Lead tetraacetate-Trifluoroacetic acid

Lead tetraacetate trifluoroacetic acid Bridgehead functionalization Formamides s, 31,123... 

Lead tetraacetate trifluoroacetic acid Oxo compds. from ethylene deriys. with rearrangement... 

A hydroxy and an arylthio group can be added to a double bond by treatment with an aryl disulfide and lead tetraacetate in the presence of trifluoroacetic acid." Manganese and copper acetates have been used instead of Pb(OAc)4. ° Addition of the groups OH and RSO has been achieved by treatment of alkenes with O2 and a thiol (RSH)." Two RS groups were added, to give vie- dithiols, by treatment of the alkene with a disulfide RSSR and Bp3-etherate."° This reaction has been carried... 

It has been reported previously (147), and will be discussed in detail later, that arylthallium ditrifluoroacetates may be converted in good yield to phenols by treatment with lead tetraacetate in trifluoroacetic acid solution followed by addition of 1 mole of triphenylphosphine. The immediate product of the above reaction, an aryl trifluoroacetate, is hydrolyzed... 

The analogue, t-butyl methyl iminodicarboxylate 25, is obtained by the reaction of methanol with t-butyl oxamate (24) in the presence of lead tetraacetate. Its stable non-hygroscopic potassium salt is converted into alkyl derivatives 26 by the action of alkyl halides such as butyl bromide, allyl bromide, propargyl bromide and ethyl bromoacetate. The products are hydrolysed by trifluoroacetic acid to salts of primary amines, whereas... 

Lead tetraacetate in acetic acid oxidizes phenolic 1-benzylisoquinolines to p-quinol acetates which usually rearrange to aporphines in trifluoroacetic acid (25). However, Blasko et al. (24) recently reported that lead tetraacetate oxidized ( )-A -norlaudanosine (34) to dibenzopyrrocoline 35 in 16% yield. 

Aziridinyl ketones can be synthesized from unsaturated carbonyls using a series of other methods. For example, azabicyclo[4.1.0]heptanone 27 was obtained from cyclohexenone 25 in its reaction with TV-bromotoluenesulfona-mide sodium salt 33 [49] (Scheme 1.10). The reaction of chalcone with N-chlorotoluenesulfonamide in the presence of silver nitrite is described in [50]. Trans-Aziridinyl ketone 18 was synthesized by reacting chalcone 22 with N,N-diamino-l,4-diazoniabicyclo[2.2.2.]octane dinitrate 34 and sodium hydride in 2-propanol [30, 51]. Aziridinyl ketones can be obtained in the reaction of a -unsaturated ketones with A,A-dichlorosulfonamines [52] and with amines in the presence of lead tetraacetate and trifluoroacetic acid [53] or in the presence of triethylammonium acetate under electrochemical reaction conditions [54]. 

Although a number of different reagents have been discovered for the selective oxidation of ethers, e.g. halogens, iodine tris(trifluoroacetate), trichloroisocyanuric acid, UFs, A(,N-dibromobenzenesul-fonamide and lead tetraacetate, few have assumed any synthetic importance. Of these, the most significant are the metallic oxidants chromic acid and ruthenium tetroxide. DDQ has also been widely used for the oxidative d rotection of benzyl ethers. It is the aim of this chapter to review the latest developments in ether oxidation by these, and other reagents, with particular emphasis on chemo- and regio-selectivity. Several reviews on the subject have appeared previously. " The related oxidation of acetals has been reviewed recently" and will not be dealt with here. 

OL-Hydroxysulfenylation. Lead tetraacetate and trifluoroacetic acid form lead(IV) trifluoroacetate in situ When an olefin and diphenyl disulfide are added to this reagent at 0 or -40°, a 3-trifluoroacetoxy sulfide is formed, which on basic work-up generates a thiohydrin (equation I). The reaction involves trans-addition. 

The oxidation of the 3-amino-2-(l,2,2-trimethylpropyl)-4(3//)-quinazolinone (3), more easily prepared than (+)-2, with lead tetraacetate in the presence of a-methylene-y-butyrolactone gave the spiroaziridine with very little asymmetric induction40. This is probably due to the competition of secondary attractive interactions between the carbonyl oxygen of the lactone and either the carbonyl or the imine group of the heterocycle. However, the same oxidation carried out in the presence of trifluoroacetic acid (3.4 mol equiv) gave only one diastereomer 440, whose relative configuration was established by X-ray crystallography. 

Particular advantage was taken of the solubility of lead tetraacetate, it is soluble even at — 78 °C in the presence of at least six mol equivalents of trifluoroacetic acid. This allows the aziridination reaction to be performed at low temperatures with a stoichiometric amount of the alkene, hence the diastereoselectivity was greatly improved (Table 2). 

Esters of phenols are obtained by treatment of aromatic hydrocarbons with peroxy acids [292], organic peroxides [1119, 1120], and lead tetraacetate or tetrakis(trifluoroacetate) [435, 449]. Benzene treated with tri-... 

More frequently, the benzylic hydrogen is replaced by an acyloxy group on refluxing with ceric ammonium nitrate in 100% acetic acid [415], with lead tetraacetate [434, 437], or with lead tetrakis(trifluoroacetate) [435]. 

Much simpler and more direct is a recently developed route via thallation. An aryithallium compound is oxidized by lead tetraacetate (in the presence of triphenylphosphine, PhjP) to the phenolic ester of trifluoroacetic acid, which on hydrolysis yields the phenol. The entire sequence, including thallation, can be carried out without isolation of intermediates. Although the full scope of the method has not yet been reported, it has two advantages over the diazonium route (a) the speed and high yield made possible by the fewer steps and (b) orientation control in the thallation step. (Review Secs. 11.7 and 11.13.)... 

Aryl coupling to a benzylic site has also been observed the monophenol (67) yielded the aryltetralin (68 55%), with thallium trifluoroacetate-boron trifluoride. Probably oxidation to quinone methide precedes the ring closure. Separate oxidation and cyclization steps were employed in the synthesis of ( )-thaliphotphine acetate. ( )-Codamine (69) underwent Wessely oxidation with lead tetraacetate to the acetoxycyclohexadienone (70), which closed in acetic anhydride-acid to ( )-thaliphorphine acetate (71), albeit in modest overall yield (14%). ... 

Potassium permanganate. Dimethyl sulfide-Chlorine. Dimethyl sulfoxide. Dimethyl sulfoxide-Chlorine. Dimethylsulf-oxide Sulfur trioxide. Dipyridine chro-mium(VI) oxide. Iodine. Iodine-Potassium iodide. Iodine tris(trifluoroacetate). Iodosobenzene diacetate. Isoamyl nitrite. Lead tetraacetate. Manganese dioxide. Mercuric acetate. Mercuric oxide. Osmium tetroxide—Potassium chlorate. Ozone. Periodic acid. Pertrifluoroacetic acid. Potassium ferrate. Potassium ferricyanide. Potassium nitrosodisulfonate. Ruthenium tetroxide. Selenium dioxide. Silver carbonate. Silver carbonate-Celite. Silver nitrate. Silver oxide. Silver(II) oxide. Sodium hypochlorite. Sulfur trioxide. Thalli-um(III) nitrate. Thallium sulfate. Thalli-um(III) trifluoroacetate. Triphenyl phosphite ozonide. Triphenylphosphine dibromide. Trityl fluoroborate. 

Lead tetraacetate, 71-72,162,278-282,321 Lead tetra(trifluoroacetate), 282-283 Lead thiocyanate, 263 L-Leucyl-L-alanylglycyl-L-valine, 391 Lewis acids, 10... 

It is not necessary to prepare the LTTFA (very hygroscopic) it can be generated in situ from lead tetraacetate and trifluoroacetic acid. 

Oxidation of hydrocarbons with a tertiary carbon, e.g. adamantane, with lead tetraacetate in trifluoroacetic acid-dichloromethane solution, in the presence of chloride ion, gave high yields of trifluoroacetate functionahzed bridgehead alcohols [57]. Subsequent hydrolysis yielded the free bridgehead alcohols (Scheme 13.34). Another important advantage of this method is the feasible conversion of the intermediate trifluoroacetate into an amide with acetonitrile. 

Aryltrimethylsilanes react also with lead tetraacetate or lead tetrakis(trifluoroacetate), in trifluoroacetic acid, to yield the corresponding aryllead tris(trifluoroacetate), which again can further react with TFA to lead to the aryltrifluoroacetates. l 5... 

Direct electrophilic plumbation of aromatic compounds can be used to prepare a small range of aryllead tricarboxylates.limited to substrates which are more electron rich than halobenzenes. Plumbation of halobenzenes can be conveniently performed by treatment with lead tetraacetate in the presence of trichloroacetic or trifluoroacetic acid. For the plumbation of compounds of intermediate reactivity between the halobenzenes and 1,3-dimethoxybenzene, the use of haloacetic acid (mono-, di- or trichloroacetic acid) is required to optimize the yield of aryllead triacetates. For 1,3-dimethoxybenzene and the more electron-rich aromatics, the reaction can be suitably performed in acetic acid. 

Reaction of arenes with lead tetraacetate in TFA (trifluoroacetic acid) can afford symmetrical dimeric compounds in moderate to good yields.(see section 7.1.3.2) Unsymmetrical biaiyls can be produced by reaction of aryllead triacetates substituted with electron-donating as well as electron-withdrawing groups with p-xylene or more highly methylated benzenes. For example, in the arylation with 4-fluorophenyllead triacetate the yields vary from 0% for nitrobenzene, 2% for benzene and toluene to 80% for pentamethylbenzene and 88% for mesitylene. 

Synthesis of phenols and aromatic nitriles.3 In a new phenol synthesis, an aromatic hydrocarbon is first thallated with the reagent in trifluoroacetic acid to give an arylthallium ditrifluoroacetate (which can be isolated) and then oxidized with lead tetraacetate in the presence of 1 equivalent of triphenylphosphine. The resulting aryl trifluoroacetate is then hydrolyzed with dilute base. The triphenyl-... 

Treatment of benzylisoquinoline (23) with lead tetraacetate furnished quinol acetate (24), which was cyclized with trifluoroacetic acid to isothebaine (25). The three related aporphines (26), (27), and (28) were synthesized by a similar pathway. 

Bridgehead derivatives. Functional groups can be introduced into saturated hydrocarbons by treatment with lead tetraacetate and trifluoroacetic acid-methylene chloride at 20° followed by addition of a nucleophile. 

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