Lactones medium-sized ring

The chemical properties of cycHc ketones also vary with ring size. Lower members (addition reactions, than corresponding acycHc ketones. The Cg—C 2 ketones are unreactive, reflecting the strain and high enol content of medium-sized ring systems. Lactones are prepared from cycHc ketones by the Bayer-ViUiger oxidation reaction with peracids. S-Caprolactone is manufactured from cyclohexane by this process ... 

A highly efficient method for the synthesis of medium-sized rings (examples of 17-, 15-, 10- and 5-membered carbocycles, lactones and lactams) without high-dilu-tion conditions was developed by Trost et al. for example, precursor 204 with a palladium catalyst led to an E-Z mixture of 205 in 86% yield, and subsequent hydrogenation then provided the 10-membered lactam ring 206 in 85% yield (Scheme 15.66) [132],... 

Macrolides. Steliou, Hanessian, and co-workers- have prepared lactones and lactams in moderate to excellent yield by treatment of ro-hydroxy or ru-amino carboxylic acids with catalytic amounts of di-r -butyltin oxide in refluxing mesitylcne or xylene in a Dean-Stark apparatus for 12 24 hours. The method has the advantage of high dilution, since the tin reagent is regenerated continuously. As expected, yields arc low for medium-sized rings. 

The formation of the twelve-membered lactone, IX/52, from the eight-mem-bered ketone, IX/51, prepared by alkylation of the aldehyde, IX/50, can be explained as an enlargement of a medium-sized ring. The driving force is probably the resonance stabilisation of the secondary nitro group in base (nitro-nate), compared to the tertiary nitro group in the starting material (Scheme IX/9) [29],... 

Syntheses of heterocycles with ring sizes from seven to thirteen have been reported. Medium-sized ring compounds such as lactones 2 are preferentially synthesized exploiting Yamaguchi conditions. In dilute toluene the activated hydroxy acid 1 cydizes in the presence of 4-(dimcthylamino)pyridine, ... 

A medium-sized ring possessing neighboring hydroxymethyl or carboxyl functional groups give bicyclic ethers or lactones. Studies have been carried out on the... 

Mesocyclic lactones. Cyclization of w-hydroxycarboxylic acids via the 0,0 -disilyl intermediates is applicable to medium-sized rings (7-membered, 35% 8- to 13-membered, 79-88%). An initial silyl carboxylate formation step is catalyzed by (Ph3P)3RhCl at room temperature which is followed by an intramolecular 0-silylation at 80°. Elimination of l,l,3,3-tetramethylbenzo-2,l,3-oxadisilazole occurs when the cyclic silylether/esters are exposed to MejSiiOTf). ... 

If the choice is between a seven- and an eight-membered lactone, the seven-membered ring 151 is preferred to the medium sized ring as in a recent series of experiments24 using the collidine-Br+ reagent 150. 

Intermolecular ketyl alkene coupling reactions have been incorporated into a cascade that ultimately affords medium sized rings [58]. Specifically, chloroalkyl ketones react with acrylates, whereupon chloroalkyl lactones are formed in situ. Photolysis of these intermediates in the presence of excess Sml2 initiates an intramolecular nucleophilic acyl substitution reaction between the halide and the lactone, creating the medium-sized ring (Eq. 50). 

Fragmentation of Lactols to Unsaturated Medium-ring Lactones. Ring cleavage to form a medium-sized ring lactone with a transannular double bond has been observed (eq 21). ... 

Krafft and co-workers used olefin metathesis to prepare several inside-outside medium-size rings as scaffolds for natural products synthesis. Reaction of bicyclic lactone 267 with 10 mol % of 4 in refluxing dicholormethane gave the corresponding tricyclic lactone 269 in 88% yield after only two hours. 

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