Force in Organic Synthesis : TFPN-Mediated Acyl Fluoride Chemistry and Its Multifunctional Applications

In organic synthesis, the activation of carboxylic acids is one of the general and core steps in constructing complex molecular structures. By activating the carboxyl group (such as acyl halides, activated esters, etc.), key chemical bonds such as esters and amides can be constructed.

3,4,5,6-Tetrafluorophthalonitrile (TFPN, structural formula shown in Figure 1 below ) is an organofluorine compound that has been rediscovered and given new functions in recent years. 。Its synthesis can be traced back to the 1960s, when LJ Belf and his colleagues at Imperial Smelting Company in the UK first reported it while studying the halogen exchange reaction of polyfluoroaromatics [1]. ；TFPN is only regarded as an intermediate of fluorinated aromatic nitriles and is used to prepare phthalocyanine dyes or precursors of polymeric functional materials.

In 2021, Sun Haoran's team discovered that TFPN is an effective reagent for preparing acyl fluoride from carboxylic acid [2]. Inspired by this, Yang Jinhua/Zhao Junfeng's team developed a new type of TFPN of bifunctional condensation reagent. Under alkaline conditions, the acyl fluoride intermediate was generated in situ through "a one-pot two-step” reaction [3]. The intermediate has both reactivity and stability: compared with acyl chloride, its structure is more stable and its functional group compatibility is wider, which can effectively suppress side reactions; compared with acid anhydride, its nucleophilic activity is stronger, and it can efficiently complete acylation conversion with alcohols and amines under mild conditions. At the same time, the acyl fluoride has excellent stability in alkaline environment, and is easy to undergo enolization when there is α-H, which can be significantly inhibited by a chiral center of the racemic side reaction of the carboxylic acid position during the condensation process α.

Figure 1 TFPN structure

The team led by Yang Jinhua and Zhao Junfeng explored its application TFPNin amide / peptide synthesis and ester / thioester / macrolide synthesis . Compared with traditional methods, TFPN has the following advantages [3-4] :

1.  Safe and stable: High stability during storage and use , low toxicity;

2.  High efficiency and mildness : The reaction conditions are mild , and the reaction can be completed efficiently in a short time ;

3.  Operation and cost-effectiveness: Inexpensive and readily available, the reaction does not require a strictly anhydrous and oxygen-free environment , and the operation is simple;

4.  Wide applicability : It is not only suitable for the synthesis of conventional amides and esters, but also performs well in complex systems such as peptides and macrolides ;

5. Good stereoselectivity : It can effectively avoid racemization problems in the formation of ester and amide bonds, ensuring the purity of optical products.

TFPN- mediated condensation reactions require polar solvents such as DMSO as the reaction medium, and the efficient conversion is achieved with the participation of the organic base DIPEA.

TFPN-mediated esterification reactions have a broad substrate range, applicable to various aliphatic and aromatic carboxylic acids, and are compatible with complex substrates with multiple functional groups. Nucleophiles such as alcohols, phenols, and thiols can also participate in the reaction smoothly. In addition, esterification reactions are usually carried out at room temperature, with yields generally exceeding 80% (Figure 2) .

Figure 2. TFPN-mediated esterification reaction

The synthesis of macrolides has long been limited by ring strain and intermolecular polymerization side reactions, but TFPN performs well in such reactions (Figure 3) . By generating acyl fluoride intermediates in situ, it greatly improves the intramolecular ring-closing efficiency and suppresses intermolecular side reactions.

Figure 3. TFPN-mediated macrolide synthesis

The construction of amide bonds, especially the preservation of chiral centers in peptide synthesis , has always been a technical challenge in the field of organic synthesis. TFPN, with its stable acyl fluoride intermediate and rapid condensation reaction , can achieve the construction of peptide bonds of conventional amides and sterically hindered, racemic amino acids in over 80% yield within 1 hour , with almost no racemization (Figure 4).

Figure 4. TFPN-mediated amide synthesis

The study indicates that TFPN has great application potential in solid-phase synthesis, enabling the efficient synthesis of pentapeptides and longer-chain peptides with yields exceeding 80% (Figure 5) . This discovery provides a powerful tool for the research and synthesis of peptide drugs and functional peptide materials .

Figure 5. TFPN used in solid-phase synthesis

3. Application potential in complex molecules and cutting-edge chemistry

TFPN-mediated condensation reactions have broad functional group tolerance and mild reaction conditions , making them promising for applications in the late-stage functionalization of bioactive molecules, bioconjugation, and the synthesis of functional polymers .

IV. Mechanism of Action of TFPN

The TFPN-mediated condensation reaction mechanism is as follows: First, the carboxylic acid forms a carboxylate anion under the action of a base, which reacts with TFPN to form an active aryl ester intermediate. Subsequently, the fluoride ion in the system attacks the active ester intermediate to generate an acyl fluoride intermediate. Finally, the nucleophile (alcohol, amine) attacks the acyl fluoride, successfully generating the target ester and amide products (Figure 6). This process achieves a transition from ""over-activation ” ”to " "moderate activation ” ”, balancing efficiency and selectivity.

Figure 6. Mechanism of action of TFPN

 

V. Outlook

 

In summary, TFPN-mediated condensation reactions, through the in-situ generation of acyl fluoride intermediates, have efficiently promoted the synthesis of esters , amides, and even challenging macrocyclic lactones and complex peptides , demonstrating outstanding value in solid-phase synthesis. Furthermore, this synthetic strategy shows broad application prospects in areas such as drug molecule derivatization and functional polymer synthesis . With further research , TFPN will play an increasingly important role in the field of organic synthesis .

VI. Company Introduction

Suzhou Haofan Biotech Co., Ltd. (Stock Code: 301393.SZ), founded in 2003 and headquartered in Suzhou High-tech Zone, is a national high-tech enterprise providing specialty raw materials to pharmaceutical R&D and manufacturing companies worldwide. Its products are mainly used in the synthesis of peptides, nucleotides, and pharmaceuticals, covering a wide range of products including condensing agents for specialty amide bonds, protective agents, linking agents, protein cross-linking agents for antibody-drug conjugates, molecular building blocks, liposomes, and phosphorus reagents. To date, it has cumulatively developed and produced over 1,500 different products.

After more than two decades of unremitting efforts and accumulation, Haofan Biotech has continuously cultivated its expertise in the global peptide synthesis reagent field. It has now developed into a leading enterprise with extensive customized product coverage and significant advantages in large-scale production, capable of meeting the specific needs of various customers. We sincerely invite customers interested in this product to contact us to learn more about product details and explore cooperation opportunities.

References:

[1] Belf, L. J., Buxton, M. W.,Fuller, G., 612. Reactions of polyfluoroaryl bromides with cuprous salts in dimethylformamide. J. Chem. Soc., 1965, 3372. DOI: 10.1039/JR9650003372

[2] Mao, S.; Kramer, J. H.; Sun, H., Deoxyfluorination of carboxylic acids with KF and highly electron-deficient fluoroarenes. J. Org. Chem., 2021, 86, 6066. DOI: 10.1021/acs.joc.0c02491

[3] Yang, J.; Zhang, D.; Chang, Y.; Zhang, B.; Shen, P.; Han, C.; Zhao, J., TFPN-mediated racemization/epimerization-free amide and peptide bond formation. Org. Chem. Front., 2024, 11, 5422. DOI: 10.1039/d4qo01009d

[4] Zhang, D.; Shen, P.; Zhang, Y.; Zheng, Q.; Zhang, J.; Han, C.; Xu, S.; Yang, J., A TFPN-mediated acyl fluoride platform: efficient synthesis of esters, thioesters, and macrolactones from carboxylic acids with diverse nucleophiles. Org. Chem. Front., 2025, 12, 5414. DOI: 10.1039/d5qo00651a