Metal free one pot synthesis of Î’-carbolines via a domino Pictet-Spengler reaction and aromatization

A convenient and efficient metal free, atom economical flexible synthesis of β-carbolines involving a domino Pictet-Spengler reaction and aromatization in oxygen atmosphere in N-methyl-2-pyrollidone (NMP) is described. Variety of aryl, heteroaryl and aliphatic aldehydes were found to be good substrates for this methodology. Several β-carbolines (6a-6t) and β-carboline methyl esters (7a-7e) were synthesized using this methodology.The same reaction carried out in argon atmosphere in the presence of catalytic amount of acid in NMP furnished, tetrahydro-β-carbolines (4a-4g).