Amidation of Alcohols with Nitriles Under Solvent-Free Conditions

Amidation of Alcohols with Nitriles under Solvent-free Conditions Using Molecular Iodine as a Catalyst Yoshio Kasashima1＊ , Atsushi Uzawa1, Kahoko Hashimoto2, Yu Yokoyama3, Takashi Mino3, Masami Sakamoto3 and Tsutomu Fujita3 1 Education Center, Faculty of Engineering, Chiba Institute of Technology (2-1-1shibazono, Narashino-shi, Chiba 275-0023, JAPAN) 2 Department of Life Environmental Sciences, Faculty of Engineering, Chiba Institute of Technology (2-17-1 Tsudanuma, Narashino-shi, Chiba 275-0016, JAPAN) 3 Graduate School of Engineering, Chiba University (1-33 Yayoi-cho, Inage-ku, Chiba-shi, Chiba 263-8522, JAPAN) Abstract: The reactions of alcohols with nitriles under solvent-free conditions, using molecular iodine as a catalyst, were investigated. The reaction of 1-phenylethanol with propanenitrile produced the amide N-(1- phenylethyl)propanamide, by dehydration and tautomerization, in 71% yield, under the following conditions: temperature＝90℃, alcohol:iodine molar ratio＝1:0.2, alcohol:nitrile molar ratio＝1:5, and reaction time＝5 h. The amidation reactivity depended on the stability of the cationic intermediate formed from the alcohol. The reaction of (−)-borneol with benzonitrile produced a racemic amide in 83% yield.

Key words: iodine, solvent-free, amidation, borneol

1 INTRODUCTION spectrometer（JASCO, Easton, MD, USA）. Gas chromatog- Compounds with amide linkages are important in the raphy/mass spectra（GC-MS）were recorded on a Shimadzu chemical industry. The Ritter reaction, which is the reac- GCMS-QP5050A（Shimadzu, Kyoto, Japan）［column: JW tion of alcohols with nitriles, is one method of producing Scientifi c DB-5ms（30 m×0.25 mm, 0.25 μm fi lm）, Agilent, amides1-5）. However, the catalysts used in this reaction are Santa Clara, CA, USA］. Optical rotations were measured generally strong acids or heavy-metal compounds, which on a JASCO DIP-370. X-ray measurements were made on a are very expensive and/or toxic. In the present study, io- Bruker axs-SMART APEX II at －100℃. dine was investigated as a catalyst for the reaction of alcohols with nitriles. Recently, iodine has been investigated as 2.2 Materials a potential efficient catalyst in several organic reactions 1-Phenylethanol（1）was synthesized as follows: because it has low toxicity6-18）. In this study, we also inves- Acetophenone（6.02 g, 50 mmol）and ethanol（50 mL） tigated solvent-free conditions, from the viewpoint of were placed in a fl ask and the mixture was stirred. Sodium “green chemistry”. borohydride（3.88 g, 102 mmol）was added and the mixture was stirred at 0℃ for 1 d. After evaporation, diethyl ether （50 mL）and then 6M aqueous HCl were added. The mixture was then extracted twice with 100 mL of diethyl ether. 2 EXPERIMENTAL The organic layer was washed with 100 mL of aqueous so- 2.1 General dium hydrocarone solution, dried with anhydrous sodium Melting points were measured on a Shibata micro melt- sulfate, and evaporated. The product was purifi ed by col- ing point apparatus（Shibata, Tokyo, Japan）, and were un- umn chromatography with hexane/ethyl acetate（4/1）as the corrected. NMR spectra were obtained using a 400 MHz or eluent. A total of 4.38 g（36.0 mmol; 72％ yield）of 1 was 300 MHz FT-NMR spectrometer（JEOL JNM-LA-400, JEOL, obtained. Tokyo, Japan, or Bruker DPX-300, Bruker, Billerica, MA,

USA）with Me4Si as the internal standard and CDCl3 as the 2.3 Amidation solvent. IR spectra were recorded on a JASCO FT/IR-230 A typical procedure is as follows:

＊Correspondence to: Yoshio Kasashima, Education Center, Faculty of Engineering, Chiba Institute of Technology, 2-1-1shibazono, Narashino-shi, Chiba 275-0023, JAPAN E-mail: [email protected] Accepted May 21, 2010 (received for review March 29, 2010) Journal of Oleo Science ISSN 1345-8957 print / ISSN 1347-3352 online http://www.jstage.jst.go.jp/browse/jos/

607 Y. Kasashima, A. Uzawa1, K. Hashimoto et al.

13 Compound 1（121 mg, 1.0 mmol）, propanenitrile（2）（272 m）, 7.74（2H, d, J＝8.9 Hz）; C-NMR（CDCl3）δ: 21.8, 49.1, mg, 5.0 mmol）and iodine（50.0 mg）were place in a reaction 55.4, 113.7, 126.2, 126.8, 127.4, 128.7, 128.7, 143.3, 162.1, tube, and the tube was sealed. The mixture was stirred at 166.0; IR（KBr）: 3335, 1628 cm－1; EI-MS m/z（rel intensi- 90℃ for 5 h. Diisopropyl ether（3 mL）was added, and then ty）: 255（M＋, 27） a 20％ aqueous solution of sodium thiosulfate（5 mL）was 2.3.7 N（- 2-Octyl）benzamide（10） 1 added to the reaction mixture to remove the iodine. The White crystals, mp 66-67℃. H-NMR（CDCl3）δ: 0.88（3H, mixture was then extracted three times with 20 mL of di- t, J＝6.6 Hz）,1.29（3H, t, J＝7.0 Hz）, 1.22-1.56（10H, m）, isopropyl ether. The organic layer was washed with 100 mL 4.12-4.26（1H, m）, 5.87（1H, bs）, 7.40-7.52（3H, m）, 13 of water, dried with anhydrous sodium sulfate, and evapo- 7.74-7.76（2H, m）; C-NMR（CDCl3）δ: 14.1, 21.1, 22.6, 26.0, rated. The product was purified by column chromatogra- 29.2, 31.8, 37.1, 45.8, 126.8, 128.5, 131.2, 135.1, 166.8; IR phy with hexane/ethyl acetate（10/1）as the eluent. A total （KBr）: 3292, 2923, 2851, 1635 cm－1; EI-MS m/z（rel inten- of 124 mg（0.70 mmol; 71％ yield）of N（- 1-phenylethyl）pro- sity）: 233（M＋, 9） panamide（3）was obtained. The GC-MS purities of all prod- 2.3.8 N-Cyclohexylbenzamide（11） 1 ucts were above 98％. White crystals, mp 137-138℃. H-NMR（CDCl3）δ: The spectroscopic data of the product from 1 is as fol- 1.13-1.30（3H, m）, 1.36-1.50（2H, m）, 1.62-1.79（3H, m）, lows: 2.01-2.06（2H, m）, 3.92-4.04（1H, m）, 6.02（1H, bs）, 13 2.3.1 N（- 1-Phenylethyl）propanamide（3） 7.39-7.51（3H, m）, 7.74-7.77（2H, m）; C-NMR（CDCl3）δ: 1 White crystals, mp 55-56℃. H-NMR（CDCl3）δ: 1.16（3H, 24.9, 25.5, 33.2, 48.6, 126.8, 128.5, 131.2, 135.1, 166.6; IR t, J＝7.6 Hz）, 1.49（3H ,d, J＝6.9 Hz）, 2.21（2H ,q, J＝7.6 （KBr）: 3318, 3240, 2929, 2851, 1627 cm－1; EI-MS m/z（rel Hz）, 5.14（1H, qd, J＝6.9, 7.3 Hz）, 5.67（1H, bs）, 7.24-7.37 intensity）: 203（M＋, 30） 13 （5H, m）; C-NMR（CDCl3）δ: 9.77, 21.7, 29.7, 48.5, 126.1, 2.3.9 N-tert-Butylbenzamide（12）－1 1 127.2, 128.6, 143.3, 172.7; IR（KBr,）; 3330, 2972, 1651 cm ; White crystals, mp 135-136℃. H-NMR（CDCl3）δ: 1.48 EI-MS m/z（rel intensity）: 177（M＋, 46）（9H, s）, 5.95（1H, s）, 7.39-7.48（3H, m）, 7.71-7.73（2H, m）; 13 2.3.2 N（- 1-Phenylethyl）acetamide（4） C-NMR（CDCl3）δ: 28.8, 51.6, 126.7, 128.4, 131.0, 135.9, 1 －1 White crystals, mp 70-71℃. H-NMR（CDCl3）δ: 1.49（3H , 166.9; IR（KBr）: 3325, 2965, 1636 cm ; EI-MS m/z（rel in- d, J＝6.8 Hz）, 1.99（3H , s）, 5.13（1H, qd, J＝6.8, 7.3 Hz）, tensity）: 177（M＋, 18） 13 5.73（1H , bs）, 7.24-7.37（5H, m）; C-NMR（CDCl3）δ: 21.7, 2.3.10 N-Benzylbenzamide（13） 1 23.4, 48.7, 126.2, 127.4, 128.6, 143.1, 169.0; IR（KBr）: 3282, White crystals, mp 92-94℃. H-NMR（CDCl3）δ: 4.65（2H, 1647 cm－1; EI-MS m/z（rel intensity）: 163（M＋, 41） d, J＝5.7 Hz）, 6.43（1H, bs）, 7.20-7.53（8H, m）, 7.78-7.81 13 2.3.3 2-Cyano-N（- 1-phenylethyl）acetamide（5）（2H, m）; C-NMR（CDCl3）δ: 44.1, 126.9, 127.6, 127.9, 1 White crystals, mp 100-101℃. H-NMR（CDCl3）δ: 1.53 128.6, 128.8, 131.5, 134.3, 138.1, 167.3; IR（KBr）: 3289, （3H, d, J＝7.0 Hz）, 3.31（2H , s）, 5.09（1H, qd, J＝7.0, 7.2 3060, 1638 cm－1; EI-MS m/z（rel intensity）: 211（M＋, 64） 13 Hz）, 6.45（1H, bs）, 7.26-7.39（5H, m）; C-NMR（CDCl3）δ: 2.3.11 （±） -exo-N-Isobornylbenzamide（15） 1 21.4, 25.9, 49.9, 114.7, 126.1, 127.8, 128.9, 141.8, 160.0; IR White crystals, mp 125-126℃. H-NMR（CDCl3）δ: 0.88 （KBr）: 3278, 3067, 2975, 2921, 2257, 1648 , cm－1; EI-MS （3H, s）, 0.92（3H, s）, 1.01（3H, s）, 1.19-1.25（1H, m）, m/z（rel intensity）: 188（M＋, 54） 1.33-1.42（1H, m）, 1.59-1.82（4H, m）, 1.93-2.00（1H, m）, 2.3.4 N（- 1-Phenylethyl）benzamide（6） 4.08-4.15（1H, m）, 6.08（1H, bs）, 7.40-7.49（3H, m）, 1 13 White crystals, mp 113-115℃. H-NMR（CDCl3）δ: 1.61 7.70-7.72（2H, m）; C-NMR（CDCl3）δ: 11.8, 20.3, 20.3, 27.0, （3H, d, J＝7.0 Hz）, 5.34（3H, qd, J＝7.0, 7.2 Hz）, 6.36（1H, 35.9, 39.2, 44.9, 47.2, 48.8, 57.1, 126.6, 128.6, 131.2, 135.1, 13 －1 bs）, 7.26-7.52（7H, m）, 7.76-7.78（2H, m）; C-NMR（CDCl3） 166.7; IR（KBr）: 3335, 2955, 1631, 1526 cm ; EI-MS m/z δ: 21.7, 49.2, 126.2, 126.9, 127.4, 128.5, 128.7, 131.4, 134.6, （rel intensity）: 257（M＋, 21）; X-ray diffraction analysis 143.1, 166.5; IR（KBr）: 3345, 1633 cm－1; EI-MS m/z（rel in- data: The X-Ray crystallographic analysis indicated the Or- ＋ tensity）: 225（M , 35） thorhombic space group Pca21, a＝9.9752（9）Å, b＝ 2.3.5 4-Chloro-N（- 1-phenylethyl）benzamide（7） 14.5775（13）Å, c＝10.2350（9）Å, V＝1488.3（2）Å3, Z＝4, ρ 1 3 －1 White crystals, mp 137-138℃. H-NMR（CDCl3）δ: 1.59 ＝1.149 Mg/m , μ＝0.070 mm . The structure was solved （3H, d, J＝6.9 Hz）, 5.30（1H, qd, J＝7.0, 7.1 Hz）, 6.43（1H, by the direct method of full-matrix least-squares, where 13 bs）, 7.25-7.39（7H, m）, 7.67-7.71（2H, m）; C-NMR（CDCl3） the ﬁ nal R and wR were 0.0526 and 0.1387 for 7933 reﬂ ec- δ: 21.6, 49.3, 126.2, 126.4, 127.5, 128.4, 128.7, 132.9, 137.6, tions. 142.9, 165.5; IR（KBr）: 3260, 1630 cm－1; EI-MS m/z（rel in- 2.3.12 N （-（1R, 2S, 5R）-5-Methyl-2-（1-methylethyl）cyclo- tensity）: 259（M＋, 28） hexyl）benzamide（16） 1 2.3.6 4-Methoxy-N（- 1-phenylethyl）benzamide（8） White crystals, mp 106-107℃. H-NMR（CDCl3）δ: 0.84 1 White crystals, mp 131-132℃. H-NMR（CDCl3）δ: 1.60 （3H, d, J＝6.9 Hz）, 0.90（3H, d, J＝6.5 Hz）, 0.92（3H, d, J＝（3H, d, J＝6.8 Hz）, 3.84（3H, s）, 5.33（1H, qd, J＝6.8, 7.2 6.9 Hz）, 1.08-1.27（2H, m）, 1.48-1.77（5H, m）, 1.93-2.10 Hz）, 6.24（1H, bs）, 6.91（2H, d, J＝8.9 Hz）, 7.26-7.41（5H, （2H, m）, 3.94-4.06（1H, m）, 5.87（1H, bs）, 7.39-7.51（3H,

608 J. Oleo Sci. 59, (11) 607-613 (2010) Iodine-catalyzed Amidation of Alcohols with Nitriles under Solvent-free Conditions

13 m）, 7.74-7.78（2H, m）; C-NMR（CDCl3）δ: 16.2, 21.2, 22.1, duce a cationic intermediate. The cationic intermediate is 23.9, 27.0, 31.9, 34.5, 43.1, 48.4, 50.4, 126.8, 128.5, 131.2, dehydrated to produce another cationic intermediate. The 135.1, 166.7; IR（KBr）: 3299, 2962, 2918, 2859, 1631 cm－1; lone electron pair of the nitrile group attacks this cation to 25 ［α］D : -65.4（c＝0.27, CHCl3）; EI-MS m/z（rel intensity）: form cationic intermediate Ⅰ. The lone electron pair of the 259（M＋, 6）; X-ray diffraction analysis data: The X-Ray water molecule attacks Ⅰ to form intermediate Ⅱ. Proton crystallographic analysis indicated the Orthorhombic elimination then occurs to produce intermediate Ⅲ, which

space group P212121, a＝9.6552（9）Å, b＝10.4439（9）Å, c tautomerizes to form the amide. ＝15.0406（13）Å, V＝1516.7（2）Å3, Z＝4, ρ＝1.136 Mg/m3, μ＝0.069 mm－1. The structure was solved by the direct method of full-matrix least-squares, where the ﬁ nal R and wR were 0.0350 and 0.0743 for 7298 reﬂ ections.

3 RESULTS AND DISCUSSION The reaction was performed as follows. 1-Phenylethanol （1）, propanenitrile（2）, and iodine were placed in a reaction tube and stirred with heating. After reaction, an aqueous solution of sodium thiosulfate was added to remove the iodine, and the product was isolated. After puriﬁ cation, the spectroscopic data of the isolated product indicated that the structure was that of the amide compound N- （1-phenylethyl）propanamide（3）. This indicated that the Ritter reaction had occurred to produce an amide from the alcohol and the nitrile. A possible reaction mechanism is shown in Scheme 1. 1-Phenylethanol reacts with iodine to form a hydroiodide, which acts as an acid catalyst to pro- Scheme 1

Table 1 Reactions of 1-phenylethanol (1) with propanenitrile (2).

a b c Entry Molar ratio I2 (eq.) Temp. (℃) time (h) Yield (%) 1 5:1 0.02 90 2 19 2 1:3 0.1 90 2 31 3 1:5 0.1 90 2 38 4 1:10 0.1 90 2 40 5 1:5 0.2 90 2 51 6 1:5 0.2 75 2 40 7 1:5 0.2 reﬂ ux 2 35 8 1:5 0.2 90 4 59 9 1:5 0.2 90 5 71 10 1:5 0.2 90 6 67 a Molar ratio of 1:2. b Molar ratio of iodine with 1. c Isolate yield.

609 J. Oleo Sci. 59, (11) 607-613 (2010) Y. Kasashima, A. Uzawa1, K. Hashimoto et al.

Table 2 Iodine-catalyzed amidation of 1 with nitriles. Table 3 Iodine-catalyzed amidation of alcohols with benzonitrile (9).

The optimum conditions for formation of 3 by amidation were investigated. It is possible for both alcohol 1 and nitrile 2 to attack the cationic intermediate. The ratio of alcohol 1 to nitrile 2 is therefore considered to be important in the reaction. The reaction was fi rst attempted using an results are shown in Table 2. When acetonitrile was used excess of alcohol 1（entry 1, alcohol:nitrile molar ratio＝（entry 2）, the yield was low（24％）. It is generally known 5:1）. The yield（19％）was low. The reaction was then at- that acetonitrile is an effi cient solvent when iodine is used tempted using an excess of nitrile 2（entries 2－4）. When as the catalyst. It is therefore supposed that some of the the alcohol:nitrile molar ratio was 1:5, the yield was 38％ acetonitrile acted not as a reagent but as a solvent. In the （entry 3）. With an alcohol:nitrile molar ratio of 1:10, the case of malononitrile（entry 3）, the yield was moderate yield only improved slightly（entry 4）. Thus, the optimum （56％）under mild conditions. For benzonitriles（entries alcohol:nitrile molar ratio was determined to be 1:5. When 4-6）, the yields were also moderate（43-62％）. the alcohol 1:iodine molar ratio was increased from 1:0.1 The reactions of benzonitrile（9）with various alcohols （entry 3）to 1:0.2（entry 5）, the yield increased to 51％. were investigated under the optimum conditions for the The effects of reaction temperature were also investigated reaction of 1 with 2（entry 9 in Table 1）. The results are （entries 5, 6, and 7）. When the reaction temperature was summarized in Table 3. The yield obtained using a tertiary lowered to 75℃（entry 6）, the yield decreased to 40％. alcohol（entry 4）was higher than those obtained using pri- When the reaction was performed under refl ux（bath tem- mary and secondary alcohols（entries 1-3）. This indicated perature＝105℃）, the yield also decreased, to 35％. Thus, that the stability of the cationic intermediate influenced the optimum reaction temperature was determined to be the reaction. In the case of benzyl alcohol（entry 8）, the 90℃. The reaction time was also studied（entries 5, 8, 9, yield was 27％; with the other alcohols used（entries 6 and and 10）. When the reaction time was extended to 5 h（en- 7）either no reaction took place or complex reactions oc- try 9）, the yield increased signifi cantly to 71％. However, curred. This was attributed to the high stability of the ben- the yield did not change when the reaction time was ex- zyl cationic intermediate. tended to 6 h（entry 10）. This reaction was next applied to terpenic alcohols.（－）- The reactions of alcohol 1 with various nitriles were in- Borneol（14）was used as the reagent because it was ex- vestigated, using the conditions for entry 9 in Table 1. The pected that the cationic intermediate formed by elimina-

610 J. Oleo Sci. 59, (11) 607-613 (2010) Iodine-catalyzed Amidation of Alcohols with Nitriles under Solvent-free Conditions

Table 4 Iodine-catalyzed amidation of (−)-borneol (14) with benzonitrile (9).

a b c Entry Molar ratio I2 (eq.) Temp. (℃) time (h) Yield (%) 1 1:5 0.2 90 24 41 2 1:5 0.2 110 24 70 3 1:5 0.2 120 24 74 4 1:5 0.2 130 24 67 5 1:5 0.2 140 24 56 6 1:5 0.2 120 4 64 7 1:5 0.2 120 5 72 8 1:5 0.2 120 6 71 9 1:5 0.2 120 48 76 10 1:4 0.2 120 5 66 11 1:6 0.2 120 5 67 12 1:5 0.1 120 5 59 13 1:5 0.15 120 5 65 14 1:5 0.3 120 6 83 a Molar ratio of 14:9. b Molar ratio of iodine with 14. c Isolated yield. tion of a water molecule would be stable. The reaction of on the nitrile group attacks both cationic intermediates 14 with benzonitrile was carried out. The results are shown equally, resulting in two amide compounds of different ste- in Table 4. Under the optimum reaction conditions（tem- reostructures, as shown in Scheme 2. perature＝90℃, time＝24 h, alcohol:nitrile molar ratio＝ Other terpenic alcohols, such as racemic isoborneol, 1:5, and alcohol:iodine molar ratio＝1:0.2）, the amide 15 myrtenol,（－）-menthol, and geraniol, were reacted with was obtained in 41％ yield（entry 1）. When the reaction benzonitrile using iodine as a catalyst. The results are sum- temperature was raised to 120℃, the yield increased to marized in Table 5. In the cases of myrtenol and geraniol, 74％（entry 3）. However, when the temperature was fur- the products were complex because of the instability of the ther increased to 130℃, the yield decreased to 67％（entry cationic intermediates. Because the cationic intermediate 4）. When the reaction time was shortened to 5 h, the yield formed from（－）-menthol is more stable than those from was unchanged（72％, entry 7）. The alcohol:nitrile molar myrtenol and geraniol, the amide 16 was obtained in 27％ ratio was adjusted from 1:4 to 1:6（entries 7, 10, and 11）, yield. The presence of unreacted alcohols was observed by but no obvious differences in the yields were observed. TLC. ORTEP diagrams of 15 and 16 are shown in Figs. 1 Amide 15 was obtained in the highest yield（83％）when the and 2, respectively. reaction was carried out under the following conditions: al- In conclusion, the reaction of alcohols with nitriles under cohol:nitrile molar ratio＝1:5, alcohol:iodine molar ratio＝ solvent-free conditions, using iodine as a catalyst, proceeds 1:0.3, temperature＝120℃, and reaction time＝6 h. to give the corresponding amides. The reactivity depends X-ray crystal structure analysis and optical rotation mea- on the stability of the cationic intermediate formed from surements conﬁ rmed that 15 was a racemate. The reason it the alcohols.（－）-Borneol reacts with benzonitrile to afford is racemic is as follows. It is known that the cationic inter- racemic amides. mediate from（－）-borneol undergoes a 6,2-hydride shift to form two cationic intermediates19, 20）. The lone electron pair

611 J. Oleo Sci. 59, (11) 607-613 (2010) Y. Kasashima, A. Uzawa1, K. Hashimoto et al.

Table 5 Iodine-catalyzed amidation of terpenic alcohols with benzonitrile.

Scheme 2

Fig. 1 ORTEP diagram of (±)-15

References 1．Benson, F. R.; Ritter, J. J. A new reaction of nitriles. Ⅲ. Amides from dinitriles. J. Am. Chem. Soc. 71, 4128- 4129（1949）. 2．Top, S.; Jaouen, G. N-Alkylation of nitriles using chro- mium tricarbonyl complexes of benzyl alcohol and its derivatives: New perspectives for the Ritter reaction. J. Org. Chem. 46, 78-82（2004）. 3．Levedev, M. Y.; Erman M. B. Lower primary alkanols Fig. 2 ORTEP diagram of (－)-16 and their esters in a Ritter-type reaction with nitriles. An efﬁ cient method for obtaining N-primary-alkyl am-

612 J. Oleo Sci. 59, (11) 607-613 (2010) Iodine-catalyzed Amidation of Alcohols with Nitriles under Solvent-free Conditions

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