Systems Claisen rearrangement

Nitrogen heterocyclic systems, Claisen rearrangements in, 8, 143 Nomenclature of heterocycles, 20, 175 Nuclear magnetic resonance spectroscopy, application to indoles, 15, 277 Nucleophiles, reactivity of azine derivatives with, 4, 145... 

Heteroaromatic sulfoxides and sulfones ligand exchange and coupling in sulfuranes and //Avo-substitutions, 49, 1 Heteroaromatic systems, Claisen rearrangements in, 42, 203 Heteroaromatics, quantitative analysis of steric effects in, 43, 173 Heterocycles aromaticity of, 17, 255 chiral induction using, 45, 1 containing the sulfamide moiety,... 

In acyclic systems, Claisen rearrangements show a well-established prefoence for chair-like transition states. With crotyl propenyl ether, the chair selectivity amounts to 97-98% at 142 C, which corresponds to an approx. 3 kcal mol difference between the fiee energy of activation (AAG ) of chair and boat TS (equation 26). The preference for a chair-like geometry in the TS is even more pronounced in the Cope reaiT ement 99.7% of the 3,4-dimethylhexa-1,5-diene rearranges at 225 C via a chair-like TS, corresponding to a AAG chair-boat of -5.7 kcal mol" . - The latter result closely parallels the difference in energy of the chair and boat conformations of cyclohexane (5-6 kcal mol" ). ... 

---