Lead tetraacetate reaction with ketones

Lead tetraacetate reacts with ketones to form a-acetoxyketones. Reported yields are seldom high, however. The reaction has been successfully applied to keto steroids. Boron trifluoride can be used to catalyze these oxidations. It is presumed to function by catalysis of enolization, and it is assumed that the enol is the reactive species. ... 

R = cyl), eg, with -nitrobenzoyl chloride. Upon reaction with lead tetraacetate, di(hydroperoxyalkyl) peroxides can also be converted to cycHc diperoxides (4). They are also converted to symmetrical or unsymmetrical cycHc triperoxides (5) in the presence of a second ketone and a catalyst, eg, CuSO -HCl (44,119). 

If homolytic reaction conditions (heat and nonpolar solvents) can be avoided and if the reaction is conducted in the presence of a weak base, lead tetraacetate is an efficient oxidant for the conversion of primary and secondary alcohols to aldehydes and ketones. The yield of product is in many cases better than that obtained by oxidation with chromium trioxide. The reaction in pyridine is moderately slow the intial red pyridine complex turns to a yellow solution as the reaction progresses, the color change thus serving as an indicator. The method is surprisingly mild and free of side reactions. Thus 17a-ethinyl-17jS-hydroxy steroids are not attacked and 5a-hydroxy-3-ket-ones are not dehydrated. 

The formation of a-acetoxyketones by oxidation of enamines with thallic acetate has been studied in detail (27) and found to be of preparative value (80 % yields) particularly in five- and six-membered-ring ketone derivatives. Enamines of linear or seven-membered-ring ketones were oxidized also, but at very much slower rates. Enamines of aldehydes with a-hydrogen substituents underwent self-eondensations during the oxidation reactions. Lead tetraacetate was less satisfactory as an oxidizing agent. 

The 1,1-dimetallic compounds, R2C(SnMe3)ZnBr, were oxidized by dry air at —10 to 0°C in the presence of Me3SiCl to give aldehydes or ketones, R2C=0. In a related indirect method, arylthallium bis(trifluoroacetates) (prepared by 12-21) can be converted to phenols by treatment with lead tetraacetate followed by triphenylphosphine, and then dilute NaOH. Diarylthallium trifluoroacetates undergo the same reaction. ... 

It has been shown that the lead tetraacetate-mediated 1,2-aryl shift of various meta-substituted / -cyclohexyl aryl ketones, e.g. (10), results in excellent yields of the corresponding rearranged esters (11). A unique reaction, providing 3-hydroxy-2-arylacrylic acid ethyl esters (14), has been observed between aryl aldehydes and ethyl diazoacetate in the presence of the iron Lewis acid [rj — (C5H5)Fe(CO)2(THF)BF4], It appears that the enol esters are formed by an unusual 1,2-aryl shift from a possible intermediate (13), which in turn is formed from the reaction of the iron aldehyde complex (12) with ethyl diazoacetate (see Scheme 4). 

Acyloxylation has also been achieved with metallic acetates such as lead tetraacetate,237 mercuric acetate,238 and palladium(II) acetate.239 In the case of the lead and mercuric acetates, not only does the reaction take place at allylic and benzylic positions and at those a to an OR or SR group but also at positions a to the carbonyl groups of aldehydes, ketones, or esters and at those a to two carbonyl groups (ZCH2Z ). It is likely that in the latter cases... 

Methyl arylacetates.2 Aryl methyl ketones are converted into methyl arylacetates by reaction with BF3 etherate and lead tetraacetate in benzene at room temperature (equation I). Thallium(lll) nitrate (4, 496) has also been used for this modified Willgerodt-Kindler reaction. 

Reactions of 4,7-phenanthroline-5,6-dione have been the subject of considerable study. It is reduced to 5,6-dihydroxy-4,7-phenanthroline by Raney nickel hydrogenation226,249 or by aromatic thiols in benzene,262 and oxidized by permanganate to 3,3 -bipyridyl-2,2 -dicarboxylic acid.263 It forms bishemiketals with alcohols226 and diepoxides with diazomethane.226 The diepoxides by reaction with hydrochloric acid form diols of type 57, R = Cl, which on oxidation with lead tetraacetate give 3,3 -bipyridyl diketones of type 58, R = Cl. Methyl ketones of type 58, R = H, are also obtained by lead(IV) acetate oxidation of the diol 57, R = H, obtained by lithium aluminum hydride reduction of 57, R = Cl. With phenyldiazomethane and diphenyldiazomethane the dione forms 1,3-dioxole derivatives,264,265 which readily hydrolyze back to the dione with concomitant formation of benzaldehyde and benzophenone, respectively. 

The Diels-Alder reaction of 3-methoxyfuran with octyl vinyl ketone took place at room temperature in quantitative yield to afford exclusively the endo cycloadduct (27) (81CC221). Reduction of the carbonyl group with lithium tri-r-butoxyaluminum hydride produced a single alcohol (28). Ozonolysis of the double bond followed by Jones oxidation yielded the lactone ester (29). Hydrolysis of the ester and lead tetraacetate oxidation gave the lactone acetate. This was converted by further hydrolysis and Jones oxidation to the bis-lactone (30), a known intermediate in the synthesis of ( )-isoavenaciolide (Scheme 6). 

Aziridinyl ketones can be synthesized from unsaturated carbonyls using a series of other methods. For example, azabicyclo[4.1.0]heptanone 27 was obtained from cyclohexenone 25 in its reaction with TV-bromotoluenesulfona-mide sodium salt 33 [49] (Scheme 1.10). The reaction of chalcone with N-chlorotoluenesulfonamide in the presence of silver nitrite is described in [50]. Trans-Aziridinyl ketone 18 was synthesized by reacting chalcone 22 with N,N-diamino-l,4-diazoniabicyclo[2.2.2.]octane dinitrate 34 and sodium hydride in 2-propanol [30, 51]. Aziridinyl ketones can be obtained in the reaction of a -unsaturated ketones with A,A-dichlorosulfonamines [52] and with amines in the presence of lead tetraacetate and trifluoroacetic acid [53] or in the presence of triethylammonium acetate under electrochemical reaction conditions [54]. 

These and related reactions of lead tetraacetate have been widely used in synthetic organic chemistry, and are the subject of several reviews.6-10 However, they have found relatively few applications in the carbohydrate field specifically. One important application has been the synthesis of ketones by way of acetoxylation of suitable unsaturated compounds. By treating 1,2-0-isopropylidene-2-propene-l, 2-diol (I) in benzene at 50° with... 

Monohydric alcohols react rapidly with lead tetraacetate to form alkoxy lead (IV) intermediates. These intermediates decompose thermally or photolytically in a variety of ways to produce ketones, esters, and cyclic ethers (62), as can be seen below (Reaction XXXVII). 

Anodic dehydrogenations, e.g., oxidations of alcohols to ketones, have been treated in Sect. 8.1 and formation of olefins by anodic elimination of C02 and H+ from carboxylic acids was covered in Sect. 9.1. Therefore this section is only concerned with anodic bisdecarboxylations of v/odicarboxylic acids to olefins. This method gives usually good results when its chemical equivalent, the lead tetraacetate decarboxylation, fails. Combination of bisdecarboxylation with the Diels-Alder reaction or [2.2] -photosensitized cycloadditions provides useful synthetic sequences, since in this way the equivalent of acetylene can be introduced in cycloadditions. 

The starting material for the present synthesis was Wieland-Miescher ketone (24), which was converted to the known alcohol (25) by the published procedure [10], Tetrahydropyranylation of alcohol (25) followed by hydroboration-oxidation afforded the alcohol (26), which on oxidation produced ketone (27). Reduction of (27) with metal hydride gave the alcohol (28) (56%). This in cyclohexane solution on irradiation with lead tetraacetate and iodine produced the cyclic ether that was oxidized to obtain the keto-ether (29). Subjection of the keto-ether (29) to three sequential reactions (formylation, Michael addition with methyl vinyl ketone and intramolecular aldol condensation) provided tricyclic ether (30) whose NMR spectrum showed it to be a mixture of C-10 epimers. The completion of the synthesis of pisiferic acid (1) did not require the separation of epimers and thus the tricyclic ether (30) was used for the next step. The conversion of (30) to tricyclic phenol (31) was... 

Favorski-type rearrangement Reaction of lead tetraacetate and BFj in benzene with the ketone (1) results in a mixture of a -acetoxylated ketones, 2a and 2b. If... 

An earlier report [i8y] of the formation of 4a-acetoxy-cholest"5"en-3 One (4) from cholest-5-en-3-one (3) can now be interpreted as a preferential a-face attack upon the enolic 3,5-diene. The stereochemistry of acetoxylation suggests a connection with the sterically-controlled 4 -deprotonation of the A -3-ketone discussed in Chapter 4, section 6, but electrophilic attack at C<4) rather than at C 6> in the neutral enol is abnormal, and probably indicates that acetoxy transfer occurs via a cyclic transition state (3 with the reagent bonded to the C(3)-oxygen substituent. Corey [188] has proposed a mechanism of this type, and suggested that the enol triacetoxy-plumbate cf. 5) may arise by direct reaction between the ketone and the reagent. Supporting such an interpretation, the 3-acetoxy 3,5 diene(6) reacted normally (p. 184) with lead tetraacetate to give the 6j -acetoxy-A -3-ketone 7) [i8g] instead of a 4-acetoxy derivative. 

Pyrazolines can also be prepared by the oxidation of pyrazolidines. 2-Pyrazolines, which are readily obtained in the reaction of a,j -unsaturated ketones with hydrazine, also undergo nitrogen extrusion at elevated temperature usually in the presence of a basic catalyst. The reaction is believed to proceed via 1-pyrazolines. Treatment of 3,3,5-trialkyl-2-pyrazolines with lead tetraacetate followed by thermolysis affords cyclopropyl acetates ". Oxidation of certain 2-pyrazolines with manganese dioxide gives 3H-pyrazoles, which in turn produce cyclopropenes in the photolysis (equation 7). ... 

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