Ring-expanded lactone product

The Baeyer-Villiger transformation of several protected derivatives having a free ketone group has been effected by m-chloroperoxybenzoic acid. Thus, 1,6-anhydro-3,4-0-isopropylidene-/f-D-/yxn-hexopyranos-2-ulose (28) was converted into the cyclic, orthoacid anhydride 29.67 As an additional example, the Baeyer-Villiger oxidation of Ferrier carbocyclization products derived from D-glucose afforded 5-deoxyhexofuranosiduronic acids, via the ring-expanded lactonic intermediates68 (Scheme 12). 

Reactions of carbocyclic P-keto esters, sulfonium ylides and enamines with activated alkynes such as DMAD are known to result in formation of (n + 2) ring expanded products. In a study of the analogous reactions of carbocyclic p-keto phosphonates, it was found that in the cases of the simple cyclic P-keto phosphonates 1, ring expansion occurred to give 2 in reasonable yield. Extension of the method to the tetralone 3, however, led to formation of two products, the "expected" (n + 2) ring expansion product analogous to 2 (37%), and the lactone 4 (29%). 

Baeyer-Villiger oxidation of a cyclic ketone normally gives a ring-expanded lactone22 so lactone 11 is the expected Baeyer-Villiger product of 7, not formates 8 and 9. This unexpected observation may be due to the fact that 7... 

After conjugate addition of the hydroperoxide anion to the chelated a,p-unsaturated lactone, the resulting enolate counterattacks the proximal [3-hydroperoxide group to form an epoxide. The latter then ring-expands to create another enolate, which captures a proton from water. The product hemiacetal finally undergoes ring-opening and saponification to produce 9 (Scheme 6.5). 

Ninhydrin (858) reacts with p-cresol in the presence of zinc chloride to yield the eight-membered lactone (859). Generation of the carbene (860) from the corresponding diazopyrazole in the presence of benzene derivatives PhR (R = MeO, Me, Cl, CN, or NO2) results in mixtures of isomeric substitution products (861) and ring-expanded pyrazolo-azocines (862) electron-withdrawing substituents enhance the formation of the latter cf. p. 158). The oxadiazoloben-zodiazocinone (864) is formed by the action of phosgene on the iV-oxide (863). ... 

More highly substituted aromatics have also been studied in the course of natural product synthesis. For example, rhodium(II) mandelate-catalyzed cyclization of diazoketone 41 produces the ring expanded product 42, which on hydrogenations furnishes the tricyclic lactone 43. ... 

Silver-ion assisted hydrolysis of the 4-homoadamantane-dichlorocarbene adduct 112) affords 4-homoadamantyl carboxylic acid, the ring-expanded product (773) and the unusual lactone (774), the product yields and individual ratios being rather dependent on the reaction conditions. The lactone (774) is probably a product of rearrangement of a homoadamantyl cation produced by protonation of an acid or aldehyde of structure (775 R = CHO or COjH). 

A new concept in the ring expansion of cyclic lactones has been developed by Corey et al. involving internal translactonization. In the most spectacular example, treatment of the nine-membered lactone (115 x = 6, y = 3) with a trace of acid at ambient temperature for two hours gives the 12-membered lactone (116 jc =6, y = 3) in 97% yield. This instability of a nine-membered ring is further exemplified by a six-carbon expansion of (115 x = 6, y = 6) to the 15-membered macrolide (116 JC = 6, y = 6) in 90% yield. By contrast, eight-membered lactones (e.g. 115 JC = 5, y = 3) are converted more slowly and less cleanly into the expanded products (e.g. 116 jc = 5, y = 3) while seven-membered lactones (115 jc=4) failed to translactonize altogether. 

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