Palladium-catalyzed reaction of propargyl nucleophiles with α-sulfonyl α,β-unsaturated ketones: A single-step synthesis of furo[3,4-c] heterocyclic derivatives

Full text of DOI:10.1021/jo991817h

J . Org. Chem. 2000, 65, 3223-3226
3223
Sch em e 1
P a lla d iu m -Ca ta lyzed Rea ction of P r op a r gyl
Nu cleop h iles w ith r-Su lfon yl
r,â-Un sa tu r a ted Keton es: A Sin gle-Step
Syn th esis of F u r o[3,4-c] Heter ocyclic
Der iva tives
Nuno Monteiro and Genevie`ve Balme*
Laboratoire de Chimie Organique 1, Associe´ au CNRS,
Universite´ Claude Bernard, CPE, 43 Boulevard du 11
Novembre 1918, 69622 Villeurbanne Ce´dex, France
Received November 23, 1999
The search for new methodologies that allow the rapid
construction of polycyclic structures in a single operation
is, today, an important challenge for synthetic organic
chemists.1 In this area, reactive transition metal carbene
complexes, generated in catalytic reactions, have emerged
as extremely valuable intermediate species in the design
of consecutive cyclization processes.2 These catalytic
metal carbenes have usually been generated by exposure
of R-diazocarbonyl compounds to metal complexes or
salts.3 Like free carbenes, they have been involved in a
wide range of synthetic transformations, such as self-
dimerization, cyclopropanation, and various insertion
reactions. Coordination of the carbene with the metal
tempers its reactivity and imparts greater selectivity to
the reaction. Remarkably, the observed selectivities may
be strongly influenced by the nature of the coordinated
metal complex.4
In recent years, our research efforts have been con-
cerned with the elaboration of tandem or cascade reac-
tions5 involving palladium-mediated Wacker-type cycliza-
tion processes, which were devised in our laboratory.6
Recently, a new methodology based on a Michael addi-
tion-carbocyclization sequence has permitted the sys-
tematic formation of highly functionalized tetrahydro-
furans and pyrrolidines simply through the joining of two
readily available components, a propargylic alcohol (or
amine) as the Michael donor and an arylidene (or
alkylidene) malonate as the Michael acceptor (Scheme
1, eq 1).7,8 A study of the synthetic utility of sulfone-based
activated olefins as versatile multi-coupling reagents for
the construction of more elaborate heterocycles was then
undertaken. Previous work9 suggested that the particular
ability of the sulfonyl group to act as a leaving group may
change the reaction pathway by generating carbene
palladium complexes. These metal-stabilized carbenes
may then be involved in further transformations, thus
imparting increased complexity to the reaction products
(Scheme 1, eq 2).10
Of particular interest was the design of selective
intramolecular processes aimed at the construction of
polycyclic systems. The possibility of directing our strat-
egy toward the synthesis of furan-based bicyclic com-
pounds was first investigated with this aim. Furans are
common substructures in many natural products that
exhibit interesting biological activities and can be found
in numerous commercial products, including pharma-
ceuticals, fragrances, and dyes.11 They are also valuable
building blocks in organic synthesis.11,12 The 6π-electro-
cyclization of alkenone carbenes13 is an interesting
method for synthesizing furans.14 It is of particular
importance in the preparation of 3,4-disubstituted furans,
which are rather difficult to obtain by other means.14,15
It was reasoned that, if alkenone carbenes could be
generated by applying the tandem Michael addition-
(9) Monteiro, N.; Gore, J .; Van Hemelryck, B.; Balme, G. Synlett
1994, 447.
* To whom correspondence should be addressed. E-mail: balme@
univ-lyon1.fr.
(1) (a) Posner, G. H. Chem. Rev. 1986, 86, 831. (b) Special issues:
Chem. Rev. 1996, 96 (1); Tetrahedron 1996, 52 (35).
(2) Padwa, A.; Weingarten, M. D. Chem. Rev. 1996, 96, 223.
(3) Rhodium complexes have been the most widely used. Copper,
palladium, and cobalt catalysts have also been utilized, but to a lesser
extent. For reviews, see: Adams, J .; Spero, D. M. Tetrahedron 1991,
47, 1765. Padwa, A.; Krumpe, K. E. Tetrahedron 1992, 48, 5385.
(4) See, for example: Hoye, T. R.; Dinsmore, C. J .; J ohnson, D. S.;
Korkowski, P. F. J . Org. Chem. 1990, 55, 4518.
(5) For reviews, see: (a) Tietze, L. F.; Beifuss, U. Angew. Chem.,
Int. Ed. Engl. 1993, 32, 131. (b) Ho, T. L. Tandem Organic Reactions;
J ohn Wiley & Sons: New York, 1992.
(6) For a description of the basic cyclization reactions, see: Bouyssi,
D.; Balme, G.; Fournet, G.; Monteiro, N.; Gore, J . Tetrahedron Lett.
1991, 32, 1641. Monteiro, N.; Balme, G.; Gore, J . Tetrahedron 1992,
48, 10114. For recent applications to the construction of polycyclic
systems, see: Coudanne, I.; Balme, G. Synlett 1998, 998 and references
therein.
(7) Marat, X.; Monteiro, N.; Balme, G. Synlett 1997, 845. Clique,
B.; Monteiro, N.; Balme, G. Tetrahedron Lett. 1999, 40, 1301.
(8) A related one-pot, three-component reaction had already been
reported by us: Cavicchioli, M.; Sixdenier, E.; Derrey, A.; Bouyssi, D.;
Balme, G. Tetrahedron Lett. 1997, 38, 1763.
(10) Palladium-mediated reactions in which the intermediacy of a
catalytic palladium carbene has been suggested are scarce. See: Tsuji,
J .; Watanabe, H.; Minami, I.; Shimizu, I. J . Am. Chem. Soc. 1985, 107,
2196. Trost, B. M.; Schneider, S. J . Am. Chem. Soc. 1989, 111, 4430.
Trost, B. M.; Hashmi, A. S. K. Angew. Chem., Int. Ed. Engl. 1993, 32,
1085. Trost, B. M.; Hashmi, A. S. K. J . Am. Chem. Soc. 1994, 116,
2183. Busacca, C. A.; Swestock, J .; J ohnson, R. E.; Bailey, T. R.; Musza,
L.; Rodger, C. A. J . Org. Chem. 1994, 59, 7553. Farina, V.; Hossain,
M. A. Tetrahedron Lett. 1996, 37, 6997. Hashmi, A. S. K.; Ruppert, T.
L.; Kno¨fel, T.; Bats, J . W. J . Org. Chem. 1997, 62, 7295. Schweizer,
S.; Song, Z.-Z.; Meyer, F. E.; Parsons, P. J .; de Meijere, A. Angew.
Chem., Int. Ed. Engl. 1999, 38, 1452. Sierra, M. A.; Manchen˜o, M. J .;
Saez, E.; del Amo, J . C. J . Am. Chem. Soc. 1998, 120, 6812.
(11) Donnelly, D. M. X.; Meegan, M. J . In Comprehensive Hetero-
cyclic Chemistry; Katritzky, A., Reese, C. W., Eds.; Pergamon Press:
Oxford, 1984; Vol. 4, Part 3. Lipshutz, B. H. Chem. Rev. 1986, 86, 795.
(12) Kappe, C. O.; Murphree, S. S.; Padwa, A. Tetrahedron 1997,
53, 14179.
(13) Padwa, A. Rearrangement in Ground and Excited States;
DeMayo, P., Ed.; Academic Press: New York, 1980; Vol. 3, p 501.
(14) For a recent review on the synthesis of furans, see: Hou, X. L.;
Cheung, H. Y.; Hon, T. Y.; Kwan, P. L.; Lo, T. H.; Tong, S. Y.; Wong,
H. N. C. Tetrahedron 1998, 54, 1955.
(15) Ye, X.-S.; Yu, P.; Wong, H. N. C. Liebiegs Ann./ Recl. 1997, 459.
10.1021/jo991817h CCC: $19.00 © 2000 American Chemical Society
Published on Web 04/19/2000

3224 J . Org. Chem., Vol. 65, No. 10, 2000
Notes
Ta ble 1. Rea ction betw een r-P h en ylsu lfon yl Ch a lcon e
(2a ) a n d P r op a r gyl Alcoh ol w ith Differ en t Ca ta lysts in
Va r iou s Solven tsa
Sch em e 2. Retr osyn th esis
entry
catalyst
solvent T (°C) time (h) yield (%)
b
1
2
3
4
5
6
7
8
9
Pd(OAc)2(PPh3)2 THF
Pd(OAc)2(PPh3)2 THF
20
70
70
70
70
70
80
100
85
100
-
4
3
-
52
57
27
18
15
PdCl2(PPh3)2
PdCl2(dppf)
[PdCl(allyl)]2
Pd(PPh3)4
THF
THF
THF
THF
4c
4c
4c
PdCl2(CH3CN)2
PdCl2(PPh3)2
PdCl2(PPh3)2
PdCl2(PPh3)2
CH3CN
dioxane
DME
DMF
5c,d
3.5
5
9e
51e
49e
17e
10
4c
a
t
Reactions conducted on half-millimolar scale using BuOK as
b
base. Proceeded slowly. Only small amounts of the expected
carbocyclization to arylidene â-ketosulfones, then internal
trapping of the carbene by the carbonyl oxygen would
produce a variety of furo[3,4-c]furans and furo[3,4-c]-
pyrroles (Scheme 2).16 The successful execution of this
strategy is reported.
product were formed after prolonged reaction times (>24 h). c The
reaction ceased after less time than the time alloted. Small
amounts of both the Michael acceptor and the Michael adduct were
d
recovered from the reaction. Unidentified side products were also
formed. e Yields were not improved at lower temperatures.
The reaction of propargyl alcohol 1a and R-phenylsul-
fonyl chalcone 2a was the first to be investigated. From
previous work, it was thought that a stoichiometric
Ta ble 2. In flu en ce of th e Na tu r e of th e Su lfon yl Gr ou p
on th e Rea ction betw een r-Su lfon yl Ch a lcon es a n d
P r op a r gyl Alcoh ola
t
amount of BuOK would be required as the base if the
entry
sulfonyl
yield (%)
recovered M. A.b
expected reaction were to take place efficiently.9 The
desired furofuran 3a was obtained by simple treatment
of a solution of 1a (1.5 equiv) with the chosen base (1.1
equiv) and subsequent addition of the Michael acceptor
2a together with a catalytic amount (5 mol %) of a
palladium complex (eq 3).
1c
2
3
PhSO2
MeSO2
tBuSO2
CF3SO2
57
10
<5
47
trace
32
43
4
16
a
Reactions conducted for 3 h in refluxing THF using PdCl2-
(PPh3)2 as catalyst. MA ) Michael acceptor. c Result from Table
1, entry 3.
b
than alkyl (or aryl) sulfones. Such features would be
expected to favor the initial Michael addition, as well as
the expulsion of the sulfonyl group. Reaction did indeed
occur, leading to the expected furofuran, albeit in a yield
lower than that obtained with a phenylsulfonyl group
(Table 2, entry 4). The lower reactivity observed in this
case could be due to a better stabilization of the enolate
intermediate, which would be less prone to cyclization.
The scope of the reaction was thus investigated on
phenylsulfonyl derivatives. The results are summarized
in Table 3. A range of furofurans were obtained in
moderate to good yields. The reaction tolerates various
substitution patterns of the R,â-unsaturated ketones,
both alkyl and aryl substituents giving comparable
results (Table 3, entries 1-7). Remarkably, even hin-
dered nucleophiles participate efficiently (Table 3, entry
8). Finally, the methodology was successfully extended
to the synthesis of furopyrroles (Table 3, entries 9 and
10).
According to our mechanistic understanding of the
reaction, the arylidene â-ketosulfone behaves here as a
multi-coupling reagent. It acts initially as a Michael
acceptor and then as a nucleophilic ionic center. The
cyclization is believed to be promoted by a σ-alkynyl
palladium(II) (or IV) hydride species (4) resulting from
insertion of the metal into the C-H bond of the terminal
acetylene (Scheme 3).17 This would lead to an intermedi-
ate species 5. At this stage, the well-known ability of the
sulfonyl moiety to act as a leaving group would trigger
the generation of a palladium carbene (6) via what
appears to be a unique example of sulfinic acid elimina-
tion. As illustrated in the first catalytic cycle (Scheme
Poor to moderate yields were obtained, depending on the
nature of the catalyst and solvent used (Table 1). The
best results were obtained with Pd(PPh3)2X2 (X ) Cl or
OAc) as the catalyst in ethereal solvents under reflux
(Table 1, entries 2, 3, 8, and 9). Under these conditions,
essentially complete and clean reactions were observed.
Polymerization of the Michael acceptor would possibly
account for the moderate yields obtained under such
conditions. However, substantial amounts of this mate-
rial, together with small quantities of the open-type
molecule resulting from simple 1,4-conjugate addition,
were recovered when the reaction did not proceed ef-
ficiently (Table 1, entries 4-7 and 10).
Attention was then focused on the reactivity of various
Michael acceptors that differed in the nature of the
substituent on the sulfone in order to probe possible
electronic or steric effects in the preceding reaction.
Reactions were conducted under the above optimized
conditions (Table 1, entry 3). Not surprisingly, substitut-
ing the phenyl moiety for electron-donating groups such
as methyl or tert-butyl resulted in a dramatic decrease
in the rate of the reaction, and large amounts of starting
material were recovered from the reaction mixture (Table
2, entries 2 and 3). The trifluorosulfonyl moiety is a better
electron-withdrawing group and a better leaving group
(16) Analogous furans have previously been synthesized by metal-
mediated reactions of diazo compounds: Wee, A. G. H.; Liu, B.; Zhang,
L. J . Org. Chem. 1992, 57, 4404. Padwa, A.; Kinder, F. R. J . Org. Chem.
1993, 58, 21. Gettwert, V.; Krebs, F.; Maas, G. Eur. J . Org. Chem.
1999, 1213, 3. See also ref 4.
(17) Trost, B. M.; Sorum, M. T.; Chan, C.; Harms, A. E.; Ru¨ther, G.
J . Am. Chem. Soc. 1997, 119, 698.

Notes
J . Org. Chem., Vol. 65, No. 10, 2000 3225
Ta ble 3. P a lla d iu m -Ca ta lyzed Cycliza tion of P r op a r gyl Nu cleop h iles w ith r-Su lfon yl-r,â-u n sa tu r a ted Keton esa
a
b
Reactions conducted on half-millimolar scale in refluxing THF. Ratio of 1:2:tBuOK:PdCl2(PPh3)2 ) 1.5:1:1.2:0.05. Yields refer to
pure isolated products.
Sch em e 3
3), the first cyclization reaction would require only
catalytic quantities of tBuOK in order to proceed, as this
base should be continuously regenerated during this
process. It seems reasonable, therefore, to suggest that
the base intervenes also in the second cyclization reac-
tion, possibly by abstracting the hydrogen of the inter-
mediate Pd(II or IV)-H species to form the palladium
carbene. This would produce potassium sulfinate as a
side product, hence the need for stoichiometric quantities
of base. The electrophilic vinylidene palladium 6 is then
attacked by the oxygen of the adjacent ketone, leading
to 3 in a 6π-electrocyclization process at the end of which
the catalyst is recycled.
In conclusion, an efficient single-step synthesis of a
new class of furofurans and furopyrroles from the easily
available propargyl alcohols (or amines) and arylidene
(or alkylidene) â-ketosulfones has been developed. Fur-
ther investigations will focus on the potential utility of

3226 J . Org. Chem., Vol. 65, No. 10, 2000
Notes
8.5, 2H), 7.39 (m, 2H), 7.25 (m, 2H), 7.12 (s, 1H), 5.17 (d, J )
3.0, 1H), 4.82 (s, 2H), 1.85-1.00 (M, 10H); 13C NMR (CDCl3, 50
MHz) δ 143.2, 133.1, 130.8, 129.9, 128.7, 128.4, 127.1, 124.7,
82.4, 65.4, 43.1, 30.4, 26.7, 26.6, 26.4, 26.1. Anal. Calcd for
C18H20O2: C, 80.56; H, 7.51. Found: C, 80.34; H, 7.47.
this reaction in natural product synthesis, in particular
syntheses of lignans. When considering the diversity of
reactions that commonly involve electrophilic carbenes,
we believe that the chemistry described herein will be
useful for the construction of more complex molecules.
1-P h en yl-6-isop r op yl-1H,3H-fu r o[3,4-c]fu r a n (3e): 60%;
1
liquid; H NMR (CDCl3, 300 MHz) δ 7.34 (m, 5H), 7.05 (s, 1H),
5.93 (s, 1H), 4.96 (d, 2J ) 11.4, 1H), 4.85 (d, 2J ) 11.4, 1H), 2.78
(sept, J ) 7.0, 1H), 1.03 (d, J ) 7.0, 3H), 1.01 (d, J ) 7.0, 3H);
13C NMR (CDCl3, 50 MHz) δ 150.8, 141.6, 131.4, 128.6, 128.4,
128.3, 127.6, 126.7, 79.2, 64.9, 27.6, 21.1, 20.6. HRMS m/z calcd
for C15H16O2, 228.1150; found, 228.1140.
Exp er im en ta l Section
Gen er a l Meth od s. Unless otherwise noted, all reactions were
carried out under a nitrogen atmosphere in oven-dried glassware
using standard syringe, cannula, and septa techniques. Com-
mercial reagents and solvents were used as purchased, except
for tetrahydrofuran, which was distilled over calcium hydride.
Thin-layer chromatography was carried out on Merck silica 60/
F-254 aluminum-backed plates. Flash chromatography was
performed using Merck silica gel 60 (40-63 µm). Melting points
are uncorrected. NMR spectra were recorded in CDCl3. Chemical
shifts (δ) are quoted in parts per million. J values are given in
hertz.
Gen er a l P r oced u r e for th e Cycliza tion of r-P h en ylsu l-
fon yl-r,â-Un sa tu r a ted Keton es w ith P r op a r gyl Nu cleo-
p h iles. To potassium tert-butoxide (60 mg, 0.6 mmol) in THF
(1.5 mL) was added the propargyl alcohol or amine (0.75 mmol),
and the resulting mixture was stirred at room temperature for
10 min. The Michael acceptor (0.5 mmol) and PdCl2(PPh3)2 (17.5
mg, 0.025 mmol) were then successively added, and the reaction
mixture was heated under reflux for 3 h. The reaction was then
quenched with a saturated aqueous solution of ammonium
chloride, and the organic material was extracted with ethyl
acetate. The organic layer was dried (Na2SO4) and concentrated
in vacuo. The residue was purified by chromatography on silica
gel (eluent, ethyl acetate/petroleum ether).
1-P h en yl-6-(4-n itr o)p h en yl-1H,3H-fu r o[3,4-c]fu r a n (3f):
1
47%; solid; mp 139-141 °C; H NMR (CDCl3, 300 MHz) δ 8.05
(d, J ) 8.8, 2H), 7.45-7.35 (m, 8H), 6.16 (s, 1H), 5.05 (d, 2J )
2
11.4, 1H), 4.93 (d, J ) 11.4, 1H); 13C NMR (CDCl3, 75 MHz) δ
146.1, 141.9, 138.9, 135.5, 134.2, 133.0, 132.2, 129.0, 127.9, 124.5,
124.1, 80.0, 65.0. Anal. Calcd for C18H13NO4: C, 70.35; H, 4.26;
N, 4.56. Found: C, 70.46; H, 4.41; N, 4.56.
1-P h en yl-6-(4-m et h oxy)p h en yl-1H ,3H -fu r o[3,4-c]fu r a n
(3g): 45%; solid; mp 60-62 °C; 1H NMR (CDCl3, 300 MHz) δ
7.55-7.15 (m, 8H), 6.79 (d, J ) 8.8, 2H), 6.14 (s, 1H), 5.00 (d, 2J
) 11.4, 1H), 4.93 (d, 2J ) 11.4, 1H), 3.75 (s, 3H); 13C NMR
(CDCl3, 50 MHz) δ 158.8, 144.0, 139.9, 133.2, 129.2, 128.8, 128.6,
127.9, 126.9, 125.8, 123.2, 114.1, 79.8, 64.9, 55.3. Anal. Calcd
for C19H16O3: C, 78.06; H, 5.52. Found: C, 78.33; H, 5.30.
1,6-Dip h en yl-7,7-d im eth yl-1H,3H-fu r o[3,4-c]fu r a n (3h ):
1
50%; solid; mp 70-72 °C; H NMR (CDCl3, 300 MHz) δ 7.45-
7.05 (m, 11H), 6.16 (s, 1H), 1.61 (s, 6H); 13C NMR (CDCl3, 50
MHz) δ 143.5, 141.7, 140.2, 130.1, 129.3, 128.7, 128.5, 128.4,
128.3, 127.0, 124.4, 79.9, 79.0, 29.8, 29.4. Anal. Calcd for
C20H18O2: C, 82.73; H, 6.25. Found: C, 82.49; H, 6.18.
N-Meth yl-1,6-diph en yl-1H,3H-fu r o[3,4-c]pyr r ole (3i): 54%;
solid; mp 78-80 °C; 1H NMR (CDCl3, 300 MHz) δ 7.35-7.25
(m, 5H), 7.22 (s, 1H), 7.15-7.05 (m, 5H), 4.62 (s, 1H), 4.16 (d, 2J
) 12.1, 1H), 3.62 (d, 2J ) 12.1, 1H), 2.45 (s, 3H); 13C NMR
(CDCl3, 50 MHz) δ 144.1, 140.3, 131.2, 130.7, 130.4, 129.6, 129.0,
128.6, 128.2, 128.0, 126.7, 124.6, 69.3, 52.4, 39.7. Anal. Calcd
for C19H17NO: C, 82.88; H, 6.22; N, 5.09. Found: C, 82.48; H,
6.29; N, 4.89.
N-Ben zyl-1,6-diph en yl-1H,3H-fu r o[3,4-c]pyr r ole (3j): 52%;
solid; mp 123-125 °C; 1H NMR (CDCl3, 300 MHz) δ 7.45-7.05
(m, 16H), 4.93 (s, 1H), 3.97 (d, 2J ) 12.1, 1H), 3.91 (d, 2J ) 13.2,
1H), 3.62 (d, 2J ) 13.2, 1H), 3.58 (d, 2J ) 12.1, 1H); 13C NMR
(CDCl3, 75 MHz) δ 144.2, 140.9, 139.3, 131.1, 130.9, 130.5, 129.7,
129.3, 128.7, 128.5, 128.3, 128.2, 128.0, 127.0, 126.7, 124.6, 67.2,
56.8, 49.6. HRMS m/z calcd for C25H21NO, 351.1623; found,
351.1622.
1,6-Dip h en yl-1H,3H-fu r o[3,4-c]fu r a n (3a ): 57%; solid; mp
96-98 °C; 1H NMR (CDCl3, 300 MHz) δ 7.45-7.10 (m, 11H),
2
2
6.16 (s, 1H), 5.02 (d, J ) 11.4, 1H), 4.92 (d, J ) 11.4, 1H); 13
C
NMR (CDCl3, 50 MHz) δ 144.0, 139.7, 133.3, 130.1, 129.9, 128.8,
128.7, 128.6, 127.9, 127.2, 124.4, 79.9, 64.9. HRMS m/z calcd
for C18H14O2, 262.0994; found, 262.0982.
1-(3,4-Dioxym eth ylen e)p h en yl-6-p h en yl-1H,3H-fu r o[3,4-
c]fu r a n (3b): 52%; solid; mp 143-145 °C; 1H NMR (CDCl3, 300
MHz) δ 7.35-7.13 (m, 6H), 6.92 (dd, J ) 8.1 and 1.5, 1H), 6.81
(d, J ) 1.5, 1H), 6.78 (d, J ) 8.1, 1H), 6.07 (s, 1H), 5.93 (bs, 1H),
5.92 (bs, 1H), 4.99 (d, 2J ) 11.8, 1H), 4.88 (d, 2J ) 11.8, 1H); 13
C
NMR (CDCl3, 50 MHz) δ 148.2, 148.0, 143.9, 133.8, 133.3, 130.1,
129.9, 128.6, 127.2, 124.4, 121.8, 108.2, 108.1, 101.2, 79.8, 64.7.
Anal. Calcd for C19H14O4: C, 74.50; H, 4.61. Found: C, 74.77;
H, 4.57.
1-(4-Flu or o)ph en yl-6-ph en yl-1H,3H-fu r o[3,4-c]fu r an (3c):
1
58%; solid; mp 73-75 °C; H NMR (CDCl3, 300 MHz) δ 7.40-
7.00 (m, 10H), 6.16 (s, 1H), 5.00 (d, 2J ) 11.4, 1H), 4.90 (d, 2J )
11.4, 1H); 13C NMR (CDCl3, 50 MHz) δ 165.4, 160.4, 144.0, 135.6,
135.5, 133.2, 130.0, 129.9, 129.8, 129.7, 128.6, 128.5, 127.3, 124.4,
115.9, 115.5, 79.2, 64.8. Anal. Calcd for C18H13FO2: C, 77.13; H,
4.67. Found: C, 76.83; H, 4.37.
Su p p or tin g In for m a tion Ava ila ble: General procedure
and characterization for R-sulfonyl R,â-unsaturated ketones
and copies of 1H NMR spectra for compounds 3a -3j. This
material is available free of charge via the Internet at
http://pubs.acs.org.
1-Cycloh exyl-6-p h en yl-1H,3H-fu r o[3,4-c]fu r a n (3d ): 42%;
1
solid; mp 81-83 °C; H NMR (CDCl3, 300 MHz) δ 7.55 (d, J )
J O991817H