Lactone byproducts

Good yields of 1 1 adducts have also been obtained from Lewis acid catalyzed reactions of methyl chloropropiolate or DMAD with alkenes. With methyl chloropropiolate, cyclobutenes are obtained exclusively from mono- and 1,2-di-substituted alkenes and mixtures of ene adducts and cyclobutenes are obtained with 1,1-di-, tri- and tetra-substituted alkenes. With DMAD, ene adducts are obtained exclusively from 1,1-di-, tri- and tetra-substituted alkenes and mixtures of ene adducts and cyclobutenes are obtained hrom 1,2-disubstituted alkenes. EtAlCb is a more effective catalyst than AlCb since it is a proton scavenger as well as a Lewis acid. With AlCb, lactone byproducts are also formed. - The relative reactivity of alkenes in these Lewis acid catalyzed reactions was found to be 1,1-di- > tri- > tetra- mono- > 1,2-di-substituted. With reactive ene components such as methylenecyclohexane, ethyl-idenecyclohexane and -pinene, good yields of ene adducts can be obtained with DMAD by thermal reaction at 110-130 "C for 0.25-6 d. ... 

In the presence of a double bond at a suitable position, the CO insertion is followed by alkene insertion. In the intramolecular reaction of 552, different products, 553 and 554, are obtained by the use of diflerent catalytic spe-cies[408,409]. Pd(dba)2 in the absence of Ph,P affords 554. PdCl2(Ph3P)3 affords the spiro p-keto ester 553. The carbonylation of o-methallylbenzyl chloride (555) produced the benzoannulated enol lactone 556 by CO, alkene. and CO insertions. In addition, the cyclobutanone derivative 558 was obtained as a byproduct via the cycloaddition of the ketene intermediate 557[4I0]. Another type of intramolecular enone formation is used for the formation of the heterocyclic compounds 559[4l I]. The carbonylation of the I-iodo-1,4-diene 560 produces the cyclopentenone 561 by CO. alkene. and CO insertions[409,4l2]. 

The paraffin wax is oxidized by air in a liquid phase process at 110-130°C. Catalysts for this radical reaction are cobalt or manganese salts [54]. The quality of the obtained mixture of homologous carboxylic acids is impaired by numerous byproducts such as aldehydes, ketones, lactones, esters, dicarboxylic acids, and other compounds. These are formed despite a partial conversion of the paraffin and necessitate an expensive workup of the reaction product [50,55]. 

Acetals of L-galactono-1,4-lactone (an abundant byproduct of the sugar beet industry) have thermotropic liquid crystalline properties. Acetalization in DMF containing H2S04 in the presence of anhydrous CuS04 gave (after 12 to 24 h at 40 °C) yields of 20-35% (Scheme 8.27). 

Demethylation of the methoxy groups in lactone 142 was achieved with BBr3 in dichloromethane. The reaction conditions were not optimized, and the yield of a-hydroxylated enterolactone 144 was low (15%). Several byproducts, such as both regioisomers of the mono-methylether, were obtained. 

Baeyer-Villiger oxidation afforded the desired lactone 28 accompanied with hydro-xycarboxylic acid 29 as a byproduct. After removal of the acid 29, the lactone was reduced with DIBAL-H and employed in the Wittig reaction to form the PG structure 31 (Scheme 4). 

Carbonyl oxides are extremely photolabile even under matrix conditions and irradiation with red light (600 nm) rapidly produces dioxrranes (82). The dioxi-ranes are stable under these conditions but at 400-nm irradiation are converted into esters (83) or lactones. Ketones have been observed as byproducts in the carbene-O2 reactions in frozen matrices. Since the reaction of triplet carbene with O2 is very... 

An alternative workup procedure takes advantage of the solubility of the lactone in MeOH. Upon completion of the reaction, the residual oil was dissolved in EtOAc and washed with 5% aq citric acid (50 mL), H20 (2 x 50 mL), 5% NaHC03 (50 mL), and H20 (2 x 50 mL). The organic phase was dried and concentrated, and the oil triturated with MeOH to afford the crystalline product yield 4.9 g (55%). The latter workup procedure, while very simple and economic, cannot be applied to other N-protected lactones, e.g. to the TV-Boc-4-hydroxy proline lactone, where careful flash chromatography was required for separation of other polar byproducts including Ph3PO. 

This oxidation, which was developed with ascorbic acid,13 produces D-erythronolactone (4) 14 Hydrogen peroxide is first reduced to water and a hydroxy radical, leading to the formation from 3 of the isoascorbic acid radical 12 The hydroxy radical oxidizes 12 to dehydroisoascorbic acid (13), which in a subsequent step adds hydrogen peroxide. Adduct 14 is than cleaved with base via anion 15 to compound 16. Alkaline hydrolysis of the ester leads to hydroxy acid 17 and the byproduct oxalic acid Subsequent lactonization produces D-erythronolactone (4). 

M. Csiba, J. Cleophax, S. Petit, and S. D. Gero, Expedient and practical three-step synthesis of vitamin C from a byproduct of the sugar industry the L-galactono-1,4-lactone pathway, J. Org. Chem., 58 (1993) 7281-7282. 

An efficient modification of the manganese(III) mediated malonate radical addition to styrene has been examined. Use of cerium(IV) nitrate in methanol at room temperature results in the direct formation of the butyrolactone 17 in low yield along with other byproducts [95JCS(P1)1881]. Other intermolecular single electron processes for the formation of lactones have been reported [95JOC458] [95BCSF843],... 

Note that the polymerizations of lactones and lactams give polyesters and polyamides, respectively, polymers that can also be synthesized by conventional step-growth polymerization from noncyclic monomers. Although the polymer prepared from cyclic monomers looks like a condensation polymery in strict terms it is not, because no small-molecule byproduct was pro-... 

Lactonization is not obligatory, as the byproduct formed in the reaction of 2-acetamido-2-deoxy-D-glucose with methoxycarbonyl-methylenetriphenylphosphorane was proved67 to have structure 134. This compound rapidly consumes one mole of periodate per mole, and shows signals at r 7.95 p.p.m. (doublet) and r 6.15 p.p.m. in its n.m.r. spectrum, corresponding to the a-methylenic and the ester group, respectively. Use of 2-acetamido-4,6-0-benzylidene-2-deoxy-D-arabino-hexose instead of the unprotected sugar does not prevent... 

With some hydroxycarboxylic acids lactone formation is observed in the reaction with carbodiimides.Sometimes N-acylureas are formed as byproducts. For example, in the reaction of -hydroxycarboxylic acids 468 with DCC, y-butyrolactones 469 are produced." ... 

Acyl halides and alkynes also give lactones upon reaction with Ni(CO)4 in an aqueous acetone medium. The result in this system is typically a 3,y-unsaturated lactone, formed together with some product derived from condensation with molecules of solvent (equation 18). Lactones are also formed in low yield as byproducts from the reactions of acylnickel carbonyl anions (derived from addition of RLi to Ni(CO)4) with terminal alkynes at -30 A single example of y-aminolactone formation is reported from 2-butyne, CO and diethylamine, catalyzed by (Et2NH)2NiBr2. ... 

Monomer 33 was made to undergo transesterification polymerization using Ti(OC4H9)4, while monomer 34 was appropriate for a Knoevenagel polycondensation. The transesterification polymerization resulted in the formation of an intractable material of unknown structure. Homopolymerization of 34 by the Knoevenagel technique afforded polymer 35 with a low molecular weight (M 6800). A major byproduct in this polymerization was a macrocyclic lactone, formed via an intramolecular Knoevenagel condensation (Scheme 10-14). 

This lactonic diol, byproduct of sugar beet, can be converted to acetals with crystal-liquid properties when treated with long-chain halides. 

Also the influence of the catalyst concentration at the constant phos-phorus/palladiutn ratio of 3 1 was investigated. Figure 23 shows the results which were obtained when 250 tranol of butadiene per experiment were reacted with CO2. The yield of the 6-lactone passes a maximum at about 0.16 mmol of catalyst and decreases very fast at lower catalyst concentrations. Also the selectivity reaches at 0.16 mmol the favourable value of about 90 % and only few byproducts such as esters or oligomers of butadiene are formed. 

Catalysis works best when some amount of phosphine particularly 1,2-bis(diphenylphosphino)ethane (DPPE) is used as additive along with [Co2(CO)gj. Yield of the thio lactone is susceptible to the amoxmt of solvent used. Reaction goes very well in higher dilution. Yields of double CO inserted products vary with type of thiols and acetylenes used. Reaction works best with ethanethiol (70% yields). Aromatic thiols were less effective and monocarbonylation product forms in major byproduct [43]. 

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