Mercury acetate dehydrogenation

Camoensine and camoensidine were isolated from Camoensia maxima Welw. ex Benth. (183). Camoenzine is considered to be an isomer of leontidine. The mass spectra of these alkaloids were identical. Dehydrogenation of camoensine (157) with mercury acetate formed the immonium base (158), which was converted to leontidine (152) by sodium borohydride (Scheme 26). Camoensine... 

Alkyl groups attached to aromatic rings are oxidized more readily than the ring in alkaline media. Complete oxidation to benzoic acids usually occurs with nonspecific oxidants such as KMnO, but activated tertiary carbon atoms can be oxidized to the corresponding alcohols (R. Stewart, 1965 D. Arndt, 1975). With mercury(ll) acetate, allyiic and benzylic oxidations are aJso possible. It is most widely used in the mild dehydrogenation of tertiary amines to give, enamines or heteroarenes (M. Shamma, 1970 H. Arzoumanian. 1971 A. Friedrich, 1975). 

The employment of non-protic electrophiles for the foregoing type of cyclizations as illustrated in Scheme 8 has the particular merit of leaving a useful point of departure for further transformations. Comparable cyclizations of 2-allyl-3-aminocyclohexenones with mercury(II) acetate are preceded by dehydrogenation to the corresponding 2-allyl-3-aminophenol as shown in Scheme 9 82TL3591). The preferred direction of cyclization depends upon the nucleophilicity of the amino group. 

Dehydrogenation of ethyl 2-methyl-4-hydroxy-5,6,7,8-tetrahydro-4a//-pyrido]l,2-/j]pyridazine-3-carboxylate with mercury(II) acetate in ethanol at 45-50°C or over PtOa in boiling ethanol afforded anhydro 3-ethoxycar-bonyl-2-methyl-4-hydroxy-5,6,7,8-tetrahydropyrido[l,2-h]pyridazinium hydroxide (48) (71CPB159). The last compound could be reduced to the starting tetrahydropyrido[l,2-h]pyridazine over Pt02 in ethanol under hydrogen. 

The protoberberinium alkaloids are derivatives of the 5,6-dihydrodibenzo[n,g]quin-olizinium ion (95). There exist also alkaloids which are deriyatives of berbine (5,6,13,13a-tetrahydro-8i7-dibenzo[a,g]quinolizine, 94). Ban et al. have shown that dehydrogenation of berbine with mercury(II) acetate will afford the parent protoberberinium salt (95) in 75% yield (60CPB183). 

In a further study of routes to steroids with an aromatic ring C, 18-norandrost-13-enes (273) were found to give 7a-hydroxy-18-norandrosta-8,l 1,13-trienes (274) on reaction with selenium dioxide, while the 18-norandrosta-7,13-dienes reacted with mercury(n) acetate to give the 7a-acetate (276), as well as its 7j8-epimer. Mechanisms, including stepwise dehydrogenations, are discussed.226... 

In contrast to lead tetraacetate, simple addition to the double bond does not occur as a side re-action. While allylic rearrangement is common and mixtures of products are frequently obtained, the reaction often proceeds in very high yield and is simple to carry out the alkene is simply heated in an appropriate solvent with mercury(II) acetate until reaction is complete. Mercury(II) acetate has also been us for dehydrogenation, particularly in the steroid field. One interesting example incorporating simultaneous dehydrogenation and allylic oxidative rearrangement is seen in the reaction of abietic acid (37 equation 16). ... 

---