Lactones catalysis

The benzoic acid derivative 457 is formed by the carbonylation of iodoben-zene in aqueous DMF (1 1) without using a phosphine ligand at room temperature and 1 atm[311]. As optimum conditions for the technical synthesis of the anthranilic acid derivative 458, it has been found that A-acetyl protection, which has a chelating effect, is important[312]. Phase-transfer catalysis is combined with the Pd-catalyzed carbonylation of halides[3l3]. Carbonylation of 1,1-dibromoalkenes in the presence of a phase-transfer catalyst gives the gem-inal dicarboxylic acid 459. Use of a polar solvent is important[314]. Interestingly, addition of trimethylsilyl chloride (2 equiv.) increased yield of the lactone 460 remarkabiy[3l5]. Formate esters as a CO source and NaOR are used for the carbonylation of aryl iodides under a nitrogen atmosphere without using CO[316]. Chlorobenzene coordinated by Cr(CO)j is carbonylated with ethyl formate[3l7]. 

Aldoketenes also form piedorninantly the lactone dimers, although the ratio of isomers can be influenced by base catalysis. Ketoketenes dimerize symmetrically, and at a slower rate, to 1,3-cyclobutanediones, unless acidic or basic catalysts are present. 

The hydrolysis of the lactone A shows a signifieant catalysis by acetate ion in acetate buffer, with the rate expression being... 

Transition metal catalysis in Baeyer-Villiger oxidation of cyclic ketones with formation of lactones 98AG(E)1198. 

The ring opening reactions of unsaturated azlactones and other lactones - by methanol in the presence of diazomethane are analogous in principle. (The ring closure of pseudouric acid which occurs under the influence of diazomethane can also be understood as an example of base catalysis.)... 

In addition to its other properties, interest in the potential use of the vasodilative properties of prostaglandin El, alprostadil ( ), has led to several conceptually different syntheses.For this purpose, the classic Corey process has to be modified by reversing the order of addition of the side chains to allow for convenient removal of the unwanted double bond in the upper side chain. For example, Corey lactone is protected with dihydropyran (acid catalysis), reduced to the lactol with diisobutyaluminum hydride, and then subjected to the usual Wittig reaction to give intermediate This is... 

There is still a great deal of effort being made on the study of the mechanisms and catalysis of lactide, glycolide, and lactone polymerizations,367,379-383 and many reviews have been published on this topics.365,384 386 Since it is basically a chain-growth, rather titan a step-growth, process, it is beyond the scope of this book and will not be extensively discussed here. Nevertheless, it is worth mentioning that very close resemblances exist between the mechanisms... 

The two Diels-Alder adducts (48) and (49) fregio-selectivity is poor here in the absence of Lewis acid catalysis) give lactones (50) and (51). ... 

Lipase catalysis is often used for enantioselective production of chiral compounds. Lipase induced the enantioselective ring-opening polymerization of racemic lactones. In the lipase-catalyzed polymerization of racemic (3-BL, the enantioselec-tivity was low an enantioselective polymerization of (3-BL occurred by using thermophilic lipase to give (/ )-enriched PHB with 20-37% enantiomeric excess (ee). ... 

Reactive polyesters were enzymatically synthesized. Lipase catalysis chemoselecfively induced the ring-opening polymerization of a lactone having exo-methylene group to produce a polyester having the reactive exo-methylene group in the main chain (Scheme 16). This is in contrast to the anionic... 

Terminal-functionalized polymers such as macromonomers and telechelics are very important as prepolymer for construction of functional materials. Single-step functionalization of polymer terminal was achieved via lipase catalysis. Alcohols could initiate the ring-opening polymerizahon of lactones by lipase catalyst. The lipase CA-catalyzed polymerizahon of DDL in the presence of 2-hydroxyethyl methacrylate gave the methacryl-type polyester macromonomer, in which 2-hydroxyethyl methacrylate acted as initiator to introduce the methacryloyl group quanhtatively at the polymer terminal ( inihator method ).This methodology was expanded to the synthesis of oo-alkenyl- and alkynyl-type macromonomers by using 5-hexen-l-ol and 5-hexyn-l-ol as initiator, respechvely. 

The catalysis has made reactions of certain functionalized boronates possible. For example, a carbocupration and alkylation allowed the synthesis of boronate 5. Reaction with aldehydes gave a-methylene lactones with high stereoselectivity.53... 

The intermediate N-acylpyridinium salt is highly stabilized by the electron donating ability of the dimethylamino group. The increased stability of the N-acylpyridinium ion has been postulated to lead to increased separation of the ion pair resulting in an easier attack by the nucleophile with general base catalysis provided by the loosely bound carboxylate anion. Dialkylamino-pyridines have been shown to be excellent catalysts for acylation (of amines, alcohols, phenols, enolates), tritylation, silylation, lactonization, phosphonylation, and carbomylation and as transfer agents of cyano, arylsulfonyl, and arylsulfinyl groups (lj-3 ). 

Polyester syntheses have been achieved by enzymatic ring-opening polymerization of lactide and lactones with various ring-sizes. Here, we focus not only on these cyclic esters but also other cyclic monomers for lipase-catalyzed ringopening polymerizations. Figure 8 summarizes cyclic monomers for providing polyesters via lipase catalysis. 

Several small-size (four-membered) lactones have been reported to be polymerized through lipase catalysis. The polymerization of /Tpropiolactone (/ -PL) by Pseudomonas family lipases as catalyst in bulk produced a mixture of linear... 

Ring-opening polymerization of a-methyl-substituted medium-size lactones, a-methyl-y-valerolactone and a-methyl-c-caprolactone, proceeded by using lipase CA catalyst in bulk [82]. As to (R)- and (S)-3-methyl-4-oxa-6-hexa-nolides (MOHELs), lipase PC induced the polymerization of both isomers. The apparent initial rate of the S-isomer was seven times larger than that of the R-isomer, indicating that the enantioselective polymerization of MOHEL took place through lipase catalysis [83]. 

The copolymerization of lactones took place through enzyme catalysis [92]. The copolymerization of e-CL with d-VL catalyzed by lipase PF affords the corresponding copolymer having a molecular weight of several thousand. From 13C NMR analysis, the copolymer was found to be of random structure having both units, suggesting the frequent occurrence of transesterifications between the polyesters. In the copolymerization of 8-OL with e-CL or DDL, random copolyesters were also formed [84], whereas the copolymer from e-CL and PDL was not statistically random [88]. 

Living polymerization of lactones has been successfully performed by catalysis of rare earth metal complexes to obtain Mw/Mn of 1.07-1.08 [8]. The lowest polydispersity index attained so far with the AlEt3/H20 system is 1.13. 

Cycloaddition of the nitrone 161 to the lactone 160 in boiling benzene for 6 h gave a 53 37 10 mixture of the three optically active adducts 162-164 in 66% combined yield (Scheme 9.50). Formation of the diastereoisomers 162-164 can be rationalized in terms of a highly preferred anti approach of the nitrone to the hydroxymethyl group in the transition state. The isomer ratio in the adducts was found to be dependent upon the solvent used in the reaction. Optimization of the reaction or the dia-stereoselectivity by Lewis acid catalysis failed. However, attempts to accelerate the cycloadditions by microwave irradiation, using 1,4-dioxane as the solvent, were successful and the reaction time decreased from hours to less than 10 min with only a... 

With cobalt catalysts, hydroformylation of ethyl cinnamate gave 91% of the hydrogenation product ethyl hydrocinnamate (15) and only 8% of the expected lactone, 16 (72). However, rhodium catalysis was effective in directing the reaction in favor of hydroformylation (70). The comparative results obtained with cobalt and rhodium are outlined in Table XXV. 

On reaction with hydroxylamine in the presence of appropriate bases, such derivatives of D-glucofuranurono-6,3-lactones as 25, 26, and 33 form114 N-hydroxyamides. On the other hand, when treated with hydroxylamine without base catalysis, compound 4 yields115 aWeJjt/do-D-glucurono-6,3-lactone oxime. 

In equation 8.2-6a, the slope of -1 with respect to pH refers to specific hydrogen-ion catalysis (type B, below) and the slope of + 1 refers to specific hydroxyl-ion catalysis (Q if k0 predominates, the slope is 0 (A). Various possible cases are represented schematically in Figure 8.5 (after Wilkinson, 1980, p. 151). In case (a), all three types are evident B at low pH, A at intermediate pH, and C at high pH an example is the mutarotation of glucose. Cases (b), (c), and (d) have corresponding interpretations involving two types in each case examples are, respectively, the hydrolysis of ethyl orthoacetate, of P -lactones, and of y-lactones. Cases (e) and (f) involve only one type each examples are, respectively, the depolymerization of diacetone alcohol, and the inversion of various sugars. 

The a-arylation of carbonyl compounds (sometimes in enantioselective version) such as ketones,107-115 amides,114 115 lactones,116 azlactones,117 malonates,118 piperidinones,119,120 cyanoesters,121,122 nitriles,125,124 sul-fones, trimethylsilyl enolates, nitroalkanes, esters, amino acids, or acids has been reported using palladium catalysis. The asymmetric vinylation of ketone enolates has been developed with palladium complexes bearing electron-rich chiral monodentate ligands.155... 

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