Alkenes, reaction with lead tetraacetate

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. 

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). ... 

The reaction of olefins with lead tetraacetate has not been a useful method in organic synthesis, because reactions such as addition of an oxygen functional group to the double bond, substitution of hydrogen at the allylic position, and C-C bond cleavage can occur to give complex mixtures of products. With some specific alkenes, however, reaction with lead tetraacetate can afford synthetically important compounds cleanly. For instance, reaction of the diacid with 6 equiv. lead tetraacetate in acetonitrile gave the dilactone in excellent yield (Scheme 13.36) [59]. 

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. 

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... 

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]. 

The aziridination of alkenes by in situ oxidation of primary amines has only been achieved intramolecularly42-47. Using A-chlorosuccinimide, the reaction proceeds via intermediate /V-chloro amines42. A good yield of the aziridine can only be obtained when the molecule is sufficiently rigid to force the amino group close to the alkene double bond. Better results are generally obtained by oxidation of the alkenyl amines with lead tetraacetate. 

Allylic esters result from the reaction of alkenes with itri-butyl per-oxyacetate [233], or the more reactive peroxybenzoate [233, 234, 1113], in the presence of cuprous bromide with mercuric acetate [404, or with lead tetraacetate [1114] (equation 127). 

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. 

In addition, the reaction can be further catalyzed by a variety of bases such as lithium acetate and pyridine. A typical decarboxylation is carried out by dissolving the catalyst (0.535 mmole), pyridine (1.39 mmoles), and the alkanoic acid (21.2 mmoles) in a solvent (benzene, chlorobenzene). Lead tetraacetate (9.86 mmoles) in the same solvent is added, and the resulting mixture is stirred in the dark for one hour. Although alkenes have been reported to react with lead tetraacetate, under these experimental conditions the alkene is not attacked.1... 

The many iV-aminoheterocycles convertible to aziiidines by oxidation with lead tetraacetate, generally at ambient temperature in dichloromediane, are listed in Scheme 33.S.SS.10 -1U xhe most frequently used is A -aminophthalimide, which gives good yields with a wide variety of alkenes, both electron-rich and electron-poor, most recently steroidal alkenes. Prior to the appearance of ref. 100, these reactions were all assumed to occur via (singlet) nitrenes, and indeed all the early evidence was consistmt with this suggestion, except perh s, in retrospect, the absence of products of C—insertion. 

With key intermediate 252 in hand, Hudlicky turned his attention to the crucial oxidative dearomatizationyiniramo-lecular [4+2] cycloaddition sequence (Scheme 12.45). Thus, the carbonyl moiety in 252 was converted to the requisite terminal alkene via reaction with methyltriphenylphospho-nium bromide, before the MOM ether was cleaved under acidic conditions. Reaction of the free phenol in cyclization precursor 253 with lead tetraacetate resulted in the desired arene oxidation and isolation of cycloaddition product 255 in 50% yield, via intermediary formed dienone 254. Interestingly, 255 was formed as sole cycloaddition product, and the product of the endocyclic cycloaddition reaction was only observed once in minor amounts, probably because of unfavorable steric interactions. 

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]. 

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... 

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