Enamines via Mercuric Acetate Oxidation of Tertiary Amines

Enamines via Mercuric Acetate Oxidation of Tertiary Amines 

The oxidation of amines by mercuric acetate is an old reaction (54) which up until recent years was employed primarily to modify alkaloid structures (55). A systemic study of the oxidizing action of mercuric acetate by Leonard and co-workers led to the development of a general method for the synthesis of enamines from cyclic tertiary amines. An observation made after a large number of compounds were oxidized, but which is worth noting at the onset, is that a tertiary hydrogen alpha to the nitrogen atom is removed preferentially to a secondary a-hydrogen. 

The first compound studied (56) was quinolizidine (41), which can be readily converted to J -dehydroquinolizidine (42) in 60% yield by the action of 4 moles of mercuric acetate in 5% aqueous acetic acid on 1 mole of the amine. Mercurous acetate precipitates as the reaction progresses at 

Steam-bath temperatures. Extension of the reaction to more complicated systems gave similar results. 

Sparteine (43) is oxidized to a mixture of isomers /J -didehydro-sparteine (44) and id -dehydrosparteine (45) (57). The other two stereoisomers of sparteine, a-isosparteine (46) (3S,j9) and S-isosparteine (sparta-lupine) (47) (58,60) have been subjected to mercuric acetate oxidation, each giving Zl -didehydrosparteine (44). 

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III. Enamines via Mercuric Acetate Oxidation of Tertiary Amines... 

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