Synthesis of Naturally Occurring Unsaturated Fatty Acids by Sterically Controlled Carbonyl Olefination

It is shown that carbonyl olefination, i.e. the reaction of carbonyl compounds with alkylidene phosphoranes, can be sterically controlled. In some cases cis‐olefins can be obtained by proper choice of the reaction conditions; trans‐olefins are formed only in the presence of suitable structural factors. These cis‐and trans‐olefination reactions have opened new, stereo‐specific routes to unsaturated and polyunsaturated fatty acids with differing positions and sequences of cis‐ and trans‐double bonds and to ω‐hydroxy and branched chain fatty acids.