Jin-Hong Lin

Synthesis and decarboxylative Wittig reaction of difluoromethylene phosphobetaine

A key intermediate, difluoromethylene phosphobetaine, in the Wittig reaction of ClCF2CO2Na-Ph3P with aldehydes was synthesized and characterized, which confirmed the reaction mechanism. The decarboxylation of this stable intermediate was a convenient approach for Wittig difluroolefination. Its reactivity could be adjusted by the modification of the substituent on the phosphorus.

Conversion between Difluorocarbene and Difluoromethylene Ylide

The interconversion between difluoromethylene ylide and difluorocarbene is described. The difluoromethylene ylide precursor, Ph3P(+)CF2CO2(-), could be turned into an efficient difluorocarbene reagent, whereas the classical difluorocarbene reagents, HCF2Cl and FSO2CF2CO2TMS, could generate highly reactive difluoromethylene ylide. Thus the Wittig difluoro-olefination and difluorocyclopropanation could be selectively realized by using the same reagent. In addition, the ylides obtained from different carbene sources showed different reactivity in Wittig reactions.

Difluorocarbene-Derived Trifluoromethylthiolation and [18F]Trifluoromethylthiolation of Aliphatic Electrophiles

The first trifluoromethylthiolation and [(18)F]trifluoromethylthiolation of alkyl electrophiles with in situ generated difluorocarbene in the presence of elemental sulfur and external (radioactive) fluoride ion is described. This transition-metal-free approach is high yielding, compatible with a variety of functional groups, and operated under mild reaction conditions. The conceptual advantage of this exogenous-fluoride-mediated transformation enables unprecedented syntheses of [(18)F]CF3S-labeled molecules from most commonly used [(18)F]fluoride ions. The rapid radiochemical reaction time (≤1 min) and high functional-group tolerance allow access to a variety of aliphatic [(18)F]CF3S compounds in high yields.

Recent advances in asymmetric fluorination and fluoroalkylation reactions via organocatalysis

The past decade has witnessed the significant advances of asymmetric organocatalytic fluorination, monofluoroalkylation, gem-difluoroalkylation, and trifluoromethylation. This digest summarizes the latest progress of these reactions. In the research area of asymmetric organocatalytic fluorination, a new catalysis concept, chiral anion phase-transfer catalysis strategy, has emerged and has proved to be highly efficient. Asymmetric organocatalytic monofluoroalkylation and gem-difluoroalkylation have been much less explored and the Lewis base/acid catalysis has been the most used strategy. Compared with electrophilic trifluoromethylation, nucleophilic trifluoromethylation has been intensively studied in the research field of asymmetric organocatalytic trifluoromethylation

1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU)-Promoted Decomposition of Difluorocarbene and the Subsequent Trifluoromethylation

Difluorocarbene derived from various carbene precursors could be effectively decomposed by 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). This decomposition process was successfully applied in the subsequent trifluoromethylation of a variety of (hetero)aryl iodides without the addition of an external fluoride ion. Mechanistic investigation revealed the detailed difluorocarbene conversion process in which the decomposed difluorocarbene is finally transformed into a fluoride ion and carbon monoxide.

Copper-catalyzed trifluoromethylation of alkenes with an electrophilic trifluoromethylating reagent

Summary An efficient method for the copper-catalyzed trifluoromethylation of terminal alkenes with an electrophilic trifluoromethylating reagent has been developed. The reactions proceeded smoothly to give trifluoromethylated alkenes in good to excellent yields. The results provided a versatile approach for the construction of Cvinyl–CF3 bonds without using prefunctionalized substrates.

Cross-Coupling between Difluorocarbene and Carbene-Derived Intermediates Generated from Diazocompounds for the Synthesis of gem-Difluoroolefins

Cross-coupling between difluorocarbene and carbene-derived intermediates generated from diazocompounds was developed to give gem-difluoroolefins, which constitutes a fast practical pathway to achieve hindered gem-difluoroolefins. The cross-coupling between difluorocarbene and aryl diazoacetates proceeded smoothly in the presence of a copper source, whereas its coupling with diaryl diazomethanes occurred well under metal-free conditions. A mechanism involving a copper-difluorocarbene complex was proposed.

The asymmetric synthesis of CF3- or –CF2-substituted tetrahydroquinolines by employing a chiral phosphoric acid as catalyst

CF(3)- or -CF(2)-containing tetrahydroquinolines have been asymmetrically synthesized from the reaction of fluorinated N-arylimines with benzyl N-vinylcarbamate in the presence of a chiral phosphoric acid.

Pd-Catalyzed Transfer of Difluorocarbene

The study of transition-metal difluorocarbene complex has long been a subject of active investigation, but the transition-metal-catalyzed transfer of difluorocarbene remains a significant challenge. The Pd-catalyzed transfer of difluorocarbene is described to realize the coupling reaction of boronic acids with difluorocarbene to give (difluoromethyl)arenes and -olefins. Mechanistic investigations reveal that the Pd═CF2 complex is an important intermediate for this transformation. This complex is prone to trimerization without the presence of starting materials.

An Unconventional Mechanistic Insight into SCF3 Formation from Difluorocarbene: Preparation of 18F-Labeled α-SCF3 Carbonyl Compounds

Trifluoromethylthiolation by sulfuration of difluorocarbene with elemental sulfur is described for the first time, which overrides long-standing trifluoromethyl anion-based theory. Mechanistic elucidation reveals an unprecedented chemical process for the formation of thiocarbonyl fluoride and also enables transition-metal-mediated trifluoromethylthiolation and [18 F]trifluoromethylthiolation of α-bromo carbonyl compounds with broad substrate scope and compatibility.