Fluoride-Catalyzed Arylation of α-(Trifluoromethyl)styrene Derivatives with Silicon-Masked, Functionalized Aryl Pronucleophiles

Abstract

An operationally simple transition-metal-free protocol for the arylation of α-(trifluoromethyl)styrene derivatives with silicon-protected functionalized aryl pronucleophiles is disclosed. Catalytic amounts of an anionic Lewis base such as fluoride trigger the release of the aryl nucleophile from N-aryl-N′-silyldiazenes by desilylation along with denitrogenation. The thus-generated carbon nucleophiles engage in an allylic displacement with α-(trifluoromethyl)styrene electrophiles to afford the corresponding geminal difluoroalkenes.

Bond-Forming Processes Enabled by Silicon-Masked Aryl- and Alkyl-Substituted Diazenes

“…Our recent contributions to this field show its high potential as aryl, diazenyl, and alkyl anionic key intermediates can be selectively formed in situ under mild reaction conditions, giving rise to novel synthetic approaches as viable alternatives to the already existing methodologies. In this context, the silylated aryldiazenes were first engaged as aryl anion equivalents, from which the nucleophilic species are formed in situ by the action of a Lewis base, in synthetically useful protocols including the 1,2-arylation of carbonyl compounds and imines, as well as the assembly of fluorinated systems proceeding through nucleophilic substitutions. , The silicon-protected aryldiazenes were further utilized as nitrogen-centered pronucleophiles through the intermediacy of in situ-generated diazenyl anion equivalents in an unprecedented palladium-catalyzed C­(sp 2 )–N­(sp 2 ) cross-coupling, providing a general access to nonsymmetric azobenzene derivatives . From the latter investigation, a denitrogenative cross-coupling was additionally established, emphasizing the crucial role of the ligand coordinated to the palladium precatalyst .…”

“…By using the identical catalytic system, geminal difluoroalkenes decorated with a broad range of substituents on both coupling partners (as in 28aa – pa , gb – gd ) were obtained in good yields through a S N 2′ mechanism ( 11 + 27 → 28 ; Scheme ). Importantly, in comparison to the previously reported transition-metal-free arylation protocols, − the depicted strategy engaging the aryl-substituted silyldiazenes as latent carbon nucleophiles represents a valuable mild alternative.…”

Unveiling the Selectivity of Ru(II)-Catalyzed C–H Activation for Defluorinative Cyclization of 2-Arylbenzimidazole and Trifluoromethyl Diazo: A DFT Study

“…Common substrates used in the introduction of trifluoromethyl or gem -difluoroalkenyl agents include trifluoromethyl ketone, trifluoromethyl olefin and trifluoromethyl diazo, ,, etc. In particular, trifluoromethyl diazo has the advantages of high activity and easy preparation and can form metal carbenes with common transition metals, such as Rh, Pd, Au, Ag and Cu .…”

Silylation of Allylic C(sp3)–H Bonds Enabled by the Catalytic Generation of Allylpotassium Complexes

“…The latter then rapidly undergoes K/Si transmetalation with diazene 1a to give the potassium diazenyl complex B bound to the linear allylsilane moiety via a cation−π interaction. The denitrogenative decomposition of B generates the tert -butylpotassium complex C , which rapidly evolves through intramolecular metalation of one of the allylic C–H bonds to give the resting-state D and isobutane . In line with the accumulation of D in the reaction medium, its endothermic reprotonation with the allylic substrate (either 1- or in situ isomerized 2-alkene) becomes rate-limiting and may therefore compete with a second silylation step to give bis-silylated products such as 2b 2 or 15a 2 .…”