Mechanisms of heterocycle ring formation. Part 5. A carbon-13 nuclear magnetic resonance study of pyrazolinone synthesis by the reaction of β-ketoesters with substituted hydrazines

Abstract

The 16 reactions between each of four hydrazines and four β-ketoesters have been followed by ¹³C n.m.r. spectroscopy. Peaks were assigned to starting materials, intermediates, and products, and reaction mechanisms determined and rationalized. Most reactions proceed by attack of the least hindered hydrazine nitrogen atom on the keto carbon group of the ketoester. Relative rates of nucleophilic attack determine the build-up of intermediate and in some cases the nature of the products formed.