Isatin-3-hydrazones oxindoles

The first microwave-assisted Wolff-Kishner reduction was described by Parquet and Lin in 199763. The transformation of isatin to oxindole was performed on a small scale in a domestic microwave oven in two steps with a total reaction time of 40 s, as compared to 3—4 h if classical heating was utilised (Scheme 4.36). The first step involved the transformation of the carbonyl group into the hydrazone with 55% hydrazine in ethylene glycol and medium power microwave irradiation for 30 s. In the subsequent reduction step, KOH in ethylene glycol was used to substitute the more hazardous sodium ethoxide. The reaction mixture was irradiated for 10 s and the product was obtained in a yield of 32%. 

Heating of hydrazones 86 with sodium hydroxide gave oxindole and isatin azine,319 and heating with sodium ethoxide gave oxindole,... 

Formaldehyde f-butyl hydrazone, H2C=N-NH-Bu has been used as a formyl anion equivalent it reacts with isatins to give functionalized 3-hydroxy-2-oxindoles. 

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