J. Org. Chem. 2001, 66, 7287-7293
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Phenol-Containing Macrocyclic Diamides as New Catalysts in the Highly Regioselective Conversion of Epoxides to β-Hydroxy Thiocyanates Hashem Sharghi,* Mohammad Ali Nasseri, and Khodabakhsh Niknam† Department of Chemistry, Shiraz University, Shiraz 71454, I.R. Iran, and Department of Chemistry, Persian Gulf University, Bushehr 75168, I.R. Iran
[email protected] Received March 26, 2001
The regioselective ring-opening reactions of some epoxides with ammonium thiocyanate in the presence of a series of new phenol-containing macrocyclic diamides and also dibenzo-18-crown-6-, 18-crown-6-, benzo-15-crown-5-, and pyridine-containing macrocyclic diamide have been studied. The epoxides were subject to cleavage by NH4SCN in the presence of these catalysts under mild reaction conditions in various aprotic solvents. In this study, reagents and conditions have been discovered with which the individual β-hydroxy thiocyanates can be synthesized in high yield and with more than 90% regioselectivity. The results can be discussed in terms of a four-step mechanism: (1) formation of complex between catalyst and NH4SCN, (2) release of SCN- nucleophile from the complex, (3) reaction of the active nucleophile at the less sterically hindered site in the epoxide, and (4) regeneration of catalyst. The major advantages of this method are as follows: (1) high regioselectivity, (2) simple regeneration of catalyst, (3) its reuse through several cycles without a decrease in activity, and (4) ease of workup of the reaction. Introduction Epoxides are one of the most versatile intermediates in organic synthesis, and a large variety of reagents are known for the ring opening of these compounds.1 Their electrophilic reaction with different nucleophilic anions has been an interesting subject in organic synthesis.2-7 Between these anions, the reaction of thiocyanate ion with epoxides, in the absence or in the presence of catalyst, is a widely studied and suitable method for the preparation of thiiranes.8-15 The formation of thiiranes from the reaction of epoxides and thiocyanate ion has been proposed to occur through the intermediacy of the corresponding β-hydroxy thiocyanate, but this intermediate has not been isolated due to its rapid conversion to the corresponding thiirane.13-17 There are two methods †
Persian Gulf University. (1) (a) Bonini, C.; Righi, G. Synthesis 1994, 225 (b) Iranpoor, N.; Mohammadpour Baltork, I. Synth. Commun. 1990, 20, 2789. (c) Shimizu, M.; Yoshida, A.; Fujisawa, T. Synlett 1992, 204. (d) Smith, J. G. Synthesis 1984, 629. (2) Iranpoor, N.; Kazemi, F.; Salehi, P. Synth. Commun. 1997, 27, 1247. (3) Iranpoor, N.; Salehi, P. Tetrahedron 1995, 51, 909. (4) (a) Guy, A.; Dubuffet, T.; Doussor, J.; Godefroy-Falguieres, A. Synlett 1991, 403. (b) Guy, A.; Doussot, J.; Ferroud, C.; GodefroyFalguieres, A. Synthesis 1992, 821. (5) Chini, M.; Crotti, P.; Macchia, F. Tetrahedron Lett. 1990, 31, 5641. (6) Ciaccio, J. A.; Stanescu, C.; Bontemps, J. Tetrahedron Lett. 1992, 33, 1431. (7) Chini, M.; Crotti, P.; Favero, L.; Macchia, F. Tetrahedron Lett. 1991, 32, 4775. (8) Sander, M. Chem. Rev. 1966, 66, 297. (9) Vedejs, E.; Krafft, G. A. Tetrahedron 1982, 38, 2857. (10) Kolc, K.; Kubicz, E.; Mlochowski, J. Heterocycl. Chem. 1984, 22, 2517. (11) Tamami, B.; Kiasat, A. R. Synth. Commun. 1996, 26, 3953. (12) Jankowski, K.; Harvey, R. Synthesis 1972, 627. (13) Iranpoor, N.; Kazemi, F. Tetrahedron 1997, 53, 11377. (14) Iranpoor, N.; Kazemi, F. Synthesis 1996, 821. (15) Iranpoor, N.; Zeynizadeh, B. Synth. Commun. 1998, 28, 3913.
reported in the literature for the synthesis of β-hydroxy thiocyanates. In one method, thiocyanohydrins are prepared by opening of a cyclic sulfate with NH4SCN to form the corresponding β-sulfate, which is hydrolyzed to the thiocyanohydrines. A second method employed the addition to the epoxide of thiocyanic acid generated in situ at low temperature.18-21 For these syntheses, it has been reported that the presence of some hydroquinone or DDQ are required to stabilize the produced β-hydroxy thiocyanate and inhibit its conversion to thiirane.16,22 Although the reagents such as Ti (O-i-Pr)4,23 Ph3P(SCN)2,24 TiCl3 (or ZnCl2),25 and Pd(PPh3)426 are useful, they are limited to specific oxiranes and are not applicable as versatile reagents in preparation of β-hydroxy thiocyanates.27 In conjunction with the ongoing work in our laboratory on the synthesis and complex formation of macrocyclic compounds with different molecules,28-32 we found that (16) Iranpoor, N.; Kohmareh, G. A. Phosphorus, Sulfur Silicon 1999, 152, 135. (17) Price, C. C.; Kirk, P. F. J. Am. Chem. Soc. 1953, 75, 2396. (18) Gao, Y.; Sharpless, K. B. J. Am. Chem. Soc. 1988, 110, 7538. (19) Vantamelen, E. E. J. Am. Chem. Soc. 1951, 73, 3444. (20) Kawashima, K.; Eshiguro, T. Chem. Pharm. Bull. 1978, 26, 951. (21) Vasileva, S. A.; Minnigulov, F. Khim. Geterotsikl Soedin. 1997, 8, 1061 (22) Wagner-Jaurgg, G. Ann. 1949, 87, 561. (23) Najera, C.; Sansano, J. M. Tetrahedron 1991, 47, 5193. (24) Tamura, Y.; Kawasaki, T.; Kita, Y. J. Chem. Soc., Perkin Trans. 1 1981, 1577. (25) Olszewski, A.; Gros, P.; Fort, Y. Tetrahedron Lett. 1997, 38, 8699. (26) Choudary, B. M.; Shobha, S.; Kantam, M. L. Synth. Commun. 1990, 20, 2313. (27) Tanabe, Y.; Mori, K.; Yoshida, Y. J. Chem. Soc., Perkin Trans. 1 1997, 671. (28) Sharghi, H.; Eshghi, H. Tetrahedron 1995, 51, 913. (29) Gangali, M. R.; Eshghi, H.; Sharghi, H.; Shamsipour, M. J. Electroanal. Chem. 1996, 405, 177. (30) Sharghi, H.; Massah, A. R.; Abedi, M. Talanta 1999, 49, 531.
10.1021/jo0103266 CCC: $20.00 © 2001 American Chemical Society Published on Web 10/10/2001
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J. Org. Chem., Vol. 66, No. 22, 2001 Scheme 1
Sharghi et al. Scheme 2
phenol-containing macrocyclic diamides efficiently catalyzed the addition of ammonium thiocyanate to epoxide to form β-hydroxy thiocyanate. Five new phenol-containing macrocyclic diamides as well as dibenzo-18-crown6-, 18-crown-6-, benzo-15-crown-5-, and pyridine-containing macrocyclic diamide 1933 were selected as catalysts in these reactions. Discussion (A) Preparation of Catalyst. Although macrocyclic amides are originally regarded as intermediates to prepare aza crowns, only a few procedures have been developed for their preparations. Among these, carboxylic acid derivatives, such as malonic and R,ω-dicarboxylic acid esters,34 labile diacid dichlorides,35,36 and bis(R-chloroamide)compounds,37-39 were allowed to react with various diamides under high dilution or for long reaction periods. In previous studies,28,31 we reported a new efficient synthesis of macrocyclic diamides. No high-dilution technique was required in this method. We applied this approach to the synthesis of dilactams 11-15 which contain phenolic groups (Scheme 1). As shown in Scheme 1, p-methoxyphenol was reacted with hexamine in trifluoroacetic acid to give yellow needles of 2,6-diformyl-4-methoxyphenol 1 in 32% yield.40 Dicarboxylic acid 2 was obtained as a pale yellow solid in 60% yield by oxidation of dialdehyde 1 in the presence of Ag2O in aqueous NaOH solution. Treatment of 2 with thionyl chloride gave 86% yield of dicarboxylic acid dichloride 3. The diamine 8 was obtained by reduction of the corresponding dinitro compound 7 with palladium on carbon (5%) and hydrazine in 81% yield (Scheme 2). p-Bromophenol reacted with formaline (37% aqueous solution) in (31) Sharghi, H.; Massah, A. R.; Eshghi, H.; Niknam, Kh. J. Org. Chem. 1998, 63, 1455. (32) Sharghi, H.; Niknam, K.; Massah, A. R. J. Heterocycl. Chem. 1999, 36, 601. (33) Si, J.; Wu, Y.; Cai, L.; Lin, Y., Du, B.; Xu, T.; An, J. J. Inclusion Phenom. Mol. Recognit. Chem 1994, 17, 249. (34) (a) Tabushi, I.; Taniguchi, Y.; Kato, H. Tetrahedron Lett. 1977, 1049. (b) Tabushi, I.; Okino, H.; Kuroda, Y. Tetrahedron Lett. 1976, 4339. (35) (a) Pentranek, J.; Ryba, O. Collect. Czech. Chem. Commun. 1980, 45, 1567. (b) Pentranek, J.; Ryba, O. Collect. Czech. Chem. Commun. 1983, 48, 1945. (36) (a) Pellisard, D.; Louris, R. Tetrahedron Lett. 1972, 4589. (b) Dietrich, B.; Lehn, J. M.; Sauvage, J. P.; Blanzat, J. Tetrahedron 1973, 29, 1629. (37) Krakowiak, K. E.; Bradshaw, J. S.; Izatt, R. M. J. Org. Chem. 1990, 55, 3364. (38) Bradshaw, J. S.; Krakowiak, K. E.; Izatt, R. M.; ZameckaKrakowiak. D. J. Tetrahedron Lett. 1990, 31, 1077. (39) (a) Krakowiak, K. E.; Bradshaw, J. S.; Izatt, R. M. J. Heterocycl. Chem. 1990, 27, 1585. (b) Bradshaw, J. S.; Krakowiak, K. E.; An. H.; Izatt, R. M. J. Heterocycl. Chem. 1990, 27, 2113. (40) Lindoy, L. F.; Meehan, G. V.; Svenstrup, N. Synthesis 1998, 1029.
Scheme 3
the presence of sodium hydroxide followed by protection of the phenolic group with dimethyl sulfate. Treatment of 5 with PBr3 gave the dibromide 6, which reacted with o-nitrophenol to afford dinitro compound 7. The diamino compounds 10a-d were obtained by reduction of the corresponding dinitro compounds 9a-d (Scheme 3). o-Nitrophenol reacted with the dichlorides of oligoethylene glycols in the presence of potassium carbonate in dimethylformamide to give the corresponding dinitro compounds 9a-d in the range of 67-85% yields.41 The cyclization reaction between diacid dichloride 3 and the diamines 8 and 10a-d was performed without using high-dilution techniques. In a preliminary study, the effect of some solvents (CHCl3, CH3CN, CH2Cl2, C6H6, acetone) on the yield of the macrocyclization reaction has been investigated, and CH2Cl2 has been chosen as the most suitable solvent for these macrocyclization reactions. In addition, the cyclization reaction was carried out with fast addition of a solution of diamine (2 mmol) in dry CH2Cl2 (10 mL) into a solution of dicarboxylic acid dichloride 3 (2 mmol) in dry CH2Cl2 (10 mL) over 5 s with vigorous stirring at room temperature. The reaction mixture was stirred for further 20 min to give macrocyclic dilactams 11-15 in good yields (Scheme 3). Crown ethers 16-19 were also used as catalysts in thiocyanation of epoxides. (B) Thiocyanation of Epoxides. Epoxides of convenient volatility to allow GC analysis were chosen for study. As catalysts, some phenol-containing macrocyclic(41) Dutasta, T. P.; Dechlercq, J. P.; Esteban-Calderon, C.; Tinant, B. J. Am. Chem. Soc. 1989, 111, 7136.
Conversion of Epoxides to β-Hydroxy Thiocyanates Scheme 4
J. Org. Chem., Vol. 66, No. 22, 2001 7289 Table 1. Thiocyanative Cleavage of Styrene Oxide with NH4SCN in the Presence of Various Macrocyclic Compounds in Different Solvent under Reflux Condition
entry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
diamides that were synthesized according to Scheme 4 were used. Also, dibenzo-18-crown-6 16, 18-crown-6 17, benzo-15-crown-5 18, and pyridine-containing macrocyclic diamide 19 were selected to represent some com-
catalyst (0.01 mol %) 11 12 13 14 15 16 17 18 19 11 11 11 11 11 11
solvent
time (min)
yielda (%)
CH3CN CH3CN CH3CN CH3CN CH3CN CH3CN CH3CN CH3CN CH3CN CH3CN Et2O t-BuOH EtOH THF CH2Cl2 1,4-dioxane
35 40 50 50 90 85 70 90 70 190b 70 60 60 65 70 70
93 93 90 85 55 70 75 65 70 c d 50 40 30
