A comparative product investigation between Grignard reactions of benzophenone and coupling reactions of electrogenerated benzophenone radical anions and alkyl radicals in THF

The 1,6- to 1,2-addition product ratios of the Grignard reactions of benzophenone with t-, s- and n-C4H9MgCl have been compared with the corresponding ratios obtained by the electrolysis of benzophenone in presence of t-, s- and n- C4H9S+(CH3)(2), ClO4- in THF. The Grignard reaction ratios 0.81, 0.50 and 0.19, respectively, were obtained whereas the corresponding electrolysis ratios were 2.26, 1.23 and 1.61. From this comparison of product ratios ii. is concluded that none of the Grignard reactions of benzophenone proceeds through a complete free coupling process of benzophenone radical anions and butyl radicals. The ET character of the Grignard reactions of benzophenone with t-, s- and n- C4H9MgCl was estimated to be 65, 61 and 26%, respectively.