Preparation of substituted transition-metal (η1-propargyl complexes and their [3+2] cycloaddition reactions with sulfur dioxide and disulfur monoxide. Transition-metal - Carbon bond cleaving reactions of the cycloadducts which yield oxathiolene oxides and dithiolene oxides

Article abstract of DOI:10.1016/S0022-328X(03)00167-0

The preparations of several new cyclopentadienyl iron dicarbonyl η¹-2-alkynyl complexes are reported. Their [3+2] cycloaddition reactions with sulfur dioxide and disulfur monoxide yielded transition-metal substituted 1,2-oxathiolene-2-oxides and 1,2-dithiolene-1-oxides, respectively. The transition-metal was cleaved from the oxathiolene-oxide and dithiolene-oxide containing complexes to produce new sulfur heterocycles.

Full text of DOI:10.1016/S0022-328X(03)00167-0

Journal of Organometallic Chemistry 673 (2003) 67ꢁ76
/
www.elsevier.com/locate/jorganchem
Preparation of substituted transition-metal (h1-propargyl complexes
and their [3ꢀ2] cycloaddition reactions with sulfur dioxide and
disulfur monoxide. Transition-metalꢁcarbon bond cleaving reactions
/
/
of the cycloadducts which yield oxathiolene oxides and dithiolene
oxides
Elizabeth E. Scott, Erling T. Donnelly, Mark E. Welker *
Department of Chemistry, Wake Forest University, P.O. Box 7486, Winston-Salem, NC 27109, USA
Received 14 January 2003; received in revised form 13 March 2003; accepted 14 March 2003
Abstract
The preparations of several new cyclopentadienyl iron dicarbonyl h1-2-alkynyl complexes are reported. Their [3ꢀ
/
2] cycloaddition
reactions with sulfur dioxide and disulfur monoxide yielded transition-metal substituted 1,2-oxathiolene-2-oxides and 1,2-
dithiolene-1-oxides, respectively. The transition-metal was cleaved from the oxathiolene-oxide and dithiolene-oxide containing
complexes to produce new sulfur heterocycles.
# 2003 Elsevier Science B.V. All rights reserved.
Keywords: Propargyl complexes; Alkynyl complexes; [3ꢀ2] Cycloaddition; Sulfur heterocycles
/
1. Introduction
chemistry as a new synthetic method for the preparation
of unusual sulfur heterocycles. We are interested in five-
membered-ring sulfur heterocycles as synthetic targets
because of (1) their cancer chemopreventive effects since
they function as anticarcinogenic enzyme inducers [3]
and (2) a recent report that 1,2-dithiolanes and 1,2-
dithianes look particularly promising as inhibitors of
HIV type 1 replication [4].
Cycloaddition reactions between transition-metal h1-
2-alkynyl (1) and h1-allyl complexes (1) and unsaturated
electrophilic reagents (2) were first reported about 30
years ago [1]. These [3ꢀ2] cycloaddition reactions have
/
been shown to yield transition-metal substituted five-
membered-ring heterocycles and carbacycles (3) [1].
We recently reported some oxathiolene-oxides and
dithiolene-oxides which function as inducers of ferritin
expression, glutathione S-transferases, and NAD(P)H
quinone oxidoreducatase [5]. In continuation of our
efforts in this area, we report here the preparation of
cyclopentadienyl iron dicarbonyl-h1-alkynyl complexes
which were targeted for preparation based on their
potential to lead to new anticarcinogenic enzyme
Over the last 15 years we have also reported a number
of examples of these types of cycloaddition reactions [2].
We have been particularly interested in developing this
inducers. Subsequent [3ꢀ2] cycloaddition reactions of
/
these complexes with sulfur dioxide and disulfur mon-
oxide are reported along with demetallation reactions of
these metal substituted cycloadducts. The biological
activities of these compounds will be reported elsewhere.
* Corresponding author. Tel.: ꢀ
4321.
E-mail address: welker@wfu.edu (M.E. Welker).
/
1-336-758-5758; fax: ꢀ1-336-758-
/
0022-328X/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00167-0

68
E.E. Scott et al. / Journal of Organometallic Chemistry 673 (2003) 67ꢁ76
/
2. Experimental
the chiral centers were subsequently removed by dehy-
1
dration. H-NMR (CDCl3) 4.30 (dd, Jꢃ
/
10, 3 Hz, a-Cl
2.1. General
H in 1 diastereomer), 3.70 (dd, Jꢃ6, 4 Hz, a-Cl H in 1
/
diastereomer), 2.85 (br s, 1H, OH), 2.45 (s, 1H), 2.05 (m,
1H), 1.92 (m, 1H), 1.80 (m, 2H), 1.6 (m, 2H), 1.45 (m,
2H). EIMS (m/z) [Mꢀ] 158 (6), 123 (16), 105 (13), 95
(31), 81 (100), 68 (47), 53 (47).
All proton nuclear magnetic resonance (NMR) spec-
tra were obtained using a Bruker 300 MHz spectrometer
operating at 300.1 MHz and referenced to the residual
proton signal of a deuterated solvent. All 13C-NMR
spectra were obtained using a Bruker 300 MHz spectro-
meter operating at 75.48 MHz, or a Bruker 500 MHz
spectrometer operating at 125.8 MHz. Spectra were
referenced to the residual carbon signal of a deuterated
solvent. Infrared (IR) spectra were obtained on either a
2.3. 1-Chloro-2-ethynylcyclohexene (6)
In a flame-dried flask cooled under N2, 2-chloro-1-
ethynylcyclohexanol (5) (19.062 g, 120.0 mmol) was
added to pyridine (100 ml) and cooled to 0 8C. POCl3
(20.236 g, 132.0 mmol) was added over 30 min. The
reaction mixture was stirred at room temperature for 15
h, then heated to 70 8C for 1 h. After cooling, ice (200 g)
was added, the layers were separated and the aqueous
PerkinꢁElmer 1620 FTIR or a Mattson Genesis II
/
FTIR. Melting points were obtained on a Mel-Temp
apparatus and are reported uncorrected. All elemental
analyses were performed by Atlantic Microlab, Inc., of
Norcross, Georgia. All high-resolution mass spectral
analyses were performed by Duke Mass Spectrometry
Facility, Duke University. Diethyl ether and tetrahy-
drofuran were distilled from sodium/benzophenone
under nitrogen immediately prior to use. Dichloro-
methane was distilled from calcium hydride immediately
before use. All reactions were carried out under an
atmosphere of dry nitrogen gas unless otherwise noted.
Cyclopentadienyliron dicarbonyl dimer, mercury, and
dichlorobis(triphenylphosphine) palladium (II) were
purchased from Strem Chemicals. Ammonium cerium
(IV) nitrate, 4?-iodoacetophenone, 4-iodobenzotrifluor-
ide, triethylamine, p-toluene sulfonyl chloride, sulfur
dioxide (g), and pyridine were purchased from Aldrich.
Sulfur dioxide (1 M) in chloroform was purchased from
Alfa Aesar. Propargyl alcohol was purchased from
Farchan Laboratories. Deuterated solvents were pur-
chased from Cambridge Isotope Laboratories. All
reagents were used as received. 4,5-Diphenyl-3,6-dihy-
dro-1,2-dithiin-1-oxide (26) was prepared using an
adaptation of our previously reported procedure [6].
layer was extracted with diethyl ether (3ꢂ50 ml). The
/
combined extracts were washed with 10% HCl, water
and saturated NaHCO3. The product was dried with
magnesium sulfate and excess solvent was removed by
rotary evaporation. Another wash with 1.2 M HCl (2ꢂ
/
50 ml) was carried out to remove residual pyridine from
1
the product (6) (8.552 g, 60.9 mmol, 51%). H-NMR
(CDCl3) 3.2 (s, 1H), 2.35 (m, 2H), 2.22 (m, 2H), 1.65 (m,
2H), 1.55 (m, 2H). 13C-NMR (CDCl3) 138.7, 117.3,
82.2, 82.1, 34.0, 31.1, 23.8, 22.2. Anal. Calc. for C8H9Cl:
C, 68.34; H, 6.45%. Found: C, 68.51; H, 6.54%.
2.4. 3-(2?-Chloro-2?-cyclohexenyl)-2-propyn-1-ol (7)
1-Chloro-2-ethynylcyclohexene (6) (7.606 g, 54.1
mmol) was dissolved in anhydrous diethyl ether (175
ml), cooled to ꢄ78 8C, and treated with 2.5 M n-
/
Butyllithium (23.8 ml, 59.5 mmol) in hexane. The
mixture was stirred for 90 min and then paraformalde-
hyde (3.25 g, 36.1 mmol) was added. The mixture was
then allowed to warm to room temperature overnight,
poured into NH4Cl (100 ml) and extracted with diethyl
2.2. 2-Chloro-1-ethynyl-cyclohexanol (5)
ether (3ꢂ50 ml). The organic extracts were dried with
/
magnesium sulfate, rotary evaporation was used to
remove the solvent, and the product was vacuum dried.
A flame-dried two-neck flask cooled under N2,
containing 0.5 M ethynylmagnesium bromide in THF
(450 ml, 225.0 mmol) was cooled to 0 8C. 2-Chlorocy-
clohexanone (4) (25.0 g, 189.0 mmol) was added slowly
over several minutes. The solution was stirred at 0 8C for
15 min and then stirred for 1 h at room temperature,
then poured into cold NH4Cl (200 ml). After vigorous
shaking and separation of the layers, extraction with
The product (7) (5.717 g, 33.5 mol, 62%) was obtained
1
by vacuum distillation at 110ꢁ
/
115 8C (1 mmHg). H-
NMR (CDCl3) 4.20 (s, 2H), 2.20 (t, Jꢃ/6.5 Hz, 2H),
2.08 (t, Jꢃ
/
6.5 Hz, 2H), 1.98 (s, 1H), 1.5 (m, 2H), 1.4 (m,
2H). 13C-NMR (CDCl3) 137.7, 117.6, 92.1, 84.3, 52.0,
34.0, 31.2, 23.7, 22.1. EI HRMS (m/z) Calc. for [Mꢀ]
(C9H11ClO): 170.0498. Found: 170.0495.
diethyl ether (3ꢂ50 ml) was used to obtain the product.
/
The solvent was removed by rotary evaporation at
25 8C. The crude product was distilled through a short
Vigreux column at 10 mmHg. The desired product (5)
(19.062 g, 120.0 mmol, 63%) came off in the temperature
2.5. 1-Tosyl-3-(2?-Chloro-2?-cyclohexenyl)-2-propyne
(8)
3-(2?-Chloro-2?-cyclohexenyl)-2-propyn-1-ol (7) (4.21
g, 25.0 mmol) was dissolved in anhydrous diethyl ether
(100 ml) and p-toluene sulfonyl chloride (4.525 g, 23.7
range of 82ꢁ
/
84 8C as a 1:1 mixture of diastereomers. No
attempt was made to separate the diastereomers since

E.E. Scott et al. / Journal of Organometallic Chemistry 673 (2003) 67ꢁ
/
76
69
mmol) was added. The solution was cooled to ꢄ
and powdered KOH (7.0125 g, 125.0 mmol) was added
one equivalent at a time over 30ꢁ45 min. The mixture
was then stirred at ꢄ15 8C for 90 min. Ice water (100
ml) was then added and the product was extracted with
diethyl ether (2ꢂ50 ml). The extracts were dried with
magnesium sulfate and the solvent was removed by
rotary evaporation. The product (8) (7.02 g, 21.6 mmol,
86%) was then dried under high vacuum. 1H-NMR
/
15 8C
(KBr) 3609, 2927, 2872, 1616 cmꢄ1. 1H-NMR (CDCl3):
7.53 (d, Jꢃ8.8 Hz, 2H), 7.49 (d, Jꢃ8.8 Hz, 2H), 4.51
(s, 2H), 2.83 (s, 1H). 13C-NMR (CDCl3) 132.25 (s),
130.69 (q, Jꢃ32.7 Hz), 126.79 (q, Jꢃ1.1 Hz), 125.59
(q, Jꢃ3.8 Hz), 124.22 (q, Jꢃ272.2 Hz), 90.17 (s), 84.56
/
/
/
/
/
/
/
/
/
(s), 51.67 (s). Anal. Calc. for C9H7F3O: C, 60.01; H,
3.53%. Found: C, 59.71; H, 3.73%.
2.7. General procedure for synthesis of alkynyl tosylates
(CDCl3) 7.74 (d, Jꢃ
/
6.5 Hz, 2H), 7.28 (d, Jꢃ6.5 Hz,
/
2H), 4.85 (s, 2H), 2.39 (s, 3H), 2.20 (m, 2H), 2.00 (m,
2H), 1.6 (m, 2H), 1.5 (m, 2H). 13C-NMR (CDCl3) 145.3,
139.3, 133.7, 130.2, 128.5, 116.9, 87.5, 85.2, 59.0, 34.0,
30.8, 23.5, 22.0, 21.9. Anal. Calc. for C16H17SOCl: C,
59.16; H, 5.28%. Found: C, 59.31; H, 5.17%.
In an adaptation of a literature procedure, [2d] the
corresponding propargyl alcohol was dissolved in
diethyl ether (50 ml) and p ꢁtoluene sulfonyl chloride
/
(one equivalent) was added. The solution was cooled to
0 8C and freshly powdered potassium hydroxide (57.0
equivalents) was added five equivalents at a time over a
30 min period. The reaction mixture was allowed to stir
at 0 8C for 2 h. Ice water (50 ml) was then added, and
2.6. General procedure for synthesis of substituted phenyl
propargyl alcohols
the mixture was extracted with diethyl ether (3ꢂ25 ml).
The solution was dried over MgSO4, and the solvent was
removed under reduced pressure. The product was
/
Following a literature procedure, [2d] the appropriate
iodobenzene was dissolved in 10ꢁ30 ml of triethylamine,
/
and propargyl alcohol was added. The reaction mixture
was degassed using nitrogen. Pd(PPh3)2Cl2 (0.01 mol%)
and CuI (0.02 mol%) were added to the solution, and the
solution was again degassed with nitrogen. The reaction
was stirred at room temperature for 2 h. Water (20 ml)
was then added, and the reaction mixture was extracted
triturated with distilled pentane, cooled to ꢄ15 8C,
/
and the solvent decanted. The remaining product was
dried under vacuum.
2.7.1. 1-Tosyl-3-(4?-acetylphenyl)-2-propyne (14)
3-(4?-Acetylphenyl)-2-propyn-1-ol (12) (1.48 g, 8.50
mmol), p-toluene sulfonyl chloride (1.62 g, 8.50 mmol),
and potassium hydroxide (19.4 g, 485 mmol) were
reacted using the above procedure to yield the product
with ethyl acetate (3ꢂ20 ml). The organic layers were
/
combined and dried over MgSO4 and filtered. The
solvent was removed under reduced pressure.
2.6.1. 3-(4?acetylphenyl)-2-propyn-1-ol (12)
(14) (2.03 g, 6.20 mmol, 76%) as a tan solid. M.p. 69ꢁ
/
73 8C. IR (KBr) 2990, 1685, 1178 cmꢄ1 1H-NMR
.
4?-Iodoacetophenone (9) (3.00 g, 12.20 mmol), pro-
pargyl alcohol (11) (0.72 ml, 12.4 mmol), Pd(PPh3)2Cl2
(0.089 g, 0.127 mmol), and CuI (0.048 g, 0.25 mmol)
were reacted using the above procedure. The crude
product was purified using recrystallization in pentane.
The resulting product (12) was an orange solid (1.707 g,
(CDCl3) 7.80 (m, 4H), 7.27 (m, 4H), 4.89 (s, 2H), 2.53 (s,
3H), 2.34 (s, 3H). 13C-NMR (CDCl3) 197.49, 145.53,
137.35, 133.71, 132.27, 130.23, 128.60, 128.49, 126.56,
88.29, 84.11, 58.58, 26.97, 22.00. Anal. Calc. for
C18H16O4S: C, 65.84; H, 4.91%. Found: C, 66.47; H,
4.97%.
9.81 mmol, 80%), m.p. 73ꢁ
1661 cmꢄ1. 1H-NMR (CDCl3): 7.89 (d, Jꢃ
6.8 Hz, 2H), 4.51 (s, 2H), 2.58 (s, 3H), 1.61
/
76 8C. IR (NaCl) 3381, 2910,
/
6.7 Hz, 2H),
7.50 (d, Jꢃ
/
(s, 1H). 13C-NMR (CDCl3) 197.62, 136.90, 132.17,
128.60, 127.82, 90.91, 85.27, 51.98, 26.96. EI HRMS
(m/z) Calc. for [Mꢀ] (C11H10O2): 174.0681. Found:
174.0678.
2.7.2. 1-Tosyl-3-(4?-trifluoromethylphenyl-2-propyne
(15)
3-(4?-Trifluoromethylphenyl)-2-propyn-1-ol (13) (0.31
g, 1.5 mmol), p-toluene sulfonyl chloride (0.29 g, 1.5
mmol), and potassium hydroxide (3.54 g, 88.5 mmol)
were reacted using the above procedure to yield the
2.6.2. 3-(4?-Trifluoromethylphenyl)-2-propyn-1-ol (13)
4-Iodobenzotrifluoride (10) (0.908 g, 3.34 mmol),
propargyl alcohol (11) (0.21 ml, 3.6 mmol),
Pd(PPh3)2Cl2 (0.027 g, 0.038 mmol), and CuI (0.010 g,
0.052 mmol) were reacted using the above procedure.
The crude product was purified using pentane to
precipitate the by-product. The pentane was removed
from the remaining orange solution using rotary eva-
poration. The resulting product (13) was a waxy orange
product (15) (0.44 g, 1.2 mmol, 82%) as an orange solid.
1
M.p. 67ꢁ
NMR (CDCl3) 7.85 (d, Jꢃ
Hz, 2H), 7.35 (m, 4H), 4.95 (s, 2H), 2.40 (s, 3H). 13C-
NMR (CDCl3) 145.57, 133.70, 132.40, 131.20 (q, Jꢃ
32.81 Hz), 130.24, 128.58, 127.41, 125.58 (q, Jꢃ11.28
Hz), 124.09 (q, Jꢃ272.35), 87.72, 83.46, 58.52, 21.93.
/
70 8C. IR (KBr) 3056, 1617, 1176 cmꢄ1. H-
/
8.4 Hz, 2H), 7.54 (d, Jꢃ8.1
/
/
/
/
Anal. Calc. for C17H13F3O3S: C, 57.62; H, 3.70%.
Found: C, 57.66; H, 3.70%.
solid (0.307 g, 1.63 mmol, 49%), m.p. 35ꢁ37 8C. IR
/

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E.E. Scott et al. / Journal of Organometallic Chemistry 673 (2003) 67ꢁ76
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2.8. General procedure for synthesis of iron alkynyl
complexes
g, 5.65 mmol) in THF using the procedure described
above. The resulting crude product was purified by
jacketed cold column chromatography on deactivated
alumina in 100% pentane. The product (19) (0.677 g,
Following a literature procedure, [2d] the iron anion
was generated by stirring
a
THF solution of
1.88 mmol, 33%) was a yellow brown solid. M.p. 51ꢁ
/
[CpFe(CO)2]2 over a sodium amalgam for 3 h. The
anion was then added via a double-ended needle to a
THF solution of the corresponding alkynyl tosylate at
0 8C. The reaction mixture was warmed to room
temperature and stirred for 1 h. The solvent was
removed under reduced pressure. Diethyl ether was
added to the resulting residue, and the solution was
filtered through celite. The diethyl ether was removed
under reduced pressure. The crude product was purified
by cold column chromatography (jacketed column with
ice water recirculating through the jacket) on deacti-
vated alumina.
53 8C. IR (KBr) 3208, 2988, 2016, 1963 cmꢄ1. 1H-NMR
(CDCl3) 7.46 (m, 4H), 4.86 (s, 5H), 1.82 (s, 2H). 13C-
NMR (CDCl3) 216.30, 132.09, 131.28, 130.08, 128.46,
125.45 (q, Jꢃ
HRMS (m/z) Calc. for [Mꢀ
361.0139. Found: 361.0135.
/
3.8 Hz), 105.27, 86.29, 82.37, 68.28. FAB
/
H]ꢀ (C17H12O2Fe):
2.9. General procedure for synthesis of metallosulfinate
esters
Following a literature procedure, [2d] the appropriate
propargyl complex was dissolved in CH2Cl2 (15 ml) and
degassed with nitrogen. Either SO2 (1 M in CHCl3) was
added to the reaction mixture, or the reaction mixture
2.8.1. Cyclopentadienyl-(3-(2?-chloro-1?-cyclohexenyl)-
2-propynyl)-dicarbonyliron (17)
was cooled to ꢄ78 8C and SO2 (g) was bubbled through
/
The iron anion was generated by stirring dicyclopen-
tadienyl dicarbonyl iron (16) (3.81 g, 108.0 mmol) in
THF over a 1% sodium amalgam (2.49 g, 108.0 mmol)
for 5 h. The anion was then added to a solution of the 1-
tosyl-3-(2?-chloro-2?-cyclohexenyl)-2-propyne (8) (7.02
g, 216.0 mmol) in THF using the procedure described
above. The product (17) (2.051 g, 6.21 mmol, 58%) was
purified via column chromatography (alumina, 20:1
pentane:ether). 1H-NMR (CDCl3) 4.80 (s, 5H), 2.28
(m, 2H), 2.18 (m, 2H), 1.72 (s, 2H) 1.63 (m, 2H), 1.51
(m, 2H). Anal. Calc. for C16H15O2FeCl: C, 58.13; H,
4.57%. Found: C, 57.24; H, 4.72%.
the reaction mixture for 5 min. The reaction was allowed
to warm to room temperature, and stir overnight. The
solvent was removed under reduced pressure, and the
resulting solid was vacuum dried. The products were
purified by cold column chromatography on silica gel.
2.9.1. Cyclopentadienyl(1-oxo-3-(4?-acetylphenyl)-1,2-
oxathiol-3-enyl)dicarbonyliron (23)
Cyclopentadienyl(3-(4?-acetylphenyl)-2-propynyl)di-
carbonyliron (18) (0.839 g, 2.52 mmol) was treated with
SO2 (g) as described above to generate the product (23)
as a yellow brown solid (0.934 g, 2.347 mmol, 93%).
M.p. 124ꢁ
NMR (CDCl3) 8.02 (d, Jꢃ
/
127 8C. IR (KBr) 2033, 1982, 1603 cmꢄ1. 1H-
8.1 Hz, 2H), 7.55 (d, Jꢃ8.1
15.0 Hz,
2.8.2. Cyclopentadienyl(3-(4?-acetylphenyl)-2-
propynyl)dicarbonyliron (18)
/
/
Hz, 2H), 5.57 (d, Jꢃ
/
15.0 Hz, 1H), 5.21 (d, Jꢃ
/
The iron anion was generated from [CpFe(CO)2]2
(0.939 g, 2.65 mmol) and then added to a solution of 1-
tosyl-3-(4?-acetylphenyl)-2-propyne (14) (1.995 g, 6.08
mmol) in THF using the procedure described above.
The resulting crude product was purified by jacketed
cold column chromatography on deactivated alumina in
19:1 pentane:diethyl ether. The product (18) (1.02 g, 3.04
mmol, 58%) was a yellow brown solid. Rf: 0.41 (3:1
1H), 4.79 (s, 5H), 2.65 (s, 3H). 13C-NMR (CDCl3)
213.13, 213.03, 197.76, 155.14, 150.41, 139.18, 136.66,
130.58, 128.50, 93.32, 85.50, 26.70. FAB HRMS (m/z)
Calc. for [Mꢀ
/
H]ꢀ (C18H15O5FeS): 398.9990. Found:
398.9980.
2.9.2. Cyclopentadienyl(1-oxo-3-(4?-
trifluoromethylphenyl)-1,2-oxathiol-3-
enyl)dicarbonyliron (24)
Cyclopentadienyl(3-(4?-trifluoromethylphenyl)-2-pro-
pynyl)dicarbonyliron (19) (0.677 g, 1.880 mmol) was
treated with SO2 (g) for 5 min to generate the crude
product. This product was then purified by cold column
chromatography on silica gel in 3:1 ethyl acetate:pen-
tane to yield a brown solid (24) (0.337 g, 0.968 mmol,
pentane:diethyl ether). M.p. 93ꢁ
/
96 8C. IR (NaCl) 2015,
7.9 Hz, 2H),
1961 cmꢄ1. 1H-NMR (CDCl3) 7.91 (d, Jꢃ
/
7.31 (d, Jꢃ8.3 Hz, 2H), 4.79 (s, 5H), 2.50 (s, 3H), 1.76
/
(s, 2H). 13C-NMR (CDCl3) 197.73, 135.04, 131.44,
131.16, 128.63, 106.80, 88.95, 86.42, 83.42, 26.87 (CO
carbons not found). FAB HRMS (m/z) Calc. for [Mꢀ
/
H]ꢀ (C18H15O3Fe): 335.0371. Found: 335.0370.
51%), M.p. 101ꢁ
1618, 1324, 1132 cmꢄ1. H-NMR (CDCl3) 7.70 (d, Jꢃ
7.6 Hz, 2H), 7.56 (d, Jꢃ7.5 Hz, 2H), 5.56 (d, Jꢃ14.9
Hz, 1H), 5.21 (d, Jꢃ
14.9 Hz, 1H), 4.79 (s, 5H). 13C-
NMR (CDCl3) 213.49, 213.40, 155.69, 150.63, 138.36,
131.17, 125.90 (q, 3.6 Hz), 122.63, 93.74, 85.90 (qua-
/
104 8C. IR (KBr) 2930, 2033, 1983,
1
2.8.3. Cyclopentadienyl(3-(4?-trifluoromethylphenyl-2-
propynyl)dicarbonyliron (19)
The iron anion was generated from [CpFe(CO)2]2
(1.002 g, 2.83 mmol) and then added to a solution of 1-
tosyl-3-(4?-trifluoromethylphenyl)-2-propyne (15) (2.000
/
/
/
/

E.E. Scott et al. / Journal of Organometallic Chemistry 673 (2003) 67ꢁ
/
76
71
ternary carbon a to CF3 could not be located). Anal.
Calc. for C17H11F3O4SFe: C, 48.14; H, 2.61%. Found:
C, 48.15; H, 2.77%.
reaction was stirred at 25 8C for 24 h. The solvent was
removed under reduced pressure, and the crude product
was purified by cold column chromatography.
2.11.1. Cyclopentadienyl(1-oxo-5-(4?-acetylphenyl)-1,2-
dithiol-4-enyl)dicarbonyliron (28)
2.9.3. Cyclopentadienyl(1-oxo-3-(2?-chloro-1?-
cyclohexenyl)-1,2-oxathiol-3-enyl)dicarbonyliron (25)
Cyclopentadienyl-(3-(2?-chloro-1?-cyclohexenyl)-2-
propynyl)dicarbonyliron (17) (0.400 g, 1.21 mmol) was
dissolved in freshly distilled CH2Cl2 (10 ml), and treated
with SO2 (g) as described above. The product (25) (0.093
g, 0.236 mmol, 20%) was isolated following silica
chromatography (0 8C) (50:50 pentane:diethyl ether,
Cyclopentadienyl(3-(4?-acetylphenyl)-2-propynyl)di-
carbonyliron (18) (0.318 g, 0.952 mmol) and 4,5-
diphenyl-3,6-dihydro-1,2-dithiin 1-oxide (26) (0.409 g,
1.428 mmol) were dissolved in THF and allowed to react
as described above. The reaction was stirred for 24 h to
generate the crude product. The desired product was
then isolated by cold column chromatography on silica
gel using four column volumes of 1:9 diethyl ether:pe-
troleum ether, two column volumes of 100% diethyl
ether, and then 1:9 ethanol:diethyl ether to yield a
brown solid (28) (0.220 g, 0.531 mmol, 56%), Rf: 0.28
1
then ether, then methanol). H-NMR (CDCl3) 5.38 (d,
Jꢃ
2.42 (m, 2H), 2.30 (m, 2H), 1.75 (m, 2H), 1.68 (m, 2H).
FAB HRMS Calc. for [Mꢀ
H]ꢀ (C16H16SO4FeCl):
394.9807. Found: 394.9807.
/
15 Hz, 1H), 5.02 (d, Jꢃ/16 Hz, 1H), 4.94 (s, 5H),
/
(100% diethyl ether). M.p. 92ꢁ
/
97 8C (decomposition).
IR (KBr) 2031, 1982 cmꢄ1. H-NMR (CDCl3) 8.03 (d,
Jꢃ8.1 Hz, 2H), 7.55 (d, Jꢃ8.1 Hz, 2H), 5.02 (d, Jꢃ
1
2.10. Procedure for synthesis of 4,5-diphenyl-3,6-
dihydro-1,2-dithiin-1-oxide (26)
/
/
/
16.5 Hz, 1H), 4.76 (s, 5H),), 4.57 (d, Jꢃ16.5 Hz, 1H),
/
2.26 (s, 3H). 13C-NMR (CDCl3) 213.37, 213.20, 197.85,
1
159.82 (not visible by D-NMR, assigned via HMBC),
150.66, 141.37, 137.74, 131.80, 128.43, 85.85, 60.08,
4,5-Diphenyl-3,6-dihydro-1,2-dithiin-1-oxide (26) was
prepared in three steps using a procedure previously
reported by our group [6]. Reported here are a new
purification technique for 2,3-diphenyl-1,3-butadiene
(32), and previously unreported 13C-NMR data for
4,5-diphenyl-3,6-dihydro-1,2-dithiin-1-oxide (26).
26.75. FAB HRMS (m/z) Calc. for [Mꢀ
H]ꢀ
(C18H15O4S2Fe1): 414.9761. Found: 414.9761.
/
2.11.2. Cyclopentadienyl(1-oxo-5-(4?-
trifluoromethylphenyl)-1,2-dithiol-4-enyl-dicarbonyliron
(29)
2.10.1. ,3-Diphenyl-1,3-butadiene (32)
Cyclopentadienyl(3-(4?-trifluoromethylphenyl)-2-pro-
pynyldicarbonyliron (19) (0.436 g, 1.211 mmol) and 4,5-
diphenyl-3,6-dihydro-1,2-dithiin 1-oxide (26) (0.624 g,
2.179 mmol) were dissolved in THF and allowed to react
as described above. The reaction was stirred for 24 h to
generate the crude product. The desired product was
then isolated by cold column chromatography on silica
gel using four column volumes of 1:9 diethyl ether:pe-
troleum ether then 1:9 ethanol:diethyl ether to yield a
brown solid (29) (0.318 g, 0.723 mmol, 60%), Rf: 0.22
This compound was synthesized using a previously
reported procedure [6] but the work-up was modified as
described here. Cold pentane was added to a flask
containing crude 2,3-diphenyl-1,3-butadiene (32). The
resulting pale yellow solution was decanted from an
orange oil that formed in the bottom of the flask. The
solvent was then removed from the pale yellow solution
under reduced pressure to yield 2,3-diphenyl-1,3-buta-
diene (32) identical to previously reported material by
spectroscopic comparison [6].
(100% diethyl ether). M.p. 51ꢁ
1982 cmꢄ1. 1H-NMR (CDCl3) 7.72 (d, Jꢃ
7.57 (d, Jꢃ8.3 Hz, 2H), 5.01 (d, Jꢃ16.1 Hz, 1H), 4.78
(s, 5H), 4.59 (d, Jꢃ
16.4 Hz, 1H). 13C-NMR (CDCl3)
213.70, 213.56, 160.55, 150.93, 132.33 (overlap of
carbons m and p to CF3 by HMBC), 130.95 (q, Jꢃ
32.8 Hz), 125.82 (q, Jꢃ3.6 Hz), 86.32, 60.45 could not
/
55 8C. IR (KBr) 2031,
/8.2 Hz, 2H),
2.10.2. 4,5-Diphenyl-3,6-dihydro-1,2-dithiin 1-oxide (26)
This compound was synthesized using a previously
reported procedure [6]. Reported here is additional
spectroscopic data for 26. 13C-NMR (CDCl3) 140.99,
140.44, 138.90, 132.25, 129.59, 129.55, 128.63, 128.60,
127.87, 127.53, 62.09, 35.70.
/
/
/
/
/
locate CF3 carbon). Anal. Calc. for C17H11F3O3S2Fe: C,
46.37; H, 2.52%. Found: C, 47.15; H, 2.77%. FAB
2.11. General procedure for synthesis of
metallothiosulfinate esters
HRMS (m/z) Calc. for [Mꢀ
/
H]ꢀ (C17H12O3F3S2Fe):
440.9529. Found: 440.9537.
In an adaptation of a literature procedure, [7] the
appropriate propargyl complex (one equivalent) and
2.11.3. Cyclopentadienyl(1-oxo-5-(1?-cyclohexenyl)-1,2-
dithiol-4-enyl)-dicarbonyliron (30)
4,5-diphenyl-3,6-dihydro-1,2-dithiin 1-oxide (26) (1.5ꢁ
1.8 equivalents) were dissolved in THF (50 ml). The
/
In a flame-dried flask under N2, cyclopentadienyl-3-
(1?-cyclohexenyl)-2-propynyldicarbonyliron (20) (0.331

72
E.E. Scott et al. / Journal of Organometallic Chemistry 673 (2003) 67ꢁ76
/
g, 1.12 mmol) and 26 (0.400 g, 1.40 mmol) were allowed
to react in THF (10 ml) as described above. The product
(30) (0.266 g, 0.930 mmol, 83%) was isolated following
Hz, 1H), 5.62 (d, Jꢃ16.0 Hz, 1H), 3.75 (s, 3H) 2.63 (s,
/
3H). 13C-NMR (CDCl3) 197.27, 161.56, 155.62, 138.26,
132.08, 131.88, 129.33, 128.39, 83.07, 52.77, 26.70.
HRMS (m/z) Calc. for [Mꢀ] (C13H12O5FS): 280.0405.
Found: 280.0399.
1
silica chromatography (pentane then ether). H-NMR
16 Hz,
(CDCl3) 5.85 (s, 1H), 4.95 (s, 5H), 4.8 (d, Jꢃ
/
1H), 4.35 (d, Jꢃ
/
16 Hz, 1H), 2.20 (m, 4H), 1.70 (m, 2H),
1.65 (m, 2H). 13C-NMR (CDCl3) 214.3, 214.0, 154.2,
133.9, 133.3, 129.0, 86.2, 59.3, 30.7, 26.1, 23.0, 21.9. IR
(CDCl3, cmꢄ1) 3170, 3025, 2985, 2940, 1645, 1550,
2.12.2. 4-(Carbomethoxy)-5-(4?-trifluoromethylphenyl)-
1,2-oxathiol-4-en-1-yl oxide (34)
1470, 1390, 1315, 1280, 1215, 1170, 1095, 1040 cmꢄ1
.
Cyclopentadienyl(1-oxo-3-(4?-trifluoromethylphenyl)-
1,2-oxathiol-3-enyl)dicarbonyliron (24) (0.400 g, 0.943
mmol) in CH2Cl2 (20 ml) was treated with ceric
ammonium nitrate (2.131 g, 3.887 mmol) in methanol
(30 ml) for 30 min. The crude product was purified by
chromatography on silica gel using 1:1 diethyl ether:-
pentane to yield the product as a pale yellow solid (34)
Anal. Calc. for C16H16O3S2Fe: C, 51.07; H, 4.29%.
Found: C, 50.62; H, 4.43%.
2.11.4. Cyclopentadienyl(1-oxo-5-(4?-methoxyphenyl)-
1,2-dithiol-4-enyl)-dicarbonyliron (31)
In a flame-dried flask under N2, cyclopentadienyl-3-
(4?-methoxyphenyl)-2-propynyl-dicarbonyliron
(21)
(0.012 g, 0.039 mmol, 4%). Rf: 0.21 (1:1 diethyl ether:
1
(0.132 g, 0.410 mmol) and 26 (0.125 g, 0.437 mmol)
were allowed to react in THF (10 ml) as described
above. The product (31) (0.101 g, 0.251 mmol, 57%) was
isolated following purification on silica eluting with
pentane). H-NMR (CDCl3) 7.72 (d, Jꢃ
/
8.5 Hz, 2H),
16.0 Hz, 1H), 5.63
16.0 Hz, 1H), 3.76 (s, 3H). 13C-NMR (CDCl3)
7.67 (d, Jꢃ
/
8.4 Hz, 2H), 5.94 (d, Jꢃ
/
(d, Jꢃ
/
161.48, 155.27, 131.91, 129.77 (overlap of carbons m
and p to CF3 by HMBC), 129.60, 125.14, 83.04, 52.65
(could not locate CF3 carbon). HRMS (m/z) Calc. for
1
pentane, then ether, then methanol. H-NMR (CDCl3)
7.31 (d, Jꢃ
/
7.5 Hz, 2H), 6.92 (d, Jꢃ/7.5 Hz, 2H), 4.94
(d, Jꢃ15.5, 1H), 4.70 (s, 5H), 4.49 (d, Jꢃ
/
/15.5, 1H),
[Mꢀ
H]ꢀ (C12H10O4F3S): 307.0252. Found: 307.0241.
/
3.81 (s, 3H). Anal. Calc. for C17H14S2O4Fe: C, 50.76; H,
3.51%. Found: C, 50.62; H, 3.54%.
2.13. General procedure for synthesis of thiosulfinate
esters
2.12. General procedure for synthesis of sulfinate esters
In an adaptation of a literature procedure, [2d] the
appropriate metallosulfinate ester was dissolved in
distilled CH2Cl2, and in a separate flask ceric ammoni-
um nitrate (four equivalents) was dissolved in HPLC
grade methanol. The ceric ammonium nitrate solution
was transferred to the metallosulfinate ester solution.
In an adaptation of a literature procedure, [7] the
appropriate metallothiosulfinate ester was dissolved in
distilled CH2Cl2 (6 ml) and HPLC grade methanol (16
ml). Ceric ammonium nitrate (four to eight equivalents)
was then added. The reaction was stirred at room
temperature for 15ꢁ
and extracted with ethyl acetate (3ꢂ
omethane (3ꢂ20 ml). The organic layer was dried over
/30 min. Water (20 ml) was added
The reaction was stirred at room temperature for 15ꢁ
min. Water (20 ml) was added and extracted with ethyl
acetate (3ꢂ20 ml). The organic layer was dried over
/
30
/20 ml) or dichlor-
/
/
MgSO4, and the solvent was removed under reduced
pressure.
MgSO4, the solvent was removed under reduced pres-
sure, and the resulting solid was vacuum dried. The
products were purified by cold column chromatography
on silica gel.
2.13.1. 4-Carbomethoxy-5-(4?-acetylphenyl)-1,2-dithiol-
4-en-1-yl oxide (35)
2.12.1. 4-(Carbomethoxy)-5-(4?-acetylphenyl)-1,2-
oxathiol-4-en-1-yl oxide (33)
Cyclopentadienyl(1-oxo-5-(4?-acetylphenyl)-1,2-
dithiol-4-enyl)dicarbonyliron (28) (0.124 g, 0.300 mmol)
and ceric ammonium nitrate (0.661 g, 1.206 mmol) were
stirred in CH2Cl2 and HPLC grade methanol for 30 min.
The organic layer was extracted with ethyl acetate. The
crude product was purified on a silica gel prep plate in
3:1 diethyl ether:pentane to yield a yellow oil (35) (0.021
g, 0.071 mmol, 24%), Rf: 0.27 (3:1 diethyl ether:pen-
Cyclopentadienyl(1-oxo-3-(4?-acetylphenyl)-1,2-ox-
athiol-3-enyl)dicarbonyliron (23) (0.768 g, 1.930 mmol)
in CH2Cl2 (50 ml) was treated with ceric ammonium
nitrate (4.163 g, 7.594 mmol) in methanol (75 ml) for 15
min. The crude product was purified by chromatogra-
phy on silica gel using 3:1 diethyl ether:pentane to yield
the product (33) as a pale yellow oil (0.043 g, 0.154
mmol, 8%). Rf: 0.41 (3:1 diethyl ether: pentane). IR
1
tane). IR (KBr) 1724, 1686 cmꢄ1. H-NMR (CDCl3)
7.99 (m, 2H), 7.54 (m, 2H), 5.17 (d, Jꢃ
4.74 (d, Jꢃ
17.9 Hz, 1H) 3.67 (s, 3H), 2.63 (s, 3H). 13C-
NMR (CDCl3) 197.33, 162.99, 157.83, 129.42, 128.71,
/17.9 Hz, 1H),
(KBr) 1729, 1687 cmꢄ1. 1H-NMR (CDCl3) 8.02 (d, Jꢃ
8.4 Hz, 2H), 7.63 (d, Jꢃ8.4 Hz, 2H), 5.93 (d, Jꢃ16.0
/
/
/
/

E.E. Scott et al. / Journal of Organometallic Chemistry 673 (2003) 67ꢁ
/
76
73
52.95, 46.54, 26.72. EI HRMS (m/z) Calc. for [Mꢀ]
(C13H12O4S2): 296.0177. Found: 296.0168.
1652.9, 1602.8, 1559.0, 1473.7, 1380.1, 1296.8, 1248.3,
1216.3, 1172.6, 1095.8 cmꢄ1
.
2.13.2. 4-Carbomethoxy-5-(4?-trifluoromethylphenyl)-
1,2-dithiol-4-en-1-yl oxide (36)
3. Results and discussion
Cyclopentadienyl(1-oxo-5-(4?-trifluoromethylphenyl)-
1,2-dithiol-4-enyl)dicarbonyliron (29) (0.065 g, 0.127
mmol) and ceric ammonium nitrate (0.488, 0.890
mmol) were stirred in CH2Cl2 and HPLC grade
methanol for 30 min as described above. The residue
was then dissolved in diethyl ether and filtered through a
cotton plug to remove cerium salts. The solvent was
removed under reduced pressure to yield a gum (36)
(0.039 g, 0.121 mmol, 95%). Rf: 0.23 (1:1 diethyl
3.1. Preparation of alkynyl complexes
All alkynyl complexes used were synthesized via
addition of a THF solution of the cyclopentadienyl
iron dicarbonyl (Fp) anion to a THF solution of the
appropriate 2-alkynyl tosylate. Many literature proce-
dures [8] typically use 2-alkynyl halides but the tosylates
are more convenient to work with since they are usually
solids and many times produce higher yields of propar-
gyl complex, presumably because they are less suscep-
tible than the halides to reduction by the
cyclopentadienyl iron dicarbonyl anion [2]. The cyclo-
hexenyl and 4-methoxyphenyl substituted alkynyl com-
plexes (20 and 21) used here have been reported
previously by our group [2b].
Cyclohexenyl and phenyl substituted sulfur electro-
philes were quite active in our initial anticarcinogenic
enzyme induction and anti HIV-1 screens [5]. Increasing
compound electrophilicity correlated with biological
activity, so we were interested in the preparation of a
halogen containing cyclohexene substituted propynyl
electrophile and the preparation of phenyl propynyl
electrophiles where the phenyl group was substituted
with an electron withdrawing group.
The chlorocyclohexenyl substituted alkynyl tosylate
(8) was prepared as described below. Ethynyl magne-
sium bromide was first added to 2-chlorocyclohexanone
(4). The tertiary alcohol produced (5) was isolated as a
1:1 mixture of diastereomers and no attempt was made
to separate them since the chiral centers were subse-
quently removed by dehydration using POCl3/pyridine.
The enyne (6) thus produced was deprotonated with
BuLi and condensed with paraformaldehyde to produce
propargyl alcohol (7). The alcohol (7) was converted to
the tosylate (8).
ether:pentane). IR (KBr) 1720 cmꢄ1
(CDCl3) 7.71 (d, Jꢃ8.23 Hz, 2H), 7.55 (d, Jꢃ
Hz, 2H), 5.17 (d, Jꢃ18.1 Hz, 1H), 4.74 (d, Jꢃ18.1 Hz,
.
1H-NMR
/
/
8.51
/
/
1H), 3.69 (s, 3H). 13C-NMR (CDCl3) 162.90, 157.49,
136.61, 134.11, 131.79, 129.47, 125.30, 122.52, 64.39,
52.75. EI HRMS (m/z) Calc. for [Mꢀ] (C12H9O3F3S2):
321.9945. Found: 321.9915.
2.13.3. 4-Carbomethoxy-5-(1?-cyclohexenyl)-1,2-dithiol-
4-en-1-yl oxide (37)
Cyclopentadienyl(1-oxo-5-(1?-cyclohexenyl)-1,2-
dithiol-4-enyl)dicarbonyliron (30) (0.118 g, 0.314 mmol)
was dissolved in CH2Cl2 (10 ml) and purged with CO
gas. Ceric ammonium nitrate (0.816 g, 1.57 mmol) was
dissolved in methanol (15ꢁ20 ml) and also purged with
/
CO gas and added to 30 as described above. The mixture
was allowed to warm to 25 8C and stirred for 2 h under a
balloon of CO. The product (37) (0.015 g, 0.058 mmol,
19%) was isolated following silica chromatography
using a jacketed column (0 8C) (pentane then 50:50
1
pentane:diethyl ether). H-NMR (CDCl3) 5.95 (s, 1H),
4.95 (d, Jꢃ
/
15 Hz, 1H), 4.45 (d, Jꢃ15 Hz, 1H), 3.75 (s,
/
3H), 2.11 (m, 4H), 1.68 (m, 2H), 1.58 (m, 2H). EI
HRMS (m/z) Calc. for [Mꢀ] (C11H14O3S2): 258.0384.
Found: 258.0388.
2.13.4. 4-Carbomethoxy-5-(4?-methoxyphenyl)-1,2-
dithiol-4-en-1-yl oxide (38)
Cyclopentadienyl(1-oxo-5-(4?-methoxyphenyl)-1,2-
dithiol-4-enyl)dicarbonyliron (31) (0.030 g, 0.0746
mmol) was dissolved in CH2Cl2 (10 ml) and purged
with CO gas. Ceric ammonium nitrate (0.327 g, 0.596
Substituted phenyl propargyl alcohols (12ꢁ
prepared by Pd/Cu catalyzed cross-coupling of the
appropriate aromatic iodide (9ꢁ10) with propargyl
alcohol (11) [2d]. The substituted propargyl alcohols
(12ꢁ13) were then converted to tosylates (14ꢁ15) in high
yield [2d].
These substituted alkynyl tosylates (8, 14, 15) were
then also treated with the cyclopentadienyl iron dicar-
bonyl anion (16) (Fp-) to yield the iron alkynyl
/
13) were
/
mmol) was dissolved in methanol (15ꢁ/20 ml) and also
/
/
purged with CO gas and added to 31 as described above.
The mixture was allowed to warm to room temperature
and stirred for 2 h under a balloon of CO. The product
(38) (0.013 g, 0.0457 mmol, 61%) was purified on silica
with 50:50 pentane:diethyl ether. 1H-NMR (CDCl3)
complexes (17ꢁ19) using a procedure analogous to one
/
7.49 (d, Jꢃ
(d, Jꢃ15 Hz, 1H), 4.28 (d, Jꢃ
IR (CDCl3, cmꢄ1) 3155.1, 2985.4, 2901.8, 1734.0,
/
7.5 Hz, 2H), 6.89 (d, Jꢃ
/
7.5 Hz, 2H), 4.80
we [2d] and others [8] have reported previously. Alkynyl
complexes (20 and 21) also used for cycloadditions here
were reported previously [2d].
/
/15 Hz, 1H), 3.78 (s, 6H).

74
E.E. Scott et al. / Journal of Organometallic Chemistry 673 (2003) 67ꢁ76
/
3.2. Cycloaddition reactions of alkynyl complexes with
sulfur dioxide and disulfur monoxide and subsequent
demetallation reactions of the cycloadducts
dioxide were performed under conditions analogous to
our prior work [2d]. These reactions are proposed to
occur through a stepwise cyclization process involving
an allene complex (22) [8]. The 4?-acetylphenyl substi-
tuted complex (23) was prepared in high yield (93%) and
the 4?-trifluoromethylphenyl substituted complex (24)
was prepared in good yield (51%). The reduction in yield
3.2.1. Cycloadditions with sulfur dioxide
The transition-metal mediated [3ꢀ
of the iron alkynyl complexes (17ꢁ
/
2] cycloadditions
19) with sulfur
/

E.E. Scott et al. / Journal of Organometallic Chemistry 673 (2003) 67ꢁ
/
76
75
here is presumably due to the presence of the strongly
electron withdrawing CF3 group which may act to slow
cyclization. The 2?-chloro-1?-cyclohexenyl complex (17)
cyclized in surprisingly poor yield (20%) to produce 25.
The 1?-cyclohexenyl complex (20) had cyclized with SO2
in 76% yield previously [2d] so the presence of the chloro
group has had a large negative steric and/or electronic
effect on the outcome of this cyclization. Diastereotopic
1H-NMR methylene protons a to oxygen and diaster-
reaction would presumably generate an intermediate
(27) analogous to 22 which cyclizes to produce the
isolated dithiolene oxide complexes (28ꢁ31) in good
/
yield. 2,3-Diphenyl-1,3-butadiene (32) can be recovered
and reused in the preparation of 26 if desired. The
oxathiolene oxide complexes (28ꢁ31) are surprisingly
/
polar, requiring highly polar mobile phases for elution
from silica, and have spectroscopic characteristics
analogous to those described previously for 23ꢁ25.
/
eotopic 13C-NMR metal carbonyls are characteristic
spectroscopic signatures of all of these oxathiolene oxide
3.2.3. Demetallation reactions
Organic compounds for biological testing were iso-
lated by oxidative carbonylation of the iron substituted
complexes (23ꢁ25).
/
3.2.2. Cycloadditions with disulfur monoxide
cycloadducts. Oxidative carbonylation adds a polar
electron withdrawing group to the heterocycle and our
earlier studies had shown this to be advantageous [5]. In
general, we found oxidative carbonylation of oxathio-
We have previously reported the preparation and use
of 4,5-diphenyl-3,6-dihydro-1,2-dithiin-1-oxide (26) as a
source of disulfur monoxide [6]. This compound (26)
was prepared for use in these studies with slight
modifications as described in Section 2. Disulfur mon-
oxide source (26) is quite stable thermally and does not
spontaneously undergo retro Diels-Alder reaction to
liberate disulfur monoxide under the conditions used for
lene oxide containing complexes (23ꢁ25) to be unsatis-
/
factory, whereas yields for oxidative carbonylation of
dithiolene oxides were much better. Oxathiolene oxides
(33) and (34) from complexes (23) and (24) could only be
isolated in 8 and 4% yields, respectively. Attempts to
demetallate the chlorocyclohexenyl complex (25) using
Ce(IV) for oxidative carbonylation or Me2CuLi for
reductive methylation [2] produced only small amounts
of organic cycloadducts which could not be obtained in
the [3ꢀ
proposed that these transition-metal alkynyl complexes
(18ꢁ21) act as nucleophiles to drive a nucleophile
induced electrocyclic ring opening reaction of 26. This
/2] cycloadditions reported here. Rather, we have
/

76
E.E. Scott et al. / Journal of Organometallic Chemistry 673 (2003) 67ꢁ76
/
quantities sufficient for characterization. We encoun-
tered some yield reductions in demetallations of ox-
athiolene oxides that we had reported previously [2d]
but nothing this dramatic. The presence of the electron
withdrawing substituents in these heterocycles must
greatly accelerate competitive ring opening reactions to
which these heterocycles are susceptible [9]. Yields for
References
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217;
the production of dithiolene oxides (35ꢁ38) were gen-
/
erally much higher and we attribute this to their reduced
susceptibility to ring opening in polar protic solvents.
(b) A.L. Hurley, M.E. Welker, C.S. Day, J. Organometal. Chem.
598 (2000) 150;
(c) B.L. Hayes, M.E. Welker, Organometallics 17 (1998)
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4. Summary
In summary, we have extended metal alkynyl [3ꢀ2]
cyclization reactions with SO2 and S2O to produce new
iron substituted 1,2-oxathiolene-2-oxides and 1,2-dithio-
/
lene oxides. The [3ꢀ2] cycloaddition reactions of these
/
metal substituted alkynyl complexes are not adversely
affected by the presence of the electron withdrawing
groups found in many of the alkynyl complexes we used.
The iron substituted heterocycles can be demetallated
but the presence of the electron withdrawing substitu-
ents was found to be extremely detrimental to the
oxathiolene oxide demetallations. We will report on
the biological activities of these new heterocycles in due
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Acknowledgements
We thank the NIH NIGMS for their support. Low
resolution mass spectra were obtained on instruments
purchased with the partial support of NSF and the NC
Biotechnology Center. The Duke University Center for
Mass Spectrometry performed high resolution mass
spectral analyses.
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