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 (CF 3 ) 2 C = CHCHO with butadiene or 1,3‐pentadiene provide the corresponding cyclohexane derivatives 2, 3 and 4 . Condensation of 3 with (C 2 H 5 O) 2 P‐(O)CH 2 C(O)CH 3 or of 2 with acetone in the presence of bases yields 5 and 7 . While 5 reacts with CH 2 = 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 (C 6 H 5 ) 3 PCHC(O)CH 3 to give 9 which on treatment with CH 3 MgI provides 10 . Dehydration of 10 with 50% H 2 SO 4 forms 11 . In this reaction sequence byproduct 12 is formed presumably by addition of CF 3 C(O)CF 3 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.