Triphenylphosphite as a good reagent for the diasteroselective synthesis of phosphonate esters

The reaction between dialkyl acetylenedicarboxylates and N-H acids such as pyrazole and indazole in the presence of triphenylphosphite at room temperature led to stable phosphonate ester derivatives 4a-f. The configuration of compounds 4a-f (2S*, 3R*) was determined on the basis of coupling constants predicted from the Karplus equation.