Efficient Synthesis of Quinolines

There are different approaches to synthesize quinolines utilizing the Povarov reaction. The first one is the most simple, a one-pot process of the Povarov reaction followed by final 

SCHEME 13.120 One-pot synthesis of quinolines 531 hy a Povarov reaction and subsequent oxidation with DDQ. 

SCHEME 13.121 Domino one-pot synthesis of quinolines 533 hy Povarov reaction and subsequent oxidation by Oj or air [202a, 212]. 

The other possible synthesis of quinoUnes by Povarov additionally, in combination with 2-aminonaphthalene 

By using methyl or ethyl acetylenedicarboxylates, suitable for the Povarov reaction but also more complex aro- 

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Reductions of aromatic nitro compounds provide a simple and general access to various heterocyclic compounds through the domino process (Scheme 9.23). Quinolines are important skeletal moieties present in various natural products and biologically active compounds [58]. Most common methods of their preparation involve condensation of o-amino benzaldehydes with an enolizable carbonyl compound (Friedlander synthesis) [59]. Miller et al. [60] reported an efficient synthesis of quinolines 109, in which a reduction of o-nitroaryl carbaldehyde by SnCl2 followed by condensation with an enolizable carbonyl compound in the presence of ZnCl2 yielded 109 through a domino process. In 2001, Bunce et al. [61] reported a domino nitroarene reduction/reductive amination sequence for the preparation of tetrahydroquinoline-4-carboxylic ester 110 with excellent yields. 

Shaabani, A., Soleimani, E. and Badri, Z. 2006. Silica sulfuric acid as an inexpensive and recyclable solid acid catalyzed efficient synthesis of quinolines. Chem. Mont. 137 181-184. 

M.K. Chaudhuri, S. Hussain, An efficient synthesis of quinolines under solvent-free conditions, J. Chem. Sd. 118 (2006) 199-202. 

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