Vitamin E with a 13C-labeled isoprenoid side chain, [6''-13C]all-rac-.alpha.-tocopherol (1), was synthesized using 6-methoxymethoxy-2,5,7,8-tetramethyl-2-[(E)-4-methyl-5-(thiazolin-2-yl)thio-3-penten-1-yl]chroman (6) as a key intermediate and ethyl [1-13C]bromoacetate as a 13C source. The overall yield of 1 based on ethyl [1-13C]bromoacetate was 19.2%.