Mercury -intermediates

In this connection, our finding that the allylic mercury intermediate represents the only isolated product following reaction in THF, CH2CI2, or HMPA is pertinent. The generation of this species appears to be rapid in all media. The ensuing step in which Hg(II) is reduced to Hg(O) likely serves as the rate-determining step. If so, the role of nonpolar benzene may be to stabilize the transition state and accelerate the overall rate. No allylic alcohol having an exocyclic double bond was formed, a feature that hints to the possible operation of thermodynamic control. 

A mild and highly convenient procedure for the hydration of a carbon-carbon double bond involves the initial reaction of an alkene with mercury(n) acetate in aqueous tetrahydrofuran, the resulting mercurial intermediate is reduced in situ by alkaline sodium borohydride solution. The yields of alcohols which are... 

The mercuric ion-catalyzed hydration of alkynes probably proceeds in a similar manner to the oxymercuration of alkenes (see Section 5.1). Electrophilic addition of Hg to the triple bond leads to a vinylic cation, which is trapped by water to give an vinylic organomercury intermediate. Unlike the alkene oxymercuration, which requires reductive removal of the mercury by NaBH4, the vinylic mercury intermediate is cleaved under the acidic reaction conditions to give the enol, which tautomerizes to the ketone. Hydration of terminal alkynes follows the Mai kovnikov rule to furnish methyl ketones. ° ... 

The mercury derivatives of bicyclic and monocyclic cyclopropanes underwent ready addition across electron-deficient C —C double bonds. This addition reaction was performed with isolation of the mercury intermediate, e.g. 6, giving and often without isolation of the mercury intermediate giving and 9 directly. Depending on the solvent used (MeOH or HOAc) either methoxide or acetate acted as the nucleophile in the ring-opening reaction. 

Synthesis of alkyl azides.1 Terminal alkenes and strained cyclic alkenes react with the reagent to give a mercurial intermediate, which on reduction with sodium borohydride gives an azide. Internal olefins do not react. The method is an extension of the hydroxymercuration reaction of Brown (2,265-267). 

An organic mercurial intermediate is formed, which is the compoimd actually undergoing a replacement-type sulfonation, as follows ... 

The main product is j8-chIorovinyldichloroarsine with the trans isomer predominating. The proportion of the ds isomer is increased when other catal)rsts such as mercuric and cuprous chloride are used 180, 181, 182), though this is never very great. The Lewisite phase usually separates from the reaction mixture and this is believed to be the reason for the predominant formation of the dichloroarsine. If acetone is added to the reaction mixture separation of the Lewisite layer does not take place, and the main product is tris- -chlorovinylarsine 181). Mercuric-chloride-catalyzed addition appears to proceed through a mercurial intermediate 181). 

The proposed mechanism of the Ferrier carbocyclization reaction is oudined in Scheme 12.13. First, oxymercuration of the exo-olefin in 48 affords mercurial-hemiacetal 49, whose aglycon moiety (-OMe) eliminates to give mercurial-aldehyde derivative 50. This mercurial intermediate 50 was isolable when a stoichiometric amount of Hg salt was employed at low temperature. Intramolecular aldol-type cyclization of 50 provides product 51. 

Kocovsky et al. later demonstrated that C Hg bonds can be used for stereospedfic lactone synthesis. Both cis- and f ra s-fused hicycUc lactones can be prepared by ringopening reactions of cydopropanes followed by cydocarbonylation of the organo-mercurial intermediate (Scheme 2.11). p-Benzoquinone was found to be superior to Cu(II) as a stoichiometric oxidant [23]. 

The main evidence (apart from the characterization of the mercuriated intermediates) from which proposed mechanisms for the ring closure have been developed is the impact of the orientation of the substituent at C-3 of the starting materials on the stereochemical outcomes. Table 1 indicates that the... 

Reaction of olefins with mercuric acetate in aqueous THF followed by in situ reduction of the mercurial intermediate is a convenient method for Markovnikov hydration of the double bond (Scheme 20). Using chiral... 

For mercury intermediate coupling applies (equation (8)) and if excitation exists solely via the 6 Pi admixture polarisation should be +0.82. Ihe polarisation measurement thus provides detailed information about the relative contributions of the two mechanisms. 

The reaction of alkenyl mercurials with alkenes forms 7r-allylpalladium intermediates by the rearrangement of Pd via the elimination of H—Pd—Cl and its reverse readdition. Further transformations such as trapping with nucleophiles or elimination form conjugated dienes[379]. The 7r-allylpalladium intermediate 418 formed from 3-butenoic acid reacts intramolecularly with carboxylic acid to yield the 7-vinyl-7-laCtone 4I9[380], The /i,7-titisaturated amide 421 is obtained by the reaction of 4-vinyl-2-azetidinone (420) with an organomercur-ial. Similarly homoallylic alcohols are obtained from vinylic oxetanes[381]. 

Mercuration. Mercury(II) salts react with alkyl-, alkenyl-, and arylboranes to yield organomercurials, which are usehil synthetic intermediates (263). For example, dialkyhnercury and alkyhnercury acetates can be prepared from primary trialkylboranes by treatment with mercury(II) chloride in the presence of sodium hydroxide or with mercury(II) acetate in tetrahydrofuran (3,264). Mercuration of 3 -alkylboranes is sluggish and requires prolonged heating. Alkenyl groups are transferred from boron to mercury with retention of configuration (243,265). 

Acetoiicetyliition Reactions. The best known and commercially most important reaction of diketene is the aceto acetylation of nucleophiles to give derivatives of acetoacetic acid (Fig. 2) (1,5,6). A wide variety of substances with acidic hydrogens can be acetoacetylated. This includes alcohols, amines, phenols, thiols, carboxyHc acids, amides, ureas, thioureas, urethanes, and sulfonamides. Where more than one functional group is present, ring closure often follows aceto acetylation, giving access to a variety of heterocycHc compounds. These reactions often require catalysts in the form of tertiary amines, acids, and mercury salts. Acetoacetate esters and acetoacetamides are the most important industrial intermediates prepared from diketene. 

Mercuric chloride is widely used for the preparation of red and yellow mercuric oxide, ammoniated mercury/7(9/USP, mercuric iodide, and as an intermediate in organic synthesis. It has been used as a component of agricultural fungicides. It is used in conjunction with sodium chloride in photography (qv) and in batteries (qv), and has some medicinal uses as an antiseptic. 

The heavy metals, copper, chromium, mercury, nickel, and 2inc, which are used as catalysts and complexing agents for the synthesis of dyes and dye intermediates, are considered priority poUutants (313). 

The acid promoted cyclization of AT-(2-chloroallyl)enaminones (Scheme 35a) provides the expected 3-methyltetrahydroindoles, whereas similar treatment of iV-(2-chloroallyl)anilines yields unexpectedly 2-, rather than 3-, methylindoles (Scheme 35b) (75JCS(Pl)U46). The course of the latter cyclization is not resolved although various intermediates, such as those shown, have been considered. The ring closure in the furan synthesis shown in Scheme 35c is catalyzed by mercury(II) ion (79JCs(Pl)316l). 

Bis(2,4,6-trinitrophenyl)methane when treated with NaAc in acetic acid produced (580) as a thermostable explosive (80MIP41600). The conversion of o-nitrotoluene into 2,1-benzisoxazole was effected by mercury(II) oxide catalysis. A mercury containing intermediate was isolated and was demonstrated to be converted into 2,1-benzisoxazole (67AHC(8)277). The treatment of o-nitrotoluene derivative (581) with sulfuric acid gave (582) in 35% yield (72MI41607). 

Methyl ketones are important intermediates for the synthesis of methyl alkyl carbinols, annulation reagents, and cyclic compounds. A common synthetic method for the preparation of methyl ketones is the alkylation of acetone derivatives, but the method suffers limitations such as low yields and lack of regioselectivity. Preparation of methyl ketones from olefins and acetylenes using mercury compounds is a better method. For example, hydration of terminal acetylenes using HgSO gives methyl ketones cleanly. Oxymercuration of 1-olefins and subsequent oxidation with chromic oxide is... 

The most common synthetic application of mercury-catalyzed addition to alkynes is the conversion of alkynes to ketones. This reaction is carried out under aqueous acidic conditions, where the addition intermediate undergoes protonation to regenerate Hg. ... 

Phenylmercury halides give the corresponding phenylmercury derivative, CgH5HgC(CF3)3 (61%) [156], and perfluorocyclobutene gives the corresponding cyclobutyl derivative [156], Mechanistically, the reaction could be interpreted as formation of the fluorocarbanion via nucleophilic addition of fluoride ion to the fluoroolefin followed by capture of the intermediate fluorocarbanion by the mercury salt [156]. The regiochemistry of the reaction is consistent with this mechanism [156] (equation 119). 

The stability of the o-bromothienyllithium reagents at —70°C contrasts sharply with the behavior of o-bromophenyllithium which is very unstable even at — 100°C, readily splitting off lithium bromide to form benzyne (dehydrobenzene).Only by heating bis-(3-iodo-2-thienyl)mercury to 240°C in the presence of tetracyclone could some evidence for the intermediate existence of 2,3-dehydrothiophene be obtained. ... 

Mercury-sensitized irradiation of 1,2,3-triphenylisoindole (65) in the presence of oxygen gives a peroxide (103). This peroxide is relatively stable compared with the peroxide (104) derived from similar oxidation of 1,3-diphenylisobenzofuran and can be reconverted to the isoindole (65) by pyrolysis or by treatment with zinc and acetic acid. Reduction of 103 under mild conditions affords o-dibenzoylbenzene (46) and aniline. Aerial oxidation of 47 gives 46 and methylamine, presumably via a peroxide intermediate similar to 103. °... 

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