Syntheses of 1,2-Oxaphospholane 2-Oxides and 1,2-Oxaphosphole 2-Oxides

1,2-Oxaphospholane and 1,2-oxaphosphole 2-oxides, ?-phosphonolactones and ?-phosphinolactones, also called ?-phostones and ?-phostines, are important five-membered 1,2-oxaphosphaheterocycles and crucial motifs of some biologically active compounds. Various synthetic methods of these 1,2-oxaphosphaheterocycles have been developed till now. They can be divided as cyclization, annulation, cycloaddition, ring expansion and contractions. The cyclizations mainly include intramolecular nucleophilic substitution of 3-haloalkylphosphonic and phosphinic acid derivatives, esterification of 3-hydroxyalkylphosphonic/phosphinic acids, transesterification of alkyl 3-hydroxyalkylphosphonates/phosphinates, halocyclization of alkyl alk-2/3-enylphosphonates, halocyclization of allenylphosphonic acid derivatives, the transition metal-catalyzed oxidative cyclizations of benzyl/2-methylphenylphosphonic/phosphinic acids, and the Pd-catalyzed cyclization of ?-bromoalkyl phosphonates/phosphinates. The annulations covers [4+1] and [3+2] annulations. In this review, we have described various strategies and further development for the synthesis of 1,2-oxaphospholane and 1,2-oxaphosphole 2-oxides.