We provide organic chemists with the building blocks and tools needed to successfully design and control small molecule synthesis. Regardless of the synthetic methods employed to create synthetic pathways in carbon-carbon, carbon-oxygen, and carbon-nitrogen bonds, we cover common reaction applications in cross-coupling, fluorination, metathesis, C-H functionalization, and photocatalysis. Discover our functionalized heterocycles, catalysts, ligands, chiral reagents, and more according to structure-activity relationships for unique chemical reactions.

C–H functionalization

C–H functionalization is often referred to as the ultimate goal in the field of synthetic organic chemistry. Recent advancements spanning organic chemistry, organometallics, and catalysis have significantly advanced our understanding of C–H bond reactivity and the development of robust reactions that capitalize on this knowledge. These progressions indicate that the time has come to widely incorporate these strategies into the retrosynthetic toolkit. The reliable and controlled conversion of C–H bonds into C–C, C–N, C–O, or C–X bonds offers advantages in terms of efficiency and reduction of waste.

Innovative techniques for C–H activation expand the range of sites within a molecule that can be targeted, creating more opportunities to transform it into a more intricate final product. Moreover, it enables the selective targeting of entirely different types of chemical bonds in organic synthesis, particularly with a high degree of chemoselectivity. When combined with traditional functional-group chemistry, C–H functionalization significantly simplifies the process of chemical synthesis for constructing complex natural compounds and pharmaceutical agents.

Cross-coupling

In the realm of organic synthesis, a cross-coupling reaction takes place when two fragments are united using a metal catalyst as a mediator. Cross-coupling has played a pivotal role in catalytic chemistry for the past three decades, with its origins traced back to the groundbreaking contributions of Heck, Negishi, and Suzuki. Their pioneering work in palladium-catalyzed cross-coupling led to their recognition with the Nobel Prize in Chemistry in 2010. Serving as one of the most versatile and potent methods for forging chemical bonds in synthetic organic chemistry, the cross-coupling field has matured to a point where virtually any pair of fragments can be linked with the appropriate catalyst. With its utilization experiencing exponential growth, this field has expanded to encompass a plethora of strategies for forming carbon-carbon, carbon-nitrogen, and carbon-oxygen bonds. These strategies include pivotal reactions such as:

– Buchwald-Hartwig amination, which involves coupling an aryl (pseudo)halide with an amine, constituting a foundational reaction across diverse scientific disciplines.

– Heck coupling, which brings together an unsaturated halide and an alkene to yield substituted alkenes.

– Negishi coupling, where an aryl (pseudo)halide combines with an organozinc nucleophile to establish C-C bonds.

– Sonogashira coupling, facilitating the connection between an aryl (pseudo)halide and a terminal alkyne to produce disubstituted acetylenes.

– Stille coupling, involving the union of an aryl (pseudo)halide with a stannane, stands as a versatile reaction for carbon-carbon bond formation, marked by minimal restrictions on the R-groups.

– Suzuki-Miyaura coupling, entailing the cross-coupling of an aryl (pseudo)halide with an organoborate, represents a versatile method for generating carbon-carbon bonds.

Fluorination

The incorporation of fluorine, known as fluorination, holds significant potential to modify the biological characteristics of a compound due to the distinctive properties of fluorine, including its electronegativity and compact size. In the realm of pharmaceutical research, fluorine is frequently introduced into target compounds to enhance bioavailability and bolster the profile of metabolic stability. This field has expanded to encompass a range of methodologies for introducing fluorine, which include several pivotal reactions.

**NUCLEOPHILIC FLUORINATION**

Nucleophilic fluorination techniques employ a fluoride source, often alkali or ammonium fluoride, for the direct replacement of alcohols, additions to aldehydes, ketones, and carboxylic acids. These methods exhibit remarkable chemoselectivity in small molecule synthesis, along with enabling polyfluorination for materials synthesis.

**ELECTROPHILIC FLUORINATION**

Electrophilic fluorination involves merging a carbon-centered nucleophile with an electrophilic source of fluorine. While traditional sources like fluorine gas have been toxic and strong oxidizers, research has yielded milder, safer, and highly stable alternatives for electrophilic fluorination. These reagents have proven invaluable in a spectrum of applications, spanning electrophilic aromatic substitution to the formation of α-fluoro-keto species.

**DIFLUOROMETHYLATION**

Difluoromethylation entails generating difluoromethyl groups through nucleophilic addition and radical functionalization of (C–H) bonds. The significance of the difluoromethyl group (R-CF2H) has been underscored in drug development, agrochemicals, and material research, attributed to its isosteric nature with a carbinol group (CH2OH).

**TRIFLUOROMETHYLATION**

Trifluoromethylation stands as a swiftly advancing domain within chemical research, seamlessly integrating with catalysis to craft novel chemical methodologies for incorporating trifluoromethyl groups into molecules.

**PERFLUOROALKYLATION**

Perfluoroalkylation involves the reaction between a nucleophilic perfluoroalkyl group and alkyl, alkenyl, and aryl halides or carbonyl compounds. The stability of perfluoroalkyl reagent groups renders them appealing for a range of applications, including cross-coupling with allyl phosphates.

Methathes

Olefin metathesis is an organic chemical reaction characterized by the rearrangement of carbon-carbon double bonds through the redistribution of alkene fragments. This process has spurred the exploration of novel disconnections in organic synthesis, opening avenues for advancements in polymer chemistry, drug discovery, and the synthesis of natural compounds. Three primary categories of metathesis reactions exist: ring-closing metathesis and cross metathesis are routinely employed for small molecule synthesis, while ring-opening metathesis finds frequent use in polymerization.

A notable and widespread application of olefin metathesis in organic synthesis is ring-closing metathesis (RCM), an intramolecular reaction that forms a ring from an acyclic diene. This approach enables the creation of carbon-rich rings containing sp3-centers and heteroatoms, a prominent theme in contemporary medicinal chemistry.

In cross metathesis, two olefins engage in an intermolecular reaction, producing an olefin product with substituents derived from both starting olefins. This methodology is well-regarded for its compatibility with various functional groups, alongside its ability to tolerate residual moisture and oxygen. The utilization of ruthenium-catalyzed macrocyclization has established itself as a versatile technique for synthesizing large rings (with a minimum of 12 atoms).

Ring-opening metathesis polymerization (ROMP) is instrumental in designing polymers with adjustable properties, constituting a significant advancement in simplified synthesis. Due to its cost-effectiveness and the easy accessibility of starting materials, this robust polymerization process is suitable for the large-scale production of polymers.

Organic reaction toolbox

An arsenal of organic reactions serves as a systematic approach for categorizing indispensable chemical processes essential for addressing synthetic challenges and innovating novel small molecules. When constructing a synthetic route, chemists employ an array of reactions to transform one small molecule into another. Through the strategic use of protecting groups and more direct creation of molecular intricacy, deviations in pathways can be circumvented. These reactions are typically grouped into three primary categories, delineating how reactants come together to yield different products.

The first category centers on the distinctive reaction attributes of the 19 primary functional groups (such as alkane, alkene, alkyne, alkyl halide, alcohol, ether, thiol, sulfide, ketone, aldehyde, carboxylic acid, ester, acyl halide, acid anhydride, amide, amine, nitrile, epoxide, and aryl). These attributes dictate the reactivity tendencies when these groups are present in a molecule. By concentrating on reactions applicable to a particular functional group, scientists narrow down the range of feasible reactions for the desired transformation.

An alternative classification method involves grouping reactions based on the functional groups they generate. This approach proves valuable as chemists frequently work in reverse, beginning from the target molecule. For instance, if the desired terminal functional group is an alcohol, potential reactions could encompass a Grignard reaction with an aldehyde or ketone, reduction reactions involving a carboxylic acid, aldehyde, ketone, or ester, or a hydration reaction of an alkene.

The third category of reactions pertains to those altering the carbon-carbon framework through bond formation or cleavage. Remarkable advancements in synthetic techniques for forming C-C bonds have led to an extensive repertoire of over 100 diverse reactions. These progressions stem from several factors, including the establishment of robust and dependable protocols for cross-coupling, increased accessibility to various organometallic reagents, and the creation and enhancement of stoichiometric reagents designed to introduce specific carbon-containing moieties.

Photocatalysis 

Visible light photoredox catalysis, commonly known as photoredox catalysis, has emerged as a potent tool in the field of organic synthesis, building upon the groundwork laid by early trailblazers in radical chemistry and photochemistry. Photoredox chemistry facilitates the formation of fresh bonds through open shell pathways, enabling the rapid creation of intricate compounds that explore novel realms of chemical diversity. Operating in the presence of visible light, photocatalysts offer a gateway to previously unattainable bond formations through an extensive spectrum of synthetic processes, encompassing cross-coupling, C–H functionalization, alkene and arene functionalization, and trifluoromethylation, among others.

The potency of photocatalysis is attributed, in part, to its capacity to activate easily accessible, uncomplicated starting materials via single electron transfer routes, thereby generating reactive open shell species under mild reaction conditions. Once generated, these distinct open shell entities can partake in diverse radical trapping and quenching events, ultimately leading to the production of high-value products.

Photocatalysis has found successful application in the endeavors of academic research teams, industrial chemists, and collaborative initiatives between academia and industry. These collective endeavors have yielded innovative methodologies, novel synthetic connections, and an enhanced comprehension of the mechanistic intricacies of photoredox pathways.