Mercury oxide allylic oxidation

The cyclized analog of meralluride is prepared by a similar synthesis. Thus, condensation of camphoric acid (42) (obtained by oxidation of camphor) with ammonia gives the bicyclic succinimide (44). Reaction with allyl isocyanate followed by ring opening and then reaction with mercuric acetate affords the mercury derivative (45) as the acetate rather than the hydroxide as above. Reaction with sodium chloride converts that acetate to the halide (46). Displacement on mercury with the disodium salt of thioglycollic acid affords the diuretic mercaptomerine (47). ... 

To circumvent some of the above-mentioned drawbacks of sulfur-based mercury chemodosimeters, a system based on the alkyne oxymercuration of 58 has been developed (Fig. 22) [146]. 58 shows high selectivity, a limit of detection of ca. 8 ppm, resistance against strong oxidants, and a positive reaction even in the presence of cysteine, which is known to form stable mercury complexes and is used for the extraction of mercury from tissue samples. Another metal that is well-known for its catalytic ability is palladium, catalyzing different reactions depending on its oxidation state. Since this metal is toxic, assessment of the maximum allowable concentration of Pd in consumer products such as pharmaceuticals requires highly sensitive and selective detection schemes. For this purpose, indicator 60 was conceived to undergo allylic oxidative insertion to the fluorescein... 

Alkyl groups attached to aromatic rings are oxidized more readily than the ring in alkaline media. Complete oxidation to benzoic adds usually occurs with nonspecific oxidants such as KMn04, but activated tertiary carbon atoms can be oxidized to the corresponding alcohols (R. Stewart, 1965 D. Arndt, 1975). With mercury(II) acetate, allylic and benzylic oxidations are also 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). 

Allyl ethers are also formed under PTC conditions (see Expt 5.73). These ethers are stable under moderately acidic and basic conditions. Deprotection is achieved by treatment with potassium t-butoxide in dimethyl sulphoxide, which results in rearrangement to the corresponding prop-l -enyl ether, followed by reaction with a mercury(n) chloride/mercury(n) oxide reagent mixture.78... 

The terms in equation (23) which are independent of the acid concentration show little or no solvent isotope effect. This and considerations following from the Bronsted Catalysis Law make it unlikely that these terms represent cleavage of the complexed substrate by water. A ratedetermining, unimolecular rearrangement from the a- to the v-allylic mercurial was suggested. Oxidative cleavage of some sort is another possibility. 

Isomerisation of allyl ethers to enol ethers by Wilkinson s catalyst in refluxing aqueous ethanol is accompanied by competing reduction of the double bond to the propyl ether409-412 However, treatment of Wilkinson s catalyst with butyl-lithium results in a red rhodium catalyst that is able to isomerise a wide range of substituted and unsubstituted allylic ethers without competing reduction.413-414 In the example shown in Scheme 4.215, the unpurified enol ether product was cleaved by treatment with a mixture of mercury(Il) chloride and mercury(II) oxide in acetone to liberate the anomeric centre in 91% yield for the two steps.413-414... 

Neurotoxic chemicals and motor neuropathy Chlorpyrifos, dichlorvos (DDVP), EPN, n-hexane, 2-hexanone, lead, lead chromate, lead II thiocyanate, leptophos, methamidophos, mipafox, omethoate, parathion, trichlor-fon, trichloronate, triorthocresyl phosphate Neurotoxic chemicals and sensorimotor neuropathy acrylamide, allyl chloride, arsenic and compounds, arsenic trichloride, calcium arsenate, carbon disulfide, dichloroacetylene, ethylene oxide, gallium arsenide, lead arsenate, mercuric chloride, mercuric nitrate, mercurous nitrate, mercury, nitrous oxide, phenyl arsine oxide, thallium and soluble compounds, thallous nitrate... 

On the basis of this and other evidence allylic mercuty(II) acetates are believed to be the reaction intermediates in all allylic oxidations with mercury(II) acetate. The isolation of the less stable secondary... 

That mercury(ll) acetate allylic oxidatimi can be a usrful reaction in the case of complex and sensitive substrates is demonstrated by the oxidation of avomectin A2a (38). The reaction, carried out in anhydrous toluene at 100 C for 40 min, was mnaikably selective, allylic oxidation occurring exclusively at the 3,4-double bond with rearrangement to give (39) in up to 73% yield (equation 17). 

Overall, many transition metal complexes have been investigated. Among those not mentioned above which may carry out catalytic allylic oxidation to give enones under certain drcumstances are Co(PPh3)Cl/02, Mn(TPP)Cl/02, [Fe(PPh3)]20AJV, Ni(phthalocyanine)/02 and an unusual mercury(II) acetate example in which the enone is formed rather than the expected acetate. 

Other transition metal salts mediate in similar oxidations. For example, mercury(II) acetate, a milder reagent than LTA, effects a-acetoxylation through a comparable mechanism. However the corresponding yields for these processes are poor. 3,3-Dimethylcyclohexanone, for example, is oxidized to the a-acetoxy derivative in only 14% yield.The, 7-unsaturated ketone, isopugelone, exhibits no oxidation at the a- or a -positions, but affords a product derived from isomerization of the alkene and allylic oxidation. Not surprisingly therefore the reagent has found little synthetic application for this transformation. 

While allylic oxidation products may arise by elimination of a metal hydride from an intermediate adduct or metal-alkene complex, allylmercury species (34) are thought to be intermediates in the case of mercury(II) acetate. A number of pathways have beien suggested, for example involving radical and carbenium ion intermediates, and addition-elimination and rearrangement inocesses. ... 

Winstein showed that the solvolysis of crotylmercury(II) acetate under kinetically controlled conditions gives >99.5% of a-methylallyl acetate (equation 13). Subsequent work indicate that both the solvolysis of ciimamylmercury( acetate and this mercury(II) acetate oxidation of allylbenzene give ca. 60% cinnamyl acetate (35) a 40% a-phenylallyl acetate (36 equation 14). An equilibrium exists between (35) and (36) favoring the primary ester which constitutes >99.5% of the equilibrium mixture at 75 C. Oxidation of a range of both 1- and 2-alkenes under kinetically controlled conditions exclusively gave the secondary allylic esters. 

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). ... 

Finally, mercury(U) oxide in combination with fluoroboric acid and ethanol in THF solution has been shown to convert aUylbenzenes into the rearranged allylic ethyl ethers. ... 

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