meta-Benzyne Reacts as an Electrophile

Examination of gas-phase reactions of various nucleophiles with meta -benzyne analogues that carry a positively charged substituent has revealed that the meta -benzyne moiety is susceptible to nucleophilic attack. Addition of nucleophiles to the meta -benzyne moiety occurs rapidly without energy-demanding uncoupling of the singlet biradicals' formally unpaired electrons. The resulting zwitterionic intermediate may undergo fragmentation either by a homolytic bond cleavage to yield net-radical type products or by a heterolytic bond cleavage that generally leads to replacement of the original charged group with the incoming nucleophile. The intermediate was characterized experimentally and computationally and found to be a low-energy species. The nonradical reactivity reported here is common for meta -benzynes with positively charged substituents, and is predicted also to dominate the chemistry of anionic and neutral meta -benzynes.