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40.1.3.1.4.2 Variation 2: By Aza-Oxa-Cope Rearrangement

DOI: 10.1055/sos-SD-040-00396

Feng, J. Q.; Li, C.-J.Science of Synthesis, (200940606.

Another elegant amination procedure for the formation of allylamines from allylic alcohols involves the [3,3]-sigmatropic rearrangement of allylic trichloroacetimidates 86 into allylic amides 87 (the Overman rearrangement) by heating them in xylene at reflux (Scheme 31). The products can then be hydrolyzed to the desired amines [‌111‌,‌112‌] The yields obtained are generally good for reactions giving primary and secondary amides, but low for products where the amide nitrogen is bound to a tertiary carbon atom (1040%). The hydrolysis of the amides is quite slow and stirring for 30hours in 3M sodium hydroxide in water and ethanol is necessary. The sigmatropic rearrangement may also be carried out at ambient temperature if a catalytic amount of mercury(II) trifluoroacetate is added and yields, and selectivities are comparable to those of the thermal reactions.[‌111‌,‌112‌] A two-step mechanism is proposed for the catalyzed reactions, so that an electrophilic addition of a mercury(II) ion to the double bond forms a cation, which is then captured intramolecularly by the nucleophilic imino nitrogen atom.[‌111‌] Even though the relatively high basicity of the imidates means that only a few metals are able to catalyze the type of rearrangement shown in Scheme 31,[‌113‌] some soluble palladium(II) complexes are quite effective. However, ligand variety is reduced as phosphines inhibit the reaction.[‌114‌,‌115‌] This inhibitory effect probably arises because the strong electron-donating ability of a phosphine ligand diminishes the Lewis acid character of any palladium(II) complex that contains it.

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References