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The Baker–Venkataraman rearrangement is the
Collective Volume (1963) 4: 478 (PDF)
.'' After the base-catalyzed rearrangement, treatment with acid generally affords the chromone or flavone core, though other milder methods have been reported.
To complete the construction of the chromone or flavone core, cyclodehydration is required. This was commonly afforded by treatment with strong acid, however many milder conditions have now been developed. One proposed mechanism for this dehydration is as follows:
:
chemical reaction
A chemical reaction is a process that leads to the chemistry, chemical transformation of one set of chemical substances to another. When chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an Gibbs free energy, ...
of 2-acetoxyacetophenones with base to form 1,3-diketone
In organic chemistry, a ketone is an organic compound with the structure , where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group (a carbon-oxygen double bond C=O). The simplest ketone is acetone ( ...
s.
This rearrangement reaction
In organic chemistry, a 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 at ...
proceeds via enolate
In organic chemistry, enolates are organic anions derived from the deprotonation of carbonyl () compounds. Rarely isolated, they are widely used as reagents in the Organic synthesis, synthesis of organic compounds.
Bonding and structure
Enolate ...
formation followed by acyl transfer. It is named after the scientists Wilson Baker and K. Venkataraman.
The Baker–Venkataraman rearrangement is often used in the synthesis of chromone
Chromone (or 1,4-benzopyrone) is a derivative of benzopyran with a substituted keto group on the pyran ring. It is an isomer of coumarin.
Derivatives of chromone are collectively known as ''chromones''. Most, though not all, chromones are also ...
s and flavone
Flavone is an organic compound with the formula . A white solid, flavone is a derivative of chromone with a phenyl (Ph) substituent adjacent to the ether group. The compound is of little direct practical importance, but substituted derivatives, ...
s. ''(also in thCollective Volume (1963) 4: 478 (PDF)
.'' After the base-catalyzed rearrangement, treatment with acid generally affords the chromone or flavone core, though other milder methods have been reported.
Mechanism
A base abstracts the hydrogen atom alpha to the aromaticketone
In organic chemistry, a ketone is an organic compound with the structure , where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group (a carbon-oxygen double bond C=O). The simplest ketone is acetone ( ...
, forming an enolate. Then, the enolate attacks the ester carbonyl to form a cyclic alkoxide
In chemistry, an alkoxide is the conjugate base of an alcohol and therefore consists of an organic group bonded to a negatively charged oxygen atom. They are written as , where R is the organyl substituent. Alkoxides are strong bases and, whe ...
. The cyclic intermediate is opened up to form a more stable phenolate
Phenolates (also called phenoxides) are anions, salt (chemistry), salts, and esters of phenols, containing the phenolate ion. They may be formed by reaction of phenols with strong base.
Properties
Alkali metal phenolates, such as sodium phenoxi ...
, which is protonated during acidic work-up to give the desired product.
To complete the construction of the chromone or flavone core, cyclodehydration is required. This was commonly afforded by treatment with strong acid, however many milder conditions have now been developed. One proposed mechanism for this dehydration is as follows:
:
See also
* Allan–Robinson reaction * Kostanecki acylationReferences
External links
*https://www.organic-chemistry.org/namedreactions/baker-venkataraman-rearrangement.shtm {{DEFAULTSORT:Baker-Venkataraman rearrangement Rearrangement reactions Name reactions