The Fritsch-Buttenberg-Wiechell rearrangement, named for Paul Ernst Moritz Fritsch, Wilhelm Paul Buttenberg, and Heinrich G. Wiechell, is a
chemical reactionA chemical reaction is a process that leads to the transformation of one set of chemical substances to another. They are studied by chemists under a field of science called chemistry. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, often coming about...
whereby a 1,1-diaryl-2-bromo-
alkeneIn organic chemistry, an alkene, olefin, or olefine is an unsaturated chemical compound containing at least one carbon-to-carbon double bond...
rearrangesA rearrangement reaction is a broad class of organic reactions where the carbon skeleton of a molecule is rearranged to give a structural isomer of the original molecule . Often a substituent moves from one atom to another atom in the same molecule...
to a 1,2-diaryl-
alkyneAlkynes are hydrocarbons that have a triple bond between two carbon atoms, with the formula CnH2n-2. Alkynes are traditionally known as acetylenes, although the name acetylene also refers specifically to C2H2, known formally as ethyne using IUPAC...
by reaction with a strong base such as an
alkoxideAn alkoxide is the conjugate base of an alcohol and therefore consists of an organic group bonded to a negatively charged oxygen atom. They can be written as RO–, where R is the organic substituent. Alkoxides are strong bases and, when R is not bulky, good nucleophiles and good...
.
This rearrangement is also possible with
alkylIn chemistry, an alkyl group is a hydrocarbon; typically an alkyl is a part of a larger molecule. The term is usually used loosely; there is no general formula for an alkyl group. In structural formulae, an alkyl group is represented with an R. Usually, alkyl groups resemble hydrocarbons, but...
substituents.
The strong base deprotonates the vinylic
hydrogenHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly flammable diatomic gas with the molecular formula H
2...
, which after alpha-elimination forms a
vinylA vinyl compound is any organic compound that contains a vinyl group , −CH=CH2. These are derivatives of ethene, CH2=CH2, with one hydrogen atom replaced with some other group...
carbeneIn chemistry, a carbene is a organic molecule containing a carbon atom with six valence electrons and having the general formula RR'C:. Carbenes are classified into two varieties, singlets and triplets. Most carbenes are very short lived, although persistent carbenes are known.The prototypical...
.
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The Fritsch-Buttenberg-Wiechell rearrangement, named for Paul Ernst Moritz Fritsch, Wilhelm Paul Buttenberg, and Heinrich G. Wiechell, is a
chemical reactionA chemical reaction is a process that leads to the transformation of one set of chemical substances to another. They are studied by chemists under a field of science called chemistry. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, often coming about...
whereby a 1,1-diaryl-2-bromo-
alkeneIn organic chemistry, an alkene, olefin, or olefine is an unsaturated chemical compound containing at least one carbon-to-carbon double bond...
rearrangesA rearrangement reaction is a broad class of organic reactions where the carbon skeleton of a molecule is rearranged to give a structural isomer of the original molecule . Often a substituent moves from one atom to another atom in the same molecule...
to a 1,2-diaryl-
alkyneAlkynes are hydrocarbons that have a triple bond between two carbon atoms, with the formula CnH2n-2. Alkynes are traditionally known as acetylenes, although the name acetylene also refers specifically to C2H2, known formally as ethyne using IUPAC...
by reaction with a strong base such as an
alkoxideAn alkoxide is the conjugate base of an alcohol and therefore consists of an organic group bonded to a negatively charged oxygen atom. They can be written as RO–, where R is the organic substituent. Alkoxides are strong bases and, when R is not bulky, good nucleophiles and good...
.
This rearrangement is also possible with
alkylIn chemistry, an alkyl group is a hydrocarbon; typically an alkyl is a part of a larger molecule. The term is usually used loosely; there is no general formula for an alkyl group. In structural formulae, an alkyl group is represented with an R. Usually, alkyl groups resemble hydrocarbons, but...
substituents.
Reaction Mechanism
The strong base deprotonates the vinylic
hydrogenHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly flammable diatomic gas with the molecular formula H
2...
, which after alpha-elimination forms a
vinylA vinyl compound is any organic compound that contains a vinyl group , −CH=CH2. These are derivatives of ethene, CH2=CH2, with one hydrogen atom replaced with some other group...
carbeneIn chemistry, a carbene is a organic molecule containing a carbon atom with six valence electrons and having the general formula RR'C:. Carbenes are classified into two varieties, singlets and triplets. Most carbenes are very short lived, although persistent carbenes are known.The prototypical...
. A 1,2-aryl migration forms the desired product, the 1,2-diaryl-alkyne.
Scope
One study explored this reaction for the synthesis of novel
polyyneThe polyynes are a group of organic compounds with alternating single and triple bonds, for example buta-1,3-diyne , C
4H
2....
s :