Lactones potassium acetate

In the course of investigations (175) on the structure of evemitrose, the corresponding 1,5-lactone 129, obtained upon oxidation of the sugar, yielded the a,/ -unsaturated derivative 130 when refluxed with methanolic potassium acetate. The same enonolactone 130 was obtained from L-mycar-ose (125c). 

Acetate esters are common by-products of LTA decarboxylation procedures. The yield of diese products, derived from further oxidation of the alkyl radical and quenching of the subsequent carbocation by acetate ions, can be improved by working in acetic acid in die presence of potassium acetate. Selective monodecarboxylation of 1,3- and 1,4-dicarboxyIic acids leads, via an analogous mechanism, to y- and 8-lactones in mo rate to good yields, as illustrate in equation (39). 

In the preaeuoe of potassium acetate,ketene reacts with aromatlo aldehydes to give a little J -lactono, bat the principal product ia a mixed anhydride. It has been definitely ehowni that this anhydride does not come from the reaction of keteno with the lactone whir may be formed in a first step ... 

Reaction with olefins.2 When ceric acetate is heated with styrene in glacial acetic acid containing 10% potassium acetate at 110° for 20 hr. the major product is the lactone (1), 70% yield. For the synthetic preparation of lactones, the more available ceric ammonium nitrate can be used in place of ceric acetate. 

Oxidative [l,2,l]-eliminations, in which hydrogen is formally cleaved off, are of preparative importance. Thus, 7-aminotheophylline (61) can be oxidized with lead tetraacetate to give the azapterin 62 (74 %)43), and in the. conversion of the 5-O-tosyl-D-glucurone lactone 63 to give 64 under the influence of potassium acetate/crown ether44 a dehydration takes place (atmospheric oxygen ). 

A lactone and a free sugar of this series have been obtained during investigations of nucleophilic displacements at C-5 of a hexonic acid derivative, in reactions (similar to those previously reported1) by which related enamines were formed. Treatment of 2,3,4,6-tetra-O-benzyl-N,N-dimethyl-5-0-(methylsulfonyl)-D-gluconamide with potassium acetate in N V-dimethylformamide gave 2,4,6-tri-0-benzyl-3-deoxy - L - threo - hex - 2 - enono -1,5 - lactone (53, R = O) which, with... 

Attempts to carry out a similar sequence of reactions on j8-bromo-cyanolycopodine LIV were thwarted for a long time by the tendency of this compound to eliminate hydrogen bromide. Treatment with potassium acetate in methanol, amines, and other bases always led to the same nonketonic, very unreactive compound, which was eventually shown to be the enol ether LV 41). With silver acetate in benzene, however, LIV yielded a mixture of LV and an acetoxy compound in an approximate ratio of 3 1. Treatment of the acetate in the same sequence of reactions used in the a-series gave the carboxylic acid LVI. When LVI was treated with sodium borohydride and the acidified reaction mixture extracted into chloroform a neutral compound was isolated. In its IR-spectrum it had 1743 cm in Nujol which shifted to 1761 cm i in chloroform solution, but there was no absorption in the hydroxyl region. The IR-speetrum and the elemental analysis were in agreement with the lactone structure LVII. When this work was carried out, however, the IR-evidence alone was not sufficient to differentiate between a y- and a S-lactone ([Pg.331]

The reaction of styrene with cerium(IV) acetate in glacial acetic acid containing 10% potassium acetate at 110 °C for 20 hours gives a lactone (scheme 8) (Heiba and Dessau, 1971). The reaction works with ammonium hexanitratocerate(IV) as well. The photochemical reaction of trans-)0-methylstyrene gives an ester as the major product (scheme 9). 

In order to avoid the multiple deprotonation observed during P-lactone polymerizations, in 1976 both BoUeau and Penczek showed, independently, that the introduction of macrocyclic ligand such as a crown ether [31] or a cryptand [32] in the anionic polymerization of PL (initiated with potassium acetate) would lead to a living polymerization (Scheme 9.7). As shown later by same authors, the M of the growing polyester became a linear function of monomer conversion, while the semilogarithmic monomer conversion kinetic plot was a Unear function of time [33]. 

For substituted lactones this method gave a low yield of the spiroketal 189 (<5%). For 5,6-dimethylvalerolactone a second scheme has been suggested involving treatment of ketoalcohol 190 with potassium carbonate in methanol to form enole ether acetal 191 in quantitative yield (90JOC5894). 

The third synthetic scheme is employed when the phenylthio substituent is in the a-position of the lactone function, which interferes with the cyclization (90JOC5894). Acetylenic ketone 194 (95% yield) is readily transformed to the acetal 195 (with potassium carbonate in methanol) however, under the above conditions neither its hydrolysis nor cyclization to the spiroketal occurs. The spirocyclic pyrone 197 is formed in quantitative yield on treatment of 195 with p-toluenesulfonic acid in a 4 1 THF-H2O mixture at reflux for 12 h. 

Schemes 15 and 16 summarize the syntheses of intermediates that represent rings A and D of vitamin Bi2 by the Eschenmoser group. Treatment of lactam/lactone 51, the precursor to B-ring intermediate 8 (whose synthesis has already been described, see Scheme 8), with potassium cyanide in methanol induces cleavage of the y-lac-tone ring and furnishes intermediate 76 after esterification of the newly formed acetic acid chain with diazomethane. Intermediate 76 is produced as a mixture of diastereomers, epimeric at the newly formed stereocenter, in a yield exceeding 95%. Selective conversion of the lactam carbonyl in 76 into the corresponding thiolactam...

Figure I indicates the approach used to synthesize poly(oxyethylene)-b-poly(pivalolactone) telechelomers. An acetal capped anionic initiator, X (13) polymerizes ethylene oxide (EO) to give 2> a potassium alkoxide of a masked polyether, and this "new" initiator is to be used to polymerize pivalolactone (PVL). Since potassium alkoxides are strong nucleophiles, they can randomly attack at both the carbonyl carbon and the 3-methylene carbon in lactones, (Figure 2) such a random attack would result in a pivalolactone segment containing irregularities. Lenz (15), and Hall (16), and Beaman (17) have investigated PVL polymerization and have shown that the less nucleophilic carboxylate anion is preferable in polymerizing PVL smoothly. The weaker carboxylate anion will attack only at the methylene...

Addition of alcohols to lactones results in the formation of orthoacid or orthoester derivatives. Thus, reaction of lactone 95a with potassium cyanide in ethanol led to displacement of the tosyl group by cyanide and addition of ethanol to the lactone carbonyl group, to give the orthoacid derivative 95b, which was isolated as its acetate 95c. Mild deacylation of 95c led back to 95b, but under more vigorous reaction conditions the open-chain methyl aldon-ate was obtained (90). 

The Pd-catalyzed coupling reaction of the propargyl acetate 53 and 4-pentynoic acid (54) in the presence of potassium bromide produced the unsaturated exo-enol lactone 55 [66], The reaction proceeded via oxypalladation of the triple bond of 54 with an allenylpalladium intermediate, which was formed from Pd(0) and 53 and the carboxylate as shown in Scheme 3.30. 

A. Tri-O-acetyl-D-xylono-l,4-lactone 2. a) Bromine oxidation. A 250-mL, threenecked, round-bottomed reaction flask equipped with a magnetic stirrer, thermometer, and an addition funnel is charged with 30.0 g (0.20 mol) of D-xylose and 80 mL of water. After the clear aqueous solution is cooled with an ice-water bath, 34.0 g 0.23 mol) of potassium carbonate is added in portions, keeping the temperature below 20°C. After the mixture is cooled to below 5°C, 12 mL (0.22 mol) of bromine is added dropwise over 90 min, keeping the temperature of the reaction mixture below 10°C (Note 1). The orange solution is stirred at that temperature for 30 min, then at room temperature overnight. The reaction is quenched by careful addition of 88% formic acid (2.5 mL) to afford a colorless solution (Note 2). The solution is concentrated at 50°C on a rotary evaporator and 20 mL of acetic acid is added. The mixture is Concentrated again at 50°C to remove any residual water (Note 3). 

While high polymers of /3-lactones can also be formed by cationic polymerization, most of the commercial production seems to be by the anionic route. Carboxylate salts such as sodium acetate or benzoate are commonly the initiators, but other nucleophiles, such as triethylamine, betaine, potassium f-butoxide, aluminum and zinc alkoxides, various metal oxides and tris(dimethylamino)benzylphosphonium chloride (the anion of which is the initiator), are of value. Addition of crown ethers to complex the counter cation increases the rate of reaction. When the reaction is carried out in inert but somewhat polar organic solvents, such as THF or ethyk acetate, or without solvent, chain propagation is very fast and proceeds without transfer reactions. 

Acetals are acid sensitive but alkaline stable because their hydrolysis requires activation of the oxygen atom by protonation or coordination with a Lewis acid. An ingenious way of differentiating two 2-methoxytetrahydroluran moieties during a synthesis of bilobalide [91] is to treat the tetracyclic intermediate with potassium hydroxide. Expulsion of a methoxide ion is triggered by attack of the y-lactone ring five carbons away. 

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