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Easily accessible 3,3′-diindolylmethanes (DIMs) were utilized to generate a focused library of indolo[2,3-b]quinolines (2), chromeno[2,3-b]indoles (3), and 3-alkenyl-oxindoles (4) under 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)-mediated oxidative conditions. DIMs with ortho-NHTosyl (NHTs) phenyl group afforded indolo[2,3-b]quinolines (2), whereas DIMs with ortho-hydroxy phenyl groups yielded chromeno[2,3-b]indoles (3) and 3-alkenyl-oxindoles (4). The mild conditions and excellent yields of the products make this method a good choice to access a diverse library of bioactive molecules from a common starting material. Two optimized compounds 2a and 2n displayed excellent activity against clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA). Compound 2a showed the minimum inhibitory concentration values in the concentration between 1 and 4 μg/mL, whereas compound 2n revealed the values of 1–2 μg/mL. Furthermore, both the compounds were highly bactericidal and capable to kill the MRSA completely within 360 min. Collectively, the results suggested that both compounds 2a and 2n possess enormous potential to be developed as anti-MRSA agents.

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A metal-free one-pot cascade annulation of acyclic substrates dienaminodioate, cinnamaldehydes and allyl amine was achieved for the synthesis of polyfunctional biaryl-2-carbaldehydes. The reaction proceeds at room temperature by a trifluoroacetic acid mediated Diels-Alder pathway. Synthetic applications of the resulting biaryl-2-carbaldehyde have been demonstrated by conversion into an array of diverse molecules with biological and materials chemistry relevance. The present work offers a complementary route to the existing metal mediated cross-coupling methods for the preparation of biaryls.