6.4 Substitution via Benzynes

Halobenzenes (except fluorobenzene) directly react with strong base such as sodamide to give benzyne that can be reacted with any nucleophile present the reaction medium. For example, the addition of malonic ester to liquid ammonia having amide ion afford the corresponding enolate that reacts with benzyne as it is produced.

• 

Furthermore, ortho substituted benzenes from which two stable molecules can be generated by elimination afford benzynes on thermolysis.

If the nucleophile is not present in the reaction medium, benzyne dimerizes to give biphenylene.