 1.5
11l 12
11m 4
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2-furyl
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10m
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PhCH=CH
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2-NO2PhCH=CH 11o
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10p OMe 3,4-(MeO)2Ph
11p 1.5
aMg and bromoform were used in excess (8 atom g and 22 equiv, respectively). Isolated yield after
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purification by silica gel column chromatography. Michael adduct 12l was isolated in 65% yield as a
nearly single diastereomer (>95:5, inseparable), see Figure 1.d Rearranged product 13n was isolated in
70% yield, see Figure 1.
While addition of bromoform to ꢀ-styrenyl enones 10m and 10o afforded the expected cyclopropanes
in 69% and 52%, respectively (entries 14 and 16), we were pleasantly surprised to isolate the rearranged
product 13n in 70% yield when enone 10n was treated with bromoform under our experimental
conditions. This suggested that other dibromocyclopropyl ketones with electron donating aromatic rings
would be amenable for rearrangement upon appropriate activation, for instance, by a Lewis acid. Thus,
selected dibromocyclopropyl ketones 11e-f, 11h and 11p were refluxed with acidic alumina to afford
fused bromofurans 13e-f, 13h and 13p in excellent yield (Table 2, entries 1-3 and 5).
Figure 1. X-ray Structure of 11d and Chemical Structures of 12l and 13n
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Table 2. Alumina Mediated Cloke-Wilson Rearrangement of Dibromocyclopropanesa
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entry 11
X
Ar
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time (h) % yieldb
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H
H
H
H
2,4-(OMe)2Ph
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13f
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11f
3,4-(OMe)2Ph
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11n
11p
3,4,5-(OMe)3Ph
2-MeOPhCH=CH
13h 15
13n 4.5c
13p 4
OMe 3,4-(OMe)2Ph
aMg, bromoform and acidic Al2O3 were used in excess (8 atom g, 22 equiv and 25 equiv, respectively). b
Isolated yield after purification by silica gel column chromatography. c For direct transformation of 10n
to 13n; 11n was not isolable in this case; see also Table 1 and Figure 1.
The above results encouraged us to expand the scope of our methodology to other enones, viz easily
accessible indanone derivatives 14 (Table 3). Thus, selected indanone derived enones 14a-f were
subjected to Mg mediated dibromocyclopropanation to afford the products 15a-f in moderate to good
yield (53-78%, entries 1-6). Although these reactions required longer time (~ 12 h), as compared to
dibromocyclopropanation of tetralone derived enones 10 (see Table 1), we were gratified to note that
subsequent ring expansion via Cloke-Wilson rearrangement took place smoothly in all the cases. Thus,
cyclopropyl ketones 15a-f when refluxed with acidic alumina in CHCl3 for 2.5 to 4 h, the desired
bromofurans 16a-f were isolated in excellent yield (82-89%, entries 1-6). Quite remarkably and unlike
in the case of tetralone derived cyclopropanes 11 (see Tables 1-2), the rearrangement of indanone
derived cyclopropanes 15 took place regardless of the nature of ꢀ-aryl substituent (Table 3).
Table 3. Dibromocyclopropanation-Cloke-Wilson Rearrangement of Indanonesa
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The Journal of Organic Chemistry
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entry 14 Ar
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% yieldb 16
time
(h)
% yieldb
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14a Ph
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76d
14b 4-MePh
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14c 3,4-Me2Ph 15c
14d 4-FPh 15d
14e 1-Naphthyl 15e
14f 4-OMePh 15f
2.5
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Mg, bromoform and acidic Al2O3 were used in excess (8 atom g, 22 equiv and 25 equiv,
b
c
respectively). Isolated yield after purification by silica gel column chromatography. Crude product
was directly subjected to the next step due to instability. d For two steps.
Finally, the scope of our methodology was further extended by converting benzosuberone derived
enones 17 to bromofuran 19 via Mg mediated dibromocyclopropanation and subsequent alumina
mediated Cloke-Wilson rearrangement (Table 4). In these cases, the dibromocyclopropanation was
complete in 4 h or less to afford the products in good yield (65-74%, entries 1-3 and 5). Since
cyclopropane 18d was not amenable for purification, the crude residue obtained after workup was
directly subjected to alumina mediated rearrangement to bromofuran 19d (84% yield, entry 4).
Cyclopropanes 18a-c and 18e also underwent facile rearrangement to deliver bromofurans 19a-c and
19e, respectively, in excellent yields (81-90%, entries 1-3 and 5).
Table 4. Dibromocyclopropanation-Cloke-Wilson Rearrangement of Benzosuberonesa
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entry 17
Ar
18
time (h) % yieldb 19
time (h) % yieldb
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17a Ph
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18b
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17b 4-MePh
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c
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-
17e 3,4-(MeO)2Ph 18e
74
aMg, bromoform and acidic Al2O3 were used in excess (8 atom g, 22 equiv and 25 equiv,
b
c
respectively). Isolated yield after purification by silica gel column chromatography. Crude product
was directly subjected to next step due to instability. d For two steps.
Later on, a representative open chain ꢀ,ꢀ-disubstituted enone 20 underwent bromoform addition
satisfactorily to give cyclopropane 21 in 56% yield (Scheme 2a). However, attempted transformation of
21 to the desired bromofuran 22 afforded only an intractable mixture. Reactivity of enones derived from
highly fused cycloalkanones was subsequently investigated taking enone 23 as a model substrate
(Scheme 2b). This mono-Wittig product of acenaphthaquinone, prepared as a 1:1 mixture of E/Z
isomers, underwent smooth reaction with bromoform under our conditions to afford cyclopropane 24 as
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a single diastereomer in 70% yield. Subsequent alumina mediated rearrangement of 24 to bromofuran
25 took place in excellent (83%) yield.
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Scheme 2
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The formation of a single diastereomer of cyclopropane 24 from a 1:1 E/Z mixture of 23 further
confirmed the stepwise nature of the dibromocyclopropanation. It is obvious that both E and Z isomers
of 23 give rise to the same enolate of the intermediate Michael adduct that cyclizes to give cyclopropane
24 as a single diastereomer. This stereoconvergence, though at the expense of stereospecificity, is
remarkable.
The structure and stereo/regiochemistry of the products were determined by detailed NMR analysis
and further unambiguously established by single crystal X-ray analysis of representative compounds. A
positive NOE between the protons ortho to methoxy group in 4-methoxyphenyl with the methylene
protons ꢀ to carbonyl of tetralone moiety in cyclopropane 11c suggested their cis relationship and,
therefore, the trans relationship of the aromatic ring and the C=O group. Finally, the structure was
unambiguously established by X-ray analysis of cyclopropane 11d (see Figure 1) and 24 (vide infra,
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also see Scheme 3, the experimental section and the Supporting Information). In the bromofuran series,
while the benzylic methylene protons in 13f showed positive NOE with one of the protons of benzo
group, there was no NOE between either of the methylene protons with the 3,4-dimethoxyphenyl
protons suggesting that it could be 3-bromofuran and not 2-bromofuran. The possibility of 2-
bromofuran was ruled out also based on the 13C NMR chemical shift of C-Br (ꢀ 97.8). The structure was
later unequivocally established by X-ray analysis of an analog 19e (see Table 4 and also the
experimental section and the Supporting Information).
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Scheme 3
The proposed mechanism of cyclopropanation and rearrangement taking chalcone 10 as a
representative example is presented in Scheme 3. The cyclopropanation step involves formation of
tribromomethyl magnesium bromide II from Mg and excess bromoform and its addition to chalcone 10
in a 1,4-fashion. The resulting enolate cyclizes spontaneously in most cases to give cyclopropyl ketone
11 as a single diastereomer. Examination of the X-ray data confirms that the C=O group and the Ar
group avoid each other (dihedral angle 142.6° in 11d and 137° in 24) during cyclization to afford a
single diastereomer of the spirocyclopropane (see the Supporting Information).15 This also explains the
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stereoconvergence observed in the transformation of 23 to 24 as both E and Z isomers of 23 give rise to
the same enolate which eventually cyclizes to cyclopropane 24 (Scheme 2). In the rearrangement step,
the Lewis acid mediated activation of carbonyl with or without the electron donating ability of the ꢀ-aryl
substituent triggers the regioselective cleavage of cyclopropane in 11. The resulting enolate IV then
cyclizes intramolecularly to dihydrofuran V. Spontaneous elimination of HBr from V completes the
process to deliver fused 3-bromofuran 13.
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Possible transformation of tetraline fused bromofurans 13 to angularly fused naphthofurans 26 was
demonstrated via complete aromatization of a representative example 13f using DDQ in dioxane
(Scheme 4).
Scheme 4
Conclusions
Treatment of cycloalkanone derived chalcones with Mg and CHBr3 in THF affords
spirodibromocyclopropanated products, rather than Michael adducts, as single stereoisomers. These
adducts undergo facile regioselective ring expansion in the presence of acidic Al2O3 to afford 2-aryl-3-
halofurans fused to benzocycloalkanes as single regioisomers. The stereoconvergence in the
cyclopropanation of mixture of E and Z chalcones and complete aromatization of tetralone derived 3-
bromofurans via DDQ dehydrogenation have been demonstrated with representative examples.
Experimental Section
1
13
13
General. The melting points recorded are uncorrected. NMR spectra (1H, H decoupled C, C-APT,
1
19
1H-1H-COSY and H-1H-NOESY) were recorded with TMS and F spectra with CFCl3 as the internal
standard. The coupling constants (J values) are given in Hz. High resolution mass spectra were recorded
under ESI Q-TOF conditions. X-ray data were collected on a diffractometer equipped with graphite
monochromated Mo Kꢀ radiation. The structure was solved by direct methods shelxs97 and refined by
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full-matrix least squares against F2 using shelxl97 software. Chalcones 10, 14, 17 and 20 were prepared
via condensation of ketones with aromatic aldehydes.16 Chalcone 23 was prepared as a 1:1 mixture of
isomers via Wittig reaction of acenaphthaquinone with benzyl bromide.17 Mg turnings were activated by
washing with 1% dil HCl, water and acetone followed by drying in an oven overnight. Bromoform was
commercially available and was used as such.
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General Procedure for Addition of Bromoform to Chalcones 10, 14, 17, 20 and 23. To a stirred
solution of magnesium (196 mg, 8 atom g) and chalcone 10, 14, 17, 20 or 23 (1 mmol) in THF (20 mL)
was added bromoform (5.4 g, 2 mL, 22 mmol) dropwise over a period of 10 min at 0 °C. The reaction
mixture was gradually brought to room temperature over a period of 1.5 h during which the solution
turned dark brown. The reaction mixture was subsequently quenched with saturated aqueous NH4Cl (10
mL). The aqueous layer was extracted with ethyl acetate (5 × 20 mL) and the combined organic layers
were washed with H2O (3 × 10 mL), dried (anhyd Na2SO4), and concentrated in vacuo to afford the
crude product, which was subjected to silica gel column chromatography (ethyl acetate/hexane mixture,
5-15%, gradient elution) to afford product 11, 15, 18, 21 or 24.
2, 2-Dibromo-3-phenyl-3', 4’-dihydro-1'H-spiro[cyclopropane-1,2'-naphthalen]-1'-one (11a).
Colorless solid; Yield 62%, 251 mg; mp 88-90 oC; IR (KBr, cm-1) 2929 (m), 2852 (w), 1676 (vs), 1599
(m), 1300 (s), 1215 (m), 757 (s); 1H NMR (400 MHz, CDCl3) ꢀ 8.19 (dd, J = 7.9, 1.2 Hz, 1H), 7.58 (td,
J = 7.5, 1.4 Hz, 1H), 7.43–7.35 (m, 4H), 7.35 – 7.31 (m, 3H), 4.02 (s, 1H), 3.52 (ddd, J = 16.9, 13.1, 4.2
Hz, 1H), 2.96 (ddd collapsed to dt, J = 16.9, 3.0 Hz, 1H), 2.61 (ddd, J = 14.1, 13.1, 4.2 Hz, 1H), 2.03
(ddd, J = 14.1, 4.2, 3.0 Hz, 1H); 13C NMR (100 MHz, CDCl3) ꢀ 191.2, 144.1, 134.3, 133.3, 131.5,
130.1, 129.1, 128.6, 128.4, 127.7, 127.2, 42.9, 39.2, 36.1, 29.7, 27.0; MS (ES+, Ar) m/z (rel intensity)
328 ([(MH+2)-Br]+, 25), 327 ([(M+2)-Br]+, 100), 326 ([MH-Br]+, 25), 325 ([M-Br]+, 98); HRMS (ES+,
Ar) calcd for C18H14OBr ([M-Br]+) 325.0228, found 325.0238.
2, 2-Dibromo-3-(p-tolyl)-3', 4’-dihydro-1'H-spiro[cyclopropane-1,2'-naphthalen]-1'-one (11b).
o
Colorless solid; Yield 73%, 306 mg; mp 156-158 C; IR (KBr, cm-1) 3057 (w), 2971 (w), 2910 (w),
1680 (vs), 1297 (s), 1223 (m), 780 (m); 1H NMR (400 MHz, CDCl3) ꢀ 8.17 (dd, J = 7.7, 0.8 Hz, 1H),
7.55 (td, J = 7.6, 1.3 Hz, 1H), 7.38 (td, J = 7.7, 0.8 Hz, 1H), 7.31 (dd, J = 7.6, 1.3 Hz, 1H), 7.19
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(unresolved m, 4H), 3.95 (s, 1H), 3.50 (ddd, J = 16.9, 13.9, 4.1 Hz, 1H), 2.93 (ddd collapsed to dt, J =
16.9, 3.0 Hz, 1H), 2.58 (ddd collapsed to td, J = 13.9, 4.1 Hz, 1H), 2.36 (s, 3H), 2.01 (ddd, J = 13.9, 4.1,
1
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5
6
13
3.0 Hz, 1H); C NMR (100 MHz, CDCl3) ꢀ 191.3, 144.1, 137.5, 134.3, 131.6, 130.3, 130.0, 129.4,
7
8
9
129.1, 128.4, 127.2, 42.9, 39.0, 36.4, 29.7, 27.0, 21.4; MS (ES+, Ar) m/z (rel intensity) 342 ([(MH+2)-
Br]+, 25), 341 ([(M+2)-Br]+, 98), 340 (MH-Br]+, 25), 339 ([M-Br]+, 100); HRMS (ES+, Ar) calcd for
C19H16OBr ([M-Br]+) 339.0385, found 339.0395.
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2, 2-Dibromo-3-(4-methoxyphenyl)-3', 4’-dihydro-1'H-spiro[cyclopropane-1,2'-naphthalen]-1'-one
o
(11c). Colorless solid; Yield 68%, 296 mg; mp 110-112 C; IR (KBr, cm-1) 2928 (vs), 2857 (m), 1683
(m), 1600 (m), 1515 (m), 1248 (m), 1023 (m); 1H NMR (400 MHz, CDCl3) ꢀ 8.16 (dd, J = 7.8, 1.2 Hz,
1H), 7.55 (td, J = 7.6, 1.4 Hz, 1H), 7.38 (td, J = 7.8, 1.2 Hz, 1H), 7.31 (dd, J = 7.6, 1.4 Hz, 1H), 7.21 (d,
J = 8.7 Hz, 2H), 6.91 (d, J = 8.7 Hz, 2H), 3.92 (s, 1H), 3.82 (s, 3H), 3.49 (ddd, J = 16.9, 13.9, 4.2 Hz,
1H), 2.94 (ddd collapsed to dt, J = 16.9, 3.0 Hz, 1H), 2.55 (ddd collapsed to td, J = 13.9, 4.2 Hz, 1H),
2.00 (ddd, J = 13.9, 4.2, 3.0 Hz, 1H); 13C NMR (100 MHz, CDCl3) ꢀ 191.3, 159.1, 144.1, 134.3, 131.6,
131.2, 129.1, 128.4, 127.2, 125.3, 114.1, 55.4, 42.9, 38.7, 36.7, 29.7, 27.0; MS (ES+, Ar) m/z (rel
intensity) 358 ([(MH+2)-Br]+, 21), 357 ([(M+2)-Br]+, 98), 356 (MH-Br]+, 21), 355 ([M-Br]+, 100);
1
HRMS (ES+, Ar) calcd for C19H16O2Br ([M-Br]+) 355.0334, found 355.0348. Confirmed by H-1H
COSY and 1H-1H NOESY experiments.
2,2-Dibromo-3-(3-methoxyphenyl)-3',4'-dihydro-1'H-spiro[cyclopropane-1,2'-naphthalen]-1'-one
o
(11d). Colorless solid; Yield 71%, 309 mg; mp 130-132 C; IR (KBr, cm-1) 2937 (m), 2840 (s), 2739
(m), 1696 (vs), 1599 (s), 1578 (s), 1511 (s), 1316 (s), 1260 (s), 1161 (s), 1027 (s), 834 (s); 1H NMR (400
MHz, CDCl3) ꢀ 8.16 (dd, J = 7.6, 1.3 Hz, 1H), 7.56 (td, J = 7.4, 1.4 Hz, 1H), 7.38 (td, J = 7.6, 1.3 Hz,
1H), 7.30 (dd, J = 7.4, 1.4 Hz, 1H), 7.26 (s, 1H), 6.90–6.84 (m, 3H), 3.97 (s, 1H), 3.82 (s, 3H), 3.50
(ddd, J = 16.9, 13.0, 4.2 Hz, 1H), 2.95 (ddd collapsed to dt, J = 16.9, 3.0 Hz, 1H), 2.58 (ddd, J = 14.1,
13
13.0, 4.2 Hz, 1H), 2.03 (ddd, J = 14.1, 4.2, 3.0 Hz, 1H); C NMR (100 MHz, CDCl3) ꢀ 191.1, 159.7,
144.0, 134.7, 134.3, 131.5, 129.6, 129.1, 128.4, 127.2, 122.3, 115.8, 113.2, 55.4, 42.9, 39.3, 36.0, 29.8,
27.0; MS (ES+, Ar) m/z (rel intensity) 358 ([(MH+2)-Br]+, 25), 357 ([(M+2)-Br]+, 100), 356 ([(MH-
Br]+, 21), 355 ([M-Br]+, 98); HRMS (ES+, Ar) calcd for C19H16O2Br ([M-Br]+) 355.0334, found
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355.0327. Selected X-ray Data: C19H16Br2O2, M = 436.14, Triclinic, space group P-1, a = 7.0570(2)Å, b
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2
3
o
= 11.2036(2) Å, c = 12.3063(3) Å, ꢀ = 63.4440(10) , ꢀ = 84.1330(10)o, ꢁ = 71.8540(10)o, V =
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826.26(3) Å3, Dc = 1.753Mg/m3, Z = 2, F(000) = 432, ꢀ = 0.71073 Å, µ = 4.912 mm-1, Total/ unique
reflections = 12706 / 2829 [R(int) = 0.0541], T = 293(2) K, ꢁ range = 1.85 to 25.00°, Final R [I>2ꢁ(I)]:
R1 = 0.0461, wR2 = 0.1094, R (all data): R1 = 0.0738, wR2 = 0.1239.
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2, 2-Dibromo-3-(2,4-dimethoxyphenyl)-3',4'-dihydro-1'H-spiro[cyclopropane-1,2'-naphtha-len]-
o
1'-one (11e). Colorless solid; Yield 60%, 279 mg; mp 88-90 C; IR (KBr, cm-1) 3001 (w), 2938 (m),
2836 (w), 1614 (vs), 1583 (s), 1500 (vs), 1465 (s), 1382 (m), 1291 (vs), 1210 (vs), 1160 (vs), 1033 (s),
820 (vs); 1H NMR (400 MHz, CDCl3) ꢀ 8.17 (dd, J = 7.7, 1.1 Hz, 1H), 7.54 (td, J = 7.6, 1.4 Hz, 1H),
7.37 (td, J = 7.7, 1.1 Hz, 1H), 7.30 (dd, J = 7.6, 1.4 Hz, 1H), 7.15 (dd, J = 8.4, 1.0 Hz, 1H), 6.50 (dd, J =
2.4, 1.0 Hz, 1H), 6.46 (dd, J = 8.4, 2.4 Hz, 1H), 3.83 (s, 3H), 3.82 (s, 3H), 3.74 (s, 1H), 3.49 (ddd, J =
16.8, 13.6, 4.1 Hz, 1H), 2.91 (ddd collapsed to dt, J = 16.8, 3.0 Hz, 1H), 2.60 (ddd collapsed to td, J =
13
13.6, 4.1 Hz, 1H), 2.09 (ddd, J = 13.6, 4.1, 3.0 Hz, 1H); C NMR (100 MHz, CDCl3) ꢀ 191.4, 160.7,
160.2, 144.2, 134.1, 131.7, 130.7, 129.1, 128.4, 127.1, 114.9, 103.8, 98.8, 55.7, 55.5, 43.1, 37.7, 36.3,
29.6, 27.0; MS (ES+, Ar) m/z (rel intensity) 388 ([(MH+2)-Br]+, 28), 387 ([(M+2)-Br]+, 100), 386
([(MH-Br]+, 28), 385 ([M-Br]+, 98); HRMS (ES+, Ar) calcd for C20H18O3Br ([M-Br]+) 385.0439, found
385.0450.
2, 2-Dibromo-3-(3,4-dimethoxyphenyl)-3',4'-dihydro-1'H-spiro[cyclopropane-1,2'-naphtha-len]-
1'-one (11f). Colorless solid; Yield 65 %, 302 mg; mp 154-156 oC; IR (KBr, cm-1) 2930 (m), 2857 (w),
1679 (s), 1599 (m), 1510 (vs), 1455 (m), 1259 (m), 1241 (s), 1223 (m), 1138 (m), 1026 (s); 1H NMR
(400 MHz, CDCl3) ꢀ 8.16 (dd, J = 7.8, 0.9 Hz, 1H), 7.55 (td, J = 7.6, 1.3 Hz, 1H), 7.38 (td, J = 7.8, 0.9
Hz, 1H), 7.31 (dd, J = 7.6, 1.3 Hz, 1H), 6.88–6.80 (m, 3H), 3.94 (s, 1H), 3.90 (s, 3H), 3.89 (s, 3H), 3.50
(ddd, J = 16.9, 13.9, 4.1 Hz, 1H), 2.95 (ddd collapsed to dt, J = 16.9, 3.0 Hz, 1H), 2.56 (ddd collapsed to
13
td, J = 13.9, 4.1 Hz, 1H), 2.02 (ddd, J = 13.9, 4.1, 3.0 Hz, 1H); C NMR (100 MHz, CDCl3) ꢀ 191.3,
149.0, 148.6, 144.1, 134.4, 131.6, 129.1, 128.5, 127.2, 125.7, 122.2, 113.3, 111.1, 56.2, 56.0, 43.0, 39.1,
36.6, 29.8, 27.1; MS (ES+, Ar) m/z (rel intensity) 388 ([(MH+2)-Br]+, 28), 387 ([(M+2)-Br]+, 100), 386
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([MH-Br]+, 28), 385 ([M-Br]+, 98); HRMS (ES+, Ar) calcd for C20H18O3Br ([M-Br]+) 385.0439, found
385.0454.
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2,2-Dibromo-3-(2,3,4-trimethoxyphenyl)-3',4'-dihydro-1'H-spiro[cyclopropane-1,2'-naph-thalen]-
o
1'-one (11g). Colorless solid; Yield 70%, 347 mg; mp 94-96 C; IR (KBr, cm-1) 2935 (w), 1681 (m),
8
1600 (w), 1497 (m), 1466 (m), 1300 (m), 1222 (m), 1098 (s); 1H NMR (400 MHz, CDCl3) ꢀ 8.15 (dd, J
= 7.7, 1.2 Hz, 1H), 7.54 (td, J = 7.6, 1.4 Hz, 1H), 7.37 (td, J = 7.7, 1.2 Hz, 1H), 7.30 (dd, J = 7.6, 1.4
Hz, 1H), 6.95 (dd, J = 8.6, 1.1 Hz, 1H), 6.63 (d, J = 8.6 Hz, 1H), 3.95 (s, 3H), 3.87 (s, 3H), 3.86 (s, 3H),
3.82 (s, 1H), 3.49 (ddd, J = 16.9, 13.6, 4.2 Hz, 1H), 2.92 (ddd collapsed to dt, J = 16.9, 3.0 Hz, 1H),
2.67 (td, J = 13.6, 4.2 Hz, 1H), 2.10 (ddd, J = 13.6, 4.2, 3.0 Hz, 1H); 13C NMR (100 MHz, CDCl3) ꢀ
191.3, 153.7, 153.6, 144.2, 142.5, 134.2, 131.6, 129.1, 128.4, 127.1, 124.5, 120.1, 106.6, 61.1, 61.0,
56.1, 43.2, 37.1, 36.4, 29.6, 27.0; MS (ES+, Ar) m/z (rel intensity) 418 ([(MH+2)-Br]+, 25), 417
([(M+2)-Br]+, 100), 416 ([(MH-Br]+, 25), 415 ([M-Br]+, 98); HRMS (ES+, Ar) calcd for C21H20O4Br
([M-Br]+) 415.0545, found 415.0546.
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2,2-Dibromo-3-(3,4,5-trimethoxyphenyl)-3',4'-dihydro-1'H-spiro[cyclopropane-1,2'-naph-thalen]-
o
1'-one (11h). Colorles ssolid; Yield 71%, 352 mg; mp 118-120 C; IR (KBr, cm-1) 2930 (br m), 1680
(m), 1586 (m), 1508 (m), 1292 (m), 1241 (m), 1127 (s); 1H NMR (400 MHz, CDCl3) ꢀ 8.16 (dd, J = 7.7,
1.1 Hz, 1H), 7.56 (td, J = 7.6, 1.4 Hz, 1H), 7.39 (td, J = 7.7, 1.1 Hz, 1H), 7.32 (dd, J = 7.6, 1.4 Hz, 1H),
6.48 (d, J = 0.8 Hz, 2H), 3.94 (s, 1H), 3.86 (s, 9H), 3.51 (ddd, J = 16.9, 13.6, 4.1 Hz, 1H), 2.97 (ddd
collapsed to dt, J = 16.9, 3.0 Hz, 1H), 2.55 (ddd collapsed to td, J = 13.6, 4.2 Hz, 1H), 2.03 (ddd, J =
13
13.6, 4.1, 3.0 Hz, 1H); C NMR (100 MHz, CDCl3) ꢀ 191.2, 153.4, 144.0, 137.6, 134.4, 131.5, 129.1,
128.6, 128.4, 127.2, 107.1, 61.1, 56.4, 43.0, 39.5, 36.1, 29.9, 27.1; MS (ES+, Ar) m/z (rel intensity) 418
([(MH+2)-Br]+, 25), 417 ([(M+2)-Br]+, 100), 416 ([(MH-Br]+, 25), 415 ([M-Br]+, 100); HRMS (ES+,
Ar) calcd for C21H20O4Br ([M-Br]+) 415.0545, found 415.0557.
2,
2-Dibromo-3-(4-(trifluoromethyl)phenyl)-3',4'-dihydro-1'H-spiro[cyclopropane-1,2'-
o
naphthalen]-1'-one (11i). Colorless solid; Yield 69%, 327 mg; mp 182-184 C; IR (KBr, cm-1) 2938
(w), 1675 (m), 1328 (s), 1302 (m), 1160 (m), 1126 (s), 751 (m); 1H NMR (400 MHz, CDCl3) ꢀ 8.17 (dd,
J = 8.1, 0.9 Hz, 1H), 7.64 (d, J = 8.2 Hz, 2H), 7.57 (td, J = 7.6, 1.3 Hz, 1H), 7.42 (d, J = 8.2 Hz, 2H),
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7.40 (td, J = 8.1, 0.9 Hz, 1H), 7.32 (dd, J = 7.6, 1.3 Hz, 1H), 4.01 (s, 1H), 3.51 (ddd, J = 16.9, 13.6, 4.2
Hz, 1H), 2.97 (ddd collapsed to dt, J = 16.9, 2.9 Hz, 1H), 2.59 (ddd collapsed to td, J = 13.6, 4.2 Hz,
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7
13
1H), 1.96 (ddd, J = 13.6, 4.1, 2.9 Hz, 1H); C NMR (100 MHz, CDCl3) ꢀ 190.8, 144.0, 137.4, 134.6,
19
131.4, 130.6, 130.2, 129.8, 129.2, 128.5, 127.3, 125.6 (q, J = 16 Hz) 43.1, 38.8, 34.9, 29.7, 26.9; F
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NMR (376 MHz, CDCl3) ꢀ -62.6; MS (ES+, Ar) m/z (rel intensity) 396 ([(MH+2)-Br]+, 25), 395
([(M+2)-Br]+, 100), 394 ([MH-Br]+, 25), 393 ([M-Br]+, 100); HRMS (ES+, Ar) calcd for C19H13OBrF3
([M-Br]+) 393.0102, found 393.0104.
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2,
2-Dibromo-3-(4-fluorophenyl)-3',4'-dihydro-1'H-spiro[cyclopropane-1,2'-naphthalen]-1'-one
o
(11j). Colorless solid; Yield 75%, 318 mg; mp 144-146 C; IR (KBr, cm-1) 2978 (w), 2915 (w), 1682
(vs), 1599 (m), 1512 (s), 1300 (s), 1300 (s), 1224 (vs); 1H NMR (400 MHz, CDCl3) ꢀ 8.16 (dd, J = 7.7,
0.9 Hz, 1H), 7.56 (td, J = 7.6, 1.3 Hz, 1H), 7.38 (td, J = 7.7, 0.9 Hz, 1H), 7.31 (dd, J = 7.6, 1.3 Hz, 1H),
7.29–7.24 (m, 2H), 7.12–7.03 (m, 2H), 3.93 (s, 1H), 3.50 (ddd, J = 16.9, 13.6, 4.2 Hz, 1H), 2.95 (ddd
collapsed to dt, J = 16.9, 2.9 Hz, 1H), 2.56 (ddd collapsed to td, J = 13.6, 4.2 Hz, 1H), 1.97 (ddd, J =
13
13.6, 4.1, 2.9 Hz, 1H); C NMR (100 MHz, CDCl3) ꢀ 191.0, 162.3 (d, JC-F = 246.0 Hz), 144.0, 134.4,
131.8, 131.5, 129.2, 129.1 (d, JC-F = 6.0 Hz), 128.5, 127.2, 115.8, 115.6, 42.9, 38.5, 35.8, 29.6, 26.9; 19F
NMR (CDCl3) ꢀ -114.0 (dtt, J = 11.3, 7.5, 3.8 Hz, 1F); MS (ES+, Ar) m/z (rel intensity) 346 ([(MH+2)-
Br]+, 25), 345 ([(M+2)-Br]+, 100), 344 ([MH-Br]+, 25), 343 ([M-Br]+, 100); HRMS (ES+, Ar) calcd for
C18H13OBrF ([M-Br]+) 343.0134, found 343.0131.
2,2-Dibromo-3-(naphthalen-1-yl)-3',4'-dihydro-1'H-spiro[cyclopropane-1,2'-naphthalen]-1'-one
o
(11k). Colorless solid; Yield 71%, 322 mg; mp 182-184 C; IR (KBr, cm-1) 2923 (m), 2851 (w), 1678
(vs), 1457 (w), 1298 (w), 1262 (w), 1021 (w), 757 (s), 741 (s); 1H NMR (400 MHz, CDCl3) ꢀ 8.23 (d, J
= 7.8 Hz, 1H), 8.11 (d, J = 8.2 Hz, 1H), 7.90 (d, J = 7.8 Hz, 1H), 7.87–7.81 (m, 1H), 7.64-7.52 (m, 3H),
7.46–7.39 (m, 3H), 7.33 (d, J = 7.8 Hz, 1H), 4.32 (s, 1H), 3.55 (ddd, J = 16.9, 13.5, 4.2 Hz, 1H), 2.95
(ddd collapsed to dt, J = 16.9, 3.0 Hz, 1H), 2.74 (ddd collapsed to td, J = 13.5, 4.2 Hz, 1H), 2.18 (ddd, J
= 13.5, 4.1, 3.0 Hz, 1H); 13C NMR (100 MHz, CDCl3) ꢀ 191.4, 144.1, 134.5, 134.0, 133.2, 131.6, 130.7,
129.2, 128.8, 128.6 (× 2), 127.3, 127.1, 126.8, 126.3, 125.2, 125.1, 43.4, 38.4, 36.8, 30.3, 27.2; MS
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(ES+, Ar) m/z (rel intensity) 378 ([(MH+2)-Br]+, 25), 377 ([(M+2)-Br]+, 100), 376 ([MH-Br]+, 25), 375
([M-Br]+, 100); HRMS (ES+, Ar) calcd for C22H16OBr ([M-Br]+) 375.0385, found 375.0378.
2, 2-Dibromo-3-(furan-2-yl)-3',4'-dihydro-1'H-spiro[cyclopropane-1,2'-naphthalen]-1'-one (11l).
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o
Colorless solid; Yield 60%, 237 mg; mp 114-116 C; IR (KBr, cm-1) 2926 (m), 2856 (w), 1686 (vs),
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1600 (s), 1455 (m), 1365 (m), 1299 (s), 1225 (s), 1023 (m), 786 (m), 737 (s); H NMR (400 MHz,
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CDCl3) ꢀ 8.13 (dd, J = 7.7, 1.3 Hz, 1H), 7.55 (td, J = 7.7, 1.3 Hz, 1H), 7.43-7.45 (m, 1H), 7.37 (t, J =
7.7 Hz, 1H), 7.32 (d, J = 7.7 Hz, 1H), 6.39 (d, J = 1.3 Hz, 2H), 3.92 (s, 1H), 3.49 (ddd, J = 16.9, 12.9,
4.5 Hz, 1H), 2.98 (dt, J = 16.9, 3.2 Hz, 1H), 2.50 (ABq, J = 14.3 Hz, the upper half is further split into
13
dd, J = 4.5, 2.7 Hz, the lower half is further split into dd, J = 12.9, 4.2 Hz, 2H); C NMR (100 MHz,
CDCl3) ꢀ 190.2, 147.8, 143.9, 142.7, 134.4, 131.4, 129.1, 128.5, 127.2, 110.6, 110.0, 43.5, 34.4, 34.3,
29.1, 27.1; MS (ES+, Ar) m/z (rel intensity) 318 ([(MH+2)-Br]+, 20), 317 ([(M+2)-Br]+, 100), 316
([MH-Br]+, 20), 315 ([M-Br]+, 98), 236 (48); HRMS (ES+, Ar) calcd for C16H12O2Br ([M-Br]+)
315.0021, found 315.0024.
(E)-2,2-Dibromo-3-styryl-3',4'-dihydro-1'H-spiro[cyclopropane-1,2'-naphthalen]-1'-one
(11m).
Dark green solid; Yield 69%, 298 mg; mp 96-98 oC; IR (KBr, cm-1) 3019 (w), 1684 (m), 1600 (w), 1301
(w), 1216 (s), 757 (vs); 1H NMR (400 MHz, CDCl3) ꢀ 8.13 (dd, J = 7.9, 1.3 Hz, 1H), 7.55 (td, J = 7.5,
1.4 Hz, 1H), 7.44–7.24 (m, 7H), 6.85 (d, J = 15.8 Hz, 1H), 5.95 (dd, J = 15.8, 8.8 Hz, 1H), 3.54 (d, J =
8.8 Hz, 1H), 3.51–3.44 (m, 1H), 2.99 (dt, J = 16.8, 3.4 Hz, 1H), 2.42–2.36 (m, 2H); 13C NMR (100
MHz, CDCl3) ꢀ 190.6, 143.8, 137.0, 136.7, 134.3, 131.6, 129.1, 128.8, 128.4, 128.2, 127.2, 126.4,
122.2, 43.7, 38.8, 38.0, 28.3, 26.9; MS (ES+, Ar) m/z (rel intensity) 354 ([(MH+2)-Br]+, 31), 353
([(M+2)-Br]+, 100), 352 ([MH-Br]+, 31), 351 ([M-Br]+, 100); HRMS (ES+, Ar) calcd for C20H16OBr
([M-Br]+) 351.0385, found 351.0388.
(E)-2,2-Dibromo-3-(2-nitrostyryl)-3',4'-dihydro-1'H-spiro[cyclopropane-1,2'-naphthalen]-1'-one
(11o). Dark Green solid; Yield 52%, 247 mg; mp 126-128 oC; IR (KBr, cm-1) 3027 (w), 2967 (w), 1683
(m), 1600 (w), 1454 (w), 1300 (m), 1223 (m), 761 (s); 1H NMR (400 MHz, CDCl3) ꢀ 8.12 (dd, J = 7.7,
1.3 Hz, 1H), 7.99–7.91 (m, 1H), 7.62–7.58 (m, 2H), 7.53 (td, J = 7.7, 1.3 Hz, 1H), 7.46–7.41 (m, 1H),
7.39-7.29 (m, 3H), 5.94 (dd, J = 15.7, 8.5 Hz, 1H), 3.58 (d, J = 8.5 Hz, 1H), 3.49 (ddd, J = 16.9, 14.2,
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4.5 Hz, 1H), 3.00 (dt, J = 16.9, 3.1 Hz, 1H), 2.45 (td, J = 14.2, 4.5 Hz, 1H), 2.34 (ddd, J = 14.2, 4.5, 3.1
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3
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Hz, 1H); C NMR (100 MHz, CDCl3) ꢀ 190.1, 147.5, 143.6, 134.4, 133.4, 132.4, 132.1, 131.4, 129.1,
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8
9
129.0, 128.7, 128.4, 128.0, 127.2, 124.9, 44.0, 38.3, 37.2, 28.4, 26.9; MS (ES+, Ar) m/z (rel intensity)
399 ([(MH+2)-Br]+, 25), 398 ([(M+2)-Br]+, 100), 397 ([MH-Br]+, 25), 396 ([M-Br]+, 100); HRMS
(ES+, Ar) calcd for C20H15NO3Br ([M-Br]+) 396.0235, found 396.0223.
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2,2-Dibromo-3-(3,4-dimethoxyphenyl)-7'-methoxy-3',4'-dihydro-1'H-spiro[cyclopropane-1,2'-
o
naphthalen]-1'-one (11p). Colorless solid; Yield 65%, 323 mg; mp 104-106 C; IR (KBr, cm-1) 2934
(m), 2837 (w), 1682 (s), 1609 (m), 1518 (s), 1498 (s), 1421 (m), 1323 (m), 1261 (vs), 1242 (vs), 1030
(vs), 733 (s); 1H NMR (400 MHz, CDCl3) ꢀ 7.62 (d, J = 2.8 Hz, 1H), 7.21 (d, J = 8.4 Hz, 1H), 7.13 (dd,
J = 8.4, 2.8 Hz, 1H), 6.87–6.77 (m, 3H), 3.93 (s, 1H), 3.88 (s, 3H), 3.87 (s, 3H), 3.86 (s, 3H), 3.41 (ddd,
J = 16.6, 13.4, 4.1 Hz, 1H), 2.89 (dd, J = 16.6, 3.3 Hz, 1H), 2.53 (td, J = 13.4, 4.1 Hz, 1H), 2.00 (dt, J =
13
13.4, 3.3 Hz, 1H); C NMR (100 MHz, CDCl3) ꢀ 191.3, 158.7, 149.0, 148.6, 136.7, 132.2, 130.3,
125.6, 122.8, 122.2, 113.2, 111.1, 110.2, 56.1, 56.0, 55.7, 42.8, 39.1, 36.5, 30.1, 26.2; MS (ES+, Ar)
m/z (rel intensity) 418 ([(MH+2)-Br]+, 25), 417 ([(M+2)-Br]+, 100), 416 ([MH-Br]+, 25), 415 ([M-Br]+,
100); HRMS (ES+, Ar) calcd for C21H20O4Br ([M-Br]+) 415.0545, found 415.0557.
2-(2, 2,2-Tribromo-1-(cyclopenta-1,3-dien-1-yl)ethyl)-3,4-dihydronaphthalen-1(2H)-one (12l).
Colorless solid; Yield 65% (dr > 95:5, inseparable), 309 mg; mp 124-126 oC; IR (KBr, cm-1) 2928 (w),
1676 (vs), 1600 (m), 1455 (w), 1286 (m), 1235 (m), 1223 (m), 1017 (m); 1H NMR (400 MHz, CDCl3) ꢀ
7.95 (dd, J = 7.8, 1.2 Hz, 1H), 7.45 (td, J = 7.6, 1.3 Hz, 1H), 7.36 (dd, J = 2.2, 0.8 Hz, 1H), 7.24 (td, J =
7.8, 1.2 Hz, 1H), 7.22 (dd, J = 7.6, 1.3 Hz, 1H), 6.55 (d, J = 3.2, 0.8 Hz, 1H), 6.32 (dd, J = 3.2, 2.2 Hz,
1H), 5.35 (d, J = 2.9 Hz, 1H), 3.27 (ddd, J = 10.9, 4.1, 3.0 Hz, 1H), 3.17 (dt, J = 16.7, 5.1 Hz, 1H),
3.07–3.00 (m, 1H), 2.99–2.90 (m, 1H), 2.73–2.62 (m, 1H); 13C NMR (100 MHz, CDCl3) ꢀ 196.2, 152.4,
143.1, 142.0, 133.6, 132.4, 128.6, 128.1, 126.9, 110.9, 110.7, 58.9, 53.4, 43.8, 28.7, 27.0; MS (ES+, Ar)
m/z (rel intensity) 481 ([(MH+6)]+, 35), 479 ([(MH+4)]+, 98), 477 ([(MH+2)]+, 100), 475 ([MH]+, 35),
399 ([(M+4)-Br]+, 35), 397 ([(M+2)-Br]+, 70), 395 ([M-Br]+, 35), 317 ([(MH+2)-Br2]+, 35), 315 ([MH-
Br2]+, 35); HRMS (ES+, Ar) calcd for C16H14O2Br3 ([MH]+) 474.8544, found 474.8552.
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2,2-Dibromo-3-phenylspiro[cyclopropane-1,2'-inden]-1'(3'H)-one (15a). Colorless solid; Yield 68%,
267; mp 106-108 oC; IR (KBr, cm-1) 3063 (w), 2980 (w), 2917 (w), 1678 (vs), 1596 (m), 1296 (s), 1221
(m), 806 (m), 786 (vs), 775 (vs), 760 (s), 746 (s), 736 (vs); 1H NMR (400 MHz, CDCl3) ꢀ 7.88 (dd, J =
7.6, 1.2 Hz, 1H), 7.68 (td, J = 7.6, 1.2 Hz, 1H), 7.54 (dt, J = 7.6, 0.8 Hz, 1H), 7.48 (td, J = 7.6, 0.8 Hz,
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1H), 7.43–7.35 (m, 3H), 7.34-7.30 (m, 2H), 3.64 (s, 1H), 3.44 (ABq, J = 18.2 Hz, 2H); C NMR (100
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MHz, CDCl3) ꢀ 197.8, 151.6, 136.5, 135.2, 133.3, 130.0, 128.7, 128.2, 128.1, 126.2, 124.4, 44.7, 44.5,
37.5, 34.0; MS (ES+, Ar) m/z (rel intensity) 314 ([(M+3)-Br]+, 25), 313 ([(M+2)-Br]+, 100), 312 ([MH-
Br]+, 25), 311 ([M-Br]+, 100); HRMS (ES+, Ar) calcd for C17H12OBr ([M-Br]+) 311.0072, found
311.0079.
2,2-Dibromo-3-(p-tolyl)spiro[cyclopropane-1,2'-inden]-1'(3'H)-one (15b). Colorless solid; Yield
68%, 276 mg; mp 104-106 oC; IR (KBr, cm-1) 3016 (w), 2918 (w), 1713 (m), 1607 (w), 1467 (w), 1279
(w), 1217 (w), 1037 (w), 769 (vs); 1H NMR (400 MHz, CDCl3) ꢀ 7.85 (d, J = 7.6 Hz, 1H), 7.65 (t, J =
7.4 Hz, 1H), 7.51 (d, J = 7.6 Hz, 1H), 7.45 (t, J = 7.4 Hz, 1H), 7.18 (unresolved m, 4H), 3.58 (s, 1H),
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3.41 (ABq, J = 18.3 Hz, 2H), 2.35 (s, 3H); C NMR (100 MHz, CDCl3) ꢀ 197.8, 151.6, 137.9, 136.6,
135.1, 130.2, 129.8, 129.4, 128.1, 126.1, 124.3, 44.6, 44.4, 37.9, 33.9, 21.4; MS (ES+, Ar) m/z (rel
intensity) 328 ([(M+3)-Br]+, 21), 327 ([(M+2)-Br]+, 100), 326 ([MH-Br]+, 18), 325 ([M-Br]+, 100);
HRMS (ES+, Ar) calcd for C18H14OBr ([M-Br]+) 325.0228, found 325.0227.
2,2-Dibromo-3-(3,4-dimethylphenyl)spiro[cyclopropane-1,2'-inden]-1'(3'H)-one (15c). Colorless
o
solid; Yield 72%, 302 mg; mp 112-114 C; IR (KBr, cm-1) 3053 (w), 2920 (w), 1713 (vs), 1606 (s),
1517 (m), 1466 (m), 1278 (s), 1203 (m), 1036 (s), 1022 (m), 770 (s), 737 (s), 714 (m), 515 (m); 1H
NMR (400 MHz, CDCl3) ꢀ 7.86 (d, J = 7.7 Hz, 1H), 7.66 (td, J = 7.7, 1.0 Hz, 1H), 7.53 (d, J = 7.7 Hz,
1H), 7.46 (t, J = 7.7 Hz, 1H), 7.14 (d, J = 7.8 Hz, 1H), 7.07 (s, 1H), 7.03 (d, J = 7.8 Hz, 1H), 3.57 (s,
1H), 3.50 (d, J = 18.3 Hz, 1H), 3.43 (ABq, J = 18.3 Hz, 1H), 2.27 (s, 3H), 2.26 (s, 3H); 13C NMR (100
MHz, CDCl3) ꢀ 197.9, 151.7, 137.0, 136.6, 135.1, 131.1, 130.6, 129.9, 128.1, 127.1, 126.1, 124.4, 44.6,
44.5, 38.0, 34.0, 20.0, 19.7; MS (ES+, Ar) m/z (rel intensity) 342 ([(M+3)-Br]+, 25), 341 ([(M+2)-Br]+,
100), 340 ([MH-Br]+, 25), 339 ([M-Br]+, 100); HRMS (ES+, Ar) calcd for C19H16OBr ([M-Br]+)
339.0385, found 339.0373.
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2,2-Dibromo-3-(4-fluorophenyl)spiro[cyclopropane-1,2'-inden]-1'(3'H)-one (15d). Colorless solid;
Yield 53%, 217 mg; mp 126-128 oC; IR (KBr, cm-1) 2925 (s), 2863 (m), 1714 (vs), 1604 (m), 1512 (s),
1276 (m), 1225 (m), 1157 (m), 1035 (m), 1015 (m), 771 (s), 738 (vs); 1H NMR (400 MHz, CDCl3) ꢀ
7.86 (d, J = 7.7 Hz, 1H), 7.67 (td, J = 7.7, 1.1 Hz, 1H), 7.53 (d, J = 7.7 Hz, 1H), 7.47 (t, J = 7.7 Hz, 1H),
7.32–7.24 (m, 2H), 7.07 (t, J = 8.7 Hz, 2H), 3.57 (s, 1H), 3.40 (ABq, J = 18.3 Hz, 2H); 13C NMR (100
MHz, CDCl3) ꢀ 197.5, 162.5 (d, JC-F = 247.0 Hz), 151.4, 136.5, 135.3, 131.7 (d, JC-F = 9.0 Hz), 129.1,
129.0, 128.2, 126.1, 124.4, 115.9, 115.7, 44.4, 43.9, 37.3, 33.9; MS (ES+, Ar) m/z (rel intensity) 332
([(M+3)-Br]+, 21), 331 ([(M+2)-Br]+, 100), 330 ([MH-Br]+, 23), 329 ([M-Br]+, 100); HRMS (ES+, Ar)
calcd for C17H11OBrF ([M-Br]+) 328.9977, found 328.9977.
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2,2-Dibromo-3-(naphthalen-1-yl)spiro[cyclopropane-1,2'-inden]-1'(3'H)-one (15e). Colorless solid;
Yield 78%, 345 mg; mp 144-146 oC; IR (KBr, cm-1) 3019 (m), 1712 (w), 1606 (w), 1279 (w), 1216 (s),
759 (s), 669 (m); 1H NMR (400 MHz, CDCl3) ꢀ 7.95 (d, J = 7.6 Hz, 1H), 7.90–7.83 (m, 3H), 7.67 (td, J
= 7.6, 1.0 Hz, 1H), 7.54–7.42 (m, 6H), 3.93 (s, 1H), 3.46 (ABq, J = 18.5 Hz, 2H); 13C NMR (100 MHz,
CDCl3) ꢀ 198.0, 151.9, 136.6, 135.3, 133.9, 132.5, 130.3, 129.0, 128.9, 128.2, 127.6, 126.9, 126.4,
126.2, 125.1, 124.5, 124.4, 44.7, 43.5, 38.4, 34.8; MS (ES+, Ar) m/z (rel intensity) 364 ([(M+3)-Br]+,
24), 363 ([(M+2)-Br]+, 100), 362 ([(MH-Br]+, 24), 361 ([M-Br]+, 100); HRMS (ES+, Ar) calcd for
C21H14OBr ([M-Br]+) 361.0228, found 361.0217.
2',2'-Dibromo-3'-phenyl-8,9-dihydrospiro[benzo[7]annulene-6,1'-cyclopropan]-5(7H)-one (18a).
o
Colorless solid; Yield 65%, 225 mg; mp 124-126 C; IR (KBr, cm-1) 3060 (w), 3026 (w), 2946 (m),
2867 (w), 1667 (vs), 1598 (m), 1447 (m), 1293 (m), 1252 (s), 1209 (m), 964 (m), 776 (m), 755 (vs), 701
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(m), 559 (m); H NMR (400 MHz, CDCl3) ꢀ 7.94 (dd, J = 7.6, 1.3 Hz, 1H), 7.54 (td, J = 7.6, 1.3 Hz,
1H), 7.40–7.36 (m, 3H), 7.34–7.25 (m, 4H), 4.11 (s, 1H), 3.38 (td, J = 13.6, 5.1 Hz, 1H), 2.95 (dt, J =
13.6 Hz, 3.7 Hz, 1H), 2.61–2.51 (m, 1H), 2.19 (dt, J = 15.5, 8.9 Hz, 1H), 1.81 (ddd, J = 15.5, 8.4, 1.4
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Hz, 1H), 1.76–1.68 (m, 1H); C NMR (101 MHz, CDCl3) ꢀ 197.9, 141.7, 136.4, 134.0, 133.8, 130.6,
130.2, 129.8, 128.5, 127.6, 127.1, 45.9, 42.1, 37.8, 32.7, 26.4, 23.4; MS (ES+, Ar) m/z (rel intensity)
342 ([(M+3)-Br]+, 21), 341 ([(M+2)-Br]+, 100), 340 ([MH-Br]+, 21), 339 ([M-Br]+, 93); HRMS (ES+,
Ar) calcd for C19H16OBr ([M-Br]+) 339.0385, found 339.0375.
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2',2'-Dibromo-3'-(p-tolyl)-8,9-dihydrospiro[benzo[7]annulene-6,1'-cyclopropan]-5(7H)-one (18b).
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Colorless solid; Yield 69%, 299 mg; mp 110-112 C; IR (KBr, cm-1) 2932 (m), 2865 (w), 1668 (vs),
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1598 (m), 1515 (w), 1450 (m), 1293 (m), 1251 (s), 1208 (w), 1029 (w), 964 (w), 769 (m), 742 (m); H
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NMR (400 MHz, CDCl3) ꢀ 7.92 (d, J = 7.6 Hz, 1H), 7.53 (t, J = 7.6 Hz, 1H), 7.38 (t, J = 7.6 Hz, 1H),
7.27 (d, J = 7.6 Hz, 1H), 7.19 (unresolved, 4H), 4.05 (s, 1H), 3.37 (td, J = 13.8, 5.0 Hz, 1H), 2.94 (dt, J
= 13.8, 3.4 Hz, 1H), 2.59–2.51 (m, 1H), 2.36 (s, 3H), 2.18 (dt, J = 15.5, 8.9 Hz, 1H), 1.80 (dd, J = 15.5,
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8.4 Hz, 1H), 1.76-1.60 (m, 1H); C NMR (100 MHz, CDCl3) ꢀ 198.1, 141.7, 137.4, 136.5, 133.7,
131.0, 130.6, 130.1, 129.7, 129.3, 127.1, 45.8, 42.0, 38.2, 32.7, 26.4, 23.4, 21.4; MS (ES+, Ar) m/z (rel
intensity) 356 ([(M+3)-Br]+, 20), 355 ([(M+2)-Br]+, 93), 354 ([MH-Br]+, 22), 353 ([M-Br]+, 100);
HRMS (ES+, Ar) calcd for C20H18OBr ([M-Br]+) 353.0541, found 353.0536.
2',2'-Dibromo-3'-(4-fluorophenyl)-8,9-dihydrospiro[benzo[7]annulene-6,1'-cyclopropan]-5(7H)-
o
one (18c). Colorless solid; Yield 70%, 306 mg; mp 128-130 C; IR (KBr, cm-1) 3068 (w), 2949 (m),
2868 (w), 1667 (s), 1598 (s), 1512 (s), 1450 (m), 1295 (s), 1253 (s), 1226 (s), 1158 (m), 964 (m), 896
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(m), 773 (m), 739 (m); H NMR (400 MHz, CDCl3) ꢀ 7.92 (dd, J = 7.6, 1.4 Hz, 1H), 7.53 (td, J = 7.6,
1.4 Hz, 1H), 7.37 (td, J = 7.6, 0.9 Hz, 1H), 7.26-7.25 (m, 3H), 7.09–7.03 (m, 2H), 4.03 (s, 1H), 3.36 (td,
J = 14.0, 5.1 Hz, 1H), 2.95 (dt, J = 14.0, 3.6 Hz, 1H), 2.56–2.50 (m, 1H), 2.16 (dt, J = 15.4, 8.9 Hz, 1H),
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1.78–1.62 (m, 2H); C NMR (100 MHz, CDCl3) ꢀ 197.8, 162.3 (d, JC-F = 250.0 Hz), 141.7, 136.3,
133.9, 132.0, 131.9, 130.6, 129.7 (d, JC-F = 3.0 Hz), 128.5 (d, JC-F = 26.4 Hz), 115.6 (d, JC-F = 21.0 Hz),
45.9, 41.4, 37.6, 32.7, 26.3, 23.4; MS (ES+, Ar) m/z (rel intensity) 360 ([(M+3)-Br]+, 22), 359 ([(M+2)-
Br]+, 100), 358 ([MH-Br]+, 22), 357 ([M-Br]+, 100); HRMS (ES+, Ar) calcd for C19H15OBrF ([M-Br]+)
357.0290, found 357.0292.
2',2'-Dibromo-3'-(3,4-dimethoxyphenyl)-8,9-dihydrospiro[benzo[7]annulene-6,1'-cyclopropan]-
o
5(7H)-one (18e). Colorless solid; Yield 74%, 355 mg; mp 98-100 C; IR (KBr, cm-1) 2933 (vw), 2835
(w), 1667 (s), 1597 (m), 1517 (s), 1450 (m), 1251 (vs), 1140 (m), 1027 (s), 767 (m), 739 (m); 1H NMR
(400 MHz, CDCl3) ꢀ 7.92 (d, J = 7.6 Hz, 1H), 7.53 (t, J = 7.6 Hz, 1H), 7.38 (t, J = 7.6 Hz, 1H), 7.26-
7.28 (m, 1H), 6.80-6.87 (m, 3H), 4.04 (s, 1H), 3.89 (s, 3H), 3.88 (s, 3H), 3.37 (td, J = 14.0, 5.1 Hz, 1H),
2.95 (dt, J = 14.0, 3.6 Hz, 1H), 2.63–2.49 (m, 1H), 2.16 (dt, J = 15.5, 9.1 Hz, 1H), 1.83 (dd, J = 15.5,
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8.3 Hz, 1H), 1.79–1.66 (m, 1H); C NMR (100 MHz, CDCl3) ꢀ 198.1, 148.9, 148.5, 141.8, 136.5,
133.8, 130.6, 129.8, 127.2, 126.4, 122.4, 113.3, 111.1, 56.2, 56.0, 46.0, 41.9, 38.3, 32.7, 26.4, 23.5; MS
(ES+, Ar) m/z (rel intensity) 402 ([(M+3)-Br]+, 23), 401 ([(M+2)-Br]+, 100), 400 ([MH-Br]+, 23), 399
([M-Br]+, 93); HRMS (ES+, Ar) calcd for C21H20O3Br ([M-Br]+) 399.0596, found 399.0598.
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(2, 2-Dibromo-1-methyl-3-phenylcyclopropyl)(phenyl)methanone (21). Colorless solid; Yield 56%,
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o
237 mg; mp 124-126 C; IR (KBr, cm-1) 2928 (w), 1683 (s), 1610 (m), 1514 (m), 1450 (w), 1248 (s),
1173 (w), 1033 (w), 972 (w), 745 (m); 1H NMR (400 MHz, CDCl3) ꢀ 8.06–8.03 (m, 2H), 7.66–7.61 (m,
1H), 7.59–7.55 (m, 2H), 7.30 (dd, J = 8.8 Hz, 2H), 6.93 (d, J = 8.8 Hz, 2H), 3.82 (s, 3H), 3.53 (s, 1H),
13
1.44 (s, 3H); C NMR (100 MHz, CDCl3) ꢀ 196.6, 159.1, 134.4, 133.7, 131.4, 130.2, 128.9, 125.5,
114.1, 55.4, 43.6, 38.9, 36.9, 19.8; MS (ES+, Ar) m/z (rel intensity) 346 ([(M+3)-Br]+, 8), 345 ([(M+2)-
Br]+, 40), 344 ([(MH-Br]+, 8), 343 ([M-Br]+, 40), 264 (100); HRMS (ES+, Ar) calcd for C18H16O2Br
([M-Br]+) 343.0334, found 343.0350.
2',2'-Dibromo-3'-phenyl-2H-spiro[acenaphthylene-1,1'-cyclopropan]-2-one (24). Colorless solid;
Yield 70%, 300 mg; mp 132-134 oC; IR (KBr, cm-1) 3055 (w), 2924 (w), 2852 (w), 1722 (vs), 1599 (w),
1
1492 (w), 1429 (w), 1373 (w), 1252 (m), 1089 (w), 780 (m), 749 (m); H NMR (400 MHz, CDCl3) ꢀ
8.16 (d, J = 8.2 Hz, 1H), 8.12 (d, J = 7.1 Hz, 1H), 7.88 (d, J = 8.2 Hz, 1H), 7.79 (dd, J = 8.2, 7.1 Hz,
1H), 7.46 (dd, J = 8.2, 7.1 Hz, 1H), 7.38–7.30 (m, 3H), 7.18-7.22 (m, 2H), 6.73 (d, J = 7.1 Hz, 1H), 4.06
13
(s, 1H); C NMR (100 MHz, CDCl3) ꢀ 195.6, 142.9, 133.2, 132.4, 132.2, 131.7, 130.6, 130.5, 128.4,
128.2, 127.8, 125.1, 122.9, 47.8, 45.6, 37.6; MS (ES+, Ar) m/z (rel intensity) 350 ([(M+3)-Br]+, 25),
349 ([(M+2)-Br]+, 100), 348 ([MH-Br]+, 25), 347 ([M-Br]+, 100); HRMS (ES+, Ar) calcd for
C20H12OBr ([M-Br]+) 347.0072, found 347.0078. Selected X-ray Data: C20H12Br2O, M = 428.12,
Triclinic, space group P -1, a = 11.7848(4) Å, b = 12.5578(8) Å, c = 12.5773(4) Å, ꢀ = 97.749(3) o, ꢀ =
117.692(2)o, ꢁ = 92.803(3) o, V = 1619.82(13) Å3, Dc = 1.756 Mg/m3, Z = 4, F(000) = 840, ꢀ = 0.71073
Å, µ = 5.01 mm-1, Total/ unique reflections = 27307 / 8087 [R(int) = 0.0618], T = 293(2) K, ꢁ range =
1.7–28.5°, Final R [I>2ꢁ(I)]: R1 = 0.0375, wR2 = 0.0801, R (all data): R1 = 0.0768, wR2 = 0.0925.
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General Procedure for the Acidic Al2O3 Mediated Conversion of Dibromocyclopropanes
11/15/18/21/24 to Bromofurans 13/16/19/22/25. To a stirred the solution of dibromocyclopropane
11/15/18/21/24 (0.1 mmol) in chloroform (5 mL) was added activated acidic Al2O3 (250 mg, 25 equiv,
excess) and the reaction mixture was refluxed. After completion (monitored by TLC), the reaction
mixture was concentrated in vacuo and the crude residue was subjected to silica gel column
chromatography (EtOAc/hexane mixture, gradient elution) to afford bromofuran 13/16/19/22/25.
3-Bromo-2-(2,4-dimethoxyphenyl)-4,5-dihydronaphtho[1,2-b]furan (13e). Colorless liquid; Yield
83%, 32 mg; IR (KBr, cm-1) 2933 (m), 2835 (w), 1605 (w), 1505 (s), 1268 (s), 1251 (s), 1027 (s), 1222
(m), 1144 (m), 1027 (m), 763 (m); 1H NMR (400 MHz, CDCl3) ꢀ 7.50 (dd, J = 7.5, 1.0 Hz, 1H), 7.48 (d,
J = 8.4 Hz, 1H), 7.21-7.25 (m, 2H), 7.14 (td, J = 7.5, 1.0 Hz, 1H), 6.57-6.61 (m, 2H), 3.88 (s, 3H), 3.87
(s, 3H), 3.04 (t, J = 7.9 Hz, 2H), 2.75 (t, J = 7.9 Hz, 2H); 13C NMR (100 MHz, CDCl3) ꢀ 161.9, 158.7,
149.2, 147.5, 134.8, 132.1, 128.2, 127.7, 126.9, 121.5, 119.4, 111.9, 104.8, 101.0, 99.2, 55.8, 55.6, 28.8,
20.2; MS (ES+, Ar) m/z (rel intensity) 387 ([M+3]+, 95), 386 ([M+2]+, 25), 385 (MH+, 100), 388 (25);
HRMS (ES+, Ar) calcd for C20H18O3Br ([MH]+) 385.0439, found 385.0456.
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3-Bromo-2-(3,4-dimethoxyphenyl)-4,5-dihydronaphtho[1,2-b]furan (13f). Colorless solid; Yield
o
85%, 33 mg; mp 126-128 C; IR (KBr, cm-1) 2926 (s), 2852 (w), 1662 (vs), 1597 (s), 1454 (w), 1268
(vs), 1048 (s), 740 (s); 1H NMR (400 MHz, CDCl3) ꢀ 7.62 (dd, J = 8.4, 2.1 Hz, 1H), 7.59 (d, J = 2.1 Hz,
1H), 7.56–7.52 (m, 1H), 7.28–7.23 (m, 1H), 7.22–7.18 (m, 1H), 7.15 (td, J = 7.4, 1.3 Hz, 1H), 6.94 (d, J
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= 8.4 Hz, 1H), 3.98 (s, 3H), 3.93 (s, 3H), 3.02 (t, J = 7.9 Hz, 2H), 2.72 (t, J = 7.9 Hz, 2H); C NMR
(100 MHz, CDCl3) ꢀ 148.9, 148.5, 147.9, 134.9, 128.3, 127.3, 127.1, 127.0, 123.2, 122.5, 119.4, 118.6,
111.2, 108.8, 97.8, 56.1 (× 2), 28.6, 20.1; MS (ES+, Ar) m/z (rel intensity) 387 ([M+3]+, 100), 386
([M+2]+, 32), 385 (MH+, 98), 384 (M+, 15), 337 (17), 300 (16), 291 (40), 265 (85), 263 (88); HRMS
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(ES+, Ar) calcd for C20H18O3Br ([MH]+) 385.0439, found 385.0429. Confirmed by H-1H 2D-NOESY
experiment.
3-Bromo-2-(3,4,5-trimethoxyphenyl)-4,5-dihydronaphtho[1,2-b]furan (13h). Yellow solid; Yield
o
87%, 36 mg; mp 116-118 C; IR (KBr, cm-1) 2923 (s), 2851 (m), 1655 (w), 1484 (m), 1464 (m), 1288
1
(m), 1096 (m); H NMR (400 MHz, CDCl3) ꢀ 7.57–7.54 (m, 1H), 7.29 (s, 2H), 7.27–7.20 (m, 2H),
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7.19–7.14 (td, J = 7.3, 1.2 Hz, 1H), 3.96 (s, 6H), 3.91 (s, 3H), 3.03 (t, J = 8.0 Hz, 2H), 2.73 (t, J = 8.0
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Hz, 2H); C NMR (100 MHz, CDCl3) ꢀ 153.4, 148.9, 147.7, 138.1, 135.0, 128.3, 127.4, 127.2, 127.0,
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125.7, 122.6, 119.5, 103.0, 98.7, 61.1, 56.4, 28.6, 20.0; MS (ES+, Ar) m/z (rel intensity) 418 ([M+4]+,
18), 417 ([M+3]+, 100), 416 ([M+2]+, 25), 415 (MH+, 100), 400 (15); HRMS (ES+, Ar) calcd for
C21H20O4Br ([MH]+) 415.0545, found 415.0564.
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(E)-3-Bromo-2-(2-methoxystyryl)-4,5-dihydronaphtho[1,2-b]furan (13n). Yellow solid; Yield 70%,
o
266 mg; mp 148-150 C; IR (KBr, cm-1) 2961 (w), 2929 (w), 2840 (w), 1659 (br, w), 1480 (w), 1466
(w), 1244 (s), 1030 (m), 959 (m), 749 (s); 1H NMR (400 MHz, CDCl3) ꢀ 7.60 (dd, J = 7.5, 1.2 Hz, 2H),
7.53 (d, J = 16.4 Hz, 1H), 7.30–7.24 (m, 2H), 7.21 (dd, J = 7.5, 1.2 Hz, 1H), 7.16 (td, J = 7.5, 1.2 Hz,
1H), 7.07 (d, J = 16.4 Hz, 1H), 6.98 (t, J = 7.4 Hz, 1H), 6.92 (d, J = 8.3 Hz, 1H), 3.94 (s, 3H), 3.01 (t, J
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= 7.9 Hz, 2H), 2.71 (t, J = 7.9 Hz, 2H); C NMR (100 MHz, CDCl3) ꢀ 157.3, 149.8, 149.4, 135.1,
129.0, 128.2, 127.3, 127.2, 127.0, 126.9, 126.2, 123.0, 122.0, 120.9, 119.8, 114.5, 111.2, 101.9, 55.7,
28.6, 19.9; MS (ES+, Ar) m/z (rel intensity) 384 ([M+4]+, 30), 383 ([M+3]+, 100), 382 ([M+2]+, 25),
381 (MH+, 100); HRMS (ES+, Ar) calcd for C21H18O2Br (MH+) 381.0490, found 381.0501.
3-Bromo-2-(3,4-dimethoxyphenyl)-8-methoxy-4,5-dihydronaphtho[1,2-b]furan (13p). Colorless
o
solid; Yield 84%, 35 mg; mp 114-116 C; IR (KBr, cm-1) 2923 (m), 2846 (w), 1651 (vs), 1495 (w),
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1262 (m), 1223 (m), 1026 (m), 752 (m); H NMR (400 MHz, CDCl3) ꢀ 7.62 (dd, J = 8.5, 2.0 Hz, 1H),
7.58 (d, J = 2.0 Hz, 1H), 7.12 (d, J = 8.3 Hz, 1H), 7.09 (d, J = 2.6 Hz, 1H), 6.95 (d, J = 8.5 Hz, 1H),
6.70 (dd, J = 8.3, 2.6 Hz, 1H), 3.98 (s, 3H), 3.93 (s, 3H), 3.85 (s, 3H), 2.95 (t, J = 7.9 Hz, 2H), 2.70 (t, J
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= 7.9 Hz, 2H); C NMR (100 MHz, CDCl3) ꢀ 158.8, 149.0, 148.9, 148.5, 148.0, 129.1, 128.2, 127.1,
123.2, 123.1, 118.7, 112.1, 111.2, 108.9, 105.4, 97.9, 56.2, 56.1, 55.6, 27.8, 20.4; MS (ES+, Ar) m/z (rel
intensity) 418 ([M+4]+, 25), 417 ([M+3]+, 100), 416 ([M+2]+, 25), 415 (MH+, 100); HRMS (ES+, Ar)
calcd for C21H20O4Br ([MH]+) 415.0545, found 415.0565.
3-Bromo-2-phenyl-4H-indeno[1,2-b]furan (16a). Colorless solid; Yield 84%, 26 mg; mp 104-106 oC;
IR (KBr, cm-1) 2923 (s), 2857 (m), 1712 (m), 1605 (m), 1438 (br, m), 1259 (br, m), 1023 (w), 944 (m),
1
757 (m); H NMR (400 MHz, CDCl3) ꢀ 8.07–8.04 (m, 2H), 7.54–7.47 (m, 2H), 7.47–7.44 (m, 2H),
13
7.37-7.31 (m, 2H), 7.22 (td, J = 7.5, 1.1 Hz, 1H), 3.52 (s, 2H); C NMR (100 MHz, CDCl3) ꢀ 158.1,
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151.8, 145.4, 133.0, 131.7, 130.7, 128.7, 127.9, 127.3, 125.8, 125.5, 125.3, 117.2, 96.2, 29.6; MS (ES+,
Ar) m/z (rel intensity) 330 (17), 329 (100), 328 (17), 327 (100), 313 ([(M+2)H]+, 17), 311 (MH+, 17);
HRMS (ES+, Ar) calcd for C17H12OBr ([MH]+) 311.0072, found 311.0057.
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3-Bromo-2-(p-tolyl)-4H-indeno[1,2-b]furan (16b). Colorless solid; Yield 89%, 29 mg; mp 100-102
oC; IR (KBr, cm-1) 2925 (vs), 2852 (m), 1709 (m), 1605 (m), 1457 (m), 1259 (m), 1023 (m), 752 (m);
1H NMR (400 MHz, CDCl3) ꢀ 7.95 (d, J = 8.2 Hz, 2H), 7.52 (d, J = 7.5 Hz, 1H), 7.48 (d, J = 7.5 Hz,
1H), 7.35 (t, J = 7.5 Hz, 1H), 7.27 (d, J = 8.2 Hz, 2H), 7.21 (td, J = 7.5, 1.1 Hz, 1H), 3.51 (s, 2H), 2.40
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(s, 3H); C NMR (100 MHz, CDCl3) ꢀ 157.7, 152.1, 145.3, 137.9, 133.1, 131.6, 129.4, 127.9, 127.2,
125.8, 125.5, 125.2, 117.1, 95.5, 29.6, 21.6; MS (ES+, Ar) m/z (rel intensity) 343 (86), 341 (100), 327
([(M+2)H]+, 18), 325 (MH+, 19); HRMS (ES+, Ar) calcd for C18H14OBr ([MH]+) 325.0228, found
325.0226.
3-Bromo-2-(3,4-dimethylphenyl)-4H-indeno[1,2-b]furan (16c). Colorless solid; Yield 85%, 29 mg;
o
mp 94-96 C; IR (KBr, cm-1) 2921 (vs), 2852 (m), 1706 (s), 1646 (s), 1432 (w), 1402 (w), 1259 (w),
1023 (m), 966 (w), 883 (w), 749 (m); 1H NMR (400 MHz, CDCl3) ꢀ 7.81–7.78 (m, 2H), 7.52 (d, J = 7.5
Hz, 1H), 7.48 (d, J = 7.5 Hz, 1H), 7.35 (t, J = 7.5 Hz, 1H), 7.18-7.22 (m, 2H), 3.51 (s, 2H), 2.35 (s, 3H),
13
2.31 (s, 3H); C NMR (100 MHz, CDCl3) ꢀ 157.6, 152.2, 145.3, 136.9, 136.7, 133.1, 131.6, 129.9,
128.3, 127.2, 126.7, 125.8, 125.1, 123.2, 117.0, 95.4, 29.6, 20.1, 19.9; MS (ES+, Ar) m/z (rel intensity)
341 ([M+3]+, 100), 340 ([M+2]+, 38), 339 (MH+, 98), 338 (M+, 39); HRMS (ES+, Ar) calcd for
C19H16OBr ([MH]+) 339.0385, found 339.0388.
3-Bromo-2-(4-fluorophenyl)-4H-indeno[1,2-b]furan (16d). Pale yellow solid; Yield 82%, 27 mg; mp
o
114-116 C; IR (KBr, cm-1) 2928 (s), 2868 (m), 1712 (m), 1605 (m), 1487 (br, w), 1236 (s), 1158 (w),
1065 (m), 947 (m), 840 (m), 757 (vs); 1H NMR (400 MHz, CDCl3) ꢀ 8.05–7.99 (m, 2H), 7.51-7.47 (m,
2H), 7.35 (t, J = 7.4 Hz, 1H), 7.22 (td, J = 7.4, 1.1 Hz, 1H), 7.17–7.11 (m, 2H), 3.49 (s, 2H); 13C NMR
(100 MHz, CDCl3) ꢀ 162.3 (d, JC-F = 247.0 Hz), 158.0, 151.0, 145.3, 132.9, 131.5, 127.5, 127.4 (d, JC-F
= 8.0 Hz), 126.9 (d, JC-F = 3.0 Hz), 125.8, 125.4, 117.1, 115.8 (d, JC-F = 22.0 Hz), 95.9, 29.5; MS (ES+,
Ar) m/z (rel intensity) 331 ([(M+2)H]+, 25), 329 ([MH]+, 25), 248 (100), 250 (81), 265 (43), 281 (69);
HRMS (ES+, Ar) calcd for C17H11OBrF ([MH]+) 328.9977, found 328.9971.
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3-Bromo-2-(naphthalen-1-yl)-4H-indeno[1,2-b]furan (16e). Colorless viscous liquid; Yield 87%, 32
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mg; IR (KBr, cm-1) 2918 (s), 2857 (m), 1602 (w), 1432 (m), 1289 (m), 1265 (m), 1128 (w), 1021 (m),
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933 (w), 798 (m), 774 (s), 755 (vs); H NMR (400 MHz, CDCl3) ꢀ 8.11–8.09 (m, 1H), 7.97–7.92 (m,
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8
2H), 7.80 (d, J = 7.1 Hz, 1H), 7.60–7.54 (m, 5H), 7.37 (t, J = 7.5 Hz, 1H), 7.27–7.23 (m, 1H), 3.62 (s,
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2H); C NMR (100 MHz, CDCl3) ꢀ 159.0, 153.0, 145.3, 134.0, 133.2, 131.8, 130.5, 130.0, 129.3,
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128.6, 127.3, 126.9, 126.4, 126.3, 125.9, 125.4, 125.2, 117.2, 99.2, 29.7; MS (ES+, Ar) m/z (rel
intensity) 364 ([M+4]+, 25), 363 ([M+3]+, 100), 362 ([M+2]+, 30), 361 (MH+, 100); HRMS (ES+, Ar)
calcd for C21H14OBr (MH+) 361.0228, found 361.0234.
3-Bromo-2-(4-methoxyphenyl)-4H-indeno[1,2-b]furan (16f). Pale yellow solid; Yield 76%, 259 mg;
o
mp 198-200 C; IR (KBr, cm-1) 3050 (w), 2995 (w), 2963 (w), 2935 (w), 2855 (w), 1656 (br, s), 1608
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(s), 1486 (s), 1255 (vs), 1241 (s), 1177 (s), 1027 (vs), 946 (m), 831 (s), 755 (s); H NMR (400 MHz,
CDCl3) ꢀ 7.98 (d, J = 9.0 Hz, 2H), 7.50 (d, J = 7.5 Hz, 1H), 7.48 (d, J = 7.5 Hz, 1H), 7.34 (t, J = 7.5 Hz,
1H), 7.20 (td, J = 7.5, 1.1 Hz, 1H), 6.99 (d, J = 9.0 Hz, 2H), 3.87 (s, 3H), 3.50 (s, 2H); 13C NMR (100
MHz, CDCl3) ꢀ 159.4, 157.4, 152.0, 145.2, 133.2, 131.6, 127.2 (× 2), 125.7, 125.0, 123.5, 116.9, 114.2,
94.7, 55.5, 29.6; MS (ES+, Ar) m/z (rel intensity) 344 ([MH+3]+, 15), 343 ([(MH+2)]+, 93), 342
([MH+1]+, 34), 341 (MH+, 100); HRMS (ES+, Ar) calcd for C18H14O2Br (MH+) 341.0177, found
341.0177.
3-Bromo-2-phenyl-5,6-dihydro-4H-benzo[6,7]cyclohepta[1,2-b]furan (19a). Colorless liquid; Yield
88%, 30 mg; IR (KBr, cm-1) 2931 (w), 1680 (vs), 1599 (s), 1582 (m), 1490 (m), 1455 (m), 1432 (m),
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1300 (s), 1288 (m), 1222 (m), 1052 (m); H NMR (400 MHz, CDCl3) ꢀ 8.07 (m, 2H), 7.96 (d, J = 7.7
Hz, 1H), 7.47 (t, J = 7.7 Hz, 2H), 7.38–7.28 (m, 2H), 7.20-7.15 (m, 2H), 2.94 (t, J = 10.5 Hz, 2H), 2.75
(t, J = 6.5 Hz, 2H), 2.06 (tt, J = 10.5, 6.5 Hz, 2H); 13C NMR (100 MHz, CDCl3) ꢀ 147.0, 146.9, 139.4,
129.9, 129.6, 129.3, 128.6, 127.9, 127.2, 126.4, 125.5, 125.1, 124.4, 101.6, 35.7, 27.6, 24.4; MS (ES+,
Ar) m/z (rel intensity) 342 ([MH+3]+, 24), 341 ([(MH+2)]+, 100), 340 ([MH+1]+, 24), 339 ([MH]+,
100); HRMS (ES+, Ar) calcd for C19H16OBr ([MH]+) 339.0393, found 339.0385.
3-Bromo-2-(p-tolyl)-5,6-dihydro-4H-benzo[6,7]cyclohepta[1,2-b]furan (19b). Colorless liquid; Yield
88%, 31 mg; IR (KBr, cm-1) 3025 (w), 2926 (vs), 2851 (m), 1646 (br, s), 1498 (s), 1446 (m), 1266 (m),
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1109 (m), 819 (s), 761 (vs), 737 (s); 1H NMR (400 MHz, CDCl3) ꢀ 7.98 (d, J = 7.7 Hz, 2H), 7.94 (d, J =
7.8 Hz, 1H), 7.33–7.26 (m, 3H), 7.23–7.14 (m, 2H), 2.93–2.90 (m, 2H), 2.74 (t, J = 6.4 Hz, 2H), 2.41 (s,
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3H), 2.06 (quintet, J = 6.4 Hz, 2H); C NMR (100 MHz, CDCl3) ꢀ 147.4, 146.6, 139.4, 138.0, 129.6,
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129.5, 129.4, 127.3, 127.2, 126.5, 125.7, 125.1, 124.5, 101.0, 35.9, 27.7, 24.5, 21.6; MS (ES+, Ar) m/z
(rel intensity) 356 ([M+4]+, 23), 355 ((M+3)+, 100), 354 ([M+2]+, 22), 353 ([MH]+, 82); HRMS (ES+,
Ar) calcd for C20H18OBr (MH+) 353.0541, found 353.0555.
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3-Bromo-2-(4-fluorophenyl)-5,6-dihydro-4H-benzo[6,7]cyclohepta[1,2-b]furan (19c). Colorless
liquid; Yield 81%, 29 mg; IR (KBr, cm-1) 3069 (w), 2928 (s), 2861 (m), 1604 (m), 1557 (w), 1497 (s),
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1447 (m), 1234 (s), 1159 (m), 835 (s), 761 (s), 737 (m); H NMR (400 MHz, CDCl3) ꢀ 8.08–8.03 (m,
2H), 7.91 (d, J = 7.7 Hz, 1H), 7.32–7.28 (m, 1H), 7.21–7.12 (m, 4H), 2.93–2.90 (m, 2H), 2.73 (t, J = 6.5
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Hz, 2H), 2.05 (quintet, J = 6.5 Hz, 2H); C NMR (100 MHz, CDCl3) ꢀ 162.4 (d, JC-F = 248.6 Hz),
147.0, 146.4, 139.5, 129.70, 129.4, 127.5 (d, JC-F = 8.1 Hz), 127.4, 126.6, 126.4 (d, JC-F = 3.3 Hz),
125.1, 124.5, 115.8 (d, JC-F = 21.8 Hz), 101.3, 35.8, 27.7, 24.5; MS (ES+, Ar) m/z (rel intensity) 359
([M+4]+, 22), 359 ([M+3]+, 100), 358 ([M+2]+, 22), 357 (MH+, 100); HRMS (ES+, Ar) calcd for
C19H15OBrF (MH+) 357.0290, found 357.0292.
3-Bromo-2-(4-methoxyphenyl)-5,6-dihydro-4H-benzo[6,7]cyclohepta[1,2-b]furan (19d). Colorless
liquid; Yield 84%, 310 mg (from reaction at 1 mmol scale); IR (KBr, cm-1) 3054 (s), 2987 (m), 1607
(m), 1500 (s), 1442 (m), 1422 (m), 1266 (vs), 1180 (m), 896 (m), 739 (vs); 1H NMR (400 MHz, CDCl3)
ꢀ 8.01 (dt, J = 9.0, 2.1 Hz, 2H), 7.91 (dd, J = 8.2, 1.0 Hz, 1H), 7.29 (ddd, J = 8.2, 6.7, 2.1 Hz, 1H),
7.19–7.12 (m, 2H), 6.98 (dt, J = 9.0, 2.1 Hz, 2H), 3.86 (s, 2H), 2.92 (t, J = 10.5 Hz, 2H), 2.72 (t, J = 6.5
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Hz, 2H), 2.04 (tt, J = 10.5, 6.5 Hz, 2H); C NMR (100 MHz, CDCl3) ꢀ 159.5, 147.3, 146.4, 139.3,
129.6 (× 2), 127.2, 127.1, 126.5, 125.0, 124.4, 122.9, 114.1, 100.1, 55.5, 35.9, 27.8, 24.5; MS (ES+, Ar)
m/z (rel intensity) 371 ([(MH+2)]+, 100), 370 ([(MH+1)]+, 50), 369 (MH+, 100), 368 (M+, 45); HRMS
(ES+, Ar) calcd for C20H18O2Br (MH+) 369.0490, found 369.0482.
3-Bromo-2-(3,4-dimethoxyphenyl)-5,6-dihydro-4H-benzo[6,7]cyclohepta[1,2-b]furan (19e). Pale
yellow solid; Yield 90%, 36 mg; mp 96-98oC; IR (KBr, cm-1) 2929 (m), 2835 (w), 1647 (vs), 1503 (vs),
1462 (m), 1440 (m), 1252 (s), 1027 (s), 762 (s); 1H NMR (400 MHz, CDCl3) ꢀ 7.91 (dd, J = 8.5, 0.9 Hz,
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1H), 7.63 (ABq, J = 8.4 Hz, the lower half further split into d, J = 2.1 Hz, 2H), 7.33–7.27 (td, J = 6.9,
1.9 Hz, 1H), 7.20–7.13 (m, 2H), 6.95 (d, J = 8.4 Hz, 1H), 3.98 (s, 3H), 3.94 (s, 3H), 2.92 (t, J = 10.5 Hz,
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2H), 2.73 (t, J = 6.5 Hz, 2H), 2.05 (tt, J = 10.5, 6.5 Hz, 2H); C NMR (100 MHz, CDCl3) ꢀ 149.1,
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148.9, 147.2, 146.4, 139.4, 129.7, 129.5, 127.2, 126.5, 125.0, 124.4, 123.1, 118.8, 111.2, 109.0, 100.4,
56.1 (× 2), 35.8, 27.7, 24.5; MS (ES+, Ar) m/z (rel intensity) 401 ([MH+1]+, 75), 399 (MH+, 100), 359
(60), 357 (60); HRMS (ES+, Ar) calcd for C21H20O3Br (MH+) 399.0596, found 399.0596; Selected X-
ray Data: C21H19BrO3, M = 399.27, Orthorhombic, space group P212121, a = 7.9204 (3) Å, b = 8.6133
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o
(3) Å, c = 25.5389 (11) Å, ꢀ = 90.00 o, ꢀ = 90.00 o, ꢁ = 90.00 , V = 1742.28 (12) Å3, Dc = 1.756
Mg/m3, Z = 4, F(000) = 840, ꢀ = 0.71073 Å, µ = 5.01 mm-1, Total/ unique reflections = 27307 / 8087
[R(int) = 0.0618], T = 293(2) K, ꢁ range = 1.7–28.5°, Final R [I>2ꢁ(I)]: R1 = 0.0375, wR2 = 0.0801, R
(all data): R1 = 0.0768, wR2 = 0.0925.
9-Bromo-8-phenylacenaphtho[1,2-b]furan (25). Yellow solid; Yield 83%, 29 mg; mp 112-114 oC; IR
(KBr, cm-1) 2922 (m), 2846 (w), 1602 (m), 1435 (w), 1410 (w), 1259 (w), 1240 (w), 760 (vs); 1H NMR
(400 MHz, CDCl3) ꢀ 8.11–8.08 (m, 2H), 7.86 (d, J = 6.9 Hz, 1H), 7.76 (t, J = 7.6 Hz, 3H), 7.56 (d, J =
6.9 Hz, 1H), 7.54 (d, J = 6.9 Hz, 1H), 7.48 (t, J = 7.6 Hz, 2H), 7.38–7.34 (m, 1H); 13C NMR (100 MHz,
CDCl3) ꢀ 158.3, 152.9, 131.0, 130.9, 130.5, 129.6, 129.4, 128.8, 128.1, 127.8, 127.7, 127.6, 127.4,
126.6, 125.6, 122.1, 120.0, 94.2; MS (ES+, Ar) m/z (rel intensity) 350 ([M+4]+, 26), 349 ([M+3]+, 100),
348 ([M+2]+, 25), 347 (MH+, 100); HRMS (ES+, Ar) calcd for C20H12OBr (MH+) 347.0072, found
347.0078.
3-Bromo-2-(3,4-dimethoxyphenyl)naphtho[1,2-b]furan 26f (via DDQ dehydrogenation of 13f). A
suspension of dihydronaphthofuran 13f (0.2 mmol, 77 mg) and DDQ (0.28 mmol, 64 mg) in dioxane (5
mL) was refluxed with stirring for 15 h (monitored by TLC). The solvent was removed in vacuo and the
residue was purified by silica gel column chromatography using 5% ethyl acetate-pet ether as eluent.
Colorless solid; Yield 80%, 61 mg; mp 88-90 oC; IR (KBr, cm-1) 3058 (w), 2929 (s), 2834 (w), 1645 (s),
1505 (m), 1381 (m), 1248 (m), 1267 (s), 1222 (m), 1094 (m), 1027 (s), 811 (m), 749 (s); 1H NMR (400
MHz, CDCl3) ꢀ 8.35 (d, J = 8.2 Hz, 1H), 7.94 (d, J = 8.2 Hz, 1H), 7.81 (dd, J = 8.4, 2.0 Hz, 1H), 7.77
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(d, J = 2.0 Hz, 1H), 7.73–7.71 (m, 1H), 7.64–7.62 (m, 1H), 7.59 (d, J = 8.5 Hz, 1H), 7.53–7.49 (m, 1H),
7.00 (d, J = 8.5 Hz, 1H), 4.03 (s, 3H), 3.96 (s, 3H); 13C NMR (100 MHz, CDCl3) ꢀ 149.9, 149.7, 149.0,
148.7, 132.1, 128.7, 126.8, 125.7, 125.5, 124.4, 122.8, 121.0, 120.0, 119.9, 117.9, 111.3, 109.7, 93.6,
56.2, 56.1; MS (ES+, Ar) m/z (rel intensity) 386 ([M+4]+, 23), 385 ((M+3)+, 100), 384 ([M+2]+, 22),
383 (MH+, 100); HRMS (ES+, Ar) calcd for C20H16O3Br ([MH]+) 383.0283, found 383.0275.
Acknowledgment. INNN thanks DST India for financial assistance. EG thanks CSIR India for a
senior research fellowship. The authors thank SAIF, IIT Madras, and University of Madras for X-ray
data and Dr. G. N. Gururaja for helpful discussions.
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Supporting Information Available. Complete characterization data and copies of NMR spectra for
all the new compounds as well as CIF for compounds 11d, 19e and 24. This material is available free of
charge via the internet at http://pubs.acs.org.
References and Notes
(1) Selected reviews: (a) Pietruszka, J. Chem. Rev. 2003, 103, 1051. (b) Donaldson, W. A.
Tetrahedron 2001, 57, 8589. (c) Chen, D. Y. K.; Pouwer, R. H.; Richard, J.-A. Chem. Soc. Rev. 2012,
41, 4631. Selected recent articles: (d) Wang, L.-N.; Zhang, J.-Z.; Li, X.; Wang, X.-N.; Xie, C.-F.; Zhou,
J.-C.; Lou, H.-X. Org. Lett. 2012, 14, 1102. (e) Kumaraswamy, G.; Padmaja, M. J. Org. Chem. 2008,
73, 5198.
(2) Selected reviews: (a) Lebel, H.; Marcoux, J.-F.; Molinaro, C.; Charette, A. B. Chem. Rev. 2003,
103, 977. (b) Ref 1b.
(3) Review: Carson, C. A.; Kerr, M. A. Chem. Soc. Rev. 2009, 38, 3051.
(4) (a) A general review: Wong, H. N. C.; Hon, M. Y.; Tse, C. W.; Yip, Y. C.; Tanko, J.; Hudlicky, T.
Chem. Rev. 1989, 89, 165. Vinylcyclopropane-cyclopentene rearrangement, reviews: (b) Hudlicky, T.;
Reed, J. W. Angew. Chem. Int., Ed. 2010, 49, 4864. (c) Goldschmidt, Z.; Crammer, B. Chem. Soc. Rev.
1988, 17, 229. (d) Baldwin, J. E. Chem. Rev. 2003, 103, 1197. (e) Hudlicky, T.; Kutchan, T. M.; Naqvi,
S. M. Org. React. 1985, 33, 247. Cyclopropylketone-(dihydro)furan rearrangement, review: (f) Ma, S.
Pure Appl. Chem. 2008, 80, 695. Selected articles: (g) Ernest, W. Heterocycles 1980, 14, 1703. (h)
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