Behaviour of 2'-Aminochalcones Towards Vilsmeier-Haack Reagent: Synthesis of Some New N-Formyl-2-Aryl/Hetryl-4-Chloro-1,2-Dihydro-4(1h)-Quinilonies
The extensive synthetic utility of traditional Vilsmeier-Haack reagent in organic synthesis is well recognized. Vilsmeier-Haack Arnold reactions that were initially used for the formylation of activated aromatic substrate 1-3 and carbonyl compounds 4 have now evolved into a powerful synthetic tool for the construction of many heterocyclic compounds such as indoles, furans, pyrrols, pyrazoles, oxazoles, pyridines, quinazolines 5-14. A great deal of work has been reported on the synthesis of
... e synthesis of various substituted quinolines by both normal 15-17 and reverse vilsmeier approaches 18-20. The preparation of quinolines is significant from both synthetic as well as biological point of view. Quinolines and their derivatives occur in numerous natural products 21. Many quinolines display interesting physiological activities and have found attractive applications as pharmaceuticals and as general synthetic blocks 22,23. Although many synthesis have been developed for quinolines 24,25 and a wide range of derivatives of quinolines have been synthesized by adopting various methods reported in literature, there has been continuous demand for the development of newer and convenient methods for the synthesis of quinlones. Of the various methods developed so far for the synthesis of quinolines and reduced quinolines, convenient synthesis involving the cyclization of 2'-aminochalcones for the convenient synthesis of 2-Aryl-4-chloro-N-formyl-1,2-dihydroquinoines Discussion Although Balasubramanian et al. carried out Vilsmeier-Haack reaction of seven derivatives of 2'-aminochalcones(Ar= phenyl, p-chlorophenyl, p-tolyl, p-anesyl, o-chlorophenyl, o-tolyl, m-chlorophenyl) 1a-1g, to our surprise no reaction on the chalcones containing electron withdrawing substituent such as-NO2 was investigated. Further, Vilsmeier Haack reaction of hetryl analogs of 2'-aminochalcones has not been reported as yet. The main objective of the present work is to study the scope of method of Balasubramanian et al. for the synthesis of wide variety of 4-chloro-N-formyl-1,2-dihydroquinolines including 2-hetryl analogs. The chalcones 1h-1l were treated with 2.5 equivalent of Vilsmeier reagent at 90 o C for 3h. As expected, reactions proceeded similar to the reported observations affording 2-aryl/hetryl-4-chloro-N-formyl-1,2-dihydroquinolines(2h-2l) Scheme-1 NH 2 O Ar N CHO Ar Cl POCl 3 /DMF 2.5 eq, 90 o C 1 2 Abstract The Vilsmeier-Haack reaction of 2'-aminochalcones provides a convenient approach to 2-aryl / hetryl-4-chloro-N-formyl-1,2-dihydroquinolines.