Grignard reagent formation from aryl halides. There is no aryl radical intermediate along the dominant reaction channel

Abstract

For Grignard reagent formation from magnesium and an aliphatic halide RX in an ether solvent, a route through R is the major pathway. Part of the evidence is that by-products of side reactions of R are formed in substantial yields. Similar reactions of phenyl and o-(3-butenyl)phenyl halides give very low (sometimes trace) yields of by-products derived from side reactions of R , despite the fact that aryl R are much more reactive than alkyl in both solvent attack and cyclization [ o-(3-butenyl)phenyl case]. Grignard reactions of aryl halides appear to proceed largely through a pathway along which R is not an intermediate. This is probably a dianion pathway, that is, one along which RX 2− is an intermediate or transition state.