1. Introduction

Nitrogen-containing S(VI) functional groups such as sulfoximines and sulfonimidamides have attracted sustained interest in medicinal chemistry and organic synthesis in recent years. Compared with conventional sulfones and sulfonamides, these structures introduce an additional nitrogen substitution site at sulfur and may also exhibit sulfur-centered chirality, thereby providing structural and stereochemical features distinct from those of conventional S(VI) functional groups.[1,2]

A key challenge in the synthesis of these structures is how to construct the C–S bond efficiently while retaining the possibility of subsequently adjusting the sulfur oxidation state and the pattern of nitrogen substitution.

N-Sulfinylamines (general formula R¹–N=S=O) constitute an important class of S(IV) reagents for addressing this challenge. Sulfinylamines have been known for more than a century. Their central sulfur atom exhibits pronounced electrophilic reactivity, while the N=S=O unit is also capable of participating in radical addition and cycloaddition reactions.[2]

A variety of synthetic methods developed in recent years have shown that the same N=S=O unit can establish new carbon–sulfur linkages through three classes of reactions involving distinct electronic processes:

1. Two-electron addition involving carbon nucleophiles or organometallic species;

2. Single-electron radical addition involving carbon-centered radicals;

3. Formal cycloaddition with strained small rings.

Although these three classes of reactions proceed through different mechanisms, they often converge on sulfinamide-type S(IV) products, which can subsequently be converted into S(VI) compounds such as sulfonamides, sulfonimidamides, and sulfonimidoyl halides.[1]

This article focuses primarily on two questions:

In what electronic state does the carbon fragment react with N=S=O, and how can the resulting S(IV) structure be further converted into the desired S(VI) functional group?

2. Structural Fundamentals of N-Sulfinylamines and Related Nitrogen-Containing Sulfur Functional Groups

2.1 N-Sulfinylamine and Sulfinamide Are Structurally Distinct

The English names N-sulfinylamine and sulfinamide are very similar, but their atomic connectivity is different.

N-Sulfinylamine:

R¹–N=S=O

Its defining feature is a continuous N=S=O unit. Sulfur is directly multiply bonded to nitrogen and does not contain a pre-existing carbon substituent.

Sulfinamide:

R²–S(=O)–NR¹R³

Its defining feature is that sulfur already possesses a C–S bond, an S=O bond, and an S–N bond.

Accordingly, for most of the reactions discussed in this article, the relationship between the two can be understood as follows:

N-Sulfinylamine is the starting sulfur reagent used to form the C–S bond, whereas sulfinamide is an S(IV) product formed after a carbon fragment has been added to sulfur.

This structural distinction is fundamental to understanding the reactions discussed below.[2]

2.2 Several Related Nitrogen-Containing Sulfur Functional Groups

3. Why the N=S=O Unit Can Participate in Different Types of Bond-Forming Reactions

Sulfinylamine can be regarded as a monoaza analogue of sulfur dioxide, SO₂, and its N=S=O unit displays pronounced bond polarization.[2]

In R¹–N=S=O, oxygen and nitrogen strongly attract electron density, giving the central sulfur atom a pronounced electrophilic character. Electron-rich carbon species can therefore add at the sulfur center.

However, this alone does not fully explain the diversity of sulfinylamine reactivity. The more important feature is that the N=S=O unit can redistribute its electrons in different ways under different electronic conditions.

The N=S=O unit therefore provides a common structural platform: sulfur can accept a new carbon fragment, while the S=N unit can adjust its bond order and electron distribution during bond formation.

4. Two-Electron Addition: Formation of C–S Bonds by Exploiting Sulfur Electrophilicity

4.1 Fundamental Process of Direct Nucleophilic Addition

For reagents with pronounced carbon nucleophilicity, such as organolithium reagents, Grignard reagents, and organozinc reagents, N-sulfinylamine can directly accept a carbon fragment.

The net bond-forming process can be summarized as:

R²–M + R¹–N=S=O → R²–S(=O)–N(M)–R¹ → hydrolysis/protonation → R²–S(=O)–NH–R¹

where:

· R² represents the newly introduced carbon fragment;

· R¹ represents the substituent originally attached to the nitrogen atom of the sulfinylamine;

· M represents a metal component such as Li, MgX, or ZnX.

From an electronic perspective, the carbon nucleophile forms a C–S bond with sulfur, while the bond order of the original N=S bond decreases, generating the new sulfinamide framework.[2,12]

It is important to distinguish this representation from the actual processes operating in Ni-, Cu-, or Pd-catalyzed systems. The equation above is useful for understanding the net electronic changes in direct organometallic addition. In transition-metal-catalyzed systems, however, the carbon fragment generally first enters the metal catalytic cycle, and the actual bond-forming process may involve steps such as transmetalation, migratory insertion, or reduction rather than simple addition of a free carbanion.

4.2 Organoboron Reagents: Controlling Aryl Transfer through Metal Catalysis

In 2021, Lo and Willis reported the Ni(II)-catalyzed reaction of aryl and heteroaryl boroxines with N-sulfinyltritylamine (TrNSO), directly affording N-Tr sulfinamides.[3]

The significance of this reaction lies in replacing conventional highly reactive organolithium or Grignard carbon sources with milder organoboron carbon sources.

In the reaction, the aryl group first enters the nickel catalytic cycle and is subsequently transferred to the N=S=O unit. This reduces the presence of highly concentrated, strongly basic carbanionic species and therefore provides improved tolerance toward certain sensitive functional groups.

The resulting sulfinamide is not the synthetic endpoint. The Willis group further converted it by oxidative chlorination into a sulfonimidoyl chloride intermediate, which could subsequently undergo:

1. Reaction with an amine to form a sulfonimidamide;

2. Hydrolysis to form a primary sulfonamide;

3. Fluorination to form a sulfonimidoyl fluoride.[3]

This demonstrates that the value of N-sulfinylamine addition lies not only in forming a sulfinamide, but also in first establishing the desired C–S bond and then accessing different S(VI) structures from the resulting S(IV) intermediate.

4.3 Asymmetric Catalysis: Simultaneous C–S Bond Formation and Control of Sulfur Chirality

The S(IV) sulfur center of a sulfinamide generally adopts a trigonal-pyramidal geometry. When the substitution environment around sulfur is unsymmetrical, a configurationally stable sulfur stereogenic center can be formed.

In 2024, Shi, Yuan, Li, Yang, Zhang, and co-workers reported the Cu-catalyzed asymmetric addition of aryl boroxines to sulfinylamines. Computational studies indicated that aryl migratory insertion is the key enantioselectivity-determining step, while noncovalent interactions between the chiral ligand and the sulfinylamine contribute to stereochemical control.[4]

In the same year, Xi, Fang, Wang, Shi, and co-workers developed a Ni-catalyzed asymmetric 2,3-addition of arylboronic acids to sulfinylamines, which also afforded S-chiral sulfinamides.[5]

The central objective of these reactions is not simply to improve the efficiency of C–S bond formation, but rather to combine:

C–S bond formation + stereochemical control at sulfur

within a single catalytic process.

For sulfoximines or sulfonimidamides that ultimately require a single sulfur configuration, sulfur chirality can therefore be established at the sulfinamide stage.

4.4 Aryl Halides: Direct Formation of C–S Bonds from Common C–X Bonds

In 2024, Wei, Moseley, Bär, Sempere, and Willis reported Pd-catalyzed reactions of aryl and alkenyl (pseudo)halides with N-sulfinylamines.[6]

This method enables the direct use of aryl halides or alkenyl pseudohalides without first converting the substrates into organolithium, Grignard, or organoboron compounds. The reaction was shown to tolerate substrates containing protic and electrophilic functional groups and could be applied to the modification of complex aryl frameworks and natural-product derivatives.[6]

From the perspective of route design, different catalytic approaches correspond to different starting-material situations:

5. Radical Addition: Why Carbon Radicals Preferentially Form C–S Bonds

Two-electron reactions require the carbon fragment to exhibit nucleophilic character, whereas radical methods remove this requirement.

Starting materials such as carboxylic acids and alkyltrifluoroborates can first be converted into carbon-centered radicals, which are then trapped by N-sulfinylamines. This approach therefore accommodates many alkyl structures that are unsuitable for conversion into strongly basic organometallic reagents.[7–10]

5.1 Fundamental Process of Radical Addition

The radical process can be summarized as:

R²• + R¹–N=S=O → R²–S(=O)–N•–R¹ → R²–S(=O)–NH–R¹

The first step forms the C–S bond and generates a sulfinamidyl radical in which the radical character is localized primarily at nitrogen. This radical is subsequently converted into the sulfinamide through reduction, proton transfer, hydrogen-atom transfer, or related processes; the precise termination step depends on the catalytic system employed.

This differs fundamentally from two-electron addition:

1. In two-electron addition, carbon donates an electron pair to sulfur;

2. In radical addition, the new C–S bond is formed through a single-electron radical process.

5.2 Why Does the Radical Add to Sulfur Rather Than Nitrogen?

This is a key question for understanding the radical chemistry of sulfinylamines.

R¹–N=S=O contains both sulfur and nitrogen, and a carbon-centered radical could, in principle, form either a C–S bond or a C–N bond.

Mechanistic studies by the Larionov group on decarboxylative sulfinamidation provided an important explanation for this selectivity.[8]

Computational results showed that:

Although the product resulting from carbon-radical addition to nitrogen can be more thermodynamically favorable, the pathway for addition to sulfur has a substantially lower kinetic barrier.[8]

Distortion/interaction activation-strain analysis showed that addition at nitrogen requires greater geometric distortion of the sulfinylamine, while approach of the radical toward the more sterically congested nitrogen terminus results in stronger Pauli repulsion.

By comparison, attack at sulfur involves:

1. Less structural deformation of the sulfinylamine;

2. Weaker steric repulsion;

3. More favorable stabilizing interactions between the reacting fragments.[8]

The selectivity is therefore determined by which bond-forming pathway is faster.

Using radical-clock experiments, the Larionov group measured an addition rate constant of approximately 2.8 × 10⁸ M⁻¹ s⁻¹ for an alkyl radical reacting with the sulfinylamine under investigation, demonstrating the high trapping rate of sulfinylamines toward alkyl radicals.[8]

This result helps explain why sulfinylamines can efficiently compete for carbon-centered radicals and form C–S bonds in complex radical reaction systems.

5.3 Decarboxylation of Carboxylic Acids: Direct Access to Alkyl Sulfinamides from Common Carboxylic Acids

In 2023, Andrews, Kalepu, Palmer, Poole, Christensen, and Willis reported visible-light-promoted decarboxylative sulfinamidation of carboxylic acids.[7]

The reaction employs an acridine photocatalyst and irradiation at approximately 400 nm. The carboxylic acid generates an alkyl radical through a photoinduced process, after which the radical is trapped by sulfinylamine to form the corresponding sulfinamide.[7]

The simplified process is:

R²–CO₂H → R²• + CO₂ → addition to R¹–N=S=O → sulfinamide

In related acridine-catalyzed systems, decarboxylation of the carboxylic acid is considered to involve proton-coupled electron transfer, or PCET.[7]

The importance of this route lies in the ready availability and high structural diversity of carboxylic acids. After removal of the carboxyl carbon, the original carboxylic-acid framework can be directly converted into a new C(sp³)–S bond.

Thus, the radical route expands the types of carbon sources that can be used for C–S bond formation rather than merely changing the reaction conditions.

5.4 Trifluoroborates: Stable Precursors for the Generation of Carbon Radicals

In 2024, Yan, Wang, Zhang, Zhao, Tang, and Li, as well as Das, Mondal, Dhibar, Ruth, and Sahoo, independently reported photocatalytic reactions of potassium organotrifluoroborates with sulfinylamines.[9,10]

Alkyltrifluoroborates can undergo single-electron oxidation to generate alkyl radicals, which subsequently react with N=S=O to form C–S bonds. The system reported by the Sahoo group tolerated functional groups including ketones, esters, amides, nitriles, and halides, and the resulting sulfinamides could be further converted into different S(VI) compounds.[10]

Compared with conventional organolithium or Grignard reactions, the two approaches involve carbon in different electronic states:

Organolithium/Grignard reagents: carbon nucleophile → two-electron C–S bond formation

Alkyl BF₃K: carbon radical → single-electron C–S bond formation

When a molecule contains carbonyl, nitrile, halide, or other groups that are incompatible with strongly nucleophilic reagents, the radical pathway can therefore offer a distinct functional-group compatibility profile.

6. Formal Cycloaddition: Using the N=S Unit to Construct C–S and C–N Bonds Simultaneously

The first two classes of reactions primarily address the question of how to introduce a carbon fragment onto sulfur. Formal cycloaddition further exploits both the sulfur and nitrogen atoms of the N=S unit.

In 2021, Oliver, Loch, Augustin, Steinbach, Sharique, Tambar, Jones, Bannwarth, and Werz reported the (3+2) and (4+2) cycloaddition reactions of N-sulfinylamines with donor–acceptor cyclopropanes and cyclobutanes, respectively constructing five- and six-membered heterocycles containing adjacent S and N atoms.[11]

6.1 Why Donor–Acceptor Small Rings Readily Participate in These Reactions

Donor–acceptor small rings are commonly described as D–A cyclopropanes/cyclobutanes, where D–A denotes donor–acceptor.

These substrates possess two important characteristics:

1. Cyclopropanes and cyclobutanes possess ring strain;

2. Donor and acceptor substituents strongly polarize specific C–C bonds.

In the GaCl₃ system used in this study, the Lewis acid can activate the D–A small ring while also coordinating strongly to the sulfinyl group of the sulfinylamine, thereby promoting subsequent ring opening and bond-forming processes.

The N=S unit then participates in formation of new C–S and C–N bonds, directly incorporating the originally linear sulfinylamine into a heterocyclic framework.[11]

6.2 Why Are These Reactions Described as “Formal Cycloadditions”?

Based on the number of atoms incorporated into the product, these reactions can be described as formal (3+2) or (4+2) cycloadditions:

D–A cyclopropane + N=S → five-membered S/N-containing heterocycle

D–A cyclobutane + N=S → six-membered S/N-containing heterocycle

The term “formal cycloaddition” does not imply that all new bonds are formed simultaneously through a classical concerted pericyclic transition state.

Experimental and computational results from the study support a stepwise process involving Lewis-acid-promoted activation of the small ring, ring opening, and subsequent bond formation. The precise sequence of ionic transfer and bond-forming events may vary among different substrates.[11]

Accordingly, the fundamental difference between this class of reactions and conventional nucleophilic addition is that:

N-Sulfinylamine not only provides the sulfur atom for C–S bond formation but also uses its nitrogen atom to form a C–N bond, thereby directly constructing a cyclic framework containing adjacent S and N atoms.

When the target molecule itself contains this type of five- or six-membered sulfur–nitrogen heterocycle, this reaction can reduce the number of steps otherwise required to first install a sulfur functional group and then construct the ring.

7. From the S(IV) Structure of Sulfinamides to S(VI) Functional Groups

Although two-electron addition and radical addition employ different carbon sources, both frequently generate the same type of core structure:

R²–S(=O)–NHR¹

that is, a sulfinamide.

This S(IV) structure already contains the key newly constructed C–S bond, but sulfur can still undergo further oxidation and functionalization. Sulfinamides are therefore commonly used as precursors to a variety of S(VI) functional groups.[3,7,10,12]

7.1 The N-Substituent Determines the Mode of Subsequent Transformation

Commonly used sulfinylamines differ not only in their reactivity at sulfur, but also in the substituent attached to nitrogen.

A representative advantage of TIPS-NSO is its ability to react with Grignard, organolithium, or organozinc reagents and, after desilylation, furnish primary sulfinamides. Ding, Zhang, Davies, and Willis subsequently used a hypervalent iodine reagent and an amine to convert primary sulfinamides into NH-sulfonimidamides.[12]

This design introduces two important components of the sulfonimidamide separately:

1. The C–S bond is first established through sulfinylamine addition;

2. The second nitrogen substituent is subsequently introduced by an amine.

This strategy provides greater flexibility in the substitution patterns accessible in sulfonimidamides.

7.2 Divergent Transformation of a Common Intermediate Using t-BuO-NSO

In the decarboxylative reaction reported by the Willis group in 2023, N-sulfinyl-O-(tert-butyl)hydroxylamine (t-BuO-NSO) was used to trap alkyl radicals, affording a common N-alkoxy sulfinamide intermediate.[7]

Depending on the nucleophile used in the subsequent step, this intermediate can undergo different transformations:

N-alkoxy sulfinamide

→ NaOH treatment → primary sulfonamide

→ amine treatment → sulfonimidamide

Experimental results showed that the same carboxylic acid can therefore undergo a common initial C–S bond-forming step, after which the downstream conditions determine which type of S(VI) functional group is obtained.[7]

This illustrates an important synthetic principle:

Construction of the C–S bond and determination of the final S(VI) functional group can be separated into two stages.

The first stage determines which carbon fragment is attached to sulfur; the second determines whether the common S(IV) intermediate is converted into a sulfonamide or a sulfonimidamide.

8. Route Selection from Carbon Source to the Target S(VI) Structure

Once the three reaction classes are understood, route selection can proceed directly from the available carbon source and the desired target structure.

8.1 Selecting the C–S Bond-Forming Method According to the Carbon Source

8.2 Further Selection According to the Target Structure

① Target: a conventional linear sulfinamide

The main comparison should be between two-electron addition and radical addition, with the choice based on the available carbon source and the required functional-group compatibility.

② Target: a structure containing an S-stereogenic center

Asymmetric Cu- or Ni-catalyzed aryl addition can be considered, followed by verification that subsequent oxidation or substitution steps preserve the required stereochemical information.[4,5]

③ Target: an alkyl S(VI) functional group

If the carbon fragment is derived from a carboxylic acid or BF₃K reagent, the radical route can avoid the need to preconvert an sp³ carbon center into a highly reactive organometallic reagent.[7–10]

④ Target: a five- or six-membered ring containing adjacent S/N atoms

Formal cycloaddition of a D–A cyclopropane or cyclobutane can simultaneously construct the ring together with both heteroatom-linking bonds.[11]

⑤ Target: a sulfonamide or sulfonimidamide

In addition to the initial C–S bond-forming step, the N-substituent of the sulfinylamine and the subsequent oxidation, amination, or deprotection of the sulfinamide must also be considered.[3,7,12]

8.3 Core Sequence for Route Selection

For a specific target molecule, four questions can be considered in sequence:

1. In what form is the carbon fragment currently available?

Is it present as an aryl halide, an organoboron reagent, a carboxylic acid, a trifluoroborate, or an organometallic reagent?

2. Is this carbon fragment better suited to forming the C–S bond through a two-electron or a single-electron process?

This directly determines whether a nucleophilic-addition or radical pathway should be selected.

3. Does the target require simultaneous formation of C–S and C–N bonds?

If the target itself is a cyclic structure containing adjacent S and N atoms, a formal cycloaddition may be more direct than first forming a linear sulfinamide and subsequently closing the ring.

4. Which S(VI) functional group is ultimately required?

This determines whether the sulfinamide should subsequently undergo oxidation, amination, fluorination, deprotection, or another transformation, and this requirement may in turn influence the choice of the initial sulfinylamine reagent.

9. Representative Chemicals Related to N-Sulfinylamine Bond Formation and the Synthesis of Nitrogen-Containing S(VI) Functional Groups

Table 1. Key N-Sulfinylamine Reagents and Starting Materials for Their Preparation

Table 2. Reagents Related to Catalytic Systems for N-Sulfinylamine Bond-Forming Reactions

Table 3. Reagents Related to the Conversion of Sulfinamides into S(VI) Functional Groups

Note: The products listed above are representative Aladdin products relevant to scientific research. Their specific applications should be determined in conjunction with product specifications, batch COAs, and the intended reaction or evaluation system. Additional information on product specifications, grades, and COAs can be searched on the Aladdin website using the “product name/CAS number/catalog number.”

References

[1] Wei, M.-K.; Willis, M. C. The Catalytic Synthesis of Aza-Sulfur Functional Groups. Synthesis 2025, 57, 1429–1440. DOI: 10.1055/s-0043-1775106.

[2] Davies, T. Q.; Willis, M. C. Rediscovering Sulfinylamines as Reagents for Organic Synthesis. Chem. Eur. J. 2021, 27, 8918–8927. DOI: 10.1002/chem.202100321.

[3] Lo, P. K. T.; Willis, M. C. Nickel(II)-Catalyzed Addition of Aryl and Heteroaryl Boroxines to the Sulfinylamine Reagent TrNSO: The Catalytic Synthesis of Sulfinamides, Sulfonimidamides, and Primary Sulfonamides. J. Am. Chem. Soc. 2021, 143, 15576–15581. DOI: 10.1021/jacs.1c08052.

[4] Shi, Y.; Yuan, Y.; Li, J.; Yang, J.; Zhang, J. Catalytic Asymmetric Synthesis of Sulfinamides via Cu-Catalyzed Asymmetric Addition of Aryl Boroxines to Sulfinylamines. J. Am. Chem. Soc. 2024, 146, 17580–17586. DOI: 10.1021/jacs.4c03473.

[5] Xi, L.; Fang, X.; Wang, M.; Shi, Z. Asymmetric 2,3-Addition of Sulfinylamines with Arylboronic Acids Enabled by Nickel Catalysis. J. Am. Chem. Soc. 2024, 146, 17587–17594. DOI: 10.1021/jacs.4c04050.

[6] Wei, M.-K.; Moseley, D. F.; Bär, R. M.; Sempere, Y.; Willis, M. C. Palladium-Catalyzed Addition of Aryl Halides to N-Sulfinylamines for the Synthesis of Sulfinamides. J. Am. Chem. Soc. 2024, 146, 19690–19695. DOI: 10.1021/jacs.4c06726.

[7] Andrews, J. A.; Kalepu, J.; Palmer, C. F.; Poole, D. L.; Christensen, K. E.; Willis, M. C. Photocatalytic Carboxylate to Sulfinamide Switching Delivers a Divergent Synthesis of Sulfonamides and Sulfonimidamides. J. Am. Chem. Soc. 2023, 145, 21623–21629. DOI: 10.1021/jacs.3c07974.

[8] Dang, H. T.; Porey, A.; Nand, S.; Trevino, R.; Manning-Lorino, P.; Hughes, W. B.; Fremin, S. O.; Thompson, W. T.; Dhakal, S. K.; Arman, H. D.; Larionov, O. V. Kinetically-Driven Reactivity of Sulfinylamines Enables Direct Conversion of Carboxylic Acids to Sulfinamides. Chem. Sci. 2023, 14, 13384–13391. DOI: 10.1039/D3SC04727J.

[9] Yan, M.; Wang, S.-F.; Zhang, Y.-P.; Zhao, J.-Z.; Tang, Z.; Li, G.-X. Synthesis of Sulfinamides via Photocatalytic Alkylation or Arylation of Sulfinylamine. Org. Biomol. Chem. 2024, 22, 348–352. DOI: 10.1039/D3OB01782F.

[10] Das, S.; Mondal, P. P.; Dhibar, A.; Ruth, A.; Sahoo, B. Unifying N-Sulfinylamines with Alkyltrifluoroborates by Organophotoredox Catalysis: Access to Functionalized Alkylsulfinamides and High-Valent S(VI) Analogues. Org. Lett. 2024, 26, 3679–3684. DOI: 10.1021/acs.orglett.4c01270.

[11] Oliver, G. A.; Loch, M. N.; Augustin, A. U.; Steinbach, P.; Sharique, M.; Tambar, U. K.; Jones, P. G.; Bannwarth, C.; Werz, D. B. Cycloadditions of Donor–Acceptor Cyclopropanes and -butanes using S=N-Containing Reagents: Access to Cyclic Sulfinamides, Sulfonamides, and Sulfinamidines. Angew. Chem. Int. Ed. 2021, 60, 25825–25831. DOI: 10.1002/anie.202106596.

[12] Ding, M.; Zhang, Z.-X.; Davies, T. Q.; Willis, M. C. A Silyl Sulfinylamine Reagent Enables the Modular Synthesis of Sulfonimidamides via Primary Sulfinamides. Org. Lett. 2022, 24, 1711–1715. DOI: 10.1021/acs.orglett.2c00347.

For more related articles, see below:

Deoxyfluorination of Hydroxyalkyl-Substituted Aryl/Alkenyl Boronates: C–F Bond Construction and C–B Bond Retention via a BF3K Intermediate

Experimental Selection Logic for C-C Bond Construction: Understanding Fragment Coupling, Carbonyl Chain Extension, Olefination, and Late-Stage Bond-Forming Pathways by Bond-Forming Task

Haloheterocycles and Cross-Coupling: A Research-Oriented Selection Framework from Substrate Identification to Bond-Forming Routes (Including Product Navigation and Tables 1–5)

SuFEx and Sulfonyl Fluorides: From S(VI)–F Click Ligation Reactions to Covalent Tools in Chemical Biology

Turning Halohydrocarbons into “Transferable Carbon Fragments”: Key Rules and Application Navigation for Grignard Reagents RMgX (Tables 1–4)

Make “Aryl Chlorides + Low Pd Loading + Scale-Up Reproducibility” Reliable: The Initiation and Durability Logic of Pd–NHC (Palladium–N-Heterocyclic Carbene) Cross-Coupling (with Selection Navigation and Product Tables)

N-Heterocyclic Carbene (NHC) Ligands

Making Sense of Rhodium Catalysis: Three Core Engines—Rh(I), Rh(II), and Cp*Rh(III)—plus a Quick Selection Guide to Representative Product Tables A–G

Choosing Boron Sources to Make Reactions Robust: How Boronic Acids, Boronate Esters, BF₃K Salts, and MIDA Improve Suzuki–Miyaura Start-Up and Scale-Up Reproducibility (with Product Tables 1–5)

New Synthesis Method of New Nickel Reagent and Boric Acid (Ester)

Selective Deprotection and Sulfonyl Group Migration of N-Aryl Sulfonamides Mediated by TfOH (Trifluoromethanesulfonic Acid): Reaction Patterns and Synthetic Implications

SuFEx and Sulfonyl Fluorides: From S(VI)–F Click Ligation Reactions to Covalent Tools in Chemical Biology

Radical Initiator Selection Guide