Y-lactone synthesis

Andreana et al. [25] have recently invoked RCM to prepare /J,y-unsaturated <5-lactones (Scheme 3). Exposure of dienes of general type 13 to either 2 or 4 (which could be used at lower loadings) readily furnished lactones 14. For other examples of a,/ -unsaturated <5- and y-lactone synthesis by RCM see Ref. [26]. Variation of the configuration at the chiral carbons and the ligand for the asymmetric dihydroxylation reaction allows access to an array of biologically important dideoxy-sugar derivatives. 

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. 

Lactones are among the most abundant substructures in natural products." This fact had kindled enormous activity in the field of y-lactone synthesis." 7-Lactones have been prepared by direct cycloacylation of 7-hydroxy acids, eiAer as such or generated as transient intermediates, and by cycloalkyl ation, either of 7-halocarboxylates or of 3,7- or 7,S-unsaturated acids by additions to the double bond. 

Acetylallene Is a valuable starting material in a,p-unsaturated y-lactones synthesis the tandem nucleophilic addition-aldol reaction of 1, iodide ion and aldehydes gives 3-iodohomoallylic alcohols in good yields, which can be further... 

Phthalones and their structure analogues 75KGS435. a,j9-Unsaturated y-lactones, synthesis using Diels-Alder reaction ... 

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. ... 

---