Processes for the preparation of 3-aminocarboxylic acids and their esters

A process for the preparation of optically active compounds of the formula IA or IB

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• as free bases or as acid addition salts thereof, in which
• R2 is hydrogen, unsubstituted or substituted alkyl, or unsubstituted or substituted aryl,
• R3 is—in each case unsubstituted or substituted—alkyl, aryl or heterocyclyl, or is esterified carboxyl or carboxyl,
• R4 is hydrogen, unsubstituted or substituted alkyl, mono- or disubstituted amino, hydroxyl, unsubstituted or substituted alkoxy or unsubstituted or substituted aryloxy,
• or R3 and R4, together with the carbon atoms connecting them, form a 5- or 6-membered ring, and
• R5 is hydrogen, unsubstituted or substituted alkyl, unsubstituted or substituted aryl or organic silyl, wherein an acid addition salt of the formula(e) IIIA and/or IIIB,
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• in which n is an integer greater than or equal to 1, in particular 1 to 3, Xn−is an acid anion, R1 and R6 are—in each case unsubstituted or substituted—alkyl, aryl or heterocyclyl, with the proviso that R1 is a radical other than R6 and that at least one of the two radicals is unsubstituted or substituted aryl or unsubstituted or substituted heterocyclyl, in particular aryl, and R2, R3, R4 and R5 are as defined for compounds of the formulae IA and IB;
• R1 and R6 are as defined for compounds of the formula II and Xn−is an acid anion, is converted by removal of the chiral auxiliary group R1R6CH— into a corresponding salt of the formula(e) IVA and/or (preferably or) IVB
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• in which n and the radicals R2 to R5 are as defined for compounds of the formula IA or IB and Xn− is an acid anion,
• and, if desired, an acid addition salt of the formula IVA or IVB obtained is converted in the presence of a base into the free compounds of the formula IA or IB;
• and/or, if desired, the group R5 is removed from an ester of the formula IVA or IVB, if it has another of the meanings mentioned apart from hydrogen.