Studies on heterocyclic chemistry. Part XVI. Reaction of 4-o-nitrobenzylidene-Δ2-pyrazolin-5-ones with trialkyl phosphites: synthesis of phosphorus-substituted pyrazolo[3,4-b]quinoline derivatives

Abstract

The reaction of 4-o-nitrobenzylidene-Δ²-pyrazolin-5-ones with trialkyl phosphites is much more complicated than that of the related 4-o-nitrobenzylidene-Δ²-oxazolin-5-ones, affording dialkyl 9a-alkoxy-9,9a-dihydropyrazolo-[3,4-b]quinolin-4-ylphosphonates as the major products (7–25% yield).