2.4.2 Diimide (HN=NH)

Diimide can be prepared in situ, by the copper-catalyzed oxidation of hydrazine in the presence of hydrogen peroxide or oxygen as terminal oxidant or the decomposition of azodicarboxylic acid or sulfonylhydrazines (Scheme 6).

Scheme 6

D. J. Pasto, Encyclopedia of Reagents for Organic Synthesis, John Wiley and Sons, Inc., L. A. Paquette, Ed., New York, 1995, 3, 1892.

• The reduction using diimide finds unique applications because:

• The reagent is extremely tolerant of other functional groups

• The reduction is highly stereoselective and takes place cis-addition, from the less-hindered face.

• Reactivity decreases with increasing substitution about the alkene bond.

• Alkynes show greater reactivity compared to alkenes.

• Alkenes with electron withdrawing groups show greater reactivity compared to those with electron donating groups.

• Use of deuterium or tritium-labeled diimide gives a method of cis-reduction without scrambling of label.