“…The Prins reaction is a powerful and versatile methodology for the construction of oxygenated heterocyclic compounds. − This reaction, together with its N - and S -variants, has been extensively used for the preparation of different-ring-size carbo- or heterocycles in the so-called Prins cyclization, a transformation that requires the use of an aldehyde or a related compound, an alkene (the so-called π-component) and a nucleophile, in a process that is typically promoted by a Lewis or Brønsted acid (Scheme ). The key step on this reaction is the formation of an oxocarbenium ion that reacts with 1 equiv of the π-component in an intermolecular (Scheme , top) or intramolecular fashion (Scheme , bottom).…”