Synthesis of 1,2-oxaphosphinane 2-oxides and 1,2-oxaphosphinine 2-oxides: δ-Phosphonolactones and δ-phosphinolactones

1,2-Oxaphosphinane and 1,2-oxaphosphinine 2-oxides and their benzo derivatives, δ-phosphonolactones and δ-phosphinolactones, also called δ-phostones and δ-phostines, are important six-membered oxaphosphaheterocycles and crucial core structures of some biologically active compounds and organic materials. Numerous synthetic methods of these oxaphosphaheterocycles have been developed. They mainly focus on the cyclization strategies, including construction of P–O, O–C, P–C, and C–C bonds via cyclizations, and [4+2], [5+1], and [3+3] annulations. Cycloadditions, ring contractions and expansions have also been applied in the synthesis of 1,2-oxaphosphinane and 1,2-oxaphosphinine 2-oxide derivatives. In this review, we have described various strategies for the synthesis of 1,2-oxaphosphinane and 1,2-oxaphosphinine 2-oxide derivatives and further development.