Intramolecular Pauson-Khand reactions of aromatic enynes

Article abstract of DOI:10.1081/SCC-100105127

The synthesis of a series of O-alkenylated ethynylphenol derivatives and their NMO promoted intramolecular Pauson-Khand reactions are reported. The effects of substitution on both the alkene and alkyne moiety have been investigated.

Full text of DOI:10.1081/SCC-100105127

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INTRAMOLECULAR PAUSON-KHAND REACTIONS OF
AROMATIC ENYNES
Carl J. Lovely* a & Hemalatha Seshadri a
a Department of Chemistry and Biochemistry, The University of Texas at Arlington,
Arlington, TX, 76019, U.S.A.
Available online: 09 Nov 2006
To cite this article: Carl J. Lovely* & Hemalatha Seshadri (2001): INTRAMOLECULAR PAUSON-KHAND REACTIONS OF
AROMATIC ENYNES, Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic
Chemistry, 31:16, 2479-2490
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SYNTHETIC COMMUNICATIONS, 31(16), 2479–2490 (2001)
INTRAMOLECULAR PAUSON-KHAND
REACTIONS OF AROMATIC ENYNES
Carl J. Lovely* and Hemalatha Seshadri
Department of Chemistry and Biochemistry, The University of
Texas at Arlington, Arlington, TX 76019
ABSTRACT
The synthesis of a series of O-alkenylated ethynylphenol deri-
vatives and their NMO promoted intramolecular Pauson-
Khand reactions are reported. The effects of substitution on
both the alkene and alkyne moiety have been investigated.
Reactions that are capable of producing products with an enhance-
ment of molecular complexity from simple substrates have received signifi-
cant attention over the last few years.1,2 The formal [2þ2þ1] co-cyclization
of an alkyne, an alkene and carbon monoxide mediated by Co2(CO)8, the
Pauson-Khand reaction (PKR), typifies this type of reaction (Figure 1).3–7
Figure 1. Intramolecular Pauson-Khand cyclization.
2479
Copyright & 2001by Marcel Dekker, Inc.
www.dekker.com

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LOVELY AND SESHADRI
The PKR is known both inter- and intramolecularly and is often the method
of choice for the synthesis of cyclopentyl containing targets.8–10 Recent
efforts to improve the applicability of this reaction have focused on the
development of experimental alternatives to the original thermal conditions
such as the use of additives, e.g., amines,11amine oxides,12,13 phosphines,
phosphites, DMSO,14 and light15 permitting the formation of adducts in
good yield and often with enhanced stereocontrol. Furthermore, recent
reports of catalytic variants15–22 and the development of the so-called
hetero-PKR augment the utility of this transformation.23–25 Indeed, this
reaction can be truly considered atom economical. Despite these important
advances, there are still significant limitations to the types of substrate that
successfully participate in this reaction, particularly in the intramolecular
variant. For example, the majority of substrates used in this reaction are 1,6-
enynes, and to a lesser extent, 1,7-enynes, possessing favorable structural
fragments, such as gem-dimethyl substituents.3 As part of a broader study
aimed at increasing the scope of this reaction, we have evaluated the ability
of aromatic enynes, derived from o-ethynylphenol, to take part in the intra-
molecular PKR. The purpose of these studies was two fold. First, we wished
to establish whether substrates of this general type would participate in the
PKR reaction. Second, the substrates were designed to assess the viability of
a intramolecular PKR approach to a number of natural products containing
indanes annulated to other rings, e.g., viburanes and cyathins (Figure 2), in
which the aromatic ring would serve as a latent cyclohexyl or cycloheptyl
moiety.26–28 While this work was in progress a related study reported the
Figure 2. Some annulated indane natural products.

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utility of aromatic enynes derived from 2-vinylphenols in the intramolecular
PKR.29–31
Our studies commenced with the synthesis of the requisite enynes 4–6,
which were obtained by alkylation of the appropriate o-ethynylphenols 2
and 3 with allyl bromide in the presence of anhydrous K2CO3 in acetone.32
Reaction of enyne 4 with K2CO3 in a mixture of THF and methanol
provided the corresponding desilylated enyne.33 The phenols required for
the preparation of 4–6 were obtained from the Sonogashira coupling of
iodophenol with terminal acetylenes according to literature procedures.34
Reageats and conditions: a. Lit. 34 b. Allyl bromide, K2CO3, acetone, RT; c. K2CO3,
MeOH, THF (1:1); d. Co2(CO)3, CH2Cl2, then NMO, 0ꢀC ! rt.
Scheme 1.
After some initial experimentation it was found that the portionwise
addition of ten to twelve equivalents of N-methylmorpholine oxide (NMO)
to an ice-cold dichloromethane solution of the dicobalt hexacarbonyl com-
plex of the enyne, prepared by the addition of an excess of Co2(CO)8 to 5,
underwent an efficient cyclization reaction, producing the tricyclic enone 7
in an excellent 75% isolated yield as a colorless crystalline solid.31,35 As
several of our planned targets possessed substituents on Cl of the PKR
product it was necessary to investigate the effect of terminal substitution
on the cyclization reaction. It was found that both the trimethylsilyl and the
phenyl substituted enynes 4 and 6 underwent cyclization. While the phenyl

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substituted acetylene reacted almost as efficiently as 5, providing the PK
adduct in good yield, the yield of the cyclic product derived from 4 was
severely attenuated.31 Presumably this is a result of a congested transition
state which forces the trimethylsilyl substituent to interact unfavorably
either with other parts of the cobalt cluster, or with the C9-hydrogen on
the benzene ring, whereas the phenyl substituent can adopt a conformation
such that it can avoid or minimize these unfavorable interactions.
The influence of terminal alkyne substitution on the efficiency of the
cyclization prompted us to investigate the effect of substitution on the
alkene moiety. Compounds 11 and 15 were readily prepared by reaction
of o-ethynylphenol 10 with the appropriate chloroalkene in the presence
of NaI and K2CO3, providing the requisite enynes in moderate to good
yield. On the other hand, it proved more efficient to prepare the cinnamy-
lated product by conversion of cinnamyl chloride into the iodide and
treating the resulting iodide solution, after removal of the precipitated
NaCl, with phenol 10. In this way, 56% of the desired compound 12
was obtained. It was found that the terminal methyl substituted alkene
underwent cyclization to provide the tricyclic adduct 13 in 48% yield as
a single diastereomer, presumably derived from the E-isomer. We were
unable to detect the presence of the other stereoisomer by 1H-NMR spectro-
scopy or isolate cyclic products derived from the Z-isomer. Analogously, the
O-cinnamylated derivative provided the cyclic product 14 in 16% yield.
It should be noted that the 1H-NMR spectrum of the purified product
contained 2–3% of another compound that we have tentatively assigned
Reagents and conditions: a. ClCH2CH¼CHCH3, NaI, ClCH2C(CH2)=NaI, or
PhCH¼CHCH2I, K2CO3, acetone; b. Co2(CO)3, CH2Cl2, then NMO, 0ꢀC!rt.
Scheme 2.

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as the cyclic product with an endo oriented Ph group, derived from a small
amount of the Z-isomer. On the other hand, the internal methyl substituted
alkene failed to provide any cyclic products.
In summary, aromatic enynes derived from o-ethynylphenol are effec-
tive substrates in the intramolecular PKR. The cyclizations proceeded with
reasonable efficiency with both mono- and terminally disubstituted olefins,
apparently internal substitution is not tolerated in this particular system.
Substitution on the acetylene is tolerated leading to cyclic products even
with the bulky trimethylsilyl group. We are currently exploring other aspects
of this chemistry and evaluating the synthetic utility of the cycloadducts and
will report these results elsewhere.
EXPERIMENTAL
General Methods
All of the transition metal complexes were purchased from Strem
Chemicals. All other reagents were purchased from commercial suppliers
and were used without purification. All reactions involving air or H2O-
sensitive compounds were conducted in oven-dried (overnight) glassware
under an atmosphere or dry nitrogen. CH2Cl2 was distilled from CaH2 under
a nitrogen atmosphere. Melting points were determined on a Thomas Hoover
Capillary Melting Point apparatus and are uncorrected. NMR spectra
(1H & 13C) were recorded on JEOL Eclipse 500 MHz instrument using
CDCl3 as solvent. Mass spectra were recorded by electron impact (at 70 eV)
either on a Finnigan MAT TSQ-70 or Kodiak (Bear Instruments, Inc.)
spectrometers. All mass spectral data are reported as m/z (relative intensity).
Infrared (IR) spectra were obtained either on a Biorad FTS-40 or a Jasco
FT/IR-410 infrared spectrophotometer as neat films for liquids or KBr
pellets for solid samples. Elemental analyses were performed in house on
a Perkin Elmer 2400 CHN Elemental Analyzer or determined by
Quantitative Technologies Inc, New Jersey. Analytical thin layer chromato-
graphy (TLC) was performed on Whatman silica gel 60F254 aluminum pre-
coated plates (0.25 mm layer). All purifications were performed using ICN
silica gel (200–400 mesh).
2-(Trimethylsilylethynyl)-(2-propenyloxy)benzene (4)
Allyl bromide (0.51g, 4.2 mmol) was added to a suspension of
234(0.64 g, 3.3 mmol) and K2CO3 (0.74 g, 5.4 mmol) in acetone (75 mL).

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The mixture was stirred at room temperature for 6 h. The reaction mixture
was then poured into H2O (50 mL) and extracted with EtOAc (3 ꢁ 50 mL).
The organic phases were combined, dried (MgSO4) and concentrated under
reduced pressure. The resulting crude mixture was purified by flash chro-
matography (silica gel, 95/5 n-hexane/EtOAc) to afford 4 (0.44 g, 73%) as a
colorless liquid: 1H NMR (CDCl3): d ¼ 0.26 (s, 9H), 4.58 (m, 2H), 5.29 (app.
dq, 1H, J ¼ 1.7, 10.6 Hz), 5.54 (app. dq, 1H, J ¼ 1.7, 17.2 Hz), 6.06 (dddd,
1H, J ¼ 4.6, 4.6, 10.6, 17.2 Hz), 6.84 (d, 1H, J ¼ 8.4 Hz), 6.89 (dt, 1H, J ¼ 0.9,
7.6 Hz), 7.25 (m, 1H), 7.43 (dd, 1H, J ¼ 1.8, 7.6 Hz); 13C NMR (CDCl3):
d ¼ 0.1, 69.1, 98.6, 101.3, 112.5, 113, 116.9, 120.7, 129.9, 132.9, 133.9,
159.6; IR (neat, cm–1): 2106, 1640, 1594, 751, 1161; EIMS (m/z): 72, 114,
158, 198, 214, 230 (100%, Mþ). Anal. Calcd. for C14H18OSi: C, 72.99; H,
7.87. Found: C, 72.99; H, 8.00.
2-Ethynyl-(2-propenyloxy)benzene(5)33
K2CO3 (1.05 g, 7.6 mmol) was added to a solution of 4 (0.44 g,
1.9 mmol) in MeOH/THF (10 mL, 1:1). The mixture was stirred at room
temperature for 10 h. The reaction mixture was concentrated under reduced
pressure and filtered through a plug of silica gel (EtOAc). The residue was
purified by flash chromatography (silica gel, 95/5 n-hexane/EtOAc) to fur-
nish 5 (0.318 g, quantitative) as a colorless liquid; 1H NMR (CDCl3):
d ¼ 3.29 (s, 1H), 4.63 (m, 2H), 5.47 (dd, 1H, J ¼ 1.6, 17.2 Hz) 5.29 (dd, 1H,
J ¼ 1.6, 10.4 Hz), 6.07 (dddd, 1H, J ¼ 4.9, 4.9, 10.4, 17.2 Hz), 6.87 (d, 1H,
8.3 Hz), 6.91(dt, 1H, J ¼ 0.9, 7.5 Hz); 7.28 (dt, 1H, J ¼ 1.6, 8.3 Hz), 7.47 (dd,
1H, J ¼ 1.6, 7.5 Hz); 13C NMR (CDCl3): d ¼ 69.4, 80.1, 81.3, 111.9, 112.4,
117.6, 120.7, 130.1, 132.9, 134.2, 159.7; IR (neat, cm–1): 750, 1250, 1660,
2100; EIMS (m/z): 77, 89, 121 (100%), 131, 157, 158, (Mþ). Anal. Calcd. for
C11H10O: C, 83.52; H, 6.37. Found: C, 83.41; H, 6.38.
2-(Phenylethynyl)-(2-propenyloxy)benzene (6)
Allyl bromide (1.03 g, 8.5 mmol) was added to a suspension of 334
(0.83 g, 4.2 mmol) and K2CO3 (1.18 g, 8.6 mmol) in acetone (40 mL). The
mixture was stirred at room temperature for 8 h. The reaction mixture was
concentrated under reduced pressure, washed with EtOAc and filtered
through a plug of silica gel. The residue was purified by flash chromatogra-
phy (silica gel, 97/3 n-hexane/EtOAc) to furnish 6 (0.393 g, 37%) as a color-
1
less liquid: H NMR (CDCl3): d ¼ 4.64–4.65 (m, 2H), 5.32 (dd, 1H, J ¼ 1.3,
10.6 Hz), 5.56 (dd, 1H, J ¼ 1.3, 17.3 Hz), 5.55–5.59 (m, 1H), 6.10 (dddd, 1H,

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2485
J ¼ 5.3, 5.3, 10.6, 17.3 Hz), 6.87 (d, 1H, J ¼ 8.3 Hz), 6.95 (t, 1H, J ¼ 7.5 Hz),
7.35 (m, 4H), 7.49 (t, 1H, J ¼ 8.3 Hz), 7.55 (d, 2H, J ¼ 7.5 Hz); 13C NMR
(CDCl3): d ¼ 69.3, 85.9, 93.6, 112.6, 113.2, 117.2, 120.8, 123.8, 128.1,
128.3, 131.7, 133.1, 133.5, 159.1; IR (neat, cm–1): 3069, 2217, 1726, 1587,
1449, 1115, 749; EIMS (m/z): 156, 164 (100%), 206, 234 (Mþ). Anal. Calcd.
for C17H14O: C, 87.15; H, 6.02. Found: C, 87.05; H, 5.97.
2-Ethynyl-(2-butenyloxy)benzene (11)
1-Chloro-2-butene (0.46 g, 5.1 mmol) was added to a suspension of
K2CO3 (0.70 g, 5.1mmol), NaI (0.76 g, 5.1mmol) and 10 34 (0.23 g, 1.9 mmol)
in acetone (20 mL). The reaction mixture was stirred for 12 h. This was then
concentrated under reduced pressure and filtered through a plug of silica
gel (EtOAc). The residue was purified by flash chromatography (silica gel,
98/2 n-hexane/EtOAc) to furnish 11 (0.197 g, 60%) as a yellow liquid:
1H NMR (CDCl3): d ¼ (E/Z 3:1) 1.75 (d, 4H, J ¼ 6.3 Hz, E- & Z-isomer),
3.27 (s, 1H, Z-isomer), 3.28 (s, 1H, E-isomer), 4.56 (d, 2H, J ¼ 5.5 Hz,
E-isomer), 4.70 (d, 0.7H, J ¼ 4.4 Hz, Z-isomer), 5.71–5.76 (m, 1.3 H, E- &
Z-isomer), 5.83–5.89 (m, 1.3H, E- & Z-isomer), 6.86–6.91(m, 2.7H, E- &
Z-isomers), 7.25, 7.3 (m, 1.3H, E- and Z-isomers), 7.44–7.7 (m, 1.3H, E-
and Z-isomers); 13C NMR (CDCl3): d ¼ 13.5, 17.9, 64.8, 69.4, 80.2, 81.2,
111.8, 111.9, 112.4, 112.4. 120.5, 120.6, 125.7, 125.9, 128.5, 130.1, 130.2,
134.2, 134.3; IR (neat, cm–1) 3292, 2107, 1651, 1585, 1108, 746; EIMS
(m/z): 55, 89, 118 (100%), 172 (Mþ). Anal. Calcd. for C12H12O: C, 83.69;
H, 7.02. Found: C, 83.60; H, 7.02.
2-Ethynyl-(3-phenyl-2-propenyloxy)benzene (12)
Cinnamyl chloride (1.03 g, 6.7 mmol) was added to a solution of NaI
(1.26 g, 8.4 mmol) in acetone (25 mL). The reaction mixture was stirred at
room temperature for 1.5 h. The NaCl formed in the reaction was removed
by filtration, the solvent was removed under reduced pressure and the cin-
namyl iodide formed was cooled to 0ꢀC. To this o-ethynylphenol 10, (0.52 g,
4.4 mmol), K2CO3 (0.98 g, 6.6 mmol), and acetone (10 mL) were added.
The reaction mixture was stirred at room temperature for 6 h. The reaction
mixture was concentrated under reduced pressure and filtered through a plug
of silica gel (EtOAc). The residue was purified by flash chromatography
(silica gel, 98/2 n-hexane/EtOAc) to furnish 12 (0.58 g, 56%) as a yellow
colored semi-solid compound (E/Z 20/1); 1H NMR (CDCl3); d ¼
3.32 (s, 1.05H, E- & Z-isomers), 4.78 (m, 0.1H, Z-isomer), 4.81(dd, 2H,

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LOVELY AND SESHADRI
J ¼ 1.6, 5.5 Hz, E-isomer), 6.43 (dt, 1.05H, J ¼ 5.6, 15.9 Hz, E- & Z-isomers),
6.78 (d, 1.05H, J ¼ 15.9 Hz, E- & Z-isomers), 6.91–6.95 (m, 3.15H, E- &
Z-isomers), 7.25–7.34 (m, 3.15H, E- & Z-isomers), 7.40–7.42 (m, 2.1H,
E- & Z-isomers), 7.49 (dd, 1.05H, J ¼ 1.7, 7.5 Hz, E- & Z-isomers); 13C
NMR (CDCl3); d ¼ 69.4, 80.2, 81.4, 111.9, 112.6, 120.8, 124.3, 126.7, 128,
128.7, 130.3, 133.0, 134.3, 136.5, 159.8; IR (neat, cmꢂ1): 3021, 2144, 1522,
1216, 1110, 761; EIMS (m/z): 77, 107, 121 (100%), 234 (Mþ).
2-Ethynyl-(2-methyl-2-propenyloxy)benzene (15)
3-Chloro-2-methylpropene (0.76 g, 8.4 mmol) was added to a suspen-
sion of K2CO3 (1.16 g, 8.4 mmol), NaI (1.26 g, 8.4 mmol) and 3 (0.25 g,
2.1mmol) in acetone (75 mL). The reaction mixture was stirred for 12 h.
This was then concentrated under reduced pressure and filtered through a
plug of silica gel (EtOAc). The residue was purified by flash chromatography
(silica gel, 98/2 n-hexane/EtOAc) to furnish 15 (0.269 g, 74%) as a yellow
colored liquid: 1H NMR (CDCl3): d ¼ 1.85 (s, 3H), 3.29 (s, 1H), 4.52 (s, 2H),
4.99–5.0 (m, 1H), 5.15–5.16 (m, 1H), 6.8 (d, 1H, J ¼ 8.4 Hz), 6.90 (app. tt,
1H, J ¼ 0.83, 7.5 Hz), 7.26–7.3 (m, 1H), 7.46 (dd, 1H, J ¼ 1.6, 7.5 Hz);
13C NMR (CDCl3): d ¼ 19.3, 72.1, 80.1, 81.8, 111.9, 112.4, 112.6, 120.6,
130.1, 134.1, 140.5, 159.9; IR (neat, cm–1): 3287, 2103, 1588, 1447, 1110,
748; EIMS (m/z): 89, 157 (100%), 172 (Mþ). Anal. Calcd. for C12H12O:
C, 83.69; H, 7.02. Found: C, 83.50; H, 7.12.
General Procedure for NMO Promoted PK Cyclization
Co2(CO)8 (2 eq.) was added to a stirred solution of enyne (1eq.) in
CH2Cl2. Stirring was continued at room temperature until the formation of
the complex was complete (monitored by TLC). The reaction mixture was
cooled to 0ꢀC (ice-bath) then NMO (10–12 eq.) was added in three equal
portions in thirty-minute intervals. After the reaction was complete (6–8 h at
room temperature, monitored by TLC), the reaction mixture was concen-
trated under reduced pressure and filtered though a silica gel plug (EtOAc).
Flash chromatography on the residue gave products as colorless solids.
3a,4-Dihydro-3H-cyclopenta[c]chromen-2-one (7)31
7 (0.334 g, 75%) was prepared as described in the general procedure,
utilizing 5 (0.39 g, 2.4 mmol), CH2Cl2 (100 mL), Co2(CO)8 (1.69 g, 4.9 mmol)

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INTRAMOLECULAR PAUSON-KHAND REACTIONS
2487
and NMO (3.31 g, 28.3 mmol): mp 110–111ꢀC (Lit. 100–102ꢀC)31; H1 NMR
(CDCl3): d ¼ 2.02 (dd, 1H, J ¼ 4.4, 17.9 Hz), 2.66 (dd, 1H, J ¼ 6.8, 17.9 Hz),
3.22–3.28 (m, 1H), 3.82 (dd, 1H, J ¼ 10.6, 13.2 Hz), 4.56 (dd, 1H, J ¼ 5.5,
10.6 Hz), 6.3 (s, 1H), 6.93 (d, 1H, J ¼ 8.5 Hz), 6.97 (1H, t, J ¼ 7.6 Hz), 7.32
(dd, 1H, J ¼ 7.6, 8.5 Hz), 7.51(d, 1H, J ¼ 7.6 Hz); 13C NMR (CDCl3):
d ¼ 36.5, 37.9, 70.2, 117.5, 118.0, 121.4, 122.0, 127.3, 133.4, 156.2, 168.9,
206.2; IR (KBr, cm–1): 2957, 1703, 1437, 1111, 742; EIMS (m/z): 63, 115,
131, 157, 186 (Mþ, 100%).
1-Trimethylsilyl-3a, 4-dihydro-3H-cyclopenta[c]chromen-2-one (8)
Cyclization following the general procedure utilizing 4 (0.101 g,
0.44 mmol) CH2Cl2 (20 mL), Co2(CO)8 (0.296 g, 0.86 mmol) and NMO
(0.61g, 5.2 mmol) afforded 8 (0.03 g, 26%) as a colorless solid: mp
94–95ꢀC; 1H NMR (CDCl3): d ¼ 0.3 (s, 9H), 1.95 (dd, 1H, J ¼ 4.1,
18.0 Hz), 2.62 (dd, 1H, J ¼ 7.1, 18.0 Hz), 3.18–3.22 (m, 1H), 3.89 (1H, dd,
J ¼ 12.8, 10.7 Hz), 4.61 (1H, dd, J ¼ 5.5, 10.7 Hz), 6.90–6.95 (m, 2H), 7.34 (t,
1H, J ¼ 7.5 Hz), 7.44 (d, 1H, J ¼ 7.5 Hz): 13C NMR (CDCl3): d ¼ 0.1, 37.2,
38.0, 70.9, 117.3, 119.5, 119.8, 129.8, 132.8, 134.5, 155.9, 174.9, 210.5; IR
(KBr, cmꢂ1): 3352, 2897, 1685, 1606, 1120, 759; EIMS (m/z): 173, 228, 243
(100%), 258 (Mþ). Anal. Calcd. for C15H18O2Si: C, 69.73; H, 7.02. Found:
C, 69.95; H, 7.39.
1-Phenyl-3a,4-dihydro-3H-cyclopenta[c]chromen-2-one (9)31
Cyclization following the general procedure utilizing 6 (0.096 g,
0.41mmol) CH 2Cl2 (17 mL), Co2(CO)8 (0.281g, 0.82 mmol) and NMO
(0.58 g, 4.9 mmol) afforded 10 (0.078 g, 73%) as a colorless solid: mp
133–135ꢀC (Lit. 70–72ꢀC)31; H NMR (CDCl3): d ¼ 2.16 (dd, 1H, J ¼ 4.2,
1
18.2 Hz), 2.84 (dd, 1H, J ¼ 7.1, 18.2 Hz), 3.29–3.24 (m, 1H), 4.01 (dd, 1H,
J ¼ 10.7, 13.1 Hz), 4.69 (dd, 1H, J ¼ 5.4, 10.7 Hz), 6.70 (t, 1H, J ¼ 7.6 Hz),
6.94 (d, 1H, J ¼ 8.1Hz), 7.19–7.45 (m 7H); 13C NMR (CDCl3): d ¼ 34.8,
36.7, 70.3, 117.8, 120.6, 128.2, 128.3, 128.9, 129.2, 132.1, 132.8, 156.3,
160.6, 204.6; IR (KBr, cm–1): 3061, 1698, 1630, 1601, 1152, 756; EIMS
(m/z): 115, 262 (100%, Mþ).
3-Methyl-3a,4-dihydro-3H-cyclopenta[c]chromen-2-one (13)
Cyclization following the general procedure utilizing 11 (0.049 g,
0.29 mmol) CH2Cl2 (10 mL), Co2(CO)8 (0.197 g, 0.58 mmol) and NMO

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LOVELY AND SESHADRI
(0.576 g, 5.22 mmol) afforded 13 (0.026 g, 45%) as a yellow solid: mp
80–81ꢀC; 1H NMR (CDCl3); d ¼ 1.23 (d, 3H, J ¼ 7.35 Hz), 2.09–2.14 (m,
1H), 2.87–2.89 (m, 1H), 3.87 (dd, 1H, J ¼ 10.6, 13.3 Hz), 4.66 (dd, 1H,
J ¼ 5.6, 10.6 Hz), 6.37 (s, 1H), 6.99 (d, 1H, J ¼ 8.4 Hz), 7.01(t, 1H,
J ¼ 7.5 Hz), 7.36 (t, 1H, J ¼ 7.8 Hz), 7.57 (d, 1H, J ¼ 7.8 Hz); 13C NMR
(CDCl3): d ¼ 13.6, 44.3, 44.5, 69.8, 117.4, 118.0, 120.6, 121.5, 127.3, 133.3,
156.3, 166.1, 208.2; IR (KBr, cm–1): 3080, 2976, 1696, 1610, 1460, 1118, 761;
EIMS (m/z): 77, 114, 157, 170, 200 (100%, Mþ).
3-Phenyl-3a,4-dihydro-3H-cyclopenta[c]chromen-2-one (14)
Cyclization following the general procedure utilizing 12 (0.035 g,
0.17 mmol) CH2Cl2 (8 mL), Co2(CO)8 (0.12 g, 0.4 mmol) and NMO
(0.248 g, 2.19 mmol) afforded 14 (0.007 g, 16%) as a colorless solid:
mp decomposes >150ꢀC; H1 NMR (CDCl3): d ¼ 3.25 (d, 1H, J ¼ 4.9),
3.4 (m, 1H), 4.01 (dd, 1H, J ¼ 10.7, 13.0 Hz), 4.67 (dd, 1H, J ¼ 5.6,
10.4 Hz), 6.46 (s, 1H), 7.04 (d, 1H, J ¼ 8.2 Hz), 7.2 (t, 1H, J ¼ 7.6 Hz),
7.30–7.39 (m, 5H), 7.64 (d, 1H, J ¼ 7.6 Hz); 13C NMR (CDCl3): d¼ 69.4,
81.3, 111.9, 112.6, 120.8, 124.3, 126.7, 128.0, 128.7, 130.2, 133.0, 134.3,
134.3, 136.5, 205.2; IR (KBr, cmꢂ1): 2865, 1689, 1614, 1036, 746; EIMS
(m/z): 57 (100%), 69, 148, 202, 262 (Mþ). Anal. Calcd. for C18H14O2: C,
82.42; H, 5.38. Found: C, 82.01; H, 5.05.
ACKNOWLEDGMENTS
We would like to thank The University of Texas at Arlington (Start-up
Funds) and the Robert A. Welch Foundation for the provision of financial
support for this project.
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LOVELY AND SESHADRI
34. Arcadi, A.; Cacchi, S.; Del Rosario, M.; Fabrizi, G.; Marinelli, F.
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35. Attempts to perform this reaction under thermal activation led to the
isolation of 5% of the cyclization product.
Received in the USA March 5, 2000

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