ALPHA-PYRAZOLYLALKYLPHOSPHONATES .1. SYNTHESIS OF 1-(3-PYRAZOLYL OR 5-PYRAZOLYL)-ALKYLPHOSPHONATES

alpha-Pyrazolylalkylphosphonates. Part I. Synthesis of 1-(3- or 5-pyrazolyl)-alkylphosphonates. New 1-(pyrazol-3(-5)-yl)-alkylphosphonates are easily and efficiently prepared by heterocyclization reactions of various 2,4-dioxo-alkylphosphonates (keto-esters, diketones or keto-aldehydes) with hydrazine, methylhydrazine or phenylhydrazine. Whereas regioselective cyclization is observed when keto-esters are reacted with any of the three hydrazines and when diketones or keto-aldehydes are condensed with unsubstituted hydrazine, a mixture of two annular isomers is generally obtained when diketones or keto-aldehydes are condensed with substituted hydrazines. An unambiguous identification of these regioisomers is proposed, resulting from combined P-31 and C-13 NMR spectroscopic arguments.