Lead tetraacetate cleavage

The spiroacetal morpholine work of Scheme 38 subsequently inspired research on the preparation of a novel family of morpholino-glycosides from sucrose via lead tetraacetate cleavage and reductive amination (Scheme 40). Significantly, the latter work, which was done with the present author, unveiled a completely new structural class of sweeteners, more intense than sucrose but having a similar taste profile. 

Some related iV-aryl compounds were examined in model experiments in connection with lead tetraacetate cleavage of samandarin derivatives.194 Oxidation in aqueous acetic acid at 60-70° of 1 -deoxy-1-(p-toluidino)-l-arabinitol (LXXXV) and -D-mannitol yielded two moles of formaldehyde per mole, one mole being derived from the terminal carbinol group and the second from subsequent hydrolysis of the Schiff base (LXXXVI) pro-... 

The mixture of catechols was subjected to the lead tetraacetate cleavage conditions, giving the corresponding muconates (197 only shown) which were reoxidized and esterified to the corresponding C-2 methyl esters (199 only shown), again with no C-2 epimerization observed. Unfortunately, the hydrolysis with concomitant pyrone formation gave rise to a complex mixture of products, ruling out this method for the synthesis of acromelic acid B 6 (Scheme 75—major isomers only shown). 

If the molecule is indeed bent out of a plane the nitro substituent should produce the potentiality for molecular asymmetry. Hence the nitro derivative was treated with p-boronobenzoic acid in benzene under a water separator to yield the cyclic boronate ester carboxylic acid (8). a derivative directly suitable for optical resolution. As a carboxylic acid. (8) gave a crystalline salt with quinine which, after four recrystallizations (aD — 37.4°), liberation of the organic acid, and hydrolysis gave optically active nitroglycol (6), X = NO,. Lead tetraacetate cleavage of the dextrorotatory (6), X = N02. gave optically active (5), X = NO,. the racemization of polarimetry in a chloroform solution. 

If structure VI for hydroxylycoctonine is correct the product of lead tetraacetate cleavage of hydroxylycoctonam (XX) should be XXI. This was confirmed by alkaline hydrolysis of XXII to the corresponding acid, which spontaneously cyclized to the lactone XXIII. 

The introduction of a 9(11) double bond into steroids is of practical interest, since such olefins can be converted to the 9-fluoro-l 1 -hydroxy grouping found in most useful corticosteroids. Ester 6 had a benzophenone-4-hexanoic acid tethered to the hydroxyl group of androstan-17/3-ol that curled under the steroid ring and photochemically inserted into the C-9 a-hydrogen, forming product 7 with a 9(11) double bond after lead tetraacetate cleavage of the carbinol product and hydrolytic cleavage of the tether (Scheme 6-3) [33]. A product with a 14,15 double bond was also produced. 

Saccharides linked glycosidically to an a-hydroxy carbonyl compound cleave readily on treatment with hydrazine. Such glycosides are commonly encountered following periodate or lead tetraacetate cleavage of oligosaccharides. 

MokhaUalati MK, Pridgen LN. Lead tetraacetate cleavage of chiral phenylglycinol derived secondary amines without rac-emisation. Synth. Commtm. 1993 23 2055-2064. 

Cleavage of an alkenoic acid can be carried out with permanganate, a permanganate—periodate mixture, periodate or with nitric acid, dichromate, ozone, or, if the unsaturation is first converted to a dihydroxy compound, lead tetraacetate (71,73). Oxidative ozonolysis is a process for the manufacture of azelaic acid [123-99-9] and pelargonic acid (74). 

Lead tetraacetate fragmentation has not been applied to the 20-hydroxy-18, 20-cyclo steroids. However, preferential cleavage of the 17,20-bond would be expected, as was observed in the chromic acid oxidation of a saturated 20-hydroxy-18,20-cyclo steroid in hot acetic acid which affords the 18-acetyl-17-ketone in 50-60% yield. 

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. 

Lead tetraacetate and periodic acid complement one another in their applicability as reagents for glycol cleavage. The water sensitive lead tetraacetate is used in organic solvents, while periodic acid can be used for cleavage of water-soluble diols in aqueous medium. 

Furthermore, photochemically induced homolytical bond cleavage can also be applied when the prepolymer itself does not contain suitable chromophoric groups [113-115]. Upon thermolysis of ACPA in the presence of styrene, a carboxyl-terminated polystyrene is formed. This styrene-based prepolymer was reacted with lead tetraacetate and irradiated with UV light yielding free radicals capable of initiating the polymerization of a second monomer (Scheme 33) [113]. 

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. 

Alcohols (diols, polyols, sugan) Lead(IV) acetate -dichloro fluorescein Diol cleavage of vicinal diols, e. g. sugars, sugar alcohols. The lead tetraacetate consumed is no longer available to decompose the fluorescent dichlorofluorescein. [3, 8]... 

Lead tetraacetate is an important reagent for glycol cleavage, which has the stoichiometry... 

A much higher ratio of unsaturated saturated hydrocarbons is observed than in the case of cleavage with lead tetraacetate. ... 

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