Lead tetracetate, oxidation

The conversion of these substrates into phthalazines is interesting rather than useful in its present state of development. The lead tetracetate oxidation of 4,7-diphenyl-17/-1,2,3-triazolo[4,5-tf]pyridazin-l-amine (301) in the presence of 2,3,4,5-tetraphenyl-l-cyclopentadienone (302) gave 1,4,5,6,7,8-hexaphenylphtha-lazine (303) [reactants, CaO, CH2CI2, Pb(OAc)4 portionwise, 20°C, min 20% see original with respect to mechanism]. ... 

The dehydrogenation of dioximes symmetrically substituted (17, R=Ri, Scheme 6.4) with a variety of oxidants, including potassium ferricyanide, halogens, hypohalides, nitric acid, nitrogen dioxides, and lead tetracetate, is a common route to symmetrically substituted furoxans. 

Under suitable conditions, further oxidation of the coupled products produces isolable dimer cation radicals. Thus treatment of 9-alkylcarbazoles with lead tetracetate in acetic acid-perchloric acid, or with 2,3-dichloro-5,6-dicyano-p-benzoquinone in acetic acid-perchloric acid, or with tris-(p-bromophenyl)ammoniumyl perchlorate in methylene chloride, or with nitrosonium borofluoride in acetonitrile all gave isolable cation radical perchlorates such as 17. These were reducible with aqueous sodium dithi-onite to the corresponding bicarbazoles the dimer cation radicals could be produced again by reoxidation of the dimer using 2,3-dichloro-5,6-dicyano-p-benzoquinone in acid solution. ... 

I. Periodic Acid (HIO4) or Lead Tetracetate (PblOAc) ), Oxidative Cleavage... 

Lead dioxide is widely used as an oxidizing agent in the arts as well as in the laboratory. It reacts with strong bases with the formation of plumbates, M2Pb03 and dissolves in strong acids, presumably forming plumbic salts. It will not react with weaker acids, such as acetic (c/. the preparation of lead tetracetate, synthesis 17). 

Fig (5) The ketoalcohol (34) prepared from ketone (33) has been converted to methoxyabietatriene(38), by standard organic reactions. Hydroboration, oxidation of (38), followed by oxidation, yielded the ketone (39), which is converted to the alcohol (40), by metal hydride reduction. On subjection to transanular oxidation with lead tetracetate and benzene alcohol (40) fiimishes (41) whose conversion to pisiferic acid has already been described. 

Oxidative cleavage of the 1,2-dihydroxy- and a-hydroxyketone moieties to carbonyl and carboxylic acid groups, respectively, was accomplished with lead tetracetate and periodic acid (Scheme 74) <1997JOC7430, 2005AGE6187>. 

One synthesis of cyclopentenone [80], requiring a resolution, involved initial ring contraction of phenol when treated with alkaline hypochlorite (49). Resolution of the resulting cis acid [85] was effected with brucine. The desired enantiomer [86] formed the more soluble brucine salt and was thus obtained from the mother liquors of the initial resolution. Oxidative decarboxylation with lead tetracetate, partial dechlorination with chro-mous chloride, and alcohol protection gave chloro enone [87]. Zinc-silver couple (50) dechlorinated [87] to the desired cyclopentenone [80]. 

Foucaud and Baudru166 have reported the preparation of several 5-amino-and 5-alkoxyoxazoles by the thermolysis of iV-imidoaziridines (98). The latter are readily obtained by the oxidation of iV-aminophthalimides (A—NH2) and N-aminosuccinimides (M—NH2 and Q—NH2) with lead tetracetate in the presence of the jewi-disubstituted olefins with two electron-attracting groups (with at least one of them of the type -COZ), e.g.,... 

Oxidation of phenols. Phenols are oxidized by lead tetracetate to o- and p-quinol acetates or biphenyls depending on reaction conditions. For example,... 

Potassium permanganate oxidation of lappaconine (86) yielded oxolap-paconine (88). Further oxidation of oxolappaconine with periodic acid produced secooxolappaconine (89). However, some controversy has developed about the lead tetracetate cleavage of the C-8-C-9 vicinal diol... 

OXIDATIVE DECARBOXYLATION Bis(triphenylphosphine)nickel dicarbonyl. Lead tetracetate. Oxygen, singlet. 

No benzocyclopropenone has been isolated but they appear to be formed as intermediates in the decomposition of benzotriazin-4-ones, in photolysis of 3-p-tolylsulphaminobenzotriazinone [160] or by oxidation of 3-aminobenzotriazinone by lead tetracetate [161]. It is likely that a nitrene is formed initially and collapses, with loss of nitrogen, to form the benzocyclopropenone. Isolated... 

Thus,as shown in Equation 8.17,the oxidation of the diarylenol,2-(2, 4, 6 -trimethyl-phenyl)-2-phenyl-l-ethenol with lead tetracetate in warm ethanoic acid (acetic acid, CH3CO2H) yields the corresponding acetoxyaldehyde. 

Condensation of silylimine of (5)-lactic aldehyde with lithium enolate of t-butyl isovalerate affords the -lactam in 80% chemical yield and in a 97 3 diastereomeric ratio. The mixture was desilylated and treated with lead tetracetate to give, in one step, through a radical fragmentation reaction, the 4-acetoxy derivative as a 1 1 4(R) 4(S) imeric mixture. The lack oi stereospecificity is not easy to rationalize expecially if one considers that the analogous lead tetraacetate induced oxidative decarboxylation is completely trans stereoselective. Both reactions should have the same radical intermediate. However, this lack of stereospecificity is not important for the success of the synthesis since the mixture of diastereoisomers exclusively affords the trans 4-substituted azetidinone by the subsequent Merck procedure (Scheme 9). 

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