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Photoassisted Cobalt-Catalyzed Asymmetric Reductive Grignard-Type Addition of Aryl Iodides

Xuan Jiang, Hao Jiang, Qian Yang, Ying Cheng, Liang-Qiu Lu*, Jon A. Tunge and Wen-Jing Xiao*

*College of Chemistry, Central China Normal University, 152 Luoyu Road, Wuhan 430079, P. R. China, Email: luliangqiumail.ccnu.edu.cn, wxiaomail.ccnu.edu.cn

X. Jiang, H. Jiang, Q. Yang, Y. Cheng, L.-Q. Lu, J. A. Tunge, W.-J. Xiao, J. Am. Chem. Soc., 2022, 144, 8347-8354.

DOI: 10.1021/jacs.2c02481



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Abstract

A visible-light-induced cobalt-catalyzed asymmetric reductive 1,2-addition of aryl iodides to aldehydes provides chiral benzyl alcohols in very good yield, and high ee. This methodology offers mild reaction conditions, good functionality tolerance, excellent enantiocontrol, the avoidance of mass metal wastes, and the use of precious metal catalysts.

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proposed mechanism

(R,R)-BDPP


4CzIPN



General Procedures

Conditions A: In an argon-filled glove box, a 10 mL vial equipped with a magnetic stirrer bar was charged sequentially with (R,R)-BDPP (0.024 mmol, 12 mol%) and CoI2 (0.02 mmol, 10 mol%), followed by the addition of DCM (2 mL). After stirring at room temperature for 2 h, aryl iodide (0.3 mmol) and aldehyde (0.2 mmol), photocatalyst 4CzIPN (0.004 mmol, 2 mol%), i-Pr2NEt (0.4 mmol, 2.0 eq.) and HE (0.28 mmol, 1.4 eq.) were added to the resulting mixture. Then, the mixture was stirred at rt under 5 W blue LEDs for approximately 30 h until the reaction was completed, as monitored by TLC analysis. The concentrated reaction residue was purified by flash column chromatography on silica gel to afford desired product. Note: The racemic samples were prepared according to the general procedure by replacing the chiral ligand with DPPP.

Conditions B: In an argon-filled glove box, a 10 mL vial equipped with a magnetic stirrer bar was charged sequentially with (R,R)-BDPP (0.024 mmol, 12 mol%) and CoI2 (0.02 mmol, 10 mol%), followed by the addition of THF (2 mL). After stirring at room temperature for 30 min, aryl iodide (0.3 mmol) and aldehyde (0.2 mmol), photocatalyst 4CzIPN (0.004 mmol, 2 mol%), i-Pr2NEt (0.4 mmol, 2.0 eq.) and HE (0.4 mmol, 2.0 eq.) were added to the resulting mixture. Then, the mixture was stirred at rt under 5 W blue LEDs for approximately 48 h until the reaction was completed, as monitored by TLC analysis. The concentrated reaction residue was purified by flash column chromatography on silica gel to afford desired product.


Key Words

arylation, Hantzsch ester, photochemistry


ID: J48-Y2022