Of lead tetraacetate

In the reaction of lead tetraacetate with 1,3- or 1,4-dihydtopetoxides (10) to produce cychc monoperoxides there are two electron transfers to the metal (eq. 14). 

Other approaches to the generation of the azallyl cation have been found. One of the most useful involves the use of lead tetraacetate (73TL2143). The anodic oxidation of aziridines also leads to the azallyl cation intermediate (75JA1600). 

Phenylpftenanttirldlne (3).3 Amine hydrochloride 1 (2.72 g, 9 28 mmol) in EtOH (75 mL) was treated with 0 926 N cold solution of KCXI. Colorless crystals appear The mixture was shaken lor 30 mtn in ice, water was added and the product was filtered and dryed (PaOs) to afford 2.7 g of 2 (100%), rnp 102°C (hexane) 2 (2 0 g, 6 6 mmol) in anh pyndine (20 mL) was treated with an excess of NaOCHa (exothermc) Alter 20 h the solvent was removed In vacuum, the residua triturated with EtaO and the extract treated with dry HCI to obtain the hydrochlonda of 3, mp 107-108°C (from petroleum ether), mp 95-100° (Irom water) Olphenylmethyieneanlllna (5). To a suspension of lead tetraacetate (4.9 g, fO mmol) in PhH (100 mL) under Na was added a solution of tnphenyhnethylamine 4 (2 6 g, 10 mmol) in PhH (100 mL) dropwise under stirring The mixture was refluxed for 1 h, cooled, filtered, washed and the solvent evaporated The residue was crystallized from EtOH to give 2 2 g of 5 (85%), mp 111-112°C. 

A. p-Methoxyphenyllead triaaetate. A 1-L Erlenmeyer flask, equipped with a magnetic stirring bar, is charged with 50 g (0.11 moll of lead tetraacetate (Note 1), chloroform (200 mL), and 140 g (1.09 moll of dichloroacetic acid (Note 21. To this solution is added 16 g (0.15 mol) of anisole (Note 3), and the mixture is stirred at 25°C until lead tetraacetate can no longer be detected (Note 41. The reaction mixture is washed with water (2 x 250 mil and the chloroform solution is treated with 1.5 L of hexane (Note 51. The yellow... 

Dissolved in hot glacial acetic acid, any lead oxide being removed by filtration. White crystals of lead tetraacetate separated on cooling. Stored in a vacuum desiccator over P2O5 and KOH for 24h before use. 

Lead Tetraacetate Degradation A solution of 10 g of 3a, 17a, 20-trihydroxy-5j5-pregnan-ll-one in 100 ml of glacial acetic acid is treated with a solution of 14.1 g of lead tetraacetate (Arapahoe Chemicals Inc., Boulder, Colorado 85-90% active material) in acetic acid at room temperature and the resulting solution is allowed to stand overnight. Several volumes of water are then added and the mixture is extracted thoroughly... 

The interaction of lead tetraacetate with an alcohol leads to an intermediate lead alkoxide [e.g., (1)] which decomposes either thermally or photolytically. 

Note 1. If unpurified, but vacuum dried lead tetraacetate is used in the above procedure erratic results are obtained. If, however, commercial lead tetraacetate containing about 10% acetic acid is employed and 0.5% (v/v) of acetic acid is added to the reaction solution consistently high yields of ether are obtained. An excess of lead tetraacetate (up to 5 eq) is required for complete conversion. In the presence of acetic acid the reaction time must be extended to about 40 hr. 

An excess of lead tetraacetate is used in each case. Best results are obtained when the molar ratios of substrate iodine lead tetraacetate are kept around... 

No systematic study of the minimal required amount of lead tetraacetate has been made. In cases where the product of the hypoiodite reaction is an iodo ether (20-hydroxy steroids) the reaction can be interrupted at the iodohydrin stage by reducing the amount of iodine to about 0.5 mole. For the oxidation of iodo ethers to lactones, chromium trioxide-sulfuric acid in acetone has been used. Silver chromate is often added to the reaction mixture but comparable yields are obtained without the addition of silver salt. 

Note 2. The molar ratios of lead tetraacetate iodine substate are 5.3 1.8 1. These ratios can be lowered and similar results obtained with ratios around 3 1.2 1. Excess iodine and lead tetraacetate react under the influence of light and heat to give methyl iodide and carbon dioxide. 

Note I. The ratio of lead tetraacetate iodine substrate is 2.85 1.31 1. A minimal amount of 1 mole of iodine per mole of substrate is necessary cf. procedure below). 

Thermal decomposition of lead tetraacetate gives rise to methyl radicals, again through the initial formation of acetoxy radicals. " An ionic mechanism for the decomposition has also been postulated, and it is possible that both mechanisms may occur, depending on the conditions. 

The reaction of lead tetraacetate (LTA) with monohydric alcohols produces functionalization at a remote site yielding derivatives of tetrahydrofuran (THF) 12). An example is the reaction of 1-pentanol with LTA in nonpolar solvents which produces 30% THF. The reaction, which is believed to proceed through free-radical intermediates, gives a variable distribution of oxidation products depending on solvent polarity, temperature, reaction time, reagent ratios, and potential angle strain in the product. 

The use of lead tetraacetate to carry out oxidative bisdecarboxylation of diacids has been found to be a highly useful procedure when used in conjunction with the Diels-Alder addition of maleic anhydride to dienes, the latter process providing a ready source of 1,2-dicarboxylic acids. The general pattern is illustrated in the reaction... 

In many instances, however, the intermediate triazoline can be isolated and separately converted into the aziridine, often with poor stereoselectivity. The first practical modification to the original reaction conditions generated the (presumed) nitrenes by in situ oxidation of hydrazine derivatives. Thus, Atkinson and Rees prepared a range of N-amino aziridine derivatives by treatment of N-aminophthali-mides (and other N-aminoheterocydes) with alkenes in the presence of lead tetraacetate (Scheme 4.10) [7]. 

The Action of Lead Tetraacetate on Sugar mercaptals, E. J. Boume, W. M. Corbett, M. Stacey, and... 

Solvent-grade benzene was dried over sodium wire prior to use. If the benzene is wet, a considerable amount of starting 1-adamantanol remains unreacted owing to hydrolysis of lead tetraacetate. 

A. endo-7-Iodomethylbicyclo[3.3.1]nonan-3-one. A 2-1., threenecked, round-bottomed flask equipped with an eflicient mechanical stirrer and a reflux condenser is charged with 600 ml. of dry ben2 ene (Note 1). The flask is immersed in a water bath, stirring is initiated, and 58.3 g. (0.132 mole) of lead tetraacetate (Note 2), 37.4 g. (0.147 mole) of iodine, and 10.0 g. (0.066 mole) of 1-adamantanol (Note 3) are added (Note 4). The bath temperature is gradually raised to 80° over a 20-minute period and is then allowed to cool to 70-75°. Stirring is continued for 2 hours at 70-75° (Note 5) and for an additional hour while the mixtiu e is cooled to room temperature. The inorganic salts are filtered and carefully washed with five 50-ml. portions of ethyl ether. The... 

Acetoxylation at an allylic position is the typical reaction of lead tetraacetate but no kinetic data are available. Product studies favour a heterolytic mecha-nism . 

The auto-decomposition of lead tetraacetate in acetic acid, which normally occurs at reflux temperature , can be studied at 50 °C in the presence of sodium acetate The principal products of both the uncatalysed and catalysed decompositions are acetoxyacetic acid and carbon dioxide. The kinetic order of the normal decay of Pb(IV) is complex and evidence was obtained that oxidation of products is significant after the earliest stages. The evidence indicates that slow, simple homolytic breakage of lead tetraacetate to give Pb(OAc)3- and AcO-does not occur but that the solvent plays an integral part, e.g. 

A solution of lead tetraacetate in pyridine rapidly oxidises the most recalcitrant trans-diols, especially if a considerable excess of oxidant (3-4 moles) is used, implying yet a further mechanism for the action of this versatile oxidant ... 

Diphenylcyclopropene thione is transformed to diphenyl cyclopropenone by means of lead tetraacetate (presumably via 279/280), whilst perphthalic acid oxidizes to cation 281, which gives the unstable S-oxide 282 with NaHC03208. ... 

Ethyl 2-(D-amiino-tetrahydroxybutyl)-5-methyl-4-furoate (5.5 g.) is mixed with 80 ml. of dry benzene and 20 ml. of glacial acetic acid, and cooled in ice plus water. While stirring and cooling, 182 g. of lead tetraacetate (purity, 99.7%)62 is added during about sixty minutes stirring is continued until all the oxidant has been consumed. The lead dioxide is then removed by filtration, and the benzene solution is extracted twice with water.58 The benzene layer is dried with calcium chloride and the solvent is evaporated under diminished pressure, giving an oily residue which rapidly crystallizes in colorless plates yield, 3.6 g. (quantitative). The product is purified by recrystallization from dilute acetic acid or by steam distillation m.p., 57°. 

Oxidative cyclization of acylhydrazones 110a, derived from aldehydes or ketones, with the use of lead tetraacetate (LTA) has been developed into a useful route to several disubstituted and tetrasubstituted oxadiazole derivatives 122, being a convenient source of relatively stable carbenes, like N(0)C , S(0)C , 0(0)C , or S(S)C <2000J(P1)2161 >. Some representative recent examples of the syntheses are collected in Table 2. 

The use of lead tetraacetate as an oxidant gives O-acetyl derivatives of the corresponding hydroxamic acids (475, 476, 506). 

Many of the early reports of spin-trapping experiments were focused on mechanistic investigations, and some of these feature in the early reviews (see p. 4). Unfortunately, it is in this application that inferences drawn may be most suspect. For example, the inability of the method to differentiate between radical trapping on the one hand, and a combination of nucleophile trapping with one-electron oxidation on the other, is a serious shortcoming. An early example of this was the tentative conclusion that acetoxyl radicals were spin-trapped by PBN competitively with their decarboxylation in reactions of lead tetraacetate. In view of the rapidity of the decarboxylation reaction, trapping of acetate ion and subsequent oxidation seems a likely alternative. 

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... 

There have been examples of sonochemical switching in homogeneous reactions. The decomposition of lead tetraacetate in acetic acid in the presence of styrene at 50 °C generates a small quantity of diacetate via an ionic mechanism. Under otherwise identical conditions sonication of the mixture gives 1-phenylpropyl acetate predominantly through an intermediate methyl radical which adds to the double bond (Scheme 3.8) [55,56]. These results are in accord with the proposition that radical processes are favoured by sonication. 

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