Lead tetraacetate oxidations

If the pyrazolone is unsubstituted on position 1, there is still another possibility lead tetraacetate oxidation of (397) yields the oxopyrazolenine (398) (73CRV93) which is a very reactive azadienophile (73JCS(P1)221). 

The lead tetraacetate oxidation of alcohols is usually carried out in boiling benzene although cyclohexane and methylcyclohexane have also been... 

Another example of this rearrangement has been used to prepare 1,2,3-triazole 146 from furazanic phenylhydrazone 147 (Scheme 84) [93JCS(P1)2491]. Interestingly, furoxanic Z-phenylhydrazones 150 underwent thermal recyclization to 1,2,3-triazole A-oxides 152, evidently through intermediate 151. Treatment of the hydrazone 150 with rerr-BuOK leads to the nitromethyl derivative 149 [OOOMIl] (Scheme 84). Lead tetraacetate oxidation of 147 with subsequent Lewis acid treatment of the initially formed intermediate afforded indazole 148 (Scheme 84) (85JHC29). 

Cycloalkoxy radical intermediates are readily generated from a parent alcohol by various methods (e.g., nitrite ester photolysis, hypohalite thermolysis, lead tetraacetate oxidation) (83MI1). Once formed, reactive cycloalkoxy radicals undergo /3-scission to produce a carbonyl compound and a new carbon-centered radical. 

Deoxy-3-fluoro-D-glucose (see Section 11,2), a weak substrate for yeast hexokinase, is phosphorylated enzymically - to give the 6-phosphate 588, which is transformed into 2-deoxy-2-fluoro-D-arabinose 5-phos-phate (589) by lead tetraacetate oxidation. 

Only terr-hydroperoxides have been examined kinetically and discussion will be restricted to these. The stoichiometry of the lead tetraacetate oxidation is not straightforward, but the main product is the corresponding /erZ-alcohoP and one mole of /er/-butyl hydroperoxide consumes just over two moles of oxidant . The kinetics with this substrate are " ... 

Hydroxylation at C-5 or C-l3 has also been successfully achieved by lead tetraacetate oxidation, which was extensively studied in connection with isoquinoline alkaloids by Umezawa s group. (+)-Govanine (96) and (+)-discretine (97) were oxidized with lead tetraacetate in acetic acid to afford 5-acetoxy products 100,101, and 102 via p-quinol acetates (e.g., 99) (Scheme 23)... 

Scheme 24. Determination of absolute configuration using lead tetraacetate oxidation.

Lead tetraacetate oxidation was applied to construct a benzo[c]-phenanthridine skeleton. The Hofmann degradation product 224 derived from the phenolic protoberberine 59a was oxidized with lead tetraacetate to afford the p-quinol acetate 225, which was cyclized to the benzo[c]-... 

Scheme 40. Synthesis of dihydronitidine (229) and its analog by lead tetraacetate oxidation. Reagents a, Mel b, KOH c, Pb(OAc)4, KOAc d, HCl e, CH2N2.

Unexpected formation of the oxoadamantane skeleton is observed during a series of transformations of the alkaloid lycopoline 153 lead tetraacetate oxidation of the alcohol (131) gives a 90% yield of the oxaadamantane (132), which is opened to 133 with boron trifluoride in acetic anhydride and re-cyclized to 132 with aqueous hydrogen bromide. 

A 1,4-dioxepin fused derivative 122 of the anticancer agent acronycine was prepared by lead tetraacetate oxidation of c/.s-l,3-dihydroxy-l,2-dihydroacronycine followed by treatment with sodium borohydride <00NPL183>. 

For the reaction carried out in the presence of pyridine, a-deuteration did not affect the second-order rate constant significantly. However, small isotope effects of 1.19 and 1.21 were observed for the lead tetraacetate oxidation of PhCH(OD)COOD and... 

This work was extended to include the lead tetraacetate oxidation of methyl esters of meta- and para-substituted mandelic acids183,184 shown in equation 121. A kinetic study by Banerjee and collaborators showed the kinetic dependence on the ester concentration changed from second order in 1% (v/v) acetic acid in benzene to first order when the solvent contained more than 10% (v/v) acetic acid. These workers observed a significant decrease in AH (from 82.9 to 53.6 kcalmol-1) and in AS (from —5.84 to —35.6 e.u.) when the solvent composition was changed from 1% acetic acid to greater than or equal to 10% acetic acid in benzene. 

The pyridine-catalysed lead tetraacetate oxidation of benzyl alcohols shows a first-order dependence in Pb(OAc)4, pyridine and benzyl alcohol concentration. An even larger primary hydrogen kinetic isotope effect of 5.26 and a Hammett p value of —1.7 led Baneijee and Shanker187 to propose that benzaldehyde is formed by the two concurrent pathways shown in Schemes 40 and 41. Scheme 40 describes the hydride transfer mechanism consistent with the negative p value. In the slow step of the reaction, labilization of the Pb—O bond resulting from the coordination of pyridine occurs as the Ca—H bond is broken. The loss of Pb(OAc)2 completes the reaction with transfer of +OAc to an anion. 

Lead tetraacetate, oxidation of a hydrazone to a diazo compound, 50, 7 Lithio ethyl acetate, 53, 67 Lithium, reductions in amine solvents, 50, 89 Lithium aluminum hydride, reduction of exo-3,4-dichloro-bicyclo-[3.2.l]oct-2-ene to 3-chlorobicyclo[3.2.l]oct-2-ene, 51, 61... 

Synthesis of alkaloids enamide cyclizations for, 22, 189 (1983) lead tetraacetate oxidation in, 36, 70 (1989)... 

SCHEME 40. Hale, Hough, and Richardson s studies on the reductive animation (1988) and Fischer cyclization (1987) of a 3, 4 -dialdehyde derived from lead tetraacetate oxidation of sucrose. The glycosyl morpholines were very sweet ... 

The diacetamide compounds were regularly obtained in all degradations employing ammonia with or without silver oxide until Hockett and Chandler applied the method to hexaacetyl-D-gluco-D-flruZo-heptono-nitrile (XLIX) and obtained a monoacetamide derivative that was identified as iV-acetyl-D-glucofuranosylamine (L). The furanose structure of L was established by lead tetraacetate oxidation. They... 

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