Lead acetate tetraacetate

Lead tetraacetate Acetic acid, lead(4+) salt (8,9) (546-67-8)... 

Acetic acid 2-isopropyl-5-methyl cyclohexyl ester. See Menthyl acetate Acetic acid, lead salt. See Lead acetate Acetic acid, lead(4+) salt. See Lead tetraacetate Acetic acid, lead (+2) salt trihydrate. See Lead acetate tri hydrate... 

Lead tetraacetate acetic acid Ketones from a-hydroxyhydrazones... 

In Table III-33 results for the methylation of thiazoles in acetic acid are given (lead tetraacetate is used as radical source), but in this case some discrepancies appear, the acidic medium being too weak, and the heterocyclic base not fully protonated. Thiazole has also been methylated by the DMSO-H2O2 method (201), and the results are in agreement with those described previously. 

Treatment of (89) with lead tetraacetate generates the unstable open-ring aldehyde (90) which is quickly converted to a dimethylacetal (91). Following basic hydrolysis of the methyl ester and acetates, the acetal is cleaved with aqueous acid to produce TxB2. A number of other approaches, including one starting from the Corey aldehyde, have been described (58). 

In a similar manner to the formation of pyridazines from AT-aminopyrroles, cinnolines or phthalazines are obtainable from the corresponding 1-aminooxindoles or 2-amino-phthalimides. If the relatively inaccessible 1-aminooxindoles are treated with lead tetraacetate, mercuric acetate, r-butyl hypochlorite (69JCS(C)772) or other agents, cinnolones are formed as shown in Scheme 105. The reaction was postulated to proceed via an intermediate... 

Lead tetraacetate from Merck i Company, Inc. was used. Acetic acid was removed from the reagent at 0.1 m for 24 hr, In the dark. In a desiccator containing potassium hydroxide pellets. 

The first synthesis of p-methoxyphenyllead triacetate by direct plumbation was reported by Harvey and Morman, who obtained the compound in 2418 yield by heating anisole and lead tetraacetate in acetic acid at SO C for 4... 

Dibenz[yellow-green colour (due to other pentacyclic impurities) has been removed by crystn from benzene or by selective oxidation with lead tetraacetate in acetic acid [Moriconi et al. J Am Chem Soc 82 3441 7960]. 

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. 

Dipping solution I Dissolve 1 g lead(IV) acetate (lead tetraacetate) in 100 ml ethanol. 

Although lead tetraacetate can attack many polar and nonpolar functions in the steroid molecule, its greatest reactivity is towards vicinal diols. These diols are generally cleaved so rapidly under stoichiometric conditions that other alcohol functions in the molecule need not be protected. Thus lead tetraacetate in acetic acid at room temperature splits the 17a,20-diol group in (9) to yield the 17-ketone (10), the allylic A -3jS-alcohol remaining intact during this oxidation. Since lead tetraacetate is solublein many anhydrous... 

The nitrate group is stable to the dilute alkaline conditions required for saponification of secondary acetates although it is cleaved during Wolff-Kishner reduction.Nitrates are stable to chromic acid oxidation in acetic acid, to organic peracids, and to lead tetraacetate.This group is readily split by reduction with zinc in acetic acid. 

The 17,20-glycol grouping (with or without an additional C-21 alcohol) can be cleaved to the 17-ketone by any of the four reagents. However, the presence of a 20-ketone has a marked influence on reactivity. Thus, 17a-hydroxy-20-ketones lacking additional oxygenation at C-21 are readily cleaved only by chromium trioxide. A recent report,however, claims that 17a-hydroxypregnenolone 3-acetate can be quantitatively cleaved to dehydroepiandrosterone acetate using lead tetraacetate in an aprotic solvent... 

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... 

A direct method for introduction of a C-21 acetoxyl group into a 20-keto-pregnane is by reaction with lead tetraacetate at room temperature. Although originally the reaction carried out in hot acetic acid gave low yields, a careful study by Henbest has defined conditions so that yields as high as 86 % can be obtained at room temperature. The preferred solvent is 5 % methanol in benzene, with boron trifluoride etherate as catalyst. With either methanol or benzene, the yield is less than 4%. 

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. 

Lead tetraacetate fragmentation has not been applied to the 20-hydroxy-18, 20-cyclo steroids. However, preferential cleavage of the 17,20-bond would be expected, as was observed in the chromic acid oxidation of a saturated 20-hydroxy-18,20-cyclo steroid in hot acetic acid which affords the 18-acetyl-17-ketone in 50-60% yield. 

The formation of a-acetoxyketones by oxidation of enamines with thallic acetate has been studied in detail (27) and found to be of preparative value (80 % yields) particularly in five- and six-membered-ring ketone derivatives. Enamines of linear or seven-membered-ring ketones were oxidized also, but at very much slower rates. Enamines of aldehydes with a-hydrogen substituents underwent self-eondensations during the oxidation reactions. Lead tetraacetate was less satisfactory as an oxidizing agent. 

Use of the imonium group for protection of enones was explored. Stability to peracids, lead tetraacetate, bromine, and acetic anhydride was claimed (727). The usual resistance of enamines (but not their salts) to additions of Grignard reagents was used for selective addition to a 3,17-diketosteroid by formation of the usual 3-monoenamine 728). 

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