Catalysis lactone reactions

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... 

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... 

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. 

Phase-transfer catalysis can be used to mimic high dilution reaction conditions and has been utilized to good effect in the synthesis of large ring lactones [67J. Macrocyclic nitrolactones have also been obtained by rearrangement of 2-(3-hydroxy-propyI)-2-nitrocycloalkanones using a stoichiometric amount of tetra-n-butyl-ammonium fluoride [68]. 

In Sect. 7.6, we examined the hydrolysis of lactones. Emphasis was placed on the reversibility of the reaction and the possibility of both chemical and enzymatic catalysis. Some enzymes active in lactone hydrolysis and the hydrolytic inactivation of a number of pharmacologically active lactones were discussed. 

The lactonization-elimination step was investigated independently with a broad array of A,A-disubstituted 2-(hydroxymethyl)benzamides. The rate of this reaction was highly sensitive to the nature of the /V-subslilucnls and to pH (minimum at pH 5 - 6). Above pH 6, general base catalysis occurred. 

It is not surprising that in attempted AICI3 catalysis of the reaction between thiophenol and various lactones, considerable amounts of thianthrene were obtained from a side reaction (81JOC5163). A low yield of thianthrene itself was obtained by converting o-bromobenzene thiol into its copper derivative (66JOC4071), but a good yield of thianthrene-2,3,7,8-tetracarboxylic acid 83 was observed from a hot reaction between 84 with cuprous oxide in DMF (82MI5). The saturated o-chlorobenzene thiols, 85... 

Pahnans et al. prepared 5 by the reaction of [RuCl2(p-cymene)]2 and 2-phenyl-2-aminopropionamide in the presence of potassium carbonate. They used 5 in an iterative tandem catalysis for the synthesis of chiral oligoesters. The enzymatic ring opening of 6-methyl-e-caprolactone was combined with ruthenium-catalyzed alcohol racemization to produce optically active oligomers of 6-methyl-e-capro-lactone [23] (Scheme 1.17). 

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