IODOMETHYLENE LACTONE FORMATION - AN IMPROVED SYNTHESIS

Detailed examination of the free radical induced cyclisation of the propiolate ester of trans-2-iodocyclopentanol has revealed a rather inefficient radical chain. The optimum conditions found used dibenzoyl peroxide as initiator and benzene as the reaction solvent High concentrations of initiator were required and significant quantities of iodobenzene were formed Portionwise addition of initiator was found to be beneficial, but use of inert atmospheres gave no advantage. Although the reaction was quite highly selective to give predominantly the (E)-iodomethylene lactone, trace quantities of the Z-isomer were isolated. Other minor by-products could be attributed to trapping of the intermediate vinyl radical by the solvent. An alternative, improved route to iodomethylene lactones via fluoride ion desilylation of the trimethylsilyl substituted derivatives has been developed.