Cycloadditions and condensations as essential tools in spiropyrazoline synthesis.

Heterocycles with potential bioactive properties are of greater interest to researchers engaged in the areas of natural product synthesis and heterocyclic methodology. Several FDA (Food and Drug Administration) approved pharmaceutical drugs incorporate a heterocyclic motif in their core structure. Spiroisoxazolines and spiropyrazolines belong to the class of five membered heterocycles that have received greater attention over the past four decades. Spiropyrazolines structurally resemble naturally occurring spiroisoxazolines, have extra nitrogen in place of isoxazoline oxygen, and offer the viability to construct useful analogs for the exploration of possible bioactivity. As of today, no reports on the construction of these spiropyrazolines were available and the current review is aimed at providing a comprehensive discussion of the protocols applied in the synthesis of functionalized spiropyrazolines.