Lactonization synthesis oxidations

Starting from 5-O-acetyl-1,2-0-isopropylidene-a-D-glucofuran-urono-6,3-lactone, Kinoshita and coworkers178 achieved the synthesis of 3-amino-3-deoxy-l,2-0-isopropylidene-a-D-allofuranuronic acid by the following sequence of reactions methanolysis of the lactone ring, oxidation at C-3 to form methyl 5-0-acetyl-l,2-0-isopropyli-dene-a-D-riho-3-hexulofuranuronate, followed by stereospecific reduction of the oxime of the latter. 

A diol was converted to a lactone by oxidation with stoich. RuOyCCl as part of the total synthesis of the quassinoid ( )-amaroMe [355] stoich. (PPh )[Ru(0)2Cl3]/... 

One of the earliest examples of the synthetic promise of radical reactions for preparing polycyclic products was provided by Corey s y-lactone synthesis. This approach was actually based on a well-known reaction of a-carbonyl radicals, generated by manganese(iii) oxidation of carboxylic acids, with unsaturated substrates. The mechanism of the basic steps shown for the preparation of lactone 418 (Scheme 2.140) involves initial addition of the a-carbonyl radical 419 to the double bond of styrene, followed by oxidation of the radical intermediate 419a to carbocation 419b, and subsequent intramolecular reaction with the carboxyl nucleophile to yield the lactone product. 

Scheme 9. Lactone synthesis by <5-carbonylation of alcohols under oxidative conditions...

Palladium(Il) chloride-copperfll) chloride-oxygen. 18,283 19,261-262 20,294 Oxidation. As an extension of the lactone synthesis from 1-trimethylsilyl-... 

Epoxidation. With Mn-salen as a catalyst, enol derivatives give 2-hydroxy acetals. Unsaturated acids form lactones during oxidation in the presence of an iron porphyrin. Glycosylation. The action of a PhlO-MejSiOTf combination on thioglycosides consists of oxidation and Lewis acid catalysis, thus allowing the synthesis of disaccharides. 

Synthesis of aldonohydroximino lactones via oxidations of sugar oximes has been reported The oxidations were effected by... 

The synthesis of 7-lactones by oxidative addition of acetic acid to alkenes in the presence of Mn(0Ac)2 has been documented for some... 

Kocovsky et al. later demonstrated that C Hg bonds can be used for stereospedfic lactone synthesis. Both cis- and f ra s-fused hicycUc lactones can be prepared by ringopening reactions of cydopropanes followed by cydocarbonylation of the organo-mercurial intermediate (Scheme 2.11). p-Benzoquinone was found to be superior to Cu(II) as a stoichiometric oxidant [23]. 

Surprisingly, methyl esters are also suitable substrates whereby intramolecular cyclization occurs with concomitant loss of methyl iodide. Larock used internal alkynes as coupling partners for lactone synthesis (Scheme 2.33) [74]. The proposed mechanism involves oxidative addition of Pd(0) to the aryl iodide, followed by addition across the alkyne and cyclization of the carbonyl O of the ester to form an oxonium ion. Reductive elimination followed by loss of the methyl group then yields the product [74]. Shen and coworkers also reported a variant utilizing o-2,2-dibromovinylbenzoates (Scheme 2.34) [79]. 

Oxycarboxylation of alkenes, unlike carbocarboxylation, yields two new C—O bonds in a single step. The Dong group also reported the first example of alkene dioxygenation as a route to lactone synthesis via Pd catalysis (Scheme 2.37). The proposed mechanism for this transformation involves a novel Pd(II)/Pd(IV) pathway made possible by the hypervalent iodine-mediated oxidation that occurs... 

Scheme 2.48 Lactone synthesis by oxidative lactonization of diols.

A novel Y-lactone synthesis (Figure 9) uses the high Sjj1 reactivity of p-methoxybenzyl chloride to give 1 1 addition products with a variety of alkenes. The oxidative degradation of the aromatic ring and lactoni-sation are achieved in a one pot reaction, and preliminary experiments indicate that a-substituted Y-lactones are also accessible by this method. ... 

The Baeyer-Wliger oxidation of cyclic ketones provides general access to six- and seven-membered lactones. However, due to relatively less availability of cyclobutanones, y-lactone synthesis through the Baeyer-Villiger oxidation is not so common process. Recent achievements in this oxidation are reviewed in a paper by Ishihara and Uyanik [17]. 

In y-lactone synthesis through enantioselective Baeyer-Villiger oxidation, notable result was demonstrated by Mura-hashi et al. in 2002 (Scheme 8) [18]. They successfully found that planar-chiral bisflavin tethered by frans-cyclohexane-l,2diamine backbone works as an effective catalyst for enantioselective Baeyer-Villiger oxidation of cyclobutanone 19a with H2O2. Ding et al. recently reported chiral phosphoric acid 22a-catalyzed reaction with up to 88% ee of (R)-20a [19]. 

Ishii et al. also found that phthalimide N-oxyl 94 generated by cocatalyzed oxidation of N-hydroxyphthalimide under O2 atmosphere abstracts a hydrogen atom of C-H moiety in secondary alcohol. They also expanded Ms reaction to y-lactone synthesis through this radical generation from cyclopentanol 92 followed by radical addition to acrylates (Scheme 42) [65]. 

M.C. Bagley, Z. lin, D.J. Philips, A.E. Craham, Barium manganate in microwave-assisted oxidation reactions synthesis of lactones by oxidative cyctization of diols. Tetrahedron Lett. 50 (2009) 6823-6825. 

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