Nucleophilic F-18-fluorination of bromodifluoromethyl derivatives was performed using [F-18] Bu4NF in the presence of DBU(1,8-diazabicyclo[5.4.0]undec-7-ene). This novel procedure provided a diverse set of [F-18] trifluoroacetamides in good to excellent radiochemical conversions. A mechanism where DBU acts as organomediator in this transformation is proposed.
The nucleophilic fluorination of bromodifluoromethyl derivatives mediated by the complex (PPh3)(3)CuF is described. Under the reaction conditions, different trifluoroacetates, trifluorolcetones, trifluoroarenes and trifluoroacetamides were obtained in good yields.
The dissertation work that is summarized in this thesis describes novel syntheses of organofluorine compounds with a broad coverage of different fluorine-containing motifs.
Chapter 2.1 covers works on the exploration of new trifluoromethylthiolating reactions of diazocarbonyl compounds. A rhodium-catalyzed oxy-trifluoromethylthiolation reaction enabled the synthesis of densely functionalized carbonyl compounds. Different oxygen nucleophiles, for instance alcohols, ethers and acetals underwent this transformation.
A zinc triflimide mediated three-component reaction established an arylation-trifluoromethylthiolation of diazocarbonyl compounds. In situ generation of triarylboranes was rendered most effective for the arylation event. Both procedures made use of the high reactivity of a recently developed electrophilic trifluoromethylthiolating reagent.
The second chapter (2.2) is dedicated to the late-stage construction of trifluoromethyl motifs. By means of halide exchange, nucleophilic fluoride from a copper(I)-complex could be used to exchange bromide with fluoride in the α-position to carbonyl groups as well as in benzylic positions.
The third chapter (2.3) covers the development of an enantioselective fluorocyclization reaction. In situ generated aryliodine(III)-fluoride species were used as organocatalysts. Through this oxidative olefin difunctionalization reaction, quaternary C-F stereogenic centers could be constructed with high enantiomeric excesses. DFT calculations enabled deeper understanding of the mechanism and the origin of stereoselectivity.
A new Zn-mediated trifluoromethylthiolation-based bifunctionalization reaction is developed. In this process, simultaneous C-SCF3 and C-C bond formation takes place in a multicomponent reaction, in which an aryl and a SCF3 group arise from different reagents. Our studies show that the reaction mechanism is similar to the Hooz multicomponent coupling. The process involves in situ generation of BAr3, which reacts with a diazocarbonyl compound, and the reaction is terminated by an electrophilic SCF3 transfer. The reaction can also be extended to fluorination based bifunctionalization which proceeds with somewhat lower yield than the analogous trifluoromethylthiolation reaction.
A new Rh-catalyzed, three-component reaction for the oxytrifluoromethylthiolation of alpha-diazoketones was developed. The SCF3 functionality was introduced using a stable dibenzenesulfonimide reagent under mild conditions. Alcohols, acetals, and ethers were used as the alkoxy sources. Cyclic ethers underwent a trifunctionalization reaction through the introduction of SCF3, OR, and N(SO2Ph)(2) substituents in a single step.
1,1-Disubstituted styrenes with internal oxygen and nitrogen nucleophiles undergo oxidative fluorocyclization reactions with in situ generated chiral iodine(III)-catalysts. The resulting fluorinated tetrahydrofurans and pyrrolidines contain a tertiary carbon–fluorine stereocenter. Application of a new 1-naphthyllactic acid-based iodine(III)-catalyst allows the control of tertiary carbon–fluorine stereocenters with up to 96% ee. Density functional theory calculations are performed to investigate the details of the mechanism and the factors governing the stereoselectivity of the reaction.