Overall 5-endo-trig iodocyclizations of homoallylic alcohols, with a range
of substitution patterns, leading to beta-iodotetrahydrofurans are usually
highly efficient and stereoselective when carried out in anhydrous acetonit
rile in the presence of sodium hydrogen carbonate. Such cyclizations, which
are not exceptions to Baldwin's rules as they are electrophile-driven, app
ear to proceed via a well-ordered chair-like transition state. The iodine c
an be replaced by hydroxy, acetoxy and azide groups.