Bimolecular vinylation of arenes by vinyl cations

Abstract

Styrene derivatives can be easily synthesized from vinyl triflates and arenes under mild reaction conditions, using [Li][Al(OC(CF3)3)4] as a catalyst and LiHMDS as a base.

Tropylium-Promoted Hydroboration Reactions: Mechanistic Insights Via Experimental and Computational Studies

“…Therefore, we decided to carry out further 11 B and 19 F NMR spectroscopic analyses of the reaction between tropylium salts and HBpin to get more insights (Figure 2). The pertinent sections of 11 B NMR spectra of HBpin and tropylium tetrafluoroborate (1a) mixture at 4/1 ratio after 30 min at room temperature are presented in Figure 2.…”

“…Similar outcomes were observed with longer reaction times or at 70 °C (see Scheme d for a representative spectrum of the mixture after 30 min at room temperature). It beckoned another hypothesis we had at the beginning of this work that tropylium ion could act as a hydride abstractor , to generate a borenium ion from HBpin, as observed by Crudden, Thomas, and others. , This could then quickly react with the alkyne to form a vinyl cation intermediate, , which subsequently takes a hydride from another molecule of HBpin to generate the target product and start another reaction cycle (Scheme c) . There were also known examples of borenium-mediated haloboration reactions via analogous reaction pathways …”

“…Although we could not fully interpret these signals, we believe that they correspond to BHF 2 25 and BH 2 F (never been characterized by experimental NMR spectroscopy before), 26 which were presumably produced via substituent exchange reactions between HBpin and BF 3 (vide infra). 7e, 27 It should be noted that in 19 (major peaks) isotopes for each species (see page S11 in the experimental Supporting Information). Mechanistic DFT Calculations.…”

“…The pertinent sections of 11 B NMR spectra of HBpin and tropylium tetrafluoroborate (1a) mixture at 4/1 ratio after 30 min at room temperature are presented in Figure 2. 22 After matching signals with known boron species in the literature, we were able to identify FBpin 23 (∼21 ppm in 11 B and ∼−153 ppm in 19 F NMR) at all ratios. We did not observe any signals corresponding to [FHBpin] − , formed by the coordination of fluoride with HBpin, which was reported by the Thomas group in their work with iron and cobalt tetrafluoroborate salts.…”

“…The Journal of Organic Chemistry could only identify the presence of BF 3 , plus the formation of some unidentified boranes in the 11 B NMR spectrum (Scheme 3e, also see 11 B− 19 F NMR studies and discussion later). On the other hand, we have carried out an extensive density functional theory (DFT) calculation 21 to validate our hypotheses in either Scheme 3b or 3c.…”