Base catalysed rearrangements involving ylide intermediates. Part 4. [1,3] Sigmatropic rearrangements of 4-dimethylaminobutenes and [3,3] sigmatropic rearrangements of 3-dimethylaminohexa-1,5-dienes

Abstract

The [1,3] sigmatropic rearrangement (11)→(12) of the 9-dimethylamino-9-(1-phenylallyl)fluorene is a stereoselective process (84 : 16) at 170°. Analogous [1,3] rearrangements (16)→(17) of other fluorene derivatives show that the reaction rate is increased by electron donating 9-substituents in the order O^– > NMe₂ > OMe. Similar substituent effects are observed for the [3,3] Cope rearrangement (25)→(26) of hexa-1,5-dienes. 4-Phenyl, 4,4-dimethyl, and 3-dimethylamino substituents are particularly effective in accelerating the rate of the rearrangement (25)→(26).