AbstractWhereas the usefulness of the tetrahydro‐pyranyl residue for the activation of esters is rather limited, it is of definite value for the temporary etherification of the hydroxyl groups of tyrosine and serine derivatives. The stability of tetrahydro‐pyranyl ethers towards alkali and the rapid hydrolysis by acids permit a great variety of transformations of these amino acid derivatives. The only disadvantage adherent to the use of the tetrahydro‐pyranyl group is the introduction of a new asymmetric c