Stereoisomeric flavour compounds LXVII. 2‐, 3‐, and 4‐Alkyl‐branched acids, part 1: General approach to the synthesis of the enantiopure acids

A general approach to the synthesis of 2‐, 3‐, and 4‐alkyl‐branched acids of high enantiomeric purity is described. The enantiopure 2‐alkyl‐branched acids are prepared via liquid chromatographic resolution of diastereomeric phenylglycinol amides and their absolute configuration is deduced from the 1H‐NMR data of the separated diastereomers. Chain elongation methods, by Arndt–Eistert synthesis, via 2‐alkylated alkyl carbonitrile or by malonic ester synthesis, are used to prepare 3‐ and 4‐alkyl‐branched acids of high configurational purity and known absolute configuration starting from the enantiomeric 2‐alkyl‐branched acids.