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Cyclization and halogenation of substituted o-allylphenols with diacetoxyiodobenzene in the presence of iodine or bromine
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Chinese Chemical Letters 19 (2008) 661–664 www.elsevier.com/locate/cclet
Cyclization and halogenation of substituted o-allylphenols with diacetoxyiodobenzene in the presence of iodine or bromine Qi Zhong Zhou *, Chun Lin He, Zhen Chu Chen Department of Chemistry, Zhejiang University, Hangzhou 310027, China Received 26 December 2007
Abstract Substituted 2-halomethyl-2,3-dihydrobenzofurans were synthesized in one pot and in mild yield from substituted o-allylphenols with diacetoxyiodobenzene in the presence of I2 or Br2 in dry CH2Cl2 under reflux. # 2008 Qi Zhong Zhou. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: 2-Halomethyl-2,3-dihydrobenzofuran; Diacetoxyiodobenzene; Cyclization; Halogenation
Diacetoxyiodobenzene (DIB, PhI(OAc)2) is a widely used, very powerful and important reagent in modern organic synthesis. Recently, DIB has been applied to the synthesis of many kinds of iodonium salts [1], iodonium ylides [2] and various alkynyl and vinyl selenides [3]. Amino acid-derived iodobenzene dicarboxylates prepared from DIB and Nprotected amino acid are effective reagents for oxidative conversion of alkenes to amino acid esters [4]. Acetoxylation of unactivated sp3 and sp2 C–H to esters using DIB as oxidant in the presence of catalytic palladium has important potential utility in organic synthesis [5]. A novel lactonization and subsequent rearrangement occurred with phenonium ion participation induced by DIB as hypernucleofuge [6]. Oxidative glycosylation took place from glycal substrates by applying DIB and suitable catalytic acid [7]. Intermolecular or intramolecular aziridination happened at C C bond with DIB catalyzed by Rhodium (II) or copper (II) [8]. Optically pure cyclic sulfamidates were synthesized by asymmetric intramolecular amidation of optically pure sulfamate esters with DIB catalyzed by chiral ruthenium complex in the presence of Al2O3 [9]. Researchers have found that v-alkenyl-subsituted urea molecules were intramolecularly diaminated with DIB in the presence of catalytic palladium [10]. In the presence of iodine, DIB generated Suarez fragmentation of an anomeric alkoxy radical from the substrates [11]. When cyclic a, b or g-amino acid treated with DIB and iodine in the presence of light, a radical decarboxylation process took place [12]. Many kinds of acyclic nucleoside analogues and other C-1 substitued alditols were prepared via one-pot oxidative bfragmentation-nucleophilic addition when the carbohydrates treated with DIB and iodine in the presence of light [13]. Various iodoalkanes and 1-acetoxy-2-iodocycloalkanes were synthesized by activation of alkanes or cycloalkanes upon reaction with DIB and iodine [14]. To the best of our knowledge, substituted 2-halomethyl-2,3-dihydrobenzofurans were the important reagents for the synthesis of medicine and drugs for plant growth regulation, etc. Usually, substituted 2-iodomethyl-2,
* Corresponding author. E-mail addresses: [email protected], [email protected] (Q.Z. Zhou). 1001-8417/$ – see front matter # 2008 Qi Zhong Zhou. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2008.04.003
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Q.Z. Zhou et al. / Chinese Chemical Letters 19 (2008) 661–664
Table 1 Optimization of the reaction conditions of [RCOOI] with o-allylphenola
Entry
Solvent
Iodobenzene dicarboxylate
Temperature
2a(%) b
1 2 3 4 5 6 7 8
CH2Cl2 CH2Cl2 Acetone C2H5OH THF CH3CN CH2Cl2 CH2Cl2
(CH3COO)2IPh (CH3COO)2IPh (CH3COO)2IPh (CH3COO)2IPh (CH3COO)2IPh (CH3COO)2IPh (PhCOO)2IPh (CF3COO)2IPh
r.t. Reflux Reflux Reflux Reflux Reflux Reflux Reflux
0 46 39 23 41 46 39 15
a b
All of the reactions were carried out on a scale of 2 mmol of o-allylphenol in dry CH2Cl2. Isolated yields.
3-dihydrobenzofurans were synthesized from o-allylphenol with HgCl2 followed by treatment with KI and then with I2 [15], iodocyclisation of substituted o-allylphenol with SnCl4 + I2 [16], ZnCl2 (or EPZ-10R) [17] and I2 [18]. However, as we know, there is no report on the synthesis of substituted 2-bromomethyl-2,3-dihydrobenzofurans from substituted o-allylphenols. In organic solvent, acetoxyiodide intermediate ([CH3COOI]) was easily generated by treatment with DIB and I2 [19]. It is a useful and active intermediate. It can be added to C C bond [20] and carbonBBcarbon bond [19]. Recently, the utility of [CH3COOI] in organic synthesis attracted our strong interest because it is easily and efficiently formed. Herein, we wish to present our research results on the reaction of substituted o-allylphenols with [CH3COOX] (X = I or Br). In dry CH2Cl2, DIB reacted with iodine or bromine to generate [CH3COOX] (X = I or Br) completely in 30 min at room temperature. Under refluxing of a solution of substituted o-allylphenols in CH2Cl2, [CH3COOX] treatment provides a novel method to prepare both substituted 2-iodomethyl-2,3-dihydro benzofurans and substituted 2bromomethyl-2,3-dihydrobenzofurans in one pot. We initially examined the reaction of [CH3COOI] with o-allylphenol in CH2Cl2 at room temperature. After 2 days, TLC showed no new product appeared. After refluxed for 40 h, we were pleased to isolate 2-iodomethyl-2,3dihydrobenzofuran in 46%. Our further investigations proved that dry MeCN was also a good solvent for the reaction (entry 6, Table 1), but solvents such as dry acetone, dry ethanol and dry THF did not work very well (entries 3, 4 and 5, Table 1). (PhCOO)2IPh and (CF3COO)2IPh reacted with iodine to generate [PhCOOI] and [CF3COOI], which did not work well (entries 7 and 8, Table 1). With the optimized conditions in hand, we next examined the reaction of various substituted o-allylphenols with [CH3COOI] (Table 2). DIB reacted with Br2 instead of I2 to generate [CH3COOBr] intermediate. [CH3COOBr] reacted with substituted o-allylphenols to produce substituted 2-bromomethyl-2,3-dihydrobenzofurans which have higher yield than others (entries 6, 7 and 8, Table 2) [21]. A plausible mechanism to rationalize this reaction is outlined in Scheme 1. The [CH3COOX] generated from DIB and I2 (or Br2) first reacted with the relatively electron rich C C bond to generate the cyclic iodonium intermediate 3,
Scheme 1.
Q.Z. Zhou et al. / Chinese Chemical Letters 19 (2008) 661–664
663
Table 2 Reaction of various substituted o-allylphenols with [CH3COOX]a (X = I or Br) Entry
Substrate
Product
Yield b
1
46
2
48
3
50
4
55
5
60
6
75 c
7
66 c
8
60 c
a b c
All of the reactions were carried out on a scale of 2 mmol of the substituted o-allylphenols in dry CH2Cl2. Isolated yields. DIB reacted with Br2 in stead of I2 to generate [CH3COOBr] intermediate.
then CH3COO attack the H of the ortho OH and after that ortho O attack the cyclic iodonium to form 2-halomethyl2,3-dihydrobenzofuran (see Scheme 1). In summary, we provide a novel method to prepare both substituted 2-iodomethyl-2,3-dihydrobenzofurans and substituted 2-bromomethyl-2,3-dihydrobenzofurans with [CH3COOX] (X = I or Br) and substituted o-allylphenols in one pot and in mild yield. Further investigation of [CH3COOX] in organic synthesis was also in progress. Acknowledgments We thank the National Science Foundation of China for financial support (No. 29472036). References [1] (a) M. Ochiai, K. Miyamoto, Y. Yokota, T. Suefeji, M. Shiro, Angew. Chem. Int. Ed. 44 (2005) 75; (b) M. Fujita, H.J. Lee, T. Okuyama, Org. Lett. 8 (2006) 1399. [2] (a) Q. Zhu, J. Wu, R. Fathi, Z. Yang, Org. Lett. 4 (2002) 3333; (b) W. Adam, E.P. Gogonas, L.P. Hadjiarapoglou, Eur. J. Org. Chem. (2003) 1064; (c) W. Adam, E.P. Gogonas, L.P. Hadjiarapoglou, J. Org. Chem. 68 (2003) 9155. [3] J.P. Das, U.K. Roy, S. Roy, Organometallics 24 (2005) 6136. [4] A.Y. Koposov, V.V. Boyarskikh, V.V. Zhdankin, Org. Lett. 6 (2004) 3613. [5] (a) A.R. Dick, K.L. Hull, M.S. Sanford, J. Am. Chem. Soc. 126 (2004) 2300; (b) L.V. Desar, K.L. Hull, M.S. Sanford, J. Am. Chem. Soc. 126 (2004) 9542. [6] A.C. Boye, D. Meyer, C.K. Ingison, A.N. French, T. Wirth, Org. Lett. 5 (2003) 2157. [7] L. Shi, Y. Kim, D.Y. Gim, J. Am. Chem. Soc. 123 (2001) 6939. [8] (a) A. Padwa, A.C. Flick, C.A. Leverett, T. Stengel, J. Org. Chem. 69 (2004) 6377; (b) H. Han, I. Bae, E.J. Yoo, J. Lee, Y. Do, S. Chang, Org. Lett. 6 (2004) 4109.
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[9] J. Liang, S. Yuan, J. Huang, C. Che, J. Org. Chem. 69 (2004) 3610. [10] J. Streuff, C.H. Hovelmann, M. Nieger, K. Muniz, J. Am. Chem. Soc. 127 (2005) 14586. [11] (a) X. Cheng, N. Khan, D.R. Mootoo, J. Org. Chem. 65 (2000) 2544; (b) X. Cheng, N. Khan, G. Kumaran, D.R. Mootoo, Org. Lett. 3 (2001) 1323. [12] (a) A. Boto, R. Hernandez, Y. de Leon, J.R. Murguia, A. Rodriguez-Afonso, Tetrahedron Lett. 45 (2004) 6841; (b) A. Boto, R. Hernandez, Y. de Leon, J.R. Murguia, A. Rodriguez-Afonso, Eur. J. Org. Chem. (2005) 673. [13] A. Boto, R. Hernandez, E. Suarez, Tetrahedron Lett. 42 (2001) 9167. [14] J. Barluenga, F. Gonzalez-Bobes, J.M. Gonzalez, Angew. Chem. Int. Ed. 41 (2002) 2556. [15] R. Adams, F.L. Roman, W.N. Sperry, J. Am. Chem. Soc. 44 (1922) 1781. [16] K. Orito, T. Hatakeyama, M. Takeo, H. Suginome, M. Tokuda, Synthesis (1997) 23. [17] V.A. Mahajan, P.D. Shinde, A.S. Gajare, M. Karthikeyan, R.D. Wakharkar, Green Chem. 4 (2002) 325. [18] M. Fousteris, C. Chevrin, J. LeBras, J. Muzart, Green Chem. 8 (2006) 522. [19] E.B. Merkushev, M.C. Schwarzberg, Organiciodine Compounds in Synthesis, Tomsk Ped. Inst., Tomsk, USSR, 1978. [20] K. Aoki, Y. Ogata, Bull. Chem. Soc. Jpn. 41 (1968) 1476. [21] Typical procedure for the synthesis of 2a–2h: A suspension of DIB (1 mmol) and I2 (1 mmol) was stirred at r.t. in dry CH2Cl2 for 30 min. Then 2 mmol of o-allylphenol was added. Then the reaction was stirred at reflux for 40 h. Till cooled, the reaction mixture was washed with 10 mL saturated sodium thiosulfate solution. After dried with sodium sulfate, the organic solvent was concentrated and then the residue was subjected to column chromatography with ethyl ether/hexane (1:8) to afford a white solid. 2a: 1H NMR (CDCl3, 60 MHz, dppm): 6.84–7.09 (m, 4H), 4.84–5.37 (m, 1H), 3.06–3.70 (m, 4H); IR (NaCl, film) 1610, 1590; MS (EI): m/z (%) = 260(M+, 100). 2b: m.p. 42–43 8C; 1H NMR (CDCl3, 60 MHz, dppm): 6.56–7.12 (m, 3H), 4.64–4.98 (m, 1H), 3.05–3.39 (m, 4H); IR (KBr): 1605, 1595; MS (EI): m/z (%) = 294 (M+, 100). 2c: m.p. 42–44 8C; 1H NMR (CDCl3, 60 MHz, dppm): 6.48–7.53 (m, 3H), 4.57–5.04 (m, 1H), 2.98–3.50 (m, 4H), 2.22 (s, 3H); IR (KBr): 1615, 1595; MS (EI): m/z (%) = 274 (M+, 100). 2d: m.p. 51–53 8C; 1H NMR (CDCl3, 60 MHz, dppm): 6.97–7.94 (m, 6H), 4.60–5.13 (m, 1H), 2.66–3.50 (m, 4H); IR (KBr): 1675, 1610, 1585; MS (EI): m/z (%) = 310 (M+, 100). 2e: m.p. 58–60 8C; 1H NMR (CDCl3, 60 MHz, dppm): 6.82–7.68 (m, 6H), 4.41–5.02 (m, 1H), 2.72–3.54 (m, 4H); IR (KBr): 1640, 1610, 1590; MS (EI): m/z (%) = 310 (M+, 69). 2f: oil; 1H NMR (CDCl3, 60 MHz, dppm): 7.30–7.52 (m, 4H), 4.40–4.78 (m, 1H), 3.37–3.82 (m, 4H); IR (NaCl, film): 1610, 1592. 2g: oil; 1H NMR (CDCl3, 60 MHz, dppm): 6.70–7.43 (m, 3H), 4.25–4.78 (m, 1H), 3.40–3.72 (m, 4H), 2.17 (s, 3H); IR (NaCl, film):1615, 1595; MS (EI): m/z (%): 228 (M+, 26). 2h: oil; 1H NMR (CDCl3, 60 MHz, dppm): 7.08–7.45 (m, 3H), 4.28–4.76 (m, 1H), 3.32–3.80 (m, 4H); IR (NaCl, film): 1610, 1590.
Chinese Chemical Letters 19 (2008) 661–664 www.elsevier.com/locate/cclet
Cyclization and halogenation of substituted o-allylphenols with diacetoxyiodobenzene in the presence of iodine or bromine Qi Zhong Zhou *, Chun Lin He, Zhen Chu Chen Department of Chemistry, Zhejiang University, Hangzhou 310027, China Received 26 December 2007
Abstract Substituted 2-halomethyl-2,3-dihydrobenzofurans were synthesized in one pot and in mild yield from substituted o-allylphenols with diacetoxyiodobenzene in the presence of I2 or Br2 in dry CH2Cl2 under reflux. # 2008 Qi Zhong Zhou. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: 2-Halomethyl-2,3-dihydrobenzofuran; Diacetoxyiodobenzene; Cyclization; Halogenation
Diacetoxyiodobenzene (DIB, PhI(OAc)2) is a widely used, very powerful and important reagent in modern organic synthesis. Recently, DIB has been applied to the synthesis of many kinds of iodonium salts [1], iodonium ylides [2] and various alkynyl and vinyl selenides [3]. Amino acid-derived iodobenzene dicarboxylates prepared from DIB and Nprotected amino acid are effective reagents for oxidative conversion of alkenes to amino acid esters [4]. Acetoxylation of unactivated sp3 and sp2 C–H to esters using DIB as oxidant in the presence of catalytic palladium has important potential utility in organic synthesis [5]. A novel lactonization and subsequent rearrangement occurred with phenonium ion participation induced by DIB as hypernucleofuge [6]. Oxidative glycosylation took place from glycal substrates by applying DIB and suitable catalytic acid [7]. Intermolecular or intramolecular aziridination happened at C C bond with DIB catalyzed by Rhodium (II) or copper (II) [8]. Optically pure cyclic sulfamidates were synthesized by asymmetric intramolecular amidation of optically pure sulfamate esters with DIB catalyzed by chiral ruthenium complex in the presence of Al2O3 [9]. Researchers have found that v-alkenyl-subsituted urea molecules were intramolecularly diaminated with DIB in the presence of catalytic palladium [10]. In the presence of iodine, DIB generated Suarez fragmentation of an anomeric alkoxy radical from the substrates [11]. When cyclic a, b or g-amino acid treated with DIB and iodine in the presence of light, a radical decarboxylation process took place [12]. Many kinds of acyclic nucleoside analogues and other C-1 substitued alditols were prepared via one-pot oxidative bfragmentation-nucleophilic addition when the carbohydrates treated with DIB and iodine in the presence of light [13]. Various iodoalkanes and 1-acetoxy-2-iodocycloalkanes were synthesized by activation of alkanes or cycloalkanes upon reaction with DIB and iodine [14]. To the best of our knowledge, substituted 2-halomethyl-2,3-dihydrobenzofurans were the important reagents for the synthesis of medicine and drugs for plant growth regulation, etc. Usually, substituted 2-iodomethyl-2,
* Corresponding author. E-mail addresses: [email protected], [email protected] (Q.Z. Zhou). 1001-8417/$ – see front matter # 2008 Qi Zhong Zhou. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2008.04.003
662
Q.Z. Zhou et al. / Chinese Chemical Letters 19 (2008) 661–664
Table 1 Optimization of the reaction conditions of [RCOOI] with o-allylphenola
Entry
Solvent
Iodobenzene dicarboxylate
Temperature
2a(%) b
1 2 3 4 5 6 7 8
CH2Cl2 CH2Cl2 Acetone C2H5OH THF CH3CN CH2Cl2 CH2Cl2
(CH3COO)2IPh (CH3COO)2IPh (CH3COO)2IPh (CH3COO)2IPh (CH3COO)2IPh (CH3COO)2IPh (PhCOO)2IPh (CF3COO)2IPh
r.t. Reflux Reflux Reflux Reflux Reflux Reflux Reflux
0 46 39 23 41 46 39 15
a b
All of the reactions were carried out on a scale of 2 mmol of o-allylphenol in dry CH2Cl2. Isolated yields.
3-dihydrobenzofurans were synthesized from o-allylphenol with HgCl2 followed by treatment with KI and then with I2 [15], iodocyclisation of substituted o-allylphenol with SnCl4 + I2 [16], ZnCl2 (or EPZ-10R) [17] and I2 [18]. However, as we know, there is no report on the synthesis of substituted 2-bromomethyl-2,3-dihydrobenzofurans from substituted o-allylphenols. In organic solvent, acetoxyiodide intermediate ([CH3COOI]) was easily generated by treatment with DIB and I2 [19]. It is a useful and active intermediate. It can be added to C C bond [20] and carbonBBcarbon bond [19]. Recently, the utility of [CH3COOI] in organic synthesis attracted our strong interest because it is easily and efficiently formed. Herein, we wish to present our research results on the reaction of substituted o-allylphenols with [CH3COOX] (X = I or Br). In dry CH2Cl2, DIB reacted with iodine or bromine to generate [CH3COOX] (X = I or Br) completely in 30 min at room temperature. Under refluxing of a solution of substituted o-allylphenols in CH2Cl2, [CH3COOX] treatment provides a novel method to prepare both substituted 2-iodomethyl-2,3-dihydro benzofurans and substituted 2bromomethyl-2,3-dihydrobenzofurans in one pot. We initially examined the reaction of [CH3COOI] with o-allylphenol in CH2Cl2 at room temperature. After 2 days, TLC showed no new product appeared. After refluxed for 40 h, we were pleased to isolate 2-iodomethyl-2,3dihydrobenzofuran in 46%. Our further investigations proved that dry MeCN was also a good solvent for the reaction (entry 6, Table 1), but solvents such as dry acetone, dry ethanol and dry THF did not work very well (entries 3, 4 and 5, Table 1). (PhCOO)2IPh and (CF3COO)2IPh reacted with iodine to generate [PhCOOI] and [CF3COOI], which did not work well (entries 7 and 8, Table 1). With the optimized conditions in hand, we next examined the reaction of various substituted o-allylphenols with [CH3COOI] (Table 2). DIB reacted with Br2 instead of I2 to generate [CH3COOBr] intermediate. [CH3COOBr] reacted with substituted o-allylphenols to produce substituted 2-bromomethyl-2,3-dihydrobenzofurans which have higher yield than others (entries 6, 7 and 8, Table 2) [21]. A plausible mechanism to rationalize this reaction is outlined in Scheme 1. The [CH3COOX] generated from DIB and I2 (or Br2) first reacted with the relatively electron rich C C bond to generate the cyclic iodonium intermediate 3,
Scheme 1.
Q.Z. Zhou et al. / Chinese Chemical Letters 19 (2008) 661–664
663
Table 2 Reaction of various substituted o-allylphenols with [CH3COOX]a (X = I or Br) Entry
Substrate
Product
Yield b
1
46
2
48
3
50
4
55
5
60
6
75 c
7
66 c
8
60 c
a b c
All of the reactions were carried out on a scale of 2 mmol of the substituted o-allylphenols in dry CH2Cl2. Isolated yields. DIB reacted with Br2 in stead of I2 to generate [CH3COOBr] intermediate.
then CH3COO attack the H of the ortho OH and after that ortho O attack the cyclic iodonium to form 2-halomethyl2,3-dihydrobenzofuran (see Scheme 1). In summary, we provide a novel method to prepare both substituted 2-iodomethyl-2,3-dihydrobenzofurans and substituted 2-bromomethyl-2,3-dihydrobenzofurans with [CH3COOX] (X = I or Br) and substituted o-allylphenols in one pot and in mild yield. Further investigation of [CH3COOX] in organic synthesis was also in progress. Acknowledgments We thank the National Science Foundation of China for financial support (No. 29472036). References [1] (a) M. Ochiai, K. Miyamoto, Y. Yokota, T. Suefeji, M. Shiro, Angew. Chem. Int. Ed. 44 (2005) 75; (b) M. Fujita, H.J. Lee, T. Okuyama, Org. Lett. 8 (2006) 1399. [2] (a) Q. Zhu, J. Wu, R. Fathi, Z. Yang, Org. Lett. 4 (2002) 3333; (b) W. Adam, E.P. Gogonas, L.P. Hadjiarapoglou, Eur. J. Org. Chem. (2003) 1064; (c) W. Adam, E.P. Gogonas, L.P. Hadjiarapoglou, J. Org. Chem. 68 (2003) 9155. [3] J.P. Das, U.K. Roy, S. Roy, Organometallics 24 (2005) 6136. [4] A.Y. Koposov, V.V. Boyarskikh, V.V. Zhdankin, Org. Lett. 6 (2004) 3613. [5] (a) A.R. Dick, K.L. Hull, M.S. Sanford, J. Am. Chem. Soc. 126 (2004) 2300; (b) L.V. Desar, K.L. Hull, M.S. Sanford, J. Am. Chem. Soc. 126 (2004) 9542. [6] A.C. Boye, D. Meyer, C.K. Ingison, A.N. French, T. Wirth, Org. Lett. 5 (2003) 2157. [7] L. Shi, Y. Kim, D.Y. Gim, J. Am. Chem. Soc. 123 (2001) 6939. [8] (a) A. Padwa, A.C. Flick, C.A. Leverett, T. Stengel, J. Org. Chem. 69 (2004) 6377; (b) H. Han, I. Bae, E.J. Yoo, J. Lee, Y. Do, S. Chang, Org. Lett. 6 (2004) 4109.
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Q.Z. Zhou et al. / Chinese Chemical Letters 19 (2008) 661–664
[9] J. Liang, S. Yuan, J. Huang, C. Che, J. Org. Chem. 69 (2004) 3610. [10] J. Streuff, C.H. Hovelmann, M. Nieger, K. Muniz, J. Am. Chem. Soc. 127 (2005) 14586. [11] (a) X. Cheng, N. Khan, D.R. Mootoo, J. Org. Chem. 65 (2000) 2544; (b) X. Cheng, N. Khan, G. Kumaran, D.R. Mootoo, Org. Lett. 3 (2001) 1323. [12] (a) A. Boto, R. Hernandez, Y. de Leon, J.R. Murguia, A. Rodriguez-Afonso, Tetrahedron Lett. 45 (2004) 6841; (b) A. Boto, R. Hernandez, Y. de Leon, J.R. Murguia, A. Rodriguez-Afonso, Eur. J. Org. Chem. (2005) 673. [13] A. Boto, R. Hernandez, E. Suarez, Tetrahedron Lett. 42 (2001) 9167. [14] J. Barluenga, F. Gonzalez-Bobes, J.M. Gonzalez, Angew. Chem. Int. Ed. 41 (2002) 2556. [15] R. Adams, F.L. Roman, W.N. Sperry, J. Am. Chem. Soc. 44 (1922) 1781. [16] K. Orito, T. Hatakeyama, M. Takeo, H. Suginome, M. Tokuda, Synthesis (1997) 23. [17] V.A. Mahajan, P.D. Shinde, A.S. Gajare, M. Karthikeyan, R.D. Wakharkar, Green Chem. 4 (2002) 325. [18] M. Fousteris, C. Chevrin, J. LeBras, J. Muzart, Green Chem. 8 (2006) 522. [19] E.B. Merkushev, M.C. Schwarzberg, Organiciodine Compounds in Synthesis, Tomsk Ped. Inst., Tomsk, USSR, 1978. [20] K. Aoki, Y. Ogata, Bull. Chem. Soc. Jpn. 41 (1968) 1476. [21] Typical procedure for the synthesis of 2a–2h: A suspension of DIB (1 mmol) and I2 (1 mmol) was stirred at r.t. in dry CH2Cl2 for 30 min. Then 2 mmol of o-allylphenol was added. Then the reaction was stirred at reflux for 40 h. Till cooled, the reaction mixture was washed with 10 mL saturated sodium thiosulfate solution. After dried with sodium sulfate, the organic solvent was concentrated and then the residue was subjected to column chromatography with ethyl ether/hexane (1:8) to afford a white solid. 2a: 1H NMR (CDCl3, 60 MHz, dppm): 6.84–7.09 (m, 4H), 4.84–5.37 (m, 1H), 3.06–3.70 (m, 4H); IR (NaCl, film) 1610, 1590; MS (EI): m/z (%) = 260(M+, 100). 2b: m.p. 42–43 8C; 1H NMR (CDCl3, 60 MHz, dppm): 6.56–7.12 (m, 3H), 4.64–4.98 (m, 1H), 3.05–3.39 (m, 4H); IR (KBr): 1605, 1595; MS (EI): m/z (%) = 294 (M+, 100). 2c: m.p. 42–44 8C; 1H NMR (CDCl3, 60 MHz, dppm): 6.48–7.53 (m, 3H), 4.57–5.04 (m, 1H), 2.98–3.50 (m, 4H), 2.22 (s, 3H); IR (KBr): 1615, 1595; MS (EI): m/z (%) = 274 (M+, 100). 2d: m.p. 51–53 8C; 1H NMR (CDCl3, 60 MHz, dppm): 6.97–7.94 (m, 6H), 4.60–5.13 (m, 1H), 2.66–3.50 (m, 4H); IR (KBr): 1675, 1610, 1585; MS (EI): m/z (%) = 310 (M+, 100). 2e: m.p. 58–60 8C; 1H NMR (CDCl3, 60 MHz, dppm): 6.82–7.68 (m, 6H), 4.41–5.02 (m, 1H), 2.72–3.54 (m, 4H); IR (KBr): 1640, 1610, 1590; MS (EI): m/z (%) = 310 (M+, 69). 2f: oil; 1H NMR (CDCl3, 60 MHz, dppm): 7.30–7.52 (m, 4H), 4.40–4.78 (m, 1H), 3.37–3.82 (m, 4H); IR (NaCl, film): 1610, 1592. 2g: oil; 1H NMR (CDCl3, 60 MHz, dppm): 6.70–7.43 (m, 3H), 4.25–4.78 (m, 1H), 3.40–3.72 (m, 4H), 2.17 (s, 3H); IR (NaCl, film):1615, 1595; MS (EI): m/z (%): 228 (M+, 26). 2h: oil; 1H NMR (CDCl3, 60 MHz, dppm): 7.08–7.45 (m, 3H), 4.28–4.76 (m, 1H), 3.32–3.80 (m, 4H); IR (NaCl, film): 1610, 1590.