Bromonitromethane—a versatile electrophile

Abstract

Pathways in reactions of bromonitromethane with a variety of nucleophiles have been investigated.

With thiolates, the electrophilic centre is bromine and the initial products are disulphides. When the thiolate ion itself carries an electrophilic centre such as carbonyl or cyano β-to sulphur, the product is a nitrothiophene derived from subsequent reaction of the first-formed disulphide with nitronate ion displaced in the initial process. This provides a generalisation of earlier nitrothiophene synthesis by this route.

In reactions with arenesulphinate ion, the electrophilic centre is also bromine and equilibration between the initial reactants and the initial products, sulphonyl bromide and nitronate ion, is established. The components of the equilibrium subsequently react either with each other or with the solvent. Reactions with sulphides are slow and distal substituents such as hydroxy- or cyano- so much reduce reactivity that no reaction is observed. Dimethyl sulphide attacks bromonitromethane at the carbon atom, and subsequent attack on the nitromethyl sulphonium salt initially formed gives methylthionitromethane and trimethylsulphonium bromide.

Iodide ion attacks at bromine to give iodine, presumably via iodine bromide, but with tervalent phosphorus nucleophiles, attack is at oxygen giving the corresponding oxides and HCN in a double deoxygenation sequence. For hydroxide, methoxide, and hydride ions (from sodium borohydride), nucleophilic attack is at hydrogen and the nitronate ion produced is inert to further attack. There is no evidence of carbene formation by α-elimination.

When the anion of bromonitromethane is allowed to react with tributylboron, the anionic migration–displacement which follows boron–carbon bond formation, yields 1-nitropentane.

The anion of bromonitromethane is unreactive towards aldehydes and electrophilic alkenes.