Grignard reagents react with 4,4,5,5-tetramethyl-1,3,2-dioxaborolane, pinacolborane, under ambient reaction conditions to afford the corresponding pinacolboronate esters.  This reaction is very general, one equivalent of halide (aliphatic, aromatic, heteroaromatic, vinyl or allylic) is transformed into the corresponding Grignard reagent followed by the addition of a single equivalent of pinacolborane in THF.  Iodine also reacts with pinacolborane at ambient reaction conditions  in THF to form the iodo-alkoxy borate species (4-iodobutoxy)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane. One equivalent of iodine and PinBH react to form iodo-PinB, which then interacts with THF by cleavage of one carbon-oxygen bonds to form the corresponding iodo-alkoxy pinacolborate.  Treatment with aryl Grignard reagent reacts with iodo-alkoxy pinacolborate in THF to then form the corresponding aryl pinacolboronate ester while reforming and liberating THF as a leaving group.

Reaction of pinacolborane with iodine and magnesium under ambient Grignard and Barbier conditions utilizing THF as a leaving group

243rd National Meeting (2012)

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