Lead tetraacetate with alkenes

The reaction of lead tetraacetate with alkenes and arenes involve first an electrophilic addition step. The intermediate organolead derivative then can follow various pathways to yield oxidation products. 

The very reactive species Pb(OCOCH3)2F2, formed in situ by the reaction of lead tetraacetate with hydrogen fluoride [274], has been used very effectively for adding fluorine to alkenes, especially in the synthesis of the biologically important 6a-fluoro steroidal hormones [275]. 

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]. 

Alkenes can also be oxidized with metallic acetates such as lead tetraacetate or thallium(III) acetate " to give bis-acetates of glycols. Oxidizing agents such as benzoquinone, Mn02, or 02, along with palladium acetate, have been used to convert conjugated dienes to l,4-diacetoxy-2-alkenes (1,4 addition). ... 

A hydroxy and an arylthio group can be added to a double bond by treatment with an aryl disulfide and lead tetraacetate in the presence of trifluoroacetic acid." Manganese and copper acetates have been used instead of Pb(OAc)4. ° Addition of the groups OH and RSO has been achieved by treatment of alkenes with O2 and a thiol (RSH)." Two RS groups were added, to give vie- dithiols, by treatment of the alkene with a disulfide RSSR and Bp3-etherate."° This reaction has been carried... 

Dicarboxylic acids undergo to-decarboxylation on reaction with lead tetraacetate to give alkenes. This reaction has been of occasional use for the synthesis of strained alkenes. 

V-Phthalimidoaziridines may be obtained by reaction of alkenes with 7V-aminophthali-mide which has been treated with lead tetraacetate (equation 152)550-554. These compounds are useful in the synthesis of a-hydrazino acid derivatives which are inhibitors of amino acid metabolising enzymes. 

A general method for direct aziridination of alkenes, discovered nearly thirty years ago, involved oxidation of a number of A-aminoheterocyclic compounds, such as 240, with lead tetraacetate (LTA) in the presence of the alkene to give 241 375. The intermediates in these aziridinations were originally believed to be the corresponding TV-nitrenes but have recently been shown to be (at least for A-aminoquinazolinone 240 and A-aminophthalimide) the corresponding A-acetoxyamino compounds 242375. 

It would appear that a similar mechanism probably applies to the many aziiidinations of alkenes with lead tetraacetate and a wide variety of other A -aminoheterocycles. In any case, such reactions are now thought unlikely to occur via a nitrene in competition eiqieriments, A -aminqphthalimide/lead tetraacetate reacts with styrene in preference to methyl aciylate (1.5 1), whereas with the supposed genuine nitrene (27) (whose nature is also in doubt " ) prepared by pyrolysis (Scheme 32), the ratio is reversed (1 3). Other sources of supposed (27) by pyrolysis include (28) and (29). Very recently, strong... 

In contrast to lead tetraacetate, simple addition to the double bond does not occur as a side re-action. While allylic rearrangement is common and mixtures of products are frequently obtained, the reaction often proceeds in very high yield and is simple to carry out the alkene is simply heated in an appropriate solvent with mercury(II) acetate until reaction is complete. Mercury(II) acetate has also been us for dehydrogenation, particularly in the steroid field. One interesting example incorporating simultaneous dehydrogenation and allylic oxidative rearrangement is seen in the reaction of abietic acid (37 equation 16). ... 

Oxidation of methoxylamine and some other 0-substituted hydroxylamines by lead tetraacetate in the presence of alkenes can also lead to the formation of aziridines. The oxidation of 2,4-dinitrobenzenesul-fenamide is analogous. In view of the results reported with aminolactams, these reactions do not necessarily establish the intermediacy of nitrenes in the oxidations. 

The conversion to primary acetates is carried out in higher yield if the hydroalumination is conducted with only 2 equiv. of the alkene followed by reaction with lead tetraacetate (equation II). ... 

Diazides were less selectively prepared by the reaction of alkenes with azidotrimethylsilane and lead tetraacetate (see also Section 7.2.2.6.) or with anodically generated azide radicals75. 

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