Homocoupling Reactions of Functionalized Benzylic Manganese Reagents

Homocoupling Reactions of Functionalized Benzylic Manganese Reagents 

We examined the homocoupling of benzyl halides under the influence of active manganese in a wide variety of conditions. As shown in Table 8.15, lequiv of active manganese and 2 equiv of benzyl bromide produced 47% of homocoupling products. But the homocoupling yield was decreased to 27% by using 1 equiv of benzyl bromide. 

Best results were obtained when the active manganese was added to the neat benzyl bromide. The reaction was completed within 10 min at rt without a catalyst [39]. Several other benzyl halides produced good to excellent yields of homocoupling products, which showed a wide tolerance of functional groups such as nitrile, ester, nitro, chloro, bromo, methoxy, and methyl groups (Table 8.16). 

Our method is more efficient compared to the previous attempts to prepare functionalized bibenzyl compounds [40] in terms of mild conditions and speed of the reaction. More significantly, no transition metal catalyst (Pd or Ni) was required for completion of the reaction nor was a solvent required. 

Palladium-Catalyzed Cross-Coupling Reactions of Benzylic Manganese Reagents 

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