Preparation of Nitro-functionalised Organo

The technique of iodine-magnesium exchange allows the preparation of Grignard reagents which are not accessible by other means, particularly those with a nitro group in the ortho position. This allows cross-coupling reactions to take place to give highly functionalised products (Sapountzis I et al, Angew Chem Int Edn, 2002, 41, 1610). The use of phenylmagnesium chloride works best, whereas methyl and isopropyl Grignards give complex mixtures.

In the case of 2,5 diiodonitrobenzene, only the ortho iodine is replaced, showing that chelation by NO₂ may be significant. Transmetallation to organo copper or zinc species sometimes improves the yield.

For those that enjoy a mechanistic puzzle, let me recommend a feature article by Samir Zard in Chemical Communications (2002, 1555), which describes some novel reactions leading to acetylenes.

The reaction may proceed via oxazolinones, which can be generated from keto esters, and can then yield alkynes.

Conditions have been found which give good yields of acetylenes including cycloalkynes.