Mutual influence of (dimethylhydrazono)methyl groups and α-hydroxy ketone moieties in hetaryl analogues of unsymmetric benzoins

Reactions between phenylglyoxal hydrate and the N,N-dimethylhydrazones of furfural and pyrrole-2-carbaldehyde run regioselectively at the 5-position of the heterocycle. The resulting hetaryl analogues of alpha-benzoins quantitatively isomerize to beta-compounds, the (dimethylhydrazono)methyl group activating the hetaryl residue and thus affording faster isomerization than in their unfunctionalized counterparts. The (dimethylhydrazono)methyl group is easily convertible into the aldehyde or nitrile group and can also be involved in rehydrazonation.