Acetoxymercuration

Refluxing a solution of tellurophene and mercury (II) acetate in ethanol yielded 2,5-his[acetoxymercurio]tellurophene.  

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The stereo-defined enol ester 432 is prepared by the reaction of the vinyl-mercurial 431, obtained by acetoxymercuration of 2-butyne. with mercury(II) carboxylates using a catalytic amount of Pd(OAc)2[392]. 

Unsaturation value can be determined by the reaction of the akyl or propenyl end group with mercuric acetate ia a methanolic solution to give acetoxymercuric methoxy compounds and acetic acid (ASTM D4671-87). The amount of acetic acid released ia this equimolar reaction is determined by titration with standard alcohoHc potassium hydroxide. Sodium bromide is normally added to convert the iasoluble mercuric oxide (a titration iaterference) to mercuric bromide. The value is usually expressed as meg KOH/g polyol which can be converted to OH No. units usiag multiplication by 56.1 or to percentage of vinyl usiag multiplication by 2.7. 

Mercury(II) acetate tends to mercurate all the free nuclear positions in pyrrole, furan and thiophene to give derivatives of type (74). The acetoxymercuration of thiophene has been estimated to proceed ca. 10 times faster than that of benzene. Mercuration of rings with deactivating substituents such as ethoxycarbonyl and nitro is still possible with this reagent, as shown by the formation of compounds (75) and (76). Mercury(II) chloride is a milder mercurating agent, as illustrated by the chloromercuration of thiophene to give either the 2- or 2,5-disubstituted product (Scheme 25). 

The acid cleavage of the aryl— silicon bond (desilylation), which provides a measure of the reactivity of the aromatic carbon of the bond, has been applied to 2- and 3-thienyl trimethylsilane, It was found that the 2-isomer reacted only 43.5 times faster than the 3-isomer and 5000 times faster than the phenyl compound at 50,2°C in acetic acid containing aqueous sulfuric acid. The results so far are consistent with the relative reactivities of thiophene upon detritia-tion if a linear free-energy relationship between the substituent effect in detritiation and desilylation is assumed, as the p-methyl group activates about 240 (200-300) times in detritiation with aqueous sulfuric acid and about 18 times in desilylation. A direct experimental comparison of the difference between benzene and thiophene in detritiation has not been carried out, but it may be mentioned that even in 80.7% sulfuric acid, benzene is detritiated about 600 times slower than 2-tritiothiophene. The aforementioned consideration makes it probable that under similar conditions the ratio of the rates of detritiation of thiophene and benzene is larger than in the desilylation. A still larger difference in reactivity between the 2-position of thiophene and benzene has been found for acetoxymercuration which... 

A83543A aglycon 595 f. acetic acid 5 acetoxonium ion 538, 762 acetoxymercuration 390 acetylene coupling 268, 275 f. active ester 624 P-acylamino a,p-unsaturated system 111... 

Nitro-4-lodo-1-Oxy-Naphthalene (2-Nitro-4-iodo-l-naphthol). (02N)C1oHs(I).OH, mw 315.09, N 4.45%, OB to C02 -101.56%, clear golden needles, mp 115° (decompn). Prepn from 4-nitro-2-acetoxymercuric-naphthol-(l) by reacting with iodine... 

Typical yields are in the range of40-70% regardless of the method used. We should mention that the acetoxymercuration and acetoxythallation of vinylallenes also lead to cyclopentenones, albeit not via epoxide formation [28]. 

Acetoxymercuration of thiocoumarin occurs readily at the 6-position, offering a potential (but as yet unexploited) route to numerous substituted thiocoumarins. 

Vinylcyclopentenones. 1,2,4,6-Tetraenes are converted into 4-vinylcyclopen-tenones by epoxidation under the mild conditions of Anderson and Veysoglu (5,120).1 Acetoxymercuration is not useful for this cyclization. 

At C-2 position, carbohydrate radicals were formed starting from unsaturated sugars by acetoxymercuration followed by reduction of the carbon-mercury bond... 

Aryltrialkoxo complexes, with Ti(IV), 4, 328 Aryltrimethylsilylalkynes, acetoxymercuration, 2, 439 Aryltrimethylstannane, in carbonylative cross-coupling,... 

The selective halomercuration and acetoxymercuration of the carbocyclic ring of quinolines can be achieved using mercury salts. However, no new work has occurred in this area since publication of CHEC-II <1996CHEC-II(5)91>. 

The mercuration of thiophene shows some peculiarities. The rate of acetoxymercuration of thiophene is extraordinarily high,166 the relative rate krjkB being 6.2 x 105. The a f3 reactivity ratio is likewise very high and no amount of /3 isomer was detected in the reaction mixture.167 These facts are in contrast with the normally relatively... 

Relative rates of substitution for a number of substituted thiophenes sufficient to test the applicability of po+ relationships are available for seven reactions bromination by molecular bromine, chlorination by molecular chlorine, protodetritiation, proto-dedeuteriation, acetoxymercuration, tin tetrachloride-catalyzed acetylation, and trifluoroacetylation. The relevant data are assembled in Table XXIII. 

SnCL-catalyzed acetylation by AC2O in dichloroethane at 25°. See Linda and Marino.130 and unpublished results. 9 Reaction with (CF3C0)20 in dichloroethane at 75°. See dementi and Marino.143- 302 h Acetoxymercuration in acetic acid at 50°.121... 

Mercury (II) acetate reacts with l,6,6aA4-trithiapentalenes or their 3-aza derivatives to give the corresponding l-oxa-6,6aA4-dithiapentalenes or l-oxa-6,6aA4-dithia-3-azapen-talenes <71AHC(l3)16l p. 179,199). This reaction proceeds first by acetoxymercuration of a sulfur atom, followed by hydrolysis of the intermediate dithiolylium cation as indicated in Scheme 1. 

S—S—N sequences are similarly attacked, giving O—S—N sequences <78JCS(P1)195). Compounds containing an O—S—O sequence behave differently, acetoxymercuration occurring at positions 3 or 4 as indicated in Section 4.38.3.2.6. 

Intramolecular solvomercuration of aryl alkynes (if. 11, 320). The triple bond of alkynylbenzenes substituted at the oz/Zio-position with suitable groups undergoes intramolecular acetoxymercuration with Hg(OAc), in HOAc to afford aromatic heterocycles such as benzofuranes, benzothiophenes, and chmmones. 

Ferrocene reacts with acetyl chloride and aluminum chloride to afford the acylated product (287) (Scheme 84). The Friedel-Crafts acylation of (284) is about 3.3 x 10 times faster than that of benzene. Use of these conditions it is difficult to avoid the formation of a disubstituted product unless only a stoichiometric amount of AlCft is used. Thus, while the acyl substituent present in (287) is somewhat deactivating, the relative rate of acylation of (287) is still rapid (1.9 x 10 faster than benzene). Formation of the diacylated product may be avoided by use of acetic anhydride and BF3-Et20. Electrophilic substitution of (284) under Vilsmeyer formylation, Maimich aminomethylation, or acetoxymercuration conditions gives (288), (289), and (290/291), respectively, in good yields. Racemic amine (289) (also available in two steps from (287)) is readily resolved, providing the classic entry to enantiomerically pure ferrocene derivatives that possess central chirality and/or planar chirality. Friedel Crafts alkylation of (284) proceeds with the formation of a mixture of mono- and polyalkyl-substituted ferrocenes. The reaction of (284) with other... 

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