Base-Controlled Divergent Synthesis of Fluorine-Containing Benzo[4,5]imidazo[2,1-b][1,3]thiazines from 2-Mercaptobenzimidazoles and β-CF3-1,3-Enynes

Base-mediated synthesis of ring-fluorinated imidazo[1,2-a]pyridines via sequential C-F substitutions

Developing innovative approaches for the synthesis of compounds that integrate imidazo[1,2-a]pyridines and fluoro fragments is crucial. Herein, an expedient [3 + 3] annulation method for synthesizing ring-fluorinated imidazo[1,2-a]pyridines via two consecutive C-F substitutions from readily available 1C,3N-dinucleophiles and β-CF3-1,3-enynes is presented. This protocol exhibits several appealing features, including readily available and inexpensive substrates, a broad range of functional groups, step and atom economy, and mild reaction conditions without any transition-metal catalysts.

Tunable base-controlled chemoselective synthesis of trifluoromethyl-containing N-substituted benzimidazole-2-thiones and monofluorinated 4H-benzo[4,5]imidazo[2,1-b][1,3]thiazine

A highly efficient base-controlled synthesis of N-β-trifluoromethyl-substituted 2H-benzo[d]imidazole-2-thiones and 2-fluoro-4H-benzo[4,5]imidazo[2,1-b][1,3]thiazines via hydroamination or defluorinative cyclizations of α-(trifluoromethyl)styrenes with 2-mercaptobenzimidazole was developed.

Construction of 3,6-Difluoropyridones via a Double Defluorinative [3 + 3] Annulation of α-Fluoro-α-sulfonylacetamides with 2-CF3-Alkenes

A remarkably simple and efficient double defluorinative [3 + 3] annulation approach involving N-phenyl-α-fluoro-α-phenylsulfonylacetamide and 2-CF3-alkenes to access N-phenyl-3,6-difluoropyridone derivatives has been achieved. The key to the success of this single-step synthesis of difluoropyridones is the strategic utilization of 2-CF3-alkenes for consecutive allylic and vinylic substitution reactions and a desulfonylation cascade. We could also show that these difluoropyridones serve as a versatile platform for C-6-selective defluorinative functionalizations.

Divergent Synthesis of Benzo[4,5]imidazo[2,1-b][1,3]thiazines and α-Trifluoromethyl-β-arylthio Tertiary Alcohols from 2-Mercaptobenzimidazoles and α-CF3 Alkenes

An efficient and metal-free approach for the divergent synthesis of 2-fluoro-3-aryl-4H-benzo[4,5]imidazo[2,1-b][1,3]thiazines and α-trifluoromethyl-β-arylthio tertiary alcohols from 2-mercaptoimidazoles and α-CF3 alkenes has been developed. The chemoselectivity was well controlled by base or light; a series of 2-fluoro-3-aryl-4H-benzo[4,5]imidazo[2,1-b][1,3]thiazines were afforded via base-mediated sequential SN2'- and SNV-type reactions. Meanwhile, α-trifluoromethyl-β-arylthio tertiary alcohols could be selectively achieved through visible-light-driven and electron donor-acceptor (EDA) complex-initiated radical cascade thiolation/hydroxylation in the absence of base, transition metal, and external photocatalyst.

Base-Mediated Regioselective [3 + 3] Annulation of Alkylidene Malononitriles with Trifluoromethyl Alkenes via Dual C-F Bond Cleavage

A base-mediated regioselective [3 + 3] annulation of alkylidene malononitriles with trifluoromethyl alkenes was described. The reaction proceeds through sequential intermolecular SN2' and intramolecular SNV-type cyclization by cleaving dual C-F bonds in a trifluoromethyl group, which discriminate multiple carbon-nucleophilic sites using a single base. Various bicycles bearing a monofluorocyclohexene motif were assembled from readily available starting materials under mild conditions via a one-pot cascade approach.

Recent Advances on Fluorine Chemistry

The purpose of this Special Issue is to showcase the latest findings in fluorine chemistry [...].

Picking Two out of Three: Defluorinative Annulation of Trifluoromethyl Alkenes for the Synthesis of Monofluorinated Carbo- and Heterocycles

The increasing demand of organofluorine compounds in medicine, agriculture, and materials sciences makes sophisticated methods for their synthesis ever more necessary. Nowadays, not only the C-F bond formation but also the selective C-F bond cleavage of readily available poly- or perfluorine-containing compounds have become powerful tools for the effective synthesis of organofluorine compounds. The defluorinative cross-coupling of trifluoromethyl alkenes with various nucleophiles or radical precursors in an SN 2' manner is a convergent route to access gem-difluoroalkenes, which in turn react with nucleophiles or radical precursors via an SN V-type reaction. If the SN V reactions occur intramolecularly, the dual C-F bond cleavage of trifluoromethyl alkenes allows facile assembly of monofluorinated cyclic skeletons with structural complexity and diversity. In this personal account, we summarized the advances in this field on the basis of coupling and cyclization partners, including binucleophiles, alkynes, diradical precursors and radical precursors bearing a nucleophilic site. Accordingly, the annulation reactions can be achieved by base-mediated sequential SN 2'/SN V reactions, transition metal catalyzed or mediated reactions, photoredox catalysis, and the combination of photocatalytic reactions with SN V reaction. In the context of seminal works of others in this field, a concise summary of the contributions of the authors is also offered.

Divergent Synthesis of F- and CF3-Containing N-Fused Heterocycles Enabled by Fragmentation Cycloaddition of β-CF3-1,3-Enynes with N-Aminopyridiniums Ylides

The two novel cyclization modes of β-CF3-1,3-enynes are presented herein for the divergent construction of F- and CF3-containing N-fused heterocycles. Fluorinated pyrazolo[1,5-a]pyridines were afforded from β-CF3-1,3-enynes with N-aminopyridiniums ylides via detrifluoromethylative [2 + 3] cyclizations, followed by fluorine transfer from a CF3 unit. Whereas reaction with N-aminoisoquinoliniums ylides gave CF3-substituted pyrrolo[2,1-a]isoquinoline by unprecedented fragmentation [3 + 2]-cycloadditions. Additionally, gram-scale experiments and synthetic utility are demonstrated by further derivatization of fluorinated heterocycles.