Mercury oxide alkenes

Intramolecular alkylnitrene addition to an alkenic moiety situated S,e to the electron deficient center has been utilized for the preparation of bi- and tri-cyclic aziridines (Scheme 11) (68JA1650). Oxidation of the primary alkylamine can be effected cleanly with NCS, LTA or mercury(II) oxide. 

Like alkenes (Sections 7.4 and 7.5), alkynes can be hydrated by either of two methods. Direct addition of water catalyzed by mercury(II) ion yields the Markovnikov product, and indirect addition of water by a hydroboration/ oxidation sequence yields the non-Markovnikov product. 

The chemistry of alkynes is dominated by electrophilic addition reactions, similar to those of alkenes. Alkynes react with HBr and HC1 to yield vinylic halides and with Br2 and Cl2 to yield 1,2-dihalides (vicinal dihalides). Alkynes can be hydrated by reaction with aqueous sulfuric acid in the presence of mercury(ll) catalyst. The reaction leads to an intermediate enol that immediately isomerizes to yield a ketone tautomer. Since the addition reaction occurs with Markovnikov regiochemistry, a methyl ketone is produced from a terminal alkyne. Alternatively, hydroboration/oxidation of a terminal alkyne yields an aldehyde. 

Only the head-to-tail adducts were obtained in the [2+2] photoaddition of 4-hydroxy-l-phenyl[l,8]naphthyridin-2(l//)-one with various alkenes in methanol (Scheme 3). The photolysis of the hypoiodites generated by the in situ reaction of the cycloadducts with excess mercury(ll) oxide-iodine reagent in benzene induced a regioselective scission of the non-ring junction bond of the alkoxyl radical to give substituted 3,9-dihydro-9-phenylyfuro[2,3- ][l,8]naphthyridin-4(2//)-one and/or 3,5-dihydro-5-phenylfuro[3,2-f][l,8]naphthyridin-4-(2//)-ones <1996T6125>. 

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. 

The Julia-Lythgoe alkenation procedure gives predominantly E-aUcene, depending on the reaction conditions. For example, oxidation of sulfide 4.55 with m-CPBA gave sul-fone 4.56, which on treatment with a base and aldehyde 4.57 followed by reduction with sodium-mercury (Na-Hg) and disodium hydrogen phosphate in MeOH afforded the E-alkene 4.58 in 68% yield. ... 

Another synthetic route to monoorganothallium compounds is the reaction of aryl or vinyl derivatives of mercury(II) or tin(IV) with TIX3 (X = halide, carboxy-late). Monoalkylthallium derivatives are intermediates m the oxidation of alkenes and alkynes by thallium(III) salts (oxythallation) (see Section 7). 

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). ... 

Alkenes can be oxidized to ketones of the same chain length by using salts of copper, palladium, and mercury as catalysts and air, electrolysis [120], hydrogen peroxide, or chromium compounds as oxidants [60, 65, 140, 565] (equation 90). 

The anodic behavior of A -substituted alkenes can be described as the oxidation of an electron-rich double bond. Tetraamino-substituted alkenes are extremely easily oxidized. Tetrakis(dimethylamino)ethylene exhibits two reversible one-electron processes at —0.75 and —0.61 V vs. SCE at a dropping mercury electrode in acetonitrile [140]. The anodic behavior of A, A -dimethylaminoalkenes has been studied intensively by cyclic voltammetry and electron spin resonance (ESR) spectroscopy [141]. The anodically E° = 0.48 V vs. SCE) generated cation radical of l,l-bis(iV,iV-dimethylamino)ethylene is shown to undergo C-C coupling, forming l,l,4,4-tetrakis(A, iV-dimethylamino)butadiene, which subsequently is further oxidized to its dication at —0.8 V [141,142]. With vicinal diamino ethylenes, usually two reversible one-electron oxidations are observed [143], while gem-inal diamino ethylenes exhibit an irreversible behavior [141]. Aryl-substituted vicinal diamino ethylenes (endiamines) can undergo a double cyclization to give an indolo-oxazoline when oxidized at 0.4 V vs. SCE in acetonitrile in the presence of 2,6-lutidine [144] ... 

Treatment of an alkene with mercuric acetate in aqueous THF results in the electrophilic addition of mercuric ion to the double bond to form an intermediate mercuri-um ion. Nucleophilic attack by H2O at the more substituted carbon yields a stable organomercury compound, which upon addition of NaBH4 undergoes reduction. Replacement of the caiton-mercury bond by a carbon-hydrogen bond during the reduction step proceeds via a radical process. The overall reaction represents Markovnikov hydration of a double bond, which contrasts with the hydroboration-oxidation process. 

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