Synthesis of heterocyclic methylenebisphosphonates by 1,3-dipolar cycloaddition of ethyl diazoacetate to 1,2-benzoxaphosphorin-3-phosphonates
作者:Nevena I. Petkova、Rositca D. Nikolova、Anka G. Bojilova、Nestor A. Rodios、Jurgen Kopf
DOI:10.1016/j.tet.2008.12.048
日期:2009.2
Reaction of salicylaldehydes with tetraethyl ester of methylenebisphosphonic acid, under Knoevenagel reaction conditions, gives the corresponding 1,2-benzoxaphosphorin-3-phosphonates 5 in good yields. The [3+2] regio- and stereoselective cycloaddition of 5a and 5b with ethyldiazoacetate gives two P-4 epimers of the corresponding pyrazoline bisphosphonate tetraethyl esters 9 and 10. Analogously, ethyl