Ring-opening reactions. Part 4. The role of strain and stereochemical effects on the elimination and substitution reactions of small rings; the reactivity of 1,1-dimethylaziridinium systems

The kinetic behaviour of 1,l -dimethyl- and 1,1,2,3-tetramethyl-aziridinium ions has been compared in the light of the strong tendency of 1,1,2,ω-tetramethyl cyclic ammonium ions to undergo ring opening via the exocyclic elimination reaction. Surprisingly, with the aziridinium member of the latter series, ring-opening substitution takes place more readily than exocyclic elimination by a large factor. The operation of combined strain and stereochemical rate-enhancing effects in substitution, as suggested by previous work on the 1,1-dimethyl cyclic ammonium ions, is now confirmed.