The acid-catalyzed alkene-aldehyde condensation, known as the Prins reaction, is reviewed. Lewis acids, organic acids and supported catalysts have been reported to assist both the Prins acyclic reaction and the Prins cyclization. Acetals and oxocarbenium ions (generated from aldehydes and alcohols) have been described as reacting systems in the Prins reaction. Prins cyclizations have been used to form mainly five- and six-membered rings, albeit formation of seven to nine rings have been described. The Prins reaction (and cyclization) has been developed as a key strategic element in the total synthesis of different natural products.

This review deals with the metal promoted asymmetric ring opening of achiral epoxides using achiral carbon-, nitrogen-, oxygen-, sulphur- and halogen-containing nucleophiles. The use of chiral bases in the asymmetric deprotonation of achiral epoxides yields chiral allylic alcohols. Finally, kinetic resolution of racemic epoxides can be achieved using chiral metal complexes.

The Prins reaction and the Prins cyclization have stood out as important synthetic strategies, and here the latest advances in this topic are reviewed. Different mineral acids, Lewis acids, organic acids and supported acidic materials have been employed as promoters for this type of transformation, the reaction with paraformaldehyde being the most considered one. Without any doubt, the Prins cyclization forming oxygenated heterocycles is one of the most common tranformations, and many studies have been reported on this topic. The acid-promoted Prins cyclization of an oxocarbenium ion generated in situ from suitable starting materials in order to produce the corresponding tetrahydropyrans have been extensively studied and employed in the total synthesis of a wide number of natural products. Additionally, the Prins cyclization have been employed in the synthesis of five, seven, eight and nine membered rings. The aza version of this reaction has been also considered, the analogous aza-cyclization allowing the synthesis of piperidine derivatives, which are widely distributed in natural products.