The Cornforth Rearrangement.

摘要

The rates of Cornforth rearrangements of 2-aryl-5- methoxyoxazole-4-carboxylic amides have been studied. Variation of substituents in the 2-phenyl group indicates that a small positive charge develops at the adjacent carbon on passing to the transition state. Similar variation of substituents in a phenyl group attached to the amide nitrogen indicates that a similar small negative charge develops in the amide moiety. The effect of changes in the solvent also indicates that the transition state is not strongly polar. Either the transition state must occur early in the reaction or the open chain intermediate must be less polar than a classical zwitterionic structure would suggest. (Author)