Alkyl Isosteres.

By substituting an ER3- unit (E = Group 13 element) or E'R3+ (E' = Group 15 element) for CR3 one gets to methyl isosteres, compounds analogous to alkyls and isoelectronic or iso-valence-electronic to them. The substituent charge can be used to stabilize countercharged aromatic systems; some compounds of this type are known. Nature makes available all kinds of escape routes to such formally zwitterionic species. Strategies for impeding the often facile reaction channels that open up can be designed. We construct what we believe are viable further examples of zwitterionic methyl isosteres based on 3-, 5-, 7-, and 8-membered rings. A similar strategy is laid out for dicationic and dianionic xylene isosteres.