Carbon lactone synthesis

Braunstein P, Matt D, Nobel D (1988) Carbon-dioxide activation and catalytic lactone synthesis by telomerization of butadiene and C02. J Am Chem Soc 110 3207-3212... 

In planning the synthesis of a series of carbapyranoses in their chiral non racemic format, Zanardi and co-workers [7d] utilized the seven-carbon lactone 149, in turn prepared by elaboration of butenolide 12 (vide supra, Scheme 3). 

Andreana et al. [25] have recently invoked RCM to prepare /J,y-unsaturated <5-lactones (Scheme 3). Exposure of dienes of general type 13 to either 2 or 4 (which could be used at lower loadings) readily furnished lactones 14. For other examples of a,/ -unsaturated <5- and y-lactone synthesis by RCM see Ref. [26]. Variation of the configuration at the chiral carbons and the ligand for the asymmetric dihydroxylation reaction allows access to an array of biologically important dideoxy-sugar derivatives. 

Fig. 5. Biosynthetic pathways for (I) 6-methylsalicylic acid and (II) the triacetic acid lactone. The structures of the intermediates have not been identified. The stereochemical course of the prochiral carbons (C-2 and C-4 in the triketide intermediate, C-3 and C-5 in 6-MSA) was investigated using R)- and (S)- [l- C,2- H]malonic acid extender substrate analogs in a coupled assay with 6-MSAS and succinyl-CoA transferase. The distinguishable hydrogens originating from the chiral malonyl CoA are labeled with H and H. Triacetic acid lactone synthesis is catalyzed by 6-MSAS in the absence NADPH...

The overall procedure of the spiro y-lactone and 7-lactone synthesis can be considered as a molecular-assembling process in which three simple independent species (i.e., a conjugated diene, a ketone, and carbon dioxide) are used to build a complex organic molecule in a well-controlled fashion. 

Lactones, synthesis by pericyclic photochemical reactions 86YGK1O58. Natural lactones with carbon skeleton of picrotoxane, synthesis of ... 

One alternative approach to lactone synthesis with CO in the absence of C—X and C—M bonds involves the decarboxylation of cyclic carbonates where lactone formation occurs with concomitant loss of CO2 (Scheme 2.22) [48-50]. Since CO2 is the sole byproduct, this process is considerably more green than carbonylation of C—X and C—M bonds. 

Choi JC, Shiraishi K, Takenaka Y, Yasuda H, Sakakura T. Synthesis and reactivity of five-membered paUadalactones from arylaUenes and carbon dioxide relevance to catalytic lactone synthesis. Organometallics. 2013 32 3411-3414. 

The wM-diacetate 363 can be transformed into either enantiomer of the 4-substituted 2-cyclohexen-l-ol 364 via the enzymatic hydrolysis. By changing the relative reactivity of the allylic leaving groups (acetate and the more reactive carbonate), either enantiomer of 4-substituted cyclohexenyl acetate is accessible by choice. Then the enantioselective synthesis of (7 )- and (S)-5-substituted 1,3-cyclohexadienes 365 and 367 can be achieved. The Pd(II)-cat-alyzed acetoxylactonization of the diene acids affords the lactones 366 and 368 of different stereochemistry[310]. The tropane alkaloid skeletons 370 and 371 have been constructed based on this chemoselective Pd-catalyzed reactions of 6-benzyloxy-l,3-cycloheptadiene (369)[311]. 

Allylalion of the alkoxymalonitrile 231 followed by hydrolysis affords acyl cyanide, which is converted into the amide 232. Hence the reagent 231 can be used as an acyl anion equivalent[144]. Methoxy(phenylthio)acetonitrile is allylated with allylic carbonates or vinyloxiranes. After allylation. they are converted into esters or lactones. The intramolecular version using 233 has been applied to the synthesis of the macrolide 234[37]. The /i,7-unsaturated nitrile 235 is prepared by the reaction of allylic carbonate with trimethylsilyl cyanide[145]. 

The reaction can be applied to the synthesis of q, /3-unsaturated esters and lactones by treatment of the ketene silyl acetal 551 with an allyl carbonate in boiling MeCN[356]. The preparation of the q,, 3-unsaturated lactone 552 by this method has been used in the total synthesis of lauthisan[357]. 

The slow oxidation of primary alcohols, particularly MeOH, is utilized for the oxidation of allylic or secondary alcohols with allyl methyl carbonate without forming carbonates of the alcohols to be oxidized. Allyl methyl carbonate (564) forms 7r-allylpalladium methoxide, then exchange of the methoxide with a secondary or allylic alcohol 563 present in the reaction medium takes place to form the 7r-allylpalladium alkoxide 565, which undergoes elimination of j3-hydrogen to give the ketone or aldehyde 566. The lactol 567 was oxidized selectively with diallyl carbonate to the lactone 568 without attacking the secondary alcohol in the synthesis of echinosporin[360]. 

The results obtained showed that carbon, oxygen, or nitrogen functionalities are readily introduced into the a,p positions of the lactone moiety. In this way, useful precursors for natural product synthesis are accessible (88TL5317). 

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... 

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