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5807-5817
shown in Scheme 1. The active iodine species reacts with ketone
or beta-keto ester and forms an intermediate. Then the hydroxy
functionality of the salicylaldehyde reacts with an intermediate
and gives the corresponding O-C cross coupled product. Further
more, these O-C cross coupled products enolizes and migrates
the double bond of enol, to the carbonyl carbon of the
salicylaldehyde and leads to the formation of 2,3-disubstituted
dihydrofurans. By elimination of water or acetic acid from 2,3-
disubstituted dihydrofurans leads to the formation of 2-acetyl
benzofuran, benzofuran-2-carboxylate ethyl esters and
benzofuran 2- carboxylate benzyl esters (Scheme 1).
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Conclusion
In conclusion, we have demonstrated TBAI/TBHP mediated
oxidative cross coupling of phenols and carboxylic acids with
ketones under metal-free, base free and solvent free conditions
towards environmentally benign synthesis of aryloxyketones,
acyloxyketones and benzofurans. It is noteworthy to have
operationally simple method, under mild conditions, use of
commercially available and cheaper catalyst (TBAI) as well as an
oxidant (TBHP). This method avoids the use of hazardous
reagents, toxic metals and metal oxidants. Furthermore,
investigations on the reaction mechanism and to expand the
scope of these reactions are underway in our laboratory.
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PSK and BRK are thankful to the UGC and CSIR for
providing the financial support as a senior research fellowship
(SRF). Dr.KCA and Dr.KRR thanks to IFCPAR (CEFIPRA) for
financial support (5305-1).
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