IODOMETHYLENE LACTONE FORMATION - AN IMPROVED SYNTHESIS

Detailed examination of the free radical induced cyclisation of the pr opiolate ester of trans-2-iodocyclopentanol has revealed a rather inef ficient radical chain. The optimum conditions found used dibenzoyl per oxide as initiator and benzene as the reaction solvent High concentrat ions of initiator were required and significant quantities of iodobenz ene were formed Portionwise addition of initiator was found to be bene ficial, but use of inert atmospheres gave no advantage. Although the r eaction was quite highly selective to give predominantly the (E)-iodom ethylene lactone, trace quantities of the Z-isomer were isolated. Othe r minor by-products could be attributed to trapping of the intermediat e vinyl radical by the solvent. An alternative, improved route to iodo methylene lactones via fluoride ion desilylation of the trimethylsilyl substituted derivatives has been developed.