Introduction:
Chromone is the parent member of a group of plant coloring pigments, the flavones (2-arylchromones) that are found both free and as glycosides. 2,3-substituted Chromones can be synthesized from salicylic acid derivatives and from 2-hydroxyphenyl ketones. 3-substituted Chromones can be synthesized through the condensation of the enolate of 2-hydroxyphenyl ketone and ethyl formate.
Synthesis of Chromones:
The synthesis of 2- and 3- substituted Chromones usually start from 2-hydroxyphenyl ketones. In the first of two illustrations, a route to flavone is illustrated in the figure shown by employing 2-hydroxyacetophenone (2-hydroxyphenylethanone) and benzoyl chloride as starting materials.
Primarily, the phenolic group of the acetophenone is O-acylated by benzoyl chloride, by using pyridine as a base (a Schotten-Baumann kind reaction). Under such conditions, the O-benzoyl derivative instantly enolises and is O-acylated again to result a dibenzoate. Without isolation, this product is cyclised via treatment with aqueous potassium hydroxide to result 2-hydroxy-2,3-dihydroflavone. Dehydration to flavone is then influenced by the action of glacial acetic acid having sulphuric acid.
Fig: Synthesis of 2-substituted Chromones
2-substituted Chromones can as well be synthesized from the salicylic acid derivatives (figure shown below).
Fig: Synthesis of 2-substituted Chromones from Salicylic Acid Derivatives
An identical route to 3-substituted Chromones and iso flavone (R=Ph) relies on a Claisen-like condensation between the enolate of a 2-hydroxyphenyl ketone and ethyl formate (that is, methanoate) (figure shown).
This affords a 2-hydroxydihydrochromone which, as in the first illustration is subjected to the acid-promoted dehydration in the final step.
Fig: Synthesis of 3-substituted Chromones
Tutorsglobe: A way to secure high grade in your curriculum (Online Tutoring)
Expand your confidence, grow study skills and improve your grades.
Since 2009, Tutorsglobe has proactively helped millions of students to get better grades in school, college or university and score well in competitive tests with live, one-on-one online tutoring.
Using an advanced developed tutoring system providing little or no wait time, the students are connected on-demand with an expert at www.tutorsglobe.com. Students work one-on-one, in real-time with a tutor, communicating and studying using a virtual whiteboard technology. Scientific and mathematical notation, symbols, geometric figures, graphing and freehand drawing can be rendered quickly and easily in the advanced whiteboard.
Free to know our price and packages for online chemistry tutoring. Chat with us or submit request at [email protected]
TutorsGlobe.com Free Energy and Spontaneous Reactions Assignment Help-Homework Help by Online Access Chemistry Tutors
tutorsglobe.com indehiscent dry fruits assignment help-homework help by online simple dry fruits tutors
tutorsglobe.com mirabilis jalapa assignment help-homework help by online intermediate inheritance tutors
tutorsglobe.com software metrics assignment help-homework help by online software engineering tutors
gauss law tutorial all along with the key concepts of electric flux, calculation of electric flux, gauss's law for magnetism, application of gauss's law, spherical symmetry and spherical charge distribution
Free CAHSEE Study Guide, CAHSEE Test Papers, CAHSEE Practice papers, CAHSEE Test pattern and general information, Find CAHSEE exam information and resource, material free at Tutorsglobe.com
We bring to you finest Marketing Management Essay Writing Assignment Help service from best PhD tutors to score A++ at viable prices.
Cleavage-morula and Blastocyst formation tutorial all along with the key concepts of From fertilization to cleavage, Pattern of embryonic cleavage, Blastula formation, nucleated cells, blastomeres, mitosis promoting factor, DNA synthesis and growth stages
Many see share options as a poor means of rewarding directors. Warren Buffett, one of the worlds shrewdest and so many successful investors, has made clear his opposition to their use.
www.tutorsglobe.com offers accounting profession and careers, and accounting basics tutorial.
Organization of External Structure tutorial all along with the key concepts of Tagmatisation, Antenna, The Mouth Part, The Thorax, Insect Legs, Insect Wings, The Abdomen and Spiracles
www.tutorsglobe.com offers sates of matter homework help, sates of matter assignment help, online tutoring assistance, physical chemistry solutions by online qualified tutor's help.
Crystal diffraction-II tutorial all along with the key concepts of Reciprocal Lattice, Ewald's Construction in the reciprocal lattice, Bragg Law in Vector Form, Brillouin Zones
Avail unsurpassed Operating System Assignment Help service from 24x7 available top-rated tutors at viable prices to score high grades.
tutorsglobe.com spermatophytes assignment help-homework help by online biodiversity tutors
1939354
Questions Asked
3689
Tutors
1458816
Questions Answered
Start Excelling in your courses, Ask an Expert and get answers for your homework and assignments!!