HFPO Trimer-Based Alkyl Triflate, a Novel Building Block for Fluorous Chemistry. Preparation, Reactions and 19F gCOSY Analysis

Triflate 4, CF3(CF2)2O-CF(CF3)CF2O-CF(CF3)CH2-OTf (RFOCH2OTf), of the HFPO trimer-based alcohol 3 (RFOCH2OH) is a novel highly fluorinated building block for fluorous chemistry. In analogy to similar polyfluorinated triflates with methylene spacer, its reactivity is limited to strong and soft nucleophiles. Whereas reactions with cyanide anion, phenolate anion, enolate of diethyl malonate or lithium salt of benzaldehyde bis(phenylsulfanyl)acetal were unsuccessful, the corresponding imidazole 5, iodide 6 or azide 7 were prepared in good yields. Reaction of imidazole 5 with (perfluorohexyl)methyl triflate (9) afforded highly fluorinated non-crystalline imidazolium salt 8, TfO-RFOCH2-(C3H3N2)+-CH2C6F13-n, which could be employed as fluorous ionic liquid or intermediate for fluorous carbenes. Complete assignment of complex 19F NMR spectra of all compounds employed was accomplished using 19F gCOSY NMR method.

Synthesis of Methoxy Substituted Centrally Chiral Triynes as Precursors of Functionalised Nonracemic Helicene-Like Compounds

A modular synthesis of a series of methoxy substituted optically pure aromatic triynes (-)-(S)-5-9 and (-)-(R)-10 is presented. It relies on key operations such as substitution of benzylic bromine with an alkoxy group and aryl-alkyne coupling reaction to combine appropriate methoxy substituted benzene/naphthalene building blocks and chiral alkynol synthons such as (-)-(2S)-but-3-yn-2-ol and (-)-(1R)-1-phenylprop-2-yn-1-ol. The triyne molecules comprise a diphenylacetylene, 1-(phenylethynyl)naphthalene or 1,1'-ethyne-1,2-diyldinaphthalene core unit. They are intended to serve as [2+2+2] cyclisation precursors of methoxy substituted nonracemic helicene-like compounds with a penta-, hexa- and heptacyclic helical scaffold.