Reaction of Pyrrole Aldehydes and Ketones with Ethylene Glycol
Wade, Robert A.
MetadataShow full item record
Ketalization of several pyrrolyl ketones or aldehydes resulted in products lacking the acyl function. It was found that the rate and extent of ketalization depended on the number, inductive strength, and position of electron withdrawing substituents present on the pyrrole ring. Steric hinderance at the carbonyl function undergoing attack reduced the rate of reaction as expected. It was possible to form ketals where nitro, carboethoxy, or acetyl groups were present in addition to the carbonyl function undergoing attack. These groups tended to have a stabalizing effect upon the resulting ketal of a magnitude proportional to their electron withdrawing capability. Where the electron withdrawing groups were weak or present in addition to electron releasing groups (i.e. methyl), a new rearrangement was observed giving the deacylated pyrrole and the mono-ester of ethylene glycol derived from the carbonyl group undergoing nucleophilic attack. A mechanism is proposed which involves a rearrangement of the hemiketal intermediate.