6-Phenoxymethyl-4-hydroxytetrahydropyran-2-ones and 6-thiophenoxymethyl-4-hydroxytetrahydropyran-2-ones and the corresponding dihydroxycarboxylic acid derivatives, salts and esters, processes for the preparation of these compounds, their use as pharmaceuticals, pharmaceutical preparations and novel phenols and thiophenols Compounds of the general formula I ##STR1## and the corresponding open-chain dihydroxycarboxylic acids of the formula II ##STR2## in which X, Y and Z have the meanings given, and pharmacologically tolerated salts thereof with bases and pharmacologically tolerated esters thereof, processes for the preparation of these compounds, their use as pharmaceuticals and pharmaceutical preparations are described. Novel phenols and thiophenols of the formula III ##STR3## in which X, Y and Z have the meanings given, are also described.