Xanthate Transfer Cyclization of Glycolic Acid-Derived Radicals. Synthesis of Five- to Eight-Membered Ring Ethers

Article abstract of DOI:10.1021/jo00101a027

A novel method for the preparation of functionalized five- to eight-membered ring ethers is described.This method involves the xanthate transfer radical cyclization of 2-(alken-1-oxy)-2-<(ethoxythiocarbonyl)sulfanyl>acetic acid methyl esters 6 to give good yields of xanthate-substituted five- to eight-membered ethers 7 and/or 8, depending on the length of the carbon chain.These cyclic ethers are usually obtained as mixtures of diastereomers.The cyclizations are performed at 150-160 deg C in tert-butylbenzene with di-tert-butyl peroxide as the initiator.This group-transfer radical cyclization was successfully applied in a total synthesis of lauthisan (44).The use of benzoyl xanthate (56) as a catalyst allows a visible light-induced xanthate transfer cyclization to a tetrahydrofuran in high yield.