Rearrangement ammonium Claisen

The third mechanism starts with addition of the AT-allylamine 103 to the cumulated acceptor system of an allene carbonester 108 (Acc=CHC02Me) to form an intermediate iV-allyl ammonium amide enolate 109 (allene carbonester Claisen rearrangement). The anion stabilizing group is exclusively placed... 

The behavior of tra s-[RuCl(=C=C=C=CH2)(dppm)2][PF6] towards the tertiary amine allyldimethylamine merits to be highlighted since the reaction led to the dimethylamino-allenylidene complex 32 through an Aza-Cope (or Claisen) rearrangement of the initially generated quaternary vinyl-allyl-ammonium salt [RuCl C=CC(NMe2CH2CH=CH2)=CH2 (dppm)2][PF6] (31) (Scheme 8) [47]. 

Reactions of alkynyliodonium salts with multidentate nucleophiles can be employed for the synthesis of heterocyclic compounds. Recent examples include preparations of thiazoles, selenazoles, and 2-mercaptothiazoles by the treatment of alkynyliodonium mesylates or tosylates with thioamides, selenoamides, and ammonium dithiocarbamate (Scheme 62) [169-171]. A novel hetero-Claisen rearrangement of tricovalent iodine(III) intermediates was proposed to account for the 2,4-disubstitution pattern of the thiazoles [169]. 

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 thio-Claisen rearrangement can also be performed with secondary thioamides, providing allylation on the nitrogen atom rather than carbon atom. An elaborate example was reported by Fuchs and Smith [183]. They introduced an allyl ammonium salt to achieve SN2 alkylation of sulfur, and the product readily rearranged to furnish the expected thiolactam. However they finally preferred to employ in the first step an allyl mesylate, which was more easily synthesised. 

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. 

Thus, the 0-methallyl ether of nonylphenol was rearranged by the Claisen reaction to afford an o-hydroxy C-methallyl compound, ethoxylation of which with excess ethylene oxide provided an intermediate for vinylic polymerisation with vinyl acetate in aqueous solution containing ammonium persulphate at 70°C (ref. 25). 

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... 

A domino process of enamine 136 formation, N-allylation, aza-Claisen rearrangement and a final Mannich condensation was introduced by Florent [22g]. Aldehyde 135 was subsequently treated with pyrrolidine and allyl iodide 137 to give an E/Z mixture of the ammonium salts 138. Heating to 80 °C induced the Claisen rearrangement. The newly formed iminium ions 139 underwent intramolecular Mannich cycUzations. The final amine eUmination delivered the spiro ketones 140 with 38% yield as a 2 1 mixture of diastereomers. The formed material should serve as a key compound in diverse cyclopentenone prostaglandine total syntheses (Scheme 10.30). 

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