Photoisomerisation of (E)-Iodoalkylidene Lactones. A Route to (Z)-Iodoalkylidene Lactones

Article abstract of DOI:10.1016/S0040-4020(01)85076-6

Photochemically induced free-radical cyclisation of iodo acetylenic esters provides low yields of mixtures from which both (E)- and (Z)-iodoalkylidene lactones may be isolated.However, photoisomerisation of (E)-iodoalkylidene lactones, which have previously been obtained in good yields by dibenzoyl peroxide induced cyclisation of iodo acetylenic esters, provides (E)/(Z)-mixtures from which the previously inaccessible (Z)-isomers may be isolated by chromatography.Also reported is a collection of IR, UV and NMR spectral data, all of which provide useful information relating to the stereochemistry of the iodoalkylidene lactones.A comparison of the cryctal structures of the (E)- and (Z)-isomers of a trimehylsilyl iodomethylene lactone is also included.