A versatile building block for the synthesis of substituted cyclopropanephosphonic acid esters

Article abstract of DOI:10.1016/0040-4020(95)00522-A

By the effect of iodine, solid K₂CO₃ and a lipophilic quaternary ammonium salt phosphonoacetic acid allylic esters 4 were converted to cyclopropanephosphonic acid derivatives anellated to a five membered lactone ring 6 serving as good starting material for biologically active products. The reaction of cyclopropanation has been assumed to proceed by SET induced radical type elemental steps. Direct evidences were given by ESR for the 6-endo regioselectivity in the closure of electrophilic radical 11. An interesting and new exchange reaction of phosphonic ester moiety by iodine is also observed.