Synthesis of fluorinated retinal: A C6-C7 s-trans fixed retinal containing a trifluoromethyl group at the terminal position of the conjugated system.

Abstract

For the study of retinal-binding proteins by using fluorine-modified retinals, the all-trans bicyclic trifluororetinal (1), whose C6-C7 bond is fixed in the s-trans form by an ethano bridge, was synthesized. Introduction of a trifluoromethyl group was carried out in 70% yield by photochemical trifluoromethylation of the dienol ether compound (2) with trifluoromethyl iodide. From a comparison of the absorption maximum of 1 with that of the bicyclic retinal (12), it is clear that the electron-withdrawing trifluoromethyl group induces a notable hypsochromic shift (18 nm) of 1.