Reaction of diethylaminosulfur trifluoride with diols

Diethylaminosulfur trifluoride (DAST) reacts with dialcohols to give difluorides, sulfite esters or cyclic ethers depending on the number of carbons separating the two alcohol groups. Vicinal and 1,3-diols give large amounts of sulfite ester products while butane-1,4-diol gives almost exclusively the cyclic ether tetrahydrofuran. Terminal dialcohols longer than four carbons give primarily difluoride products. Semiempirical calculations indicate a preference for cyclic intermediates when four or less carbons separate the two alcohol moieties. These cyclic intermediates lead directly to the cyclic ethers and sulfite ester products.