Abstract
α-Oxoketenes are currently of major interest in synthetic and mechanistic studies. They are most conveniently generated by thermal fragmentation of 1, 3-dioxin-4-ones or acylated Meldrum's acids under a mild heating. Meldrum's acid itself also generates carboxyketene through the tautomeric 6-hydroxydioxinone under mild heating. The fragmentation of dioxinones to α-oxoketenes is of much interest from mechanistic viewpoint, because the transition structure of the ring opening is almost planner as recently revealed by ab initio calculations. α-Oxoketenes thus generated serve as powerful acylating reagents of nucleophiles to produce β-keto acid derivatives. They also serve as hetero-dienes in 4+2 cycloadditions to produce heterocyclic compounds. In addition, use of dioxinones provides ready access to hydroxylated or aminated ketenes. Intramolecular trappings of these ketenes afford lactones or lactams including macrocyclic compounds. Intramolecular dimerization of bis (oxoketene) tethered to origomethylene unit efficiently produces a series of new cyclophanes.
