Fluorinated polyenes, preparation

This methodology has been adapted to the preparation of fluorinated polyenes, as... 

Similar coupling occurs with both fluorovinyl7,8 and non-fluorovinyl3,9 iodides, and is particularly useful for the preparation of fluorinated polyenes (Equations 4.4 and 4.5). 

Another general method for the preparation of 19,19,19- and 20,20,20-trifluor-oretinals involves the aldol condensation of trifluoroacetone with an ethylenic aldehyde. When performed in the presence of acetic acid and piperidine, it affords an a, S-unsaturated ketone. Applied to cyclocitral and its homologues, the method leads to polyenic trifluoromethyl ketones. From these ketones, the various tri-fluorinated retinoids are prepared by known methods (Figure 4.24). ... 

For reasons of symmetry the resulting acids are identical when a symmetrically substituted alkcne is oxidized. For the preparation of short-chain fluorinated acids, such as trifluoroacetic acid. this method is more economical than the oxidation of an alkene with a terminal C = C bond (see Table 1). Oxidation of polyfluorinated dienes and polyenes gives fluorinated dicar-boxylic acids. 

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