The Baker–Venkataraman rearrangement is the

chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the pos ...

of 2-acetoxyacetophenones with base to form 1,3-di

ketone In organic chemistry, a ketone is a functional group with the structure R–C(=O)–R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group –C(=O)– (which contains a carbon-oxygen double bo ...

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 ...

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 synthesis of organic compounds. Bonding and structure Enolate anions are electr ...

formation followed by acyl transfer. It is named after the scientists

Wilson Baker Wilson Baker FRS (24 January 1900 – 3 June 2002) was a British organic chemist. He was born in Runcorn, the youngest of the four children of Harry and Mary Baker (née Eccles); his father was himself a chemist, having studied under Sir Henry ...

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 susbstituted derivatives, t ...

s. ''(also in th
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.

Mechanism

A base abstracts the hydrogen atom alpha to the aromatic

, 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 organic 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, salts, and esters of phenols. They may be formed by reaction of phenols with strong base. Properties Alkali metal phenolates, such as sodium phenolate hydrolyze in aqueous solution to form basic s ...

, which is protonated during acidic work-up to give the desired product. Baker-Venkataraman-Umlagerung Mechanismus

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: : Baker Venkataraman Cyclodehydration

References

External links

*https://www.organic-chemistry.org/namedreactions/baker-venkataraman-rearrangement.shtm {{DEFAULTSORT:Baker-Venkataraman rearrangement Rearrangement reactions Name reactions

Mechanism

See also

References

External links