The First Example of Polymer-supported Alkenyl Iodonium Salts: Efficient Synthesis of β-Functional Enamines

Jiang-Min Chen; Xian Huang

doi:10.1055/s-2004-815431

LETTER

The First Example of Polymer-supported Alkenyl Iodonium Salts: Efficient Synthesis of β-Functional Enamines

Jiang-Min Chen^a,c, Xian Huang*^a,b
^a Department of Chemistry, Zhejiang University, Xixi Campus, Hangzhou 310028, P. R. China
^b State key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai, 200032, P. R. China
Fax: +86(571)88807077; e-Mail: huangx@mail.hz.zj.cn;
^c Department of Chemistry, Gannan Teachers’ College, Ganzhou 341000, P. R. China

Abstract

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Abstract

Polymer-supported alkenyl(phenyl) iodonium salts were synthesized, which served as effective alkenyl transfer reagents for the preparation of β-functional enamines; the polymer support poly(4-iodostyrene) can be regenerated and recycled.

Key words

polymer-supported alkenylphenyl iodonium salts - poly(4-iodostyrene) - β-functional enamines

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References

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Preparation of Polymer-supported Alkenyl Iodonium Tosylate 3: To a solution of methyl-3-amino-crotonate (2a; 1.15 g, 10 mmol) or ethyl-3-benzylamino-crotonate (2b; 2.19 g, 10 mmol) in CH₂Cl₂ (30 mL), poly{[4-hydroxy(tosyloxy)iodo]styrene} (1.65 g, 3 mmol) was added. The suspension was stirred at 0 °C for 6 h or 2 h, respectively. After the reaction was complete, the CH₂Cl₂ was evaporated in vacuum to give oily residue. Et₂O (20 mL) was added to precipitate the product, which was filtered off and washed with acetone (10 mL × 2) and Et₂O (10 mL × 2) to afford the products. Compound 3a: white powder, 1.61 g, N%, 3.09. IR (KBr): ν = 3176, 3076 1629, 1448, 1404, 1263, 1187, 1125, 1035, 1009, 814, 684 cm^-1. Compound 3b: white powder, 1.78 g, N%, 2.44. IR (KBr): ν = 3043, 2920, 1625, 1487, 1449, 1170, 1124, 1034, 1009, 814, 683 cm^-1.

General Procedure for the Synthesis of β-Functional Enamines 4: To a suspension of 3a (1.0 g, N: 2.21 mmol/g) in CHCl₃ (10 mL) was added the solution of KSCN (0.1 g, 1 mmol) in water (3 mL). After the reaction was complete, the organic layer was separated and dried over anhyd MgSO₄. The solvent was removed under vacuum and Et₂O was added to the resulting oil to precipitate poly(4-iodostyrene). The solution was submitted to preparative TLC on silica gel with n-hexane-EtOAc (2:1, v/v) as the eluent to afford 143 mg (83%) of 4a, white powder, mp 77-78 °C. IR (KBr): n = 3410, 3312, 2998, 2949, 1672, 1628, 1506, 1434, 1371, 1264, 1185, 1134, 1071, 778, 648 cm^-1. ¹H NMR (400 MHz, CDCl₃): d = 9.26 (s, 1 H), 5.78 (s, 1 H), 3.77 (s, 3 H), 2.39 (s, 3 H). ¹³C NMR (100 MHz, CDCl₃): d = 168.8, 168.7, 113.5, 75.6, 52.0, 23.4. MS (EI): m/z (%) = 172 (38.9) [M⁺], 113 (71.4), 87 (67.7), 59 (49.5), 42 (100). Anal. Calcd for C₆H₈N₂O₂S: C, 41.85; H, 4.68; N, 16.27. Found: C, 41.78; H, 4.59; N, 16.39.