5.2.4 Reimer-Tiemann Formylation

The reaction involves formylation of phenol and analogues using chloroform in the presence of base. First, chloroform reacts with base to give electrophilic dichlorocarbene which in situ undergoes reaction with phenoxide ion. The resulting benzal chloride can be converted into salicylaldehyde by hydrolysis followed by acidification.

Mechanism

Pyrrole, which resembles phenol in reactivity towards electrophiles, undergoes reaction to give pyrrole 2-aldehyde along with 3-chloropyridine as by-product. Both products form from the same intermediates.