Formation of grignard reagents from aryl halides: Effective radical probeshint at a nonparticipation of dianions in the mechanism

[GRAPHICS] We have prepared highly efficient radical probes 2a-b involving the hex-5-e nyl rearrangement, The reaction of 2a-b with active magnesium leads to the cyclized products 4a-b, providing a direct evidence of radical intermediate s during the formation of aryl Grignard reagents. The variations of yields for cyclized products 4a-b as a function of structural modifications in 2a- b suggest that the intervention of dianions is not necessary to explain the observed results.