Lead tetraacetate synthesis

Although some of the oxidative ring closures described above, e.g. reactions with lead tetraacetate (Section 4.03.4.1.2), may actually involve radical intermediates, little use has been made of this reaction type in the synthesis of five-membered rings with two or more heteroatoms. Radical intermediates involved in photochemical transformations are described in Section 4.03.9. Free radical substitutions are described in the various monograph chapters. 

The procedure described here serves to illustrate a new, general method for effecting the < -arylation of g-dicarbonyl compounds by means of an aryllead triacetate under very mild conditions. Although the first synthesis of an aryllead triacetate was reported relatively recently, a wide range of these compounds can now be readily prepared. The most direct route to these compounds is plumbation of an aromatic compound with lead tetraacetate, and in the procedure reported here p-methoxyphenyllead triacetate has been prepared in this way. It may also be obtained by reaction of the diarylmercury with lead tetraacetate, a longer, but more general method of synthesis of aryllead triacetates. 

The first synthesis of p-methoxyphenyllead triacetate by direct plumbation was reported by Harvey and Morman, who obtained the compound in 2418 yield by heating anisole and lead tetraacetate in acetic acid at SO C for 4... 

Conjugate addition of methyl magnesium iodide in the presence of cuprous chloride to the enone (91) leads to the la-methyl product mesterolone (92) Although this is the thermodynamically unfavored axially disposed product, no possibility for isomerization exists in this case, since the ketone is once removed from this center. In an interesting synthesis of an oxa steroid, the enone (91) is first oxidized with lead tetraacetate the carbon at the 2 position is lost, affording the acid aldehyde. Reduction of this intermediate, also shown in the lactol form, with sodium borohydride affords the steroid lactone oxandrolone... 

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. 

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. 

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.

The natural diterpenoid rostratone 16 is synthesized from ethylene ketal as shown in Scheme 17.162 In this synthesis, the Pd-mediated remote acetoxylation is achieved by G-H bond activation by Na2PdCl4 giving palladacycle dimers followed by treatment with pyridine and lead tetraacetate. 

Optically pure glyceraldehyde acetonides are widely used in the synthesis of enantiomerically pure compounds (EPC synthesis).1 2 3 4 5 Whereas D-(R)-glyceraldehyde acetonide is easily obtained from the inexpensive D-mannitol,6 7 there are only a limited number of practical syntheses of the enantiomeric L-(S)-glyceraldehyde acetonide.8 9 Difficulties arise from different sources 1) availability of the starting material diisopropylidene-L-mannitol 2) length of the synthesis 10 3) nature of the reactants used mercury acetate, mercaptans, lead tetraacetate, ozone at -78°C, 4) moderate yields.11 14... 

The preparation of the title lactone has been described by a multistep synthesis from holarrhimine. The method described in detail above is essentially an application of the hypoiodite reaction published by Ch. Meystre and co-workers. These authors also describe the isolgition of the intermediate hemiacetal in pure form. Saturated lactones epimeric at C-20 have also been obtained by chromic acid oxidation of 18,20-dihydroxy compounds which were in turn prepared by treatment of 20-hydroxypregnanes with lead tetraacetate, acetolysis of the resulting 18,20 3-oxides, and hydrolysis. Saturated lactones of the... 

Murrayafoline A (7) required for this total synthesis was obtained starting from 3-formylindole (618) (577) (see Scheme 5.40). Lead tetraacetate-mediated oxidative non-phenolic biaryl coupling of 7 led to murrastifoline F (191) in 60% yield. The... 

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

L-Mannitol has been prepared by the reduction of L-mannosaccharo-dilactone or L-mannose. By far the most convenient procedure is that used by Baer and Fischer for their preparation of L-glyceraldehyde by the oxidative cleavage of l,2 5,6-diisopropylidene-L-mannitol with lead tetraacetate. L-Arabinose was converted to L-mannonolactone by the cyanohydrin synthesis and this was hydrogenated over platinum oxide to the desired L-mannitol. High hydrogen pressures, rather than low as usually employed with this catalyst, were used. 

Lead tetraacetate is used as a highly selective oxidizing agent in organic synthesis. This includes oxidation of glycols into aldehydes, preparation of cyclohexyl acetate, production of oxahc acid, and in structural analysis of sugars. 

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