N-heteroatom substitution effect in 3-aza-cope rearrangements.

Background: The nature of the heteroatom substitution in the nitrogen of a 3-aza-Cope system is explored.

Results: While N-propargyl isoxazolin-5-ones suffer 3-aza-Cope rearrangements at 60°C, the corresponding N-propargyl pyrazol-5-ones need a higher temperature of 180°C for the equivalent reaction. When the propargyl group is substituted by an allyl group, the temperature of the rearrangement for both type of compounds is less affected by the nature of the heteroatom present.