Preparation of oxetanes by silicon-directed 4-exo trig electrophilic cyclisations of homoallylic alcohols

The reaction of homoallylic alcohols with bis(sym-collidine)bromine(I) hexafluoroantimonate led in good yields to the formation of oxetanes if a silyl group was fixed on the carboncarbon double bond in terminal position. This reaction was stereospecific when no supplementary substituent was present on the double bond.