Preparation and Reactivity of Tris(trifluoromethylselanyl)carbenium [(CF 3 Se) 3 C + ] and Trifluoromethylsulfanylacetic Acid Derivatives [(CF 3 S) 3– n CX n (O)R]

Reaction pathways for the synthesis of the (CF 3 E) 3 C moieties (E = Se, S) are described. [(CF 3 Se) 3 C + ][AsF   6 ‐ ] was found to be a suitable synthon for the preparation of (CF 3 Se) 3 C derivatives. It can be prepared either from (CF 3 Se) 3 C derivatives. It can be prepared either from (CF 3 Se) 4 C or (CF 3 Se) 3 CF and AsF 5 in liquid SO 2 . Direct access to (CF 3 Se) 3 CF was realized by the reaction of FCBr 3 with Hg(SeCF 3 ) 2 . Treatment of [(CF 3 Se) 3 C + ][AsF 6 ‐ ] with potassium halides provided (CF 3 Se) 3 CX (X = F, Cl, Br). A different course took the reaction with KI, as CF 3 SeSeCF 3 and (CF 3 Se) 2 C=C(SeCF 3 ) 2 were formed as main products. Minor amounts of (CF 3 Se) 3 CC(SeCF 3 ) 3 were formed which could be isolated and unambiguously characterized. Only two routes led to a threefold CF 3 S‐substituted acetic acid ester (CF 3 S) 3 CC(O)OR [R = CH 3 , (CH 3 ) 3 C]: Metatheses between (CF 3 S) 2 CBrC(O)OCH 3 and Hg(SCF 3 ) 2 and metalation of (CF 3 S) 2 CHC(O)OR [R = CH 3 , (CH 3 ) 3 C] with NaH followed by reaction with CF 3 SCl. Other precursors such as (CF 3 S) 2 CXC(O)OR′ [X = H, Br; R′ = Me 3 Si, ( n ‐C 4 H 9 ) 3 Sn] and (CF 3 S) 2 CBrC(O) Y (Y = Cl, Br) were synthesized but could not be converted to the corresponding (CF 3 S) 3 C derivatives. Attempts to hydrolyze (CF 3 S) 3 CC(O)OR to (CF 3 S) 3 CC(O)OH failed.