Hydrazine s. a. Wolff-Kishner

Hydrazides (s. a. Carboxylic acid hydrazides) reduction with borane 26,56 Hydrazine (s. a. Wolff-Kishner reduction) 26,15 reaction with dicarboxylic acid anhydrides 8, 482... 

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%. 

The reaction of hydrazine with a,/S-unsaturated aldehydes and ketones (the anomalous Wolff-Kishner reaction, Houben-Weyl, Vol. 4/3, p71) sometimes provides a one-pot procedure in which the cyclopropane is formed directly, but often the intermediate 2,3-dihydro-l//-pyrazole is isolated and heated either alone or with a basic catalyst to effect elimination of nitrogen. Hence in the conversion of chalcone to 1,2-diphenylcyclopropane the intermediate 3,5-diphenyl-2,3-dihydro-l//-pyrazole (10) was isolated and heated with potassium hydroxide. 

The Wolff-Kishner reaction is a classical reduction method of ketones to alkanes. This method involves converting the ketone to its corresponding hydrazine treatment of the resulting hydrazine with base affords the alkane and nitrogen gas. Because elevated temperatures (> 200 °C) and strong base are required, this method is harsh when sensitive functionality is present. However, milder methods have been developed including the Myers modification where the reaction temperatures are much lower (s 100 °C). 

The Wolff-Kishner reduction, discovered independently by N. Kishner in 1911 and L. Wolff in 1912 and reported within months of Clemmensen s discovery, is an alternative method for reduction of a carbonyl group to a methylene group. In this reduction, a mixture of the aldehyde or ketone, hydrazine, and concentrated potassium hydroxide is heated at reflux in a high-boiling solvent such as diethylene glycol (bp 245°C). 

Huang Minion modification of the Wolff-Kishner reduction. A mixture of 2-pivalyl-l,3-indandione and diethylene glycol treated with hydrazine hydrate, gradually heated during 1 hr. to 150° in an open flask, excess KOH added, the temp, raised to 200° and kept there for 1 hr. l,4-dihydro-3-tert-butylindeno-[l,2-c]pyrazole. Y 91.9%. F. e., also isolation of intermediates, s. R. A. Braun and W. A. Mosher, Am. Soc. 80, 4919 (1958). 

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