Optically active .omega.-halo-2-amino-alkanecarboxylic acid derivatives, process for the preparation thereof and their use for the preparation of optically active phosphorus-containing .alpha.-amino acids

An optically active compound of the formula I, ##STR10## in which R.sub.1 is (C.sub.1 -C.sub.6)alkyl which is unsubstituted or is substituted by one or more radicals selected from the group consisting of hydroxyl, (C.sub.1 -C.sub.4)alkoxy, [(C.sub.1 -C.sub.4)alkyl]carbonyl and [(C.sub.1 -C.sub.4)alkoxy]carbonyl;

• or is (C.sub.2 -C.sub.6)alkenyl, (C.sub.2 -C.sub.4)alkynyl or a group of the formula R.sub.2 --CO-- or R.sub.3 --SO.sub.2 --,
• R.sub.2 is (C.sub.1 -C.sub.11)alkyl, (C.sub.6 -C.sub.13)aryl or substituted (C.sub.6 -C.sub.13)aryl, (C.sub.1 -C.sub.6)alkoxy, which is unsubstituted or substituted by one or more radicals, selected from the group consisting of (C.sub.6 -C.sub.13)aryl and substituted (C.sub.6 -C.sub.13)aryl,
• R.sub.3 is (C.sub.1 -C.sub.4)alkyl, phenyl or substituted phenyl,
• X is halogen, and
• n is zero or one, except for the compound of the formula I in which
• R.sub.1 =benzyloxycarbonyl, X=bromo or iodo and n=1.