New protocols for the synthesis of 3,4-annulated and 4-substituted quinolines from β-bromo-α,β-unsaturated aldehydes and 1-bromo-2-nitrobenzene or 2-bromoacetanilide

The palladium[0]-mediated Ullmann cross-coupling of readily available β-bromo-α,β-unsaturated aldehydes of the general form 2 with 1-bromo-2-nitrobenzene (3, X = Br) delivers products, 4, that undergo reductive cyclization to novel quinolines (5) upon exposure to indium in aqueous ammonium chloride or to Raney-nickel in the presence of dihydrogen. Analogous cross-coupling of 2-bromoacetanilide (6) with 2 affords products of type 7 that undergo in situ and K2CO3-mediated cyclization to give the same types of quinolines (5).