Radical addition of alkyl halides to formaldehyde in the presence of cyanoborohydride as a radical mediator. A new protocol for hydroxymethylation reaction.

Hydroxymethylation of alkyl halides was achieved using paraformaldehyde as a radical C1 synthon in the presence of tetrabutylammonium cyanoborohydride as a hydrogen source. The reaction proceeds via a radical chain mechanism involving an alkyl radical addition to formaldehyde to form an alkoxy radical, which abstracts hydrogen from a hydroborate anion.