PERICYCLIC REARRANGEMENTS

The effect of media on reactivity is a classic concern for organic chemists. Whether one is considering the solvent in which to conduct a reaction, or the effect of a low dielectric interior in an enzyme active site, the medium has profound effects on reactivity and binding. The elimination and decarboxylation reactions of benzisoxazoles and 3-carboxybenzisoxazoles are extremely medium-sensitive, and occur more rapidly in aprotic solvents. A combined experimental and theoretical investigation is being undertaken to explore these reactions in the gas phase and with individual-molecule solvation in order to understand how solvation and biological catalysis affect reaction energetics and transition structures. Medium also plays a role in the rearrangements of anionic Cope substrates. Anion-accelerated Cope rearrangements, of which the anionic oxy-Cope is the most well-known, are predicted to proceed very rapidly in the gas phase. Probe reagents are used that can differentiate between the starting material and product, which have the same m/z ratio, in order to discern whether rearrangement has occurred. Theory is utilized to explore transition structures and to lend insight into how and why these reactions experience such great acceleration.