text: Opening of terminal epoxides by adventitious hydroxide may occur under the conditions of rearrangement; if this is not desired, anhydrous solvents, reagents, and glassware must be used. Freshly prepared sodium methoxide in methanol is commonly used to effect rearrangement without opening. Nucleophilic opening can be accomplished through the use of sodium azide, excess hydroxide, or cuprate reagents in the presence of lithium chloride. Electrophilic trapping is carried out under standard conditions in the presence of an electrophile such as benzyl bromide. Silyl halides have also been used as electrophilic trapping agents.
  To prevent epoxide migration, weakly basic conditions may be employed. Neither aqueous potassium carbonate nor aqueous amine bases cause epoxide rearrangement. Low temperatures are also beneficial when epoxide migration is not desired.