Synthesis of 7-hydroxydibenzopyran-6-ones via benzannulation of coumarins
H Surya Prakash Rao1,2, M Prabakaran1, Nandurka Muthanna1
1Department of Chemistry, Pondicherry University, Pondicherry - 605 014, India. profhspr@gmail.com.
Abstract:
We have successfully demonstrated a facile synthesis of a variety of 7-hydroxydibenzopyran-6-ones via a two-step protocol from 3-acylcoumarins having a latent Nazarov dienone functionality. Condensation of 3-acylcoumarins and ethyl cyanoacetate under basic (wet K2CO3) and microwave irradiation conditions followed by decarboethoxylative aromatization with Br2 or DDQ furnished dibenzopyran-6-ones in high yields. The formation of ring C of the dibenzopyran-6-one motif critically depended on an active methylene compound and C7 substitution on coumarins. The Ar-Br or ArOTf substitution in dibenzopyran-6-ones was leveraged for the palladium-catalysed Suzuki coupling with diverse aryl boronic acids to increase the structural diversity. Reductive decyanation of C10 cyano dibenzopyran-6-ones furnished some of the isomers of urolithin A.
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