Process for the preparation of phosphorus-containing L-amino acids, their derivatives and intermediates for this process

A process for the preparation of a compound of the formula I or salt thereof, ##STR16## in which R.sup.1 and R.sup.2 independently of each other are hydrogen, (C.sub.1 -C.sub.6)-alkyl, which is unsubstituted or is mono- of polysubstituted by halogen or aryl, or (C.sub.3 -C.sub.10)-cycloalkyl,

• R.sup.3 and R.sup.4 independently of each other are hydrogen, (C.sub.1 -C.sub.6)-alkyl, (C.sub.2 -C.sub.6)-alkenyl, (C.sub.2 -C.sub.6)-alkynyl, where the last three radicals mentioned can be straight-chain or branched and can have hetero atoms in the chain, (C.sub.1 -C.sub.6)-alkylcarbonyl, aryl-(C.sub.1 -C.sub.4)-alkylcarbonyl, (C.sub.1 -C.sub.6)-alkoxycarbonyl, (C.sub.1 -C.sub.6)-alkylsulfonyl, benzyl, benzyloxycarbonyl, aryloxycarbonyl or arylsulfonyl, where the last four radicals mentioned are unsubstituted or substituted in the aryl radical,
• R.sup.5 is hydrogen or (C.sub.1 -C.sub.4)-alkyl, which is straight-chain or branched and is unsubstituted or substituted by halogen, aryl or a heterocycle, or (C.sub.3 -C.sub.7)-cycloalkyl and
• n is the number 0 or 1,
• which comprises
• a) reacting an optically active S-homoserine lactone of the formula II, ##STR17## in which R.sup.3 and R.sup.4 are defined as in formula I, with hydrogen chloride in the presence of an alcohol of the formula R.sup.5 --OH to give a compound of the formula III ##STR18## in which R.sup.3, R.sup.4 and R.sup.5 are defined as in formula I, except that R.sup.5 =H, and
• b) reacting the resulting compound of formula III with a compound of formula IV,
• R.sup.1 (O).sub.n -P(OR.sup.2).sub.2 (IV)
• in which
• R.sup.1, R.sup.2 and n are defined as in formula I and, if desired, hydrolyzing the product to give the compound of formula I, in which R.sup.5 =H.