CLARIFICATION OF MECHANISM OF REACTION OF TERMINAL PROPARGYLIC CHLORIDES WITH ALKYL GRIGNARD-REAGENTS

In the absence of transition metal impurities in the magnesium used to prepare the alkyl Grignard reagent, terminal propargylic chlorides react with Grignard reagents to form an allene carbene-zwitterion intermediate. Reaction of this intermediate with a second molecule of the Grignard reagent generates a mixture of propargyl and allen-y1 Grignard reagents which on hydrolysis generates a mixture of two alkynes and the allene. No evidence was found for the occurrence of carbonium ion, free radical, or SN2' reaction pathways. © 1978, American Chemical Society. All rights reserved.