Medium- and large-ring lactones

Both alcohols and phenols add to ketenes to give carboxylic esters (R2C=C= O+ROH —> R2CHC02R). This has been done intramolecularly (with the ketene end of the molecule generated and used in situ) to form medium- and large-ring lactones. In the presence of a strong acid, ketene reacts with aldehydes or ketones (in their enol forms) to give enol acetates. 

The procedure described is a simple, rapid, and convenient method for conversion of n-sized cycloalkenones into n+4 alkenolides. Significant but limited progress has been reported in the recent literature toward the preparation of medium and large ring lactones via ring-expansion reactions. One of the most notable and useful developments in this area involves conversion of a cycloalkanone into a bicyclic vinylic ether which is oxidatively cleaved to form a ring-enlarged keto lactone.3... 

Tabuchi, T., Kawamura, K., Inanaga, J., Yamaguchi, M. Preparation of medium- and large-ring lactones. Sml2-lnduced cyclization of w-(a-bromoacyloxy) aldehydes. Tetrahedron Lett. 1986, 27, 3889-3890. 

In 1982 Funk et al. reported the Ireland-Claisen rearrangement of medium and large ring lactones bearing endocyclic aUyhc alkenes to afford carbocycles (Scheme 4.94) [87]. The rearrangements resulted in a net 4-atom ring contraction... 

The Upase-catalyzed ROP of small-, medium- and large-ring lactones has often been reported. By definition. Upases hydrolyze triglycerides in an aqueous medium at one or more of the three ester bonds, and have been characterized by their drastically increased activity at the Hpid-water interface of a micellar or emulsified substrate. In a nonpolar medium, these enzymes are capable of initiating the ROP of cychc lactones, and this properly has been exploited for the synthesis of polyesters, especially from macrolides. 

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