Darstellung geeigneter Vorstufen zur Synthese von 16,16,16,17,17,17‐Hexafluorretinalen

Preparation of Suitable Precursors for the Synthesis of 16,16,16,17,17,17‐Hexafluororetinals Cycloaddition reactions of (CF3)2C = CHCHO with butadiene or 1,3‐pentadiene provide the corresponding cyclohexane derivatives 2, 3 and 4. Condensation of 3 with (C2H5O)2P‐(O)CH2C(O)CH3 or of 2 with acetone in the presence of bases yields 5 and 7. While 5 reacts with CH2 = CHMgBr to give 6, treatment of 7 with diluted HCI provides 8. Compounds 7 and 8 proved to be not suitable as starting materials for the preparation of 16,16,16,17,17,17‐hexafluororetinals. A better synthon is the diene 11. This is obtained in a threestep reaction starting from hexafluoroacetone and (C6H5)3PCHC(O)CH3 to give 9 which on treatment with CH3MgI provides 10. Dehydration of 10 with 50% H2SO4 forms 11. In this reaction sequence byproduct 12 is formed presumably by addition of CF3C(O)CF3 to 9. At elevated temperatures under pressure 11 adds ethylene to form 13. Functionalization of 13 in 2‐position is achieved by hydroboration/oxidation yielding 14 which is oxidized with pyridinium dichromate to 15. Oxidation and bromination reaction of 13 are described. Abele, H., Haas*, A., Lieb, M., Zwingenberger, J. Darstellung geeigneter Vorstufen zur Synthese von 16,16,16,17,17,17‐Hexafluorretinalen Preparation of Suitable Precursors for the Synthesis of 16,16,16,17,17,17‐Hexafluororetinals