Thallium triacetate ketones

Oxidation of enamines derived from cyclic and acyclic ketones with thallium triacetate in equivalent amount leads to the formation of the corresponding 2-acetoxy ketones75 (Scheme 52). The reactions are stereoselective (the antiparallel attack of the oxidizing agent is preferred over a parallel attack on 3- and 4-/-butylcyclohexanone enamines) and the attack occurs preferentially at the tetrasubstituted enamine double bond, when there is more than one possibility due to isomerism. 

Enamines are readily available ketone derivatives." Exposure of these compounds to certain transition metal salts has been shown to produce a-oxygenated imines which are rapidly hydrolyzed to their ketone counterparts. Thus, for example, morpholino enamines, prepared in situ, are a-acetoxylated on treatment with thallium triacetate. The process is thought to involve either direct nucleophilic extraction of an acetate unit or the intermediacy of an organothallium species which subsequendy undergoes anchimerically assisted intramolecular acetoxy migration to generate the a-acetoxyimine (Scheme IS). 

Oxidation of enamines6 [before references]. Enamines are oxidized by thallium triacetate at room temperature in glacial acetic acid or chloroform to give, after hydrolysis, the a-acetoxy derivative of the parent ketone. Thus morpholinocyclo-hexene is converted into 2-acetoxycyclohexanone in about 70% yield. The reaction can also be carried out on a combination of cyclohexane and morpholine (in situ generation of the enamine). Pyrrolidine enamines give somewhat lower yields. 

Yields are generally higher than those obtained by direct oxidation of the ketones with thallium triacetate or lead tetraacetate. The reaction is also stereospecific. Thus oxidation of the morpholine enamine of 4-/-butylcyclohexanone gives only trans-2-acetoxy-4-t-butylcyclohexanone. 

Rearrangements Aluminum bromide. Calcium carbonate. Dimethylthiocarbamyl chloride Dimsylsodium. 1,3-Dithiane. Lithium diethylamide. Manganese dioxide. Methyl vinyl ketone, 4a —> 5a. Michler s ketone. Norbornene. Perchloric acid. Pinacol-type see Potassium /-butoxide. Potassium /-butoxide. Silver perchlorate. Thallium triacetate. Triethyloxonium-fluoroborate. 

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