PREPARATION AND REACTIVITY OF TRIS(TRIFLUOROMETHYLSELANYL)CARBENIUM [(CF3SEC-DERIVATIVES [(CF3S)(3-N)CX(N)(O)R](] AND TRIFLUOROMETHYLSULFANGLACETIC ACID)

Reaction pathways for the synthesis of the (CF(3)E)(3)C moieties (E = Se, S) are described. [(CF3SeC+][AsF6-] was found to led to be a suita ble synthon for the preparation of (CF3Se)(3)C derivatives. It can be prepared either from (CF3Se)(4)C or (CF3Se)(3)CF and AsF5 in liquid SO 2. Direct access to (CF3Se)(3)CF was realized by the reaction of FCBr3 with Hg(SeCF3)(2). Treatment of [(CF3SeC+][AsF6-] with potassium hali des provided (CF3Se)(3)CX (X = F, Cl, Br). A different course took the reaction with KI, as CF3SeSeCF3 and (CF3Se)(2)C=C(SeCF3)(2) were form ed as main products. Minor amounts of (CF3Se)(3)CC(SeCF3)(3) were form ed which could be isolated and unambiguously characterized. Only two r outes threefold CF,S-substituted acetic acid ester (CF3S)(3)CC(O)OR [R = CH3, (CH3)(3)C]: Metatheses between (CF3S)(2)CBrC(O)OCH3 and Hg(SCF 3)(2) and metalation of (CF3S)(2)CHC(O)OR [R = CH3, (CH3)(3)C] with Na H followed by reaction with CF3SCl. Other precursors such as (CF3S)(2) CXC(O)OR' [X = H, Br; R' = Me(3)Si, (n-C4H9)(3)Sn] and (CF3S)(2)CBrC(O )Y (Y = Cl, Br) were synthesized but could not be converted to the cor responding (CF3S)(3)C derivatives. Attempts to hydrolyze (CF3S)(3)CC(O )OR to (CF3S)(3)CC(O)OH failed.