Lactones from carbon dioxide

CHsjOH. CHlCgHg). CH(COOH). CH. COOH COOH. CHlCgHg). CH(CHaOH). CH. COOH COOH. CH(C2Hg). CH(COOH). CH. CH OH AomoPilopic acid is very stable, and is probably therefore the y-lactonic acid of one of these three hydroxy-acids. Further, pilopic acid seems to be produced from its higher homologue by loss of carbon dioxide and oxidation of the contiguous carbon atom. Of the four y-lactonic acids derivable from these three hydroxy-acids only two (I and II) answer these conditions,... 

W=X is N=N or C=N, never if it is C=C. The ring stability of 3-furyl-carbenes conforms with this rule. Ring opening is again the main reaction in a biradical which is generated by extruding carbon dioxide from a lactone at 675°C and which then collapses to an acetylenic ketone.277... 

The photoelimination of carbon dioxide from esters and lactones is a process that has been the subject of detailed investigations. Discussion here is limited to nitrogen containing systems. 3,4-Diphenylsydnone (464), on irradiation in benzene, is converted via the nitrile imine 465 into 2,4,5-triphenyl-1,2,3-triazole (466)388 initial bond formation between N-2 and C-4 followed by loss of carbon dioxide to give the diazirine 467 is proposed to account for the formation of the nitrile imine. Nitrile imines generated in this way have been trapped with alkenes and alkynes to give pyrazoles389... 

The controversy centered, on the structure of the free acids which were obtained from the esters by hydrolysie,and the question was not easily settled for apparently the reactions of the compound could be interpreted in two ways. In perfect accord with the unsaturated formula the acid added hydrobromic acid easily1 to give a product wnich was shown to be CKatJr-CHa-CH< ) ) on heating the vlnaconic acid", carbon dioxide was evolved and a monobasic acid and lactone CHa - CH - CHs were obtained. Tne forma-... 

Table 2 also shows surface concentration of quinones and esters or lactones, often referred to as "neutral oxygen compounds" in the rubber literature actually these are basic oxygens, but not basic in an aqueous environment. The quinone content is estimated from the amount of carbon monoxide evolved in pyrolysis minus the weak acid content (presumed to be phenolic acids,not neutralized at pH 8.2), and the ester and lactone content is estimated from the carbon dioxide evolved in pyrolysis minus the strong acid content (presumed to be carboxylic acids neutralized at pH 8.2). 

In most cases, uronic acids are liberated from acidic polysaccharides by hydrolysis leading to irreproducible concomitant formation of lactones. Several methods to circumvent this problem have been published describing conversion of the uronic acid into methyl esters followed by reduction with borohydride or borodeuteride reagents and subsequent hydrolysis and GC-MS detection [129]. Other techniques are based on the liberation and quantification of carbon dioxide. Direct determination of uronic acid residues in hydrolyzates has frequently been performed according to colorimetric assays, which are rather insensitive and have thus mostly been replaced by high-performance anion exchange chromatography (HP-AEC) methods [130-132]. 

Allene carboxylic acids have been cyclized to butenolides with copper(II) chloride. Allene esters were converted to butenolides by treatment with acetic acid and LiBr. Cyclic carbonates can be prepared from allene alcohols using carbon dioxide and a palladium catalyst, and the reaction was accompanied by ary-lation when iodobenzene was added. Diene carboxylic acids have been cyclized using acetic acid and a palladium catalyst to form lactones that have an allylic acetate elsewhere in the molecule. With ketenes, carboxylic acids give anhydrides and acetic anhydride is prepared industrially in this manner [CH2=C=0 + MeC02H (MeC=0)20]. 

S-Benzylthiuronium Salt of Diginonic Acid. Thirty-five milligrams of diginonic lactone prepared by bromine oxidation of the sugar is saponified in 3 cc. of 0.1 iV barium hydroxide solution by refluxing for thirty minutes on the steam bath. After cooling, the solution is neutralized with carbon dioxide, boiled for two minutes, filtered, and the filtrate is concentrated to dryness. The residue is taken up in 4 cc. of hot methanol and treated with a hot solution of 48 mg. of /S-benzylthiuronium sulfate in 1 cc. of methanol. After centrifuging from barium sulfate, the clear solution is concentrated to dryness. The residue crystallizes on the addition of acetone. The salt is purified by solution in the minimum amount of hot methanol followed by addition of 3 volumes of hot acetone. If necessary, the hot solution thus obtained is filtered, concentrated and seeded, with addition of more acetone if necessary. The salt crystallizes in rosettes of fine plates and melts at 137-138 after several recrystallizations in the same manner. 

The a-exomethylene-y-lactone framework has been successfully constructed via two electrosynthetic pathways, that is, both by the direct and by the concerted decarboxylation processes as mentioned earlier [Eq. (45)] [151]. The electrodecarboxylation of XCa is probably initiated by a one-electron oxidation of the sulfur atom, giving first the cation radical (XCb) and subsequently a concerted elimination of the thiyl radical and carbon dioxide to LXXXIX. On the other hand, the electrochemical decarboxylation of LXXXVIIIa involves an El-type elimination of a proton from the cation intermediate (LXXXVIIIb) generated from direct two-electron oxidation of the carboxyl group. The latter method generally requires a higher oxidation potential than that required for the concerted method. Therefore, the concerted electrodecarboxylation method becomes more advantageous, especially when the substrates or products are unstable under oxidative conditions. 

From a mechanistic point of view the first steps of the catalytic cycle should be similar to the telomerization of butadiene itself (Scheme 2). The catalytic precursor generates the Pd(0) species A that reacts to the bis-(ri -allyl) complex C. The C,C bond formation between two C4 units is followed by insertion of carbon dioxide into a Pd,C bond affording the carboxylate intermediate D. Different pathways have been discussed to describe the multiple product formation (refer to ). Interestingly, a bis-(carboxylato) complex may be prepared directly from the reaction of lactone 1, palladium acetate and P(i-Pr)3. This complex was structurally characterized by Behr and co-workers and shows good activity as catalyst. Reviewing the literature, there are some remarkable facts and open questions of theoretical and technical interest ... 

Table 10. Cyclopropyl Derivatives by Elimination of Carbon Dioxide from y-Lactones...

There are few other reaetions in whieh elimination of two ring atoms from a five-membered ring precursor give a cyclopropene. However, a low yield of cyclopropene (1 a) or of 1 -methyl-cyclopropcnc (1 b) was obtained by elimination of carbon dioxide from the corresponding a,/ -unsaturated y-lactone using mercury vapor sensitized photolysis. ... 

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