Synthesis of 4-iodo-3-furanones utilizing electrophile-induced tandem cyclization/1,2-migration reactions

Article abstract of DOI:10.1021/jo070695n

(Chemical Equation Presented) Two protocols for the construction of 4-iodo-3-furanones through a sequence consisting of cyclization and Immigration of 2-alkynyl-2-silyloxy carbonyl compounds were developed. In one, electrophilic cyclization is directly in

Full text of DOI:10.1021/jo070695n

substituted R′-hydroxy 1,3-diketones,8 as pioneered by the work
of Smith and co-workers.9 While there are numerous alternative
strategies for 3(2H)-furanone synthesis,10 a particularly effective
approach is through transition metal-catalyzed 5-endo hetero-
cyclization of an alkenyl alcohol.11 In 2006, we reported the
construction of 3(2H)-furanones from 2-alkynyl-2-hydroxy
carbonyl compounds12 using catalytic amounts of PtCl2 as a
proton equivalent.13,14 This tandem reaction consisting of
heterocyclization and 1,2-migration is believed to proceed via
a cyclic oxonium ion intermediate.15 For example, reaction of
alkynyl carbonyl compound 1 with 5 mol % of PtCl2 in toluene
at 80 °C produced the 3(2H)-furanone 2 in good yield (93%)
(eq 1). Despite the synthetic value of this reaction, 3(2H)-
Synthesis of 4-Iodo-3-furanones Utilizing
Electrophile-Induced Tandem Cyclization/
1,2-Migration Reactions
Benedikt Crone and Stefan F. Kirsch*
Department Chemie, Technische UniVersita¨t Mu¨nchen,
Lichtenbergstrasse 4, D-85747 Garching, Germany
stefan.kirsch@ch.tum.de
ReceiVed April 4, 2007
furanones bearing an additional substituent at C4 are not
accessible. A novel electrophile-induced tandem cyclization/
1,2-migration reaction of 2-alkynyl-2-silyloxy carbonyl com-
pounds is disclosed herein, which produces fully substituted
3(2H)-furanones containing an iodo substituent at C4. We also
report a AuCl3-catalyzed modification to enhance the scope of
accessible 4-iodo-3-furanones.
Two protocols for the construction of 4-iodo-3-furanones
through a sequence consisting of cyclization and 1,2-
migration of 2-alkynyl-2-silyloxy carbonyl compounds were
developed. In one, electrophilic cyclization is directly induced
by N-iodosuccinimide (NIS). In the second less limited
variant, AuCl3 catalyzes the tandem reaction in the presence
of NIS to provide highly substituted heterocycles in moderate
to excellent yields.
As an alternative to transition metal-catalyzed cyclizations
of unsaturated frameworks,16 electrophilic cyclizations have been
frequently utilized to construct a wide range of carbocycles and
(8) For synthetic equivalents of R′-hydroxy-1,3-diketones, see inter
alia: (a) Chimichi, S.; Boccalini, M.; Cosimelli, B.; Dall’Acqua, F.; Viola,
G. Tetrahedron 2003, 59, 5215. (b) Inoue, Y.; Ohuchi, K.; Imaizumi, S.
Tetrahedron Lett. 1988, 29, 5941. (c) Curran, D. P.; Singleton, D. H.
Tetrahedron Lett. 1983, 24, 2079.
(9) Smith, A. B., III; Levenberg, P. A.; Jerris, P. J.; Scarborough, R.
M., Jr.; Wovkulich, P. M. J. Am. Chem. Soc. 1981, 103, 1501.
(10) For selected examples, see: (a) Winkler, J. D.; Oh, K.; Asselin, S.
M. Org. Lett. 2005, 7, 387. (b) Sampson, P.; Roussis, V.; Drtina, G. J.;
Koerwitz, F. L.; Wiemer, D. F. J. Org. Chem. 1986, 51, 2525. (c) Sayama,
S. Heterocycles 2005, 65, 1347. (d) Kato, K.; Nouchi, H.; Ishikura, K.;
Takaishi, S.; Motodate, S.; Tanaka, H.; Okudaira, K.; Mochida, T.;
Nishigaki, R.; Shigenobu, K.; Akita, H. Tetrahedron Lett. 2006, 62, 2545.
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Chem. 2005, 70, 8478. (b) Baldwin, J. E.; Thomas, R. C.; Kruse, L. I.;
Silberman, L. J. Org. Chem. 1977, 42, 3846.
Polysubstituted 3(2H)-furanones are key structural elements
in many naturally occurring compounds such as geiparvarin,1
eremantholide A,2 and jatrophone.3 Moreover, a variety of
3(2H)-furanones are known to have pharmaceutical activity4
(e.g., inhibitory activity on COX-2,5 inhibitory activity on
MAO,6 and cytotoxic activity7 against tumor cells). Strategies
toward 3(2H)-furanones mainly utilize classical condensation
methods such as the acid-catalyzed cyclocondensation of
(1) (a) Jerris, P. J.; Smith, A. B., III. J. Org. Chem. 1981, 46, 577. (b)
Dreyer, D. L.; Lee, A. Phytochemistry 1972, 11, 763. (c) Lahey, F. N.;
MacLeod, J. K. Aust. J. Chem. 1967, 20, 1943.
(2) Le Quesne, P. W.; Levery, S. B.; Menachery, M. D.; Brennan, T. F.;
Raffauf, R. F. J. Chem. Soc., Perkin Trans. 1 1978, 1572.
(3) (a) Smith, A. B., III; Guaciaro, M. A.; Schow, S. R.; Wovkulich, P.
M.; Toder, B. H.; Hall, T. W. J. Am. Chem. Soc. 1981, 103, 219. (b)
Kupchan, S. M.; Sigel, C. W.; Matz, M. J.; Gilmore, C. J.; Bryan, R. F. J.
Am. Chem. Soc. 1976, 98, 2295.
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C.; Russell, J.; Ward, J. J. Med. Chem. 1992, 35, 1183. (b) Togashi, M.;
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Kuwahara, S.; Ubukata, M.; Magae, J. J. Med. Chem. 2003, 46, 4113. (c)
Mack, R. A.; Zazulak, W. I.; Radov, L. A.; Baer, J. E.; Stewart, J. D.;
Elzer, P. H.; Kinsolving, C. R.; Georgiev, V. S. J. Med. Chem. 1988, 31,
1910.
(12) For the synthesis of 2-alkynyl-2-hydroxy carbonyl compounds,
see: (a) Kirsch, S. F. J. Org. Chem., 2005, 70, 10210. (b) Dhondi, P. K.;
Chisholm, J. D. Org. Lett. 2006, 8, 67.
(13) (a) Kirsch, S. F.; Binder, J. T.; Lie´bert, C.; Menz, H. Angew. Chem.,
Int. Ed. 2006, 45, 5878. (b) Binder, J. T.; Crone, B.; Kirsch, S. F.; Lie´bert,
C.; Menz, H. Eur. J. Org. Chem. 2007, 1636.
(14) For related cyclizations, see: (a) Liu, Y.; Liu, M.; Guo, S.; Tu, H.;
Zhou, Y.; Gao, H. Org. Lett. 2006, 8, 3445. (b) Smith, C. R.; Bunnelle, E.
M.; Rhodes, A. J.; Sarpong, R. Org. Lett. 2007, 9, 1169. (c) Hashmi, A. S.
K.; Schwarz, L.; Choi, J.-H.; Frost, T. M. Angew. Chem., Int. Ed. 2000,
39, 2285. (d) Gul´ıas, M.; Rodr´ıguez, R.; Castedo, L.; Mascarenas, J. L.
Org. Lett. 2003, 5, 1975. (e) Marshall, J. A.; Sehon, C. A. J. Org. Chem.
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(5) Shin, S. S.; Byun, Y.; Lim, K. M.; Choi, J. K.; Lee, K.-W.; Moh, J.
H.; Kim, J. K.; Jeong, Y. S.; Kim, J. Y.; Choi, Y. H.; Koh, H.-J.; Park,
Y.-H.; Oh, Y. I.; Noh, M.-S.; Chung, S. J. Med. Chem. 2004, 47, 792.
(6) Carotti, A.; Carrieri, A.; Chimichi, S.; Boccalini, M.; Cosimelli, B.;
Gnerre, C.; Carotti, A.; Carrupt, P.-A.; Testa, B. Bioorg. Med. Chem. Lett.
2002, 12, 3551.
(15) For similar intermediates, see: (a) Yao, T.; Zhang, X.; Larock, R.
C. J. Org. Chem. 2005, 70, 7679. (b) Yao, T.; Zhang, X.; Larock, R. C. J.
Am. Chem. Soc. 2004, 126, 11164. (c) Patil, N. T.; Wu, H.; Yamamoto, Y.
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10.1021/jo070695n CCC: $37.00 © 2007 American Chemical Society
Published on Web 06/08/2007
J. Org. Chem. 2007, 72, 5435-5438
5435

TABLE 1. Formation of 4-Iodo-3-furanones 5 from Alkynyl
Carbonyl Compounds 3a
SCHEME 1. Synthesis of 1,3-Diones 4 from Alkynyl
Carbonyl Compound 3
heterocycles.17 Thus, the reaction of trimethylsilyl ether 3a was
initially examined with use of 3 equiv of I2 as the electrophile
in the presence of NaHCO3 in CH3CN at room temperature.
Under these conditions, the attempted rearrangement of alkynyl
carbonyl compound 3a afforded at most small amounts of
4-iodo-3-furanone 5a. The major product, isolated in 68% yield,
was the unexpected enedione 4a resulting from a formal
Meyer-Schuster rearrangement (Scheme 1).18,19 The presence
of the NaHCO3 proved to be important for the reaction as the
yield for the formation of 4a was significantly lowered without
the base.
Rearrangement of alkynyl carbonyl compound 3a to 4-iodo-
3-furanone 5a was achieved in the presence of N-iodosuccin-
imide (NIS) as a stronger electrophile.20 From a preliminary
survey, two particular useful reaction conditions were identi-
fied: 1.5 equiv of NIS, CH2Cl2 (0.1 M), 23 °C (Method A);
and 5 mol % of AuCl3, 1.5 equiv of NIS, CH2Cl2 (0.1 M),
23 °C (Method B). For example, exposure of trimethylsilyl ether
3a to 1.5 equiv of NIS at room temperature in CH2Cl2 provided
furanone 5a in 88% yield after 2 h (Table 1, entry 1).21 In the
presence of 5 mol % of AuCl3 under identical conditions, a
significant increase in reaction rate was observed with only a
marginal increase in yield (Table 1, entry 2).
As summarized in Table 1, spirocyclic compounds 5 were
obtained in high yields by using NIS in CH2Cl2 in the absence
of AuCl3 (Method A). The reaction tolerated substitution on
the alkyne with R3 being both aryl, alkenyl, and alkyl groups.
However, the conversion of acyclic substrates into the desired
4-iodo-3-furanones was sluggish under these conditions. While
substrate 3i underwent phenyl migration in poor yield (Table
1, entry 14), the reaction of substrates with R1 ) Et failed to
give furanone formation, providing instead a mixture of
unidentified products (Table 1, entries 16 and 18). As observed
without AuCl3, a broad variety of trimethylsilyl ethers 3 were
effectively converted into the corresponding spirocyclic 4-iodo-
3-furanones 5a-h (Table 1, entries 1-13) utilizing both NIS
and catalytic amounts of AuCl3 (Method B). Of primary
importance, acyclic substrates such as 3j and 3k also underwent
formation of the desired rearrangement products in the presence
of AuCl3, albeit in low yields (Table 1, entries 17 and 19). Since
4-iodo-3-furanones 5a-h are prone to slow decomposition at
room temperature, extensive storage should occur at -20 °C.22
a Yield of pure product after column chromatography. b 3g and 3h are
racemic. c After complete consumption of 3, formation of 5 was not observed
by H NMR.
1
A plausible mechanism is shown in Scheme 2. Coordination
of the iodine electrophile to the triple bond produces iodonium
intermediate A (Method A), which after nucleophilic attack of
the carbonyl oxygen generates oxonium ion B. Subsequent 1,2-
shift gives 4-iodo-3-furanone 5 through a formal R-ketol
rearrangement.23 For the gold-catalyzed conversion (Method
B),24 a mechanism was envisaged that proceeds through
coordination of the soft cation to the alkynyl functionality (C)
followed by 1,2-migration of the resulting oxonium ion D.
(19) Since the double bond geometry of 4a could not be determined
unequivocally, 4a was transformed into 8a. The double bond configuration
1
of 8a was assigned by H NMR NOE studies
(17) For selected examples, see: (a) Worlikar, S. A.; Kesharwani, T.;
Yao, T.; Larock, R. C. J. Org. Chem. 2007, 72, 1347. (b) Yao, T.; Larock,
R. C. J. Org. Chem. 2003, 68, 5936. (c) Zhang, X.; Campo, M. A.; Yao,
T.; Larock, R. C. Org. Lett. 2005, 7, 763. (d) Zhang, X.; Sarkar, S.; Larock,
R. C. J. Org. Chem. 2006, 71, 236. (e) Sniady, A.; Wheeler, K. A.;
Dembinski, R. Org. Lett. 2005, 7, 1769. (f) Barluenga, J.; Trincado, M.;
Marco-Arias, M.; Ballesteros, A.; Rubio, E.; Gonzalez, J. M. Chem.
Commun. 2005, 2008. (g) Hessian, K. O.; Flynn, B. L. Org. Lett. 2003, 5,
4377. (h) Huang, Q.; Hunter, J. A.; Larock, R. C. J. Org. Chem. 2002, 67,
3437. (i) Yue, D.; Larock, R. C. Org. Lett. 2004, 6, 1037. (j) Arcadi, A.;
Cacchi, S.; Di Giuseppe, S.; Fabrizi, G.; Marinelli, F. Org. Lett. 2002, 4,
2409. (k) Aillaud, I.; Bossharth, E.; Conreaux, D.; Desbordes, P.; Monteiro,
N.; Balme, G. Org. Lett. 2006, 8, 1113.
(20) Filimonov, V. D.; Krasnokutskaya, E. A.; Poleshchuk, O. K.; Lesina,
Y. A.; Chaikovskii, V. K. Russ. Chem. Bull. Int. Ed. 2006, 55, 1328.
(21) The addition of NaHCO3 did not affect the yield in this reaction.
(22) 5i-k derived from acyclic starting materials decompose rapidly at
room temperature.
(23) (a) Nagao, Y.; Tanaka, S.; Ueki, A.; Kumazawa, M.; Goto, S.; Ooi,
T.; Sano, S.; Shiro, M. Org. Lett. 2004, 6, 2133. (b) Hartung, R. E.; Hilmey,
D. G.; Paquette, L. A. AdV. Synth. Catal. 2004, 346, 713. (c) Paquette, L.
A.; Hofferberth, J. E. Org. React. 2003, 62, 477. (d) Brunner, H.; Sto¨hr, F.
Eur. J. Org. Chem. 2000, 2777.
(18) Swaminathan, S.; Narayanan, K. V. Chem. ReV. 1971, 71, 429.
5436 J. Org. Chem., Vol. 72, No. 14, 2007

SCHEME 2. Plausible Mechanism
Experimental Section
General Experimental Details. All commercially available
chemicals were used without further purification. The 2-alkynyl-
2-silyloxy carbonyl compounds (3a-k) were synthesized as previ-
ously reported.13b
3-Iodo-2-phenyl-1-oxaspiro[4.4]non-2-en-4-one (5a). General
Procedure for the 4-Iodo-3-furanone Formation Starting from
2-Alkynyl-2-silyloxy Carbonyl Compounds: Method A. N-
Iodosuccinimide (59 mg, 0.262 mmol) was added to a solution of
3a (50 mg, 0.175 mmol) in CH2Cl2 (2.5 mL). The reaction vial
was sealed and protected from light. The resulting slightly red
solution was stirred at room temperature for 120 min (until TLC
analysis indicated complete conversion). The mixture was quenched
by addition of saturated aqueous Na2S2O3 (10 mL). The layers were
separated and the aqueous layer was extracted with CH2Cl2 (2 ×
10 mL). The combined organic layers were washed with brine, dried
(Na2SO4), and concentrated under reduced pressure. Purification
of the residue by flash chromatography on silica (P/EtOAc ) 95/
05) gave 4-iodo-3-furanone 5a as a colorless solid (52 mg, 0.153
mmol, 88%).
Method B. A solution of AuCl3 (5 mol %, 10.6 mg) in MeCN
(0.05 mL) was added to a solution of 3a (200 mg, 0.699 mmol)
and N-iodosuccinimide (236 mg, 1.049 mmol) in CH2Cl2 (13 mL).
The reaction vial was sealed and protected from light. The resulting
solution was stirred at room temperature for 20 min (until TLC
analysis indicated complete conversion). The mixture was quenched
by addition of saturated aqueous Na2S2O3 (10 mL). The layers were
separated and the aqueous layer was extracted with CH2Cl2 (2 ×
10 mL). The combined organic layers were washed with brine, dried
(Na2SO4), and concentrated under reduced pressure. Purification
of the residue by flash chromatography on silica (P/EtOAc ) 95/
05) gave 4-iodo-3-furanon 5a as a colorless solid (220 mg, 0.647
mmol, 93%). 1H NMR (360 MHz, CDCl3) δ 1.98-2.02 (m, 6 H),
2.08-2.14 (m, 2 H), 7.50-7.53 (m, 2 H), 7.59 (tt, J ) 7.0, 1.6 Hz,
1 H), 8.18-8.20 (m, 2 H); 13C NMR (90.6 MHz, CDCl3) δ 25.9,
38.0, 65.4, 97.2, 128.8, 129.2, 129.9, 132.9, 180.2, 203.3; LRMS
(EI) 340 (55) [M+], 299 (69), 129 (100), 105 (22); HRMS 339.9963
[339.9960 calcd for C14H13O2I (M+)].
Unlike substrates containing free hydroxy groups (e.g., 1), the
silylated counterparts 3 lack the proton source required for
protodemetalation of organogold intermediate E. Thus, a rapid
iododemetalation25 in the presence of external NIS might lead
to the formation of 3-furanone 5 containing the iodo substituent
at C4.
Further transformations of the 4-iodo-3-furanone products
using known chemistry were also investigated. For example,
Suzuki coupling5,26 (eq 2) and Sonogashira reaction27 (eq 3)
afforded the anticipated products in good yields, thus ac-
complishing the synthesis of fully substituted 3(2H)-furanones.
2,3-Diphenyl-1-oxaspiro[4.4]non-2-en-4-one (6a). General Pro-
cedure for the Suzuki-Coupling of 4-Iodo-3-furanones. A
solution of Na2CO3 (97 mg, 0.915 mmol) in water (0.25 mL) was
added to a solution of 4-iodo-3-furanone 5a (100 mg, 0.294 mmol)
and phenylboronic acid (47 mg, 0.382 mmol) in DMF (1 mL). The
reaction mixture was degassed with argon for 10 min. After addition
of Pd(OAc)2 (0.6 mg, 1 mol %) the reaction mixture was stirred at
40 °C for 18 h. The reaction mixture was quenched by addition of
saturated aqueous NH4Cl (10 mL) and diluted with Et2O (10 mL).
The layers were separated and the aqueous layer was extracted with
Et2O (2 × 10 mL). The combined organic layers were washed with
brine, dried (Na2SO4), and concentrated under reduced pressure.
Purification of the residue by flash chromatography on silica (P/
EtOAc ) 98/02) gave furanone 6a as a colorless solid (81 mg,
0.279 mmol, 95%). 1H NMR (360 MHz, CDCl3) δ 1.95-2.07 (m,
6 H), 2.13-2.20 (m, 2 H), 7.27-7.38 (m, 7 H), 7.46 (tt, J ) 7.5,
1.8 Hz, 1 H), 7.63-7.65 (m, 2 H); 13C NMR (90.6 MHz, CDCl3)
δ 26.1, 37.9, 97.4, 115.3, 127.8, 128.7, 128.9, 129.9, 130.4, 130.5,
132.0, 178.8, 205.0; LRMS (EI) 290 (54) [M+], 249 (100), 178
(48), 105 (35); HRMS 290.1304 [290.1307 calcd for C20H18O2
(M+)].
In conclusion, two protocols for the synthesis of 4-iodo-3-
furanones starting from 2-alkynyl-2-silyloxy carbonyl com-
pounds are described that combine a heterocyclization with a
1,2-alkyl shift. In combination with a subsequent cross-coupling
reaction, this transformation provides a convenient and flexible
approach to fully substituted 3(2H)-furanones.
(24) For selected reviews on gold catalysis, see: (a) Fu¨rstner, A.; Davies,
P. W. Angew. Chem., Int. Ed. 2007, 46, 3410. (b) Jime´nez-Nunez, E.;
Echavarren, A. M. Chem. Commun. 2007, 333. (c) Hashmi, A. S. K.;
Hutchings, G. J. Angew. Chem., Int. Ed. 2006, 45, 7896. (d) Zhang, L.;
Sun, J.; Kozmin, S. A. AdV. Synth. Catal. 2006, 348, 2271. (e) Hoffmann-
Ro¨der, A.; Krause, N. Org. Biomol. Chem. 2005, 3, 387.
2-Phenyl-3-phenylethynyl-1-oxaspiro[4.4]non-2-en-4-one (7a).
General Procedure for the Sonogashira-Coupling of 4-Iodo-3-
furanones. 4-Iodo-3-Furanone 5a (96 mg, 0.282 mmol), PdCl2-
(PPh3)2 (11 mg, 0.05 equiv), phenylacetylene (29 mg, 1.0 equiv),
and CuI (6 mg, 0.1 equiv) were taken up in THF (2 mL) at 0 °C.
Diisoproylamine (91 mg, 3.0 equiv) was added, and the resulting
mixture was stirred at 23 °C for 7 h. The reaction mixture was
diluted with Et2O (20 mL) and washed with aqueous HCl (1 M,
20 mL). The layers were separated and the aqueous layer was
(25) For examples of trapping vinylgold species by electrophilic iodine,
see: (a) Buzas, A.; Gagosz, F. Org. Lett. 2006, 8, 515. (b) Buzas, A.; Istrate,
F.; Gagosz, F. Org. Lett. 2006, 8, 1957. (c) Buzas, A.; Gagosz, F. Synlett
2006, 2727. (d) Kirsch, S. F.; Binder, J. T.; Crone, B.; Duschek, A.; Haug,
T. T.; Lie´bert, C.; Menz, H. Angew. Chem., Int. Ed. 2007, 46, 2310.
(26) (a) Miyaura, N.; Yanagi, T.; Suzuki, K. Synth. Commun. 1981, 11,
513. (b) Suzuki, A. In Metal-catalyzed Cross-coupling Reactions; Diederich,
F., Stang, P. J., Eds.; Wiley-VCH: Weinheim, Germany, 1998; Chapter 2.
(27) (a) Tykwinski, R. R. Angew. Chem., Int. Ed. 2003, 42, 1566. (b)
Sonogashira, K. J. Organomet. Chem. 2002, 653, 46.
J. Org. Chem, Vol. 72, No. 14, 2007 5437

extracted with Et2O (2 × 10 mL). The combined organic layers
were washed with brine, dried (Na2SO4), and concentrated under
reduced pressure. Purification of the residue by flash chromatog-
raphy on silica (P/EtOAc ) 98/02) gave furanone 7a as a colorless
Acknowledgment. This project was supported by the Fonds
der Chemischen Industrie (FCI) and the Deutsche Forschungs-
gemeinschaft (DFG). We thank Prof. Dr. Th. Bach and his group
for helpful discussions and support.
1
solid (85 mg, 0.271 mmol, 96%). H NMR (360 MHz, CDCl3) δ
1.96-2.04 (m, 6 H), 2.12-2.20 (m, 2 H), 7.33-7.39 (m, 3 H),
7.51-7.61 (m, 5 H), 8.36-8.39 (m, 2 H); 13C NMR (90.6 MHz,
CDCl3) δ 26.0, 37.9, 79.5, 98.4, 98.5, 99.5, 123.7, 128.4, 128.6,
128.7, 129.0, 129.8, 131.9, 133.2, 181.5, 203.8; LRMS (EI) 314
(100) [M+], 286 (27), 202 (18), 105 (63); HRMS 314.1307
[314.1307 calcd for C22H18O2 (M+)].
Supporting Information Available: Representative experi-
mental procedures for Method A and Method B, and copies of 1H
and 13C NMR of 5, 6, and 7. This material is available free of
charge via the Internet at http://pubs.acs.org.
JO070695N
5438 J. Org. Chem., Vol. 72, No. 14, 2007