Tetrahydroquinolines nitroarenes

One notable result is the treatment of 2-hydroxy cyclic ether analog, 2-deoxy-D-ribose with aniline in water catalyzed by InCl3 to afford the novel tricyclic tetrahydroquinoline compounds (Eq. 12.60). The reaction can also be catalyzed by recoverable cation-exchange resin instead of indium chloride.132 By using a stoichiometric amount of indium metal, a domino reaction of nitroarenes with 2,3-dihydrofuran generates the same products. 133... 

NJC641>. Similarly, the reaction of nitroarenes with TiOj, as a photocatalyst, in the presence of alcohols leads to the formation of the tetrahydroquinoline <99TL1145>. 

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. 

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