Silver-Catalyzed Tandem Synthesis of Naphthyridines and Thienopyridines via Three-Component Reaction
2013
Verma, Akhilesh K. | Kotla, Siva K Reddy | Choudhary, Deepak | Patel, Monika | Tiwari, Rakesh K.
An efficient approach for the silver-catalyzed regioselective tandem synthesis of highly functionalized 1,2-dihydrobenzo[1,6]naphthyridines 6a–z and 7a–e by the reaction of ortho-alkynylaldehydes 3a–n with amines 4a–d and ketones 5a–c/active methylene compounds 5d–g, under mild reaction conditions, is described. The scope of the developed chemistry was successfully extended for the direct synthesis of 1,2-dihydrobenzo[4,5]thieno[2,3-c]pyridines 8a–e, which is known as the sulfur analogue of β-carbolines. Naphthyridines 6a–z and thienopyridines 8a–e were obtained via dual activation concept using l-proline as organocatalyst; however, naphthyridines 7a–e were synthesized without using organocatalyst. The reaction shows selective N–C bond formation on the more electrophilic alkynyl carbon, resulting in the regioselective 6-endo-dig-cyclized products. Reactivity behavior of electron-deficient and electron-rich ortho-alkynylaldehydes in the synthesis of naphthyridines and thienopyridine by three-component reaction is supported by the control experiment.
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