Orthoformylated

Orthoformylated is an adjective used in organic chemistry to describe a compound that has undergone orthoformylation, the introduction of a formyl group (-CHO) at the ortho position of an aromatic ring relative to an existing substituent such as a hydroxyl, amino, or alkyl group. The defining feature is the placement of the formyl group next to the directing group on the ring, creating adjacent substituents.

A classic example is salicylaldehyde, also known as 2-hydroxybenzaldehyde, which features an aldehyde and a neighboring hydroxyl group. In synthetic practice, orthoformylation has been achieved by several methods. The Duff reaction, which uses hexamethylenetetramine and acid, converts phenols into o-formylated products. Other historical routes include the Gattermann–Käse formylation and related procedures that preferentially install formyl groups onto activated rings, particularly at the ortho position to activating groups. Modern variants of formylation also employ Vilsmeier–Haack–type conditions for activated aromatics.

Applications of orthoformylated compounds span natural product synthesis, dyes, fragrances, and pharmaceutical intermediates. The ortho relationship can influence subsequent reactivity, directing further functionalization and enabling the construction of complex molecules through sequential transformations.

Etymology and usage: The term combines the prefix ortho- (indicating adjacency on the ring) with formyl, referring to the aldehyde substituent, and is used to denote compounds bearing an ortho-formyl group. In literature, orthoformylated species are discussed as intermediates or targets in aromatic functionalization strategies.