Transition-Metal-Free Hydrogenation of Aryl Halides: From Alcohol to Aldehyde
Hong-Xing Zheng1, Xiang-Huan Shan1, Jian-Ping Qu2
1Department of Chemistry, University of Science and Technology of China , Hefei 230026, China.
Abstract:
A transition-metal- and catalyst-free hydrogenation of aryl halides, promoted by bases with either aldehydes or alcohols, is described. One equivalent of benzaldehyde affords an equal yield as that of 0.5 equiv of benzyl alcohol. The kinetic study reveals that the initial rate of PhCHO is much faster than that of BnOH, in the ratio of nearly 4:1. The radical trapping experiments indicate the radical nature of this reaction. Based on the kinetic study, trapping and KIE experiments, and control experiments, a tentative mechanism is proposed. As a consequence, a wide range of (hetero)aryl iodides and bromides were efficiently reduced to their corresponding (hetero)arenes. Thus, for the first time, aldehydes are directly used as hydrogen source instead of other well-established alcohol-hydrogen sources.
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