Process for preparing octenoic acid derivatives

Compounds of the formula (IIa)

• in which
• R10 is in each case independently
• (a) a heterocarbon group which comprises at least one heteroatom selected from the group consisting of O and N with at least one carbon-heteroatom multiple bond at the C-1 position, said group being bonded via the C-1 atom and being selected from COOR6, in which R6 is hydrogen, alkyl, aryl, arylalkyl or trialkylsilyl, wherein the alkyl and the aryl may each be unsubstituted or substituted;
• (b) nitrile;
• (c) C(O)R7, wherein R7 is:
• (i) hydrogen, (ii) halogen, (iii) O−, (iv) OM, wherein M is an alkali metal or an equivalent of an alkaline earth metal,
• (v) OCOR12, wherein R12 is unsubstituted or substituted branched lower alkyl having from 1 to 5 carbon atoms or pivaloyl,
• (vi) OCOCF3,
• (vii) OSO2CH3, or
• (viii) OSO2CF3;
• (d) a protecting or activating group customary for carboxylic acids;
• or,
• (e) C(O)NR4R5, wherein R4 and R5 are independently hydrogen, alkyl, aryl, arylalkyl, or trialkylsilyl, wherein the alkyl and the aryl may each be unsubstituted or substituted, or R4 and R5 together with the nitrogen form a six-membered heterocyclic ring system which may optionally have from 1 to 3 additional heteroatoms;
• or salts thereof,
• wherein R4 and R5 together with the nitrogen cannot be a 4(S)-substituted oxazolidin-2-on-3-yl in each R10 when both radicals are C(O)NR4R5, wherein substituted means substituted by one or more of the following groups selected from halogen, hydroxyl, cyano, C1-C6-alkoxy, nitro, amino, C1-C6-alkylamino, di-C1-C6-alkylamino, carboxyl, C1-C6-alkoxycarbonyl, aminocarbonyl, halomethyl, dihalomethyl, trihalomethyl, haloethyl, dihaloethyl, trihaloethyl, tetrahaloethyl, and pentahaloethyl.