The Scholl reaction is a coupling reaction

Coupling reaction

A coupling reaction in organic chemistry is a catch-all term for a variety of reactions where two hydrocarbon fragments are coupled with the aid of a metal catalyst...

 between two arene compounds with the aid of a Lewis acid

Lewis acid

]The term Lewis acid refers to a definition of acid published by Gilbert N. Lewis in 1923, specifically: An acid substance is one which can employ a lone pair from another molecule in completing the stable group of one of its own atoms. Thus, H+ is a Lewis acid, since it can accept a lone pair,...

 and a protic acid. It is named after its discoverer, Roland Scholl

Roland Scholl

Roland Heinrich Scholl was a Swiss chemist who taught at various European universities. Among his most notable achievements are the synthesis of coronene, the co-development of the Bally-Scholl synthesis, and various discoveries about polycyclic aromatic hydrocarbons.-Early life and...

.
The protic acid is often an impurity in the Lewis Acid and also formed in the course of a Scholl reaction. Reagents are iron(III) chloride

Iron(III) chloride

Iron chloride, also called ferric chloride, is an industrial scale commodity chemical compound, with the formula FeCl3. The colour of iron chloride crystals depends on the viewing angle: by reflected light the crystals appear dark green, but by transmitted light they appear purple-red...

 in dichloromethane

Dichloromethane

Dichloromethane is an organic compound with the formula CH2Cl2. This colorless, volatile liquid with a moderately sweet aroma is widely used as a solvent. Although it is not miscible with water, it is miscible with many organic solvents...

, copper(II) chloride

Copper(II) chloride

Copper chloride is the chemical compound with the formula CuCl2. This is a light brown solid, which slowly absorbs moisture to form a blue-green dihydrate. The copper chlorides are some of the most common copper compounds, after copper sulfate....

, PIFA and boron trifluoride

Boron trifluoride

Boron trifluoride is the chemical compound with the formula BF3. This pungent colourless toxic gas forms white fumes in moist air. It is a useful Lewis acid and a versatile building block for other boron compounds.-Structure and bonding:...

 etherate in dichloromethane, Molybdenum(V) chloride

Molybdenum(V) chloride

Molybdenum chloride is the inorganic compound with the formula [MoCl5]2. This dark volatile solid is an important starting reagent in the preparation of molybdenum compounds. In the solid state molybdenum pentachloride exists as a dimer with the formula Mo2Cl10, with a structure similar to that...

 and lead tetraacetate with BF₃ in acetonitrile

Acetonitrile

Acetonitrile is the chemical compound with formula . This colourless liquid is the simplest organic nitrile. It is produced mainly as a byproduct of acrylonitrile manufacture...

 .

Given the high reaction temperature and the requirement for strongly acidic catalysts the chemical yield often are low and the method is not a popular one. Intramolecular

Intramolecular

Intramolecular in chemistry describes a process or characteristic limited within the structure of a single molecule, a property or phenomenon limited to the extent of a single molecule.- Examples :...

 reactions fare better than the intermolecular ones, for instance in the organic synthesis

Organic synthesis

Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...

 of 9-phenylfluorene

Fluorene

Fluorene, or 9H-fluorene, is a polycyclic aromatic hydrocarbon. It forms white crystals that exhibit a characteristic, aromatic odor similar to that of naphthalene. It is combustible. It has a violet fluorescence, hence its name. For commercial purposes it is obtained from coal tar...

:
Or the formation of the pyrene

Pyrene

Pyrene is a polycyclic aromatic hydrocarbon consisting of four fused benzene rings, resulting in a flat aromatic system. The chemical formula is . This colourless solid is the smallest peri-fused PAH...

 dibenzo-(a.1)-pyrene from the anthracene

Anthracene

Anthracene is a solid polycyclic aromatic hydrocarbon consisting of three fused benzene rings. It is a component of coal-tar. Anthracene is used in the production of the red dye alizarin and other dyes...

 1-phenylbenz(a)anthracene (66% yield).
One study showed that the reaction lends itself to cascade reaction

Cascade reaction

A cascade reaction or tandem reaction or domino reaction is a consecutive series of intramolecular organic reactions which often proceed via highly reactive intermediates. It allows the organic synthesis of complex multinuclear molecules from a single acyclic precursor. The substrate contains many...

s to form more complex polycyclic aromatic hydrocarbon

Polycyclic aromatic hydrocarbon

Polycyclic aromatic hydrocarbons , also known as poly-aromatic hydrocarbons or polynuclear aromatic hydrocarbons, are potent atmospheric pollutants that consist of fused aromatic rings and do not contain heteroatoms or carry substituents. Naphthalene is the simplest example of a PAH...

s

In certain applications such as triphenylene

Triphenylene

In chemistry, the organic compound triphenylene is a flat polycyclic aromatic hydrocarbon consisting of four fused benzene rings. Triphenylene can be isolated from coal tar, but it is also made synthetically using benzyn chemistry. One molecule of triphenylene has delocalized 18-π-electron systems...

 synthesis this reaction is advocated as an alternative for the Suzuki reaction

Suzuki reaction

The Suzuki reaction is the organic reaction of an aryl- or vinyl-boronic acid with an aryl- or vinyl-halide catalyzed by a palladium complex. It is widely used to synthesize poly-olefins, styrenes, and substituted biphenyls, and has been extended to incorporate alkyl bromides...

. A recurring problem is oligomerization of the product which can be prevented by blocking tert-butyl substituents :
The exact reaction mechanism

Reaction mechanism

In chemistry, a reaction mechanism is the step by step sequence of elementary reactions by which overall chemical change occurs.Although only the net chemical change is directly observable for most chemical reactions, experiments can often be designed that suggest the possible sequence of steps in...

 is not known but could very well proceed through an arenium ion

Arenium ion

An arenium ion in organic chemistry is a cyclohexadienyl cation that appears as a reactive intermediate in electrophilic aromatic substitution. For historic reasons this complex is also called a Wheland intermediate or a sigma complex or σ-complex.Two hydrogen atoms bonded to one carbon lie in a...

. Just as in electrophilic aromatic substitution

Electrophilic aromatic substitution

Electrophilic aromatic substitution EAS is an organic reaction in which an atom, usually hydrogen, appended to an aromatic system is replaced by an electrophile...

, Activating group

Activating group

In organic chemistry, a functional group is called an activating group if a benzene molecule to which it is attached more readily participates in electrophilic substitution reactions...

s such as methoxy

Methoxy

In chemistry , methoxy refers to the functional group consisting of a methyl group bound to oxygen. This alkoxy group has the formula O–CH3.The word is used in organic nomenclature usually to describe an ether...

improve yield and selectivity :