Ethyl Bromide → alpha-Tocopherol

Participants

Reaction Steps

3.13 g (10 millimoles) of (2RS)-2,5,7,8-tetramethyl-6-hydroxy-2-(2-bromoethyl)-chroman were dissolved in 10 ml of absolute THF. A solution of ethyl-magnesium bromide which had been prepared by reacting 0.25 g (10.3 millimoles) of magnesium in 3 ml of THF with a solution of 1.1 g (10.0 millimoles) of bromoethane in 5 ml of THF and stirring for 1 hour at +40° C. was added dropwise to the above solution at -20° C. The resulting reaction mixture was stirred for 1 hour at -20° C. and then there were added to it the (2RS,6RS)-2,6,10-trimethyl-1-undecyl-magnesium chloride solution prepared in Example 2a, followed by 0.7 ml of an 0.5-molar solution of di-lithium tetrachlorocuprate in absolute THF. The batch was then stirred for 3 hours at -20° C. and 16 hours at room temperature. The reaction mixture was worked up as described in Example 1c and 3.7 g of α-tocopherol were isolated by bulb tube distillation at 220° C./0.2 mbar. This corresponds to a yield of 86% of theory.

Provenance & Evidence