The Wittig reaction of the pyrano-type reducing sugars undergoes an unexpected formation of dienes through the elimination of a benzyloxy group in the presence of t-BuOK. LiHMDS is used rather than t-BuOK to prevent alcohol elimination in the same sugar derivatives. Collectively, t-BuOK has unusual functions in the Wittig reaction that correspond with other bases such as LiHMDS, NaH, and n-BuLi. This unusual function of t-BuOK showed that a unique 4-deoxy-5-hydroxyl analogue 2 of α-galactosyl ceramide was formed exclusively.