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. 2019 Oct 16;9(57):32946-32953.
doi: 10.1039/c9ra07108c. eCollection 2019 Oct 15.

Oxidant-free, three-component synthesis of 7-amino-6 H-benzo[ c]chromen-6-ones under green conditions

B S Vachan  1 , Aishwarya Ramesh  1 , Muthu Karuppasamy  1 , Isravel Muthukrishnan  1 , Subbiah Nagarajan  2 , J Carlos Menéndez  3 , C Uma Maheswari  1 , Vellaisamy Sridharan  1   4
Affiliations

Oxidant-free, three-component synthesis of 7-amino-6 H-benzo[ c]chromen-6-ones under green conditions

B S Vachan et al. RSC Adv. .

Abstract

An oxidant-free three-component synthesis of biologically significant 7-amino-6H-benzo[c]chromen-6-ones was established involving a Sc(OTf)3 catalyzed three-component reaction between primary amines, β-ketoesters and 2-hydroxychalcones under green conditions. In this strategy, both the B and C rings of 6H-benzo[c]chromen-6-ones were constructed simultaneously starting from acyclic precursors by generating four new bonds including two C-C, one C-N and one C-O in a single synthetic operation. The mechanism of this sequential cascade process involves the initial formation of a β-enaminone intermediate followed by Michael addition with 2-hydroxychalcone, intramolecular cyclization, dehydration, lactonization and aromatization steps. Unlike the related literature approaches, this reaction delivered the products without the addition of any external oxidants to achieve the key aromatization step.

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Conflict of interest statement

There are no conflicts to declare.

Figures

Fig. 1
Fig. 1. Selected biologically important natural 6H-benzo[c]chromen-6-ones.
Scheme 1
Scheme 1. Previous annulation reactions and the hypothesis of the present work.
Scheme 2
Scheme 2. Substrate scope for the three-component synthesis of 6H-benzo[c]chromen-6-ones.
Scheme 3
Scheme 3. Proposed mechanism for the three-component synthesis of 6H-benzo[c]chromen-6-ones.
See this image and copyright information in PMC

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