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The Pomeranz–Fritsch reaction, also named Pomeranz–Fritsch cyclization, is a named reaction in organic chemistry. It is named after Paul Fritsch (1859–1913) and Cäsar Pomeranz (1860–1926). In general it is a synthesis of
First the benzalaminoacetal 1 is built by the
Isoquinolines find many applications, including: *topical anesthetics such as
*vasodilators, a well-known example, 
isoquinoline
Isoquinoline is an individual chemical specimen - a heterocyclic aromatic organic compound - as well as the name of a family of many thousands of natural plant alkaloids, any one of which might be referred to as "an isoquinoline". It is a struc ...
.
General reaction scheme
The reaction below shows the acid-promoted synthesis of isoquinoline frombenzaldehyde
Benzaldehyde (C6H5CHO) is an organic compound consisting of a benzene ring with a formyl substituent. It is among the simplest aromatic aldehydes and one of the most industrially useful.
It is a colorless liquid with a characteristic almond-li ...
and a 2,2-dialkoxyethylamine.
Various alkyl groups
In organic chemistry, an alkyl group is an alkane missing one hydrogen.
The term ''alkyl'' is intentionally unspecific to include many possible substitutions.
An acyclic alkyl has the general formula of . A cycloalkyl group is derived from a cy ...
, e.g. methyl
In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula (whereas normal methane has the formula ). In formulas, the group is often abbreviated as ...
and ethyl groups, can be used as substituent R.
In the archetypical reaction sulfuric acid
Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...
was used as proton donor, but Lewis acids such as trifluoroacetic anhydride
Trifluoroacetic anhydride (TFAA) is the acid anhydride of trifluoroacetic acid. It is the perfluorinated derivative of acetic anhydride.
Preparation
Trifluoroacetic anhydride was originally prepared by the dehydration of trifluoroacetic acid with ...
and lanthanide triflates have been used occasionally.
Later, a wide range of diverse isoquinolines were successfully prepared.
Reaction mechanism
A possible mechanism is depicted below:
First the benzalaminoacetal 1 is built by the condensation
Condensation is the change of the state of matter from the gas phase into the liquid phase, and is the reverse of vaporization. The word most often refers to the water cycle. It can also be defined as the change in the state of water vapor ...
of benzaldehyde and a 2,2-dialkoxyethylamine. After the condensation a hydrogen
Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...
-atom is added to one of the alkoxy groups. Subsequently, an alcohol is removed. Next, the compound 2 is built. After that a second hydrogen-atom is added to the compound. In the last step a second alcohol is removed and the bicyclic system becomes aromatic
In organic chemistry, aromaticity is a chemical property describing the way in which a conjugated system, conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibits a stabilization stronger than would be expected from conjugati ...
.
Applications
The Pomeranz–Fritsch reaction has general application in the preparation of isoquinoline derivatives.Isoquinolines find many applications, including: *topical anesthetics such as
dimethisoquin
Quinisocaine (INN) or dimethisoquin ( BAN and USAN) is a topical anesthetic used as an antipruritic
Antipruritics, abirritants, or anti-itch drugs, are medications that inhibit itching (Latin: ''pruritus'').
Itching is often associated with sunb ...
:
:
*vasodilators, a well-known example, papaverine
Papaverine (Latin '' papaver'', "poppy") is an opium alkaloid antispasmodic drug, used primarily in the treatment of visceral spasms and vasospasms (especially those involving the intestines, heart, or brain), occasionally in the treatment of ...
, shown below.
See also
*Bischler–Napieralski reaction
The Bischler–Napieralski reaction is an intramolecular electrophilic aromatic substitution reaction that allows for the cyclization of β-arylethylamides or β-arylethylcarbamates. It was first discovered in 1893 by August Bischler and , in affi ...
* Pictet–Spengler reaction
The Pictet–Spengler reaction is a chemical reaction in which a β-arylethylamine undergoes Condensation reaction, condensation with an aldehyde or ketone followed by ring closure. The reaction was first discovered in 1911 by Amé Pictet and The ...
References
{{DEFAULTSORT:Pomeranz-Fritsch reaction Nitrogen heterocycle forming reactions Heterocycle forming reactions Name reactions Isoquinolines