[reaction: see text] Highly efficient C2 selective substitution reactions of 2,3-epoxy alcohols with nucleophiles were developed by using NaN(3)-(CH(3)O)(3)B, NaSPh-(CH(3)O)(3)B, or NaCN-(C(2)H(5)O)(3)B system. The reaction proceeds through novel endo-mode epoxide opening of an intramolecular boron chelate, which was suggested from both experimental and quantum mechanic studies.