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β-Boron Effect Enables Regioselective and Stereospecific Electrophilic Addition to Alkenes

Yin Li, Wen-Xin Fan, Shuang Luo, Alina Trofimova, Yuan Liu, Jiang-Hao Xue, Ling Yang, Qingjiang Li, Honggen Wang* and Andrei K. Yudin*

*Sun Yat-Sen University, Guangzhou 510006, China; University of Toronto, 80 St. George St, Toronto, Ontario M5S 3H6 Canada, Email: wanghg3mail.sysu.edu.cn, andrei.yudinutoronto.ca

Y. Li, W.-X. Fan, S. Luo, A. Tofimova, Y. Liu, J.-H. Xue, L. Yang, Q. Li, H. Wang, A. K. Yudin, J. Am. Chem. Soc., 2023, 145, 7548-7558.

DOI: 10.1021/jacs.3c00860


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Abstract

A β-boron effect accounts for high regioselectivity in electrophilic addition reactions to allylic MIDA (N-methyliminodiacetic acid) boronates. The boryl moiety is retained in the product when B(MIDA) is used as the nucleophilic stabilizer.


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mechanistic pathway



General procedure for the synthesis of β-fluorinated boronates

To a 10 mL of plastic tubing charged with allylic MIDA boronates (0.2 mmol, 1.0 equiv), was added Py.9HF (60.0 equiv) in one portion. The reaction was allowed to stir at -25 C for 10 h-36 h. The reaction mixture was quenched by slowly adding basic alumina suspended in dichloromethane (1.8 g). The suspension was filtered and washed with 25 mL of dichloromethane. The combined filtrate was concentrated in vacuo and purified by column chromatography to afford the pure product.

General procedure for the synthesis of β-iodinated boronates

Allylic MIDA boronates (0.2 mmol, 1.0 equiv) was added to one of chambers which two-chambered pressure vessel with stirring bars and then the vessel was evacuated and refilled with argon for three times. Toluene (3 mL) was added under an argon atmosphere. Another chamber was loaded with HSiEt3 (0.6 mmol, 3.0 equiv) under argon atmosphere and the two chambers were cooled to -78 C. After the mixture was cooled, I2 (0.6 mmol, 3.0 equiv) was added to the chamber with HSiEt3 in one portion. Then the reaction mixture was stirred at room temperature overnight in dark. The reaction mixture of toluene was quenched with H2O and extracted with EtOAc (20 mL 3). The combined organic layers dried over Na2SO4. The organic phase was concentrated under reduced pressure and purified by column chromatography to afford the pure product.

General procedure for the synthesis of γ-iodo-β-hydroxylated boronates

To a 15-mL screw cap vial equipped with a stirring bar, were added allylic MIDA boronate (0.2 mmol, 1.0 equiv), N-iodosuccinimide (0.4 mmol, 2.0 equiv), acetone (1.6 mL) and H2O (0.4 mL). The solution was stirred at room temperature for 1-5 min. The resulting mixture was quenched with 0.2 M Na2S2O3 solution and then extracted with EtOAc. The organic phase was washed with saturated NaCl solution for three times. The combined organic layer was dried over anhydrous Na2SO4 and concentrated under reduced pressure. The residue was purified by column chromatography to afford the pure product.


Key Words

fluorides, iodides, iodohydrins, iodine, triethylsilane, NIS, σ(C-B) hyperconjugation, β-boron effect, β effect


ID: J48-Y2023