Lead oxidative cleavage with

Preparative Methods prepared in two steps from o-mannitol via bis-ketalization to l,2 5,6-bis-( -(l-methylethylidene)-D-mannitol, followed by oxidative cleavage with sodium periodate in dichloromethane. Classically obtained from o-mannit-ol by bis-ketalization and oxidative cleavage with lead tetraacetate. Bis-ketalization has been accomplished under a range of conditions " a comparative study of the most commonly employed methods has appeared. ... 

Ethier and Neville239 presented the facile oxidative methylation of 5-. vanillylidene and 5-benzylidenebarbituric acids in DMF with methyl iodide in the presence of Ag20 leading to 1,3,5,5-tetramethylbarbituric acid (66). According to the authors, the oxidative cleavage with methylation followed the interaction of silver ion with the olefinic double bond. 

Oxidative cleavage of P-aminoacyl complexes can yield P-amino acid derivatives (320,321). The rhodium(I)-catalyzed carbonylation of substituted aziridines leads to P-lactams, presumably also via a P-aminoacyl—metal acycHc compound as intermediate. The substituent in the aziridine must have 7T or electrons for coordination with the rhodium (322,323). 

The reaction is based, on the one hand, on the oxidative cleavage of vicinal diols by lead(IV) acetate and, on the other hand, on the reaction of dichlorofluorescein with lead(IV) acetate to yield a nonfluorescent oxidation product. The dichlorofluorescein only maintains its fluorescence in the chromatogram zones where the lead(IV) acetate has been consumed by the glycol cleavage reaction [1],... 

The reaction of the fervenulin 1-oxides 100 with secondary amines results in contraction of the 1,2,4-triazine ring to form 2-amino-5,7-dimethylimidazo[4,5-e] pyrimidine-4,6(5/7,7//)-diones 101. The reaction of the same fervenulin 1-oxides 100 with ammonia leads to the 1,2,4-triazine ring cleavage product, 1,3-dimethyl-5-imino-6-isonitrosouracil 102 (94KGS1253). 

The oxidative cleavage of the central carbon-carbon bond in a vicinal diol 1, by reaction with lead tetraacetate or periodic acid, yields two carbonyl compounds 2 and 3 as products. 

Finally, oxidative cleavage of the remaining aryl-silicon bond with lead tetrakis(trifluoroacetate), [Pb(OCOCF3)4]19, furnishes ( )-estrone [( )-1 ] in nearly quantitative yield. 

A cursory inspection of key intermediate 8 (see Scheme 1) reveals that it possesses both vicinal and remote stereochemical relationships. To cope with the stereochemical challenge posed by this intermediate and to enhance overall efficiency, a convergent approach featuring the union of optically active intermediates 18 and 19 was adopted. Scheme 5a illustrates the synthesis of intermediate 18. Thus, oxidative cleavage of the trisubstituted olefin of (/ )-citronellic acid benzyl ester (28) with ozone, followed by oxidative workup with Jones reagent, affords a carboxylic acid which can be oxidatively decarboxylated to 29 with lead tetraacetate and copper(n) acetate. Saponification of the benzyl ester in 29 with potassium hydroxide provides an unsaturated carboxylic acid which undergoes smooth conversion to trans iodolactone 30 on treatment with iodine in acetonitrile at -15 °C (89% yield from 29).24 The diastereoselectivity of the thermodynamically controlled iodolacto-nization reaction is approximately 20 1 in favor of the more stable trans iodolactone 30. 

By oxidative addition of aryl sulphides to low-valent nickel complexes, a C—S bond cleavage occurs to form Ni11 thiolate complexes. For example, exposure of diaryl sulphides to [(But3P)3Ni0] leads to oxidative addition, with nickel inserting into the C—S bond (280).814... 

Chemical and other physical methods of ionization were also employed for the structural determination of dienes and polyenes. Such is the case for the recent investigation of aliphatic dienes and trienes by chemical ionization with nitric oxide (NO+)25. It has been known since 1975 that olefins can be chemically ionized by NO+ [CI(NO)]26. Two distinct processes may apparently occur (i) electrophilic addition of NO+ to the ene leading to [M + NO]+ ion and (ii) an oxidative cleavage (possibly catalysed by the... 

Some of the earliest work in the oxidation of alkenes was performed by oxidation with potassium permanganate. Under acidic and neutral conditions the intermediately formed glycols are oxidized, generally leading to cleavage of the carbon-carbon bond. Thus, such procedures have seldom been synthetically applied to diene oxidation. One notable... 

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