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Synlett 2009(3): 495-499  
DOI: 10.1055/s-0028-1087552
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Highly Efficient and Facile Aryl Transfer to Aldehydes Using ArB(OH)2-GaMe3

Xuefeng Jiaa, Ling Fanga, Aijun Lina, Yi Pana, Chengjian Zhu*a,b
a School of Chemistry and Chemical Engineering, State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, P. R. of China
Fax: +86(25)83594886; e-Mail: cjzhu@nju.edu.cn;
b State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, P. R. of China
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Publication History

Received 26 August 2008
Publication Date:
21 January 2009 (online)

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Abstract

A rapid and efficient procedure for the synthesis of di­arylmethanols has successfully been achieved by the aryl transfer to aldehydes using the ArB(OH)2-GaMe3 combined systems in excellent yields (up to 98%) at room temperature.

Key words

aryl transfer - benzaldehyde - phenylboronic acid - tri­methylgallium - diarylmethanol

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General Experimental Procedure
The arylboronic acid (0.3 mmol, 1.5 equiv) was dissolved in anhyd toluene (2 mL) in a 20 mL flame-dried Schlenk reaction tube under argon atmosphere. A commercially available 1 M solution of Me3Ga in toluene (0.9 mmol, 4.5 equiv) was added via syringe dropwise, and the resulting mixture was stirred for 2 h at r.t. followed by the addition of aldehyde (0.2 mmol). After completion of the reaction (monitored by TLC), the reaction solution was quenched with H2O (3 mL) and further extracted with EtOAc (3 × 5 mL). The combined organic layer was dried over Na2SO4. Evaporation of the solvent gave the crude product, which was further purified by preparative TLC (PE-EtOAc, 5:1) to give corresponding pure diarylmethanols.

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The reactivity of nitro-substituted benzaldehyde is in agreement with the experimental results in references 3c, 4d-f, but 4-nitrobenzaldehyde is not reactive in reference 2a.

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In reference 8g,h, the mechanism of the boron-to-zinc transmetalation has been clarified by theoretical calculations and experimental study. In this process, the mixed zinc species (ArZnEt) is formed.