Ammonium chloride Claisen rearrangement

Allyl ethers of enols and phenols undergo rearrangement to C-allyl derivatives when heated to sufficiently high temperatures. The reaction, named after its discoverer (Claisen, 1912), was first observed when ethyl O-allylacetoacetate was subjected to distillation at atmospheric pressure in the presence of ammonium chloride.1 2... 

The catalytic influence of ammonium chloride on the rate of the reaction was discussed by Claisen in his first report19. Since then, numerous catalysts have been introduced to affect rate enhancements of Claisen rearrangements, e.g., Bronsted and Lewis acids, bases or transition metal complexes. The literature concerning catalytic effects in the Claisen rearrangement has been thoroughly covered until 1984 0,122. 

Stille and co-worker developed an attractive route to aza-Claisen precursors. Allylamine reacted with 2-methylpropanal (isobutyraldehyde), for example, to give allylimine 658. When this reacted with 2-methylpropanoyl chloride, N-acyl derivative 659 was produced (94% overall yield from allylamine) and reduction with LiAlH4 give a 98% yield of the tertiary amine, 660. Stille found that conversion of the amine to the ammonium salt by treatment with HCl led to clean conversion to 661 in 82% yield via a [3,3]-sigmatropic rearrangement (an aza-Claisen rearrangement). Reduction of the iminium salt led to an 81% yield of 662 from 661. Stille and co-workers also found that Lewis acids as well as HCl react with the allyl enamine precursor to facilitate the aza-Claisen rearrangement. 2... 

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