[4 + 3] Cycloaddition Reactions

摘要: Cycloaddition in its many manifestations represents one of the most powerful methods organic chemistry for making cyclic structures. The high levels convergency and stereoselectivity that frequently characterize these processes are particularly attractive from a preparative point view. Five- six-membered rings typically made by well-known 1, 3-dipolar Diels–Alder cycloaddition reactions, respectively, so-called higher-order have emerged recently as useful methodology construction medium-sized carbocycles. Seven-membered ring systems, owing primarily to their broad occurrence substructures classes natural products, important targets synthesis, but there relatively few ways currently available de novo synthesis systems. As general solution this problem, [4 + 3] between 3-diene an allyl, or more oxyallyl, cation offers rapid access functionalized seven-membered carbocycles with attendant virtues other processes. Considerable effort has been expended exploit synthetic utility several informative reviews subject available. Electronically, process is quite similar reaction can be viewed [4π(4C) + 2π(3C)] combination which allyl participates reactive 2π component. Much developmental work associated focused on approaches generation oxyallyl partner, number emerged. While wide range partners employed π-excessive heterocycles such furan pyrrole shown participants and, recently, intramolecular versions effectively applied product synthesis. This chapter literature cycloadditions involve cations closely related 2π(3C) reactants mid-1996. Those previously compiled Noyori Hayakawa 1983 review reductive dehalogenations polyhaloketones also included current so all relevant examples located document. Other 4 + 3 annulation afford employ types intermediates not covered survey. Keywords: [4 + 3] reactions; mechanism; stereochemistry; scope; limitations; reductive conditions; solvolysis conditions; base-mediated conditions; photochemical conditions; intramolecular conditions; synthesis applications; comparison methods; experimental conditions; experimental procedures; tabular survey