Preparation and Reactivity of Tris(trifluoromethylselanyl)carbenium [(CF3Se)3C+] and Trifluoromethylsulfanylacetic Acid Derivatives [(CF3S)3-nCXn(O)R]

Reaction pathways for the synthesis of the (CF3E)3C moieties (E = Se, S) are described. [(CF3Se)3C+][AsF 6‐] was found to be a suitable synthon for the preparation of (CF3Se)3C derivatives. It can be prepared either from (CF3Se)3C derivatives. It can be prepared either from (CF3Se)4C or (CF3Se)3CF and AsF5 in liquid SO2. Direct access to (CF3Se)3CF was realized by the reaction of FCBr3 with Hg(SeCF3)2. Treatment of [(CF3Se)3C+][AsF6‐] with potassium halides provided (CF3Se)3CX (X = F, Cl, Br). A different course took the reaction with KI, as CF3SeSeCF3 and (CF3Se)2C=C(SeCF3)2 were formed as main products. Minor amounts of (CF3Se)3CC(SeCF3)3 were formed which could be isolated and unambiguously characterized. Only two routes led to a threefold CF3S‐substituted acetic acid ester (CF3S)3CC(O)OR [R = CH3, (CH3)3C]: Metatheses between (CF3S)2CBrC(O)OCH3 and Hg(SCF3)2 and metalation of (CF3S)2CHC(O)OR [R = CH3, (CH3)3C] with NaH followed by reaction with CF3SCl. Other precursors such as (CF3S)2CXC(O)OR′ [X = H, Br; R′ = Me3Si, (n‐C4H9)3Sn] and (CF3S)2CBrC(O) Y (Y = Cl, Br) were synthesized but could not be converted to the corresponding (CF3S)3C derivatives. Attempts to hydrolyze (CF3S)3CC(O)OR to (CF3S)3CC(O)OH failed.